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 1068 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £887, Upfront: £10,173, Break-even: 11.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2136 kWh | 854 kWh | 1282 kWh | £227 | £128 | £355 | £4,069 | 11.5 yrs | £3,027 |
| 3 kW | 3204 kWh | 1282 kWh | 1922 kWh | £340 | £192 | £532 | £6,104 | 11.5 yrs | £4,541 |
| 4 kW | 4272 kWh | 1709 kWh | 2563 kWh | £453 | £256 | £710 | £8,138 | 11.5 yrs | £6,055 |
| 5 kW | 5340 kWh | 2136 kWh | 3204 kWh | £567 | £320 | £887 | £10,173 | 11.5 yrs | £7,568 |
| 6 kW | 6408 kWh | 2563 kWh | 3845 kWh | £680 | £384 | £1,064 | £12,207 | 11.5 yrs | £9,082 |
| 7 kW | 7476 kWh | 2990 kWh | 4485 kWh | £793 | £449 | £1,242 | £14,242 | 11.5 yrs | £10,596 |
| 8 kW | 8544 kWh | 3417 kWh | 5126 kWh | £907 | £513 | £1,419 | £16,276 | 11.5 yrs | £12,109 |
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: £1,064, Upfront: £12,273, Break-even: 11.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2136 kWh | 1282 kWh | 854 kWh | £340 | £85 | £425 | £6,169 | 14.5 yrs | £2,340 |
| 3 kW | 3204 kWh | 1922 kWh | 1282 kWh | £510 | £128 | £638 | £8,204 | 12.9 yrs | £4,559 |
| 4 kW | 4272 kWh | 2563 kWh | 1709 kWh | £680 | £171 | £851 | £10,238 | 12.0 yrs | £6,779 |
| 5 kW | 5340 kWh | 3204 kWh | 2136 kWh | £850 | £214 | £1,064 | £12,273 | 11.5 yrs | £8,999 |
| 6 kW | 6408 kWh | 3845 kWh | 2563 kWh | £1,020 | £256 | £1,276 | £14,307 | 11.2 yrs | £11,219 |
| 7 kW | 7476 kWh | 4485 kWh | 2990 kWh | £1,190 | £299 | £1,489 | £16,342 | 11.0 yrs | £13,439 |
| 8 kW | 8544 kWh | 5126 kWh | 3417 kWh | £1,360 | £342 | £1,702 | £18,376 | 10.8 yrs | £15,659 |
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: £1,152, Upfront: £13,673, Break-even: 11.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2136 kWh | 1495 kWh | 641 kWh | £397 | £64 | £461 | £7,569 | 16.4 yrs | £1,646 |
| 3 kW | 3204 kWh | 2243 kWh | 961 kWh | £595 | £96 | £691 | £9,604 | 13.9 yrs | £4,219 |
| 4 kW | 4272 kWh | 2990 kWh | 1282 kWh | £793 | £128 | £921 | £11,638 | 12.6 yrs | £6,792 |
| 5 kW | 5340 kWh | 3738 kWh | 1602 kWh | £992 | £160 | £1,152 | £13,673 | 11.9 yrs | £9,364 |
| 6 kW | 6408 kWh | 4485 kWh | 1922 kWh | £1,190 | £192 | £1,382 | £15,707 | 11.4 yrs | £11,937 |
| 7 kW | 7476 kWh | 5233 kWh | 2243 kWh | £1,388 | £224 | £1,613 | £17,742 | 11.0 yrs | £14,510 |
| 8 kW | 8544 kWh | 5981 kWh | 2563 kWh | £1,587 | £256 | £1,843 | £19,776 | 10.7 yrs | £17,083 |
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: £1,178, Upfront: £15,423, Break-even: 13.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2136 kWh | 1559 kWh | 577 kWh | £414 | £58 | £471 | £9,319 | 19.8 yrs | £108 |
| 3 kW | 3204 kWh | 2339 kWh | 865 kWh | £620 | £87 | £707 | £11,354 | 16.1 yrs | £2,786 |
| 4 kW | 4272 kWh | 3118 kWh | 1153 kWh | £827 | £115 | £943 | £13,388 | 14.2 yrs | £5,465 |
| 5 kW | 5340 kWh | 3898 kWh | 1442 kWh | £1,034 | £144 | £1,178 | £15,423 | 13.1 yrs | £8,144 |
| 6 kW | 6408 kWh | 4678 kWh | 1730 kWh | £1,241 | £173 | £1,414 | £17,457 | 12.3 yrs | £10,823 |
| 7 kW | 7476 kWh | 5457 kWh | 2018 kWh | £1,448 | £202 | £1,650 | £19,492 | 11.8 yrs | £13,502 |
| 8 kW | 8544 kWh | 6237 kWh | 2307 kWh | £1,655 | £231 | £1,885 | £21,526 | 11.4 yrs | £16,180 |
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: £1,196, Upfront: £17,173, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2136 kWh | 1602 kWh | 534 kWh | £425 | £53 | £478 | £11,069 | 23.1 yrs | £-1,501 |
| 3 kW | 3204 kWh | 2403 kWh | 801 kWh | £637 | £80 | £718 | £13,104 | 18.3 yrs | £1,248 |
| 4 kW | 4272 kWh | 3204 kWh | 1068 kWh | £850 | £107 | £957 | £15,138 | 15.8 yrs | £3,998 |
| 5 kW | 5340 kWh | 4005 kWh | 1335 kWh | £1,062 | £133 | £1,196 | £17,173 | 14.4 yrs | £6,747 |
| 6 kW | 6408 kWh | 4806 kWh | 1602 kWh | £1,275 | £160 | £1,435 | £19,207 | 13.4 yrs | £9,497 |
| 7 kW | 7476 kWh | 5607 kWh | 1869 kWh | £1,487 | £187 | £1,674 | £21,242 | 12.7 yrs | £12,246 |
| 8 kW | 8544 kWh | 6408 kWh | 2136 kWh | £1,700 | £214 | £1,914 | £23,276 | 12.2 yrs | £14,995 |
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: £1,214, Upfront: £19,623, Break-even: 16.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2136 kWh | 1645 kWh | 491 kWh | £436 | £49 | £485 | £13,519 | 27.8 yrs | £-3,810 |
| 3 kW | 3204 kWh | 2467 kWh | 737 kWh | £654 | £74 | £728 | £15,554 | 21.4 yrs | £-990 |
| 4 kW | 4272 kWh | 3289 kWh | 983 kWh | £873 | £98 | £971 | £17,588 | 18.1 yrs | £1,830 |
| 5 kW | 5340 kWh | 4112 kWh | 1228 kWh | £1,091 | £123 | £1,214 | £19,623 | 16.2 yrs | £4,650 |
| 6 kW | 6408 kWh | 4934 kWh | 1474 kWh | £1,309 | £147 | £1,456 | £21,657 | 14.9 yrs | £7,470 |
| 7 kW | 7476 kWh | 5756 kWh | 1719 kWh | £1,527 | £172 | £1,699 | £23,692 | 13.9 yrs | £10,290 |
| 8 kW | 8544 kWh | 6579 kWh | 1965 kWh | £1,745 | £197 | £1,942 | £25,726 | 13.2 yrs | £13,110 |
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.