The long-term financial case for plug-in solar depends significantly on how long the equipment actually lasts. Headline numbers about 25-year lifespans sound impressive, but understanding what degrades, how quickly, and what the real replacement costs are gives you a much clearer picture of what you are actually buying.
Solar panels: the long-lived component
Modern monocrystalline solar panels genuinely do last a very long time. The photovoltaic cells themselves have no moving parts, require no fuel and generate no heat internally. The main mechanisms of degradation are UV exposure causing encapsulant yellowing, humidity ingress at the panel edges, and microcracks in cells caused by repeated thermal cycling.
Manufacturers typically guarantee at least 80 percent of rated output after 25 years, with a linear degradation of around 0.3 to 0.5 percent per year. This means a 400W panel will still be producing roughly 310 to 340W after 25 years — comfortably worth running. Physical panel failures before 25 years are relatively uncommon with reputable brands.
Premium panel technologies like IBC and HJT typically offer lower degradation rates — around 0.25 percent per year — meaning higher output retention over the long term. They cost more upfront but the 20-year output advantage can be meaningful.
The microinverter: what you will likely replace first
The microinverter is the component most likely to need replacing during a 20-year system life. It contains active electronics, runs warm and is exposed to outdoor temperature fluctuations. Warranty terms vary significantly by brand:
- EcoFlow: 5 years
- Hoymiles: 10 years
- Anker SOLIX: 12 years
- Zendure: 10 years
Replacement microinverters cost £60 to £120 and are a straightforward swap — unclip the old one, clip in the new one, reconnect the cables. A 20-year system life might require one microinverter replacement in years 10 to 15. At £100 for the replacement, this adds around £5 per year to the system’s total cost. That does not change the financial case materially.
Mounting hardware
Good quality aluminium and stainless steel mounting hardware will outlast the panels in most UK conditions. Cheap steel brackets will rust. Spending a little more on corrosion-resistant fixings is genuinely worth it, particularly for coastal or high-rainfall locations. Check and tighten clamps annually — hardware that worked itself slightly loose over a UK winter should be re-secured in spring.
The 20-year picture
A south-facing 800W system with a good panel brand saving £140 per year generates £2,800 in electricity savings over 20 years. Subtract the kit cost of around £500 and one microinverter replacement of around £100, and the net return over 20 years is roughly £2,200. The financial case improves further if electricity prices rise from current levels. Use the savings calculator to model your own situation, and see the Best Kits page for warranty comparisons across current products.