How much will plug-in solar save me a year?
The honest answer is not simply “panel watts × sunshine × electricity price”. The biggest factor is how much of the solar electricity your home can actually use while it is being generated.
The quick answer
A small plug-in system can offset useful daytime electricity use, but a large percentage of the generation may leave the property if your house has very little demand during the day. That is why the calculator asks for your base load rather than pretending every generated kWh is worth your full import tariff.
What is a normal UK household base load?
There is no single perfect number, but UK monitoring gives us useful anchors. The Energy Follow-Up Survey reported a median base load of about 90W across monitored homes. Analysis of the Household Electricity Survey found mean base load around 175W in April–September and 207W in October–March, with considerable variation between households.
| Calculator choice | Assumption | Who it may resemble |
|---|---|---|
| Low | 90W | Efficient or lightly occupied home with little always-on equipment |
| Typical | 180W | Useful middle starting point for a normal household |
| High | 300W | Home with more refrigeration, IT, pumps, entertainment or other continuous loads |
| I know mine | Your measured W | Best option if you have a smart meter or energy monitor |
Why self-consumption matters
UK research using one-minute data from 302 homes with solar found average annual self-consumption around 45% on traditional rooftop systems, while an Oxford summary of the same work emphasised that self-consumption varies widely with household demand and daytime occupancy. Small plug-in systems are different from large rooftop arrays because their output is much smaller relative to normal household demand, so they can often self-consume a higher share.
The calculator therefore uses measured base load as its main driver and then adds a modest allowance for whether people are usually home during the day. It deliberately caps the result and does not assume perfect use of every solar kWh.
How much solar generation do we assume?
PVGIS, the European Commission's photovoltaic performance tool, estimates annual PV generation using location, solar radiation, module characteristics, temperature, wind and system losses. To keep this calculator simple, we use broad regional starting points rather than asking for a postcode: roughly 850kWh/kWp in the North, 950kWh/kWp in the Midlands and 1,050kWh/kWp in the South for a good south-ish position.
These are not promises. Real output depends on shading, tilt, exact location, panel temperature and mounting. East- or west-facing panels are reduced in the model; Energy Saving Trust notes these orientations tend to produce around 15–20% less energy than directly south-facing panels.
Why we do not include a battery
The current Great Britain plug-in solar framework is for plug-in solar systems without batteries. We have therefore removed battery assumptions from the calculator rather than showing users a route that is outside the current plug-in product framework.
Why we do not automatically count export payments
For a simple buyer decision, I think the safest approach is to value the electricity you are likely to use yourself and treat export income separately. Export arrangements can depend on metering, supplier terms and eligibility. That means the calculator is intentionally conservative.
What electricity price does the calculator use?
The default is 26.1p/kWh, close to Ofgem's average direct-debit electricity unit rate of 26.11p/kWh for 1 July to 30 September 2026. From 1 October 2026 the published average changes slightly to 26.32p/kWh. The field is editable because many households are on fixed or specialist tariffs.
What about the government's £110 a year figure?
When the new plug-in solar framework came into force on 27 August 2026, the government said households could save up to £110 a year and that an 800W class kit could provide up to 20% of average household electricity use. “Up to” is important: a household with low daytime use, poor orientation or an expensive kit may see a much longer payback period.
How to get a better estimate
- Look at your smart meter or energy monitor when the home is quiet during the day.
- Take several readings rather than one momentary value.
- Use the “I know mine” base-load option.
- Enter the exact price you will actually pay for the kit.
- Choose the panel direction honestly and allow for shading.
Sources and methodology
- UK Government / Intertek, Household Electricity Survey — household standby and monitored electricity demand.
- DECC Energy Follow-Up Survey, domestic appliances and electricity monitoring — median monitored household base load of 90W.
- McKenna, Pless & Darby (2018), Solar photovoltaic self-consumption in the UK residential sector — one-minute data from 302 UK PV households.
- European Commission Joint Research Centre, PVGIS — location-based photovoltaic performance methodology.
- Energy Saving Trust, Solar panels: costs, savings and benefits explained — orientation guidance.
- Ofgem, Energy price cap unit rates — current and October 2026 electricity unit rates.
- Department for Energy Security and Net Zero, Households can save as plug-in solar panels come to market — 27 August 2026 launch and up-to-£110 annual saving statement.
- Department for Energy Security and Net Zero, Plug-in solar regulatory amendment and interim product specification — current solar-only plug-in framework.