Why farm solar needs its own maintenance plan
- Dust and debris. Harvest, grain drying, feed delivery and machinery throw fine dust onto nearby roofs, especially from late summer into autumn.
- Ammonia and humidity. Poultry, pig and dairy buildings produce ammonia-laden, humid air that attacks frames, fixings and cable glands. Modules certified to IEC 62716 are designed for it — see choosing agricultural solar panels — but fixings and seals still need checking.
- Birds. Pigeons, starlings and jackdaws nest under roof arrays; nesting material traps heat and debris, and droppings shade cells.
- Fragile roofs. Older farm buildings often have asbestos cement or other fragile sheeting. HSE says asbestos cement roofs are always fragile and cannot bear weight, and the Work at Height Regulations 2005 require precautions for any work on or near fragile surfaces — see solar panels on asbestos roofs.
- Livestock and weather. Stock rub against ground-mount frames and fences; exposed and upland sites take more wind and snow load.
What an annual service should cover
A good contractor works through a checklist like this and compares the results with the commissioning tests carried out when the system was installed (IEC 62446-1 sets out the tests and documentation for grid-connected PV):
- Visual inspection — Every module for cracked glass, delamination, frame corrosion and failed seals — from a mobile elevating work platform or other safe access, never by walking on fragile roof sheets.
- Cleaning where monitoring shows soiling — Soft brushes and purified water; no pressure washers or detergents unless the module manufacturer allows them.
- Thermal imaging under load — Finds hot spots from damaged cells, failed bypass diodes and poor connections before they become faults.
- String voltage and current — Measured and compared with the design values and with each other.
- Insulation resistance of the DC array — Tested and recorded to the method in IEC 62446-1, and compared with the commissioning results.
- Inverter check — Fault log, cooling fans, ventilation and performance against the monitoring trend.
- AC protection — RCD and protective-device tests to BS 7671.
- Earthing and surge protection — Continuity of earthing and bonding; condition of surge protection devices.
- Combiner and junction boxes — Fuses, isolators and terminal tightness — thermal cycling loosens connections.
- Bird-proofing — Mesh intact, nesting material removed from under the array.
- Mounting and fixings — Rails, clamps, purlin fixings and roof penetrations on roofs; posts, frames and fencing on ground mounts.
- Monitoring review — Actual generation against the expected yield, string by string, to spot slow declines.
- Metering — Generation and export meter readings checked against supplier and Smart Export Guarantee records.
- Written report — Photographs, test results against commissioning values, and recommended repairs.
How to spot lost output early
Degradation on its own is slow. Jordan and Kurtz's review of field studies (Progress in Photovoltaics, 2013) put the median loss for crystalline silicon modules at about 0.5% a year. A sudden step down in output, one string falling behind the others, or a steady decline faster than that points to something maintenance can fix: a blown string fuse, a failed connector, a cracked module, new shading or heavy soiling.
To put a value on it: a 100 kWp array on a south-facing 30° roof near York generates about 96,000 kWh a year (PVGIS: 960 kWh per kWp). Every 1% of lost output is about 960 kWh — roughly £240 a year at an assumed 25p/kWh the farm would otherwise buy. Monitoring that compares each string with the others catches most problems within days rather than at the next bill.
Cleaning
Clean when the monitoring shows soiling rather than to a fixed calendar. Sites near grain handling, feed delivery, poultry or pig housing, or with heavy bird activity, soil faster; a clean shed roof in a wet area may rarely need it. Use soft brushes and purified water, avoid pressure washers and detergents unless the module manufacturer permits them, and never put people on fragile roof sheets to do it.
Inverters and batteries
Inverters are usually the first major component to need replacing, because they typically carry much shorter warranties than the panels. Check the warranty on your model, keep the fault log, and budget for at least one replacement within the life of the array. Batteries have their own warranty terms — some require installation by a manufacturer-certified installer — so keep the paperwork with the rest of the system records. See farm battery storage.
Maintaining a ground-mounted array or solar farm
Field arrays add their own jobs: managing vegetation under and between the rows (often by sheep grazing — see agrivoltaics in the UK), keeping fences, gates and drainage in order, checking frames and posts for movement, and inspecting inverter and transformer housings. For planning and design, see ground-mounted solar panels for farms.
What to ask a maintenance contractor
- A written scope showing which of the checks above are included, and how often.
- Test results recorded against the original commissioning values, not just "pass".
- How access is made safe — especially on fragile or asbestos cement roofs — and evidence of training for platform work.
- Response times for faults found by monitoring, and what a call-out costs.
- Insurance, and whether the work meets any conditions in your panel, inverter and battery warranties.
- An itemised annual price, so you can compare contractors like for like.