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 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 | 2034 kWh | 814 kWh | 1220 kWh | £218 | £122 | £340 | £4,069 | 12.0 yrs | £2,736 |
| 3 kW | 3051 kWh | 1220 kWh | 1831 kWh | £327 | £183 | £510 | £6,104 | 12.0 yrs | £4,104 |
| 4 kW | 4068 kWh | 1627 kWh | 2441 kWh | £436 | £244 | £680 | £8,138 | 12.0 yrs | £5,472 |
| 5 kW | 5085 kWh | 2034 kWh | 3051 kWh | £546 | £305 | £851 | £10,173 | 12.0 yrs | £6,840 |
| 6 kW | 6102 kWh | 2441 kWh | 3661 kWh | £655 | £366 | £1,021 | £12,207 | 12.0 yrs | £8,208 |
| 7 kW | 7119 kWh | 2848 kWh | 4271 kWh | £764 | £427 | £1,191 | £14,242 | 12.0 yrs | £9,576 |
| 8 kW | 8136 kWh | 3254 kWh | 4882 kWh | £873 | £488 | £1,361 | £16,276 | 12.0 yrs | £10,944 |
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 | 2034 kWh | 1220 kWh | 814 kWh | £327 | £81 | £409 | £6,169 | 15.1 yrs | £2,004 |
| 3 kW | 3051 kWh | 1831 kWh | 1220 kWh | £491 | £122 | £613 | £8,204 | 13.4 yrs | £4,057 |
| 4 kW | 4068 kWh | 2441 kWh | 1627 kWh | £655 | £163 | £817 | £10,238 | 12.5 yrs | £6,109 |
| 5 kW | 5085 kWh | 3051 kWh | 2034 kWh | £818 | £203 | £1,022 | £12,273 | 12.0 yrs | £8,161 |
| 6 kW | 6102 kWh | 3661 kWh | 2441 kWh | £982 | £244 | £1,226 | £14,307 | 11.7 yrs | £10,213 |
| 7 kW | 7119 kWh | 4271 kWh | 2848 kWh | £1,146 | £285 | £1,430 | £16,342 | 11.4 yrs | £12,265 |
| 8 kW | 8136 kWh | 4882 kWh | 3254 kWh | £1,309 | £325 | £1,635 | £18,376 | 11.2 yrs | £14,318 |
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: £1,107, 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 | 2034 kWh | 1424 kWh | 610 kWh | £382 | £61 | £443 | £7,569 | 17.1 yrs | £1,289 |
| 3 kW | 3051 kWh | 2136 kWh | 915 kWh | £573 | £92 | £664 | £9,604 | 14.5 yrs | £3,683 |
| 4 kW | 4068 kWh | 2848 kWh | 1220 kWh | £764 | £122 | £886 | £11,638 | 13.1 yrs | £6,077 |
| 5 kW | 5085 kWh | 3560 kWh | 1526 kWh | £955 | £153 | £1,107 | £13,673 | 12.3 yrs | £8,472 |
| 6 kW | 6102 kWh | 4271 kWh | 1831 kWh | £1,146 | £183 | £1,329 | £15,707 | 11.8 yrs | £10,866 |
| 7 kW | 7119 kWh | 4983 kWh | 2136 kWh | £1,337 | £214 | £1,550 | £17,742 | 11.4 yrs | £13,260 |
| 8 kW | 8136 kWh | 5695 kWh | 2441 kWh | £1,527 | £244 | £1,772 | £19,776 | 11.2 yrs | £15,655 |
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: £1,133, 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 | 2034 kWh | 1485 kWh | 549 kWh | £398 | £55 | £453 | £9,319 | 20.6 yrs | £-256 |
| 3 kW | 3051 kWh | 2227 kWh | 824 kWh | £597 | £82 | £680 | £11,354 | 16.7 yrs | £2,241 |
| 4 kW | 4068 kWh | 2970 kWh | 1098 kWh | £796 | £110 | £906 | £13,388 | 14.8 yrs | £4,738 |
| 5 kW | 5085 kWh | 3712 kWh | 1373 kWh | £996 | £137 | £1,133 | £15,423 | 13.6 yrs | £7,235 |
| 6 kW | 6102 kWh | 4454 kWh | 1648 kWh | £1,195 | £165 | £1,359 | £17,457 | 12.8 yrs | £9,732 |
| 7 kW | 7119 kWh | 5197 kWh | 1922 kWh | £1,394 | £192 | £1,586 | £19,492 | 12.3 yrs | £12,229 |
| 8 kW | 8136 kWh | 5939 kWh | 2197 kWh | £1,593 | £220 | £1,813 | £21,526 | 11.9 yrs | £14,726 |
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: £1,150, 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 | 2034 kWh | 1526 kWh | 508 kWh | £409 | £51 | £460 | £11,069 | 24.1 yrs | £-1,869 |
| 3 kW | 3051 kWh | 2288 kWh | 763 kWh | £614 | £76 | £690 | £13,104 | 19.0 yrs | £696 |
| 4 kW | 4068 kWh | 3051 kWh | 1017 kWh | £818 | £102 | £920 | £15,138 | 16.5 yrs | £3,262 |
| 5 kW | 5085 kWh | 3814 kWh | 1271 kWh | £1,023 | £127 | £1,150 | £17,173 | 14.9 yrs | £5,827 |
| 6 kW | 6102 kWh | 4576 kWh | 1526 kWh | £1,227 | £153 | £1,380 | £19,207 | 13.9 yrs | £8,392 |
| 7 kW | 7119 kWh | 5339 kWh | 1780 kWh | £1,432 | £178 | £1,610 | £21,242 | 13.2 yrs | £10,958 |
| 8 kW | 8136 kWh | 6102 kWh | 2034 kWh | £1,637 | £203 | £1,840 | £23,276 | 12.7 yrs | £13,523 |
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: £1,167, 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 | 2034 kWh | 1566 kWh | 468 kWh | £420 | £47 | £467 | £13,519 | 29.0 yrs | £-4,182 |
| 3 kW | 3051 kWh | 2349 kWh | 702 kWh | £630 | £70 | £700 | £15,554 | 22.2 yrs | £-1,549 |
| 4 kW | 4068 kWh | 3132 kWh | 936 kWh | £840 | £94 | £934 | £17,588 | 18.8 yrs | £1,085 |
| 5 kW | 5085 kWh | 3915 kWh | 1170 kWh | £1,050 | £117 | £1,167 | £19,623 | 16.8 yrs | £3,719 |
| 6 kW | 6102 kWh | 4699 kWh | 1403 kWh | £1,260 | £140 | £1,400 | £21,657 | 15.5 yrs | £6,353 |
| 7 kW | 7119 kWh | 5482 kWh | 1637 kWh | £1,470 | £164 | £1,634 | £23,692 | 14.5 yrs | £8,987 |
| 8 kW | 8136 kWh | 6265 kWh | 1871 kWh | £1,680 | £187 | £1,867 | £25,726 | 13.8 yrs | £11,620 |
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.