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 1017 kWh per year on a south-facing roof. We value self-used electricity at 26.8p 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: £851, Upfront: £10,173, Break-even: 12.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2035 kWh | 814 kWh | 1221 kWh | £218 | £122 | £340 | £4,069 | 12.0 yrs | £2,739 |
| 3 kW | 3052 kWh | 1221 kWh | 1831 kWh | £328 | £183 | £511 | £6,104 | 12.0 yrs | £4,109 |
| 4 kW | 4069 kWh | 1628 kWh | 2441 kWh | £437 | £244 | £681 | £8,138 | 12.0 yrs | £5,479 |
| 5 kW | 5086 kWh | 2035 kWh | 3052 kWh | £546 | £305 | £851 | £10,173 | 12.0 yrs | £6,849 |
| 6 kW | 6104 kWh | 2441 kWh | 3662 kWh | £655 | £366 | £1,021 | £12,207 | 12.0 yrs | £8,218 |
| 7 kW | 7121 kWh | 2848 kWh | 4273 kWh | £764 | £427 | £1,191 | £14,242 | 12.0 yrs | £9,588 |
| 8 kW | 8138 kWh | 3255 kWh | 4883 kWh | £873 | £488 | £1,362 | £16,276 | 12.0 yrs | £10,958 |
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: £1,022, Upfront: £12,273, Break-even: 12.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2035 kWh | 1221 kWh | 814 kWh | £328 | £81 | £409 | £6,169 | 15.1 yrs | £2,009 |
| 3 kW | 3052 kWh | 1831 kWh | 1221 kWh | £491 | £122 | £613 | £8,204 | 13.4 yrs | £4,064 |
| 4 kW | 4069 kWh | 2441 kWh | 1628 kWh | £655 | £163 | £818 | £10,238 | 12.5 yrs | £6,118 |
| 5 kW | 5086 kWh | 3052 kWh | 2035 kWh | £819 | £203 | £1,022 | £12,273 | 12.0 yrs | £8,173 |
| 6 kW | 6104 kWh | 3662 kWh | 2441 kWh | £983 | £244 | £1,227 | £14,307 | 11.7 yrs | £10,228 |
| 7 kW | 7121 kWh | 4273 kWh | 2848 kWh | £1,146 | £285 | £1,431 | £16,342 | 11.4 yrs | £12,282 |
| 8 kW | 8138 kWh | 4883 kWh | 3255 kWh | £1,310 | £326 | £1,636 | £18,376 | 11.2 yrs | £14,337 |
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: £1,108, Upfront: £13,673, Break-even: 12.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2035 kWh | 1424 kWh | 610 kWh | £382 | £61 | £443 | £7,569 | 17.1 yrs | £1,294 |
| 3 kW | 3052 kWh | 2136 kWh | 916 kWh | £573 | £92 | £665 | £9,604 | 14.4 yrs | £3,691 |
| 4 kW | 4069 kWh | 2848 kWh | 1221 kWh | £764 | £122 | £886 | £11,638 | 13.1 yrs | £6,088 |
| 5 kW | 5086 kWh | 3561 kWh | 1526 kWh | £955 | £153 | £1,108 | £13,673 | 12.3 yrs | £8,485 |
| 6 kW | 6104 kWh | 4273 kWh | 1831 kWh | £1,146 | £183 | £1,329 | £15,707 | 11.8 yrs | £10,882 |
| 7 kW | 7121 kWh | 4985 kWh | 2136 kWh | £1,337 | £214 | £1,551 | £17,742 | 11.4 yrs | £13,279 |
| 8 kW | 8138 kWh | 5697 kWh | 2441 kWh | £1,528 | £244 | £1,773 | £19,776 | 11.2 yrs | £15,676 |
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: £1,134, Upfront: £15,423, 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 | 2035 kWh | 1485 kWh | 549 kWh | £398 | £55 | £453 | £9,319 | 20.6 yrs | £-251 |
| 3 kW | 3052 kWh | 2228 kWh | 824 kWh | £598 | £82 | £680 | £11,354 | 16.7 yrs | £2,249 |
| 4 kW | 4069 kWh | 2970 kWh | 1099 kWh | £797 | £110 | £907 | £13,388 | 14.8 yrs | £4,749 |
| 5 kW | 5086 kWh | 3713 kWh | 1373 kWh | £996 | £137 | £1,134 | £15,423 | 13.6 yrs | £7,249 |
| 6 kW | 6104 kWh | 4456 kWh | 1648 kWh | £1,195 | £165 | £1,360 | £17,457 | 12.8 yrs | £9,748 |
| 7 kW | 7121 kWh | 5198 kWh | 1923 kWh | £1,395 | £192 | £1,587 | £19,492 | 12.3 yrs | £12,248 |
| 8 kW | 8138 kWh | 5941 kWh | 2197 kWh | £1,594 | £220 | £1,814 | £21,526 | 11.9 yrs | £14,748 |
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: £1,151, Upfront: £17,173, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2035 kWh | 1526 kWh | 509 kWh | £409 | £51 | £460 | £11,069 | 24.0 yrs | £-1,864 |
| 3 kW | 3052 kWh | 2289 kWh | 763 kWh | £614 | £76 | £690 | £13,104 | 19.0 yrs | £705 |
| 4 kW | 4069 kWh | 3052 kWh | 1017 kWh | £819 | £102 | £921 | £15,138 | 16.4 yrs | £3,273 |
| 5 kW | 5086 kWh | 3815 kWh | 1272 kWh | £1,024 | £127 | £1,151 | £17,173 | 14.9 yrs | £5,841 |
| 6 kW | 6104 kWh | 4578 kWh | 1526 kWh | £1,228 | £153 | £1,381 | £19,207 | 13.9 yrs | £8,409 |
| 7 kW | 7121 kWh | 5341 kWh | 1780 kWh | £1,433 | £178 | £1,611 | £21,242 | 13.2 yrs | £10,978 |
| 8 kW | 8138 kWh | 6104 kWh | 2035 kWh | £1,638 | £203 | £1,841 | £23,276 | 12.6 yrs | £13,546 |
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: £1,168, Upfront: £19,623, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2035 kWh | 1567 kWh | 468 kWh | £420 | £47 | £467 | £13,519 | 28.9 yrs | £-4,177 |
| 3 kW | 3052 kWh | 2350 kWh | 702 kWh | £630 | £70 | £701 | £15,554 | 22.2 yrs | £-1,540 |
| 4 kW | 4069 kWh | 3133 kWh | 936 kWh | £841 | £94 | £934 | £17,588 | 18.8 yrs | £1,097 |
| 5 kW | 5086 kWh | 3917 kWh | 1170 kWh | £1,051 | £117 | £1,168 | £19,623 | 16.8 yrs | £3,734 |
| 6 kW | 6104 kWh | 4700 kWh | 1404 kWh | £1,261 | £140 | £1,401 | £21,657 | 15.5 yrs | £6,370 |
| 7 kW | 7121 kWh | 5483 kWh | 1638 kWh | £1,471 | £164 | £1,635 | £23,692 | 14.5 yrs | £9,007 |
| 8 kW | 8138 kWh | 6267 kWh | 1872 kWh | £1,681 | £187 | £1,868 | £25,726 | 13.8 yrs | £11,644 |
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.