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UK balcony solar savings & payback calculator

Estimate how much an 800W balcony solar kit could save a UK flat per year — and how fast it pays for itself — at the current energy price cap.

Quick answer: At the current UK energy price cap (~27–28p/kWh) an 800W balcony solar kit producing around 760 kWh/year saves roughly £200/year through self-consumption, so a £500 kit pays back in ~2.5 years and a £1,000 system in ~5 years. Savings come from electricity you do not buy — not from exporting to the grid (SEG is rarely available on plug-in installs).

Your electricity rate (p/kWh) System size (W AC) Kit price (£) Annual production per watt (kWh/W) — UK balcony installs are usually 0.7–1.1

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Est. yearly production

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Est. yearly savings

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Payback time

Estimates only. Assumes 100% self-consumption — every kWh produced is offset against your supplier’s rate. In practice some daytime production may go to waste if your household is not drawing power at that moment; a battery (Anker SOLIX Solarbank, EcoFlow STREAM Ultra, Zendure SolarFlow) shifts that into evening use. SEG (Smart Export Guarantee) is generally not available for plug-in installs because they lack MCS certification, so we don’t model export income.

How the math works

The calculator uses a deliberately simple, transparent model:

Yearly production = system AC watts × production-per-watt (kWh/W/yr). UK middle estimate is ~0.95 kWh/W for a well-placed south-facing balcony, ~0.7 kWh/W for a shaded or strongly east/west install, ~1.1 kWh/W for a tilted unshaded panel.
Yearly savings = production × your electricity rate. UK price cap unit rate is ~27p/kWh in mid-2026; fixed tariffs vary £0.04–£0.06 either side.
Payback = kit price ÷ yearly savings.

The single biggest lever is your electricity rate, which is why UK plug-in solar payback is much faster than the global average. The 800W cap, plus modest UK insolation (~950–1,100 sun-hours/year in most of England), keeps yearly output around 600–900 kWh — making the £500 kit + ~£200/year savings the sweet-spot for most flats.

Once you’ve modelled the numbers, check our honest 2026 kit picks and the current UK legal status before buying.