Key takeaways
- • Plug-in solar in Great Britain is limited to a maximum output of 800W.
- • Savings depend heavily on how much electricity you use during daylight hours.
- • Permission may be required if you rent, lease or live in a managed building.
Payback is the point where cumulative savings equal what you spent. For plug-in solar it is driven by three numbers: total cost, annual generation and the share you actually use.
The calculation
Payback years = total cost / (annual kWh x self-consumption share x unit rate). Include the electrician, mounting hardware and delivery in total cost — kit price alone flatters the result.
Worked example
An 800W kit at £699, plus £150 for an electrician and £60 of brackets, is £909 all in. Generating 650 kWh with 70 percent self-consumption at 25p gives £114 a year, so payback is about eight years against a 25 year panel life.
What shortens it
- Higher unit rate
- Better siting and tilt
- Daytime occupancy or shiftable loads
- DIY-friendly mounting that reduces install cost
What lengthens it
- Shading, north-facing mounts and vertical siting
- Empty house during daylight
- Adding a battery purely for this system
Degradation
Panels lose roughly 0.5 percent output a year, so a ten year projection should taper slightly. Our calculator applies this automatically and shows low, central and high scenarios rather than a single optimistic figure.
Frequently asked questions
Sources
Fact-check status: reviewed. Read our editorial policy. General information only — not electrical, legal or financial advice.