Caring for your panels

Reading the monitoring

Most inverters report output to an app. Compare each month with the same month a year earlier, and with the monthly figures in your installer's estimate. A single dull month means little; output that stays well below for two or three months, in ordinary weather, points to a fault, new shade or dirt.

What a month should look like

To judge the monitoring you need a yardstick. These are PVGIS's long-term averages for a 4.4 kW system in Runcorn, on a south roof at 35 degrees and as east-west pairs at 10 degrees on a flat roof:

PVGIS 5.3 for Runcorn, 14% system losses. Scale by your own system's size; shade and dirt will lower it, a sunny month will raise it.

Flat roofs: frames, ballast and the covering

• Ballast blocks should stay where they were placed; wind and maintenance visits can shift them.
• Frames should sit square, with no bent members or loose clamps.
• The covering under and around the frames should be free of splits, and outlets should drain freely.
• Moss and leaves trapped behind frames hold water against the covering; clear them when you can do so safely.

Cleaning

Steeper panels on pitched roofs are mostly kept clean by rain. Panels tilted at 10 to 15 degrees on a flat roof collect more along their lower edge. Use soft water and a soft brush, from a safe position or by a firm with proper access; no pressure washers and no walking on panels.

Birds

Pigeons like the sheltered space under panels, on pitched and flat roofs alike. Mesh round the edge of the array keeps them out. Active nests of wild birds are protected by law, so wait until a nest is empty before it is cleared.

Against the installer's estimate

Your quote should have included a predicted yearly output worked out by the MCS method, with a shade allowance. After the first full year, set the total from the app against that figure as well as against PVGIS. A shortfall of a few per cent is normal weather. A larger gap, with no new shade to explain it, is worth raising while the workmanship warranty runs, with the monthly figures to hand.

A year's round

• Spring. After the winter storms, look from the ground or a window for shifted ballast, debris and anything lodged under the frames, and compare March and April with last year.
• Summer. The months that matter most for output. If birds start nesting under the array, wait until the nest is empty before anyone clears it.
• Autumn. Leaves collect behind low frames and in outlets on flat roofs; have them cleared before the wet months.
• Winter. Output is low whatever you do. Leave snow and frost to clear on their own rather than climbing up.

Tell your home insurer that the panels are there, since they become part of the building, and keep the installer's contact details with the paperwork.

The inverter and the paperwork

Note any warning light or error code and report it while the workmanship warranty runs. Expect to replace the inverter once during the panels' life. Keep the MCS certificate, the network notification, the electrical certificate, datasheets and warranties together for export payments, claims and a future sale.

Keep reading

• Flat-roof planner
• Paperwork
• Finding an installer
• Questions

Where the figures come from

1. MCS: The Solar PV Standard (Installation), MIS 3002 v6.0
2. EU JRC PVGIS 5.3: solar output by location, tilt and direction
3. Renewable Energy Consumer Code: members and rules