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.
Savings come from electricity you do not buy. That makes self-consumption, not panel size, the main driver.
The basic sum
Annual saving = generated kWh x share you consume x your unit rate. An 800W system generating 650 kWh, with 70 percent self-consumed at 25p, saves about £114 a year. The same system with only 40 percent self-consumption saves about £65.
Typical UK ranges
- 400W portable kit: £35-£70 a year
- 600W garden or wall kit: £60-£110 a year
- 800W balcony or roof kit: £90-£165 a year
Improving the number
Run flexible household loads such as the dishwasher or washing machine during daylight where practical. Charging laptops, tools or e-bikes during the day can also increase self-consumption. Battery storage can shift solar energy to another time, but plug-in battery systems and plug-in solar devices integrated with batteries are outside Great Britain's current simplified plug-in solar framework. Treat storage as a separate installation decision and read our battery guide.
What you should not count on
Automatic export payments. Surplus electricity can flow back towards the grid, but payment is not automatic. Smart Export Guarantee arrangements depend on eligibility, appropriate export metering and the requirements of a SEG licensee. Treat unconfirmed export income separately from self-consumption savings. Read our excess electricity guide and smart meter guide.
Use the savings calculator to enter your region, orientation, shading and tariff and see a low, central and high scenario over ten years.
The payback period, step by step
Payback is the point where cumulative savings equal what you spent. 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 payback
- Higher unit rate
- Better siting and tilt
- Daytime occupancy or shiftable loads
- DIY-friendly mounting that reduces install cost
What lengthens payback
- 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 savings calculator at /calculator applies this automatically and shows low, central and high scenarios rather than a single optimistic figure.
Run your own numbers in the calculator at /calculator before committing to a kit, and judge the purchase on the low scenario rather than the high one.
To see how these ranges apply to your home, try the plug-in solar savings calculator, then read how to choose a plug-in solar kit that suits your mounting space.
Frequently asked questions
Sources
Fact-check status: reviewed. Read our editorial policy. General information only — not electrical, legal or financial advice.