Let the rain do the washing
The district's weather does most of the cleaning. The Energy Saving Trust says that in the UK rain will clean panels tilted at 15° or more (Energy Saving Trust), and the Met Office record for Bingley shows an average of 157 days a year with at least 1 mm of rain (Met Office). On a pitched roof of slate or stone, that is plenty. The weather guide sets out when that rain falls.
The exceptions are panels at a shallow angle. The Trust says debris is more likely to build up on ground-mounted panels, or where there is more dust in the air, and that these may need cleaning occasionally. A low frame on a flat-roofed back extension can fall into that group. If a clean is needed, check the panel maker's instructions first and leave the job to someone with the right access equipment.
Never go on the roof yourself, and never lean a ladder against the array. Wet stone and slate are slippery, the panels are not built to be walked on, and the electrical side stays live in daylight whatever the inverter display says.
Pigeons, gulls and the gap under the panels
Panels sit on rails a short distance above the roof, and the sheltered gap underneath can attract nesting birds. In towns that usually means pigeons; on some roofs, gulls. The signs are droppings building up on the panels and in the gutter, nest material poking out from the edge of the array, and noise under the roof in spring.
The usual answer is mesh fitted around the edge of the array to close the gap. It is easiest to fit when the system goes in, so ask whether it is included at quote stage; fitting it later needs access to the roof and an installer or proofing firm who knows not to damage the panels or the wiring.
When you ask about mesh, ask:
- whether it clips to the panel frames or needs anything drilled;
- whether it still lets rain, leaves and grit wash out from under the array;
- how the fitter will check for nests before closing the gap;
- whether fitting it affects the panel or inverter warranty.
Timing matters because of the law. GOV.UK says all wild bird species, their eggs and nests are protected, and that it is an offence to intentionally take, damage or destroy a wild bird's nest while it is being used or built. It suggests avoiding harm by timing work outside the breeding season and by using deterrents that do not harm birds (GOV.UK). If birds are already nesting under your panels, wait until the nest is no longer in use before anyone closes the gap. GOV.UK adds that Natural England licences cover only a limited set of reasons, such as preserving public health and safety.
Moss and leaves on shaded stone roofs
Moss grows where a roof stays damp: north-facing slopes, roofs under trees, and older stone and slate roofs that spend much of the year in shade. It can creep in under the lower edge of the array, hold water against the roof and trap leaves and grit. Leaves also collect behind panels and in the gutters below them. Panels on a slope that grows moss are often in shade for part of the day, and that shade costs output as well.
The Energy Saving Trust's main maintenance advice is to keep nearby trees well trimmed to reduce shading (Energy Saving Trust). GOV.UK lists trimming trees among the activities that can affect wild birds, particularly in the breeding season, so check for nests before cutting back. The hills and valleys guide explains why a growing tree matters more than the hills, and the stone terraces guide covers the roofs themselves.
Checking output against the figures
Most systems show what they have made on the inverter's display or an app. The Energy Saving Trust says some inverters have online monitoring and can warn you by email if the system fails, and that your installer should leave written details of the maintenance checks to make, including the main inverter fault signals and basic troubleshooting (Energy Saving Trust). Ask for that before the installer leaves.
Then compare the readings with what the place should produce. PVGIS puts a 4 kW system facing south at 35° in the city centre at about 3,736 kWh a year (PVGIS 5.3; our arithmetic). For the month-by-month shape, multiply your system's size in kW by the figure for your area in the table, which is for panels at each place's best tilt. The simplest check of all is to note the generation meter's total on the same date every year and subtract last year's: one number, with no app needed.
| Month | City centre (41°) | Shipley (40°) | Keighley (39°) | Ilkley (39°) | Haworth (39°) |
|---|---|---|---|---|---|
| January | 35 | 33 | 31 | 30 | 28 |
| February | 51 | 50 | 47 | 48 | 46 |
| March | 84 | 83 | 80 | 82 | 79 |
| April | 106 | 107 | 107 | 107 | 107 |
| May | 115 | 116 | 117 | 117 | 116 |
| June | 109 | 110 | 111 | 111 | 111 |
| July | 113 | 113 | 113 | 115 | 113 |
| August | 105 | 105 | 105 | 105 | 104 |
| September | 86 | 86 | 85 | 86 | 84 |
| October | 59 | 59 | 58 | 59 | 56 |
| November | 41 | 40 | 39 | 37 | 37 |
| December | 31 | 29 | 26 | 24 | 25 |
These are averages, and a single month can be well off them in either direction, so judge a system on whole years and on the same month compared across years. East and west roofs, steeper or shallower pitches and nearby shade will all shift the numbers. What should prompt a call to the installer is a pattern rather than a dull week: no output at all on a bright day, a warning light or message on the inverter, or a month that falls well short of the same month a year earlier when the weather was much the same.
Panels, inverters and the long run
The Energy Saving Trust says solar panels should last 25 years or more, but that an inverter needs replacing after around 12 years (Energy Saving Trust). Over the life of the panels, then, plan on at least one new inverter. The Trust suggests asking the installer about the likely lifespan of the inverter and whether an extended inverter warranty is worth having, and notes that such a warranty can cost almost as much as a replacement. MCS says that using an installer it has certified gives you protection if something goes wrong (MCS), which is worth remembering if the original firm is no longer trading when a fault appears. Keep the warranty papers for the panels, the inverter and any battery with the rest of the system's documents. For what a system costs to put in, see what solar costs in the district.
Roof repairs, stone slates and listed roofs
Sooner or later a roof under panels needs attention: a slipped slate, a leaking flashing, a chimney stack to repoint. Any repair beneath the array means taking panels off and putting them back, which needs a solar installer to make the electrics safe as well as a roofer for the roof itself. Stone slates are heavy and can crack when walked on or lifted, so ask at the outset how the installer would remove panels for roof work and who would pay for any broken slates. When the work is finished, ask the installer to confirm the system is generating again, and add a note of the date and what was done to the system's papers.
Listed buildings add a step. Historic England counts 2,290 listed buildings in the district (Historic England), and MCS says that if your home is listed you will almost certainly need consent from your local authority for an installation (MCS). This guide does not try to say which repairs need consent; ask Bradford Council before any work on a listed roof, including the whole of Saltaire's listed area. The planning guide covers those areas.
Finally, keep the MCS certificate and the installer's notice to Northern Powergrid in the same folder. The network operator's page says installers must notify it within 28 days of connecting a small system (Northern Powergrid), and GOV.UK says an export tariff needs proof of MCS certification for both the installation and the installer (GOV.UK). You will want both when you change export supplier, add a battery or sell the house; the network guide and the export guide explain each, and the installer checklist covers what to ask for at handover.