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Last updated: 22 March 2018

What Is Solar Panel Efficiency?

Read About Solar Panel Efficiency and the Factors Which Affect It

Solar panel efficiency (conversion rate) measures what amount of incoming sunlight hitting the panel, is converted to electricity for use of the household. The higher the efficiency, the lesser the number of solar panels you will require to generate the needed electricity.

In this post we will take a look at the efficiency of the different types of solar panels and some factors affecting it.

Solar Cell Efficiency

It is important to understand that this is the efficiency of an individual solar cell and not the efficiency of the 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 for residential users.

Read more: New Coating Makes Solar Cells More Powerful

Solar Panel Efficiency

This is the efficiency that is of interest to homeowners and it should be evaluated when purchasing a solar panel system.

Solar PanelsMonocrystalline Solar Panel Efficiency

This type of solar panels are made of the highest purity silicon and they are the most efficient. Some models can reach up to 25.6% efficiency, which means that they convert a quarter of the sunlight they get into electricity. They are also the most space efficient panels since you will need to cover less surface.

Polycrystalline Solar Panel Efficiency

Polycrystalline panels can reach 20% efficiency They are less efficient than monocrystalline panels but they are also less expensive. Moreover, as technology is improving, the efficiency of polycrystalline panels is rising. Coupled with lower costs of production than monocrystalline panels, polycrystalline modules are an increasing popular choice in northern Europe and the UK.

Thin-film Solar Panel Efficiency

Thin-film solar panels are relatively inefficient compared to the other two types. Some models can reach 11% conversion rate and they require more space, since you will have to install more panels to satisfy your energy needs. Nevertheless, these panels are the least expensive and if space is not an issue they are a viable option. Moreover, there is constant improvement in their efficiency. First Solar, a thin-film solar panel manufacturer, recently announced that it has made a thin-film solar cell converting 20.4% of the sunlight into electricity. So if they successfully bring that efficiency to the consumer market, thin-film solar panels will give the other two types of panels a serious push.

Read more: How to: Choose a Solar Panel

Factors Affecting Solar Panel Efficiency

Shade

Your solar system has to be positioned in a clear area with no shade. If there is a shaded area the efficiency of the panels will be reduced. Also, depending on how your solar system is set up, some shade on one panel can affect the output of the rest of the panels connected to it. Micro-inverters can be a good solution for dealing with shade, since they ensure that the shaded panel doesn’t affect the rest of the panels in the system.

Roof Pitch

The tilt of your roof can impact the number of hours of sunlight that your panels get per day. The angle of the roof can be altered with racks, which will give more hours of sun exposure to your panels. You may also want to adjust the angle of the solar panels twice per year, since the sun moves in different angles during the winter and the summer. Ideally, you should consult with your installer about this issue.

Orientation

Ideally the panels should be facing south. This will ensure that they get more sunshine throughout the day and as a consequence increase their effectiveness. However, although panels reach their maximum output when facing south, they could also generate adequate amount of electricity if facing south-west or south-east.

Lifespan

The efficiency of the solar panels decreases a little bit overtime. Typically it drops 0.5% per year. However, most solar panel manufacturers offer warranties which ensure that even after 20 years, the power input of the system will stay over 80% of its original efficiency.

Maintenance

Cleaning the solar panels regularly is important since dust or dirt can accumulate on the surface. This may block some of the sunlight and reduce the efficiency of the panels. Whether you do it yourself or use the services of a professional company, you should remember to keep your panels relatively clean. However, you should always check with your supplier if they have any restriction regarding panel cleaning because sometimes this may invalidate the panel’s warranty.

Read more: The Future of Solar Energy