Photovoltaic Array
If photovoltaic solar panels are made up of individual photovoltaic cells connected together, then the Solar Photovoltaic Array, also known simply as a Solar Array is a system made up of a group of solar panels connected together.
A photovoltaic array is therefore multiple solar panels electrically wired together to form a much larger PV installation (PV system) called an array, and in general the larger the total surface area of the array, the more solar electricity it will produce.
A complete photovoltaic system uses a photovoltaic array as the main source for the generation of the electrical power supply. The amount of solar power produced by a single photovoltaic panel or module is not enough for general use.
Most manufactures produce a standard photovoltaic panel with an output voltage of 12V or 24V. By connecting many single PV panels in series (for a higher voltage requirement) and in parallel (for a higher current requirement) the PV array will produce the desired power output.
A Photovoltaic Solar Array
Photovoltaic cells and panels convert the solar energy into direct-current (DC) electricity. The connection of the solar panels in a single photovoltaic array is same as that of the PV cells in a single panel.
The panels in an array can be electrically connected together in either a series, a parallel, or a mixture of the two, but generally a series connection is chosen to give an increased output voltage. For example, when two solar panels are wired together in series, their voltage is doubled while the current remains the same.
The size of a photovoltaic array can consist of a few individual PV modules or panels connected together in an urban environment and mounted on a rooftop, or may consist of many hundreds of PV panels interconnected together in a field to supply power for a whole town or neighbourhood. The flexibility of the modular photovoltaic array (PV system) allows designers to create solar power systems that can meet a wide variety of electrical needs, no matter how large or small.
It is important to note that photovoltaic panels or modules from different manufacturers should not be mixed together in a single array, even if their power, voltage or current outputs are nominally similar. This is because differences in the solar cell I-V characteristic curves as well as their spectral response are likely to cause additional mismatch losses within the array, thereby reducing its overall efficiency.
The Electrical Characteristics of a Photovoltaic Array
The electrical characteristics of a photovoltaic array are summarised in the relationship between the output current and voltage. The amount and intensity of solar insolation (solar irradiance) controls the amount of output current ( I ), and the operating temperature of the solar cells affects the output voltage ( V ) of the PV array. Photovoltaic panel ( I-V ) curves that summarise the relationship between the current and voltage are given by the manufacturers and are given as:
Solar Array Parameters
- VOC = open-circuit voltage: – This is the maximum voltage that the array provides when the terminals are not connected to any load (an open circuit condition). This value is much higher than Vmax which relates to the operation of the PV array which is fixed by the load. This value depends upon the number of PV panels connected together in series.
- ISC = short-circuit current – The maximum current provided by the PV array when the output connectors are shorted together (a short circuit condition). This value is much higher than Imax which relates to the normal operating circuit current.
- Pmax = maximum power point – This relates to the point where the power supplied by the array that is connected to the load (batteries, inverters) is at its maximum value, where Pmax = Imax x Vmax. The maximum power point of a photovoltaic array is measured in Watts (W) or peak Watts (Wp).
- FF = fill factor – The fill factor is the relationship between the maximum power that the array can actually provide under normal operating conditions and the product of the open-circuit voltage times the short-circuit current, ( Voc x Isc ) This fill factor value gives an idea of the quality of the array and the closer the fill factor is to 1 (unity), the more power the array can provide. Typical values are between 0.7 and 0.8.
- % eff = percent efficiency – The efficiency of a photovoltaic array is the ratio between the maximum electrical power that the array can produce compared to the amount of solar irradiance hitting the array. The efficiency of a typical solar array is normally low at around 10-12%, depending on the type of cells (monocrystalline, polycrystalline, amorphous or thin film) being used.
Photovoltaic I-V characteristics curves provide the information designers need to configure systems that can operate as close as possible to the maximum peak power point. The peak power point is measured as the PV module produces its maximum amount of power when exposed to solar radiation equivalent to 1000 watts per square metre, 1000 W/m 2 or 1kW/m 2. Consider the circuit below.
Photovoltaic Array Connections
This simple photovoltaic array above consists of four photovoltaic modules as shown, producing two parallel branches in which there are two PV panels that are electrically connected together to produce a series circuit. The output voltage from the array will therefore be equal to the series connection of the PV panels, and in our example above, this is calculated as: Vout = 12V 12V = 24 Volts.
The output current will be equal to the sum of the parallel branch currents. If we assume that each PV panel produces 3.75 amperes at full sun, the total current ( IT ) will be equal to: IT = 3.75A 3.75A = 7.5 Amperes. Then the maximum power of the photovoltaic array at full sun can be calculated as: Pout = V x I = 24 x 7.5 = 180W.
The PV array reaches its maximum of 180 watts in full sun because the maximum power output of each PV panel or module is equal to 45 watts (12V x 3.75A). However, due to different levels of solar radiation, temperature effect, electrical losses etc, the real maximum output power is usually a lot less than the calculated 180 watts. Then we can present our photovoltaic array characteristics as being.
Bypass Diodes in Photovoltaic Arrays
Photovoltaic cells and diodes are both semiconductor devices made from a P-type silicon material and a N-type silicon material fused together. Unlike a photovoltaic cell which generates a voltage when exposed to light, PN-junction diodes act like solid state one way electrical valve that only allows electrical current to flow through themselves in one direction only.
The advantage of this is that diodes can be used to block the flow of electric current from other parts of an electrical solar circuit. When used in a photovoltaic solar array, these types of silicon diodes are generally called Blocking Diodes.
In the previous tutorial about photovoltaic panels, we saw that a bypass diode can be used in parallel with either a single or a number of photovoltaic solar cells. The addition of a diode prevents current(s) flowing from a good and well-exposed PV cells, overheating and burning out weak or partially shaded PV cells by providing a current path around the bad cell. Blocking diodes are used differently than bypass diodes.
Bypass diodes are usually connected in “parallel” with a PV cell or panel to shunt the current around it, whereas blocking diodes are connected in “series” with the PV panels to prevent current flowing back into them. Blocking diodes are therefore different then bypass diodes although in most cases the diode is physically the same, but they are installed differently and serve a different purpose. Consider our photovoltaic solar array below.
Diodes in Photovoltaic Arrays
As we said earlier, diodes are devices that allow current to flow in one direction only. The diodes coloured green are the familiar bypass diodes, one in parallel with each PV panel to provide a low resistance path around the panel. However, the two diodes coloured red are referred to as the “blocking diodes”, one in series with each series branch. These blocking diodes ensure that the electrical current only flows OUT of the series array to the external load, controller or batteries.
The reason for this is to prevent the current generated by the other parallel connected PV panels in the same array flowing back through a weaker (shaded) network and also to prevent the fully charged batteries from discharging or draining back through the PV array at night. So when multiple PV panels are connected in parallel, blocking diodes should be used in each parallel connected branch.
Generally speaking, blocking diodes are used in PV arrays when there are two or more parallel branches or there is a possibility that some of the array will become partially shaded during the day as the sun moves across the sky. The size and type of blocking diode used depends upon the type of photovoltaic array. Two types of diodes are available for solar power arrays: the PN-junction silicon diode and the Schottky barrier diode. Both are available with a wide range of current ratings.
The Schottky barrier diode has a much lower forward voltage drop of about 0.4 volts as opposed to the PN diodes 0.7 volt drop for a silicon device. This lower voltage drop allows a savings of one full PV cell in each series branch of the solar array therefore, the array is more efficient since less power is dissipated in the blocking diode. Most manufacturers include blocking diodes within their PV modules simplifying the design.
Build your own Photovoltaic Array
The amount of solar radiation received and the daily energy demand are the two controlling factors in the design of the photovoltaic array and solar power systems. The photovoltaic array must be sized to meet the load demand and account for any system losses while the shading of any part of the solar array will significantly reduce the output of the entire system.
If the solar panels are electrically connected together in series, the current will be the same in each panel and if panels are partially shaded, they cannot produce the same amount of current. Also shaded PV panels will dissipate power and waste as heat rather than generate it and the use of bypass diodes will help prevent such problems by providing an alternative current path.
Blocking diodes are not required in a fully series connected system but should be used to prevent a reverse current flow from the batteries back to the array during the night or when the solar irradiance is low. Other climatic conditions apart from sunlight must be considered in any design.
Since the output voltage of silicon solar cell is a temperature related parameter, the designer must be aware of the prevailing daily temperatures, both extremes (high and low) and seasonal variations. In addition, rain and snowfall must be considered in the design of the mounting structure. Wind loading is especially important in mountain top installations.
In our next tutorial about “Solar Power”, we will look at how we can use semiconductor photovoltaic arrays and solar panels as part of a Stand Alone PV System to generate power for off-grid applications.
Find Us On
- Standard Test Conditions
- Temperature Coefficient of a PV Cell
- Bypass Diode
- Solar Cell I-V Characteristic
- Photovoltaics Turning Photons into Electrons
- How Many Solar Cells Do I Need
- Photovoltaic Panel
- Photovoltaic Types
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Hi there my name is Matt D’Agati. Solar technology has grown to become probably the most promising and sought-after sourced elements of clean, renewable energy in the past few years. This is due to its numerous benefits, including financial savings, energy efficiency, and also the positive impact this has from the environment. In this specific article, we are going to talk about the advantages of choosing solar energy in homes and businesses, the technology behind it, and just how it could be implemented to increase its benefits. One of many benefits of using solar power in homes may be the financial savings it gives. Solar energy panels can handle generating electricity for your house, reducing or eliminating the need for traditional sourced elements of energy. This will probably bring about significant savings on the monthly energy bill, particularly in areas with a high energy costs. In addition, the expense of solar energy panels and associated equipment has decreased significantly over time, which makes it more affordable for homeowners to invest in this technology. Another good thing about using solar power in homes is the increased value it may provide into the property. Homes that have solar power panels installed are often valued greater than homes that don’t, while they offer an energy-efficient and environmentally friendly replacement for traditional energy sources. This increased value may be a significant benefit for homeowners that are trying to sell their house as time goes by. For businesses, the advantages of using solar power are wide ranging. One of several primary benefits is financial savings, as businesses can significantly reduce their energy costs by adopting solar power. In addition, there are many government incentives and tax credits accessible to companies that adopt solar technology, which makes it much more affordable and cost-effective. Furthermore, companies that adopt solar power can benefit from increased profitability and competitiveness, since they are seen as environmentally conscious and energy-efficient. The technology behind solar technology is not at all hard, yet highly effective. Solar energy panels are made up of photovoltaic (PV) cells, which convert sunlight into electricity. This electricity are able to be kept in batteries or fed straight into the electrical grid, with respect to the specific system design. So that you can maximize the many benefits of solar power, it is critical to design a custom system this is certainly tailored to your unique energy needs and requirements. This may make sure that you have just the right components in position, including the appropriate amount of solar energy panels plus the right types of batteries, to increase your power efficiency and value savings. One of several important aspects in designing a custom solar technology system is knowing the various kinds of solar energy panels and their performance characteristics. There are 2 main kinds of solar power panels – monocrystalline and polycrystalline – each featuring its own benefits and drawbacks. Monocrystalline solar power panels are made of an individual, high-quality crystal, helping to make them more cost-effective and sturdy. However, they are more costly than polycrystalline panels, that are produced from multiple, lower-quality crystals. Along with solar energy panels, a custom solar power system will also include a battery system to keep excess energy, in addition to an inverter to convert the stored energy into usable electricity. It is essential to choose a battery system that is capable of storing the actual quantity of energy you want for the specific energy needs and requirements. This can make certain you have a trusted way to obtain power in the case of power outages or any other disruptions to your time supply. Another advantage of using solar power may be the positive impact this has from the environment. Solar power is on a clean and renewable power source, producing no emissions or pollutants. This makes it an ideal replacement for traditional resources of energy, such as for example fossil fuels, that are a major contributor to polluting of the environment and greenhouse gas emissions. By adopting solar power, homeowners and businesses can really help reduce their carbon footprint and play a role in a cleaner, more sustainable future. In closing, the advantages of using solar energy both in homes and companies are numerous and should not be overstated. From cost benefits, energy savings, and increased property value to environmental impact and technological advancements, solar technology provides a variety of advantages. By knowing the technology behind solar technology and designing a custom system tailored to specific energy needs, you’ll be able to maximize these benefits and then make a positive effect on both personal finances while the environment. Overall, the adoption of solar energy is an intelligent investment for a sustainable and bright future. Should you want to learn about more info on this fact matter take a look at a blog:
Before some time I didn’t have much more knowledge about solar panel but before 2 or 3 yrs I have installed solar panel system in my home’s top roof and that time I examined many companies and much researched on this. So I can say all about the solar PV system. A PV module is an assembly of photo-voltaic cells mounted in a frame work for installation. Photo-voltaic cells use sunlight as source of energy and generate direct current electricity. A collection of PV modules is called a PV Panel, and a system of Panels is an Array. Arrays of a photovoltaic system supply solar electricity to electrical equipment.
can i connect two strings in parallel with different voltage (20 Panels x30V =600V 10 Panels x30V =300V) to a string monitoring Unit ( SMU) ?? if it connected what will be the voltage at common output terminal.
Would you please send a formal quotation for the following item: The Solar Photovoltaic Array system Your quotation should include shipping till Cairo, delivery time and all your terms and conditions.
HI there. Interesting read. I think I understand the logic. I live on a boat that has 4x Shell SM110-24 (rated output 110w; rated current 3.15A; rated voltage 35V). Becuase of the mast and boom these is often a shadow that passes over one or more of the panels – often leaving the other panels fully exposed to direct light. From what I read the shadow on one panel is likely to be affecting the performance of the whole array. It’s almost that I need each individual panel going back to the batteries individually – but thats a lot of wiring. What would be the best set up – series or parallel – and use of blockign diodes to minimise the impact of the shadow on one part of the array? Cheers.
A series or parallel connection for your panels depends on your system requirements. These panels already have Bypass diodes built-in to prevent high currents from partial shading, but yes shading affects the performance and efficiency of the array. Blocking diodes prevent reverse currents from the battery to the panel when the panel is not generating electricity, for example night time. If you are using a charging regulator then blocking diodes are not normally require as it has protection built-in, only if you are charging batteries directly.
In a series connected system, current is common to ALL panels. Therefore the current will be equal to the lowest wattage panel in the series chain as: I = P/V
Dear Sir/Madam, Highly informative and concise artical on the subject. Great service to the electrical engineering community. Keep it up, God bless you with lot of wisdom and knowledge. Best regards.
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Reviews and information on the best Solar panels, inverters and batteries from SMA, Fronius, SunPower, SolaX, Q Cells, Trina, Jinko, Selectronic, Tesla Powerwall, ABB. Plus hybrid inverters, battery sizing, Lithium-ion and lead-acid batteries, off-grid and on-grid power systems.
Solar Panel Efficiency
Solar panel efficiency is a measure of the amount of sunlight (irradiation) that falls on the surface of a solar panel and is converted into electricity. Due to the many advances in photovoltaic technology over recent years, the average panel conversion efficiency has increased from 15% to well over 22%. This large jump in efficiency resulted in the power rating of a standard-size panel increasing from 250W to over 420W.
As explained below, solar panel efficiency is determined by two main factors; the photovoltaic (PV) cell efficiency, based on the cell design and silicon type, and the total panel efficiency, based on the cell layout, configuration and panel size. Increasing the panel size can also increase efficiency due to creating a larger surface area to capture sunlight, with the most powerful solar panels now achieving up to 700W power ratings.
Cell Efficiency
Cell efficiency is determined by the cell structure and type of substrate used, which is generally either P-type or N-type silicon. Cell efficiency is calculated by what is known as the fill factor (FF), which is the maximum conversion efficiency of a PV cell at the optimum operating voltage and current. Note cell efficiency should not be confused with panel efficiency. The panel efficiency is always lower due to the internal cell gaps and frame structure included in the panel area. See further details below.
The cell design plays a significant role in panel efficiency. Key features include the silicon type, busbar configuration, junction and passivation type (PERC). Panels built using Back-contact (IBC) cells are currently the most efficient (up to 23.8%) due to the high purity N-type silicon substrate and no losses from busbar shading. However, panels developed using the latest N-Type TOPcon, and advanced heterojunction (HJT) cells have achieved efficiency levels well above 22%. Ultra-high efficiency Tandem Perovskite cells are still in development but are expected to become commercially viable within the next two years. For a deeper technical insight, Progress in Photovoltaics publishes listings of the latest photovoltaic cell technologies twice a year.
Panel Efficiency
Solar panel efficiency is measured under standard test conditions (STC) based on a cell temperature of 25°C, solar irradiance of 1000W/m2 and Air Mass of 1.5. The efficiency (%) of a panel is effectively calculated by dividing the maximum power rating, or Pmax (W) at STC, by the total panel area measured in square meters.
Overall panel efficiency can be influenced by many factors, including; temperature, irradiance level, cell type, and interconnection of the cells. Surprisingly, even the colour of the protective backsheet can affect efficiency. A black backsheet might look more aesthetically pleasing, but it absorbs more heat resulting in higher cell temperature, which increases resistance, this in turn slightly reduces total conversion efficiency.
Panels built using advanced ‘Interdigitated back contact’ or IBC cells are the most efficient, followed by heterojunction (HJT) cells, TOPcon cells, half-cut and multi-busbar monocrystalline PERC cells, shingled cells and finally 60-cell (4-5 busbar) mono cells. 60-cell poly or multicrystalline panels are generally the least efficient and equally the lowest cost panels.
Top 10 most efficient solar panels
The last two years have seen a surge in manufacturers releasing more efficient solar panels based on high-performance N-type HJT, TOPcon and Back-contact (IBC) cells. SunPower Maxeon panels led the industry for over a decade, but for the first time, lesser-known manufacturer Aiko Solar released the Black Hole series panels with an incredible 23.6% module conversion efficiency using a unique new ABC (All Back Contact) cell technology. Recom Tech also announced a next-generation Black Tiger series claimed to achieve 23.6% efficiency using a new TOPcon Back-contact cell architecture. LONGi Solar was only the second manufacturer to develop a module efficiency level of 22.8% with the new Hi-Mo 6 Scientists series. The Hi-Mo 6 series is based on a new hybrid IBC cell design, which LONGi calls HPBC. Canadian Solar has also revealed a new-generation Hi Hero module built using HJT cells, which is on par with the efficiency level of the renowned Maxeon series.
Other leading panels include those from Jinko, REC, and Risen, featuring N-type HJT and TOPcon cells. High-performance panels from SPIC and Belinus using IBC cells have also closed the gap, plus new panels featuring multi-busbar (MBB) half-cut N-type TOPCon cells from JA Solar, Jolywood and Qcells and most leading manufacturers have helped boost panel efficiency above 22%.
| 1 | Aiko Solar | Black Hole series | 460 W | 23.6 % |
| 2 | Recom Tech | Black Tiger | 460 W | 23.6 % |
| 3 | Longi Solar | Hi-Mo 6 Scientist | 450W | 23.0 % |
| 4 | SunPower | Maxeon 6 | 440 W | 22.8 % |
| 5 | Canadian Solar | Hi Hero HJT | 445 W | 22.8 % |
| 6 | Jinko Solar | Tiger NEO N-Type | 440 W | 22.5 % |
| 7 | Risen Energy | Hyper-Ion HJT | 440 W | 22.5 % |
| 8 | REC | Alpha Pure R | 430 W | 22.3 % |
| 9 | SPIC | Andromeda 2.0 | 440 W | 22.3 % |
| 10 | Qcells | Q.Tron-G1 | 400 W | 22.3 % |
Updated June 2023. Residential size panels. 54 to 66 cells (108-HC, 120-HC or 132-HC) and 96/104 cell formats. Does not include commercial panels greater than 2.0m in length.
Below is the latest Clean Energy Reviews downloadable chart of the most efficient residential solar panels for 2023, with PV cell technology details added for comparison.
Why efficiency matters
The term efficiency is thrown around a lot but a slightly more efficient panel doesn’t always equate to a better quality panel. Many people consider efficiency to be the most important criteria when selecting a solar panel, but what matters most is the manufacturing quality which is related to real world performance, reliability, manufacturers service, and warranty conditions. Read more about selecting the best quality solar panels here.
Faster Payback
In environmental terms, increased efficiency generally means a solar panel will pay back the embodied energy (energy used to extract the raw materials and manufacture the solar panel) in less time. Based on detailed lifecycle analysis, most silicon-based solar panels already repay the embodied energy within two years, depending on the location. However, as panel efficiency has increased beyond 20%, payback time has reduced to less than 1.5 years in many locations. Increased efficiency also means a solar system will generate more electricity over the average 20 year life of a solar panel and repay the upfront cost sooner, meaning the return on investment (ROI) will be improved further.
Longer life and lower degradation
Solar panel efficiency generally indicates performance, especially as most high-efficiency panels use higher-grade N-type silicon cells with an improved temperature coefficient and lower power degradation over time. efficient panels using N-type cells benefit from a lower rate of light-induced degradation or LID, which is as low as 0.25% of power loss per year. When calculated over the panel’s 25 to 30 year life, many of these high-efficiency panels are guaranteed to still generate 90% or more of the original rated capacity, depending on the manufacturer’s warranty details. Due to the higher purity composition, N-type cells offer higher performance by having a greater tolerance to impurities and lower defects, increasing overall efficiency.
Area Vs Efficiency
Efficiency does make a big difference in the amount of roof area required. Higher efficiency panels generate more energy per square meter and thus require less overall area. This is perfect for rooftops with limited space and can also allow larger capacity systems to be fitted to any roof. For example, 12 x higher efficiency 400W solar panels, with a 21.8% conversion efficiency, will provide around 1200W (1.2kW) more total solar capacity than the same number of similar size 300W panels with a lower 17.5% efficiency.
- 12 x 300W panels at 17.5% efficiency = 3,600 W
- 12 x 400W panels at 21.8% efficiency = 4,800 W
Real-world efficiency
In real-world use, solar panel operating efficiency is dependent on many external factors. Depending on the local environmental conditions these various factors can reduce panel efficiency and overall system performance. The main factors which affect solar panel efficiency are listed below:
The factors which have the most significant impact on panel efficiency in real-world use are irradiance, shading, orientation and temperature.
Solar Irradiance
The level of solar irradiance, also referred to as solar radiation, is measured in watts per square meter (W/m2) and is influenced by atmospheric conditions such as clouds smog, latitude and time of year. The average solar irradiance just outside the Earth’s atmosphere is around 1360 W/m2, while the solar irradiance at ground level, averaged throughout the year, is roughly 1000W/m2, hence why this is the official figure used under standard test conditions (STC) to determine the solar panel efficiency and power ratings. However, solar irradiance can be as high as 1200W/m2 in some locations during the middle of summer when the sun is directly overhead. In contrast, solar irradiance can fall well below 500W/m2 on a sunny day in winter or in smoggy conditions.
Shading
Naturally, if a panel is fully shaded, the power output will be very low, but partial shading can also have a big impact, not only on panel efficiency but total system efficiency. For example, slight shading over several cells on a single panel can reduce power output by 50% or more, which in turn can reduce the entire string power by a similar amount since most panels are connected in series and shading one panel affects the whole string. Therefore it is very important to try to reduce or eliminate shading if possible. Luckily there are add-on devices known as optimisers and micro-inverters, which can reduce the negative effect of shading, especially when only a small number of panels are shaded. Using shorter strings in parallel can also help reduce the effect of shading, as the shaded panels in one string will not reduce the current output of parallel unshaded strings.
Efficiency Vs temperature
The power rating of a solar panel, measured in Watts (W), is calculated under Standard Test Conditions (STC) at a cell temperature of 25°C and an irradiance level of 1000W/m2. However, in real-world use, cell temperature generally rises well above 25°C, depending on the ambient air temperature, wind speed, time of day and amount of solar irradiance (W/m2). During sunny weather, the internal cell temperature is typically 20-30°C higher than the ambient air temperature, which equates to approximately 8-15% reduction in total power output. depending on the type of solar cell and its temperature coefficient. To provide an average real-world estimate of solar panel performance, most manufacturers will also specify the power rating under NOCT conditions or the Nominal Operating Cell Temperature. NOCT performance is typically specified at a cell temperature of 45°C and a lower solar irradiance level of 800W/m2, which attempts to approximate the average real-world operating conditions of a solar panel.
Conversely, extremely cold temperatures can result in an increase in power generation above the nameplate rating as the PV cell voltage increases at lower temperatures below STC (25°C). Solar panels can exceed the panel power rating (Pmax) for short periods of time during very cold weather. This often occurs when full sunlight breaks through after a period of cloudy weather.
The Power Temperature Coefficient
Cell temperatures above or below STC will either reduce or increase the power output by a specific amount for every degree above or below 25°C. This is known as the power temperature coefficient which is measured in %/°C. Monocrystalline panels have an average temperature coefficient of.0.38% /°C, while polycrystalline panels are slightly higher at.0.40% /°C. Monocrystalline IBC cells have a much better (lower) temperature coefficient of around.0.30%/°C while the best performing cells at high temperatures are HJT (heterojunction) cells which are as low as.0.25% /°C.
Temperature coefficient comparison
The power temperature coefficient is measured in % per °C. Lower is more efficient
- Polycrystalline P-Type cells. 0.39 to 0.43 % /°C
- Monocrystalline P-Type cells. 0.35 to 0.40 % /°C
- Monocrystalline N-type TOPcon. 0.29 to 0.32 % /°C
- Monocrystalline N-Type IBC cells. 0.28 to 0.31 % /°C
- Monocrystalline N-Type HJT cells. 0.25 to 0.27 % /°C
The chart below highlights the difference in power loss between panels using different PV cell types. N-type heterojunction (HJT), TOPcon and IBC cells show far lower power loss at elevated temperatures compared to traditional poly and monocrystalline P-Type cells.
Power Vs Temperature chart notes:
- STC = Standard test conditions. 25°C (77°F)
- NOCT = Nominal operating cell temperature. 45°C (113°F)
- (^) High cell temp = Typical cell temperature during hot summer weather. 65°C (149°F)
- (#) Maximum operating temp = Maximum panel operating temperature during extremely high temperatures mounted on a dark coloured rooftop. 85°C (185°F)
Cell temperature is generally 20°C higher than the ambient air temperature which equates to a 5-8% reduction in power output at NOCT. However, cell temperature can rise as high as 85°C when mounted on a dark coloured rooftop during very hot 45°C, windless days which is generally considered the maximum operating temperature of a solar panel.
most efficient solar Cells
The most efficient solar panels on the market generally use either N-type (IBC) monocrystalline silicon cells or other highly efficient N-type variations, including heterojunction (HJT) and TOPcon cells. Most manufacturers traditionally used the standard and lower-cost P-type mono-PERC cells; however, many large-volume manufacturers, including JinkoSolar, JA Solar, Longi Solar, Canadian Solar and Trina Solar, are now rapidly shifting to more efficient N-type cells using HJT or TOPcon cell designs.
Efficiency of panels using different cell types
- Polycrystalline. 15 to 18%
- Monocrystalline. 16.5 to 19%
- Polycrystalline PERC. 17 to 19.5%
- Monocrystalline PERC. 17.5 to 20%
- Monocrystalline N-type. 19 to 20.5%
- Monocrystalline N-type TOPcon. 21 to 22.6%
- Monocrystalline N-type HJT. 21.2 to 22.8%
- Monocrystalline N-type IBC. 21.5 to 23.6%
Several new variations of Interdigitated Back Contact (IBC) cell architectures have emerged, of which the exact cell construction has not been fully disclosed. This includes LONGi Solar’s Hybrid Passivated Back Contact (HPBC) technology and Aiko Solar’s ABC (All Back Contact) cell technology.
Cost Vs Efficiency
All manufacturers produce a range of panels with different efficiency ratings depending on the silicon type used and whether they incorporate PERC, multi busbar or other cell technologies. Very efficient panels above 21% featuring N-type cells are generally much more expensive, so if cost is a major limitation it would be better suited to locations with limited mounting space, otherwise, you can pay a premium for the same power capacity which could be achieved by using 1 or 2 additional panels. However, high-efficiency panels using N-type cells will almost always outperform and outlast panels using P-type cells due to the lower rate of light-induced degradation or LID, so the extra cost is usually worth it in the long term.
For Example, a high-efficiency 400W panel could cost 350 or more while a common 370W panel will typically cost closer to 185. This equates to roughly 0.50 per watt compared to 0.90 per watt. Although in the case of the leading manufacturers such as Sunpower, Panasonic and REC, the more expensive panels deliver higher performance with lower degradation rates and generally come with a longer manufacturer or product warranty period, so it’s often a wise investment.
Panel Size Vs Efficiency
Panel efficiency is calculated by the power rating divided by the total panel area, so just having a larger size panel does not always equate to higher efficiency. However, larger panels using larger size cells increases the cell surface area which does boost overall efficiency.
Most common residential panels still use the standard 6” (156mm) square 60-cell panels while commercial systems use the larger format 72 cell panels. However, as explained below, a new industry trend emerged in 2020 towards much larger panel sizes built around new larger size cells which increased panel efficiency and boosted power output up to an impressive 600W.
Common Solar panel sizes
- 60 cell panel (120 HC) : Approx width 0.98m x length 1.65m
- 72 cell panel (144 HC) : Approx width 1.0m x length 2.0m
- 96/104 cell panel: Approx width 1.05m x length 1.60m
- 66 cell panel (132 HC). Approx width 1.10m x length 1.80m
- 78 cell panel (156 HC): Approx width 1.30m x length 2.4m
A standard size 60-cell (1m x 1.65m) panel with 18-20% efficiency typically has a power rating of 300-330 Watts, whereas a panel using higher efficiency cells, of the same size, can produce up to 370W. As previously explained, the most efficient standard-size panels use high-performance N-type IBC or Interdigitated Back Contact cells which can achieve up to 22.8% panel efficiency and generate an impressive 390 to 440 Watts.
Popular half-cut or split cell modules have double the number of cells with roughly the same panel size. A panel with 60 cells in a half-cell format is doubled to 120 cells, and 72 cells in a half-cell format have 144 cells. The half-cut cell configuration is slightly more efficient as the panel voltage is the same but the current is split between the two halves. Due to the lower current, half-cut panels have lower resistive losses resulting in increased efficiency and a lower temperature co-efficient which also helps boost operating efficiency.
New Larger cells and high power 600W panels
To decrease manufacturing costs, gain efficiency and increase power, solar panel manufacturers have moved away from the standard 156mm (6”) square cell wafer size in favour of larger wafer sizes. There are a variety of various cell sizes now available with the most popular being 166mm, 182mm and 210mm. The larger cells combined with new larger panel formats have enabled manufacturers to develop extremely powerful solar panels with ratings up to 700W. Larger cell sizes have a greater surface area and when combined with the latest cell technologies such as multi-busbar (MBB), TOPcon and tiling ribbon, can boost panel efficiency well above 22%.
Decoding Solar Panel Output: Voltages, Acronyms, and Jargon
For those that are new to solar power and photovoltaics (PV), unlocking the mysteries behind the jargon and acronyms is one of the most difficult early tasks. Solar panels have many different voltage figures associated with them. There is a good amount to learn when it comes to solar panel output.
Types of solar panel voltage:
- Voltage at Open Circuit (VOC)
- Voltage at Maximum Power (VMP or VPM)
- Nominal Voltage
- Temperature Corrected VOC
- Temperature Coefficient of Voltage
- Measuring Voltage and Solar Panel Testing
Voltage at Open Circuit (VOC)
What is the open circuit voltage of a solar panel? Voltage at open circuit is the voltage that is read with a voltmeter or multimeter when the module is not connected to any load. You would expect to see this number listed on a PV module’s specification sheet and sticker. This voltage is used when testing modules fresh out of the box and used later when doing temperature-corrected VOC calculations in system design. You can reference the chart below to find typical VOC values for different types of crystalline PV modules.
| 12 | 21 | 17 | 36 |
| 18 | 30 | 24 | 48 |
| 18 | 33 | 26 | 54 |
| 20 | 36 | 29 | 60 |
| 24 | 42 | 35 | 72 |
Voltage at Maximum Power (VMP or VPM)
What is the Max Power Voltage of a solar panel? Voltage at maximum power is the voltage that occurs when the module is connected to a load and is operating at its peak performance output under standard test conditions (STC). You would expect to see this number listed on a modules specification sheet and sticker. VMP is at the place of the bend on an I-V curve; where the greatest power output of the module is. It is important to note that this voltage is not easily measured, and is also not related to system performance per se. It is not uncommon for a load or a battery bank to draw down the VMP of a module or array to a few volts lower than VMP while the system is in operation. The rated wattage of a PV module can be confirmed in calculations by multiplying the VMP of the module by the current at max power (IMP). The result should give you [email protected] or power at the maximum power point, the same as the module’s nameplate wattage. The VMP of a module generally works out to be 0.5 volts per cell connected in series within the module. You can reference the chart to find typical VMP values for different types of crystalline modules.
Nominal Voltage
What is the voltage of a solar panel? Nominal voltage is the voltage that is used as a classification method, as a carry-over from the days when battery systems were the only things going. You would NOT expect to see this number listed on a PV module’s specification sheet and sticker. This nomenclature worked really well because most systems had 12V or 24V battery banks. When you had a 12V battery to charge you would use a 12V module, end of story. The same held true with 24V systems. Because charging was the only game in town, the needs of the batteries dictated how many cells inside the PV should be wired in series and or parallel, so that under most weather conditions the solar modules would work to charge the battery(s). If you reference the chart, you can see that 12V modules generally had 36 cells wired in series, which over the years was found to be the optimum number for reliable charging of 12V batteries. It stands to reason that a 24V system would see the numbers double, and it holds true in the chart. Everything worked really well in this off grid solar system as the and evolved along the same nomenclature so that when you had a 12V battery and you wanted solar power, you knew you had to get a “12V” module and a “12V” controller. Even though the voltage from the solar module could be at 17VDC, and the charge controller would be charging at 14V, while the inverter was running happily at 13VDC input, the whole system was made up of 12V “nominal” components so that it would all work together. This worked well for a good while until maximum power point technology (MPPT) became available and started popping up. This meant that not all PV was necessarily charging batteries and that as MPPT technology evolved, even when PV was used in charging batteries, you were no longer required to use the same nominal voltage as your battery bank. String inverters changed the game for modules, as they were no longer forced in their design to be beholden to the voltage needs of deep cycle batteries. This shift allowed manufacturers to make modules based on physical size, wattage characteristics, and use other materials that produced module voltages completely unrelated to batteries. The first and most popular change occurred in what are now generally called 18V “nominal” modules. There are no 18V battery banks for RE systems. The modules acquired this name because their cell count and functional voltage ratings put them right in between the two existing categories of 12V and 24V “nominal” PV modules. Many modules followed with 48 to 60 cells, that produced voltages that were not a direct match for 12V or 24V nominal system components. To avoid bad system design and confusion, the 18V moniker was adopted by many in the industry but ultimately may have created more confusion among novices that did not understand the relationship between cells in series, VOC, VMP, and nominal voltage. With this understanding, things get a lot easier, and the chart should help to unlock some of the mystery.
Temperature-Corrected VOC
The temperature-corrected VOC value is required to ensure that when cold temperatures raise the VOC of an array, other connected equipment like MPPT controllers or grid tie inverters are not damaged. This calculation is done in one of two ways. The first way involves using the chart in NEC 690.7. The second way involves doing calculations with the Temperature Coefficient of Voltage and the coldest local temperature.
Temperature Coefficient of Voltage
What is a solar panel temperature coefficient? The temperature coefficient of a solar panel is the value represents the change in voltage based on temperature. Generally, it is used to calculate Cold Temp/Higher Voltage situations for array and component selection in cooler climates. This value may be presented as a percentage change from STC voltages per degree or as a voltage value change per degree temp change. This information was not easily found in the past, but is now more commonly seen on spec pages and sometimes module stickers.
Measuring Voltage and Solar Panel Testing
How do I measure voltage on a solar panel? Voltages can be read on a solar panel with the use of a voltmeter or multimeter. What you’ll see below is an example of a voltmeter measuring VOC with a junction box. This would be the view from the back of the PV module. Using a multimeter is the best way to measure solar panel output.
When researching solar panel output, it can be overwhelming to understand the different voltage figures and acronyms used. For those new to solar power and photovoltaics (PV), decoding the terminology can be a challenge. In this blog post, we will break down the basics of solar panel output, including voltage, acronyms, and jargon, to help you get up to speed.
What are solar amps and watts?
Solar amps and watts are two measurements of the amount of electrical energy that a solar panel produces. Solar amps (A) measure the rate of electric current produced by a photovoltaic cell, while solar watts (W) measure the amount of power delivered to an electrical load. Both solar amps and watts are related to the efficiency rating of residential solar panels. The higher the efficiency rating, the higher the number of solar amps and watts produced.
There are many types of 60-cell solar panels on the market for home solar applications, each with varying efficiency ratings and amp/watt outputs. High efficiency panels are capable of producing more solar watts than low-efficiency panels, although they tend to cost more upfront. By choosing the right panel, homeowners can ensure that their solar array is producing enough power to meet their electricity needs.
Why do solar panels have so many voltages associated with them?
Solar panels have a variety of voltage figures associated with them due to the different types of solar panels, their placement in a solar panel system, and their power production. The most common type of rooftop solar panel uses a direct current (DC) and produces a low voltage. This low voltage is typically between 20 and 40 volts, depending on the specific type of panel. To increase the voltage output, multiple solar panels can be wired together in a series or parallel connection, or both, depending on the specific solar energy system.
When solar panels are connected in a series, the voltages are added together. This means that connecting two 20-volt solar panels in series would yield a total voltage output of 40 volts. Connecting three panels in series would result in a 60-volt output, and so on. This method is often used when the total voltage needs to be higher than what a single panel can provide.
In contrast, when solar panels are connected in parallel, the wattage is added together. This means that connecting two 10-watt solar panels in parallel would yield a total wattage output of 20 watts. Connecting three panels in parallel would result in a 30-watt output, and so on. This method is often used when the total wattage needs to be higher than what a single panel can provide.
The voltage output of a solar panel also depends on its power production, which is measured by the manufacturer at Standard Test Conditions (STC).
What does STC mean?
STC is defined as an irradiance of 1,000 W/m2 and cell temperature of 25 degrees Celsius. Because real-world conditions are rarely equal to STC, the actual power output of a solar panel may differ from its rated output. This is why it’s important to understand the various voltages associated with your particular solar energy system to ensure it meets your needs. To determine solar panels rated output, you need to know two figures: the solar panel wattage (measured in watts) and solar panel efficiency (measured in percent). Solar installation involves connecting solar panels to a photovoltaic system that can use or store the generated electricity. The efficiency rating of solar panels varies depending on factors such as environment, angle, and geographic location, but typically ranges between 15–20%. Knowing what wattage solar panels generate helps determine their overall performance in terms of power production for any given solar installation project. Understanding the various voltages associated with solar energy systems can be challenging for those new to the technology but once you’ve grasped this knowledge, you’ll have the knowledge you need to make informed decisions about your own solar energy installation.
How many size should my solar panel be?
When choosing a solar panel size, you must consider your energy needs and the hours of sunlight available in your area. The size of the solar panel will determine how much electricity it can produce, measured in kilowatt hours (kWh). Your energy needs will determine the type of solar panel that you need.
If you’re looking to produce a specific amount of electricity, the total number of solar panels that you need will depend on their wattage rating. Generally, the higher the wattage rating, the more electricity it will generate. You can calculate how many solar panels you need to meet your energy requirements by dividing your kWh requirement by the wattage of each panel.
For example, if you have an energy requirement of 10 kWh per day and you are using solar panels with a rating of 250 watts, then you would need 40 solar panels.
When choosing the size of your solar panel, make sure to consider the hours of sunlight available in your area as well. The more sunlight available, the fewer solar panels you’ll need to meet your energy requirements.
In summary, the size of the solar panel that you need depends on your energy needs and the hours of sunlight available in your area. You can calculate how many panels you need to meet your energy requirements by dividing your kWh requirement by the wattage of each panel.
Learning Electrical Engineering
A Solar power system contains many different components besides the basic PV modules building block. For successfully planning a Solar PV system, it is crucial to understand the function of the basic components and to know their major functions. Further, it is important to know the effect on the location of the (expected) performance of a PV system whether you are planning this for your home or a small industrial concern or you simply want to power a single load. Understanding the different components in the Solar power system and their interrelationship with each other will help in making the right choice in terms of your financial outlay.
Solar PV systems can be very simple, consisting of just a few PV modules and load such as the direct powering of a water pump motor, which only needs to operate when the sun shines. However, when a whole house is required to be powered, the system must be operational day and night. It also may have to feed both AC and DC loads, have reserve power and may even include a back-up generator to charge batteries during hours of darkness or low sun light.
Types of PV Systems.
There are three main types of PV systems: stand-alone, grid-connected, and hybrid. The basic solar power system principles and elements remain the same. Systems are adapted to meet specific requirements by varying the type and quantity of the basic elements. One key advantage of the solar power system is that it is modular by nature. A modular system design allows easy expansion, when power demands change.
Stand-Alone Solar PV Power Systems
Stand-alone systems rely on solar power only. These systems can consist of the PV modules and a load only or they can include batteries for energy storage. When using batteries charge regulators are included, which switch off the PV modules when batteries are fully charged and may switch off the load to prevent the batteries from being discharged below a certain limit.
The batteries must have enough capacity to store the energy produced during the day to be used at night and during periods of poor weather. Below is shown below for the two commonly applied stand-alone systems: A simple DC Solar power system without a battery.
Grid Connected Solar PV Power Systems
Grid-connected Solar power systems are becoming increasingly popular for building integrated applications. As shown here, they are connected to the grid via inverters, which convert the DC power into AC electricity.
In small systems such as in residential homes, the inverter is connected to the distribution board, from where the PV-generated power is transferred into the electricity grid or to AC appliances in the house. These systems do not require batteries, since they are connected to the grid, which acts as a buffer such that an oversupply of PV electricity is transported while the grid also supplies the house with electricity in times of insufficient PV power generation.