Looking after solar panels on a Liverpool home

Rain does most of the cleaning

Liverpool's weather is on your side here. The Met Office's 1991–2020 average for Crosby, just north of the city, is 824 mm of rain a year, falling on about 147 days with at least 1 mm (Met Office). On a pitched roof that water runs straight down the glass and carries most of the dust and pollen with it, so pitched panels rarely need routine washing.

The output figures used across this site already allow for some dirt. PVGIS's estimates include 14% for system losses, which covers soiling along with the wiring and the inverter (PVGIS 5.3), so a lightly dusty panel is not a fault. Panels at a shallow angle, or lying flat on a flat roof, shed water less readily and tend to collect a line of grime along their lower edge, which is one more reason to tilt them.

Cleaning makes sense in two cases: heavy soiling you can see from the ground, usually bird droppings, and a fall in output that the weather does not explain. When it is needed, use a firm with water-fed poles or proper roof access, and check the panel maker's instructions first; some warranties say what may and may not be used on the glass. Skip the pressure washer and the household cleaning products. The same goes for the occasional snowfall: leave it to slide off or melt, and never try to clear panels from a ladder.

Gulls, pigeons and bird mesh

On city roofs, birds can be more trouble than dirt. The gap between the panels and the roof is sheltered, dry and out of reach of predators, which makes it an attractive nesting place for pigeons. Once they move in, the problems are nesting material packed around cables and fixings, droppings on the roof and in the gutters, and noise. Gulls, the other usual suspect on city roofs, mostly cause trouble on top of the panels rather than underneath, with droppings that a shower will not always shift.

The usual defence against nesting is bird mesh: a wire mesh clipped around the edge of the array that closes the gap without drilling into the panels. It is far simpler to fit while the scaffold is up during installation than to add later, when access has to be arranged again. Ask whether mesh is included before you sign; the page on what solar costs lists it among the extras that change a quote. If birds have already moved in, a firm with access equipment will need to clear the space before the mesh goes on, and it is worth asking them to check the cables and fixings while they are up there.

Leaves, moss and growing shade

Leaves gather where the panels meet the roof and in the gutters below, and they hold damp against the roof covering. A look from the garden each autumn is usually enough to spot a build-up. Moss is a slower problem: it grows on older roofs, especially on slopes that see little sun, and can creep onto panel frames. Neither needs anyone on the roof unless it is clearly spreading or blocking the gutters. Where an overhanging tree belongs to a neighbour, talk to them before anything is cut back.

Shade is the one that sneaks up. A tree that cleared the roof when the panels went on may not do so ten years later, and a neighbour's new extension or loft conversion can cast a shadow where none fell before. The PVGIS figures assume an unshaded roof. If your output drifts down year after year while the weather has been ordinary, look at what has grown or been built nearby before suspecting the panels; the rooftop estimator gives the figure to compare against.

Checking the system is working

Most systems report through the inverter's display or an app, and many also have a generation meter showing total kWh. Pick one, note the reading at the start of each month, and divide each month's total by the system's size in kW. Then compare it with the PVGIS figures for central Liverpool below, which are averages over 2005–2023 (PVGIS 5.3).

As a worked example, a 4.5 kWp system on a south roof at 35°, the size the Energy Saving Trust treats as typical (Energy Saving Trust), should make about 4,343 kWh in an average year: roughly 126 kWh in December and 536 kWh in June (our arithmetic). Single months swing with the weather, so judge the year and compare like with like: this June against last June, not against May. For other directions, use the matching column: the same 4.5 kWp facing west should make about 3,447 kWh a year (our arithmetic).

Keep the record simple. A notebook or spreadsheet with the date, the reading and a word about the month's weather is enough, and after a year or two it shows the system's own pattern more clearly than any table.

The signs that need a call to the installer are clear enough. Zero output on a bright day, a fault light or error code on the inverter, or a sudden step down that does not recover over the following weeks all point to a fault rather than the weather. A slow drift is more likely to be shade or dirt. If the system includes a battery, look at its charging figures too, because on a simple app a battery fault can look like a panel fault. The guide to Liverpool's weather explains why a grey month is not, on its own, a warning sign.

How long the parts last

The Energy Saving Trust gives solar panels a life of 25 years or more and an inverter around 12 years (Energy Saving Trust). Put those side by side and most systems will need at least one inverter replacement during the panels' life, so it is worth knowing where the inverter is and what its warranty covers. A single inverter in the loft or garage can be swapped without touching the roof; microinverters or optimisers mounted behind the panels need roof access to replace. If a central inverter fails outside its warranty, the replacement need not be the same make; ask for one that suits any battery you have or might add, and file its paperwork with the rest.

Panels lose output slowly as they age, and the maker's warranty normally states how much they should still produce after a set number of years. Keep that document; it is what you would point to if output fell faster. A home battery has its own expected life and warranty terms, separate from the panels'.

Roof work, safety and the papers to keep

Many Liverpool roofs are old. 30.9% of the properties on the city's council tax list were built before 1919, and 25.6% before 1900 (VOA 2026). Panels sit on a roof for decades, so the covering underneath needs to last as long. If slates slip or a repair is needed under the array later, the panels have to be disconnected, lifted off and refitted, which usually means scaffolding again and an installer to handle the electrics. Have an older roof checked, and repaired if necessary, before anything goes on it; the page on Georgian and Victorian homes covers slate roofs in more detail.

Never go on the roof yourself, to clean, clear a nest or look at a fault. Apart from the fall, panels produce voltage whenever light reaches them, so they cannot simply be switched off at the wall. That work belongs to someone with access equipment and the right training.

Finally, keep the papers together in one folder:

• the MCS certificate, which an export supplier and a future buyer will both ask for (MCS);
• the SP Energy Networks notification and commissioning confirmation (SP Energy Networks);
• the electrical installation certificate and the handover pack;
• warranties for the panels, the inverter and the workmanship, with details of any consumer code the installer belongs to, such as RECC or HIES.

The guide to SP Energy Networks and your panels explains the grid paperwork, export payments covers what the supplier needs, and finding an installer lists what to ask for at handover. When you sell, the buyer's side may want to see the certificates, the warranties and any agreement about who holds the export tariff, so the folder should go with the house.