Your solar panels were a significant investment — the kind that pays back over decades. But like any system exposed to the elements year-round, they need periodic attention to deliver on that promise. A well-maintained residential array loses only about 0.5% of output per year, whereas a neglected one can shed 1–2% annually. This solar panel maintenance guide walks you through everything you need to do, and how often.

How Often Should You Clean Solar Panels?

For most UK homes, cleaning panels once or twice a year is sufficient. Rain handles light dust reasonably well, but bird droppings, pollen build-up, and lichen growth are stubborn and won’t wash off on their own. Research suggests soiling alone can reduce output by 5–25% depending on location and season.

A rough schedule by situation:

  • Urban or suburban locations: twice yearly (spring and autumn)
  • Rural areas near farmland or trees: three times yearly; pollen and organic debris accumulate faster
  • Coastal properties: quarterly; salt spray leaves residue that accelerates micro-corrosion over time

Clean panels in the early morning or evening when they’re cool — cold water on hot glass can cause thermal stress.

Annual Inspection Checklist

A visual inspection twice a year catches most problems before they become expensive. Work through this from ground level first, then on the roof if it’s safe and you have the right equipment.

From the ground:

  • Visible cracks, chips, or delamination on panel surfaces
  • Discolouration or “hot spots” (brownish marks on cells — a sign of cell damage)
  • Panels visibly loose or tilted out of alignment
  • Debris accumulated in panel gaps or on mounting rails
  • Shading from new tree growth, neighbour extensions, or aerials you hadn’t noticed before

On the roof (only if safe and with appropriate PPE):

  • Mounting brackets free from rust or corrosion
  • Cable conduit intact with no visible damage or pest chewing
  • Flashing around roof penetrations sealed correctly
  • No standing water pooling under panels

Inside (inverter and monitoring):

  • All indicator lights green or as expected per your inverter manual
  • No error codes in your monitoring app
  • String voltages within the normal range for your system size
  • AC and DC isolator switches operating correctly

Inverter Health: What to Watch For

The inverter is the component most likely to need attention within the first ten years. Modern string inverters carry a 5–10 year warranty; microinverters typically 25 years. Key signs of inverter problems:

  • Unexplained output drops not explained by weather or season
  • Frequent error codes (even self-clearing ones) — these signal thermal stress or component ageing
  • Unusual fan noise or the inverter running hotter than usual
  • DC input voltage readings outside the expected range in your datasheet

Log your monthly generation figures from day one. Any month that deviates more than 10% from the same month the previous year — accounting for obvious weather differences — warrants investigation. Don’t just check what your monitoring app says looks fine; actually compare year-on-year numbers.

Understanding Solar Panel Degradation Rates

All panels degrade over time. The industry standard guarantee is no more than 0.7% annual degradation, with typical 25-year performance warranties guaranteeing at least 80% of rated output at year 25.

In practice, premium panels (Panasonic HIT, REC Alpha, SunPower Maxeon) degrade closer to 0.25–0.4% per year. Budget panels may reach 1% or higher. This is why panel brand choice matters almost as much at year 15 as it does at installation.

Factors that accelerate degradation: micro-cracks from poor installation or heavy snow loads, potential-induced degradation (PID) which better-quality panels resist, and prolonged high temperatures — less of a concern in the UK than in hotter countries.

DIY vs Professional Maintenance: Costs and Trade-offs

DIY cleaning: A soft brush with a telescopic pole and a bucket of warm water (no detergent — it leaves residue) costs around £30–60 in equipment. Safe from ground level or a fixed ladder for single-storey sections. Avoid pressure washers; they force water under panel frames and can damage seals.

Professional cleaning: Typically £100–200 for a standard domestic array, including a brief visual inspection. Worth paying for second-storey or steep-pitched roofs where safety is a real consideration.

Professional inspection: A full electrical inspection from a qualified MCS-accredited installer runs £150–300. This includes thermal imaging to identify hot spots invisible to the naked eye, voltage and current checks at each string, and an earthing check. Recommended every five years and after any storm damage.

Monitoring subscriptions: Some manufacturers (SolarEdge, Enphase) offer paid monitoring plans from £5–15/month that flag underperformance automatically. Worth considering if you travel frequently or have a larger array and want peace of mind without manually checking monthly figures.

When to Call a Professional

Call an MCS-accredited installer immediately if you observe:

  • Burning smell near the inverter or any wiring
  • Visible arc marks or scorching on panels or junction boxes
  • Persistent error codes that don’t clear after a reset
  • A sudden drop in generation of more than 20% with no weather explanation
  • Physical damage to panels after hail, falling branches, or roof work

Don’t attempt to repair electrical faults yourself. Solar arrays operate at potentially lethal DC voltages and can’t be fully isolated without specialist equipment. This isn’t a DIY job.

A few hours of maintenance per year — cleaning twice, a visual walkthrough each season, and keeping an eye on your monitoring app — is enough to protect a 25-year investment. Budget roughly £150–250 annually for a mix of DIY cleaning and a periodic professional check, and you’ll keep degradation close to its theoretical minimum. The system quietly earns you money for decades — it deserves the occasional once-over.