Plug-in solar costs, savings and payback explained

Start with a dated estimate, not a promise

At our September 2026 check, Energy Saving Trust gives starting costs of around £450 and modelled annual bill savings of £70 for a household out during the day or £100 for one home all day.

Its model uses an 800 W system in Manchester, facing south at 30 degrees with no shade, annual household consumption of 2,500 kWh and electricity at 24.7p/kWh. Those assumptions matter: the figures are not a quote or forecast for your address.

Build a complete-cost comparison

Our suggested worksheet is a single total for the setup you could actually buy and use. Ask the seller to separate included items from optional ones, and mark anything unpriced as unresolved rather than writing zero. Keep monthly financing payments separate from an upfront purchase price.

• The exact kit and the mounting option for your location.
• VAT and delivery to your postcode.
• Any necessary professional assessment, socket work or installation.
• Optional monitoring or accessories you genuinely want.
• Warranty exclusions, return arrangements and possible replacement costs.

A worked example: simple payback

Suppose a complete setup costs £600 and reduces the annual bill by £80. Simple payback is £600 divided by £80: 7.5 years. These are illustrative inputs, not a supplier offer or a predicted saving.

For the same £600 outlay, £50 of annual savings gives 12 years, while £100 gives six years. This shows why changing an assumed saving can alter the conclusion more than a small discount on the kit.

This simple calculation excludes finance charges, repairs, replacements, changing electricity prices and the time value of money. It also assumes the annual saving persists. Use it as a first comparison, not a guaranteed investment return.

Do not assume spare electricity will earn money

Ofgem says Smart Export Guarantee payments depend on eligibility and metered exports, with tariff terms set by the participating supplier. Producing electricity and having an export-payment agreement are separate things.

The government distinguishes SEG certification requirements from other export tariffs suppliers may offer outside the scheme. Ask the supplier to confirm eligibility for your exact installation before including export income in a calculation. Do not budget for an advertised tariff simply because the kit can export.

Ask for the assumptions behind every savings claim

Ask which location, orientation, shading, consumption pattern and electricity price were used. Request a bill-saving estimate separately from generation and export-income estimates. Compare those assumptions with your own situation, then compare the offers that meet your needs. A precise-looking number without its assumptions is not a personalised forecast.

Plug-in solar costs: value the electricity you actually use

Generation is not the same as bill saving. Split an estimate into electricity used in the home and electricity left over, then use the tariff that actually applies to each. Keep any export income at zero until an eligible payment arrangement is confirmed.

The example below holds generation constant to isolate the effect of use at home. It assumes an invented 600kWh a year, a 25p/kWh import tariff and no export payment. It is not a prediction for any kit, postcode or roof direction.

• Use your own tariff and a location-specific generation estimate, not these illustrative inputs.
• Ask how the estimate accounts for shade and when your household uses electricity.
• Compare the recorded equipment price separately from the finished, delivered and fitted price.

Worked example: the same kit, three savings outcomes

Take a fictional finished installation costing £700, with no finance or export payments. The table changes only the annual electricity saving. These are arithmetic scenarios, not measured results or forecasts for a particular kit.

Simple payback is upfront cost divided by annual net saving. It leaves out changing tariffs, degradation, replacement equipment and the time value of money. Use it to see how sensitive a decision is, not as a guaranteed return.

• Use an itemised finished price, including delivery and any required fitting or socket work.
• Ask for a generation estimate specific to the location, direction and shade, then the share you expect to use at home.
• If you add a battery, compare its extra installed cost with its extra savings, not with the savings of the entire solar system.