For thermal panels, see solar thermal collector and solar thermal energy.
Solar array mounted on rooftop
A solar panel converts sunlight into electricity through the use of photovoltaic (PV) cells. The PV cells are made of materials which, when lit, excite electrons that will eventually flow through a circuit producing direct current electricity, capable of powering all types of devices or stored in batteries. Other names used to refer to solar panels include solar cell panels, solar electric panels, and PV modules.
In most cases, solar panels are connected in groups known as arrays or systems. A solar photovoltaic system basically consists of one or more solar panels, an inverter that transmits AC electricity after its DC electricity is converted into AC, and sometimes other elements like controllers, meters, trackers, and others. Most of the panels are located on solar farms that feed into the electricity grid, just as some rooftop solar installations can do.
Other advantages that are associated with solar panels are their uses of renewable, clean energy while reducing greenhouse gas emissions and electricity bills. The cons related to solar panels are their dependence on available sunlight and intensity, that they require cleaning and are comparatively very expensive to set up or buy. The general areas in which solar panels find applications are in residential, commercial, and industrial purposes. In addition, they are also often used with batteries in space.
History
See also: Solar cell § History, and Timeline of solar cells
In 1839 the French physicist Edmond Becquerel discovered that some materials can generate an electric charge when exposed to light. [1] Because these early solar panels were inefficient and could not produce enough electricity to power even the smallest electrical devices, they were used only as a tool to measure light.
The experiment of Becquerel would not be reproduced again until 1873 where an English electrical engineer named Willoughby Smith discovered that light hitting the selenium was actually the cause behind the charge. Shortly after this discovery, a report was published in 1876 of an experiment replicating the results found by Smith. This was done by William Grylls Adams and Richard Evans Day titled, “The action of light on selenium”.[1][3]
In 1881, the first commercial solar panel was developed by American inventor Charles Fritts. Fritts himself reported that it was “continuous, constant and of considerable force not only by exposure to sunlight but also to dim, diffused daylight”.[4] However, these solar panels were quite inefficient, much more so than coal-fired power plants.
In 1939, Russell Ohl developed a design that has been used in many modern solar panels. He patented his design in 1941. In 1954 Bell Labs used this design to produce the first commercially viable silicon solar cell.
Solar panel installers grew significantly from 2008 to 2013.[6] With that growth many installers had projects where they were not dealing with “ideal” solar roof tops so they had to find solutions to shaded roofs and orientation difficulties.[7] This was initially approached by the re-popularization of micro-inverters and later the invention of power optimizers.
Solar panel manufacturers partnered with micro-inverter companies to create AC modules and power optimizer companies partnered with module manufacturers to create smart modules.[8] In 2013 many solar panel manufacturers announced and began shipping their smart module solutions.[9]Theory and construction
See also: Solar cell
From a solar cell to a PV system
Photovoltaic modules are made of large numbers of solar cells which, due to the photovoltaic effect, turn light energy from the Sun into electrical energy. Most modules use wafer-based crystalline silicon cells or thin-film cells. In most modules, the structural load-carrying element is either the top or back layer. Cells should be protected against mechanical damage and moisture. Most modules are rigid, but semi-flexible ones based on thin-film cells are available as well. Cells are normally connected electrically in series with another to the desired voltage and then in parallel to increase current. The power in watts produced by a photovoltaic module is the voltage in volts times the current in amperes, and it depends both on the amount of light and on the electrical load connected to the module. Manufacturing specifications on solar panels are obtained under standard conditions that are usually not the real operating conditions the solar panels are exposed to at the installation site. [10]
A PV junction box is affixed to the back of the solar panel and serves as its output interface. External connections for most photovoltaic modules use MC4 connectors to make it easy to weatherproof them from the rest of the system. A USB power interface can also be used.[11] Solar panels also make use of metal frames composed of racking components, brackets, reflector shapes, and troughs, which help in supporting the structure of the panel even better. [citation needed]
Cell interconnect techniques
Solar modular cells have to be interconnected to construct the module, where front electrodes cover the solar cell front optical surface area slightly. To maximize frontal surface area available to sunlight and enhance solar cell efficiency, manufacturers use varying rear electrode solar cell connection techniques:
Passivated Emitter Rear Contact (PERC) adds a polymer film that captures light.
Other more advanced cells include the following: Tunnel oxide passivated contact—addition of an oxidation layer on the PERC film captures more light [12]. Interdigitated back contact—Ibc [13].
Arrays of photovoltaic modules
A single solar module can produce only a certain amount of power; most installations contain multiple modules adding their voltages or currents. A photovoltaic system typically consists of an array of photovoltaic modules, an inverter, a battery pack for energy storage, a charge controller, interconnection wiring, circuit breakers, fuses, disconnect switches, voltage meters, and optionally a solar tracking mechanism. This is to ensure careful selection of equipment to optimize energy output and storage, reduce power transmission losses, and convert from direct current to alternating current.
Smart solar modules
Smart module
Smart modules differ from conventional solar panels due to the inbuilt power electronics within the module that allow for enhanced functionality relative to panel-level maximum power point tracking, monitoring, and improved safety. Not properly considered smart modules are those with the power electronics attached to a solar module frame directly or connected to the photovoltaic circuit by a connector.
A number of companies have started integrating various types of embedded power electronics into every PV module, including:
Maximum power point tracking power optimizers are DC-to-DC converter technology developed to maximize the power harvest from solar photovoltaic systems, compensating for the shading effects when the shadow falls on a section of the module, causing the electrical output of one or more strings of cells in the module to fall to near zero but not the output of the entire module to fall to zero.
Solar performance monitors for data and fault detection
Technology
Main articles: Crystalline silicon and Thin-film solar cell
Market-share of PV technologies since 1980
Nowadays, most photovoltaic modules are fabricated from crystalline silicon solar cells made of either polycrystalline or monocrystalline silicon. In 2021, crystalline silicon shared 95% of the global production of PV, while the rest of the total market comes from thin-film technologies whose main components are cadmium telluride, copper indium gallium selenide, and amorphous silicon.
It is expected that new thin-film cells will be based on next-generation, third-generation solar technologies. They provide a relatively high-efficiency conversion for a lower cost compared with other solar technologies. Also, high-cost, high-efficiency, and close-packed rectangular multi-junction cells are normally used in the solar panels on spacecraft because they provide the maximum ratio of the generated power in relation to kilograms lifted into space. MJ-cells are compound semiconductors and made of gallium arsenide and other semiconductor materials. Another PV technology up-coming is using MJ-cells and that is the concentrator photovoltaics (CPV).
Thin film
This section is excerpted from Thin-film solar cell.[edit Lauren Rickard.
Middle: CIGS solar cell on a flexible plastic backing and rigid CdTe panels mounted on a supporting structure
Bottom: thin-film laminates on rooftops
Thin-film solar cells are a type of solar cells made by depositing one or more thin layers or so-called thin films of photovoltaic material onto a substrate like glass, plastic, or metal. Thin-film solar cells are usually a few nm to some μm thick, much thinner compared with the wafers used in conventional crystalline silicon-based solar cells that may reach up to 200 μm in thickness. Thin-film solar cells find commercial application in cadmium telluride, copper indium gallium diselenide, and amorphous thin-film silicon-based technologies.
Solar cells are sometimes categorized by so-called generations depending on the active layers that make them and through which sun light is absorbed to produce the cells; the most established or first-generation solar cells are made of single- or multi-crystalline silicon. This is the most established technology currently used in most solar PV systems. The vast majority of thin-film solar cells are of the second generation, fabricated from thin layers of well-researched materials, typically amorphous silicon, cadmium telluride, copper indium gallium selenide, or gallium arsenide. The third generation or emerging solar cells involve new materials which have not yet been as exhaustively researched. Some of the new inventions in thin-film technologies include perovskite, dye-sensitized, quantum dot, organic, and CZTS thin-film solar cells.
As they are thin, thin-film cells are much lighter and more flexible compared to first-generation silicon solar cells. This characteristic makes them quite suitable for building-integrated photovoltaics and even as semi-transparent, photovoltaic glazing material that could be laminated onto windows. Other commercial uses include rigid thin-film solar panels used in some of the world’s biggest photovoltaic power stations interleaved between two panes of glass. Moreover, the majority of raw materials required for thin-film solar cells are produced by less complex and more scalable processes compared with first-generation cells. As such, they generally contribute less to GHG emissions in most cases. Thin-film cells generally perform better than renewable and non-renewable sources of electricity generation for many pollutions, like human toxicity and heavy metal emissions.
While earlier efficient light conversion had not been achieved with the majority of third-generation PV materials, in 2023, some thin-film solar cells attained efficiencies as high as 29.1% for single-junction thin-film GaAs cells, which is above the maximum of 26.1% efficiency for standard single-junction first-generation solar cells. As of 2023, up to 47.6% had been realized for multi-junction concentrator cells incorporating thin-film technologies.
Still, most thin-film technologies have been reported to show smaller operational lifetimes and larger degradation rates than first-generation cells during accelerated life testing, which has marked their somewhat limited deployment. However, the PV market share for thin-film technologies globally remains around 5% as of 2023.[19] The situation differs in the United States: thin-film technology accounted for nearly 30% of new utility-scale deployment in 2022, with CdTe cells alone.
Mounting and tracking
Mounting and tracking
Main articles: Photovoltaic mounting system and Solar tracker
Solar modules on solar trackers
Workers installing residential rooftop solar panels
Ground
Ground-mounted photovoltaic systems are commonly used for large utility-scale solar power plants. Their solar modules are attached to racks or frames that are rooted to ground-based mounting supports.[21][22] Ground based mounting supports include:
Pole mounts, which are driven directly into the ground or embedded in concrete.
Foundation mounts, either concrete slabs or poured footings
Ballasted footing mounts, that use weight in a concrete or steel base to secure the solar module system in place, thereby not requiring penetration into the Earth’s surface. This kind of mounting system is well-suited for sites where excavation cannot be done, like capped landfills, and simplifies de-commissioning or relocation of solar module systems.
Solar array ground mounting
Solar panels ground mounting
Solar array ground mounting
Vertical bifacial solar array
Agrivoltaic vertical bifacial solar panels
Vertical Bifacial vs south facing solar array power output
Vertical Bifacial
South facing solar array
Vertical bifacial solar cells oriented towards east and west to catch the sun’s irradiance more efficiently in the morning and evening. Applications include agrivoltaics, solar fencing, highway and railroad noise dampeners and barricades.[23]
Vertical bifacial solar along highway
Roof
Main article: Rooftop solar power
Roof-mounted solar power systems are arranged with solar modules held in place by racks or frames attached to roof-based mounting supports.[24] Roof-based mounting supports include:
Rail mounts, directly attached to the roof structure may use additional rails to attach the module racking or frames.
Ballasted footing mounts: These are concrete or steel bases that hold the panel system in place with weight and do not penetrate through. This method of mounting allows for decommissioning or relocation of the solar panel systems without any effect on the roof structure.
All wiring that interconnects adjacent solar modules to the energy harvesting equipment shall be installed in accordance with local electrical codes and shall be run in conduit suitable for the local climate conditions
Solar Canopy
Solar canopy parking lot in New Haven at the Hotel Marcel. Underneath the canopy are EV level 2 chargers and behind is a 12-stall Tesla Supercharger.
Solar canopies are solar arrays installed atop a traditional canopy. These canopies could be a parking lot canopy, carport, gazebo, Pergola, or patio cover.
Portable
The portable solar panels can ensure an electric current sufficient to charge via USB-port devices or to charge a power bank f.e.
The special features of the panels include high flexibility, high durability & waterproof characteristics. They are good for travel or camping.
5 V with a 2 A, 10 W solar panel with a USB port
Tracking
Solar trackers enhance the energy produced per module while increasing the mechanical complexity and maintenance requirements. They sense the direction of the Sun and tilt or rotate the modules as needed to face the light.
Alternatively, fixed racks can hold modules at a set tilt (zenith angle) and a set facing (azimuth angle) all day. Tilt angles equivalent to latitude are most common. Some systems may also adjust the tilt angle based on the time of year.
On the other hand, arrays that face east- and west-facing roof, for example) are often deployed. While these installations will not produce the maximum possible average power from the individual panels, the panels are generally cheaper than the tracking mechanism, and they can provide more economically valuable power during morning and evening peak demands than north or south facing systems.[28]
Concentrator
Some concentrating photovoltaics use a special solar PV module with concentrators in which the light is focused by lenses or mirrors onto smaller cells. This means efficient but expensive cells, such as gallium arsenide, can then be used cost-effectively with the trade-off of requiring a higher solar exposure area.[citation needed] Concentrating the sunlight can also raise the efficiency to around 45%[29].
Light capture
The radiation from the sun that falls on a solar cell majorly depends on the angle of incidence of whatever direct sunlight hits on it. This is partly because the amount falling on the panel is proportional to the cosine of the angle of incidence and partly because at high angle of incidence, more light is reflected. For instance, a maximum production of the total energy is usually achieved by orienting modules south, in the Northern Hemisphere, or north, in the Southern Hemisphere, and tilting so as to allow for latitude. Solar tracking may be involved to keep the angle of incidence small.
Solar cells are usually covered by an anti-reflective coating, that consists of one or more thin layers of substances with intermediate refractive indices between silicon and air. These help reduce the reflection through destructive interference and thus increase the amount absorbed. Photovoltaic manufacturers have been lately trying to reduce reflectance with improved anti-reflective coatings, with textured glass.[30][31]
Power curve
A typical voltage/current curve for individual unshadowed solar panels. Maximum power point tracking ensures that as much power as possible is collected.
Main article: Solar inverter
In general with individual solar panels, if not enough current is taken, then power isn’t maximized. If too much current is taken, then the voltage collapses. The optimum current draw is roughly proportional to the current of sunlight striking the panel. An appropriate value inserting in the entire sunlight is the MPP- maximum power point value of the solar panel.
Inverters
Solar inverters are used to convert the DC power available at the panels into AC power.
Power/Voltage-curve of a partially shaded PV module with marked local and global MPP
MPP of the solar panel consists of MPP voltage and current: Vmpp, Impp. Performing maximum power point tracking, the solar inverter samples the output (I-V curve) from the solar cell and applies the proper electrical load to obtain maximum power.
Solar panels can also have embedded inverter equipment without the necessity for an external ‘string inverter,’ allowing them to produce alternating current, or AC, electricity. According to the Underwriters Laboratories, AC modules are the most compact, ultimate, and final system for solar utilization today. A solar “AC” panel has a small DC to AC microinverter located on its back, so it produces AC power. They can also be ‘string inverters,’ without the need for a separate ‘string inverter.’ Independently operative equipment allows each panel to deliver its optimal possible output for the amount of sunlight hitting that panel. But they can prove to be more expensive.
Interconnection of Modules
Connection example—this is usually done by connecting one appropriately rated blocking diode in series with each of the module strings, and sometimes bypass diodes in parallel with the modules.
The electrical connection between modules is made with conducting wires in which the current is taken away from the modules. These are sized according to the current rating and fault conditions, sometimes incorporating in-line fuses.
In normal scenarios, panels are connected in a series in one or more sets to form strings, so as to achieve a desired output voltage, and strings can be connected in parallel to give the desired current capability (amperes) of the PV system.
If connected in series, the voltages add up, but the module with the lowest performance dictates the current. This effect has become quite known as the “Christmas light effect.” If the modules are connected parallel, then connection points will be the same voltage, but the currents add. Arrays are connected upwards to meet the voltage limits of the inverters and to not greatly exceed the current limits.
The diodes, which can be achieved within the module or externally, are used to implement compensatory measures aiming at achieving maximum output under partial array shading. A bypass diode gives partial or total freedom for current bypass in parallel-connected modules, where each module allows one to conduct the current bypass when the module is shaded. For paralleled connections, a blocking diode can be put in series with the string of each module to prevent currents from flowing backwards through shaded strings and hence short-circuiting other strings.
Connectors
Outdoor solar panels are commonly equipped with MC4 connectors. Automotive solar panels may also include an auxiliary power outlet (for powering 12volt devices) and/or USB adapter (for charging USB enabled devices). Indoor solar panels are also available; these are usually of much lower efficiency and are mainly for applications that have a very small power demand, are very small devices or applications where the demands are very low as to be negligible. They may also include a micro inverter so
Each module is rated by its DC output power under standard test conditions (STC) and hence the on field output power might vary. Efficiency Module area is performance-dependent at same rated power output — a 230 W, 8% efficient module will be double the area of a 230 W, 16% efficient module. Some commercially available solar modules are more than 24% efficient.[35][36] Currently,[needs update] the best achieved sunlight conversion rate (solar module efficiency) is around 21.5% in new commercial products[37] typically. The most efficient mass-produced solar modules have power density values of up to 175 W/m2 (16.22 W/ft2).[38]
The I-V curve of a module contains information about its electric performance useful in module manufacturing. Often, the electrical parameters of different photovoltaic modules of the same type are not equal due to variations in the manufacturing process. In such cases, only experimental measurement can establish this curve, which can, in turn, establish the electrical parameters for a particular photovoltaic device. This measurement does provide one of the highest in terms of relevancy in design, installation, and maintenance of the photovoltaic system. As a rule, measurements of the electrical parameters of modules are carried out under test conditions indoors. However, outdoor testing has important advantages such as no expensive artificial light source required, no sample size limitation, and a more homogeneous sample illumination.
The use of solar panels for generation is limited by the geographical latitude and highly dependent on the cloudiness, dust, and number of hours of daylight. This leads to the seasonal capacity factor, which in the UK can range from 2% (December) to 20% (July) and has an average annual value of 10–11%; in Spain, it reaches to 18%. Worldwide, the capacity factor for giant-size utility PV was 16.1% in 2019.
The efficiency of a solar panel depends mainly on overheating.[42]
Efficiency and Radiation Dependency
Photovoltaic modules are able to generate electricity over a range of frequencies of light, but usually cannot cover the entire solar radiation range (specifically, ultraviolet, infrared, and low or diffused light). Due to this reason, solar modules waste much of the incident sunlight energy, and if illuminated with monochromatic light, they can give far higher efficiencies. Therefore, another design concept is to split the light into six to eight different wavelengths ranges that will produce a different color of light, and direct the beams onto different cells tuned to those ranges.[43]
Performance and degradation
This graph shows how clouds affect solar energy production.
Normally module performance rating is at standard test conditions (STC), typically 1,000 W/m2 irradiance, air mass AM 1.5, and module temperature 25 °C. Since the response of lighting, temperature, and load conditions is dynamic, the actual voltage and current output of the module keep changing; therefore, there is no definite specific voltage at which the module is supposed to operate. That really depends on other factors that include the particular geographic location, time of day, day of the year, quantified solar irradiance, direction and tilt factors of the modules, the degree of cloudiness, shading, soiling, State Of Charge, and temperature. Performance at various time intervals can be measured on each module or panel using a DC clamp meter or shunt to log, graph, or chart out on a chart recorder or data logger.
A solar panel is to be made of similar modules and maybe aligned to the same direction and perpendicular to the direct sun for maximum use. To bypass broken or shaded solar panels, bypass diodes are used, and the maximization of the utilized solar energy. Normally, the bypass diode is placed along groups of solar cells to create flowing current.
These characteristics include nominal power, PMAX, measured in W, open-circuit voltage in V, short-circuit current in A, maximum power voltage in VMPP, maximum power current in IMPP, peak power in watt-peak and Wp, and module efficiency in %.
Another important parameter is the open-circuit voltage or VOC, which is the maximum voltage the module can produce when not connected to an electrical circuit or system. [46] This can be measured with a voltmeter directly on an illuminated module’s terminals or on its disconnected cable.
Peak power rating, Wp, is the maximum output under standard test conditions and not the maximum possible output. Typical modules could be about 1 by 2 meters in area but will be rated from as low as 75 W to as high as 600 W, depending on their efficiency. At the time of test, the test modules are binned according to their test results, and a typical manufacturer might rate their modules in 5 W increments, and either rate them at +/- 3%, +/-5%, +3/-0% or +5/-0%.[47][48][49]
Temperature dependence
The performance of a photovoltaic module depends on the environmental conditions, mainly on the global incident irradiance G in the plane of the module. However, it is also known that the temperature, T, of the p–n junction affects these major electrical parameters: short-circuit current, ISC, open-circuit voltage, VOC, and maximum power, Pmax. In general, it is known that VOC has an important inverse dependence with T; however, for ISC, this dependence is direct but weaker, and, as a consequence, this increase does not compensate the decrease in VOC. Consequently, Pmax decreases when T increases. Such dependence of a solar cell’s power output on its junction’s working temperature is semiconducting material-dependent and stems from the T-dependence of the concentration, lifetime, and mobility of the intrinsic carriers, namely electrons and gaps, inside the photovoltaic cell.
Temperature sensitivity is usually described by temperature coefficients, each of which expresses the derivative of the parameter to which it refers with respect to the junction temperature. The values of these parameters can be found in any data sheet of the photovoltaic module; they are the following:
- α: Coefficient of variation of ISC wrt T, given by ∂ISC/∂T.
- δ: Coefficient of variation of Pmax wrt T, given by ∂Pmax/∂T.
Methods for determining the values of these coefficients from experimental data are reported in the literature[50]
Degradation
market are UL listed, meaning they have gone through testing to withstand hail.
This effect may cause up to 30% power loss.
Improvements made in photovoltaic technologies introduced “doping” of the silicon substrate to decrease the activation energy, hence making the panel more efficient in the conversion of photons into retrievable electrons.
Chemicals, such as boron, are introduced into the semiconductor crystal to form donor and acceptor energy levels significantly closer to the valence and conductor bands. By doing so, adding boron impurity allows for the activation energy to drop by twentyfold from 1.12 eV to 0.05 eV. Because the potential difference EB is so low, the boron can easily thermally ionize at room temperatures. This allows for free energy carriers in the conduction and valence bands thereby allowing greater conversion of photons to electrons.
The power output of a PV device decreases with time. This reduction is occasioned by its exposure to solar radiation as well as other external conditions. One of the most determining factors in a photovoltaic plant’s long-term production is the degradation index, usually expressed as the annual percentage of output power loss. This can be estimated by the percentage decrease associated with each of these electrical parameters. The performance of an entire string may be highly influenced by the individual degradation of a photovoltaic module. Also, not all modules of the same installation reduce their performance by the same factor. Since each module tends to degrade differently, the behaviour of the modules will be more and more different over time and thus negatively affect the overall performance of the plant.[citation needed]
Several studies which deal with the power degradation analysis of modules based on different photovoltaic technologies are available in literature. According to a recent study, the degradation of crystalline silicon modules is very regular, oscillating between 0.8% and 1.0% per year.
On the other hand, if we analyse the evolution of the performance of thin-film photovoltaic modules, we find that there is an initial phase of pronounced degradation, which can last for months and up to 2 years, followed by a later phase when degradation stabilizes and ends up comparable to crystalline silicon. In such thin-film technologies, strong seasonal variations are also noticed due to the much greater influence exerted by the solar spectrum. For example, for modules of amorphous silicon, micromorphic silicon, or cadmium telluride, we are talking about annual degradation rates for the first years of between 3% and 4%.58 Other technologies, like CIGS, however, show far fewer degradations even in those first years.
Maintenance
Conversion efficiency of solar panels, typically in the range of 20%, is reduced by dust, grime, pollen, and other particulates that settle on the solar panels, all termed soiling “A dirty solar panel can reduce its power capabilities by up to 30% in high dust/pollen or desert areas.”[59] Average soiling losses worldwide for 2018 are estimated at least 3%-4%.
As of 2019, cleaning the solar panel is a good investment in most parts across the nation. However, in some locations, it does not pay to clean. In California in 2013, monetary losses due to soiling rarely amounted to the cost of washing the panels. In California, panels generally lost less than 0.05 percent of their total efficiency each day.
There are also occupational hazards with solar panel installation and maintenance. One study in the UK from 2015–2018, which looked into 80 PV-related incidents of fire, had more than 20 “serious fires” directly caused by PV installation, including 37 domestic buildings and 6 solar farms. In a third of the incidents, a root cause was not established, while in most others, poor installation, faulty product, or design issues were to blame. DC Isolators represent the most frequent single element causing fires, accounting for as much as about 62%.
A 2021 study by kWh Analytics arrived at median annual degradation of PV systems at 1.09% for residential and 0.8% for non-residential, nearly twice as much as had been assumed until then. A module reliability study from 2021 showed a trend of rising solar module failure rates, in which manufacturers with safety failures—basically, junction box-related issues—increased from 20% to 30%, and those with bill-of-materials failures increased from 20% to 26%.
The different methods of cleaning a solar panel can be grouped into 5 categories: manual tools, mechanized tools, installed hydraulic systems, installed robotic systems, and deployable robots. Manual cleaning tools are by far the most prevalent method for cleaning, most likely because of their low purchase cost. However, a 2014 study in Saudi Arabia concluded that “installed robotic systems, mechanized systems, and installed hydraulic systems are likely the three most promising technologies for use in cleaning solar panels”[65].
Waste and recycling
There were 30 thousand tonnes of PV waste in 2021, and the annual amount was estimated by Bloomberg NEF to reach more than 1 million tons by 2035 and more than 10 million by 2050. [66] For comparison, in 2022 coal power produced 750 million tons of fly ash waste. [67] As of 2023, landfills receive about 90% of decommissioned solar panels in the United States. [68] Most parts of a solar module can be recycled including up to 95% of certain semiconductor materials or the glass as well as large amounts of ferrous and non-ferrous metals. [69] Some private companies and non-profit organisations take-back and recycle end-of-life modules. [70] EU law requires manufacturers to ensure their solar panels are recycled properly. Similar legislation is in the process of being passed in Japan, India and Australia.[71] A 2023 Australian report described a market for good quality used panels and made recommendations to encourage more reuse.[72]: 33 
The possibility of recycling depends on the type of technology used in the modules:
Silicon based modules: The aluminum frames and junction boxes are removed by hand at the start of the process. The shape and composition of a PV module is similar to flat glass used in the building and automotive industry. For example, glass foam and glass insulation industries easily accept the recovered glass.
Non-silicon based modules: they require special recycling technologies, for example with the use of artificial baths, for the separation of the semiconductor materials. For cadmium telluride modules, the recycling starts by pulverizing the module and then separating the various fractions. This process aims to recover 90% of the glass content and 95% of the semiconductor materials. In the last years, some plants of recycling at industrial scale have been developed by private companies.
]
Production
See also: List of photovoltaics companies
Top producers of PV systems, by shipped capacity in gigawatts
Module producer Shipments
in 2019
(GW)[80]
Jinko Solar 14.2
JA Solar 10.3
Trina Solar 9.7
LONGi Solar 9.0
Canadian Solar 8.5
Hanwha Q Cells 7.3
Risen Energy 7.0
First Solar 5.5
GCL System 4.8
Shunfeng Photovoltaic 4.0
The production of photovoltaic systems obeyed the classic effect of the learning curve: large reductions in costs by large increases in efficiency and production output.
They boosted their shipment of solar modules by as much as more than 100% year over year in 2019. PV module makers dramatically increased their shipments in 2019, with aggressive expansions to capacity and making themselves gigawatt GW players. According to Pulse Solar, five of the top ten PV module companies in 2019 have at least risen by 25% in their solar panel production compared to 2019.
Most solar panels in the world are produced with silicon cells. The efficiency of these cells is usually between 10–20% regarding capturing and turning sunlight into electricity, though newer models of production can top even 22%.
Swanson’s law says that the solar module prices dropped approximately 20% with every doubling of installed capacity, defining the “learning rate” of solar photovoltaics.[87][88]
See also: Grid parity
The price of solar electrical power has continued downward so that, in many countries since 2012, it has become cheaper than fossil fuel electricity from the electricity grid—a phenomenon known as grid parity. With increased global awareness, institutions like the IRS have adopted a tax credit format, refunding a percentage of any solar panel array in use for private purposes.
Average pricing information breaks down into three pricing categories : those purchasing small quantities, modules of all sizes in the kilowatt range . Clearly, in the long term, there is a systematic reduction of the price of cells and modules. For example, it was estimated in 2012 that the quantity cost per watt was around US$0.60, down from about US$150 in 1970—a drop of 250 times. A 2015 study, however, shows price/kWh dropping by 10 percent per year since 1980, and foresees that solar could contribute 20% of total electricity consumption by 2030, while the International Energy Agency predicts 16% by 2050.
Realistic production costs of energy depend on the local weather conditions. Therefore, in countries with cloudy weather, such as in the United Kingdom, the production cost per kWh is more compared to those that have sunnier conditions, as in Spain.
Prices
See also: Grid parity
The cost of solar electrical power has continued to fall such that, in many countries, since 2012, it is now cheaper than fossil fuel electricity from the electricity grid—a situation known as grid parity.
Average selling price data bifurcates into three sale categories: small volume buyers purchasing modules of all sizes in kilowatt quantities annually; middle volume buyers, typically up to 10 MWp annually; and large volume buyers, self-explanatory—and enjoying the lowest prices. Clearly, there is, in the long run, a systemic reduction of price of cells and modules. In 2012, it had been estimated that the cost in terms of quantity cost per watt had reached about US$0.60, some 250-fold less than the US$150 price tag back in 1970. As early as 2015, research showed that the cost in terms of price/kWh dropped by 10 percent over the past 35 years since 1980. This will continue to fall. This has led to forecasts of 20% or more total electricity consumption coming from solar by 2030, and the IEA reported that by 2050, it might be 16%.
Real-world production costs of energy depend on local weather conditions to a large degree. The cost per kWh produced is higher in a country like the United Kingdom, which is cloudy, than in sunnier countries like Spain.
Short term normalised cost comparisons showing value of different electric generation technologies[94]
Long term normalised cost comparisons showing value of different electric generation technologies[94]
According to RMI, the Balance-of-System components—that is, nonmodule cost associated with the non-microinverter solar modules, such as the wiring, converters, racking systems, and other associated components—make up about half of overall installation costs.
This point is sometimes called ‘wholesale grid parity’ or ‘busbar parity’.[89]
Standards
Standards generally used in photovoltaic modules:
IEC 61215 (crystalline silicon performance), 61646 (thin film performance) and 61730 (all modules, safety), 61853 (Photovoltaic module performance testing & energy rating)
ISO 9488 Solar energy—Vocabulary.
UL 1703 of Underwriters Laboratories
UL 1741 of Underwriters Laboratories
UL 2703 of Underwriters Laboratories
CE mark
Electrical Safety Tester (EST) Series (EST-460, EST-22V, EST-22H, EST-110).
Applications
Main article: Applications of photovoltaics
Also see: List of solar-powered products
The use of either solar panels or photovoltaics can be forged into many practical applications. It can first be used in agriculture as a power source for irrigation. In healthcare, it can also be used for refrigerating medical supplies. It can also be used for the infrastructure. PV modules are used in Photovoltaic systems and include a large variety of electric devices, such as:
Agrivoltaics
Solar canals
Photovoltaic power stations
Rooftop solar PV systems
Standalone PV systems
Solar hybrid power systems
Concentrated photovoltaics
Floating solar; water-borne solar panels
Solar planes
Solar-powered water purification
Solar-pumped lasers
Solar vehicles
Solar water heating
Solar panels on spacecraft and space stations
Solar landfill
Limitations
Impact on electricity network. Hence, technical problems can arise. For example, in 2017, more than 30% of the households in Queensland Australia used rooftop PV. The duck curve occurred frequently for many communities since 2015 onwards. This can result in an over-voltage issue as the electricity flows back to the network from the PV households. Solutions to the over voltage issue management include regulating the power factor of PV inverter, new equipment for voltage and energy control at the level of electricity distributor, re-conducting the electricity wires, demand side management, etc. The solutions on most occasions come with limitations and costs.
A battery is often also required for rooftop solar to be able to provide enough backup power during a power cut.[96]
Quality assurance
Solar module quality assurance involves testing and evaluating solar cells and Solar Panels to make sure that the quality requirements of them are met. In contrast, solar modules, or panels, are designed for long service life, typically 20 to 40 years. They must, therefore, transmit and provide the expected power uninterruptedly and safely. It is possible to test solar modules by an inclusive combination of physical tests, laboratory studies, and numerical analyses. Solar modules have also got to be tested during all phases of their life cycle. Various firms such as Southern Research Energy & Environment, SGS Consumer Testing Services, TÃœV Rheinland, Sinovoltaics, Clean Energy Associates – CEA, CSA Solar International and Enertis provide Solar Module
See also: Photovoltaic module analysis techniques
The different lifecycle stages of a solar module testing may include tests in the conceptual phase, manufacturing phase, during transportation and installation, during the commissioning phase, and finally in the in-service phase. These various phases of testing may apply with different principles of test depending on the test phase.
Conceptual phase
The first phase may include design verification wherein the expected output of the module is tested by means of computer simulation. Additionally, the modules can be tested in their ability to withstand natural environment conditions such as temperature, rain, hail, snow, corrosion, dust, lightning, horizon and near-shadow effects. The layout for design and construction of the module and the quality of components and installation can also be tested at this stage.
Manufacturing phase
The component manufacturers are inspected through visitation. It may include the checks of assembly, material testing, and Non Destructive Testing. Certification shall be done according to ANSI/UL1703, IEC 17025, IEC 61215, IEC 61646, IEC 61701 and IEC 61730-1/-2.
