A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 937 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: £758, Upfront: £10,173, Break-even: 13.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1875 kWh | 750 kWh | 1125 kWh | £191 | £112 | £303 | £4,069 | 13.4 yrs | £1,995 |
| 3 kW | 2812 kWh | 1125 kWh | 1687 kWh | £286 | £169 | £455 | £6,104 | 13.4 yrs | £2,992 |
| 4 kW | 3750 kWh | 1500 kWh | 2250 kWh | £381 | £225 | £606 | £8,138 | 13.4 yrs | £3,990 |
| 5 kW | 4687 kWh | 1875 kWh | 2812 kWh | £477 | £281 | £758 | £10,173 | 13.4 yrs | £4,987 |
| 6 kW | 5624 kWh | 2250 kWh | 3375 kWh | £572 | £337 | £910 | £12,207 | 13.4 yrs | £5,985 |
| 7 kW | 6562 kWh | 2625 kWh | 3937 kWh | £667 | £394 | £1,061 | £14,242 | 13.4 yrs | £6,982 |
| 8 kW | 7499 kWh | 3000 kWh | 4500 kWh | £763 | £450 | £1,213 | £16,276 | 13.4 yrs | £7,980 |
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: £903, Upfront: £12,273, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1875 kWh | 1125 kWh | 750 kWh | £286 | £75 | £361 | £6,169 | 17.1 yrs | £1,052 |
| 3 kW | 2812 kWh | 1687 kWh | 1125 kWh | £429 | £112 | £542 | £8,204 | 15.1 yrs | £2,628 |
| 4 kW | 3750 kWh | 2250 kWh | 1500 kWh | £572 | £150 | £722 | £10,238 | 14.2 yrs | £4,204 |
| 5 kW | 4687 kWh | 2812 kWh | 1875 kWh | £715 | £187 | £903 | £12,273 | 13.6 yrs | £5,780 |
| 6 kW | 5624 kWh | 3375 kWh | 2250 kWh | £858 | £225 | £1,083 | £14,307 | 13.2 yrs | £7,356 |
| 7 kW | 6562 kWh | 3937 kWh | 2625 kWh | £1,001 | £262 | £1,264 | £16,342 | 12.9 yrs | £8,932 |
| 8 kW | 7499 kWh | 4500 kWh | 3000 kWh | £1,144 | £300 | £1,444 | £18,376 | 12.7 yrs | £10,508 |
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: £975, Upfront: £13,673, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1875 kWh | 1312 kWh | 562 kWh | £334 | £56 | £390 | £7,569 | 19.4 yrs | £231 |
| 3 kW | 2812 kWh | 1969 kWh | 844 kWh | £501 | £84 | £585 | £9,604 | 16.4 yrs | £2,096 |
| 4 kW | 3750 kWh | 2625 kWh | 1125 kWh | £667 | £112 | £780 | £11,638 | 14.9 yrs | £3,961 |
| 5 kW | 4687 kWh | 3281 kWh | 1406 kWh | £834 | £141 | £975 | £13,673 | 14.0 yrs | £5,827 |
| 6 kW | 5624 kWh | 3937 kWh | 1687 kWh | £1,001 | £169 | £1,170 | £15,707 | 13.4 yrs | £7,692 |
| 7 kW | 6562 kWh | 4593 kWh | 1969 kWh | £1,168 | £197 | £1,365 | £17,742 | 13.0 yrs | £9,557 |
| 8 kW | 7499 kWh | 5249 kWh | 2250 kWh | £1,335 | £225 | £1,560 | £19,776 | 12.7 yrs | £11,422 |
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: £997, Upfront: £15,423, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1875 kWh | 1369 kWh | 506 kWh | £348 | £51 | £399 | £9,319 | 23.4 yrs | £-1,346 |
| 3 kW | 2812 kWh | 2053 kWh | 759 kWh | £522 | £76 | £598 | £11,354 | 19.0 yrs | £606 |
| 4 kW | 3750 kWh | 2737 kWh | 1012 kWh | £696 | £101 | £797 | £13,388 | 16.8 yrs | £2,558 |
| 5 kW | 4687 kWh | 3422 kWh | 1266 kWh | £870 | £127 | £997 | £15,423 | 15.5 yrs | £4,510 |
| 6 kW | 5624 kWh | 4106 kWh | 1519 kWh | £1,044 | £152 | £1,196 | £17,457 | 14.6 yrs | £6,463 |
| 7 kW | 6562 kWh | 4790 kWh | 1772 kWh | £1,218 | £177 | £1,395 | £19,492 | 14.0 yrs | £8,415 |
| 8 kW | 7499 kWh | 5474 kWh | 2025 kWh | £1,392 | £202 | £1,595 | £21,526 | 13.5 yrs | £10,367 |
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: £1,011, Upfront: £17,173, Break-even: 17.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1875 kWh | 1406 kWh | 469 kWh | £358 | £47 | £404 | £11,069 | 27.4 yrs | £-2,980 |
| 3 kW | 2812 kWh | 2109 kWh | 703 kWh | £536 | £70 | £607 | £13,104 | 21.6 yrs | £-970 |
| 4 kW | 3750 kWh | 2812 kWh | 937 kWh | £715 | £94 | £809 | £15,138 | 18.7 yrs | £1,040 |
| 5 kW | 4687 kWh | 3515 kWh | 1172 kWh | £894 | £117 | £1,011 | £17,173 | 17.0 yrs | £3,050 |
| 6 kW | 5624 kWh | 4218 kWh | 1406 kWh | £1,073 | £141 | £1,213 | £19,207 | 15.8 yrs | £5,060 |
| 7 kW | 6562 kWh | 4921 kWh | 1640 kWh | £1,252 | £164 | £1,416 | £21,242 | 15.0 yrs | £7,070 |
| 8 kW | 7499 kWh | 5624 kWh | 1875 kWh | £1,430 | £187 | £1,618 | £23,276 | 14.4 yrs | £9,080 |
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: £1,026, Upfront: £19,623, Break-even: 19.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1875 kWh | 1444 kWh | 431 kWh | £367 | £43 | £410 | £13,519 | 33.0 yrs | £-5,314 |
| 3 kW | 2812 kWh | 2165 kWh | 647 kWh | £551 | £65 | £615 | £15,554 | 25.3 yrs | £-3,247 |
| 4 kW | 3750 kWh | 2887 kWh | 862 kWh | £734 | £86 | £820 | £17,588 | 21.4 yrs | £-1,179 |
| 5 kW | 4687 kWh | 3609 kWh | 1078 kWh | £918 | £108 | £1,026 | £19,623 | 19.1 yrs | £889 |
| 6 kW | 5624 kWh | 4331 kWh | 1294 kWh | £1,101 | £129 | £1,231 | £21,657 | 17.6 yrs | £2,957 |
| 7 kW | 6562 kWh | 5053 kWh | 1509 kWh | £1,285 | £151 | £1,436 | £23,692 | 16.5 yrs | £5,025 |
| 8 kW | 7499 kWh | 5774 kWh | 1725 kWh | £1,468 | £172 | £1,641 | £25,726 | 15.7 yrs | £7,092 |
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.