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 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 | 1281 kWh | £227 | £128 | £355 | £4,069 | 11.5 yrs | £3,026 |
| 3 kW | 3203 kWh | 1281 kWh | 1922 kWh | £340 | £192 | £532 | £6,104 | 11.5 yrs | £4,540 |
| 4 kW | 4271 kWh | 1709 kWh | 2563 kWh | £453 | £256 | £710 | £8,138 | 11.5 yrs | £6,053 |
| 5 kW | 5339 kWh | 2136 kWh | 3203 kWh | £567 | £320 | £887 | £10,173 | 11.5 yrs | £7,566 |
| 6 kW | 6407 kWh | 2563 kWh | 3844 kWh | £680 | £384 | £1,064 | £12,207 | 11.5 yrs | £9,079 |
| 7 kW | 7475 kWh | 2990 kWh | 4485 kWh | £793 | £448 | £1,242 | £14,242 | 11.5 yrs | £10,593 |
| 8 kW | 8543 kWh | 3417 kWh | 5126 kWh | £907 | £513 | £1,419 | £16,276 | 11.5 yrs | £12,106 |
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: £1,063, 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 | 1281 kWh | 854 kWh | £340 | £85 | £425 | £6,169 | 14.5 yrs | £2,339 |
| 3 kW | 3203 kWh | 1922 kWh | 1281 kWh | £510 | £128 | £638 | £8,204 | 12.9 yrs | £4,558 |
| 4 kW | 4271 kWh | 2563 kWh | 1709 kWh | £680 | £171 | £851 | £10,238 | 12.0 yrs | £6,777 |
| 5 kW | 5339 kWh | 3203 kWh | 2136 kWh | £850 | £214 | £1,063 | £12,273 | 11.5 yrs | £8,996 |
| 6 kW | 6407 kWh | 3844 kWh | 2563 kWh | £1,020 | £256 | £1,276 | £14,307 | 11.2 yrs | £11,216 |
| 7 kW | 7475 kWh | 4485 kWh | 2990 kWh | £1,190 | £299 | £1,489 | £16,342 | 11.0 yrs | £13,435 |
| 8 kW | 8543 kWh | 5126 kWh | 3417 kWh | £1,360 | £342 | £1,702 | £18,376 | 10.8 yrs | £15,654 |
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 | £1,645 |
| 3 kW | 3203 kWh | 2242 kWh | 961 kWh | £595 | £96 | £691 | £9,604 | 13.9 yrs | £4,217 |
| 4 kW | 4271 kWh | 2990 kWh | 1281 kWh | £793 | £128 | £921 | £11,638 | 12.6 yrs | £6,789 |
| 5 kW | 5339 kWh | 3737 kWh | 1602 kWh | £992 | £160 | £1,152 | £13,673 | 11.9 yrs | £9,361 |
| 6 kW | 6407 kWh | 4485 kWh | 1922 kWh | £1,190 | £192 | £1,382 | £15,707 | 11.4 yrs | £11,934 |
| 7 kW | 7475 kWh | 5232 kWh | 2242 kWh | £1,388 | £224 | £1,612 | £17,742 | 11.0 yrs | £14,506 |
| 8 kW | 8543 kWh | 5980 kWh | 2563 kWh | £1,586 | £256 | £1,843 | £19,776 | 10.7 yrs | £17,078 |
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 | £106 |
| 3 kW | 3203 kWh | 2339 kWh | 865 kWh | £620 | £86 | £707 | £11,354 | 16.1 yrs | £2,785 |
| 4 kW | 4271 kWh | 3118 kWh | 1153 kWh | £827 | £115 | £943 | £13,388 | 14.2 yrs | £5,463 |
| 5 kW | 5339 kWh | 3898 kWh | 1442 kWh | £1,034 | £144 | £1,178 | £15,423 | 13.1 yrs | £8,141 |
| 6 kW | 6407 kWh | 4677 kWh | 1730 kWh | £1,241 | £173 | £1,414 | £17,457 | 12.3 yrs | £10,819 |
| 7 kW | 7475 kWh | 5457 kWh | 2018 kWh | £1,448 | £202 | £1,649 | £19,492 | 11.8 yrs | £13,497 |
| 8 kW | 8543 kWh | 6236 kWh | 2306 kWh | £1,654 | £231 | £1,885 | £21,526 | 11.4 yrs | £16,175 |
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 | £-1,502 |
| 3 kW | 3203 kWh | 2403 kWh | 801 kWh | £637 | £80 | £717 | £13,104 | 18.3 yrs | £1,246 |
| 4 kW | 4271 kWh | 3203 kWh | 1068 kWh | £850 | £107 | £957 | £15,138 | 15.8 yrs | £3,995 |
| 5 kW | 5339 kWh | 4004 kWh | 1335 kWh | £1,062 | £133 | £1,196 | £17,173 | 14.4 yrs | £6,744 |
| 6 kW | 6407 kWh | 4805 kWh | 1602 kWh | £1,275 | £160 | £1,435 | £19,207 | 13.4 yrs | £9,493 |
| 7 kW | 7475 kWh | 5606 kWh | 1869 kWh | £1,487 | £187 | £1,674 | £21,242 | 12.7 yrs | £12,242 |
| 8 kW | 8543 kWh | 6407 kWh | 2136 kWh | £1,700 | £214 | £1,913 | £23,276 | 12.2 yrs | £14,990 |
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: £1,213, 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 | 1644 kWh | 491 kWh | £436 | £49 | £485 | £13,519 | 27.9 yrs | £-3,811 |
| 3 kW | 3203 kWh | 2467 kWh | 737 kWh | £654 | £74 | £728 | £15,554 | 21.4 yrs | £-992 |
| 4 kW | 4271 kWh | 3289 kWh | 982 kWh | £873 | £98 | £971 | £17,588 | 18.1 yrs | £1,828 |
| 5 kW | 5339 kWh | 4111 kWh | 1228 kWh | £1,091 | £123 | £1,213 | £19,623 | 16.2 yrs | £4,647 |
| 6 kW | 6407 kWh | 4933 kWh | 1474 kWh | £1,309 | £147 | £1,456 | £21,657 | 14.9 yrs | £7,466 |
| 7 kW | 7475 kWh | 5756 kWh | 1719 kWh | £1,527 | £172 | £1,699 | £23,692 | 13.9 yrs | £10,286 |
| 8 kW | 8543 kWh | 6578 kWh | 1965 kWh | £1,745 | £196 | £1,942 | £25,726 | 13.3 yrs | £13,105 |
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.