Plug-in kit
Small, simple, yours to set up
Up to 800W into your home from a kit in the garden. The cheapest way in, with the smallest saving.
Calculator
Solar payback and comparison calculator
See a plug-in kit, rooftop panels and rooftop panels with a battery side by side: what each could cost, save and take to pay for itself. Every number is an estimate from the published figures listed at the bottom.
Plug-in, rooftop or battery
Rooftop panels
The biggest saving over time
An installer fits a whole system on your roof. You can be paid for what you export.
Rooftop + battery
More of your own power after dark
Costs more up front, and lets you use more of what your panels make.
How the estimates are worked out
- Generation. Rooftop: your system size times 750 to 770kWh a year per kWp. Plug-in: about 700kWh a year for an 800W kit, up to about 980kWh for a kit with 1,260W of panels (kits over 800W are capped at 800W in the middle of the day).
- Used at home. The share of that power your home uses straight away, set by who's home in the day (see the table below), and never more than you use in a year.
- Saving. Power used at home times your unit rate, plus rooftop exports times your export rate. Plug-in exports count as zero.
- Cost. Rooftop: the Energy Saving Trust's £7,600 for 4.5kWp, scaled to your size. Battery: £2,500 to £4,000 added. Plug-in: £849 to £989.
- Payback. Cost divided by yearly saving, rounded to whole years. It leaves out price rises and the small drop in panel output each year.
Assumptions and sources
| Who's home in the day | Rooftop | Rooftop + battery | Plug-in kit |
|---|---|---|---|
| Someone's home most of the day | 40% (from Which?'s worked example) | 70% (our assumption) | 70% |
| In and out | 30% (our assumption) | 60% (our assumption) | 49% |
| Usually out all day | 20% (our assumption) | 50% (our assumption) | 40% |
Plug-in shares: 70% for a busy four-person home with someone in all day, down to 40% for a home that's empty in the day. The battery adds 30 points to the rooftop share, which is our assumption.
The calculator doesn't guess for east or west roofs, shade or tariffs with different day and night rates. An installer's quote should give you a figure for your own home.
- Energy price cap, electricity unit rate 26.32p per kWh, Ofgem. Covers 1 October to 31 December 2026. The next cap is announced on 25 November 2026.
- Typical domestic consumption values, Ofgem. Medium home: about 2,700kWh of electricity a year
- Solar panel costs, Which?. Page dated 30 October 2026Reports the Energy Saving Trust's estimate that a typical system of about 4.5kWp costs around £7,600 to install, that about 4kWp can make more than 3,000kWh a year, and published battery prices from two large energy suppliers (around £2,500, and from £3,995).
- Smart Export Guarantee explained, Which?. 23 April 2026 (rates checked April 2026)Fixed SEG rates from 1p to 16p per kWh; the eligibility rules; a worked example of a 3.7kWp system making 2,850kWh a year.
- Plug-in solar panel checklist, Energy Saving Trust. 8 October 2026Our plug-in figures use about 700kWh a year from an 800W kit (south-facing, 30 degrees, no shade).
- Retail prices of plug-in kits registered for use in Great Britain, UK Home Solar research. Checked 15 October 2026Kits with 800W or more of panels were priced from £849 to £989 on the maker's own shop.
Questions
Why is the plug-in saving so much smaller?
A plug-in kit feeds up to 800W into your home, while a rooftop system is usually 3 to 6kWp. It costs far less too, so it can still pay for itself sooner.
Why do you start the export rate at 16p?
It was the highest fixed SEG rate in Which?'s April 2026 check. Rates went as low as 1p, so put in the rate you've been offered. It makes a big difference to rooftop payback.