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Health check for solar panels

If you have had solar panels installed, whether some years ago or just a few weeks ago, it pays to periodically check their performance to make sure they are working properly. Generally the panels require little maintenance, but it is easy to forget about them after the novelty has worn off. So here is a short checklist to help ensure they remain in optimal operating condition.Clean me PV!

CLEANING: Panels installed on a pitched roof will be mostly be cleaned by rainfall, but soiling can build up, for instance from bird droppings, paint or leaves, and this should be removed. Some window cleaners offer this service if you cannot do it yourself.

DAMAGE: After several years' exposure to the elements on your roof, panels may begin to show some signs of wear and tear, such as peeling laminate or yellowing of the glass. In rare cases if severe, this may affect performance and you should contact your installer. Panels are typically guaranteed for 10 years.

ELECTRICAL OUTPUT: Some decline in performance is expected over the operating lifetime of the panels, which is generally reckoned to be about 1% per year. Typical warranties guarantee at least 90% of the initial rated peak output for the first 10 years, and panels should be producing at least 80% at 20 years. Moreover, an initial marked drop in output over the first year of operation, perhaps as much as 5%, is not unusual.

Performance drop-off can be difficult to assess, but try to check the output on a bright sunny day in summer, when solar radiation is maximal and the panels should be generating near their limit. If the reading on your monitor is much less than the peak rated output, then this might indicate a problem. Look for warning notifications on your monitor or on the inverter display. If in doubt, contact your installer or, if a member of Stafford Area Community Solar (SACS), contact MEB Total Ltd on 0845 2263 233.

INVERTER: This is the device that converts the direct (DC) current from the panels to alternating (AC) current for use in the building or export to the grid. Operating lifetimes vary according to the type. For a single central inverter, the guarantee is typically 5 years, but is longer for string inverters, whereas microinverters may be guaranteed for up to 20 years. Replacement of a single inverter is to be expected sometime during the 20-25-year lifetime of a system; this costs about £800 at current prices.

It is vital that cooling fins on the inverter are kept clear and clean - high temperatures shorten the life of the device.

Reassurance on longevity

Testing of PV arrays up to 20 years after installation has produced reassuring results, according to the Centre for Alternative Technology (CAT). In spring 2010 they tested each of 180 panels in an array installed in 1997, and found a 9% decline in performance on average, equivalent to just 0.7% per year over the 13 years. Even the worst performing panels still were producing about 80% of peak output.

An even older system installed by a Swiss university in 1982 was tested in 2002, and found still to be achieving nearly 90% of the peak nominal output, some 20 years later. CAT concludes that the 'picture is very encouraging' and that a 'PV installation should produce electricity for 30 years or longer'.