Comprehensive Guide to Solar Panel Types
The push for renewable energy sources has led to a surge in solar energy use. In the past decade alone, the solar industry grew by almost 50%, buoyed by federal support such as the Solar Investment Tax Credit and strong commercial and industrial demand for clean energy.
As the solar sector continues to rise, it’s worth studying the backbone of the solar industry: solar panels.
This guide will illustrate the different types of solar panels available on the market today, their strengths and weaknesses, and which is best suited for specific use cases.
What is a Solar Panel?
Solar panels are used to collect solar energy from the sun and convert it into electricity.
The typical solar panel is composed of individual solar cells, each of which is made from layers of silicon, boron and phosphorus. The boron layer provides the positive charge, the phosphorus layer provides the negative charge, and the silicon wafer acts as the semiconductor.
When the sun’s photons strike the surface of the panel, it knocks out electrons from the silicon “sandwich” and into the electric field generated by the solar cells. This results in a directional current, which is then harnessed into usable power.
The entire process is called the photovoltaic effect, which is why solar panels are also known as photovoltaic panels or PV panels. A typical solar panel contains 60, 72 or 90 individual solar cells.
The 4 Main Types of Solar Panels
There are 4 major types of solar panels available on the market today: monocrystalline, polycrystalline, PERC, and thin-film panels.
Monocrystalline solar panels
Also known as single-crystal panels, these are made from a single pure silicon crystal that is cut into several wafers. Since they are made from pure silicon, they can be readily identified by their dark black color. The use of pure silicon also makes monocrystalline panels the most space-efficient and longest-lasting among all three solar panel types.
However, this comes at a cost — a lot of silicon is wasted to produce one monocrystalline cell, sometimes reaching over 50%. This results in a hefty price tag.
Polycrystalline solar panels
As the name implies, these come from different silicon crystals instead of one. The silicon fragments are melted and poured into a square mold. This makes polycrystalline cells much more affordable since there is hardly any wastage, and gives them that characteristic square shape.
However, this also makes them less efficient in terms of energy conversion and space, since their silicon purity and construction are lower than monocrystalline panels. They also have lower heat tolerance, which means they are less efficient in high-temperature environments.
Passivated Emitter and Rear Cell (PERC) panels
PERC solar panels are an improvement of the traditional monocrystalline cell. This relatively new technology adds a passivation layer in the rear surface of the cell that enhances efficiency in several ways:
- It reflects light back into the cell, increasing the amount of solar radiation that gets absorbed.
- It reduces the natural tendency of electrons to recombine and inhibit the flow of electrons in the system.
- It allows greater wavelengths of light to be reflected. Light waves over 1,180nm can’t be absorbed by silicon wafers and simply pass through, so they end up heating the cell’s metal back sheet and reduce its efficiency. The passivation layer reflects these higher wavelengths and stops them from heating up the back sheet.
PERC panels allow greater solar energy collection in a smaller physical footprint, which makes them ideal for limited spaces. They are only slightly more expensive to produce than traditional panels, due to the added materials needed, but they can be manufactured on the same equipment, and can end up having a lower average cost per watt due to their efficiency.
To get a better feel for the benefits of PERC panels, check out our blog 5 Important Benefits of PERC Solar Panels You Need to Know.
Thin-film solar panels
Thin-film panels are characterized by very fine layers that are thin enough to be flexible. Each panel does not require a frame backing, making them lighter and easier to install. Unlike crystalline silicon panels that come in standardized sizes of 60, 72, and 96-cell counts, thin-film panels can come in different sizes to suit specific needs. However, they are less efficient than typical silicon solar panels.
Thin-Film Solar Panel Variations
Unlike crystalline panels that use silicon, thin-film solar panels are made from different materials. These are:
- Cadmium telluride (CdTe)
- Amorphous silicon (a-Si)
- Copper indium gallium selenide (CIGS)
Cadmium telluride (CdTe)
CdTe has the same low-cost advantage as polycrystalline cells while possessing the lowest carbon footprint, water requirement, and energy payback time of all solar panels types. However, the toxic nature of cadmium makes recycling more expensive than other materials.
Amorphous silicon (a-Si)
Amorphous silicon panels (A-Si) derive their name from their shapeless nature. Unlike mono-and polycrystalline solar cells, the silicon is not structured on the molecular level.
On average, an a-Si cell requires only a fraction of the silicon needed to produce typical silicon cells. This allows them to have the lowest production cost, at the expense of efficiency. This is why a-Si panels are suited for applications that require very little power, such as calculators.
Copper indium gallium selenide (CIGS)
CIGS panels use a thin layer of copper, indium, gallium, and selenium deposited on a glass or plastic backing. The combination of these elements results in the highest efficiency among thin-panel types, though still not as efficient as crystalline silicon panels.
Solar Panel Types by Efficiency
Among all panel types, crystalline solar panels have the highest efficiency.
- Monocrystalline panels have an efficiency rating over 20%.
- PERC panels add an extra 5% efficiency thanks to their passivation layer.
- Polycrystalline panels hover somewhere between 15-17%.
In contrast, thin-film panels are usually 2-3% less efficient than crystalline silicon. On average:
- CIGS panels have an efficiency range of 13-15%.
- CdTe ranges between 9-11%.
- a-Si have the lowest efficiency at 6-8%.
Solar Panel Types by Power Capacity
Monocrystalline cells have the highest power capacity, thanks to their single-crystal construction that allows a higher output rating in a smaller package. Most monocrystalline panels can generate up to 300w of power capacity.
Recent advances in solar technology have allowed polycrystalline panels to bridge the gap. A standard 60-cell polycrystalline panel is now capable of producing between 240-300w. However, monocrystalline panels still beat polycrystalline in terms of power capacity per cell.
Because thin-film panels don’t come in uniform sizes, there is no standard measure of power capacity, and the capacity of one thin-film panel will differ from another based on its physical size. In general, given the same physical footprint, conventional crystalline panels output more power than a thin-film panel of the same size.
Solar Panel Types by Cost
Monocrystalline panels (or modules as they are technically known) carry a hefty price tag, due to its energy-intensive and inefficient manufacturing process with only a 50% yield for every silicon crystal.
Polycrystalline modules are cheaper because they make use of the crystal fragments leftover from monocrystalline production, which results in a simpler manufacturing process and lower production costs.
Among thin-film solar panels, CIGS is the most expensive, followed by CdTe and amorphous silicon. Apart from the lower acquisition cost, thin-film modules can be easier to install thanks to their lighter weight and flexibility, which lowers the cost of labor.
While the total cost of residential systems has declined by more than 65% over the last decade, the soft cost of a system has actually risen from 58% of total system cost in 2014 to 65% in 2020.
For more information about soft costs, check out our article on the soft costs in the solar industry. and what’s being done to reduce them.
|Panel (Module) type||Average Cost per Watt|
|Monocrystalline||1 – 1.50|
|Polycrystalline||0.70 – 1|
|Copper indium gallium selenide (CIGS)||0.60 – 0.70|
|Cadmium telluride (CdTe)||0.50 – 0.60|
|Amorphous silicon (a-Si)||0.43 – 0.50|
Note that these figures don’t include the cost of installation and labor. With labor and other overhead factors, the total can rise to 2.50 to 3.50 per watt.
Other Factors to Consider
The temperature of a solar panel can affect its ability to generate energy. This loss of output is reflected through the temperature coefficient, which is a measure of the panel’s decrease in power output for every 1°C rise over 25°C (77°F).
Monocrystalline and polycrystalline panels have a temperature coefficient between.0.3% / °C to.0.5% / °C, while thin-film panels are closer to.0.2% / °C. This means that thin-film panels can be a good option for hotter environments or places that experience more sunlight throughout the year.
The updated International Building Code of 2012 requires solar panels to match the fire rating of the roof where they are installed. This is to ensure that the modules do not accelerate the spread of flames in the event of a fire. (California goes one step further by requiring the whole PV system, which includes the racking system, to have the same fire rating).
As such, solar panels now carry the same classification rating as roofs:
- effective against severe fire test exposure
- flame spread should not exceed 6 feet
- required for wildland-urban interface areas, or areas with high fire severity and wildfire risk
UL 1703 and UL 61703 standards address hail storms, by dropping 2-inch solid steel spheres on solar panels from a height of 51 inches, and by firing 1-inch ice balls on PV panels with a pneumatic cannon to simulate hail impacts.
Because of their thicker construction, crystalline panels can withstand hail hitting at speeds of up to 50mph, while thin-film solar panels carry a lower rating due to their thin and flexible nature.
While there is no formal solar classification rating for hurricanes, the Department of Energy recently expanded its recommended design specifications for solar panels to safeguard against severe weather.
The new recommendations include:
- Modules with the highest ASTM E1830-15 rating for snow and wind loading in both the front and back.
- Fasteners with true locking capability based on DIN 65151 standard
- The use of through-bolting modules with locking fasteners instead of clamping fasteners
- The use of 3-frame rail systems for improved rigidity and support against twisting
- Tubular frames over open-shaped C channels
- Perimeter fencing around PV systems to slow down wind forces
Light-Induced Degradation (LID)
LID is a performance loss commonly seen in crystalline panels during the first few hours of sun exposure. This happens when sunlight reacts with oxygen traces left over from the manufacturing process, which affects the silicon lattice structure.
The LID loss is directly tied to the manufacturing quality and can range from 1-3%.
Summary: Solar Panel Types Compared
|Initial Cost||Highest||High||Middle||Highest to lowest:|
So, Which Solar Panel Type Should You Use?
As crystalline and thin-film panels have their own pros and cons, the choice of solar panel ultimately comes down to your specific property and condition settings.
Those living in a dense area with limited space should opt for highly efficient monocrystalline modules to make the most of the physical space and maximize utility savings. If budget permits, going for PERC panels can lower energy generation costs even more in the long run.
Those with a sufficiently larger property can save on upfront costs by using polycrystalline solar panels, where a bigger panel footprint can offset the lower panel efficiency. However, a larger footprint could also mean added labor costs, so it’s not necessarily cheaper to get a higher quantity of less expensive panels. While the initial cost may be low, it may eventually be offset by reduced efficiency and higher operating expenses in the long term.
As for thin-film solar panels, these are best suited for locations where the heavy and labor-intensive installation of crystalline silicon is not feasible. Such locations can include commercial buildings with tight spaces or thin roofs; compact spaces such as recreational vehicles and watercraft; and areas that require flexible installation instead of rigid paneling.
Keep in mind that solar panels are designed for long-term installation, which can be as long as 25 years. So whatever type you choose to go with, make sure to do your homework to ensure that it’s the best option for your needs.
Do engineers dream of solar panel efficiency?
A true next generation of solar cell technology is upon us. It is time to contemplate the benefits.
The U.S. is exploring polysilicon alternatives like perovskites.
Image: NREL/Dennis Schroeder
In its last quarterly earnings report, MeyerBurger noted that its 27% efficient perovskite-silicon tandem solar panel would potentially hit the market in 2023. The solar cell in this panel has already been tested at 29.52%.
In late June, JinkoSolar noted in its quarterly earnings report that it expects to successfully test a laminated perovskite solar cell over 30% efficiency by the end of the year. The company also said it had completed the construction of a “high-efficiency laminated perovskite cell technology platform.”
Also in late June, 1366 Technologies merged with Hunt Perovskite Technologies with a goal of offering a perovskite-silicon tandem solar cell whose efficiency is 30% greater than the best solar cells on the market.
A reminder: 1366’s CEO told pv magazine USA just six months ago:
In fact, not only do I believe that multiple gigawatts of tandem will be sold before the end of 2022, I am also confident that in a decade’s time, tandem will command more than 50% of our industry’s market share.
The more tempered members of our industry remind us, though, that historically speaking, scaling up solar panel technology from lab to market takes decades.
One professional wondered what JinkoSolar’s “technology platform” really is, and whether it’s appropriate for investors to consider it seriously yet. And another industry watcher expects the 1366 Technologies’ prediction of multiple gigawatts of tandem cell manufacturing capacity in place before the end of next year to fall flat.
This author won’t let any of that rationality dampen our excitement.
Efficiency makes the price of everything go down
The greatest benefit of increased solar panel efficiency is that on a per-watt and per-kilowatt hour basis, everything is cheaper.
In the image above, created by LONGi Solar, there is a comparison between a 380 Watt solar panel and a 425 Watt unit. The units are the same size, but the 425 Watt model has 11.8% more wattage, due to improvements in efficiency. A 380 Watt model found online – LR6-72HPH-380M – had a 19% efficiency.
Note that in the rate-of-change column, hardware and land savings total 7% when shifting from a 380 Watt to the 425 Watt unit on a 1 MW ground-based power plant.
Now imagine that we have a 30% efficient solar panel: that’s a 57% increase in electricity production over the 380 Watt unit. For the sake of simplicity, we’ll pretend benefits scale linearly with the LONGi comparison above. That means the 7% system savings turns into almost 35% savings.
These construction cost savings generally scale with electricity cost savings. Solar is already being proclaimed king of cheap energy generation. If we knock another 35% off construction costs, exclusively from improvements to solar panel efficiency, that’s some pretty sweet icing on the cake.
Three additional benefits result from breakthroughs in solar panel efficiency. First, local land savings results in a reduction in local pushback. Second, lower carbon footprint results from reduced equipment, transport, and labor needs. And of course, a massive boost to efficiency would certainly reinvigorate the spirit of the entire solar industry, for a third benefit.
The first two benefits are straightforward. For instance, pv magazine USA covered the fight to build what was the largest solar power plant east of the Rockies in 2019.
This fight highlighted that while solar is as popular as Apple pie, there has still been a drop in its popularity due partially to agricultural and rural pushback. It also revealed concern about the environmental aspects of manufacturing massive amounts of polysilicon, and the subsequent recycling of those solar panels.
If land use is reduced by one-third and electricity used to manufacture is also reduced by one-third, then it seems logical to assume that the pushback should drop off to some degree as well.
Do solar scientists dream of efficiency records?
This image is from the National Renewable Energy Laboratory’s (NREL) Best Research-Cell Efficiency Chart. Many readers know this chart not because it is directly applicable to their lives, but because it’s just so darn cool to see the blistering progress that solar technology has achieved in recent years.
Records are cool, lasers that beam energy to specialized solar cells are cool, and even carbon-nanotube solar pipe dreams are cool (even if we never figure out how to manufacture them) because that’s simply how life, and innovation, works.
If – or, more likely when – the solar manufacturers of the world sort out the manufacturing challenges behind tandem perovskitesilicon solar cells, it will open a clear path towards 34-35% efficient solar cells (the current speculative peak efficiency value of this product).
Already multi-layered solar cell products are common in expensive markets – the International Space Station for instance – but it is still too expensive for practical surface-based electricity generation.
We will finally see multijunction high efficiency products for the common person.
Of course, multi-layered products are currently available for purchase. Panasonic’s HIT goes way back, and REC’s Alpha product was released less than two years ago. But these products haven’t yet fulfilled the promises of our efficiency dreams.
Those efficiency dreams, without a doubt, lie deep within the minds of Fraunhofer’s and NREL’s researchers, as we can see from the aforementioned 68.9% solar cell which absorbs laser blasts, or the 47.1% six layer solar cell which is manufactured with surprisingly achievable technologies.
As our planet experiences record heat waves as a result of carbon emissions, killing our most vulnerable, it’s nice to have something to dream about.
The views and opinions expressed in this article are the author’s own, and do not necessarily reflect those held by pv magazine.
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How Hot Do Solar Panels Get? Effect of Temperature on PV Panel Efficiency
Imagine one of those searing hot days when all you can do is to sip a margarita somewhere in the shade. How would you perform on a day like that if you were asked to run a marathon? Not that well, right? Our body functions the best when the temperature is within our optimum range. Beyond this range we have to work much harder to maintain our performance level.
As surprising as it may sound, the same principle applies even to photovoltaic solar panels and their capacity to generate electricity!
The effect of temperature on PV solar panel efficiency
Most of us would assume that stronger and hotter the sun is, the more electricity our solar panels will produce. But that’s not the case. One of the key factors affecting the amount of power we get from a solar system is the temperature. Although the temperature doesn’t affect the amount of sunlight a solar cell receives, it does affect how much power is produced.
Solar cells are made of semiconductor materials, like the most used crystalline silicon. Semiconductors are sensitive to temperature changes. Temperatures above the optimum levels decrease the open circuit voltage of solar cells and their power output, while colder temperatures increase the voltage of solar cells.
The output of most solar panels is measured under Standard Test Conditions (STC) – this means a temperature of 25 degrees Celsius or 77 degrees Fahrenheit. The test temperature represents the average temperature during the solar peak hours of the spring and autumn in the continental United States .
According to the manufacture standards, 25 °C or 77 °F temperature indicates the peak of the optimum temperature range of photovoltaic solar panels. It is when solar photovoltaic cells are able to absorb sunlight with maximum efficiency and when we can expect them to perform the best.
The solar panel output fluctuates in real life conditions. It is because the intensity of sunlight and temperature of solar panels changes throughout the day. What interests us in this case is how does the temperature affect solar panel efficiency in real life. Let’s break it down.
What happens when the temperature of solar panels increases?
If you have photovoltaic solar panels installed at home or plan to get some in the near future, it’s useful to have a good understanding about the difference between the energy of electrons at a low energy state and electrons in the excited state, because this difference accounts for the power output produced by solar panels.
In a solar cell, you can find electrons bound at a low energy state. When these electrons receive extra energy, they enter a new state – known as the excited state – which allows them to break the bond and move. Electrons in the excited state can participate in conduction. The extra energy that elevates them to the excited state comes from two different sources – from light (sunlight) or from heat.
How much power is produced by a solar cell depends on how big is the energy difference (voltage) between these two states. Increase in temperature affects the semiconductor material parameters by increasing the energy of bound electrons. This means that the energy difference to achieve the exited state is smaller, which results in reduced power output and efficiency of solar panels .
When solar panels absorb sunlight, their temperature rises because of the sun’s heat. The common material used in solar cells, crystalline silicon, does not help to prevent them from getting hot either. As a great conductor of heat, silicon actually speeds up the heat building in solar cells on hot sunny days.
In a nutshell: Hotter solar panels produce less energy from the same amount of sunlight.
Luckily, the effect of temperature on solar panel output can be calculated and this can help us determine how our solar system will perform on summer days. The resulting number is known as the temperature coefficient.
Solar panel temperature coefficient
The temperature coefficient tells us the rate of how much will solar panel efficiency drop when the temperature will rise by one degree Celsius (1.8 °F).
For example, when the temperature coefficient is minus 0.5 percent, it means that efficiency decreases by 0.5 percent for every degree above 25 °C (or every 1.8 degrees above 77 °F).
Solar panels from different manufacturers will vary in their temperature coefficients. That is why all solar panel manufacturers provide a temperature coefficient value (Pmax) along with their product information.
In general, most solar panel coefficients range between minus 0.20 to minus 0.50 percent per degree Celsius. The closer this number is to zero, the less affected the solar panel is by the temperature rise.
If you want to find out which solar panels have the best temperature coefficient available today, we recommend checking out our recent report on the best solar panels for home use.
How hot do solar panels get? Can they overheat?
The maximum temperature solar panels can reach depends on a combination of factors such as solar irradiance, outside air temperature, position of panels and the type of installation, so it is difficult to say the exact number.
Generally, solar panels are made of dark-colored silicon cells (black or dark blue), covered by a sheet of glass and framed in metal.
Silicon and metal are good conductors of heat, contributing to faster buildup of heat inside solar cells. Even though, solar panel manufacturers and installers apply mechanisms to prevent solar panel overheating, in extremely hot conditions, the energy output of solar panels might decline significantly.
In summer 2017, The Times published an article discussing the problem of Qatar being too hot for photovoltaic solar panels. According to the article, the combination of temperatures rising up to 50 °C (122 °F) with dust reduced solar panel power output down to less than 40 percent.
What can you do to stop your panels from getting too hot?
Being aware of the effect higher temperature has on the energy output, most certified installers take steps to support natural cooling of solar systems.
A good practice for maximum efficiency is leaving at least a six-inch space between roof and panels to allow air circulation from both sides. But attaching your panels too far from the roof is not always a good idea. If the gap is too big, debris of leaves and twigs could accumulate underneath the array and cause damage to your roof or panels.
If you live in a hot climate, you should consider ground-mounted solar panels, because this way they get the most airflow to keep their temperature lower.
According to estimates, the temperature difference between the ground-mounted and roof attached solar panels can make up to 10 °C (50 °F) at the same location .
The best option is to get solar panels with temperature coefficient as close to zero as possible. The difference in total power output throughout the year can be significant.
For example, if your solar panels have a coefficient of minus 0.4 percent, their output on hot days will drop nearly twice that much compared to the output of a panel with a coefficient of only minus 0.2 percent per one degree Celsius.
White or light-colored roofing also helps to lower the temperature around your panels, since these colors reflect sunlight more and do not get heated up like dark roofing.
While above mentioned points involve passive cooling methods, some people opt even for active cooling systems.
For example, fans that blow air over panels, or circulating cold water which absorbs the heat from the panels and is then utilized in the household for showering or heating the building .
A side note: Be cautious about hosing down your panels during the hottest part of the day! It could make the glass crack and irreversibly damage your solar panels. The systems with water cooling do not expose solar panels to such a sudden temperature shock like you hosing them down would.
How does cold temperature affect solar panel output?
You may have heard people doubting solar panel performance in cold weather. Some may even think that solar panels stop working when it’s freezing outside. None of these statements is true.
Solar panels actually love colder temperatures on sunny days. The open circuit voltage produced by solar cells on cold days increases and may rise even 20 percent above the values obtained during the standard testing at 25 degrees Celsius. This means that solar panels will produce more power in an hour during the cold and sunny weather. The problem comes with the monthly production.
On average, photovoltaic solar panels still produce up to 80 percent more energy during the summer months than in winter. The main reasons are (as you may have guessed) shorter periods of sunlight per day and more days with heavy clouds in winter. It is the sunlight energy that is limited in winter, not temperature.
The angle of solar panels affects how well will solar cells utilize the sunlight. In winter, the sun is lower in the sky and sunlight is diffused over a larger area, whereas in summer, the sunlight hitting your solar panels is more concentrated. In order to get the best energy output in winter, the angle may need some adjustments to capture more light. In general, solar installers recommend 45 degrees angle. This angle also helps to prevent snow buildup on the panels.
Additional negative factors, reducing efficiency of solar panels in winter, are snow and ice. Solar panels are resistant. They do not get easily damaged by ice. It just takes some time for solar cells to defrost after a freezing night. During the time when the first sun rays shine on your solar panels, their efficiency is reduced, as the ice or snow blocks some of the sunlight that hits them. The time of unobstructed sunlight is then shorter, and you will get overall less power in winter months.
Before you decide on a solution that would work the best for you, do your research well. As you can see, there are already options to perform under different conditions and some help you to save money – even on production of warm water.
If none of them look appealing to you at the moment, do not despair. We live in the era of an amazing development in the solar energy industry.
Just as we speak many scientists are working on tackling issues of solar panel efficiency and performance optimization.
Scientists from the Stanford University have already pioneered a concept of “self-cooling” solar cells, which will be able to re-direct the heat from the cell’s surface. This design might be just one of many future solutions to tackle the problem of solar cell overheating.
So, let’s enjoy this solar revolution.
Solar Panels Get Less Efficient Over Time. Don’t Worry About It
Experts say you’re unlikely to notice your solar panels degrading over the years, and it isn’t worth waiting for more efficient panels.
Stephen J. Bronner is a New York-based freelance writer, editor and reporter. Over his more than a decade in journalism, he has written about energy, local politics and schools, startup success tips, the packaged food industry, the science of work, personal finance and blockchain. His bylined work has appeared in Inverse, Kotaku, Entrepreneur, NextAdvisor and CNET, and op-eds written on behalf of his clients were published in Forbes, HR Dive, Fast Company, NASDAQ and MarketWatch. Stephen previously served as contributors editor and news editor for Entrepreneur.com, and was the VP, Content and Strategy, at Ditto PR. He enjoys video games and punk rock. See some of his work at stephenjbronner.com.
Residential solar installations have seen a spike in recent years, with many Americans considering transitioning their energy usage to renewable sources (especially in light of new federal tax credits).
If you’re among those on the fence about solar, you might be wondering how long your solar investment will last.- and how efficient your solar panels will be in the next 20 years. The good news is your panels are likely to work just as well in the future.
While the efficiency of solar panels does drop over time, it’s usually not a big enough change to be a major worry, according to Joshua M. Pearce, a materials engineer who researches solar power systems at Western University in London, Ontario.
Can solar panels save you money?
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When a module or a PV system fails, it would usually be from something catastrophic, such as a tree fell onto your house and busted up a bunch of your panels, Pearce told CNET.
Here’s what you need to know about how your solar panels’ efficiency changes over time.
Can solar panels save you money?
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What is solar panel efficiency?
Today’s solar panels have efficiency ratings in the upper teens to lower 20s. That means when photons from the sun hit the solar panels on your roof, about a fifth of those photons are absorbed and converted into electricity. The photons that aren’t converted to electricity either bounce off the panels (like a reflection) or are absorbed, but not converted into electricity. This is because many of the sun’s rays, like those in the infrared spectrum, can’t be absorbed by today’s solar panels.
While the efficiency of today’s solar panels may not sound impressive at face value, Pearce said the technology is actually astounding compared to the efficiency of natural systems.
The most efficient biological conversion of sunlight into anything is under 2%, Pearce said. We are 10 times better than the fastest-growing plant that has existed on Earth before humanity got here. We’re doing pretty well.
Ultimately, the efficiency of solar panels should not be a major concern for consumers. When a solar installer gives you an estimate for your house, they will compensate for the efficiency of each panel by calculating the number of panels necessary for your home’s power needs.
Every single system is designed for a particular house, said Freddy Petkus, founder and owner of Critical Mass Solar, a Massachusetts-based solar installer. We do enough panels to offset your energy use no matter what kind of efficiency the panel has.
How does solar panel efficiency change over time?
Solar panel technology has come a long way over the past few decades, but we’re far from creating a perfect solar cell. Given these inefficiencies, solar panel manufacturers expect a degradation rate of about 0.5% a year, Pearce said, and their warranties will cover any panels that fail to meet those expectations. However, this is rare.
When you look at the data, most modules actually degrade even less than that, maybe 0.1%, and they last much longer than 25 years, Pearce said.
How to track solar panel efficiency
If you want to keep track of how much electricity your solar system is producing, there’s an app for that. These apps, which most solar companies provide, also allow you to track how much energy you’re consuming. While this can be valuable information for homeowners with solar systems, you’ll have an extremely difficult time tracking the efficiency of your panels with these apps.
The variation in how much solar energy your panels get from day to day and year to year will drown out any visible effects of degradation in panel efficiency, Pearce said. The average consumer has no chance of finding a 0.1% drop in efficiency with their system.
If you want to invest in equipment to track efficiency, Pearce recommends the installation of DC optimizers or micro inverters on your solar system.
Will solar panel efficiency improve in time with new technology?
Technology inevitably gets more efficient and powerful over time. According to Pearce, solar panels won’t necessarily improve due to technological breakthroughs, but rather because of better manufacturing techniques. These advancements will lead to solar panels with better glass that can absorb more solar energy, thinner layers of metal to allow for more cells and better positioning of the metal contacts.
efficient cells will also get darker and blacker, Pearce said, more like Darth Vader’s helmet, where nothing is coming off of it, you just see the evil on the inside as they suck all the light in, then turn it into electricity.
You should only wait for these improvements before investing in a solar system if you want to burn your money, the experts CNET spoke to said.
Right now in Massachusetts, the breakeven point with the major utility companies is anywhere between six to nine years to pay for solar, Petkus said. Hypothetically, if your bill is 200 a month, in 10 years you’ll have paid about 24,000 to the utility company. This is money better spent upgrading to solar.
Treat switching to solar power much like you would any other investment, Pearce said. Analyze the rate structure of your power provider to calculate the rate of return on installing a solar system. Then, try to factor in future rate increases and inflation. An estimate of about 3 per watt to install a solar system is a good baseline. The math should speak for itself.
Solar cell efficiencies will definitely improve, but waiting around for them won’t get you anywhere, Pearce said. This is a 25-year guaranteed rate of return with no taxes, because it’s all savings, and it’s inflation-proof.
Why Are Solar Panels Inefficient?
Solar energy development continues as the market evolves into more profitable photovoltaic system solutions in the long and medium term. The trend shows an exponential growth that started with around 6 GW of installed capacity in 2006 and evolved to almost 480.3 GW at the end of 2018 worldwide . Such accelerated growth could not even be foreseen back in the old days by the best specialists.
Ten years ago, solar installation costs were high above the clouds, making it very hard for homeowners to own a solar photovoltaic system. Policy and incentive schemes were also not clearly established or profitable, representing high investment risks that worked against the best environmental desires.
Among other reasons, one of the main limitations for entering the residential market was low efficiency of solar systems. Efficiency of solar panels represents how much of sunlight that hits a solar cell gets transformed into electricity. Some of the first solar panels had efficiencies between 8 to 10 percent. Other traditional sources of energy had efficiency of 40 to 55 percent with the combined cycle generators . The competition was just unbalanced.
Nowadays, solar installation costs are competitive with traditional energy sources. Policy and incentive schemes are solid and profitable for homeowners in most high-income countries. Solar cell efficiency has increased due to advancements in photovoltaic technology to the range between 15 and 22 percent. This number may not seem so competitive to many who have doubts about fully transitioning to solar energy.
Let’s have a look at reasons why are photovoltaic solar panels still inefficient.
Understanding why is solar cell efficiency low?
To understand efficiency of a solar panel, you must first understand its source of energy – the Sun.
Sun emits energy in a form of light which is composed of photons. Each photon has different energy and wavelength range (from ultraviolet to infrared). Photons are used by photovoltaic cells in solar panels to convert sunlight into electricity.
The cells are made of a semiconductor material (p-n junction), which facilitates generation of electric current when photons get absorbed. But a bigger part of sunlight that hits the cells isn’t converted into electricity. Why is that?
The problem with solar cell efficiency lies in the physical conversion of sunlight.
In 1961, William Shockley and Hans Queisser defined the fundamental principle of the solar photovoltaic industry. Their physical theory proved that there is a maximum possible efficiency of 33.7 percent which a standard photovoltaic cell (based on a p-n junction) can achieve to generate electricity from a light source . In other words, if the sun’s direct light is received by a surface per area of 1,000 watts per one square meter, then the maximum power output that a solar panel could produce is 337 watts per square meter.
This physical limitation is known as the Shockley-Queisser limit and is caused by the physical process of photon absorption by the semiconductor material that knocks loose electrons from their atoms and then passes them to the conduction Band within the solar cell . Some photons that hit a solar cell are reflected away from the cell’s surface. Out of those photons that are absorbed, some have their energy turned into heat in a process of internal recombination instead of producing electric current.
These efficiency losses are inevitable. There is no manufacturing process or technology development that can change this limit — at least not with silicon p-n junction solar cells.
The Shockley-Queisser limitation defines the theoretical level of maximum possible efficiency of a solar cell, but in the daily life, efficiency of solar energy conversion is affected also by other factors (discussed below).
Standard Test Conditions for verifying solar panel efficiency
To establish the efficiency value, manufacturers submit solar panels to several controlled factors that can exist in real world applications. They do this testing to make sure that the design endures these conditions, while at the same time, they verify estimated efficiency (as it is visible in the electrical characteristics of the datasheet).
It is important to know that many manufacturers establish solar cell efficiency based on Standard Test Conditions (STC).
STC are set on maximum possible solar irradiance (1kW per m2), at temperature of 25 degrees Celsius or 77 degrees Fahrenheit, and an air mass of 1.5 (related to the thickness of the atmosphere) .
It is rare to have the same conditions in the real life. Temperature and irradiance particularly can be very different from those values.
Nominal Operating Cell Temperature to simulate real life conditions
That is why some manufacturers add the Nominal Operating Cell Temperature (NOCT) among their technical references.
The NOCT is a parameter closer to real life situations and is defined as the temperature reached by an open circuit cell in a module under the following conditions  :
- Mounting System: Open back side (to consider air circulation behind the solar panel for refreshing purposes)
Now that you know how efficiency is specified by manufacturers, we can proceed with the factors that are taken into account for the design of solar panels to maintain acceptable efficiency values.
What factors affect solar panel efficiency in daily life?
#1 Hail, snow, ice and dust
Hail could in extreme scenarios damage the surface of solar panels and reduce their efficiency by decreasing the amount of sunlight they absorb. However, you should also know that solar panels are durable and meant to withstand hail at a speed of 20 to 30 meter per second (45 to 67 miles per hour). For a better idea, it is estimated that a hailstone with diameter of 1 centimeter or around 0.4 inches falls at a rate of 9 m/s (20 mph). Solar panels should resist even two to three times that. You should be safe during that early spring overcast.
Thick layers of snow can directly block sunlight accessing solar panels and cut efficiency down to zero . It is important to know that most solar panels can still work with a layer of three to four centimeters of snow (approx. 1.5 inches). If the layer is thicker than that, you should remove the snow.
Just like snow, dust and dirt can influence efficiency values on the same principle. When the layer is too thick to obstruct the light from reaching the solar panel surface, it will affect negatively how much energy the panel produces.
Ice is another element that affects solar panels’ efficiency between 25 to 100 percent, depending on the thickness of the ice layer. To prevent this problem, a silicon coating is applied to a solar panel surface, but even despite that it’s advisable to keep ice off your panels during the winter season .
#2 Insulation resistance
Besides the safety concerns, faulty insulation decreases solar module efficiency because current leakages can occur along the edges of solar panels. Be especially careful in areas with high humidity. Humidity speeds up corrosion of materials. Advanced level of corrosion eventually leads to insulation issues and decreases overall solar panel efficiency faster than expected.
Problems with insulation may occur in poor quality solar panels made of cheaper materials, or when solar cells are too close to the frame.
Insulation resistance is especially important for utility-scale projects as higher voltage systems require better insulation properties, which are linked directly to selected materials.
#3 Temperature of solar panels
Solar cells are sensitive to warmer temperature. Higher temperature outside means that the semiconductor material of solar panels gets hot quickly and slightly changes properties, which is linked to electrical losses and voltage drops.
It is estimated that an increase per one unit of temperature above the standard test temperature of around 25 degrees Celsius or 77 degrees Fahrenheit decreases the panel’s energy output by 0.25 to 0.5 percent (depending on the module type) .
If you think about it: temperature increase of around 60 degrees Celsius (140°F) could reduce the power outcome of your solar panel by 17.5 percent. So, the effect of temperature can be significant in countries with hot climate. Long term exposure to hot temperature may also shorten lifetime of the material.
On the other hand, you do not need to worry about colder temperatures, as long as the sun shines and solar panels receive unobstructed sunlight during the day, they will be producing at around their estimated efficiency. The only common problem in winter in regard to solar energy production is that the number of sunny days is much lower when compared to summer, and your system generates less on a monthly basis.
#4 Selection of the solar panel type
Not all solar panels are the same, neither is their price, which very often depicts not only the quality of materials and durability of the product, but also solar cell efficiency in converting sunlight in electricity. In daily life this usually means that you need less solar panels with higher efficiency rating to produce the same amount of power from their surface than you would need if you selected lower efficiency panels.
The main difference in efficiency values of different panel types lies in the nature of how they have been manufactured and what semiconductor material they are made of. The most common semiconductor used in solar cells is silicon. In case of silicon, efficiency still differs based on the type of cells. The best quality are solar cells made of monocrystalline silicon, other common forms are polycrystalline or amorphous cells.
Monocrystalline panels composed of a single crystal due to their structure allow for the best efficiency between 15 to 22 percent. Polycrystalline panels reach between 13 to 16 percent of efficiency and thin film panels made from amorphous cells have reached to 20 percent.
What also matters is how much light is reflected from the solar cell surface. The goal is to minimize light reflection and that is why many solar panels have special anti-reflection coating and are dark in color – black in case of monocrystalline and thin film panels and dark blue polycrystalline.
#5 Design configuration of solar panels
Among other factors associated with the operation of solar panels, the selection of the orientation towards the sun and the presence of a solar tracking system has a great importance on overall efficiency of your solar system.
Your solar panels will have the best power output when the solar panel surface is perpendicular to solar rays. However, as the sun moves across the sky, their angle changes as well. What you can do to ensure direct irradiance is to install a tracking system. Its downside are higher installation costs.
Solar panel efficiency also changes over the time. Every year that passes after your solar system installation, the efficiency value drops by about 0.5 percent per year. Nevertheless, solar panel manufacturers have to guarantee that the performance of your solar system will not drop below 80 percent when in warranty, which usually lasts 25 years.
Finally, shading is also an important part of the design of any solar system. If your system is shaded for the sunniest time of the day, solar panel output will be affected severely.
New solar technologies to improve efficiency
Despite low efficiency rates among current solar panels, there are several innovative proposals and technologies that aim to change how efficient can solar panels get in the close future.
#1 Reducing the shading effects of wires
Among available proposals is the reduction of the shading effect on solar cells caused by bus bars.
Bus bars are located vertically and horizontally across a solar panel. They can be easily identified by any person as silver wires forming a grid inside a solar panel. They transport electricity generated by solar cells.
These wires, even as tiny as they are, reflect the incoming light in sections where they pass by. In the end, this translates into less irradiance received by solar panels, and therefore, generation of less power.
The idea is to reduce the thickness of these wires, or in the best case to eliminate their interference with the sunlight by placing them on the back of a panel. This would achieve a uniform smooth colored panel .
#2 Innovative gallium arsenide triple-junction structure
Another interesting feature that has been set in motion is the development of the new generation of powerful solar cells from gallium arsenide.
Gallium arsenide cells have a triple-junction structure (different from silicon p-n junction) that can be chemically modified to acquire more light radiation than ordinary cells.
Among remarkable advantages of these cells is:
- Excellent ultraviolet, radiation and moisture resistance;
- Great performance in the presence of low light;
- Flexibility and low weight;
- Efficiency values over 28.8 percent (!).
#3 Cadmium telluride thin film cells
As new compounds are used for the creation of solar cells, new methodologies are also evolving around the manufacturing process to provide high efficiency solar cells.
The solar energy market is ruled by silicon semiconductors, included even in the design of thin film solar panels, but in the short to medium term, new photovoltaic materials like cadmium telluride are starting to gain their the market, as promising materials for the development of thin film panels.
The obstacle for their large-scale market introduction arises during the manufacturing process.
Some components seem to be very unstable because cadmium chloride has to be used during the manufacture. However, a new manufacture approach could deliver positive results, if cadmium chloride gets replaced with magnesium chloride .
Unlike cadmium chloride, magnesium chloride is abundant and low cost resource that can be obtained from the seawater. This material can also boost efficiency of the thin film panels up to 15 percent.
#4 Perovskite, the wonder material
The ultimate and most promising technology for improvement of efficiency is the perovskite component.
Perovskite, a compound of calcium, titanium and oxygen, offers the possibility to achieve efficiency levels above the current maximum of 22 percent at lower manufacturing costs.
The secret lies in the low costs of raw materials and fabrication methods (printing techniques) that do not require high temperatures and such a high precision as the silicon cells do.
How to easily improve efficiency of solar cells
When you would like to improve efficiency of your solar cells, you should consider the effect of factors discussed above. As you can see, there are some factors that cannot be influenced by you, such as weather and outdoor temperature, but some other factors can be controlled or selected to obtain the best possible efficiency.
The key to success is trying to tackle the factors that can be controlled.
For example: regular solar panel maintenance helps eliminate snow, dust, dirt and ice – all of which obstruct sunlight from effectively reaching the panel’s surface, and therefore reduce efficiency of solar cells.
By keeping your panels clean, you can nicely maintain their efficiency.
Other factors such as the type of a solar panel, its orientation, and the minimum shade configuration are crucial parameters that will determine overall efficiency in the long run.
Some important details that need to be considered are:
- the solar irradiation value in your area;
- average Cloud density;
- levels of air pollution;
- the angle of solar panels depending on their location and a selected mounting system.
These parameters are generally selected by a solar designer but that does not mean that you cannot intervene in the process, especially in the selection of the solar panel type.
Questions you may have about solar panel efficiency
We have discussed the limits of the conversion of sunlight into electricity for silicon p-n junction cells; the overall effect of several factors on the efficiency of solar panels; the new promising technologies or proposals to elevate such efficiency values and the options that you can implement to improve the efficiency conversion of your photovoltaic system.
Nevertheless, we haven’t discussed what exactly the use of solar panels with higher or lower efficiency values means for you. Efficiency is associated with the ability of solar cells to produce the maximum amount of electricity from a light energy source.
A single cell with low efficiency will produce less power than another cell of the same size but with higher efficiency.
Does it mean that if my solar panels have low efficiency they will produce less power?
If you select a solar panel with a power output of 200 watts and an efficiency of 14 percent, and then choose another solar panel with the same power output but with an efficiency of 20 percent, both panels will produce the same 200 watts output!
Where is the difference then?!
The difference lies in the size of the panel–lower efficiency panels require more space to produce the same power output. This means that a 14 percent efficient solar panel will be bigger in size.
So, the question that arises is…
Does solar panel efficiency matter?
The answer is: it depends. In some applications like solar cars, satellites, lighting and electronic devices size will matter, as the space availability is limited, and each inch of the panel needs to produce the maximum possible power to supply the required load.
Utility-scale projects must also take into the account optimal selection of the size and efficiency, as bigger panels require higher installation costs due to the longer wiring and stronger mounting structures (along with higher land rental costs) .
However, in residential solar systems, the availability of space on a roof or in a courtyard is sufficient to supply the desired load. Even though, this also depends on your expectations–meaning that if the demanded energy load exceeds the available space for the installation, high efficiency solar panels should be considered.
It is important to highlight that you should settle the balance between costs, efficiency, power load and space with your solar installer at the beginning because this decision will affect the overall performance of your solar system and the total cost of your project.