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 769 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: £647, Upfront: £10,173, Break-even: 15.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1538 kWh | 615 kWh | 923 kWh | £166 | £92 | £259 | £4,069 | 15.7 yrs | £1,107 |
| 3 kW | 2307 kWh | 923 kWh | 1384 kWh | £250 | £138 | £388 | £6,104 | 15.7 yrs | £1,660 |
| 4 kW | 3076 kWh | 1231 kWh | 1846 kWh | £333 | £185 | £518 | £8,138 | 15.7 yrs | £2,214 |
| 5 kW | 3846 kWh | 1538 kWh | 2307 kWh | £416 | £231 | £647 | £10,173 | 15.7 yrs | £2,767 |
| 6 kW | 4615 kWh | 1846 kWh | 2769 kWh | £499 | £277 | £776 | £12,207 | 15.7 yrs | £3,321 |
| 7 kW | 5384 kWh | 2154 kWh | 3230 kWh | £583 | £323 | £906 | £14,242 | 15.7 yrs | £3,874 |
| 8 kW | 6153 kWh | 2461 kWh | 3692 kWh | £666 | £369 | £1,035 | £16,276 | 15.7 yrs | £4,427 |
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: £778, Upfront: £12,273, 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 | 1538 kWh | 923 kWh | 615 kWh | £250 | £62 | £311 | £6,169 | 19.8 yrs | £57 |
| 3 kW | 2307 kWh | 1384 kWh | 923 kWh | £375 | £92 | £467 | £8,204 | 17.6 yrs | £1,135 |
| 4 kW | 3076 kWh | 1846 kWh | 1231 kWh | £499 | £123 | £623 | £10,238 | 16.4 yrs | £2,213 |
| 5 kW | 3846 kWh | 2307 kWh | 1538 kWh | £624 | £154 | £778 | £12,273 | 15.8 yrs | £3,291 |
| 6 kW | 4615 kWh | 2769 kWh | 1846 kWh | £749 | £185 | £934 | £14,307 | 15.3 yrs | £4,370 |
| 7 kW | 5384 kWh | 3230 kWh | 2154 kWh | £874 | £215 | £1,089 | £16,342 | 15.0 yrs | £5,448 |
| 8 kW | 6153 kWh | 3692 kWh | 2461 kWh | £999 | £246 | £1,245 | £18,376 | 14.8 yrs | £6,526 |
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: £844, Upfront: £13,673, 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 | 1538 kWh | 1077 kWh | 461 kWh | £291 | £46 | £338 | £7,569 | 22.4 yrs | £-819 |
| 3 kW | 2307 kWh | 1615 kWh | 692 kWh | £437 | £69 | £506 | £9,604 | 19.0 yrs | £522 |
| 4 kW | 3076 kWh | 2154 kWh | 923 kWh | £583 | £92 | £675 | £11,638 | 17.2 yrs | £1,863 |
| 5 kW | 3846 kWh | 2692 kWh | 1154 kWh | £728 | £115 | £844 | £13,673 | 16.2 yrs | £3,203 |
| 6 kW | 4615 kWh | 3230 kWh | 1384 kWh | £874 | £138 | £1,013 | £15,707 | 15.5 yrs | £4,544 |
| 7 kW | 5384 kWh | 3769 kWh | 1615 kWh | £1,020 | £162 | £1,181 | £17,742 | 15.0 yrs | £5,885 |
| 8 kW | 6153 kWh | 4307 kWh | 1846 kWh | £1,165 | £185 | £1,350 | £19,776 | 14.6 yrs | £7,226 |
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: £863, Upfront: £15,423, Break-even: 17.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1538 kWh | 1123 kWh | 415 kWh | £304 | £42 | £345 | £9,319 | 27.0 yrs | £-2,411 |
| 3 kW | 2307 kWh | 1684 kWh | 623 kWh | £456 | £62 | £518 | £11,354 | 21.9 yrs | £-992 |
| 4 kW | 3076 kWh | 2246 kWh | 831 kWh | £608 | £83 | £691 | £13,388 | 19.4 yrs | £428 |
| 5 kW | 3846 kWh | 2807 kWh | 1038 kWh | £760 | £104 | £863 | £15,423 | 17.9 yrs | £1,847 |
| 6 kW | 4615 kWh | 3369 kWh | 1246 kWh | £912 | £125 | £1,036 | £17,457 | 16.8 yrs | £3,267 |
| 7 kW | 5384 kWh | 3930 kWh | 1454 kWh | £1,064 | £145 | £1,209 | £19,492 | 16.1 yrs | £4,686 |
| 8 kW | 6153 kWh | 4492 kWh | 1661 kWh | £1,215 | £166 | £1,382 | £21,526 | 15.6 yrs | £6,105 |
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: £877, Upfront: £17,173, Break-even: 19.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1538 kWh | 1154 kWh | 385 kWh | £312 | £38 | £351 | £11,069 | 31.6 yrs | £-4,056 |
| 3 kW | 2307 kWh | 1731 kWh | 577 kWh | £468 | £58 | £526 | £13,104 | 24.9 yrs | £-2,584 |
| 4 kW | 3076 kWh | 2307 kWh | 769 kWh | £624 | £77 | £701 | £15,138 | 21.6 yrs | £-1,112 |
| 5 kW | 3846 kWh | 2884 kWh | 961 kWh | £780 | £96 | £877 | £17,173 | 19.6 yrs | £360 |
| 6 kW | 4615 kWh | 3461 kWh | 1154 kWh | £937 | £115 | £1,052 | £19,207 | 18.3 yrs | £1,831 |
| 7 kW | 5384 kWh | 4038 kWh | 1346 kWh | £1,093 | £135 | £1,227 | £21,242 | 17.3 yrs | £3,303 |
| 8 kW | 6153 kWh | 4615 kWh | 1538 kWh | £1,249 | £154 | £1,403 | £23,276 | 16.6 yrs | £4,775 |
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: £890, Upfront: £19,623, Break-even: 22.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1538 kWh | 1184 kWh | 354 kWh | £321 | £35 | £356 | £13,519 | 38.0 yrs | £-6,401 |
| 3 kW | 2307 kWh | 1777 kWh | 531 kWh | £481 | £53 | £534 | £15,554 | 29.1 yrs | £-4,877 |
| 4 kW | 3076 kWh | 2369 kWh | 708 kWh | £641 | £71 | £712 | £17,588 | 24.7 yrs | £-3,352 |
| 5 kW | 3846 kWh | 2961 kWh | 884 kWh | £801 | £88 | £890 | £19,623 | 22.1 yrs | £-1,828 |
| 6 kW | 4615 kWh | 3553 kWh | 1061 kWh | £962 | £106 | £1,068 | £21,657 | 20.3 yrs | £-304 |
| 7 kW | 5384 kWh | 4146 kWh | 1238 kWh | £1,122 | £124 | £1,246 | £23,692 | 19.0 yrs | £1,221 |
| 8 kW | 6153 kWh | 4738 kWh | 1415 kWh | £1,282 | £142 | £1,424 | £25,726 | 18.1 yrs | £2,745 |
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.