Solar Panel ROI Calculator — UK

Solar Panel ROI Calculator

How UK Solar ROI Is Calculated

UK solar returns come from two streams, and the calculator prices each separately. Self-consumed electricity displaces imports at your unit rate — roughly 25–28p per kWh under recent Ofgem price caps as of 2026. Exported electricity earns a Smart Export Guarantee (SEG) rate set by your supplier, anywhere from 4p to 15p per kWh. Worked example: a 4 kW south-facing array in the Midlands costs £6,000 installed and generates about 3,800 kWh a year (950 kWh per kWp). A household that is home for part of the day self-consumes about 45% — 1,710 kWh, worth £444.60 at 26p — and exports the remaining 2,090 kWh, worth £250.80 at a 12p SEG rate. Total first-year benefit: £695.40. Simple payback = £6,000 ÷ £695.40 ≈ 8.6 years. Over a 25-year panel life that is roughly £17,400 of nominal benefit against £6,000 spent — a net gain of about £11,400, or 190% ROI, before panel degradation and electricity price inflation (which work in opposite directions and partially cancel). The calculator lets you vary the self-consumption split, which is the single most sensitive input in UK solar economics.

0% VAT on Solar Installations — Until March 2027

Since April 2022, solar panel installations on residential property have been zero-rated for VAT across the UK — 0% instead of the 5% reduced rate that previously applied to energy-saving materials — and from February 2024 the zero rate was extended to battery storage, including standalone and retrofit batteries. The relief is currently legislated to run until 31 March 2027, after which the rate is scheduled to revert to 5%. On a £6,000 installation the zero rate saves £300 against the old 5% treatment and £1,200 against the 20% standard rate, and the saving is baked into quoted prices — installers charge no VAT line at all. The practical implication for anyone modeling ROI in 2026: an installation completed before the March 2027 deadline locks in today's pricing, while the same system installed afterwards would cost roughly £300 more under a restored 5% rate. There is nothing to claim and no paperwork — the relief applies automatically at the point of sale for qualifying residential installations, covering panels, inverters, batteries and installation labour. If you are quoted a separate VAT line on a domestic solar install before April 2027, query it: the quote is wrong.

Smart Export Guarantee: 4p to 15p Per kWh

The Smart Export Guarantee, in force since January 2020, obliges every electricity supplier with 150,000 or more domestic customers to buy your exported solar power at a rate above zero — but Ofgem lets each supplier set its own price, which is why rates span roughly 4p to 15p per kWh as of 2026. The spread is the difference between a mediocre and a strong ROI: on the example system's 2,090 exported kWh, a 4p tariff earns £83.60 a year while 15p earns £313.50 — a £230 annual gap on identical hardware. As of 2026 Octopus Energy has typically topped the table, paying its highest fixed export rates to customers who also take their import supply from Octopus, while EDF, British Gas, OVO and E.ON offer tiered rates that similarly favour their own import customers. You do not have to export to your import supplier — SEG tariffs are legally separate — but the best rates are usually reserved for bundled customers, so compare the combined import-plus-export deal rather than either half alone. Requirements: an MCS certificate for the installation (your installer provides this) and a smart meter capable of half-hourly export readings. Rates change frequently; check the current league table before signing.

System Costs and Yield: What a 4 kW Array Delivers

A typical 4 kW (roughly 10-panel) domestic system costs £5,000–£7,000 fully installed as of 2026 — about £1,250–£1,750 per kWp including scaffolding, an inverter, MCS certification and labour. Yield depends overwhelmingly on orientation. A south-facing roof pitched at 30–40° in central England produces about 950 kWh per kWp per year — 3,800 kWh from 4 kW. East- or west-facing arrays yield 15–20% less (roughly 760–810 kWh per kWp), which stretches the example payback from 8.6 years toward 10; a split east-west array smooths generation across the day and can actually raise self-consumption. Southern England outperforms Scotland by roughly 10–15% on irradiance. Context for sizing: the median UK household uses about 2,700 kWh of electricity a year (Ofgem's typical consumption value), so a 4 kW system generates well above annual demand — the constraint is that generation peaks at midday while consumption peaks in the evening, which is why self-consumption without a battery rarely exceeds 45%. Shading from chimneys, dormers or neighbouring trees deserves a professional survey, since even partial shading of one string can cut output disproportionately. Use MCS-certified installers only; certification is mandatory for SEG payments.

Payback: 8–12 Years for Most UK Homes

Most UK installations pay back in 8–12 years, and where you land in that band is mostly about when you use electricity. The example household — 45% self-consumption, 26p import rate, 12p SEG — hits 8.6 years. A home-all-day household with an EV charging at midday or a heat pump can push self-consumption to 60%: 2,280 kWh × 26p = £592.80 of avoided imports plus 1,520 kWh × 12p = £182.40 of export income, £775.20 in total — a 7.7-year payback. An out-at-work household self-using only 30% earns £296.40 from self-use (1,140 kWh × 26p) plus £319.20 from exporting 2,660 kWh at 12p — £615.60 total, a 9.7-year payback. After payback, panels warranted for 25 years deliver 13–17 years of pure benefit; degradation of around 0.4–0.5% a year trims late-life output modestly, leaving roughly 88–90% of original production at year 25. Two payback accelerants worth modelling in the calculator: electricity price inflation (UK unit rates have risen faster than CPI over the last decade) and time-of-use export tariffs that pay premium rates for evening exports when paired with a battery.

Adding a Battery: Higher Self-Use, Longer Payback

A home battery changes the arithmetic in both directions. A 5–10 kWh unit costs roughly £2,500–£4,500 installed as of 2026 (also 0% VAT until March 2027) and lifts self-consumption from the typical 35–45% to 70–85%, converting 12p export income into 26p import savings — worth roughly £160–£215 a year on the example 4 kW system (each redirected kWh gains the 14p spread between import and export rates). On self-consumption savings alone, a £3,500 battery adding £160–£215 a year takes 16–22 years to pay for itself — longer than its typical 10–12-year warranty — so batteries rarely stack up on that arithmetic by itself. What changes the case is time-of-use arbitrage: smart tariffs let you charge the battery overnight at cheap rates (often 7–9p per kWh as of 2026) and either avoid peak-price imports or export at premium evening rates under tariffs like Octopus Flux. Households combining an EV tariff with battery arbitrage report combined solar-plus-battery paybacks comparable to solar-only systems. Model the battery separately in the calculator: add its cost to capex, raise the self-consumption slider, and add an arbitrage line if you have a time-of-use tariff. If combined payback exceeds 12 years, install solar now and add storage later.