A typical roof here lands around 5.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 919 kWh per year on a south-facing roof. We value self-used electricity at 25.4p and exported surplus at a baseline 10p via SEG. Use the calculator above for your exact tariff.
Browse the scenarios below. Each battery size has its own expand — open the one that matches your plan (or just explore). For each system size (2–8 kW) we show annual output, how much you use directly, what gets exported, annual benefit, upfront cost, break-even, and a 20-year net. Negative numbers are possible — that’s the honest trade-off when adding more battery than your usage profile justifies.
No battery 5 kW example → Annual benefit: £743, Upfront: £10,173, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1837 kWh | 735 kWh | 1102 kWh | £187 | £110 | £297 | £4,069 | 13.7 yrs | £1,873 |
| 3 kW | 2756 kWh | 1102 kWh | 1653 kWh | £280 | £165 | £446 | £6,104 | 13.7 yrs | £2,809 |
| 4 kW | 3674 kWh | 1470 kWh | 2205 kWh | £374 | £220 | £594 | £8,138 | 13.7 yrs | £3,746 |
| 5 kW | 4593 kWh | 1837 kWh | 2756 kWh | £467 | £276 | £743 | £10,173 | 13.7 yrs | £4,682 |
| 6 kW | 5511 kWh | 2205 kWh | 3307 kWh | £561 | £331 | £891 | £12,207 | 13.7 yrs | £5,619 |
| 7 kW | 6430 kWh | 2572 kWh | 3858 kWh | £654 | £386 | £1,040 | £14,242 | 13.7 yrs | £6,555 |
| 8 kW | 7348 kWh | 2939 kWh | 4409 kWh | £747 | £441 | £1,188 | £16,276 | 13.7 yrs | £7,492 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
3 kWh battery 5 kW example → Annual benefit: £884, Upfront: £12,273, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1837 kWh | 1102 kWh | 735 kWh | £280 | £73 | £354 | £6,169 | 17.4 yrs | £907 |
| 3 kW | 2756 kWh | 1653 kWh | 1102 kWh | £420 | £110 | £531 | £8,204 | 15.5 yrs | £2,410 |
| 4 kW | 3674 kWh | 2205 kWh | 1470 kWh | £561 | £147 | £708 | £10,238 | 14.5 yrs | £3,914 |
| 5 kW | 4593 kWh | 2756 kWh | 1837 kWh | £701 | £184 | £884 | £12,273 | 13.9 yrs | £5,417 |
| 6 kW | 5511 kWh | 3307 kWh | 2205 kWh | £841 | £220 | £1,061 | £14,307 | 13.5 yrs | £6,920 |
| 7 kW | 6430 kWh | 3858 kWh | 2572 kWh | £981 | £257 | £1,238 | £16,342 | 13.2 yrs | £8,424 |
| 8 kW | 7348 kWh | 4409 kWh | 2939 kWh | £1,121 | £294 | £1,415 | £18,376 | 13.0 yrs | £9,927 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
5 kWh battery 5 kW example → Annual benefit: £955, Upfront: £13,673, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1837 kWh | 1286 kWh | 551 kWh | £327 | £55 | £382 | £7,569 | 19.8 yrs | £74 |
| 3 kW | 2756 kWh | 1929 kWh | 827 kWh | £491 | £83 | £573 | £9,604 | 16.8 yrs | £1,861 |
| 4 kW | 3674 kWh | 2572 kWh | 1102 kWh | £654 | £110 | £764 | £11,638 | 15.2 yrs | £3,648 |
| 5 kW | 4593 kWh | 3215 kWh | 1378 kWh | £818 | £138 | £955 | £13,673 | 14.3 yrs | £5,434 |
| 6 kW | 5511 kWh | 3858 kWh | 1653 kWh | £981 | £165 | £1,146 | £15,707 | 13.7 yrs | £7,221 |
| 7 kW | 6430 kWh | 4501 kWh | 1929 kWh | £1,145 | £193 | £1,337 | £17,742 | 13.3 yrs | £9,008 |
| 8 kW | 7348 kWh | 5144 kWh | 2205 kWh | £1,308 | £220 | £1,529 | £19,776 | 12.9 yrs | £10,795 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
7.5 kWh battery 5 kW example → Annual benefit: £977, Upfront: £15,423, Break-even: 15.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1837 kWh | 1341 kWh | 496 kWh | £341 | £50 | £391 | £9,319 | 23.9 yrs | £-1,506 |
| 3 kW | 2756 kWh | 2012 kWh | 744 kWh | £512 | £74 | £586 | £11,354 | 19.4 yrs | £366 |
| 4 kW | 3674 kWh | 2682 kWh | 992 kWh | £682 | £99 | £781 | £13,388 | 17.1 yrs | £2,238 |
| 5 kW | 4593 kWh | 3353 kWh | 1240 kWh | £853 | £124 | £977 | £15,423 | 15.8 yrs | £4,110 |
| 6 kW | 5511 kWh | 4023 kWh | 1488 kWh | £1,023 | £149 | £1,172 | £17,457 | 14.9 yrs | £5,982 |
| 7 kW | 6430 kWh | 4694 kWh | 1736 kWh | £1,194 | £174 | £1,367 | £19,492 | 14.3 yrs | £7,853 |
| 8 kW | 7348 kWh | 5364 kWh | 1984 kWh | £1,364 | £198 | £1,563 | £21,526 | 13.8 yrs | £9,725 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
10 kWh battery 5 kW example → Annual benefit: £991, Upfront: £17,173, Break-even: 17.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1837 kWh | 1378 kWh | 459 kWh | £350 | £46 | £396 | £11,069 | 27.9 yrs | £-3,143 |
| 3 kW | 2756 kWh | 2067 kWh | 689 kWh | £526 | £69 | £594 | £13,104 | 22.0 yrs | £-1,214 |
| 4 kW | 3674 kWh | 2756 kWh | 919 kWh | £701 | £92 | £793 | £15,138 | 19.1 yrs | £714 |
| 5 kW | 4593 kWh | 3445 kWh | 1148 kWh | £876 | £115 | £991 | £17,173 | 17.3 yrs | £2,643 |
| 6 kW | 5511 kWh | 4134 kWh | 1378 kWh | £1,051 | £138 | £1,189 | £19,207 | 16.2 yrs | £4,572 |
| 7 kW | 6430 kWh | 4822 kWh | 1607 kWh | £1,226 | £161 | £1,387 | £21,242 | 15.3 yrs | £6,500 |
| 8 kW | 7348 kWh | 5511 kWh | 1837 kWh | £1,402 | £184 | £1,585 | £23,276 | 14.7 yrs | £8,429 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
13.5 kWh battery 5 kW example → Annual benefit: £1,005, Upfront: £19,623, Break-even: 19.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1837 kWh | 1415 kWh | 423 kWh | £360 | £42 | £402 | £13,519 | 33.6 yrs | £-5,479 |
| 3 kW | 2756 kWh | 2122 kWh | 634 kWh | £540 | £63 | £603 | £15,554 | 25.8 yrs | £-3,494 |
| 4 kW | 3674 kWh | 2829 kWh | 845 kWh | £719 | £85 | £804 | £17,588 | 21.9 yrs | £-1,509 |
| 5 kW | 4593 kWh | 3536 kWh | 1056 kWh | £899 | £106 | £1,005 | £19,623 | 19.5 yrs | £477 |
| 6 kW | 5511 kWh | 4244 kWh | 1268 kWh | £1,079 | £127 | £1,206 | £21,657 | 18.0 yrs | £2,462 |
| 7 kW | 6430 kWh | 4951 kWh | 1479 kWh | £1,259 | £148 | £1,407 | £23,692 | 16.8 yrs | £4,447 |
| 8 kW | 7348 kWh | 5658 kWh | 1690 kWh | £1,439 | £169 | £1,608 | £25,726 | 16.0 yrs | £6,432 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
Figures are illustrative and use the same method as the calculator above. For exact results, adjust your roof direction, tariff, and usage in the calculator.