How to Monitor the Performance of your PV System

Do you know if your PV system is performing as well as it should? Do you know if your system is performing as well as other local PV systems? Are you interested in comparing the performance of your system with others in the UK.

Well it is relatively simple to answer all of these questions.

When you had your system installed your installer had to give you an estimate of what your PV system should generate in an average year. This is known as a SAP calculation. The SAP calculation calculates the output of a solar PV system according to the Government's Standard Assessment Procedure for Energy Rating of Dwellings (SAP 2005). This assessment takes into account such factors as shading, orientation and angle of the solar panels. It is usually quite conservative and don't take account the precise whereabouts of your property.

So as a starting point you have the installers estimate to compare your actual output.

However the PV output varies throughout the year due to the height of the sun and the length of the days among other climatic factors. It is very helpful to know what your system should be generating on a monthly basis so that you can compare your actual generation figures with a monthly estimate. Such monthly estimates can be obtained from the PVGIS website. Help in using the PVGIS calculator can be found on site.

So now you can compare your actual PV output figures with a monthly estimate specific to your actual latitude and longitude.

Finally there are organisations who collate data from hundreds to thousands of individual subscribers, enabling those subscribers to compare their systems overall performance with other individuals locally or in other parts of the world. One such websites is :-

The Microgen database organised by the University of Sheffield, also known as the Sheffield Solar Farm. This website offers a wide range of comparisons, a forum to ask questions and a monthly report.

So now you can compare your actual output with other local PV generators which will help you evaluate whether local weather conditions for example are impacting your output.

The University of Sheffield have developed an application with enables you to compare the annual generation predicted by SAP, PVGIS and the Sheffield Solar Farm's database.

You will need your installation's location by longitude and latitude. To find these figures from your postcode, you can use public tool: 2AH but add your own postcode to the end. 

So with all this potential data and comparison sites it should be possible for you to evaluate whether your system is performing properly. If it is not, then you should contact your installer.