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Last updated: 23 March 2021

How Efficient Are Solar Panels?

Which Factors Determine Solar Panel Efficiency?

Solar panels are usually able to process 15% to 22% of solar energy into usable energy, depending on factors like placement, orientation, weather conditions, and similar. The amount of sunlight that solar panel systems are able to convert into actual electricity is called performance, and the outcome determines the solar panel efficiency.

To determine solar panel efficiency, panels are tested at Standard Test Conditions (STC). STC specifies a temperature of 25°C and an irradiance of 1,000 W/m2. This is the equivalent of a sunny day with the incident light hitting a sun-facing 37°-tilted surface. Under these test conditions, a solar panel efficiency of 15% with a 1 m2 surface area would produce 150 Watts.

Apart from the standard test conditions, solar panels are extensively tested for performance in extreme conditions.

Extensive Testing of Solar Panels under Extreme Conditions

Solar Panel Extensive Testing

Extensive Testing of Solar Panels Under Extreme Conditions

No single customer wants to end up with solar panels that aren't technically sound. There are major advantages of solar energy, but it's important to have the right type of solar panel installed in your home. In order to guarantee the quality of a solar panel, it is extensively tested under extreme conditions.


A thick layer of snow can be too heavy for a solar panel. Solar cells stop working when more than 5 cm of snow accumulates on a solar panel and decreases solar panel efficiency by 100%. However, the tilt of solar panels allows the snow to simply glide off, and if not, then it can be manually removed.

For more information about how solar panels are still effective in the winter, check out our video below.

Are Solar Panels Effective in the Winter?


Wind is one the most predicted causes of solar cell damage. Solar panel manufacturers conduct extensive wind tunnel testing to decrease potential damage.


Hail testing consists of firing artificial hail at a speed of 20 to 30 m/s. Solar cells remain undamaged at these speeds.


Ice builds up on the surface of solar cells when no silicon coating is applied. The build-up of ice can potentially decrease solar panel efficiency by 25 to 100%.

Chemical Residue

For chemical residue to dissolve at least 20 mm of rainfall has to land on the surface of the solar cells. Research has shown a reduction of 0.2% in solar panel efficiency when they are covered in a layer of chemical build-up.

UV Degradation

A solar cell structure can be delaminated by UV induced degradation. Another consequence can be the discolouration of individual solar cells.

Damp heat testing

Damp heat testing is carried out to test the durability of solar panels in highly humid conditions. Humidity can lead to corrosion and to module connection failure and an overall decrease of solar panel efficiency.

Insulation Resistance

Insulation resistance is determined by material strength. In weak materials, current leakage can occur on the edges of the solar panel. 

Thermal Cycling

Thermal cycling can cause solar panel components to fail. These components include solar cells, interconnections, solder bonds and module connections. 

Upon installation, it is important to consider all the factors that could influence solar panel efficiency. Moreover, it is essential to maximise output from the get go.

Why Perform Extensive Testing of Solar Panel Efficiency Under Extreme Conditions?

Solar panel efficiency testing is carried out in order to prevent low quality solar panels from being sold in the market. The manufacturer has to prove that the solar cells have long term durability and long term efficiency. Solar panels available in the UK market are certified by first passing extensive testing.

Usually, solar cells are tested in state of the art, fully automated solar panel testing facilities. This high standard in testing enables categorisation of solar panel efficiency in groups with similar power outputs.

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What Types of Solar Panels Are Most Efficient?

There are numerous types of solar panels. The most common types of solar panels are:

  • Monocrystalline solar panels

  • Polycrystalline solar panels

  • Thin-film solar panels

Solar Panel Price vs Efficieny and Life Span

It is important to understand that the efficiency of an individual solar cell does not equate to the efficiency of solar panels (modules) as a system. While solar panel efficiency is generally around 15-20%, solar cell efficiency can reach 42% in some cases. 

However, unless otherwise stated, the performance of solar cells is measured under laboratory conditions. Therefore, although 42% is an impressive performance, laboratory conditions are different than real life and this is not applicable to residential users.

Monocrystalline Solar Panels

Monocrystalline solar panels, also called single-crystalline cells are manufactured from the purest silicon. A crystal of this type of silicon is grown in a complex process to produce a long rod. The rod is then cut into wafers that will make the solar cells. Monocrystalline solar panels are known to deliver the highest efficiency in standard test conditions when compared to the other 2 types of solar cells. The current delivered monocrystalline solar panel efficiency stands at 22-27%. You can recognise a monocrystalline panel by the rounded edge and the dark colour.

Polycrystalline Solar Panels

Solar panels made of polycrystalline solar panels, also called multi crystalline cells are slightly less efficient than those made up of monocrystalline solar cells. This is due to the nature of production. The silicon is not grown as a single cell but as a block of crystals. These blocks are then cut into wafers to produce individual solar cells. The current delivered polycrystalline solar panel efficiency stands at 15-22%.You can recognise a polycrystalline solar panel by the square cut and blue speckled colour.

Thin Film Solar Panels

Thin film solar panels are made by covering a substrate of glass, plastic or metal with one or more thin-layers of photovoltaic material. Thin film solar panels are usually flexible and low in weight. It is known that thin film solar panels degrade somewhat faster than mono and polycrystalline solar panels. Production of this kind of panels is less complex, thus their output is 5% less than monocrystalline solar panel efficiency. Normally, thin film cells deliver between 15-22% solar panel efficiency.

Thin film solar panel technology is closing the efficiency gap with more expensive types of solar panels, therefore thin film solar panels are installed on large scale projects and in record breaking solar power plants.

4 Key Attributes When Choosing Solar Panels

  • The cost for your solar panels installation per square metre.

  • Solar panel efficiency of the entire solar panel module.

  • Lifespan of individual solar cells.

  • The Aesthetics and style of your solar panel.

To help you find the best solar panels for your specific home, you can follow our 6-step video guide:

How to Find the Best Solar Panels in the UK (Cost & Efficiency Guide 2021)

Solar Panel Trends

There is massive competitiveness in the solar power market. Emerging giants like China and India are the biggest polluters and also global leaders in solar power station development. This sheer competitiveness will lead to lower prices for solar panels and more efficient storage solutions.

All these developments will ultimately seep through into the residential solar panel market. The change will lead to less expensive and more efficient solar power modules that can easily be installed for your homes. 

We understand that finding the right solar panel supplier takes some of your valuable time. We make the process of choosing the most efficient solar panel less time consuming and simple by proving you free, non-binding quotes from different suppliers. How? Simply fill in the contact form at the top of the page, stating your needs and preferences and we will get back to you with the sharpest quotes.

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Aris Vourvoulias
Written by Aris Vourvoulias, Head of Content

Aris Vourvoulias is the Head of Content in GreenMatch. Aris is a passionate author and marketer with an educational background in journalism. He continuously writes, reviews, and educates himself in the areas of business, finance, and renewable energy. He has managerial experience in many European markets, including UK, Denmark, Sweden, and Finland. He and his content team have been featured on reputable sites like GreenPeace, Guardian, iNews, Gizmodo, and more