What plug-in solar actually saves you

The government's figure, published alongside the change in the law, is that an 800W plug-in solar kit can save a household up to £110 a year.

"Households could save up to £110 a year, with panels providing up to 20% of average home electricity use." — DESNZ, "Households can save as plug-in solar panels come to market", 26 August 2026

We worked it out ourselves rather than taking that on trust, using published measurements of how much sun actually falls on a given spot in the UK, because "up to" figures are the easiest number in any product category to overstate. For an 800W system in Tunbridge Wells, our model lands at roughly £106 a year — within 4% of the official figure. We think that is worth stating plainly: it means the government's headline number holds up against an independent calculation, not just a marketing claim.

The whole model, nothing hidden

Three numbers multiply together to produce a savings figure, and every one of them is an assumption you should be able to see:

1. Annual generation, from PVGIS (the EU's free, published solar-yield tool, also used by installers and DESNZ's own modelling). For an 800W system at Tunbridge Wells (51.126°N, 0.258°E), PVGIS returns 703.98 kWh per year. Your figure will differ with location, orientation and shading — our calculator runs this for your postcode directly.

2. Self-consumption fraction. This is the number every competitor quietly inflates, and it decides almost everything (see below). We assume 60% as a central estimate for a household with typical daytime occupancy.

3. Unit rate. We use £0.25 per kWh, a round figure close to the Ofgem price cap at time of writing. Update this for your own tariff — the arithmetic scales linearly.

$$ 703.98 \text{ kWh} \times 0.60 \times £0.25/\text{kWh} = £105.60/\text{year} $$

That is our central estimate: £106 a year, rounded, for an 800W kit in the South East, on a 60% self-consumption assumption. Every figure we publish carries these three assumptions alongside it — change any one and the answer changes, which is the point of showing the working rather than a single number.

The number that decides everything: how much of it you actually use

Plug-in solar has no export payment. There is no Smart Export Guarantee route for an unmetered device plugged into a socket — you are not paid for power you generate and don't use. Every kilowatt-hour your panel produces while you are out, or while your fridge and a couple of chargers are the only things drawing power, is a kilowatt-hour that goes to waste from a savings point of view. It still gets used somewhere on the local network, but not by you, and not for your benefit.

That means the only generation that saves you money is generation that coincides with you actually drawing power at that moment. This coincidence rate — self-consumption — is doing more work in the final number than PVGIS yield or the unit rate. A household that is home all day with things running will capture far more of its own generation than one that is out at work when the sun is up. Any savings claim that doesn't state its self-consumption assumption is not a claim you can check.

Three honest scenarios

Household pattern	Self-consumption assumption	Annual saving (800W, South East)
Out most weekdays, home evenings/weekends	40%	~£70
Mixed — some remote work, typical occupancy	60% (our central estimate)	~£106
Home most of the day	80%	~£141

These are not precise predictions of your bill — they are the same model with one assumption changed, so you can see where your own household sits and judge accordingly. If in doubt, use the lower end.

Payback, on the same basis

Solar-only kits in the 800W AC class currently span £129 to £1,199 across the sellers in our comparison, read from our database as this page loaded. That is a wide band, so the useful thing is the arithmetic rather than a single answer: your price ÷ your annual saving = your payback in years.

At our central £106/year estimate, a £600 kit pays for itself in a little under six years and a £900 kit in about eight and a half. On the more conservative 40% self-consumption figure — £70 a year — the same two kits take roughly nine and thirteen years.

None of that accounts for panel degradation, for any admin cost such as a G98 notification service where a seller charges for it separately, or for changes in your tariff over the period. Take the payback figure as an order of magnitude, not a promise.

Try it for your own postcode

Our calculator runs the same three-step model — PVGIS yield for your exact location, your choice of self-consumption assumption, and your own unit rate — rather than a single national average. Put in a postcode and see your own numbers, not ours.