On the government's own estimate of £70 to £110 a year for an 800W system, a certified plug-in solar kit pays for itself in roughly 5.4 to 14.1 years depending on which kit you buy. The cheapest certified kit, at £599, sits at 5.4–8.6 years. The most expensive, at £989, sits at 9.0–14.1 years. Those are price-driven figures. What actually decides your answer is orientation, shading and how much of the generation you use while it is being made — and for a genuinely bad site, plug-in solar does not pay back at all.
This guide shows the arithmetic in full, including the parts that make it look worse. If a payback figure on another site does not tell you its assumptions, it is a marketing number.
How the payback numbers are calculated
The model is deliberately simple: kit price ÷ annual saving = years to break even. The annual saving comes from the Department for Energy Security and Net Zero's published estimate for an 800W plug-in system, which is £70 at the pessimistic end and £110 at the optimistic end. That estimate corresponds to covering up to about 20% of an average home's electricity use.
Dividing each certified kit price by both ends of that band gives the range in the ledger:
| Kit | Price | At £110/yr | At £70/yr |
|---|---|---|---|
| UKSOL Pro Compact 515W | £599 | 5.4 yrs | 8.6 yrs |
| UKSOL Pro Compact 460W ground | £699 | 6.4 yrs | 10.0 yrs |
| UKSOL Pro Duo 890W | £849 | 7.7 yrs | 12.1 yrs |
| UKSOL Pro Plus 1030W | £899 | 8.2 yrs | 12.8 yrs |
| UKSOL Pro Max 1260W | £989 | 9.0 yrs | 14.1 yrs |
What is wrong with that model
Two things, and we would rather say so than let the table do quiet work it has not earned.
It credits every kit with the same annual saving. The government's band is for an 800W system. Applying it unchanged to a 515W single panel assumes that panel generates what an 890W pair generates, which it plainly will not. The effect is to flatter small kits: the Compact 515W looks like the fastest payback on the board largely because it is the cheapest thing on the board. On like-for-like generation, the larger kits close most of that gap.
It assumes you use everything you generate. That is the bigger error, and it runs the other way — it flatters everything. Plug-in solar generates at midday. If nobody is home at midday, the surplus goes into the grid and you are paid nothing for it, because a plug-in device is not metered for export and cannot currently be paired with a certified battery. See the cost guide for why storage is out of scope.
Why self-consumption decides everything
A unit of solar electricity you consume is worth whatever you pay per unit. A unit you export from a plug-in device is worth nothing. So the whole question becomes: what fraction of midday generation does your household actually absorb?
Things that absorb it well:
- Somebody at home during the day — working from home, shift patterns, retirement, small children.
- A fridge and freezer, which run around the clock and quietly soak up a few hundred watts of the baseline.
- Timed loads you can move to the middle of the day: washing machine, dishwasher, immersion heater, tumble dryer.
- An electric vehicle charging slowly at home during daylight.
Things that destroy it:
- An empty house from 08:00 to 18:00 with everything on standby.
- All heavy appliance use in the evening, after generation has stopped.
Moving two appliance cycles a week into daylight hours is, for most households, a larger intervention on payback than choosing a different kit. It costs nothing.
How much does orientation and shading matter?
A great deal, and it is the factor you cannot change after buying. In the UK, an unshaded south-facing surface at a sensible tilt is the reference case. Rotating towards east or west costs you output; facing north costs you most of it. Shade is worse than angle: a panel in the shadow of a parapet, a neighbouring block or a tree for a few hours of every sunny day loses that generation outright.
This is where extra panel earns its price. If your only available surface faces east, a 1,260W array facing east will out-generate an 890W array facing east, and it will almost never reach the 800W AC ceiling where the extra capacity would be clipped. On a poor site, buy more panel. On a south-facing site with no shade, the cheaper kit is the better buy because you will clip against the ceiling anyway. That trade-off is worked through in 800W versus 400W plug-in solar.
When does plug-in solar not pay back?
We would rather tell you this before you spend the money.
- A north-facing balcony with no alternative mounting position. The generation is not there to be had.
- Heavy shading for most of the productive part of the day — an overhanging balcony above yours, a tall building to the south, mature trees.
- An empty house all day with no shiftable loads and no intention of changing habits. You will export most of what you make, for nothing.
- A freeholder administration fee of a couple of hundred pounds on top of a £599 kit, which can add two years to the break-even on its own.
The counterweight, and it is a real one: a plug-in kit is portable. It is bolted to a rail, not built into a roof. If you move, it moves with you, and the payback clock keeps running in the new place. That is a genuine advantage over rooftop solar and it is rarely priced in.
Five ways to shorten your payback
- Move two appliance cycles a week into daylight. Free, and it raises self-consumption more than any hardware choice.
- Pick the least shaded surface you have, even if it is a less convenient one.
- Buy the largest kit your site and budget justify — cost per watt falls from £1.52 to £0.78 as kits get bigger.
- Fit it yourself if the position is safe to reach. That is £150–£350 straight off the capital cost.
- Settle the consent question before you buy, so an administration fee does not land on top of a kit you have already paid for.
Sources and further reading
- GOV.UK — Households can save as plug-in solar panels come to market — source of the £70–£110 annual saving band and the "up to 20% of an average home's electricity" figure.
- SI 2026 No. 848 — the 800W AC ceiling and the interim product specification requirement.
- Energy Saving Trust — independent guidance on solar output, orientation and self-consumption in the UK.
- Ofgem — energy prices and export arrangements.
- ENA Connect Direct — the type-test register behind the certified kit list.
Frequently asked questions
How long does plug-in solar take to pay for itself in the UK?
Between about 5.4 and 14.1 years for the certified kits currently on sale, using the government's estimate of £70 to £110 a year for an 800W system. The cheapest £599 kit sits at the fast end; the £989 kit at the slow end. Your own figure depends on orientation, shading and how much you use during daylight.
How much can plug-in solar save per year?
The Department for Energy Security and Net Zero estimates around £70 to £110 a year for an 800W system, covering up to 20% of an average home's electricity use. That assumes you consume the generation rather than exporting it.
Do I get paid for electricity I export from a plug-in kit?
No. A plug-in device is not set up for metered export, so any surplus goes into the grid unpaid. This is why using the electricity as it is generated matters so much more than it does with an installed, MCS-certified rooftop system.
Does a bigger kit pay back faster?
Not on the simple price-divided-by-saving model, because it costs more up front. But bigger kits have a much better cost per watt — £0.78 against £1.52 — and on a shaded or poorly oriented site the extra panel is the only way to recover real output. On a perfect south-facing site the smaller kit is the better buy.
What is the single best thing I can do to improve payback?
Shift appliance use into daylight hours. A washing machine and dishwasher cycle moved from evening to midday costs nothing and directly converts generation you would have exported for free into electricity you did not have to buy.
Is plug-in solar ever a bad buy?
Yes. A north-facing balcony, heavy all-day shading, or an empty house with no shiftable loads will not produce a sensible return. Add a large freeholder administration fee and the break-even can move out past the useful life of the equipment.
How long do the panels last?
Solar panels degrade slowly and typically carry long performance warranties, so the panel is rarely the limiting component. Check the warranty terms on the specific kit, particularly for the microinverter, which is the part that works hardest.
Does payback improve if energy prices rise?
Yes, directly. Every unit you generate and use is a unit you did not buy, so the saving scales with the unit rate you would otherwise pay. The reverse is also true if prices fall.