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Efficiency of solar panels and what it depends on

When you start looking for solar panels to buy, you might see that stores and brands promote theirs as “the most efficient panels you’ve ever seen”. What does it even mean? Is it a sales tactic, or efficiency is genuinely an important thing to look for? In this article, we’ll talk about how efficient are solar panels, what this word means and how much weight does it carry. 

Efficiency of solar panels ranges from 13% to 23%

Solar panels’ efficiency is the percentage of sunlight that a PV module converts to electricity. The more efficient a panel, the smaller it has to be to produce a certain amount of power.

The efficiency of a solar panel is determined at Standard Test Conditions (STC): 77 °F or 25 °C cell temperature and irradiance of 1,000 W/m2. Here’s how it’s calculated:

Efficiency = [Power output / (Area of panel x solar irradiance)] x 100%

The most complicated and modern solar cells reach a 42% conversion rate in laboratory conditions. The efficiency of most solar panels, however, ranges from 13% to 23%. The efficiency depends on the type of panels, design, temperature, irradiance and positioning.

Solar cell efficiency isn’t the same thing as solar panel efficiency because you have to take the frame and space between cells into the calculation as well.

Monocrystalline panels are efficient, polycrystalline are cheap

The three most prominent types of solar panels are monocrystalline, polycrystalline and thin-film panels. Let's look at them in detail:

• Monocrystalline panels are made almost purely of single-crystal silicone. The cells of mono-panels often have rounded edges and are black. The efficiency of monocrystalline cells reaches up to 27% in lab conditions. The panels’ efficiency ranges from 18% to 23%.
• Polycrystalline or multicrystalline panels are also made out of silicone though not one but a block of crystals. Poly-cells have a square cut and are blue. Their efficiency is lower, but they cost 20-25% less than monocrystalline panels. Polycrystalline panels have a conversion rate between 15% and 19%.
• Thin-film solar panels are among the more modern types of panels. Photovoltaic material is applied onto a substrate of metal or glass. These panels are light and flexible. Their lifespan is only 10-15 years whereas rigid panels go over 25 y

Bifacial panels are a special case. The rear side of a module contributes to the overall production and the efficiency of these modules can go over 27%. However, you have to set up the bifacial modules correctly to maximize the reflectivity of a surface beneath the panels and improve their bifacial gain this way.

Solar efficiency also depends on the technologies that a manufacturer used when building a panel. For example, half-cut cell design, PERC cells, multibusbars increase the conversion rate of a panel.

Bad weather can decrease performance by 10-40%

Real-world irradiance levels rarely match those in a lab. Alongside STC performance, some manufacturers mention the expected output of a panel under Normal Operating Conditions (NOCT) in the datasheet. The irradiance under NOCT is specified as 800 W/m².

The energy efficiency of solar panels drops on cloudy days. Clouds lower the production of solar panels by 10-40%. Surprisingly, energy production suffers when it's too hot. Energy losses caused by heat amount to around 10% on a typical summer day.


that’s how much more energy you get from panels in summer than in winter

Irradiance levels change with the season. Solar panels get 50% more sunlight in June than in December. the winter cold at least doesn’t let panels get too hot. That’s why the best weather for solar panels is cold and sunny.

Pick south side of the roof for a solar system in US 

The positioning of your system also has an effect on the irradiance and thus on solar panels’ effectiveness. The right side of the roof for it depends on the hemisphere you're in: the south is best for the northern hemisphere and vice versa.

Sometimes you would prefer east or west over south. When? Read the article!

Not all roofs in the USA make it possible to install a solar system on the south side. You still can choose east or west in that case, but keep in mind that output is decreased by 15% on average. 

You can install solar panels at an angle that is equal to your latitude. Anything between 30° and 45° works in the US. Some change the inclination of their solar array in winter and summer — read about it in detail in our article “Best angle for solar panels and how to get it right”.

Leaders in efficiency on solar market

The most efficient solar panels are packed with the latest innovations and often are among the most expensive ones on the market. Here are some brands that make the most efficient solar panels on the market:

Sunpower is an American company founded by Richard Swanson, an electrical engineering professor at Stanford University. Sunpower solar panels are beloved by experts and customers and they consistently set solar energy efficiency records. In 2020 Sunpower spun off the manufacturing of panels as Maxeon Solar Technologies.
REC company is headquartered in Norway. Their panels are known for high quality and their panels from the Alpha series hang with the most efficient PV modules on the market, going over 22% in conversion rate.
Panasonic, a Japanese company, makes panels that retain high efficiency at high temperatures. In 2021 Nikkei, a Japanese economics newspaper, disclosed that Panasonic plans to stop solar panels production in 2022. Later the company declared that it is going to outsource the manufacturing process and instead focus on designing new panels.
LG Solar has been delivering top-tier quality products for a long time and the warranty for them often goes up to 25 years. Unfortunately, LG Electronics officially announced in February 2022 that it would stop producing and selling solar panels in order to focus on other business areas.
Solaria makes their panels both in Korea and the United States. Their panels reach a 22% conversion rate. Clients also often highlight the design of their solar panels — these are possibly the most beautiful Pv modules you’ve ever seen..

Canadian Solar panels get honorable mentions for retaining high efficiency even in low light conditions, such as cloudy and winter days. Chinese company Trina Solar also competes for top spots in the list of the most efficient solar panels while keeping their products affordable for everyone.

Vasilii Smirnov
Solar Installation Expert

While the efficiency of a solar panel is a loud and impressive word, don’t overestimate its importance. It becomes truly important when want to squeeze as much energy out of limited space as possible. For example, when your energy consumption is high and the roof is small.

If space is not a big problem, then you probably don’t need the most expensive and most efficient panels that are available. Keep in mind, however, that a home installation consists of 15–35 panels and you’ll have to find enough room for them, preferably on the same side of the roof. Having efficient panels is especially important in a mobile installation. On a boat or on an RV, you might have room for only a couple of modules.

If you aren’t sure, whether or not you’ll be able to build a powerful enough space with the space you have, we recommend checking out the A1SolarStore calculator. It will evaluate your energy consumption and propose a solar system that should cover your needs. Not only it will specify the energy capacity of this PV system, the calculator will provide you with the numbers for an area that a system will require, the equipment that you’ll need and possible savings from the installations.

Find out cost & profitability of solar system for your home or business

A1SolarStore Calculator will help you choose the right solar panels and accessories to cover your energy needs.

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Illustrations – Marina Fionova

Andrey Gorichenski
Senior Editor

Andrey had been a news editor and freelance writer for a number of medias before joining A1SolarStore team. Climate change and its impact on people's lives has always been among his interests and it partially explains his degree in Philosophy and Ethics.

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