The truth about cleaning
Scottish rainfall is more than enough to keep most panels operating above 95% of theoretical output. Cleaning provides a measurable benefit only on near-flat roofs (under 15° pitch), in dusty rural areas, near major roads or close to coastal salt spray — common around the Forth, Clyde and east-coast harbours. When you do clean, use deionised water and a soft brush — never a pressure washer.
Inverter lifetime
String inverters typically need replacement at 12–15 years (£700–£1,400). Hybrid inverters work harder and often last 10–12 years (£900–£1,800). Budget for one replacement during the 25-year panel life.
Degradation
Modern N-type panels degrade at around 0.35–0.4% per year, retaining 85–88% of original output at year 25. Budget assumptions of 0.5%/year remain conservative.
Battery lifetime
LFP (lithium iron phosphate) batteries from GivEnergy, Tesla, BYD and others are warrantied for 10–15 years and 6,000–10,000 full cycles. Expect 70–80% of original capacity at end of warranty.
Annual checklist
- Check generation vs prior year via the inverter app
- Visual inspection of DC isolator and cabling from ground
- Trim any vegetation now shading the array (especially neighbouring trees)
- Review SEG payments and switch tariffs if a better rate is available
Insurance
Most UK home insurers cover solar PV under buildings cover, sometimes requiring a phone notification post-install. Confirm with your insurer; never assume.
A five-year performance snapshot from a Fife installation
To put the theory in context, here's the year-by-year generation data from a 4kWp array on a St Andrews bungalow, commissioned March 2020 (Longi 340W panels, Solis 4kW string inverter, south-southeast aspect, no shading):
| Year | Generation (kWh) | vs year 1 | Note |
|---|---|---|---|
| 2020 | 3,610 | — | Baseline (partial year, annualised) |
| 2021 | 3,595 | -0.4% | Normal degradation |
| 2022 | 3,720 | +3.0% | Exceptionally sunny Scottish spring |
| 2023 | 3,555 | -1.5% | Below-average June cloud cover |
| 2024 | 3,510 | -2.8% | Cumulative ~1% panel degradation |
| 2025 | 3,478 | -3.6% | On track for warranty (85% at year 25) |
Total maintenance spend over 5.5 years: £0. The inverter is due a first health check in 2027; the panels have never been cleaned. Year-on-year variation is dominated by weather, not equipment.
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Frequently asked questions
01.Do solar panels need cleaning?
Rarely in the UK. Rainfall keeps panels at >95% of optimal output. Cleaning may add 2–4% yield in dusty rural or coastal locations; over-cleaning risks micro-cracks.
02.How often should the inverter be serviced?
Annual visual checks suffice for the first 10 years. Most string inverters need replacement at 12–15 years; hybrid inverters typically last 10–12 years.
03.What happens in a power cut?
Most domestic UK solar systems shut down for safety during grid outages (G98/G99 anti-islanding). Hybrid inverters with EPS or whole-home backup can continue powering essential circuits from battery.