Contenido

Un sistema fotovoltaico para el suministro de energía residencial, comercial o industrial está formado por el conjunto solar y una serie de componentes que a menudo se resumen en el balance del sistema (BOS). Este término es sinónimo de "Balance de planta" q.v. Los componentes del BOS incluyen equipos de acondicionamiento de energía y estructuras para su montaje, normalmente uno o más convertidores de potencia de CC a CA, también conocidos como inversores "Inversor (electrónica)"), un dispositivo de almacenamiento de energía, un sistema de estanterías que soporta el conjunto solar, el cableado eléctrico y las interconexiones, y el montaje de otros componentes.

Opcionalmente, un sistema de balance puede incluir alguno o todos los siguientes elementos: medidor de ingresos de créditos de energía renovable, rastreador de punto de máxima potencia (MPPT), sistema de baterías y cargador, rastreador solar por GPS, software de gestión de la energía, sensores de irradiación solar, anemómetro o accesorios específicos diseñados para satisfacer los requisitos especializados de un propietario de sistema. Además, un sistema CPV requiere lentes o espejos ópticos y a veces un sistema de refrigeración.

Los términos "panel solar" y "sistema fotovoltaico" a menudo se utilizan incorrectamente de manera intercambiable, a pesar de que el panel solar no abarca todo el sistema. Además, "panel solar" se utiliza a menudo como sinónimo de "módulo solar", aunque un panel consta de una cadena de varios módulos. El término " sistema solar " también es un nombre inapropiado para un sistema fotovoltaico.

Solar panel

The basic components of a photovoltaic system are solar cells. A solar cell is the electrical device that can directly convert photon energy into electricity. There are three technological generations of solar cells: the first generation (1G) of crystalline silicon (c-Si) cells, the second generation (2G) of thin film cells (such as CdTe, CIGS, amorphous silicon and GaAs), and the third generation (3G) of organic cells, sensitized by dyes, Perovskite and multijunction.[26][27]​.

Conventional c-Si solar cells, typically connected in series, are encapsulated in a solar module to protect them from the elements. The module consists of a tempered glass cover, a soft and flexible encapsulant, a backsheet of a weather- and fire-resistant material, and an aluminum frame around the outer edge. Electrically connected and mounted on a support structure, solar modules form a chain of modules, often called a solar panel.[28]​ A solar array is made up of one or more of these panels. A photovoltaic array, or solar array, is a linked collection of solar modules. The energy that a single module can produce is rarely enough to meet the needs of a home or business, so modules are joined together to form a set. Most photovoltaic arrays use an inverter to convert the direct current produced by the modules into alternating current that can power lights, motors, and other loads. The modules of a photovoltaic array are usually first connected in series to obtain the desired voltage; The individual strings are then connected in parallel so that the system can produce more current. Solar panels are typically measured under standard test conditions (STC) or PVUSA test conditions (PTC), in watts.[29] Typical panel values ​​range from less than 100 watts to more than 400 watts. The classification of the assembly consists of the sum of the classifications of the panels, in watts, kilowatts or megawatts.

A typical 150 watt photovoltaic module is about one square meter in size. Such a module can be expected to produce 0.75 kilowatt-hours (kWh) every day, on average, after taking into account climate and latitude, for an insolation of 5 hours of sunshine/day. The output and life of the module are degraded by the increase in temperature. Allowing ambient air to flow upwards and, if possible, backwards of the PV modules reduces this problem, as the air flow reduces the operating temperature and consequently increases the efficiency of the module. This almost always occurs for installations with a single photovoltaic module, mistakenly leading to this phenomenon being considered the same for installations with many modules. However, it has recently been shown that, in photovoltaic generators, increasing wind speed increases energy losses.[30] This seemingly counterintuitive result follows well-known laws of fluid mechanics: the interaction of the wind with the photovoltaic generator induces airflow variations that change the heat transfer from the modules to the air. [3].

The effective useful life of modules is typically 25 years or more.[31]​ The payback period for an investment in a solar PV installation varies widely and is generally less useful than a return on investment calculation.[32]​ While typically estimated at 10 to 20 years, the financial payback period can be much shorter with incentives.[33]​.

The effect of temperature on photovoltaic modules is usually quantified using coefficients that relate variations in open circuit voltage, short circuit current and maximum power to changes in temperature. In this work, complete experimental guidelines for estimating temperature coefficients are presented[34].

Due to the low voltage of a single solar cell (typically about 0.5 V), several cells are wired in series in the manufacture of a "laminate". The laminate is assembled into a weather-resistant protective box, thus forming a photovoltaic module or solar panel. The modules can then be chained together to form a photovoltaic array. In 2012, solar panels available to consumers had an efficiency of up to approximately 17%,[35]​ while panels available on the market in 2020 can reach up to 27%. A group at the Fraunhofer Institute for Solar Energy Systems is reported to have created a cell that can reach an efficiency of 44.7%, making scientists' hopes of reaching the 50% efficiency threshold much more feasible.[36][37][38][39]​.

The electrical output of photovoltaic cells is extremely sensitive to shading ("Christmas light effect").[40]​[41]​[42]​ When even a small part of a cell, module or assembly is in shade, while the rest is in sunlight, performance decreases dramatically due to internal "short circuit" (electrons reverse course through the shaded part of the p-n junction). If the current drawn from the chain of cells in series is no greater than that which the shaded cell can produce, the current (and therefore power) developed by the chain is limited. If sufficient voltage is available in the other cells in the chain, current will be forced through the cell by breaking the junction in the shaded portion. This breakdown voltage in common cells is between 10 and 30 volts. Instead of increasing the energy produced by the panel, the shaded cell absorbs energy, converting it into heat. Because the reverse voltage of a shaded cell is much greater than the forward voltage of a lit cell, a shaded cell can absorb energy from many other cells in the chain, disproportionately affecting the panel's output. For example, a shaded cell can drop 8 volts, instead of adding 0.5 volts, at a given current level, thus absorbing the energy produced by 16 other cells.[43]​ Therefore, it is important that a photovoltaic installation is not shaded by trees or other obstacles.

Several methods have been developed to determine tree shading losses in photovoltaic systems, both over large regions using LiDAR,[44]​ and at the individual system level using sketchup.[45]​ Most modules have bypass diodes between each cell or string of cells that minimize the effects of shading and only lose power from the shaded portion of the array. The main function of the bypass diode is to eliminate hot spots that form in the cells and that can damage the assembly and cause fires.

Sunlight can be absorbed by dust, snow or other impurities on the surface of the module (collectively referred to as dirt). Dirt reduces the light that hits the cells, which in turn reduces the power of the photovoltaic system. Dirt losses accumulate over time and can become large if proper cleaning is not carried out. In 2018, the global annual energy loss due to dirt was estimated to be at least 3% - 4%.[46]​ However, losses due to dirt vary greatly from region to region,[47]​ and within regions.[48]​ Maintaining a clean module surface will increase production performance over the life of the PV system. In a study conducted in an area with a lot of snow (Ontario), cleaning flat-mounted solar panels after 15 months increased their output by almost 100%. However, the sets inclined at 5° were adequately cleaned with rainwater. In many cases, especially in arid regions or in locations close to deserts, roads, industry or agriculture, regular cleaning of solar panels is cost-effective. In 2018, the estimated revenue loss induced by fouling was estimated between €5 billion and €7 billion.[49]​.

The long-term reliability of PV modules is crucial to ensure the technical and economic viability of PV as a successful energy source. The analysis of the degradation mechanisms of photovoltaic modules is key to guaranteeing a current useful life of more than 25 years.[50]​.

Solar insolation is composed of direct, diffuse and reflected radiation. The absorption factor of a photovoltaic cell is defined as the fraction of the incident solar irradiation that is absorbed by the cell.[51]​ At noon on a cloudless day at the equator, the sun's power is approximately 1 kW/m²,[52]​ on the Earth's surface, in a plane perpendicular to the sun's rays. Therefore, photovoltaic installations can follow the sun throughout the day to improve energy capture. However, tracking devices are an additional cost and require maintenance, so it is more common for photovoltaic arrays to have fixed supports that tilt the array and orient it toward solar noon (approximately south in the northern hemisphere or north in the southern hemisphere). The angle of inclination, from the horizontal, can vary depending on the season,[53]​ but if it is fixed, it must be adjusted to obtain optimal production of the assembly during the part of maximum electrical demand of a typical year for a stand-alone system.[53]​ This angle of optimal inclination of the module is not necessarily identical to the angle of inclination for the maximum annual energy production of the assembly. Optimizing the PV system for a specific environment can be complicated, as issues such as solar flux, dirt, and snow losses must be taken into account. Furthermore, subsequent work has shown that spectral effects can play a role in optimal photovoltaic material selection. For example, spectral albedo can play an important role in production depending on the surface area surrounding the PV system and the type of solar cell material. For the climate and latitudes of the United States and Europe, typical sunshine ranges from 4 kWh/m²/day in northern climates to 6.5 kWh/m²/day in the sunniest regions. A photovoltaic installation in the northern latitudes of Europe or the United States can expect to produce 1 kWh/m²/day. A typical 1 kW PV installation in Australia or in the southern latitudes of Europe or the United States can produce between 3.5 and 5 kWh per day, depending on location, orientation, inclination, insolation and other factors. In the Sahara Desert, with less cloud cover and a better solar angle, around 8.3 kWh/m²/day could ideally be obtained, as long as the wind, almost always present, does not blow sand onto the units. The area of ​​the Sahara Desert is more than 9 million km². Of these, 90,600 km² (that is, about 1%) could generate as much electricity as all the power plants in the world combined.[54]​.

Mounting

Modules are assembled in arrays on some type of mounting system, which can be classified as ground, roof, or pole mounting. In the case of solar parks, a large frame is assembled on the ground and the modules are mounted on it. In the case of buildings, many different frames have been devised for pitched roofs. For flat roofs, racks, containers and building-integrated solutions are used. Pole-mounted solar panel racks can be fixed or mobile. Pole side supports are suitable for situations where a pole has something else mounted on its top, such as a light fixture or antenna. Pole mounting elevates what would otherwise be a ground-mounted assembly above the shadows of brush and livestock, and can satisfy electrical code requirements for inaccessibility of exposed wiring. Pole-mounted panels are open to more cooling air at their bottom, increasing performance. A multiplicity of pole-mounted racks can form a parking carport or other shade structure. A frame that does not follow the sun from left to right may allow for seasonal adjustment up or down.

Cabling

Due to their outdoor use, solar cables are designed to be resistant to ultraviolet radiation and extremely high temperature fluctuations and are generally not affected by weather. Standards specifying the use of electrical wiring in photovoltaic systems include the International Electrotechnical Commission's IEC 60364, in section 712 "Solar Photovoltaic (PV) Supply Systems", the British Standard BS 7671, which incorporates regulations relating to microgeneration and photovoltaic systems, and the US Standard UL4703, in topic 4703 "Photovoltaic Cable".

Tracker

A solar tracking system tilts a solar panel throughout the day. Depending on the type of tracking system, the panel is aimed directly at the sun or at the brightest area of ​​a partly cloudy sky. Trackers greatly improve early morning and late afternoon performance, increasing the total amount of power produced by a system by 20-25% for a single-axis tracker and by 30% or more for a two-axis tracker, depending on latitude.[55][56] Trackers are effective in regions that receive a large portion of sunlight directly. In diffuse light (i.e. under clouds or fog), tracking has little or no value. Since most concentrated photovoltaic systems are very sensitive to the angle of sunlight, tracking systems allow them to produce useful power for more than a short period per day.[57]​ Tracking systems improve performance for two main reasons. First, when a solar panel is perpendicular to sunlight, it receives more light on its surface than if it were tilted. Second, direct light is used more effectively than angled light.[58]​ Special anti-reflective coatings can improve the efficiency of the solar panel for direct and angled light, somewhat reducing the tracking benefit.[59]​.

Trackers and sensors to optimize performance are often considered optional, but can increase viable output by up to 45%.[60] Arrays approaching or exceeding one megawatt often use solar trackers. Taking into account the clouds, and the fact that most of the world is not at the equator, and that the sun sets at night, the correct measure of solar energy is insolation, the average number of kilowatt-hours per square meter per day. For the climate and latitudes of the United States and Europe, typical insolation ranges from 2.26 kWh/m/day in northern climates to 5.61 kWh/m/day in the sunniest regions.[61][62]​.

For large systems, the energy gained from using monitoring systems can offset the added complexity. For very large systems, the added maintenance of tracking is a substantial detriment.[63]​ Tracking is not necessary for flat, low-concentration PV systems. For highly concentrated photovoltaic systems, dual-axis tracking is a necessity.[64]​ Price developments influence the balance between adding more fixed solar panels and having fewer tracked panels.

As the prices, reliability and performance of single-axis trackers have improved, the systems have been installed on an increasing percentage of utility-scale projects. According to data from WoodMackenzie/GTM Research, global shipments of solar trackers reached a record 14.5 gigawatts in 2017. This represents 32 percent year-over-year growth, with similar or greater growth projected as large-scale solar deployment accelerates.[65]​.

Investor

Systems designed to supply alternating current (AC), such as grid-tied applications, require an inverter to convert direct current (DC) from solar modules to AC. Grid-tied inverters must supply AC electricity in a sinusoidal manner, synchronized with the grid frequency, limit the supply voltage to no higher than the grid voltage, and disconnect from the grid if the grid voltage is off.[66]​ Islanded inverters only need to produce regulated voltages and frequencies in a sine wave form, as no synchronization or coordination with grid supplies is required.

A solar inverter can be connected to a string of solar panels. In some installations a solar microinverter is connected to each solar panel.[67]​ For safety reasons, a circuit breaker is provided on both the AC and DC sides to allow for maintenance. The AC output can be connected to the utility grid through an electricity meter.[68]​ The number of modules in the system determines the total DC watts the solar array can generate; However, the inverter ultimately governs the amount of AC watts that can be distributed for consumption. For example, a PV system comprised of 11 kilowatts DC (kW) of PV modules, paired with a 10 kilowatt AC (kW) inverter, will be limited to the inverter power of 10 kW. In 2019, the conversion efficiency of the latest generation converters reached more than 98%. While string inverters are used in residential and medium-sized commercial PV systems, central inverters cover the commercial and large-scale market. The market share of central and string inverters is approximately 44% and 52%, respectively, and less than 1% for microinverters.[69]​.

Maximum power point tracking (MPPT) is a technique used by grid-connected inverters to obtain the maximum possible power from the photovoltaic array. To do this, the inverter's MPPT system digitally samples the ever-changing power output of the solar panel and applies the appropriate resistance to find the optimal maximum power point.[70]​.

Anti-islanding is a protection mechanism to immediately shut down the inverter, preventing it from generating AC power when the connection to the load no longer exists. This occurs, for example, in the event of a blackout. Without this protection, the supply line would become a powered "island" surrounded by a "sea" of unpowered lines, as the solar array continues to supply DC power during the blackout. Isolation is a hazard to power company workers, who may not realize that an AC continues to receive power, and may prevent devices from automatically reconnecting.[71]​ Anti-islanding is not required for complete off-grid systems.

Battery

Although still expensive, photovoltaic systems increasingly use rechargeable batteries to store surplus that will then be used at night. Batteries used for grid storage also stabilize the electrical grid by leveling peak loads and play an important role in a smart grid as they can charge during periods of low demand and feed their stored energy to the grid when demand is high.

The most widely used battery technologies in current photovoltaic systems are the valve-regulated lead-acid battery - a modified version of the conventional lead-acid battery -, nickel-cadmium batteries and lithium-ion batteries. Compared to the other types, lead-acid batteries have a shorter lifespan and lower energy density. However, due to their high reliability, low self-discharge and low investment and maintenance costs, they are currently the predominant technology in small-scale residential photovoltaic systems, since lithium-ion batteries are still in the development phase and are about 3.5 times more expensive than lead batteries. Furthermore, as the storage devices of photovoltaic systems are stationary, the lower energy and power density and therefore the greater weight of lead-acid batteries are not as critical as, for example, in electric transportation[9] Other rechargeable batteries considered for distributed photovoltaic systems are sodium-sulfur and vanadium-redox, two prominent types of molten salt and flow batteries, respectively[9] In 2015, Tesla Motors launched the Powerwall, a rechargeable lithium-ion battery with the aim of revolutionizing energy consumption.[73]​.

Photovoltaic systems with an integrated battery solution also need a charge controller, as the variable voltage and current of the solar panel requires constant adjustment to prevent damage from overcharging.[74]​ Basic charge controllers can simply turn photovoltaic panels on and off, or they can measure pulses of power as needed, a strategy called PWM or pulse width modulation. More advanced charge controllers will incorporate MPPT logic into their battery charging algorithms. Charge controllers can also divert power for some purpose other than battery charging. Instead of simply turning off the free PV power when it is not needed, a user can choose to heat air or water once the battery is full.

Control and measurement

The counter must be capable of accumulating units of energy in both directions, or two counters must be used. Many meters accumulate bidirectionally, some systems use two meters, but a unidirectional meter (with detent) will not accumulate energy from any resulting feed to the grid.[75]​ In some countries, a frequency and voltage monitor with disconnection of all phases is required for installations over 30 kWp. This is done when more solar energy is generated than the power company can accommodate, and the excess cannot be exported or stored. Historically, grid operators have had to provide transmission lines and generation capacity. Now they have to provide storage as well. Typically this is hydraulic storage, but other means of storage are also used. Initially, storage was used so that baseload generators could operate at full capacity. With variable renewable energy, storage is necessary to allow energy to be generated whenever available, and consumed whenever necessary.

The two variables a grid operator has are storing electricity for when it is needed or transmitting it to where it is needed. If both fail, installations larger than 30 kWp may automatically shut down, although in practice all inverters maintain voltage regulation and stop supplying power if the load is inadequate. Grid operators have the option of reducing excess generation from large systems, although this is more commonly done with wind power than solar power, and results in a substantial loss of revenue.[76]​ Three-phase inverters have the unique option of supplying reactive power, which can be advantageous in meeting load requirements.[77]​.

Photovoltaic installations need to be monitored to detect faults and optimize their operation. There are several photovoltaic monitoring strategies depending on the performance of the installation and its nature. Monitoring can be done on site or remotely. You can measure only production, retrieve all data from the inverter, or retrieve all data from communication equipment (probes, meters, etc.). Monitoring tools can be dedicated to monitoring only or offer additional functions. Individual inverters and battery charge controllers may include monitoring using manufacturer-specific protocols and software.[78] An inverter's energy metering may have limited accuracy and may not be suitable for revenue metering purposes. A third-party data acquisition system can monitor multiple inverters, using the inverter manufacturer's protocols, and also acquire information related to weather conditions. Stand-alone smart meters can measure the total energy production of a PV installation. Independent measurements, such as satellite image analysis or a solar radiation meter (a pyranometer), can be used to estimate total sunshine for comparison.[79] Data collected by a monitoring system can be viewed remotely via the World Wide Web, such as OSOTF.

Sizing of the photovoltaic system

Knowing the annual energy consumption in kWh of an institution or a family, for example 2300Kwh, legible on their electricity bill, it is possible to calculate the number of photovoltaic panels necessary to satisfy their energy needs. When connecting to the site https://re.jrc.ec.europa.eu/pvg_tools/es/, after selecting the location in which to install the panels or clicking on the map or writing the name of the location, you must select "Network PV" and "Show results" obtaining the following table for example referring to the city of Palermo:.

Using the wxMaxima program "Maxima (software)"), the number of panels required for an annual consumption of 2300 kWh and for a crystalline silicon technology with an inclination angle of 35°, an orientation angle of 0° and total losses equal to 21.88 % is 6 rounded:.

On average, each family manages to consume 30% of energy directly from photovoltaics. The storage system can bring its self-consumption to a maximum of 70%, therefore the storage capacity of the battery that must be in the specific case is: 4.41 kWh, which is rounded to 4.8 kWh.

If the price of energy is €0.5/Kwh, the cost of energy without taxes will be €1,150 per year:.

So if a 300W panel costs €200, the 4.8Kwh battery costs €3000, the inverter to convert direct current into alternating current €1000, the charge regulator €100, the installation costs €1000, the total cost will be €6300:.

that are amortized in 5.46 years:.

the battery having a life of 10 years and the panels 25-30 years.

Esta sección incluye sistemas que son altamente especializados y poco comunes o que aún son una nueva tecnología emergente con importancia limitada. Sin embargo, los sistemas autónomos o fuera de la red ocupan un lugar especial. Eran el tipo de sistema más común durante las décadas de 1980 y 1990, cuando la tecnología fotovoltaica todavía era muy cara y era un nicho de mercado puro de aplicaciones a pequeña escala. Solo en lugares donde no había red eléctrica disponible, eran económicamente viables. Aunque todavía se están implementando nuevos sistemas autónomos en todo el mundo, su contribución a la capacidad fotovoltaica total instalada está disminuyendo. En Europa, los sistemas fuera de la red representan el 1 por ciento de la capacidad instalada. En los Estados Unidos, representan alrededor del 10 por ciento. Los sistemas fuera de la red todavía son comunes en Australia y Corea del Sur, y en muchos países en desarrollo.[8]​.

CPV

Concentrating photovoltaics (CPV) and high concentration photovoltaics (HCPV) systems use optical lenses or curved mirrors to concentrate sunlight into small but highly efficient solar cells. In addition to concentrating optics, CPV systems sometimes use solar trackers and cooling systems and are more expensive.

Especially HCPV systems are best suited to locations with high solar irradiance, concentrating sunlight up to 400 times or more, with efficiencies of 24 to 28 percent, higher than those of regular systems. There are several system designs available on the market, but they are not very common. However, it is being researched and developed.[1]​.

CPV is often confused with CSP (concentrated solar power) which does not use photovoltaics. Both technologies favor places that receive a lot of sunlight and compete directly with each other.

Hybrid

A hybrid system combines photovoltaic power with other forms of generation, usually a diesel generator. Biogas is also used. The other form of generation may be a type capable of modulating energy production based on demand. However, more than one form of renewable energy can be used, for example wind. Photovoltaic energy generation serves to reduce non-renewable fuel consumption. Hybrid systems are most often found on islands. Pellworm Island in Germany and Kythnos Island in Greece are notable examples (both are combined with wind).[80]​[81]​ The Kythnos plant has reduced diesel consumption by 11.2%.[82]​.

In 2015, a case study carried out in seven countries concluded that in all cases generation costs can be reduced through the hybridization of mini-grids and isolated networks. However, the financing costs of these hybrids are crucial and largely depend on the ownership structure of the power plant. While the cost reduction for public companies can be significant, the study also identified that the economic benefits are negligible or even negative for non-public companies, such as independent power producers.[83][84]​.

There has also been work demonstrating that the penetration limit of PV can be increased by deploying a distributed network of hybrid PV + CHP systems in the US.[85] The temporal distribution of solar flux and the electrical and heating needs of representative single-family residences in the US was analyzed and the results clearly show that hybridization of CHP with PV can enable additional deployment of PV above which is possible with a conventional centralized electricity generation system. This theory was reconfirmed with numerical simulations using per-second solar flux data to determine that the battery reserve required to provide such a hybrid system is possible with relatively small and inexpensive battery systems.[86]​ In addition, large photovoltaic and cogeneration systems can be installed in institutional buildings, which in turn provides backup for intermittent photovoltaics and reduces cogeneration runtime.[87]​.

• - The PVT system (hybrid PV/T), also known as photovoltaic thermal hybrid solar collectors, converts solar radiation into thermal and electrical energy. This system combines a solar module (PV) with a solar thermal collector in a complementary way.

• - CPVT System. A hybrid concentrated photovoltaic thermal system (CPVT) is similar to a PVT system. It uses concentrated photovoltaics (CPV) instead of conventional photovoltaic technology and combines it with a solar thermal collector.

• - CPV/CSP System. A novel CPV/CSP hybrid solar system has been proposed, which combines the photovoltaic concentrator with the non-photovoltaic technology of concentrated solar energy (CSP), also known as concentrated solar thermal.[88]​.

• - Diesel photovoltaic system. It combines a photovoltaic system with a diesel generator.[89]​ Combinations with other renewable energies are possible and include wind turbines.[90]​.

floating solar panels

Floating solar arrays are photovoltaic systems that float on the surface of drinking water tanks, quarry lakes, irrigation canals or sanitation and waste ponds. These systems are called "floating" when used solely for electrical production or "aquavoltaic" when used to synergistically enhance aquaculture[91]. A small number of these systems exist in France, India, Japan, South Korea, the United Kingdom, Singapore and the United States.[92]​[93][94][95][96]​.

The systems are said to have advantages over ground-based photovoltaics. The cost of land is more expensive and there are fewer rules and regulations for structures built on bodies of water not used for recreation. Unlike most land-based solar plants, floating arrays can be discreet because they are hidden from public view. They achieve greater efficiency than ground-based photovoltaic panels, because the water cools the panels. The panels have a special coating to prevent rust or corrosion.[97]​.

In May 2008, the Far Niente winery in Oakville, California, pioneered the installation of the world's first floating photovoltaic system by installing 994 solar photovoltaic modules with a total capacity of 477 kW on 130 pontoons and floating them in the winery's irrigation pond.[98]​ The main advantage of this system is that it avoids the need to sacrifice valuable land area that could be used for another purpose. In the case of the Far Niente winery, 0.75 acres (0.30 ha) were saved that would have been necessary for a land-based system.[99] Another advantage of a floating photovoltaic system is that the panels are kept at a cooler temperature than on land, allowing for greater efficiency in converting solar energy. The floating photovoltaic system also reduces the amount of water lost through evaporation and inhibits algae growth.[100]​.

Floating photovoltaic parks are beginning to be built on a commercial scale. Electronics and ceramics multinational Kyocera will build the world's largest, a 13.4 MW farm on the Yamakura Dam reservoir in Chiba Prefecture.[101]​ using 50,000 solar panels.[102]​[103]​ Saltwater-resistant floating farms are also being considered for ocean use, with experiments in Thailand.[104]​ The largest floating energy project announced so far It is a 350 MW power plant in the Amazon region of Brazil.[105]​.

DC network

DC networks are found in electric transport: trams and trolleybuses. Some pilot plants have been built for such applications, such as the tram depots in Hannover Leinhausen, using photovoltaic contributors[106] and Geneva (Bachet de Pesay).[107] The 150 kWp Geneva plant directly powers the tram and trolleybus electrical network with 600 V direct current, whereas it previously provided around 15% of the electricity at its inauguration in 1999.

Autonomous system

A stand-alone or isolated system is not connected to the electrical grid. Autonomous systems vary widely in size and application, from wristwatches or calculators to remote buildings or spacecraft. If the load must be powered independently of solar insolation, the generated energy is stored and buffered with a battery.[108] In non-portable applications where weight is not an issue, such as in buildings, lead-acid batteries are most commonly used due to their low cost and tolerance for abuse.

A charge controller can be incorporated into the system to prevent damage to the battery due to excessive charging or discharging. It can also help optimize solar array output using a maximum power point tracking (MPPT) technique. However, in simple PV systems where the PV module voltage matches the battery voltage, the use of MPPT electronics is generally considered unnecessary, as the battery voltage is stable enough to provide near-maximum energy harvesting from the PV module. In small devices (e.g. calculators, parking meters) only direct current (DC) is consumed. In larger systems (e.g. buildings, remote water pumps) air conditioning is usually required. To convert the DC from the modules or batteries to AC, an inverter is used. "Inverter (electronics)").

In agricultural settings, the array can be used to directly power DC pumps, without the need for an inverter "Inverter (electronics)"). In remote environments such as mountainous areas, islands, or other locations where grid power is not available, solar panels can be used as the only source of electricity, usually charging a storage battery. Autonomous systems are closely related to microgeneration and distributed generation.

• - Pico photovoltaic systems.

• - Solar street lights.

Solar street lights are light sources that are powered by photovoltaic panels generally mounted on the lighting structure. The solar array of this off-grid PV system charges a rechargeable battery, which powers a fluorescent or LED lamp at night. Solar street lights are autonomous power systems and have the advantage of saving on excavation and maintenance costs, as well as on the electricity bill, despite their higher initial cost compared to conventional street lighting. They are designed with batteries large enough to ensure they operate for at least a week and even in the worst situation, they are expected to dim only slightly.

• - Telecommunication and signaling.

• - Solar vehicles.

• - Solar pumps.

One of the most cost-effective solar applications is a solar-powered pump, as it is much cheaper to purchase a solar panel than to install power lines[111]​[112][113]​ They often meet a water need beyond the reach of power lines, taking the place of a windmill or wind pump. A common application is filling water tanks for livestock so they can drink. Another is refilling the drinking water tanks of remote or self-sufficient houses.

El costo de producir células fotovoltaicas se ha reducido debido a las economías de escala en la producción y los avances tecnológicos en la fabricación. Para las instalaciones a gran escala, los precios por debajo de $ 1,00 por vatio eran comunes en 2012.[118]​ Se había logrado una disminución de precios del 50% en Europa de 2006 a 2011 y existe la posibilidad de reducir el costo de generación en un 50% para 2020.[119]​ Las células solares de silicio cristalino han sido reemplazadas en gran medida por células solares de silicio multicristalino menos costosas, y las células solares de silicio de película delgada también se han desarrollado a costos de producción más bajos. Aunque se reducen en eficiencia de conversión de energía a partir de "siwafers" monocristalinos, también son mucho más fáciles de producir a costos comparativamente más bajos.

La siguiente tabla muestra el costo total (promedio) en centavos de dólar por kWh de electricidad generada por un sistema fotovoltaico.[120]​[121]​ Los encabezados de las filas de la izquierda muestran el costo total, por kilovatio pico (kW ), de una instalación fotovoltaica. Los costos de los sistemas fotovoltaicos han ido disminuyendo y en Alemania, por ejemplo, se informó que habían caído a USD 1389 / kW a fines de 2014.[122]​ Los encabezados de las columnas en la parte superior se refieren a la producción de energía anual en kWh esperada de cada kW instalado. Esto varía según la región geográfica porque la insolación promedio depende de la nubosidad promedio y el grosor de la atmósfera atravesada por la luz solar. También depende de la trayectoria del sol en relación con el panel y el horizonte. Los paneles generalmente se montan en un ángulo basado en la latitud y, a menudo, se ajustan estacionalmente para adaptarse a la declinación "Declinación (astronomía)") solar cambiante. El seguimiento solar también se puede utilizar para acceder a una luz solar aún más perpendicular, aumentando así la producción total de energía.

Los valores calculados en la tabla reflejan el costo total (promedio) en centavos por kWh producido. Asumen un costo de capital total del 10% (por ejemplo , una tasa de interés del 4%, un costo de operación y mantenimiento del 1%,[123]​ y la depreciación del desembolso de capital durante 20 años). Normalmente, los módulos fotovoltaicos tienen una garantía de 25 años.[124]​[125]​.

System cost in 2013

In its 2014 edition of the "Technology Roadmap: Solar Photovoltaic Energy" report, the International Energy Agency (IEA) published dollar-per-watt prices for residential, commercial, and utility-scale photovoltaic systems in eight major markets in 2013.[126]​.

Learning curve

Photovoltaic systems demonstrate a learning curve in terms of levelized cost of electricity (LCOE), reducing their cost per kWh by 32.6% for each doubling of capacity.[127]​[128][129]​ Using LCOE and cumulative installed capacity data from the International Renewable Energy Agency (IRENA) from 2010 to 2017, the learning curve equation for photovoltaic systems is it gives like.

• - LCOE: levelized cost of electricity (in USD / kWh).

• - Capacity: accumulated installed capacity of photovoltaic systems (in MW).

Standardization

The increasing use of photovoltaic systems and the integration of photovoltaic energy into existing supply and distribution structures and techniques increase the need for general standards and definitions for photovoltaic components and systems. Standards are compiled by the International Electrotechnical Commission (IEC) and apply to the efficiency, durability and safety of cells, modules, simulation programs, connectors and cables, mounting systems, overall efficiency of inverters, etc.[130]​.

National regulations

In the UK, PV installations are generally considered permitted development and do not require planning permission. If the property is listed or is in a designated area (national park, area of ​​outstanding natural beauty, site of special scientific interest or Norfolk Broads), planning permission is required.[131]​.

In the United States, Article 690 of the National Electrical Code provides general guidelines for the installation of photovoltaic systems; these may be superseded by local laws and regulations. A permit requiring the submission of structural plans and calculations is often required before work can begin. Additionally, many locations require that work be done under the guidance of a licensed electrician.

In the United States, the Authority Having Jurisdiction (AHJ) will review designs and issue permits before construction can legally begin. Electrical installation practices must meet the standards set forth in the National Electrical Code (NEC) and be inspected by the authority having jurisdiction to ensure compliance with the building code, electrical code, and fire safety code. Jurisdictions may require that equipment have been tested, certified, listed, and labeled by at least one of the Nationally Recognized Testing Laboratories (NRTL).[132]​ In the US, many localities require a permit to install a photovoltaic system. A grid-tied system typically requires a licensed electrician to make the connection between the system and the building's grid-connected wiring.[133] Installers who meet these qualifications are found in nearly every state. Several states prohibit homeowners associations from restricting solar devices.[134][135][136]​.

Although Spain generates around 40% of its electricity through photovoltaics and other renewable sources, and cities like Huelva and Seville have almost 3,000 hours of sunshine a year, in 2013 Spain issued a solar tax to account for the debt created by the investment made by the Spanish government. Those who do not connect to the grid can face a fine of up to 30 million euros ($40 million)[137]​[138]​ Such measures were finally withdrawn in 2018, when new legislation was introduced prohibiting any tax on self-consumption of renewable energy.[139]​.

Pollution and energy in photovoltaic production

Photovoltaics is a well-known method of generating clean, emission-free electricity. Photovoltaic systems are usually composed of photovoltaic modules and inverters (which transform direct current into alternating current). Photovoltaic modules are mainly made of photovoltaic cells, which have no fundamental difference from the material for making computer chips. The production process of photovoltaic cells (computer chips) requires large energy consumption and involves the use of chemicals that are highly toxic to the environment. There are few photovoltaic manufacturing plants around the world that produce photovoltaic modules with energy produced from photovoltaic cells. This measure greatly reduces the carbon footprint during the manufacturing process. The management of chemicals used in the manufacturing process is subject to local factory laws and regulations.

Impact on the electrical grid

With the rise of rooftop photovoltaic systems, the flow of energy becomes bidirectional. When there is more local generation than consumption, electricity is exported to the grid. However, the power grid is not traditionally designed to deal with two-way energy transfer. Therefore, some technical problems may arise. For example, in Queensland, Australia, there were more than 30% of households with rooftop PV at the end of 2017. The famous California duck curve of 2020 has appeared very frequently in many communities since 2015. A surge problem may appear when electricity returns to the grid.[140] There are solutions to manage the surge problem, such as power factor regulation of PV inverters, new equipment voltage and energy control at the level of electricity distributors, rerouting of electrical cables, demand management, etc. These solutions usually have limitations and costs.

Implication in the management of the electricity bill and energy investment

Customers have different specific situations, for example, different comfort/convenience needs, different electricity rates, or different usage patterns. An electricity tariff can have several elements, such as the daily access and metering rate, the energy rate (based on kWh, MWh), or the peak demand rate (for example, a price for the highest 30-minute energy consumption in a month). Photovoltaics is a promising option to reduce energy tariff when the price of electricity is reasonably high and increasing continuously, such as in Australia and Germany. However, where a peak demand charge applies, PV may be less attractive if peak demand occurs primarily in the late afternoon or early evening, for example in residential communities. In general, energy investment is largely an economic decision and investment decisions are based on the systematic evaluation of operational improvement, energy efficiency, on-site generation and energy storage options.[141]​[142]​.

• - Photovoltaic Energy Fact Sheet from the Center for Sustainable Systems at the University of Michigan.

• - Home Power Magazine http://www.homepower.com/.

• - Management of solar projects.

• - Photovoltaic Systems Engineering Archived July 19, 2019 at the Wayback Machine.

• - Best Practices for Siting Solar Photovoltaics at Municipal Solid Waste Landfills: A study prepared in partnership with the Environmental Protection Agency for the RE-Powering America's Land Initiative: Siting Renewable Energy on Potentially Contaminated Land and Mining Sites National Renewable Energy Laboratory.

Overview

A photovoltaic system converts solar radiation, in the form of light, into usable electricity. It is made up of the solar array and the rest of the system components. PV systems can be classified based on several aspects, such as grid-tied vs. stand-alone systems, building-integrated vs. rack-mounted systems, residential vs. utility systems, distributed vs. centralized systems, rooftop-mounted vs. ground-mounted systems, tracking systems vs. fixed-tilt systems, and new-build vs. retrofit systems. Other distinctions may include: systems with microinverters versus central inverters, systems using crystalline silicon versus thin film technology, and systems with modules from Chinese versus European and American manufacturers.

About 99% of European and 90% of American solar power systems are grid-connected, while off-grid systems are somewhat more common in Australia and South Korea.[8]​: Photovoltaic systems rarely use battery storage. This may change as government incentives for distributed energy storage take effect and investments in storage solutions gradually become economically viable for small systems.[9]​[10]​ A typical residential solar installation is mounted on the roof, rather than being integrated into the roof or façade of the building, which is much more expensive. Utility-scale solar plants are ground-mounted, with fixed and tilted solar panels, rather than using expensive tracking devices. Crystalline silicon is the predominant material in 90% of solar modules produced worldwide, while its rival, thin film, has lost market share.[1] About 70% of all solar cells and modules are produced in China and Taiwan, and only 5% by European and American manufacturers.[1] The installed capacity of both small rooftop systems and large solar power plants is growing rapidly and equally, although there is a notable trend towards solar systems. utility scale, as the focus of new installations is shifting from Europe to sunnier regions, such as the US Sun Belt, which are less opposed to ground-mounted solar farms and investors place more emphasis on profitability.[8]​.

Driven by technological advances and increasing scale and sophistication of manufacturing, the cost of photovoltaics is continually decreasing.[3]​ There are several million photovoltaic systems distributed around the world, primarily in Europe, with 1.4 million systems in Germany alone.[1]​ - as well as in North America, with 440,000 systems in the United States.[11]​ The energy conversion efficiency of a conventional solar module has increased from 15 to 20% since 2004.[1]​ and a photovoltaic system recovers the energy necessary for its manufacture in about 2 years. In locations with exceptional irradiance, or when thin film technology is used, the so-called energy payback time is reduced to one year or less.[1] Net metering and financial incentives, such as preferential rates for electricity generated by solar energy, have also greatly supported the installations of photovoltaic systems in many countries.[12] The levelized cost of electricity from large-scale photovoltaic systems has become competitive with conventional electricity sources in an increasingly short list. wide range of geographic regions, and network parity has been achieved in about 30 different countries.[13]​[14]​[15]​.

In 2015, the rapidly growing global photovoltaic market is approaching the 200 GW mark, about 40 times the installed capacity in 2006.[16] These systems currently contribute to 1% of global electricity generation. The leading installers of PV systems in terms of capacity are currently China, Japan and the United States, while half of the world's capacity is installed in Europe, with Germany and Italy supplying between 7% and 8% of their respective national electricity consumption with solar PV. contribute to 16% and 11% of global demand, respectively.

Connection to the solar grid

A grid-tied system is connected to a larger independent grid (typically the public power grid) and feeds power directly into the grid. This energy may be shared by a residential or commercial building before or after the revenue metering point, depending on whether the credited energy production is calculated independently of the customer's energy consumption (feed-in tariff) or only on the energy difference (net metering). These systems vary in size, from residential (2-10 kW) to solar power plants (up to tens of MW). This is a form of decentralized electricity generation. The injection of electricity into the grid requires the transformation of direct current into alternating current using a special, synchronized grid inverter. In kilowatt-sized installations, the voltage on the DC side of the system is as high as allowed (typically 1000 V, except US residential 600 V) to limit ohmic losses. Most modules (60 or 72 crystalline silicon cells) generate between 160 W and 300 W at 36 volts. Sometimes it is necessary or desirable to connect modules partially in parallel rather than all in series. A set of modules connected in series is called a "chain".[18]​.

System scale

Photovoltaic systems are generally classified into three distinct market segments: residential rooftops, commercial rooftops, and ground-mounted utility-scale systems. Their capacities range from a few kilowatts to hundreds of megawatts. A typical residential system is about 10 kilowatts and is mounted on a sloped roof, while commercial systems can reach megawatt scale and are typically installed on low-slope or even flat roofs. Although rooftop-mounted systems are small and have a higher cost per watt than large commercial-scale installations, they represent the majority of the market. However, there is a growing trend toward larger power plants, especially in the "sunbelt" region of the planet.[8]​ [19]​.

Performance

Uncertainties in income over time are primarily related to the evaluation of the solar resource and the performance of the system itself. In the best of cases, uncertainties are usually 4% due to annual climate variability, 5% due to the estimate of the solar resource (in a horizontal plane), 3% due to the estimate of irradiation in the array plane, 3% due to the nominal power of the modules, 2% due to losses due to dirt, 1.5% due to losses due to snow and 5% due to other sources of error. Identifying and reacting to manageable losses is critical to revenue and O&M effectiveness. Monitoring the performance of the facility may form part of the contractual agreements between the facility owner, the builder, and the company purchasing the energy produced. A method of creating "synthetic days" using readily available meteorological data and verification using the Open Solar Outdoors test range makes it possible to predict the performance of PV systems with a high degree of accuracy.[24]​ This method can be used to determine local-scale loss mechanisms, such as those derived from snow or the effects of surface coatings (e.g., hydrophobic or hydrophilic) on dirt or snow losses.[25]​ (Although in very snowy environments and with serious interference on the ground, annual snow losses of 30% may occur. Internet access has made it possible to further improve energy control and communication. There are specific systems from various providers. For solar PV systems using microinverters (panel-level DC to AC conversion), power data for the modules is provided automatically. Some systems allow you to set performance alerts that trigger phone, email, or text alerts when limits are reached. These solutions provide data to the system owner and installer. Installers can remotely monitor multiple installations and see the status of their entire installed base at a glance.

Contenido

Un sistema fotovoltaico para el suministro de energía residencial, comercial o industrial está formado por el conjunto solar y una serie de componentes que a menudo se resumen en el balance del sistema (BOS). Este término es sinónimo de "Balance de planta" q.v. Los componentes del BOS incluyen equipos de acondicionamiento de energía y estructuras para su montaje, normalmente uno o más convertidores de potencia de CC a CA, también conocidos como inversores "Inversor (electrónica)"), un dispositivo de almacenamiento de energía, un sistema de estanterías que soporta el conjunto solar, el cableado eléctrico y las interconexiones, y el montaje de otros componentes.

Opcionalmente, un sistema de balance puede incluir alguno o todos los siguientes elementos: medidor de ingresos de créditos de energía renovable, rastreador de punto de máxima potencia (MPPT), sistema de baterías y cargador, rastreador solar por GPS, software de gestión de la energía, sensores de irradiación solar, anemómetro o accesorios específicos diseñados para satisfacer los requisitos especializados de un propietario de sistema. Además, un sistema CPV requiere lentes o espejos ópticos y a veces un sistema de refrigeración.

Los términos "panel solar" y "sistema fotovoltaico" a menudo se utilizan incorrectamente de manera intercambiable, a pesar de que el panel solar no abarca todo el sistema. Además, "panel solar" se utiliza a menudo como sinónimo de "módulo solar", aunque un panel consta de una cadena de varios módulos. El término " sistema solar " también es un nombre inapropiado para un sistema fotovoltaico.

Solar panel

The basic components of a photovoltaic system are solar cells. A solar cell is the electrical device that can directly convert photon energy into electricity. There are three technological generations of solar cells: the first generation (1G) of crystalline silicon (c-Si) cells, the second generation (2G) of thin film cells (such as CdTe, CIGS, amorphous silicon and GaAs), and the third generation (3G) of organic cells, sensitized by dyes, Perovskite and multijunction.[26][27]​.

Conventional c-Si solar cells, typically connected in series, are encapsulated in a solar module to protect them from the elements. The module consists of a tempered glass cover, a soft and flexible encapsulant, a backsheet of a weather- and fire-resistant material, and an aluminum frame around the outer edge. Electrically connected and mounted on a support structure, solar modules form a chain of modules, often called a solar panel.[28]​ A solar array is made up of one or more of these panels. A photovoltaic array, or solar array, is a linked collection of solar modules. The energy that a single module can produce is rarely enough to meet the needs of a home or business, so modules are joined together to form a set. Most photovoltaic arrays use an inverter to convert the direct current produced by the modules into alternating current that can power lights, motors, and other loads. The modules of a photovoltaic array are usually first connected in series to obtain the desired voltage; The individual strings are then connected in parallel so that the system can produce more current. Solar panels are typically measured under standard test conditions (STC) or PVUSA test conditions (PTC), in watts.[29] Typical panel values ​​range from less than 100 watts to more than 400 watts. The classification of the assembly consists of the sum of the classifications of the panels, in watts, kilowatts or megawatts.

A typical 150 watt photovoltaic module is about one square meter in size. Such a module can be expected to produce 0.75 kilowatt-hours (kWh) every day, on average, after taking into account climate and latitude, for an insolation of 5 hours of sunshine/day. The output and life of the module are degraded by the increase in temperature. Allowing ambient air to flow upwards and, if possible, backwards of the PV modules reduces this problem, as the air flow reduces the operating temperature and consequently increases the efficiency of the module. This almost always occurs for installations with a single photovoltaic module, mistakenly leading to this phenomenon being considered the same for installations with many modules. However, it has recently been shown that, in photovoltaic generators, increasing wind speed increases energy losses.[30] This seemingly counterintuitive result follows well-known laws of fluid mechanics: the interaction of the wind with the photovoltaic generator induces airflow variations that change the heat transfer from the modules to the air. [3].

The effective useful life of modules is typically 25 years or more.[31]​ The payback period for an investment in a solar PV installation varies widely and is generally less useful than a return on investment calculation.[32]​ While typically estimated at 10 to 20 years, the financial payback period can be much shorter with incentives.[33]​.

The effect of temperature on photovoltaic modules is usually quantified using coefficients that relate variations in open circuit voltage, short circuit current and maximum power to changes in temperature. In this work, complete experimental guidelines for estimating temperature coefficients are presented[34].

Due to the low voltage of a single solar cell (typically about 0.5 V), several cells are wired in series in the manufacture of a "laminate". The laminate is assembled into a weather-resistant protective box, thus forming a photovoltaic module or solar panel. The modules can then be chained together to form a photovoltaic array. In 2012, solar panels available to consumers had an efficiency of up to approximately 17%,[35]​ while panels available on the market in 2020 can reach up to 27%. A group at the Fraunhofer Institute for Solar Energy Systems is reported to have created a cell that can reach an efficiency of 44.7%, making scientists' hopes of reaching the 50% efficiency threshold much more feasible.[36][37][38][39]​.

The electrical output of photovoltaic cells is extremely sensitive to shading ("Christmas light effect").[40]​[41]​[42]​ When even a small part of a cell, module or assembly is in shade, while the rest is in sunlight, performance decreases dramatically due to internal "short circuit" (electrons reverse course through the shaded part of the p-n junction). If the current drawn from the chain of cells in series is no greater than that which the shaded cell can produce, the current (and therefore power) developed by the chain is limited. If sufficient voltage is available in the other cells in the chain, current will be forced through the cell by breaking the junction in the shaded portion. This breakdown voltage in common cells is between 10 and 30 volts. Instead of increasing the energy produced by the panel, the shaded cell absorbs energy, converting it into heat. Because the reverse voltage of a shaded cell is much greater than the forward voltage of a lit cell, a shaded cell can absorb energy from many other cells in the chain, disproportionately affecting the panel's output. For example, a shaded cell can drop 8 volts, instead of adding 0.5 volts, at a given current level, thus absorbing the energy produced by 16 other cells.[43]​ Therefore, it is important that a photovoltaic installation is not shaded by trees or other obstacles.

Several methods have been developed to determine tree shading losses in photovoltaic systems, both over large regions using LiDAR,[44]​ and at the individual system level using sketchup.[45]​ Most modules have bypass diodes between each cell or string of cells that minimize the effects of shading and only lose power from the shaded portion of the array. The main function of the bypass diode is to eliminate hot spots that form in the cells and that can damage the assembly and cause fires.

Sunlight can be absorbed by dust, snow or other impurities on the surface of the module (collectively referred to as dirt). Dirt reduces the light that hits the cells, which in turn reduces the power of the photovoltaic system. Dirt losses accumulate over time and can become large if proper cleaning is not carried out. In 2018, the global annual energy loss due to dirt was estimated to be at least 3% - 4%.[46]​ However, losses due to dirt vary greatly from region to region,[47]​ and within regions.[48]​ Maintaining a clean module surface will increase production performance over the life of the PV system. In a study conducted in an area with a lot of snow (Ontario), cleaning flat-mounted solar panels after 15 months increased their output by almost 100%. However, the sets inclined at 5° were adequately cleaned with rainwater. In many cases, especially in arid regions or in locations close to deserts, roads, industry or agriculture, regular cleaning of solar panels is cost-effective. In 2018, the estimated revenue loss induced by fouling was estimated between €5 billion and €7 billion.[49]​.

The long-term reliability of PV modules is crucial to ensure the technical and economic viability of PV as a successful energy source. The analysis of the degradation mechanisms of photovoltaic modules is key to guaranteeing a current useful life of more than 25 years.[50]​.

Solar insolation is composed of direct, diffuse and reflected radiation. The absorption factor of a photovoltaic cell is defined as the fraction of the incident solar irradiation that is absorbed by the cell.[51]​ At noon on a cloudless day at the equator, the sun's power is approximately 1 kW/m²,[52]​ on the Earth's surface, in a plane perpendicular to the sun's rays. Therefore, photovoltaic installations can follow the sun throughout the day to improve energy capture. However, tracking devices are an additional cost and require maintenance, so it is more common for photovoltaic arrays to have fixed supports that tilt the array and orient it toward solar noon (approximately south in the northern hemisphere or north in the southern hemisphere). The angle of inclination, from the horizontal, can vary depending on the season,[53]​ but if it is fixed, it must be adjusted to obtain optimal production of the assembly during the part of maximum electrical demand of a typical year for a stand-alone system.[53]​ This angle of optimal inclination of the module is not necessarily identical to the angle of inclination for the maximum annual energy production of the assembly. Optimizing the PV system for a specific environment can be complicated, as issues such as solar flux, dirt, and snow losses must be taken into account. Furthermore, subsequent work has shown that spectral effects can play a role in optimal photovoltaic material selection. For example, spectral albedo can play an important role in production depending on the surface area surrounding the PV system and the type of solar cell material. For the climate and latitudes of the United States and Europe, typical sunshine ranges from 4 kWh/m²/day in northern climates to 6.5 kWh/m²/day in the sunniest regions. A photovoltaic installation in the northern latitudes of Europe or the United States can expect to produce 1 kWh/m²/day. A typical 1 kW PV installation in Australia or in the southern latitudes of Europe or the United States can produce between 3.5 and 5 kWh per day, depending on location, orientation, inclination, insolation and other factors. In the Sahara Desert, with less cloud cover and a better solar angle, around 8.3 kWh/m²/day could ideally be obtained, as long as the wind, almost always present, does not blow sand onto the units. The area of ​​the Sahara Desert is more than 9 million km². Of these, 90,600 km² (that is, about 1%) could generate as much electricity as all the power plants in the world combined.[54]​.

Mounting

Modules are assembled in arrays on some type of mounting system, which can be classified as ground, roof, or pole mounting. In the case of solar parks, a large frame is assembled on the ground and the modules are mounted on it. In the case of buildings, many different frames have been devised for pitched roofs. For flat roofs, racks, containers and building-integrated solutions are used. Pole-mounted solar panel racks can be fixed or mobile. Pole side supports are suitable for situations where a pole has something else mounted on its top, such as a light fixture or antenna. Pole mounting elevates what would otherwise be a ground-mounted assembly above the shadows of brush and livestock, and can satisfy electrical code requirements for inaccessibility of exposed wiring. Pole-mounted panels are open to more cooling air at their bottom, increasing performance. A multiplicity of pole-mounted racks can form a parking carport or other shade structure. A frame that does not follow the sun from left to right may allow for seasonal adjustment up or down.

Cabling

Due to their outdoor use, solar cables are designed to be resistant to ultraviolet radiation and extremely high temperature fluctuations and are generally not affected by weather. Standards specifying the use of electrical wiring in photovoltaic systems include the International Electrotechnical Commission's IEC 60364, in section 712 "Solar Photovoltaic (PV) Supply Systems", the British Standard BS 7671, which incorporates regulations relating to microgeneration and photovoltaic systems, and the US Standard UL4703, in topic 4703 "Photovoltaic Cable".

Tracker

A solar tracking system tilts a solar panel throughout the day. Depending on the type of tracking system, the panel is aimed directly at the sun or at the brightest area of ​​a partly cloudy sky. Trackers greatly improve early morning and late afternoon performance, increasing the total amount of power produced by a system by 20-25% for a single-axis tracker and by 30% or more for a two-axis tracker, depending on latitude.[55][56] Trackers are effective in regions that receive a large portion of sunlight directly. In diffuse light (i.e. under clouds or fog), tracking has little or no value. Since most concentrated photovoltaic systems are very sensitive to the angle of sunlight, tracking systems allow them to produce useful power for more than a short period per day.[57]​ Tracking systems improve performance for two main reasons. First, when a solar panel is perpendicular to sunlight, it receives more light on its surface than if it were tilted. Second, direct light is used more effectively than angled light.[58]​ Special anti-reflective coatings can improve the efficiency of the solar panel for direct and angled light, somewhat reducing the tracking benefit.[59]​.

Trackers and sensors to optimize performance are often considered optional, but can increase viable output by up to 45%.[60] Arrays approaching or exceeding one megawatt often use solar trackers. Taking into account the clouds, and the fact that most of the world is not at the equator, and that the sun sets at night, the correct measure of solar energy is insolation, the average number of kilowatt-hours per square meter per day. For the climate and latitudes of the United States and Europe, typical insolation ranges from 2.26 kWh/m/day in northern climates to 5.61 kWh/m/day in the sunniest regions.[61][62]​.

For large systems, the energy gained from using monitoring systems can offset the added complexity. For very large systems, the added maintenance of tracking is a substantial detriment.[63]​ Tracking is not necessary for flat, low-concentration PV systems. For highly concentrated photovoltaic systems, dual-axis tracking is a necessity.[64]​ Price developments influence the balance between adding more fixed solar panels and having fewer tracked panels.

As the prices, reliability and performance of single-axis trackers have improved, the systems have been installed on an increasing percentage of utility-scale projects. According to data from WoodMackenzie/GTM Research, global shipments of solar trackers reached a record 14.5 gigawatts in 2017. This represents 32 percent year-over-year growth, with similar or greater growth projected as large-scale solar deployment accelerates.[65]​.

Investor

Systems designed to supply alternating current (AC), such as grid-tied applications, require an inverter to convert direct current (DC) from solar modules to AC. Grid-tied inverters must supply AC electricity in a sinusoidal manner, synchronized with the grid frequency, limit the supply voltage to no higher than the grid voltage, and disconnect from the grid if the grid voltage is off.[66]​ Islanded inverters only need to produce regulated voltages and frequencies in a sine wave form, as no synchronization or coordination with grid supplies is required.

A solar inverter can be connected to a string of solar panels. In some installations a solar microinverter is connected to each solar panel.[67]​ For safety reasons, a circuit breaker is provided on both the AC and DC sides to allow for maintenance. The AC output can be connected to the utility grid through an electricity meter.[68]​ The number of modules in the system determines the total DC watts the solar array can generate; However, the inverter ultimately governs the amount of AC watts that can be distributed for consumption. For example, a PV system comprised of 11 kilowatts DC (kW) of PV modules, paired with a 10 kilowatt AC (kW) inverter, will be limited to the inverter power of 10 kW. In 2019, the conversion efficiency of the latest generation converters reached more than 98%. While string inverters are used in residential and medium-sized commercial PV systems, central inverters cover the commercial and large-scale market. The market share of central and string inverters is approximately 44% and 52%, respectively, and less than 1% for microinverters.[69]​.

Maximum power point tracking (MPPT) is a technique used by grid-connected inverters to obtain the maximum possible power from the photovoltaic array. To do this, the inverter's MPPT system digitally samples the ever-changing power output of the solar panel and applies the appropriate resistance to find the optimal maximum power point.[70]​.

Anti-islanding is a protection mechanism to immediately shut down the inverter, preventing it from generating AC power when the connection to the load no longer exists. This occurs, for example, in the event of a blackout. Without this protection, the supply line would become a powered "island" surrounded by a "sea" of unpowered lines, as the solar array continues to supply DC power during the blackout. Isolation is a hazard to power company workers, who may not realize that an AC continues to receive power, and may prevent devices from automatically reconnecting.[71]​ Anti-islanding is not required for complete off-grid systems.

Battery

Although still expensive, photovoltaic systems increasingly use rechargeable batteries to store surplus that will then be used at night. Batteries used for grid storage also stabilize the electrical grid by leveling peak loads and play an important role in a smart grid as they can charge during periods of low demand and feed their stored energy to the grid when demand is high.

The most widely used battery technologies in current photovoltaic systems are the valve-regulated lead-acid battery - a modified version of the conventional lead-acid battery -, nickel-cadmium batteries and lithium-ion batteries. Compared to the other types, lead-acid batteries have a shorter lifespan and lower energy density. However, due to their high reliability, low self-discharge and low investment and maintenance costs, they are currently the predominant technology in small-scale residential photovoltaic systems, since lithium-ion batteries are still in the development phase and are about 3.5 times more expensive than lead batteries. Furthermore, as the storage devices of photovoltaic systems are stationary, the lower energy and power density and therefore the greater weight of lead-acid batteries are not as critical as, for example, in electric transportation[9] Other rechargeable batteries considered for distributed photovoltaic systems are sodium-sulfur and vanadium-redox, two prominent types of molten salt and flow batteries, respectively[9] In 2015, Tesla Motors launched the Powerwall, a rechargeable lithium-ion battery with the aim of revolutionizing energy consumption.[73]​.

Photovoltaic systems with an integrated battery solution also need a charge controller, as the variable voltage and current of the solar panel requires constant adjustment to prevent damage from overcharging.[74]​ Basic charge controllers can simply turn photovoltaic panels on and off, or they can measure pulses of power as needed, a strategy called PWM or pulse width modulation. More advanced charge controllers will incorporate MPPT logic into their battery charging algorithms. Charge controllers can also divert power for some purpose other than battery charging. Instead of simply turning off the free PV power when it is not needed, a user can choose to heat air or water once the battery is full.

Control and measurement

The counter must be capable of accumulating units of energy in both directions, or two counters must be used. Many meters accumulate bidirectionally, some systems use two meters, but a unidirectional meter (with detent) will not accumulate energy from any resulting feed to the grid.[75]​ In some countries, a frequency and voltage monitor with disconnection of all phases is required for installations over 30 kWp. This is done when more solar energy is generated than the power company can accommodate, and the excess cannot be exported or stored. Historically, grid operators have had to provide transmission lines and generation capacity. Now they have to provide storage as well. Typically this is hydraulic storage, but other means of storage are also used. Initially, storage was used so that baseload generators could operate at full capacity. With variable renewable energy, storage is necessary to allow energy to be generated whenever available, and consumed whenever necessary.

The two variables a grid operator has are storing electricity for when it is needed or transmitting it to where it is needed. If both fail, installations larger than 30 kWp may automatically shut down, although in practice all inverters maintain voltage regulation and stop supplying power if the load is inadequate. Grid operators have the option of reducing excess generation from large systems, although this is more commonly done with wind power than solar power, and results in a substantial loss of revenue.[76]​ Three-phase inverters have the unique option of supplying reactive power, which can be advantageous in meeting load requirements.[77]​.

Photovoltaic installations need to be monitored to detect faults and optimize their operation. There are several photovoltaic monitoring strategies depending on the performance of the installation and its nature. Monitoring can be done on site or remotely. You can measure only production, retrieve all data from the inverter, or retrieve all data from communication equipment (probes, meters, etc.). Monitoring tools can be dedicated to monitoring only or offer additional functions. Individual inverters and battery charge controllers may include monitoring using manufacturer-specific protocols and software.[78] An inverter's energy metering may have limited accuracy and may not be suitable for revenue metering purposes. A third-party data acquisition system can monitor multiple inverters, using the inverter manufacturer's protocols, and also acquire information related to weather conditions. Stand-alone smart meters can measure the total energy production of a PV installation. Independent measurements, such as satellite image analysis or a solar radiation meter (a pyranometer), can be used to estimate total sunshine for comparison.[79] Data collected by a monitoring system can be viewed remotely via the World Wide Web, such as OSOTF.

Sizing of the photovoltaic system

Knowing the annual energy consumption in kWh of an institution or a family, for example 2300Kwh, legible on their electricity bill, it is possible to calculate the number of photovoltaic panels necessary to satisfy their energy needs. When connecting to the site https://re.jrc.ec.europa.eu/pvg_tools/es/, after selecting the location in which to install the panels or clicking on the map or writing the name of the location, you must select "Network PV" and "Show results" obtaining the following table for example referring to the city of Palermo:.

Using the wxMaxima program "Maxima (software)"), the number of panels required for an annual consumption of 2300 kWh and for a crystalline silicon technology with an inclination angle of 35°, an orientation angle of 0° and total losses equal to 21.88 % is 6 rounded:.

On average, each family manages to consume 30% of energy directly from photovoltaics. The storage system can bring its self-consumption to a maximum of 70%, therefore the storage capacity of the battery that must be in the specific case is: 4.41 kWh, which is rounded to 4.8 kWh.

If the price of energy is €0.5/Kwh, the cost of energy without taxes will be €1,150 per year:.

So if a 300W panel costs €200, the 4.8Kwh battery costs €3000, the inverter to convert direct current into alternating current €1000, the charge regulator €100, the installation costs €1000, the total cost will be €6300:.

that are amortized in 5.46 years:.

the battery having a life of 10 years and the panels 25-30 years.

Esta sección incluye sistemas que son altamente especializados y poco comunes o que aún son una nueva tecnología emergente con importancia limitada. Sin embargo, los sistemas autónomos o fuera de la red ocupan un lugar especial. Eran el tipo de sistema más común durante las décadas de 1980 y 1990, cuando la tecnología fotovoltaica todavía era muy cara y era un nicho de mercado puro de aplicaciones a pequeña escala. Solo en lugares donde no había red eléctrica disponible, eran económicamente viables. Aunque todavía se están implementando nuevos sistemas autónomos en todo el mundo, su contribución a la capacidad fotovoltaica total instalada está disminuyendo. En Europa, los sistemas fuera de la red representan el 1 por ciento de la capacidad instalada. En los Estados Unidos, representan alrededor del 10 por ciento. Los sistemas fuera de la red todavía son comunes en Australia y Corea del Sur, y en muchos países en desarrollo.[8]​.

CPV

Concentrating photovoltaics (CPV) and high concentration photovoltaics (HCPV) systems use optical lenses or curved mirrors to concentrate sunlight into small but highly efficient solar cells. In addition to concentrating optics, CPV systems sometimes use solar trackers and cooling systems and are more expensive.

Especially HCPV systems are best suited to locations with high solar irradiance, concentrating sunlight up to 400 times or more, with efficiencies of 24 to 28 percent, higher than those of regular systems. There are several system designs available on the market, but they are not very common. However, it is being researched and developed.[1]​.

CPV is often confused with CSP (concentrated solar power) which does not use photovoltaics. Both technologies favor places that receive a lot of sunlight and compete directly with each other.

Hybrid

A hybrid system combines photovoltaic power with other forms of generation, usually a diesel generator. Biogas is also used. The other form of generation may be a type capable of modulating energy production based on demand. However, more than one form of renewable energy can be used, for example wind. Photovoltaic energy generation serves to reduce non-renewable fuel consumption. Hybrid systems are most often found on islands. Pellworm Island in Germany and Kythnos Island in Greece are notable examples (both are combined with wind).[80]​[81]​ The Kythnos plant has reduced diesel consumption by 11.2%.[82]​.

In 2015, a case study carried out in seven countries concluded that in all cases generation costs can be reduced through the hybridization of mini-grids and isolated networks. However, the financing costs of these hybrids are crucial and largely depend on the ownership structure of the power plant. While the cost reduction for public companies can be significant, the study also identified that the economic benefits are negligible or even negative for non-public companies, such as independent power producers.[83][84]​.

There has also been work demonstrating that the penetration limit of PV can be increased by deploying a distributed network of hybrid PV + CHP systems in the US.[85] The temporal distribution of solar flux and the electrical and heating needs of representative single-family residences in the US was analyzed and the results clearly show that hybridization of CHP with PV can enable additional deployment of PV above which is possible with a conventional centralized electricity generation system. This theory was reconfirmed with numerical simulations using per-second solar flux data to determine that the battery reserve required to provide such a hybrid system is possible with relatively small and inexpensive battery systems.[86]​ In addition, large photovoltaic and cogeneration systems can be installed in institutional buildings, which in turn provides backup for intermittent photovoltaics and reduces cogeneration runtime.[87]​.

• - The PVT system (hybrid PV/T), also known as photovoltaic thermal hybrid solar collectors, converts solar radiation into thermal and electrical energy. This system combines a solar module (PV) with a solar thermal collector in a complementary way.

• - CPVT System. A hybrid concentrated photovoltaic thermal system (CPVT) is similar to a PVT system. It uses concentrated photovoltaics (CPV) instead of conventional photovoltaic technology and combines it with a solar thermal collector.

• - CPV/CSP System. A novel CPV/CSP hybrid solar system has been proposed, which combines the photovoltaic concentrator with the non-photovoltaic technology of concentrated solar energy (CSP), also known as concentrated solar thermal.[88]​.

• - Diesel photovoltaic system. It combines a photovoltaic system with a diesel generator.[89]​ Combinations with other renewable energies are possible and include wind turbines.[90]​.

floating solar panels

Floating solar arrays are photovoltaic systems that float on the surface of drinking water tanks, quarry lakes, irrigation canals or sanitation and waste ponds. These systems are called "floating" when used solely for electrical production or "aquavoltaic" when used to synergistically enhance aquaculture[91]. A small number of these systems exist in France, India, Japan, South Korea, the United Kingdom, Singapore and the United States.[92]​[93][94][95][96]​.

The systems are said to have advantages over ground-based photovoltaics. The cost of land is more expensive and there are fewer rules and regulations for structures built on bodies of water not used for recreation. Unlike most land-based solar plants, floating arrays can be discreet because they are hidden from public view. They achieve greater efficiency than ground-based photovoltaic panels, because the water cools the panels. The panels have a special coating to prevent rust or corrosion.[97]​.

In May 2008, the Far Niente winery in Oakville, California, pioneered the installation of the world's first floating photovoltaic system by installing 994 solar photovoltaic modules with a total capacity of 477 kW on 130 pontoons and floating them in the winery's irrigation pond.[98]​ The main advantage of this system is that it avoids the need to sacrifice valuable land area that could be used for another purpose. In the case of the Far Niente winery, 0.75 acres (0.30 ha) were saved that would have been necessary for a land-based system.[99] Another advantage of a floating photovoltaic system is that the panels are kept at a cooler temperature than on land, allowing for greater efficiency in converting solar energy. The floating photovoltaic system also reduces the amount of water lost through evaporation and inhibits algae growth.[100]​.

Floating photovoltaic parks are beginning to be built on a commercial scale. Electronics and ceramics multinational Kyocera will build the world's largest, a 13.4 MW farm on the Yamakura Dam reservoir in Chiba Prefecture.[101]​ using 50,000 solar panels.[102]​[103]​ Saltwater-resistant floating farms are also being considered for ocean use, with experiments in Thailand.[104]​ The largest floating energy project announced so far It is a 350 MW power plant in the Amazon region of Brazil.[105]​.

DC network

DC networks are found in electric transport: trams and trolleybuses. Some pilot plants have been built for such applications, such as the tram depots in Hannover Leinhausen, using photovoltaic contributors[106] and Geneva (Bachet de Pesay).[107] The 150 kWp Geneva plant directly powers the tram and trolleybus electrical network with 600 V direct current, whereas it previously provided around 15% of the electricity at its inauguration in 1999.

Autonomous system

A stand-alone or isolated system is not connected to the electrical grid. Autonomous systems vary widely in size and application, from wristwatches or calculators to remote buildings or spacecraft. If the load must be powered independently of solar insolation, the generated energy is stored and buffered with a battery.[108] In non-portable applications where weight is not an issue, such as in buildings, lead-acid batteries are most commonly used due to their low cost and tolerance for abuse.

A charge controller can be incorporated into the system to prevent damage to the battery due to excessive charging or discharging. It can also help optimize solar array output using a maximum power point tracking (MPPT) technique. However, in simple PV systems where the PV module voltage matches the battery voltage, the use of MPPT electronics is generally considered unnecessary, as the battery voltage is stable enough to provide near-maximum energy harvesting from the PV module. In small devices (e.g. calculators, parking meters) only direct current (DC) is consumed. In larger systems (e.g. buildings, remote water pumps) air conditioning is usually required. To convert the DC from the modules or batteries to AC, an inverter is used. "Inverter (electronics)").

In agricultural settings, the array can be used to directly power DC pumps, without the need for an inverter "Inverter (electronics)"). In remote environments such as mountainous areas, islands, or other locations where grid power is not available, solar panels can be used as the only source of electricity, usually charging a storage battery. Autonomous systems are closely related to microgeneration and distributed generation.

• - Pico photovoltaic systems.

• - Solar street lights.

Solar street lights are light sources that are powered by photovoltaic panels generally mounted on the lighting structure. The solar array of this off-grid PV system charges a rechargeable battery, which powers a fluorescent or LED lamp at night. Solar street lights are autonomous power systems and have the advantage of saving on excavation and maintenance costs, as well as on the electricity bill, despite their higher initial cost compared to conventional street lighting. They are designed with batteries large enough to ensure they operate for at least a week and even in the worst situation, they are expected to dim only slightly.

• - Telecommunication and signaling.

• - Solar vehicles.

• - Solar pumps.

One of the most cost-effective solar applications is a solar-powered pump, as it is much cheaper to purchase a solar panel than to install power lines[111]​[112][113]​ They often meet a water need beyond the reach of power lines, taking the place of a windmill or wind pump. A common application is filling water tanks for livestock so they can drink. Another is refilling the drinking water tanks of remote or self-sufficient houses.

El costo de producir células fotovoltaicas se ha reducido debido a las economías de escala en la producción y los avances tecnológicos en la fabricación. Para las instalaciones a gran escala, los precios por debajo de $ 1,00 por vatio eran comunes en 2012.[118]​ Se había logrado una disminución de precios del 50% en Europa de 2006 a 2011 y existe la posibilidad de reducir el costo de generación en un 50% para 2020.[119]​ Las células solares de silicio cristalino han sido reemplazadas en gran medida por células solares de silicio multicristalino menos costosas, y las células solares de silicio de película delgada también se han desarrollado a costos de producción más bajos. Aunque se reducen en eficiencia de conversión de energía a partir de "siwafers" monocristalinos, también son mucho más fáciles de producir a costos comparativamente más bajos.

La siguiente tabla muestra el costo total (promedio) en centavos de dólar por kWh de electricidad generada por un sistema fotovoltaico.[120]​[121]​ Los encabezados de las filas de la izquierda muestran el costo total, por kilovatio pico (kW ), de una instalación fotovoltaica. Los costos de los sistemas fotovoltaicos han ido disminuyendo y en Alemania, por ejemplo, se informó que habían caído a USD 1389 / kW a fines de 2014.[122]​ Los encabezados de las columnas en la parte superior se refieren a la producción de energía anual en kWh esperada de cada kW instalado. Esto varía según la región geográfica porque la insolación promedio depende de la nubosidad promedio y el grosor de la atmósfera atravesada por la luz solar. También depende de la trayectoria del sol en relación con el panel y el horizonte. Los paneles generalmente se montan en un ángulo basado en la latitud y, a menudo, se ajustan estacionalmente para adaptarse a la declinación "Declinación (astronomía)") solar cambiante. El seguimiento solar también se puede utilizar para acceder a una luz solar aún más perpendicular, aumentando así la producción total de energía.

Los valores calculados en la tabla reflejan el costo total (promedio) en centavos por kWh producido. Asumen un costo de capital total del 10% (por ejemplo , una tasa de interés del 4%, un costo de operación y mantenimiento del 1%,[123]​ y la depreciación del desembolso de capital durante 20 años). Normalmente, los módulos fotovoltaicos tienen una garantía de 25 años.[124]​[125]​.

System cost in 2013

In its 2014 edition of the "Technology Roadmap: Solar Photovoltaic Energy" report, the International Energy Agency (IEA) published dollar-per-watt prices for residential, commercial, and utility-scale photovoltaic systems in eight major markets in 2013.[126]​.

Learning curve

Photovoltaic systems demonstrate a learning curve in terms of levelized cost of electricity (LCOE), reducing their cost per kWh by 32.6% for each doubling of capacity.[127]​[128][129]​ Using LCOE and cumulative installed capacity data from the International Renewable Energy Agency (IRENA) from 2010 to 2017, the learning curve equation for photovoltaic systems is it gives like.

• - LCOE: levelized cost of electricity (in USD / kWh).

• - Capacity: accumulated installed capacity of photovoltaic systems (in MW).

Standardization

The increasing use of photovoltaic systems and the integration of photovoltaic energy into existing supply and distribution structures and techniques increase the need for general standards and definitions for photovoltaic components and systems. Standards are compiled by the International Electrotechnical Commission (IEC) and apply to the efficiency, durability and safety of cells, modules, simulation programs, connectors and cables, mounting systems, overall efficiency of inverters, etc.[130]​.

National regulations

In the UK, PV installations are generally considered permitted development and do not require planning permission. If the property is listed or is in a designated area (national park, area of ​​outstanding natural beauty, site of special scientific interest or Norfolk Broads), planning permission is required.[131]​.

In the United States, Article 690 of the National Electrical Code provides general guidelines for the installation of photovoltaic systems; these may be superseded by local laws and regulations. A permit requiring the submission of structural plans and calculations is often required before work can begin. Additionally, many locations require that work be done under the guidance of a licensed electrician.

In the United States, the Authority Having Jurisdiction (AHJ) will review designs and issue permits before construction can legally begin. Electrical installation practices must meet the standards set forth in the National Electrical Code (NEC) and be inspected by the authority having jurisdiction to ensure compliance with the building code, electrical code, and fire safety code. Jurisdictions may require that equipment have been tested, certified, listed, and labeled by at least one of the Nationally Recognized Testing Laboratories (NRTL).[132]​ In the US, many localities require a permit to install a photovoltaic system. A grid-tied system typically requires a licensed electrician to make the connection between the system and the building's grid-connected wiring.[133] Installers who meet these qualifications are found in nearly every state. Several states prohibit homeowners associations from restricting solar devices.[134][135][136]​.

Although Spain generates around 40% of its electricity through photovoltaics and other renewable sources, and cities like Huelva and Seville have almost 3,000 hours of sunshine a year, in 2013 Spain issued a solar tax to account for the debt created by the investment made by the Spanish government. Those who do not connect to the grid can face a fine of up to 30 million euros ($40 million)[137]​[138]​ Such measures were finally withdrawn in 2018, when new legislation was introduced prohibiting any tax on self-consumption of renewable energy.[139]​.

Pollution and energy in photovoltaic production

Photovoltaics is a well-known method of generating clean, emission-free electricity. Photovoltaic systems are usually composed of photovoltaic modules and inverters (which transform direct current into alternating current). Photovoltaic modules are mainly made of photovoltaic cells, which have no fundamental difference from the material for making computer chips. The production process of photovoltaic cells (computer chips) requires large energy consumption and involves the use of chemicals that are highly toxic to the environment. There are few photovoltaic manufacturing plants around the world that produce photovoltaic modules with energy produced from photovoltaic cells. This measure greatly reduces the carbon footprint during the manufacturing process. The management of chemicals used in the manufacturing process is subject to local factory laws and regulations.

Impact on the electrical grid

With the rise of rooftop photovoltaic systems, the flow of energy becomes bidirectional. When there is more local generation than consumption, electricity is exported to the grid. However, the power grid is not traditionally designed to deal with two-way energy transfer. Therefore, some technical problems may arise. For example, in Queensland, Australia, there were more than 30% of households with rooftop PV at the end of 2017. The famous California duck curve of 2020 has appeared very frequently in many communities since 2015. A surge problem may appear when electricity returns to the grid.[140] There are solutions to manage the surge problem, such as power factor regulation of PV inverters, new equipment voltage and energy control at the level of electricity distributors, rerouting of electrical cables, demand management, etc. These solutions usually have limitations and costs.

Implication in the management of the electricity bill and energy investment

Customers have different specific situations, for example, different comfort/convenience needs, different electricity rates, or different usage patterns. An electricity tariff can have several elements, such as the daily access and metering rate, the energy rate (based on kWh, MWh), or the peak demand rate (for example, a price for the highest 30-minute energy consumption in a month). Photovoltaics is a promising option to reduce energy tariff when the price of electricity is reasonably high and increasing continuously, such as in Australia and Germany. However, where a peak demand charge applies, PV may be less attractive if peak demand occurs primarily in the late afternoon or early evening, for example in residential communities. In general, energy investment is largely an economic decision and investment decisions are based on the systematic evaluation of operational improvement, energy efficiency, on-site generation and energy storage options.[141]​[142]​.

• - Photovoltaic Energy Fact Sheet from the Center for Sustainable Systems at the University of Michigan.

• - Home Power Magazine http://www.homepower.com/.

• - Management of solar projects.

• - Photovoltaic Systems Engineering Archived July 19, 2019 at the Wayback Machine.

• - Best Practices for Siting Solar Photovoltaics at Municipal Solid Waste Landfills: A study prepared in partnership with the Environmental Protection Agency for the RE-Powering America's Land Initiative: Siting Renewable Energy on Potentially Contaminated Land and Mining Sites National Renewable Energy Laboratory.