Are your PV Panels working efficiently?

Photograph of a man installing photovoltaic panels on a roof

Sustainable Crediton has been contacted by Solarsense, the installer recommended by us a few years ago, to let us know that they are now offering a PV Health Check on systems they have installed. The cost is £300 plus VAT for a health check and panel clean. If they receive three orders which they can fulfil in a day then they will reduce the price by 10%. We have attached a Solarsense flyer which describes the service on offer. We are not specifically recommending this service unless you are aware that you have a problem with your system. However having the system health check may give you the assurance and peace of mind that your system has been checked and that there are no imminent problems.

Sustainable Crediton has had only a handful of queries over the past few years from members about their systems failing to perform as originally predicted. The causes of the problems have been failed inverters or a problem with the wiring of the panels. Additionally panels don't perform as well as they should if they get very dirty. Sometimes problems crop up and owners don't realise the panels are not working or not working as well as they should and many months pass with reduced or no electricity generation.

Do you know if your PV system is performing as well as it should? 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. Our recommendation is that you take a measurement of your generation at least monthly and compare it with your installer's estimate.

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 more accurate 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 website 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 comparing your system with neighbouring systems. So now you can compare your actual output with other local PV generators which will help you evaluate whether your system is working as well as it should.

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