How Efficient Are Solar Panels?

Solar cell efficiency explained

Updated:
Reviewed by
George Duval

Solar cell efficiency is a top priority when looking for the right solar panel for your home. Even if you’re on a budget, you want to aim for high-efficiency panels, as you’ll need fewer panels to meet your needs and it’ll take less time to recoup your initial investment. A lot of factors determine the efficiency of a solar cell; from the materials used in manufacturing to geographic location, to seasonality and weather. Keep reading to learn more about how solar efficiency is measured, and what you can do to maximize the performance of your solar panels.

These solar panels are mounted on trackers, which follow the sun and maximize efficiency.
Photo Credit: Wikimedia/Raysono

What is solar cell efficiency and how is it measured?

Talking about the efficiency of solar panels can get quite technical, but simply put, it’s the amount of sunlight the solar cell converts to usable electricity. Efficiency is usually rated as a percentage. A solar panel that’s rated for 35% efficiency will convert 35% of the sunlight it receives into electricity.

Solar cell efficiency translates into kilowatt hours (kWh) of electricity generated. If you know the efficiency of your panels, you can estimate how much electricity you’ll be generating by multiplying the efficiency percentage by the total area of your solar array. If you have 4 square meters of solar cells which operate at 20% efficiency, you’ll be generating 800 kWh per year. Note that efficiency is tested at what the solar industry calls Standard Testing Conditions. This assumes that the sun will be shining at 1000W per meter square for 2.74 hours, and an average solar cell temperature of 25 degrees Celsius. These are universal standards of optimal operating conditions used to test the efficiency of the solar cell. In reality, your solar panels will be operating under different circumstances which can result in varying levels of efficiency.

What factors affect the efficiency of my solar panels?

Outside of the testing lab, solar panels are exposed to the elements and are subject to several factors that can affect performance. Changes in current and voltage due to temperature or humidity can affect how much electricity is generated from the solar cell. Changes in the amount of sunlight the panel receives will also affect performance. These are things to keep in mind when thinking about how and where to install your solar panels.

Temperature

Solar panels operate best at lower temperatures, generally between 15 and 35 degrees Celsius. But temperatures inside the solar cell may rise as high as 65 degrees Celsius, at which point the efficiency will be adversely affected. Your panels are more likely to overheat when they’re installed on surfaces like roofs or walls, as they won’t cool off as quickly as freestanding solar panels.

Reflectance

Though the outer glass of a solar cell is transparent, it still reflects a certain amount of light. Efficiency can vary depending on how much light is filtered by the glass. Untreated silicon can reflect as much as 30% of incident sunlight, which is a big loss in terms of generating potential. Higher efficiency solar cells will have glass that is treated with anti-reflective coatings.

Weather

The sun doesn’t always shine. You’re bound to see days where it’s cloudy or raining. Don’t expect good performance when there’s inclement weather.

Geographic Location

The weather goes hand in hand with where you are in the world. If you’re in a sunny place like Arizona, you’re going to get a lot more out of your solar panels than someone who lives in Michigan. Setting up solar panels at higher altitudes will also see higher efficiency as the sunlight is stronger than at sea level.

Solar cell performance throughout the day.
Credit: Wikimedia/CharlesMJames

Time of Day and Year

Solar panels reach their peak efficiency during the afternoon. With the sun at a more acute angle at dawn or dusk, expect to generate less electricity. The time of the year will affect efficiency as well, with the best performance seen during the summer, and the winter seeing the lowest performance. This is also tied to your location. The further north you go, the less efficient your solar panel will be, especially during the winter. Vice versa if you live in the southern hemisphere. Locations near the equator will see good performance all year round.

Dirt and Grime

Eventually, your solar cells will accumulate dirt and dust. If you don’t keep up with maintenance and keep the glass clean, your efficiency will drop. Although particulates on the glass seem small, they can build up quickly, blocking out sunlight and having a big effect on your overall performance.

Angle and Positioning

Solar panels do best when positioned perpendicular to the sun. The best solar panels are mounted on trackers that move with the sun, but trackers are expensive and usually used in industrial settings. The consensus in the solar industry is that solar panels do best when oriented to the west or south. The optimal angle, or tilt, of the panel, depends on your geographic location. Do some research to find the best angle for your latitude. You may have to change the tilt of the panels throughout the year to get the maximum yield as the seasons change.

Solar Cell Type

Solar technology is booming, and scientists and researchers are hard at work trying to find the best materials to optimize solar efficiency. Different materials have different conversion rates, which is also tied to the cost of your solar panels. It’s safe to say that cheaper types of solar cells tend to be less efficient. The next section goes in-depth into the different types of solar panels and how they compare.

What are the most efficient types of solar panels?

Not all solar cells are created equal. Over the years, developers have succeeded in creating different types of solar cells for different purposes. The solar panel market is dominated by three types of panels: monocrystalline, polycrystalline, and thin film. The efficiency of each type of solar cell is tied to its costs.

Monocrystalline

Monocrystalline solar cells are the most efficient type of solar cell. They’re made of a single crystal of silicon cut into wafers. Monocrystalline panels are the most expensive, and often the more aesthetically pleasing, option to choose from. They tend to be black in appearance. The efficiency of monocrystalline panels is usually higher than 20%.

Polycrystalline

Polycrystalline panels are similar to monocrystalline, except they are made of silicon fragments that are melted together into a mold. Polycrystalline panels are less efficient, and cheaper than monocrystalline. They tend to have a dark blue hue. The efficiency of polycrystalline panels are around 15% to 17%.

Polycrystalline solar panels have a blue hue.
Photo credit: Wikimedia/Alespa

Thin Film

Thin film panels have the lowest performance, with efficiencies of around 10%. Thin-film solar panels trade efficiency for their flexibility, low profile, and portability. Instead of using silicon wafers, thin film panels use a film of semiconductor material installed on a frame made of glass, plastic, or metal. Thin-film panels use several different materials, including amorphous silicon or cadmium telluride. These are the cheapest solar panels on the market.

Future technologies to improve efficiency

Scientists and engineers are working hard to improve solar cell efficiency. Researchers at universities and solar manufacturers are constantly experimenting with new materials and configurations to find cost-effective ways to capture more sunlight.

Multijunction Solar Cells

Multijunction solar panels use non-traditional materials as semiconductors to capture and use a wider range of electromagnetic wavelengths. This allows for more electrical conversion from the same amount of sunlight. The efficiency of multijunction panels tops out at around 33%, but scientists have reached efficiencies as high as 46% in laboratory settings. Multijunction solar panels are often used in high-tech aerospace operations, like those in use on the International Space Station.

Multijunction solar cells are still in the testing phase but have shown great promise.
Photo Credit: Wikimedia/NASA/George Shelton

Concentrator PV

Concentrator photovoltaics use lenses or curved mirrors to concentrate the sun’s rays, raising the intensity of the sunlight. High Concentration PV can achieve efficiencies between 30% and 40%. Concentrators are often used in tandem with multijunction cells to raise efficiency. Concentrators are already in use but are mainly used in large-scale industrial solar arrays, as they are not cost-effective for commercial or residential use.

Brands and products with the highest efficiency

The best solar panels on the market today have efficiencies that exceed 20%. The top five brands as of 2021 are listed below. Note that these are all monocrystalline solar cells.

SunPower X-Series – 22.8%

LG Neon 375 Watt – 21.7%

REC Alpha Series – 21.7%

Panasonic N340 HIT – 20.3%

Solaria PowerXT – 20.2%

Conclusion

Next to affordability and durability, efficiency is one of the major factors in deciding what kind of solar panel is right for you. The most efficient monocrystalline solar panels cost a pretty penny, but they’re well worth the investment. Polycrystalline solar cells are great for those looking to go solar while on a budget. You’ll still get great efficiency but at a lower price. If you’re willing to sacrifice efficiency for functionality, then thin film is the way to go. Thin film solar panels are the cheapest option and are great for those looking to install solar panels on a boat or trailer. Remember that there are other factors that determine the efficiency of your panels, so adjust your solar setup accordingly.

FAQs

How is solar panel efficiency defined?

Solar panel efficiency is defined as a percentage of sunlight converted to electricity. A solar panel with 20% efficiency converts 20% of incident sunlight into usable energy. This can be further broken down into estimated kWh generated yearly. If the area of the solar panel is multiplied by its efficiency, then you can estimate how much electricity you will generate. A 4 square meter solar array with 20% efficiency will generate about 800 kWh per year. This estimate varies depending on a variety of factors.

How can you improve your solar panel efficiency?

Dirt and dust buildup can block out a significant amount of usable sunlight, so make sure to keep the glass clean on your panel. Installing your solar panel at the correct angle and tilt will maximize your efficiency. Depending on where you live, you may have to change the angle of your panels throughout the year to keep up with the change of the seasons. Buying higher quality solar panels that are treated with anti-reflective coating will also help you achieve better performance.

What is the highest achieved solar cell efficiency?

The best solar panels available commercially have efficiencies of around 23%. Though scientists and researchers have built solar cells with efficiencies as high as 46%. Some of these experimental solar cells are used by organizations like NASA for high-tech aerospace operations.

What is the common market efficiency for solar cells?

Most solar panels on the market today have efficiencies between 10% and 20%. Monocrystalline panels have higher efficiencies, usually at or above 20%. Polycrystalline panels have efficiencies around 15% to 17%. Thin film solar cells are at the low end of the spectrum for efficiency, usually between 10% and 13%, but are highly flexible and portable.

George Duval

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Author Bio

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George Duval

George Duval is a writer and expert in sustainability and environmental studies. After graduating with a B.A. in Sustainability from Florida International University, George began dedicating his life to researching new ways to make the world a greener place. His expertise ranges from organic gardening, to renewable energy, to eating plant-based diets. He is currently writing and editing for a number of publications, most of which focus on the environment.

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