I used to work as engineering director of a solar energy firm, in this case concentrated PV but I learned a lot about silicon panels also.
First, if you want the feed-in tariff the panels have to be installed by a government-accredited supplier.
Second, they do not last for ever. The panels themselves are guaranteed (usually) for 25 years, and their lifetime is probably about 30. It's limited by diffusion across the p-n junctions (the thing that makes them work). Cool climates are better for lifetime so the UK may be OK in that regard. My main worry is actually of young vandals with stones. And they do need occasional cleaning.
But nobody knows how to make an inverter that lasts that long. 5-10 years life and a 5 year guarantee is normal. This of course is the part of the system that converts the DC generated by the panels to AC, and feeds it into your house or the grid.
My own choice was not to buy the panels but to lease the space on my roof to a company that did the installation and will do all the above maintenance. They get the feed-in tariff and I get the electricity in the daytime (4 kW peak though usually a good bit less). And am about to have air-source heat pump central heating installed, which will give still more benefit. Those I am buying, and they will be paid for over a few years by the RHI scheme.
Keith
