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 789 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £664, Upfront: £10,173, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1579 kWh | 632 kWh | 947 kWh | £171 | £95 | £266 | £4,069 | 15.3 yrs | £1,244 |
| 3 kW | 2368 kWh | 947 kWh | 1421 kWh | £256 | £142 | £398 | £6,104 | 15.3 yrs | £1,865 |
| 4 kW | 3158 kWh | 1263 kWh | 1895 kWh | £342 | £189 | £531 | £8,138 | 15.3 yrs | £2,487 |
| 5 kW | 3947 kWh | 1579 kWh | 2368 kWh | £427 | £237 | £664 | £10,173 | 15.3 yrs | £3,109 |
| 6 kW | 4737 kWh | 1895 kWh | 2842 kWh | £513 | £284 | £797 | £12,207 | 15.3 yrs | £3,731 |
| 7 kW | 5526 kWh | 2210 kWh | 3316 kWh | £598 | £332 | £930 | £14,242 | 15.3 yrs | £4,353 |
| 8 kW | 6316 kWh | 2526 kWh | 3789 kWh | £684 | £379 | £1,063 | £16,276 | 15.3 yrs | £4,975 |
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: £799, Upfront: £12,273, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1579 kWh | 947 kWh | 632 kWh | £256 | £63 | £320 | £6,169 | 19.3 yrs | £221 |
| 3 kW | 2368 kWh | 1421 kWh | 947 kWh | £385 | £95 | £479 | £8,204 | 17.1 yrs | £1,382 |
| 4 kW | 3158 kWh | 1895 kWh | 1263 kWh | £513 | £126 | £639 | £10,238 | 16.0 yrs | £2,542 |
| 5 kW | 3947 kWh | 2368 kWh | 1579 kWh | £641 | £158 | £799 | £12,273 | 15.4 yrs | £3,703 |
| 6 kW | 4737 kWh | 2842 kWh | 1895 kWh | £769 | £189 | £959 | £14,307 | 14.9 yrs | £4,863 |
| 7 kW | 5526 kWh | 3316 kWh | 2210 kWh | £897 | £221 | £1,118 | £16,342 | 14.6 yrs | £6,024 |
| 8 kW | 6316 kWh | 3789 kWh | 2526 kWh | £1,025 | £253 | £1,278 | £18,376 | 14.4 yrs | £7,184 |
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: £866, Upfront: £13,673, 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 | 1579 kWh | 1105 kWh | 474 kWh | £299 | £47 | £346 | £7,569 | 21.8 yrs | £-640 |
| 3 kW | 2368 kWh | 1658 kWh | 711 kWh | £449 | £71 | £520 | £9,604 | 18.5 yrs | £790 |
| 4 kW | 3158 kWh | 2210 kWh | 947 kWh | £598 | £95 | £693 | £11,638 | 16.8 yrs | £2,220 |
| 5 kW | 3947 kWh | 2763 kWh | 1184 kWh | £748 | £118 | £866 | £13,673 | 15.8 yrs | £3,650 |
| 6 kW | 4737 kWh | 3316 kWh | 1421 kWh | £897 | £142 | £1,039 | £15,707 | 15.1 yrs | £5,079 |
| 7 kW | 5526 kWh | 3868 kWh | 1658 kWh | £1,047 | £166 | £1,213 | £17,742 | 14.6 yrs | £6,509 |
| 8 kW | 6316 kWh | 4421 kWh | 1895 kWh | £1,196 | £189 | £1,386 | £19,776 | 14.3 yrs | £7,939 |
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: £886, Upfront: £15,423, Break-even: 17.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1579 kWh | 1153 kWh | 426 kWh | £312 | £43 | £355 | £9,319 | 26.3 yrs | £-2,229 |
| 3 kW | 2368 kWh | 1729 kWh | 639 kWh | £468 | £64 | £532 | £11,354 | 21.3 yrs | £-718 |
| 4 kW | 3158 kWh | 2305 kWh | 853 kWh | £624 | £85 | £709 | £13,388 | 18.9 yrs | £793 |
| 5 kW | 3947 kWh | 2881 kWh | 1066 kWh | £780 | £107 | £886 | £15,423 | 17.4 yrs | £2,304 |
| 6 kW | 4737 kWh | 3458 kWh | 1279 kWh | £936 | £128 | £1,064 | £17,457 | 16.4 yrs | £3,814 |
| 7 kW | 5526 kWh | 4034 kWh | 1492 kWh | £1,092 | £149 | £1,241 | £19,492 | 15.7 yrs | £5,325 |
| 8 kW | 6316 kWh | 4610 kWh | 1705 kWh | £1,248 | £171 | £1,418 | £21,526 | 15.2 yrs | £6,836 |
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: £900, Upfront: £17,173, 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 | 1579 kWh | 1184 kWh | 395 kWh | £320 | £39 | £360 | £11,069 | 30.8 yrs | £-3,871 |
| 3 kW | 2368 kWh | 1776 kWh | 592 kWh | £481 | £59 | £540 | £13,104 | 24.3 yrs | £-2,306 |
| 4 kW | 3158 kWh | 2368 kWh | 789 kWh | £641 | £79 | £720 | £15,138 | 21.0 yrs | £-742 |
| 5 kW | 3947 kWh | 2960 kWh | 987 kWh | £801 | £99 | £900 | £17,173 | 19.1 yrs | £823 |
| 6 kW | 4737 kWh | 3553 kWh | 1184 kWh | £961 | £118 | £1,080 | £19,207 | 17.8 yrs | £2,388 |
| 7 kW | 5526 kWh | 4145 kWh | 1382 kWh | £1,122 | £138 | £1,260 | £21,242 | 16.9 yrs | £3,952 |
| 8 kW | 6316 kWh | 4737 kWh | 1579 kWh | £1,282 | £158 | £1,440 | £23,276 | 16.2 yrs | £5,517 |
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: £913, Upfront: £19,623, Break-even: 21.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1579 kWh | 1216 kWh | 363 kWh | £329 | £36 | £365 | £13,519 | 37.0 yrs | £-6,213 |
| 3 kW | 2368 kWh | 1824 kWh | 545 kWh | £493 | £54 | £548 | £15,554 | 28.4 yrs | £-4,595 |
| 4 kW | 3158 kWh | 2432 kWh | 726 kWh | £658 | £73 | £731 | £17,588 | 24.1 yrs | £-2,976 |
| 5 kW | 3947 kWh | 3039 kWh | 908 kWh | £822 | £91 | £913 | £19,623 | 21.5 yrs | £-1,358 |
| 6 kW | 4737 kWh | 3647 kWh | 1089 kWh | £987 | £109 | £1,096 | £21,657 | 19.8 yrs | £261 |
| 7 kW | 5526 kWh | 4255 kWh | 1271 kWh | £1,151 | £127 | £1,279 | £23,692 | 18.5 yrs | £1,879 |
| 8 kW | 6316 kWh | 4863 kWh | 1453 kWh | £1,316 | £145 | £1,461 | £25,726 | 17.6 yrs | £3,498 |
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.