Do Solar Panels Work on a Cloudy Day in Scotland?

Posted on April 9, 2015 in ,

The weather in Scotland is not very predictable. So for people considering installing solar panels in Scotland, it is pertinent to ask – will the solar panels work on a cloudy day? The answer is yes they will. Of course it is better that there is abundant sunshine to make the most of the technology. However, even in low light, solar panels will keep producing electricity although their performance will drop with decreasing light intensity. As we have discussed before, the solar irradiance in the UK and Scotland is not too dissimilar to Germany who is the largest photovoltaic (PV) market in the world. So this should never really be a reason not to install solar panels.

How Do Solar Panels Work?

Solar panels are made up of solar cells or “photovoltaic” cells. Photovoltaic cells are made from two layers of semi-conducting material, commonly silicon. When sunlight hits these cells, the energy absorbed excites the electrons in the layers so that they move from one to the other which creates a current. The electricity produced is direct current (DC) so it needs to be converted to alternating current (AC) before it can be used. The more energy that is absorbed by the solar cells, the greater the amount of electricity that is produced.

solar panel efficiency cloudy day

Output of a solar panel at different light intensities. W/m2 is a measurement of the intensity of sunlight.


The efficiency of the solar panel can vary depending on the quality of the panel, the construction of the solar cells and the installation, but most solar panels have an efficiency of around 15-25%. Panel efficiency is calculated by dividing the power output of the module by the physical area of the module. There is new research all the time to increase efficiency by experimenting with different materials and it looks promising.

Light Intensity Measurements

A good installer will have software that uses historical Met office data for a given location and will give an accurate prediction of performance of solar PV based on previous light levels. A light meter is the only way to test the intensity of the light and to make an accurate prediction of the potential efficiency of the solar panels.  In this way the customer understands their return on investment.

solar light meter for cloudy day

Light meter to measure intensity


Solar panels are a good investment for a number of reasons, not least because they will save you money and help reduce our reliance on fossil fuels.