Solar panel

For solar thermal panels, seesolar thermal collectorandsolar thermal energy.

Solar array mounted on a rooftop

Asolar panelis a device that convertssunlightintoelectricityby usingphotovoltaic(PV) cells. PV cells are made of materials that produce excitedelectronswhen exposed to light. The electrons flow through a circuit and producedirect current(DC) electricity, which can be used to power various devices or be stored inbatteries.Solar panels are also known assolar cell panels,solar electric panels,orPV modules.

Solar panels are usually arranged in groups calledarraysorsystems.Aphotovoltaic systemconsists of one or more solar panels, aninverterthat converts DC electricity toalternating current(AC) electricity, and sometimes other components such ascontrollers,meters,andtrackers.Most panels are insolar farms,whichsupply the electricity gridas can somerooftop solar.

Some advantages of solar panels are that they use a renewable and clean source of energy, reducegreenhouse gas emissions,and lower electricity bills. Some disadvantages are that they depend on the availability and intensity of sunlight, require cleaning, and have high initial costs. Solar panels are widely used for residential, commercial, and industrial purposes, as well as inspace,often together withbatteries.

History

See also:Solar cell § History,andTimeline of solar cells

In 1839, the ability of some materials to create an electrical charge from light exposure was first observed by the French physicistEdmond Becquerel.Though these initial solar panels were too inefficient for even simple electric devices, they were used as an instrument to measure light.

The observation by Becquerel was not replicated again until 1873, when the English electrical engineerWilloughby Smithdiscovered that the charge could be caused by light hittingselenium.After this discovery,William Grylls Adamsand Richard Evans Day published "The action of light on selenium" in 1876, describing the experiment they used to replicate Smith's results.

In 1881, the American inventorCharles Frittscreated the first commercial solar panel, which was reported by Fritts as "continuous, constant and of considerable force not only by exposure to sunlight but also to dim, diffused daylight".However, these solar panels were very inefficient, especially compared tocoal-fired power plants.

In 1939,Russell Ohlcreated the solar cell design that is used in many modern solar panels. He patented his design in 1941.In 1954, this design was first used byBell Labsto create the first commercially viablesiliconsolar cell.

Solar panel installers saw significant growth between 2008 and 2013.Due to that growth many installers had projects that were not "ideal" solar roof tops to work with and had to find solutions to shaded roofs and orientation difficulties.This challenge was initially addressed by the re-popularization ofmicro-invertersand 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.In 2013 many solar panel manufacturers announced and began shipping their smart module solutions.

Theory and construction

See also:Solar cell

From asolar cellto aPV system

Photovoltaicmodules consist of a large number of solar cells and use light energy (photons) from the Sun to generate electricity through thephotovoltaic effect.Most modules usewafer-basedcrystalline siliconcells orthin-film cells.The structural (load carrying) member of a module can be either the top layer or the back layer. Cells must be protected from mechanical damage and moisture. Most modules are rigid, but semi-flexible ones based on thin-film cells are also available. The cells are usually connected electrically inseries,one to another to the desired voltage, and then in parallel to increase current. Thepower(inwatts) of the module is thevoltage(involts) multiplied by thecurrent(inamperes), and depends both on the amount of light and on theelectrical loadconnected to the module. The manufacturing specifications on solar panels are obtained under standard conditions, which are usually not the true operating conditions the solar panels are exposed to on the installation site.

A PVjunction boxis attached to the back of the solar panel and functions as its output interface. External connections for most photovoltaic modules useMC4 connectorsto facilitate easy weatherproof connections to the rest of the system. AUSB power interfacecan also be used.Solar panels also use metal frames consisting of racking components, brackets, reflector shapes, and troughs to better support the panel structure.

Cell connection techniques

Solar modular cells need to be connected together to form the module, with front electrodes blocking the solar cell front optical surface area slightly. To maximize frontal surface area available for sunlight and improve solar cell efficiency, manufacturers use varying rear electrode solar cell connection techniques:

• Passivated emitter rear contact (PERC) adds a polymer film to capture light
• Tunnel oxide passivated contact (TOPCon) adds an oxidation layer to the PERC film to capture more light
• Interdigitated back contact (IBC)

Arrays of PV modules

A single solar module can produce only a limited amount of power; most installations contain multiple modules adding their voltages or currents. A photovoltaic system typically includes an array of photovoltaic modules, aninverter,abattery packfor energy storage, a charge controller, interconnection wiring, circuit breakers, fuses, disconnect switches, voltage meters, and optionally asolar trackingmechanism. Equipment is carefully selected 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 are different from traditional solar panels because the power electronics embedded in the module offers enhanced functionality such as panel-levelmaximum power point tracking,monitoring, and enhanced safety.Power electronics attached to the frame of a solar module, or connected to the photovoltaic circuit through a connector, are not properly considered smart modules.

Several companies have begun incorporating into each PV module various embedded power electronics such as:

• Maximum power point tracking(MPPT)power optimizers,a DC-to-DC converter technology developed to maximize the power harvest from solar photovoltaic systems by compensating for shading effects, wherein a shadow falling on a section of a module causes the electrical output of one or more strings of cells in the module to fall to near zero, but not having the output of the entire module fall to zero.
• Solar performance monitorsfor data and fault detection

Technology

Main articles:Crystalline siliconandThin-film solar cell

Market-share of PV technologies since 1980

Most solar modules are currently produced from crystalline silicon (c-Si)solar cellsmade ofpolycrystallineormonocrystalline silicon.In 2021, crystalline silicon accounted for 95% of worldwide PV production,while the rest of the overall market is made up of thin-film technologies usingcadmium telluride(CdTe),copper indium gallium selenide(CIGS) andamorphous silicon(a-Si).

Emerging,third-generation solar technologiesuse advanced thin-film cells. They produce a relatively high-efficiency conversion for a lower cost compared with other solar technologies. Also, high-cost, high-efficiency, and close-packed rectangularmulti-junction (MJ) cellsare usually used insolar panels on spacecraft,as they offer the highest ratio of generated power per kilogram lifted into space. MJ-cells arecompound semiconductorsand made ofgallium arsenide(GaAs) and other semiconductor materials. Another emerging PV technology using MJ-cells isconcentrator photovoltaics(CPV).

Thin film

This section is an excerpt fromThin-film solar cell.[edit]

Thin-film solar cells, a second generation ofphotovoltaic(PV)solar cells:

• Top:thin-film siliconlaminates being installed onto a roof.
• Middle:CIGS solar cellon a flexible plastic backing and rigidCdTe panelsmounted on a supporting structure
• Bottom:thin-filmlaminates onrooftops

Thin-film solar cellsare a type ofsolar cellmade by depositing one or more thin layers (thin filmsor TFs) ofphotovoltaicmaterial onto a substrate, such as glass, plastic or metal. Thin-film solar cells are typically a few nanometers (nm) to a few microns (μm) thick–much thinner than thewafersused in conventionalcrystalline silicon(c-Si) based solar cells, which can be up to 200 μm thick. Thin-film solar cells are commercially used in several technologies, includingcadmium telluride(CdTe),copper indium gallium diselenide(CIGS), andamorphous thin-film silicon(a-Si, TF-Si).

Solar cells are often classified into so-called generations based on the active (sunlight-absorbing) layers used to produce them, with the most well-established orfirst-generationsolar cells being made ofsingle- ormulti-crystalline silicon.This is the dominant technology currently used in mostsolar PV systems.Most thin-film solar cells are classified assecond generation,made using thin layers of well-studied materials likeamorphous silicon(a-Si),cadmium telluride(CdTe),copper indium gallium selenide(CIGS), orgallium arsenide(GaAs). Solar cells made with newer, less established materials are classified asthird-generationor emerging solar cells. This includes some innovative thin-film technologies, such asperovskite,dye-sensitized,quantum dot,organic,andCZTSthin-film solar cells.

Thin-film cells have several advantages over first-generation silicon solar cells, including being lighter and more flexible due to their thin construction. This makes them suitable for use inbuilding-integrated photovoltaicsand as semi-transparent,photovoltaic glazing material that can belaminatedonto windows. Other commercial applications use rigid thin film solar panels (interleaved between two panes of glass) in some of theworld's largestphotovoltaic power stations.Additionally, the materials used in thin-film solar cells are typically produced using simple and scalable methods more cost-effective than first-generation cells, leading to lowerenvironmental impactslikegreenhouse gas (GHG) emissionsin many cases. Thin-film cells also typically outperformrenewableandnon-renewablesources forelectricity generationin terms of human toxicity andheavy-metal emissions.

Despite initial challenges withefficientlight conversion,especially among third-generation PV materials, as of 2023 some thin-film solar cells have reached efficiencies of up to 29.1% for single-junction thin-film GaAs cells, exceeding the maximum of 26.1% efficiency for standard single-junction first-generation solar cells.Multi-junctionconcentratorcells incorporating thin-film technologies have reached efficiencies of up to 47.6% as of 2023.

Still, many thin-film technologies have been found to have shorter operational lifetimes and larger degradation rates than first-generation cells inaccelerated life testing,which has contributed to their somewhat limited deployment. Globally, thePV marketshareof thin-film technologies remains around 5% as of 2023.However, thin-film technology has become considerably more popular in the United States, where CdTe cells alone accounted for nearly 30% of newutility-scaledeployment in 2022.

Mounting and tracking

Main articles:Photovoltaic mounting systemandSolar tracker

Solar modules mounted onsolar trackers

Workers install residential rooftop solar panels

Ground

Large utility-scalesolar power plantsfrequently use ground-mounted photovoltaic systems. Their solar modules are held in place by racks or frames that are attached to ground-based mounting supports.Ground based mounting supports include:

• Pole mounts, which are driven directly into the ground or embedded in concrete.
• Foundation mounts, such as concrete slabs or poured footings
• Ballasted footing mounts, such as concrete or steel bases that use weight to secure the solar module system in position and do not require ground penetration. This type of mounting system is well suited for sites where excavation is not possible such as capped landfills and simplifies decommissioning or relocation of solar module systems.

Solar array ground mounting

Vertical bifacial solar array

Agrivoltaicverticalbifacialsolar panels

VerticalBifacialvs south facing solar array power output

VerticalBifacial

South facing solar array

Verticalbifacial solar cellsoriented towards east and west to catch the sun'sirradiancemore efficiently in the morning and evening. Applications includeagrivoltaics,solar fencing, highway and railroad noise dampeners andbarricades.

Verticalbifacial solaralong highway

Roof

Main article:Rooftop solar power

Roof-mounted solar power systems consist of solar modules held in place by racks or frames attached to roof-based mounting supports.Roof-based mounting supports include:

• Rail mounts, which are attached directly to the roof structure and may use additional rails for attaching the module racking or frames.
• Ballasted footing mounts, such as concrete or steel bases that use weight to secure the panel system in position and do not require through penetration. This mounting method allows for decommissioning or relocation of solar panel systems with no adverse effect on the roof structure.
• All wiring connecting adjacent solar modules to the energy harvesting equipment must be installed according to local electrical codes and should be run in a conduit appropriate for the climate conditions

Solar Canopy

Solar canopyparking lot inNew Havenat Hotel Marcel. There are EVlevel 2chargers underneath the canopy and a 12-stallTesla Superchargerbehind.

Solar canopiesaresolar arrayswhich are installed on top of a traditionalcanopy.These canopies could be a parking lot canopy,carport,gazebo,Pergola,orpatio cover.

Portable

Portable solar panels can ensure electric current, enough to charge devices (mobile, radio,...) via USB-port or to charge a powerbank f.e.

Special features of the panels include high flexibility, high durability & waterproof characteristics. They are good for travel or camping.

A 5V, 2A, 10W solar panel with USB port

Tracking

Solar trackersincrease the energy produced per module at the cost of mechanical complexity and increased need for maintenance. They sense the direction of the Sun and tilt or rotate the modules as needed for maximum exposure to the light.

Alternatively, fixed racks can hold modules stationary throughout the day at a given tilt (zenith angle) and facing a given direction (azimuth angle). Tilt angles equivalent to an installation's latitude are common. Some systems may also adjust the tilt angle based on the time of year.

On the other hand, east- and west-facing arrays (covering an east–west facing roof, for example) are commonly deployed. Even though such installations will not produce the maximum possible average power from the individual solar panels, the cost of the panels is now usually cheaper than the tracking mechanism and they can provided more economically valuable power during morning and evening peak demands than north or south facing systems.

Concentrator

Some special solar PV modules includeconcentratorsin which light is focused bylensesor mirrors onto smaller cells. This enables the cost-effective use of highly efficient, but expensive cells (such asgallium arsenide) with the trade-off of using a higher solar exposure area.Concentrating the sunlight can also raise the efficiency to around 45%.

Light capture

The amount of light absorbed by a solar cell depends on theangle of incidenceof whatever direct sunlight hits it. This is partly because the amount falling on the panel is proportional to thecosineof the angle of incidence, and partly because at high angle of incidence more light is reflected. To maximize total energy output, modules are often oriented to face south (in the Northern Hemisphere) or north (in the Southern Hemisphere) and tilted to allow for the latitude.Solar trackingcan be used to keep the angle of incidence small.

Solar panels are often coated with ananti-reflective coating,which is one or more thin layers of substances with refractive indices intermediate between that of silicon and that of air. This causesdestructive interferencein the reflected light, diminishing the amount. Photovoltaic manufacturers have been working to decrease reflectance with improved anti-reflective coatings or with textured glass.

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 maximised. If too much current is taken then the voltage collapses. The optimum current draw is roughly proportional to the amount of sunlight striking the panel. Solar panel capacity is specified by the MPP (maximum power point) value of solar panels in full sunlight.

Inverters

Solar invertersconvert the DC power provided by panels toACpower.

Power/Voltage-curve of a partially shaded PV module, with marked local and global MPP

MPP (Maximum power point) of the solar panel consists of MPP voltage (V_mpp) and MPP current (I_mpp). Performingmaximum power point tracking(MPPT), a solar inverter samples the output (I-V curve) from the solar cell and applies the proper electrical load to obtain maximum power.

An AC (alternating current) solar panel has a small DC to ACmicroinverteron the back and producesAC powerwith no externalDC connector.AC modules are defined byUnderwriters Laboratoriesas the smallest and most complete system for harvesting solar energy.

Micro-inverters work independently to enable each panel to contribute its maximum possible output for a given amount of sunlight, but can be more expensive.

Module interconnection

A connection example, a blocking diode is placed in series with each module string, whereas bypass diodes are placed in parallel with modules.

Module electrical connections are made with conducting wires that take the current off the modules and are sized according to the current rating and fault conditions, and sometimes include in-line fuses.

Panels are typically connectedin seriesof one or more panels to form strings to achieve a desired output voltage, and strings can be connectedin parallelto provide the desired current capability (amperes) of the PV system.

In string connections the voltages of the modules add, but the current is determined by the lowest performing panel. This is known as the "Christmas light effect". In parallel connections the voltages will be the same, but the currents add. Arrays are connected up to meet the voltage requirements of the inverters and to not greatly exceed the current limits.

Blocking and bypassdiodesmay be incorporated within the module or used externally to deal with partial array shading, in order to maximize output. For series connections, bypass diodes are placed in parallel with modules to allow current to bypass shaded modules which would otherwise severely limit the current. For paralleled connections, a blocking diode may be placed in series with each module's string to prevent current flowing backwards through shaded strings thus short-circuiting other strings.

Connectors

Outdoor solar panels usually includeMC4 connectors.Automotive solar panels may also include anauxiliary power outletand/orUSBadapter. Indoor panels (including solar pv glasses, thin films and windows) can integrate amicroinverter(AC Solar panels).

Efficiency

See also:Solar cell efficiency

Reported timeline of champion solar module energy conversion efficiencies since 1988 (National Renewable Energy Laboratory)

Each module is rated by itsDCoutput power under standard test conditions (STC) and hence the on field output power might vary. Power typically ranges from 100 to 365Watts(W). The efficiency of a module determines the area of a module given the same rated output – an 8% efficient 230 W module will have twice the area of a 16% efficient 230 W module. Some commercially available solar modules exceed 24% efficiency.Currently,the best achieved sunlight conversion rate (solar module efficiency) is around 21.5% in new commercial productstypically lower than the efficiencies of their cells in isolation. The most efficient mass-produced solar modules have power density values of up to 175 W/m²(16.22 W/ft²).

The current versus voltage curve of a module provides useful information about its electrical performance.Manufacturing processes often cause differences in the electrical parameters of different modules photovoltaic, even in cells of the same type. Therefore, only the experimental measurement of the I–V curve allows us to accurately establish the electrical parameters of a photovoltaic device. This measurement provides highly relevant information for the design, installation and maintenance of photovoltaic systems. Generally, the electrical parameters of photovoltaic modules are measured by indoor tests. However, outdoor testing has important advantages such as no expensive artificial light source required, no sample size limitation, and more homogeneous sample illumination.

Capacity factorof solar panels is limited primarily by geographiclatitudeand varies significantly depending on cloud cover, dust, day length and other factors. In theUnited Kingdom,seasonal capacity factor ranges from 2% (December) to 20% (July), with average annual capacity factor of 10–11%, while inSpainthe value reaches 18%. Globally, capacity factor for utility-scale PV farms was 16.1% in 2019.

Overheating is the most important factor for the efficiency of the solar panel.

Radiation-dependent efficiency

Depending on construction, photovoltaic modules can produce electricity from a range offrequencies of light,but usually cannot cover the entire solar radiation range (specifically,ultraviolet,infraredand low or diffused light). Hence, much of the incidentsunlightenergy is wasted by solar modules, and they can give far higher efficiencies if illuminated withmonochromaticlight. Therefore, another design concept is to split the light into six to eight different wavelength ranges that will produce a different color of light, and direct the beams onto different cells tuned to those ranges.

Performance and degradation

This chart illustrates the effect of clouds on solar energy production.

Module performance is generally rated under standard test conditions (STC):irradianceof 1,000W/m²,solarspectrumofAM1.5 and module temperature at 25 °C.The actual voltage and current output of the module changes as lighting, temperature and load conditions change, so there is never one specific voltage at which the module operates. Performance varies depending on geographic location, time of day, the day of the year, amount ofsolar irradiance,direction and tilt of modules, cloud cover, shading,soiling,state of charge, and temperature. Performance of a module or panel can be measured at different time intervals with a DC clamp meter or shunt and logged, graphed, or charted with a chart recorder or data logger.

For optimum performance, a solar panel needs to be made of similar modules oriented in the same direction perpendicular to direct sunlight. Bypass diodes are used to circumvent broken or shaded panels and optimize output. These bypass diodes are usually placed along groups of solar cells to create a continuous flow.

Electrical characteristics include nominal power (P_MAX,measured inW),open-circuit voltage(V_OC),short-circuit current(I_SC,measured inamperes), maximum power voltage (V_MPP), maximum power current (I_MPP), peak power, (watt-peak,W_p), and module efficiency (%).

Open-circuit voltageor V_OCis the maximum voltage the module can produce when not connected to an electrical circuit or system.V_OCcan be measured with avoltmeterdirectly on an illuminated module's terminals or on its disconnected cable.

The peak power rating, W_p,is the maximum output under standard test conditions (not the maximum possible output). Typical modules, which could measure approximately 1 by 2 metres (3 ft × 7 ft), will be rated from as low as 75 W to as high as 600 W, depending on their efficiency. At the time of testing, 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%.

Influence of temperature

The performance of a photovoltaic (PV) module depends on the environmental conditions, mainly on the global incident irradiance G in the plane of the module. However, the temperature T of the p–n junction also influences the main electrical parameters: the short circuit current ISC, the open circuit voltage VOC and the maximum power Pmax. In general, it is known that VOC shows a significant inverse correlation with T, while for ISC this correlation is direct, but weaker, so that this increase does not compensate for the decrease in VOC. As a consequence, Pmax decreases when T increases. This correlation between the power output of a solar cell and the working temperature of its junction depends on the semiconductor material, and is due to the influence of T on the concentration, lifetime, and mobility of the intrinsic carriers, i.e., 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; are the following:

- β: VOC variation coefficient with respect to T, given by ∂VOC/∂T.

- α: Coefficient of variation of ISC with respect to T, given by ∂ISC/∂T.

- δ: Coefficient of variation of Pmax with respect to T, given by ∂Pmax/∂T.

Techniques for estimating these coefficients from experimental data can be found in the literature

Degradation

The ability of solar modules to withstand damage by rain,hail,heavy snow load, and cycles of heat and cold varies by manufacturer, although most solar panels on the U.S. market are UL listed, meaning they have gone through testing to withstand hail.

Potential-induced degradation(also called PID) is a potential-induced performance degradation in crystalline photovoltaic modules, caused by so-called stray currents.This effect may cause power loss of up to 30%.

Advancements in photovoltaic technologies have brought about the process of "doping" the silicon substrate to lower the activation energy thereby making the panel more efficient in converting photons to retrievable electrons.

Chemicals such asboron(p-type) are applied into the semiconductor crystal in order to create donor and acceptor energy levels substantially closer to the valence and conductor bands.In doing so, the addition of boron impurity allows the activation energy to decrease twenty-fold from 1.12 eV to 0.05 eV. Since the potential difference (E_B) is so low, the boron is able to 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 photovoltaic (PV) device decreases over time. This decrease is due to its exposure to solar radiation as well as other external conditions. The degradation index, which is defined as the annual percentage of output power loss, is a key factor in determining the long-term production of a photovoltaic plant. To estimate this degradation, the percentage of decrease associated with each of the electrical parameters. The individual degradation of a photovoltaic module can significantly influence the performance of a complete string. Furthermore, not all modules in the same installation decrease their performance at exactly the same rate. Given a set of modules exposed to long-term outdoor conditions, the individual degradation of the main electrical parameters and the increase in their dispersion must be considered. As each module tends to degrade differently, the behavior of the modules will be increasingly different over time, negatively affecting the overall performance of the plant.

There are several studies dealing with the power degradation analysis of modules based on different photovoltaic technologies available in the 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 analyze the performance of thin-film photovoltaic modules, an initial period of strong degradation is observed (which can last several months and even up to 2 years), followed by a later stage in which the degradation stabilizes, being then comparable to that of crystalline silicon.Strong seasonal variations are also observed in such thin-film technologies because the influence of the solar spectrum is much greater. 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%.However, other technologies, such as CIGS, show much lower degradation rates, even in those early years.

Maintenance

General cleaning of ground-based solar panels at the Shanta Gold mine in Tanzania

Deeper level of cleaning with pressure washing of the car port solar panels at Googleplex, Mountain View, California

Solar panel conversion efficiency, typically in the 20% range, is reduced by the accumulation of dust, grime, pollen, and other particulates on the solar panels, collectively referred to assoiling."A dirty solar panel can reduce its power capabilities by up to 30% in high dust/pollen or desert areas", says Seamus Curran, associate professor of physics at the University of Houston and director of the Institute for NanoEnergy, which specializes in the design, engineering, and assembly of nanostructures. The average soiling loss in the world in 2018 is estimated to be at least 3% – 4%.

Paying to have solar panels cleaned is a good investment in many regions, as of 2019.However, in some regions, cleaning is not cost-effective. In California as of 2013 soiling-induced financial losses were rarely enough to warrant the cost of washing the panels. On average, panels in California lost a little less than 0.05% of their overall efficiency per day.

There are alsooccupational hazards with solar panel installationand maintenance. A 2015–2018 study in the UK investigated 80 PV-related incidents of fire, with over 20 "serious fires" directly caused by PV installation, including 37 domestic buildings and 6 solar farms. In1⁄3of the incidents a root cause was not established and in a majority of others was caused by poor installation, faulty product or design issues. The most frequent single element causing fires was the DC isolators.

A 2021 study by kWh Analytics determined median annual degradation of PV systems at 1.09% for residential and 0.8% for non-residential ones, almost twice that previously assumed.A 2021 module reliability study found an increasing trend in solar module failure rates with 30% of manufacturers experiencing safety failures related to junction boxes (growth from 20%) and 26% bill-of-materials failures (growth from 20%).

Cleaning methods for solar panels can be divided into 5 groups: manual tools, mechanized tools (such as tractor mounted brushes), installed hydraulic systems (such as sprinklers), installed robotic systems, and deployable robots. Manual cleaning tools are by far the most prevalent method of cleaning, most likely because of the low purchase cost. However, in a Saudi Arabian study done in 2014, it was found that "installed robotic systems, mechanized systems, and installed hydraulic systems are likely the three most promising technologies for use in cleaning solar panels".

Waste and recycling

There were 30 thousand tonnes of PV waste in 2021, and the annual amount was estimated by Bloomberg NEF to rise to more than 1 million tons by 2035 and more than 10 million by 2050.For comparison, 750 million tons offly ashwaste was produced by coal power in 2022.In the United States, around 90% of decommissioned solar panels end up in landfills as of 2023.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.Some private companies and non-profit organizations take-back and recycle end-of-life modules.EU law requires manufacturers to ensure their solar panels are recycled properly. Similar legislation is underway inJapan,India,andAustralia.A 2023 Australian report said that there is a market for quality used panels and made recommendations for increasing reuse.

Recycling possibilities depend on the kind of technology used in the modules:

• Silicon based modules: aluminum frames and junction boxes are dismantled manually at the beginning of the process. The module is then crushed in a mill and the different fractions are separated – glass, plastics and metals.It is possible to recover more than 80% of the incoming weight.This process can be performed by flat glass recyclers, since the shape and composition of a PV module is similar to flat glass used in the building and automotive industry. The recovered glass, for example, is readily accepted by the glass foam and glass insulation industry.
• Non-silicon based modules: they require specific recycling technologies such as the use of chemical baths in order to separate the different semiconductor materials.Forcadmium telluridemodules, the recycling process begins by crushing the module and subsequently separating the different fractions. This recycling process is designed to recover up to 90% of the glass and 95% of the semiconductor materials contained.Some commercial-scale recycling facilities have been created in recent years by private companies.

Since 2010, there is an annual European conference bringing together manufacturers, recyclers and researchers to look at the future of PV module recycling.

Production

See also:List of photovoltaics companies

Top producers of PV systems, by shipped capacity in gigawatts

Module producer	Shipments in 2019 (GW)
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 PV systems has followed a classiclearning curveeffect, with significant cost reduction occurring alongside large rises in efficiency and production output.

With over 100% year-on-year growth in PV system installation, PV module makers dramatically increased their shipments of solar modules in 2019. They actively expanded their capacity and turned themselves into gigawattGWplayers.According to Pulse Solar, five of the top ten PV module companies in 2019 have experienced a rise in solar panel production by at least 25% compared to 2019.

The basis of producing most solar panels is mostly on the use of silicon cells. These silicon cells are typically 10–20% efficientat converting sunlight into electricity, with newer production models exceeding 22%.

In 2018, the world's top five solar module producers in terms of shipped capacity during the calendar year of 2018 wereJinko Solar,JA Solar,Trina Solar,Longi solar,andCanadian Solar.

Price

Swanson's law–stating that solar module prices have dropped about 20% for each doubling of installed capacity—defines the "learning rate"ofsolar photovoltaics.

See also:Grid parity

The price of solar electrical power has continued to fall so that in many countries it has become cheaper thanfossil fuelelectricity fromthe electricity gridsince 2012, a phenomenon known asgrid parity.With the rise of global awareness, institutions such as theIRShave adopted a tax credit format, refunding a portion of any solar panel array for private use.The price of a solar array only continues to fall.

Average pricing information divides in three pricing categories: those buying small quantities (modules of all sizes in the kilowatt range annually), mid-range buyers (typically up to 10MWpannually), and large quantity buyers (self-explanatory—and with access to the lowest prices). Over the long term there is clearly a systematic reduction in the price of cells and modules. For example, in 2012 it was estimated that the quantity cost per watt was about US$0.60, which was 250 times lower than the cost in 1970 of US$150.A 2015 study shows price/kWh dropping by 10% per year since 1980, and predicts that solar could contribute 20% of total electricity consumption by 2030, whereas theInternational Energy Agencypredicts 16% by 2050.

Real-world energy production costs depend a great deal on local weather conditions. In a cloudy country such as the United Kingdom, the cost per produced kWh is higher than in sunnier countries like Spain.

Short term normalized cost comparisons demonstrating value of various electric generation technologies

Long term normalized cost comparisons demonstrating value of various electric generation technologies

Following toRMI,Balance-of-System(BoS) elements, this is, non-module cost of non-microinvertersolar modules (as wiring, converters, racking systems and various components) make up about half of the total costs of installations.

For merchant solar power stations, where the electricity is being sold into the electricity transmission network, the cost ofsolar energywill need to match the wholesale electricity price. This point is sometimes called 'wholesale grid parity' or 'busbar parity'.

Standards

Standards generally used in photovoltaic modules:

• IEC61215 (crystalline siliconperformance), 61646 (thin filmperformance) and 61730 (all modules, safety), 61853 (Photovoltaic module performance testing & energy rating)
• ISO 9488 Solar energy—Vocabulary.
• UL 1703 fromUnderwriters Laboratories
• UL 1741 from Underwriters Laboratories
• UL 2703 from Underwriters Laboratories
• CE mark
• Electrical Safety Tester (EST) Series (EST-460, EST-22V, EST-22H, EST-110).

Applications

Main article:Applications of photovoltaics

See also:List of solar-powered products

There are many practical applications for the use of solar panels or photovoltaics. It can first be used in agriculture as a power source for irrigation. In health care solar panels can be used to refrigerate medical supplies. It can also be used for infrastructure. PV modules are used inphotovoltaic systemsand include alarge variety of electric devices:

• Agrivoltaics
• Solar canals
• Photovoltaic power stations
• Rooftop solar PVsystems
• Standalone PV systems
• Solar hybrid power systems
• Concentrated photovoltaics
• Floating solar;water-borne solar panels
• Solar planes
• Solar-poweredwater purification
• Solar-pumped lasers
• Solar vehicles
• Solar water heating
• Solar panels on spacecraftandspace stations
• Solar landfill

Limitations

Impact on electricity network

With the increasing levels of rooftop photovoltaic systems, the energy flow becomes 2-way. When there is more local generation than consumption, electricity is exported to the grid. However, an electricity network traditionally is not designed to deal with the 2- way energy transfer. Therefore, some technical issues may occur. For example, in Queensland Australia, more than 30% of households used rooftop PV by the end of 2017. Theduck curveappeared often for a lot of communities from 2015 onwards. An over-voltage issue may result as the electricity flows from PV households back to the network.There are solutions to manage the over voltage issue, such as regulating PV inverter power factor, new voltage and energy control equipment at the electricity distributor level, re-conducting the electricity wires, demand side management, etc. There are often limitations and costs related to these solutions.

Forrooftop solarto be able to provide enough backup power during a power cut abatteryis often also required.

Quality assurance

Solar module quality assurance involves testing and evaluatingsolar cellsand Solar Panels to ensure the quality requirements of them are met. Solar modules (or panels) are expected to have a long service life between 20 and 40 years.They should continually and reliably convey and deliver the power anticipated. Solar modules can be tested through a combination ofphysicaltests,laboratorystudies, andnumericalanalyses.Furthermore, solar modules need to be assessed throughout the different stages of theirlife cycle.Various companies such as Southern Research Energy & Environment, SGS Consumer Testing Services,TÜV Rheinland,Sinovoltaics, Clean Energy Associates (CEA),CSA SolarInternational and Enertis provide services in solar module quality assurance. "The implementation of consistent traceable and stable manufacturing processes becomes mandatory to safeguard and ensure the quality of the PV Modules"

Stages of testing

See also:Photovoltaic module analysis techniques

The lifecycle stages of testing solar modules can include: the conceptual phase,manufacturingphase,transportationand installation,commissioningphase, and the in-service phase. Depending on the test phase, different test principles may apply.

Conceptual phase

The first stage can involvedesign verificationwhere the expected output of the module is tested through computer simulation. Further, the modules ability to withstand natural environment conditions such astemperature,rain,hail, snow,corrosion,dust,lightning,horizonand near-shadow effects is tested. The layout fordesignandconstructionof the module and the quality of components and installation can also be tested at this stage.

Manufacturing phase

Inspecting manufacturers of components is carried through visitation. The inspection can include assembly checks, material testing supervision and Non Destructive Testing (NDT). Certification is carried out according to ANSI/UL1703, IEC 17025, IEC 61215, IEC 61646, IEC 61701 and IEC 61730-1/-2.

See also

• Daisy chain (electrical engineering)
• Digital modeling and fabrication
• Domestic energy consumption
• Grid-tied electrical system
• Growth of photovoltaics
• Solar charger
• Solar cooker
• Solar still