How efficient are solar panels?

Efficiency is the tool used to measure the performance of solar panels, or more specifically, how much of the light which hits a solar panel is actually converted into usable electricity. Efficiency is measured in the form of a ratio, which represents the energy output by the solar panel compared to the energy input from the sun. So the more efficient your solar panels are, the more value for money you’re getting!

Sometimes the system of measuring the efficiency of solar panels can seem misleading. The majority of panels are capable of processing 12% to 25% of the solar energy they take in which, although it doesn’t sound particularly impressive, makes them some of the most advanced solar tech to be available on the commercial market. Even now physicists are still debating how much more advanced solar panels can become, with some suggesting that the limit will be around 30%.

There are different types of solar panel available for domestic properties and each type has a different base efficiency rating. The two main types of solar cell - monocrystalline and polycrystalline - can be significantly different in terms of efficiency. Monocrystalline panels are usually considered to be more efficient (up to 25%) whereas polycrystalline panels are less so (usually between 12 and 18%).

The amount of importance you place on the exact efficiency % of solar panels should depend on the environment you wish to house them in. If you have a limited space to work with, it makes sense to invest in a more efficient system to produce more power in a smaller area. A higher efficiency rating usually equates to higher costs though, so if you have a larger area available then this can be less of a consideration.


What determines the efficiency of solar panels?

Several factors can impact the efficiency of a solar panel at any given moment. To an extent it’s expected that efficiency will decrease over time, so it’s important to maximise your base efficiency in the first instance by controlling for the following factors:


If your solar panels are located in an area which often falls into shade due to nearby trees or buildings, the ability of the panels to collect solar energy is limited.

Roof angle

Something which is not often considered when discussing solar panel efficiency but which has a significant impact is the angle at which the solar panels are installed. For roof solar panels, this is usually dictated by the pitch of the roof holding the panels. For maximum efficiency, the optimum angle is anywhere between 30 and 45 degrees.

Direction facing

The direction that your solar panels face face is a big factor in how much energy they will be able to collect throughout the day. As the sun rises in the East and sets in the West, it’s recommended to install your solar PV system in a southern-facing direction. This ensures you receive maximum sunlight throughout the day, allowing it to generate the most electricity it can.


The lifespan of the individual solar cells is a key factor in determining how efficiently the overall solar panels will perform over time. To an extent this will depend on the type of solar panel you select (see more on this below), but most come with a predicted lifespan of between 20 and 25 years.


Whilst one of the great advantages of solar panels is how low maintenance they are, it’s still important to maintain a regular cleaning schedule. This can be as infrequent as once a year, and you should also ensure your panels are inspected and serviced as necessary. The cleaner your solar panels are, the more efficiently they’ll be able to function. This is because dirt can obscure the panel and affect how much light hits the surface, which will limit the energy that it’s able to collect. This is particularly important if you have a Feed-in Tariff, as this will affect how much power you can sell back to the grid.


Excessive heat can sometimes be a cause of under-performing solar panels, potentially reducing the efficiency by up to 25%. Accompanying conditions such as a high UV index or high humidity can also lead to weathering over time. UV degradation can cause discolouration of the solar panel as well as delamination, whereas humidity can cause corrosion in the panel. This can reduce the overall efficiency of the solar panel.


How are solar panels tested for efficiency?

Before being put on the market, all solar panels undergo a series of rigorous tests to see how they will hold up in various conditions. Panels are usually tested in the following conditions:

  • Wind
  • Snow
  • Ice
  • Hail
  • UV degradation
  • Humidity
  • Chemical exposure
  • Insulation resistance
  • Thermal cycling

This is to stop low-quality products which won’t stand the test of time from being sold to consumers. As a result, any solar panel which is available for purchase has demonstrated that it can withstand extreme conditions with good durability over a long period of time, as well as maintaining a certain level of efficiency.


Ready to go solar?

Our solar panels come in a range of sizes to suit your needs. Get an estimate of costs and savings using our calculator tool, then get in touch for specialist advice and to move things forward.

Use our Solar Calculator to discover the benefits of Tonik Solar (it takes less than two minutes!)

Talk to us for specialist advice and to discuss next steps 0333 344 2686 (option 3) We'll work with you at every step, to deliver a solution you are delighted with


← Back to Solar Panels

Ask a question?