Solar payback calculations

Solar payback is not one fixed number. It depends on installation cost, roof output, how much of your own electricity you use, your export tariff and whether a battery is part of the system. This page gives you a simple way to sense-check the maths before you compare installer quotes.

Reviewed May 2026: checked against Energy Saving Trust solar and battery guidance, GOV.UK VAT guidance and Octopus solar/export tariff pages. Treat the worked examples as planning snapshots, not quotes. Ask an installer for a property-specific design and check current Octopus export options before committing.

The quick answer

Energy Saving Trust’s current solar guidance shows domestic solar payback often landing somewhere around 10 to 15 years depending on location and home-occupancy pattern, with Belfast and sunnier southern or daytime-at-home scenarios usually looking faster than more northerly or lower daytime-use cases.

Octopus’s own solar page summarises the same broad range as roughly 9 to 13 years, based on Energy Saving Trust figures. That is useful as a first check, but it should not replace your own numbers. A roof with shading, a high quote or low daytime use can take longer. A good roof, sensible quote, strong export tariff and high self-consumption can shorten it.

Start with four numbers

Before looking at payback, collect these:

1. Installed cost after VAT, scaffolding, inverter choice, battery choice and any finance cost.
2. Expected annual generation in kWh, based on roof size, direction, slope, shading and postcode.
3. Self-consumption estimate, meaning how much of the solar electricity your home will use directly or through a battery.
4. Export tariff, because unused solar is not wasted if you can sell it back to the grid.

A quote that gives only a headline saving is not enough. Ask for the assumed generation, self-consumption percentage, export rate, import rate and battery behaviour. If those assumptions are not visible, the payback figure is hard to trust.

Costs to use in a first pass

Energy Saving Trust now gives about £6,100 as a typical installed cost for an average domestic solar panel system. Real quotes can be higher or lower because roof access, scaffolding, panel count, inverter type, bird protection, consumer-unit work and installer choice all matter.

Battery storage is more variable. Energy Saving Trust’s battery guidance says systems can range from about £1,500 to £10,000, with a 5kWh battery system around £4,600 as a broad guide. A larger battery, premium brand, backup-power setup or more complex install can cost more.

Residential energy-saving installations in Great Britain currently benefit from 0% VAT when supplied and installed by an eligible installer. GOV.UK says solar panels qualify, and battery storage is also within the energy-saving materials rules. The temporary zero rate is scheduled to run until 31 March 2027 unless the rules change. Northern Ireland has different VAT conditions, so check the GOV.UK page if that applies to you.

Worked example: solar without a battery

Here is a simple snapshot using a 4kW-style system generating 3,500kWh a year. The import saving uses the current price-cap electricity unit rate in this site data, 24.7p/kWh for Q2 2026. The export example uses 12p/kWh because Octopus’s Outgoing page was showing a flat 12p/kWh export rate when this page was reviewed in May 2026. Check Octopus export tariffs before using that number in a quote comparison.

If you use 40% of the solar at home:

• Self-consumed solar: 1,400kWh x 24.7p = about £345 avoided import
• Exported solar: 2,100kWh x 12p = £252 export income
• Planning benefit: about £597 a year

At an installed cost around £6,000 to £8,000, that points to a rough payback of about 9 to 12 years. A quote near the Energy Saving Trust average would sit towards the faster end if the output estimate is realistic.

If you use 50% of the solar at home:

• Self-consumed solar: 1,750kWh x 24.7p = about £432 avoided import
• Exported solar: 1,750kWh x 12p = £210 export income
• Planning benefit: about £642 a year

The payback moves closer to 9 to 11 years. The exact shift depends on the gap between the import rate you avoid and the export rate you earn.

Worked example: solar with a battery

A battery changes the shape of the calculation. It lets you use more of your solar later in the day, and it may let you charge cheaply from the grid on a time-of-use tariff. It also adds a large upfront cost and may need replacing before the panels do.

Using the same 3,500kWh annual generation example, assume a battery lifts self-consumption to 75%:

• Self-consumed solar: 2,625kWh x 24.7p = about £648 avoided import
• Exported solar: 875kWh x 12p = £105 export income
• Planning benefit before tariff optimisation: about £753 a year

If the combined solar and battery quote is £11,000 to £15,000, the straight payback can be slower than solar-only. That does not mean the battery is pointless. It means the battery case needs to be based on the full household use pattern, not just a promise of higher self-consumption.

How Octopus tariffs can change the battery case

Octopus export tariffs matter because batteries can shift when electricity is used or exported. The right tariff can improve the numbers, but the tariff must actually be available to you.

For many new solar households, the practical starting point is still a flat export tariff such as Outgoing Octopus, paired with an import tariff that suits the rest of the home. This is simpler, easier to model and less dependent on active battery dispatch.

For existing eligible solar-and-battery customers, Flux-style tariffs can make the calculation more interesting because import and export prices vary by time of day. However, Flux has been treated on this site as legacy or closed-to-new-customer context since March 2026 unless Octopus reopens it. Do not build a new purchase case around joining Flux without checking the live Octopus tariff page first.

Intelligent Octopus Flux is a separate battery-optimisation product. Octopus’s export page currently describes it as working with supported batteries such as GivEnergy, Tesla, SolarEdge and Enphase. If your battery is not supported, or you do not want Octopus controlling charge and discharge behaviour, the headline tariff case may not apply.

The biggest payback levers

Daytime use: Running appliances when the panels are producing can be worth more than exporting the same unit, because avoided import is usually higher than flat export income.

Roof output: Direction, shading, pitch and postcode change annual generation. Energy Saving Trust notes that south-facing unshaded roofs work best, while east-facing and west-facing roofs can still be viable but often generate less.

Quote quality: A cheaper quote is not automatically better, but an inflated quote can spoil otherwise good solar economics. Compare at least a few designs and make sure each one uses similar assumptions.

Battery size: A battery that is too small may not cover evening use. A battery that is too large may spend too much of the year partly empty. Ask the installer to justify the capacity against your actual electricity use.

Import tariff: A household on a standard flat tariff, an EV tariff, Agile, Cosy or another time-of-use setup can see different benefits from the same panels and battery.

Export setup: Export income normally depends on smart metering, export MPAN setup and tariff eligibility. Check import, export and generation explained if those terms are not clear.

Should you wait?

Waiting can make sense if your roof needs work, you are about to move, battery prices are central to your decision or you are hoping for a grant or loan that has not launched yet. It can also make sense to install solar first and leave room for a battery later.

The case for not waiting is that every year without panels is a year without generation. If a sensibly priced system would save and earn several hundred pounds a year, a small future equipment saving may not outweigh the lost benefit. VAT timing also matters if the current 0% rate is not extended beyond March 2027.

A sensible decision rule

A solar quote is worth taking seriously when:

• the installer has shown the generation assumption and roof model
• the payback calculation uses realistic import and export rates
• battery savings are separated from solar savings
• the system still looks acceptable if export rates fall or import rates change
• you understand warranty, inverter replacement and maintenance assumptions
• the tariff plan fits your real household, not an idealised daytime-at-home pattern

If you are already considering Octopus for import, export or battery optimisation, compare the solar numbers alongside the tariff decision rather than treating the panels in isolation. Start with solar with Octopus, export rates explained and the tariff comparison tool.