How much do plug-in solar panels save?

Modelled savings sit at roughly £70 to £110 a year, depending on how the panels are mounted. That is a real saving on a modest outlay — and it is a long way from the numbers some sellers imply. Here is the working.

What the government modelling says

The impact assessment published alongside the plug-in solar policy models two mounting arrangements. It is the most useful public baseline available, because the assumptions are written down rather than implied.

Figures and the assumptions behind them are in the DESNZ plug-in solar final stage impact assessment. They are modelled averages for a typical household, not a promise about your garden.

Self-consumption is the number that matters

Look again at those rows. The south-facing device generates 690kWh but only 428kWh shows up as a saving. The missing 262kWh was generated at moments when the household was not using it, so it went out to the grid — and for a plug-in device, that is usually worth nothing.

This is the single most important idea on this page. A plug-in solar device does not save you money by generating. It saves you money by generating at a moment when you are consuming. Every kilowatt-hour you use as it arrives displaces one you would have bought at full retail price. Every kilowatt-hour you do not use is, in most cases, a gift to the grid.

What raises self-consumption

• Being at home during the day — remote work, shift patterns, retirement, small children.
• A garden office or workshop in use during daylight hours.
• Always-on loads: fridges, freezers, routers, aquariums, drinks coolers.
• Running the dishwasher, washing machine or tumble dryer at midday rather than at 7pm.
• Sizing sensibly — a bigger array into an empty house just exports more for nothing.

Why the surplus usually earns nothing

The Smart Export Guarantee pays households for exported electricity, but suppliers require an MCS-certified installation to enrol. Plug-in solar is a consumer device you install yourself; it does not have an MCS certificate and does not qualify. A supplier may in principle choose to offer something, but you should plan on the basis that exported units earn you nothing.

Realistic payback

Take a kit at our expected price of £599 to £699 — final pricing confirmed at launch — and the modelled savings above.

• Good case: £599 kit, south-facing at tilt, high daytime use, saving at or above £110 a year. Simple payback around 5½ to 6 years.
• Typical case: £649 kit, decent orientation, average daytime use, saving around £90. Payback around 7 years.
• Weaker case: £699 kit, vertical east–west balcony, house empty on weekdays, saving around £70 or less. Payback around 10 years.

So: roughly six to ten years for most people. Panels typically carry long performance warranties and microinverters shorter ones, so the device should outlive its payback — but that is the honest range, and anyone quoting three years is either assuming a very high electricity price or a very optimistic self-consumption rate.

Electricity prices are the biggest unknown. Higher prices shorten payback; lower prices lengthen it. We have used current retail rates rather than forecasting.

Working out your own figure

Three inputs, in order of importance:

• Orientation and tilt. South at 20–35° is the benchmark. East or west costs you meaningfully. Vertical costs you more. North is not worth doing.
• Shading. Watch the spot across a full day. Partial shade in the middle of the day is far worse than it looks.
• Your daytime baseline. Look at your smart meter readings between 10am and 4pm. If you are drawing 300W all day, a plug-in device will convert most of its output into savings. If you are drawing 80W, it will not.

Is plug-in solar worth it?

For a household with a genuine daytime load and somewhere unshaded to put panels, yes: a few hundred pounds for a device that quietly removes £70–£110 a year from the bill, installs in an afternoon and can move house with you. For a household that is out all day with a north-facing balcony, the numbers do not work, and we would rather say so.

If you have a suitable roof and a bigger budget, compare with rooftop solar, which generates several times as much and qualifies for export payments. Kit pricing is covered on the cost page.