Maintaining Solar Panel Performance

Will solar panels go on generating electricity forever?

The honest answer is we don’t know.  Most information about solar panels , once they have been installed is anecdotal with no industry wide databases telling us how solar panels are performing after many years of operation. This is one of the reasons this site was created.

The anecdotal evidence from installers who have been operating for 10 years or more (like my installers) is that panels installed in the late 90s are still working ‘fine’.

So what do we know?

We know in principle that panels  will work for a very long time. No moving parts etc are the commonsense reasons to think this. (The more complicated inverters seem to be more prone to replacement although little independent evidence of this as well). Roof panels seem to be resilient to the elements – when there’s a hailstorm its always with some relief they appear unscathed afterwards and when the snow slides off them in winter we like to imagine they’ve had a good clean!

However we also know that processes they use to generate electricity will become less efficient over time so the rate at which they produce electricity will slowly decline. Very few studies to tell us by how much but about 0.5% p.a is a common assumption for performance decline. This is another reason for joining this growing website – to establish real evidence of how well rooftop solar panels perform over time.

The common assumption of around 0.5% decline each year in efficiency has led panel manufacturers to back their products with Performance Warranties

What are Solar Panel Performance Warranties?

It is likely that your panels came with a ‘guarantee’ for 20-25 years.  Also known as Warranties and maybe a more accurate phrase given they come with lots of caveats, like a car warranty.

What do they promise? Provided panels have been installed properly they promise you that the panels will perform at least 90% of normal capacity in their first 10 years and at least 80% for the 15 years thereafter. Your guarantee may have different numbers but that’s the gist of it.

So how do you know your panels are performing as promised?

You don’t.

It may be easy to check when you live in a sun drenched Spain or Arizona  but with the UK’s wonderfully variable weather its not easy to check how your panels are performing. Well, not until this website was created anyway. You now have the opportunity f ree of cost to double check that your roof panels are performing as well others in your area, or, most critically, declining in performance at the same very slow pace as the others in your area. Only by doing this will you have a cost –free way of being certain that your panels are doing ok.

So what can I do if my panels start generating less electricity?

Clean the panels?

Some installers recommend you clean your panels every year or two. Others will say the panels are ‘self cleaning’ so don’t need someone going up on the roof. Like so many things in the world of roof panels it all depends on who you talk to. Still, once you have some evidence that your panels are not doing so well then it’s probably worth shopping around for someone kitted out to clean your roof panels safely.

How much more than a window cleaner it will cost depends on the accessibility of your roof. It will be really interesting to compare prices out there.  If you have a power washer you may be able to clean them from the ground, particularly if the panels are so dusty that you can spot the difference from the ground. Power washers are also useful for cleaning bird droppings which can have a surprisingly large effect on panel performance – particularly if it’s come from huge pigeons!


As things grow in your garden they may start shading your roof more, particularly in winter months. It seems that it only needs a small area of panels to be shaded for the generation capacity to be very noticeably reduced.  Once you get feedback from the website that your panels have a reduced power output it will be a simple matter of looking at your typical daily output curve (link to another blog here) and seeing the time of day there’s a dip. On the next sunny day look at the panels at the relevant time and see where the shading is coming from.  Then if it’s in your own garden a simple pruning will usually solve the problem.

None of the above?

If you’ve cleaned your panels, checked out the shading issues, and you still experience a greater decline in generation compared to the average then it may be worth investigating the matter with some more ‘expert’ assistance. How much you want to do this will probably depend on the loss of income you decide this power drop represents.

There are and will be an increasing number of resources available to solar panels users who are experiencing problems to help them find solutions to their issues. This website will be a central, independent source of information on how to get help when you need it.

However we anticipate the vast majority of our users will be quite happy with the performance results we provide them and simply interested in making the most of the panels they will be so pleased to have installed!