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 770 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: £648, 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 | 1540 kWh | 616 kWh | 924 kWh | £167 | £92 | £259 | £4,069 | 15.7 yrs | £1,113 |
| 3 kW | 2310 kWh | 924 kWh | 1386 kWh | £250 | £139 | £389 | £6,104 | 15.7 yrs | £1,669 |
| 4 kW | 3080 kWh | 1232 kWh | 1848 kWh | £333 | £185 | £518 | £8,138 | 15.7 yrs | £2,225 |
| 5 kW | 3850 kWh | 1540 kWh | 2310 kWh | £417 | £231 | £648 | £10,173 | 15.7 yrs | £2,782 |
| 6 kW | 4620 kWh | 1848 kWh | 2772 kWh | £500 | £277 | £777 | £12,207 | 15.7 yrs | £3,338 |
| 7 kW | 5390 kWh | 2156 kWh | 3234 kWh | £583 | £323 | £907 | £14,242 | 15.7 yrs | £3,894 |
| 8 kW | 6160 kWh | 2464 kWh | 3696 kWh | £667 | £370 | £1,036 | £16,276 | 15.7 yrs | £4,451 |
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: £779, 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 | 1540 kWh | 924 kWh | 616 kWh | £250 | £62 | £312 | £6,169 | 19.8 yrs | £64 |
| 3 kW | 2310 kWh | 1386 kWh | 924 kWh | £375 | £92 | £467 | £8,204 | 17.5 yrs | £1,145 |
| 4 kW | 3080 kWh | 1848 kWh | 1232 kWh | £500 | £123 | £623 | £10,238 | 16.4 yrs | £2,227 |
| 5 kW | 3850 kWh | 2310 kWh | 1540 kWh | £625 | £154 | £779 | £12,273 | 15.8 yrs | £3,309 |
| 6 kW | 4620 kWh | 2772 kWh | 1848 kWh | £750 | £185 | £935 | £14,307 | 15.3 yrs | £4,391 |
| 7 kW | 5390 kWh | 3234 kWh | 2156 kWh | £875 | £216 | £1,091 | £16,342 | 15.0 yrs | £5,472 |
| 8 kW | 6160 kWh | 3696 kWh | 2464 kWh | £1,000 | £246 | £1,247 | £18,376 | 14.7 yrs | £6,554 |
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: £845, 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 | 1540 kWh | 1078 kWh | 462 kWh | £292 | £46 | £338 | £7,569 | 22.4 yrs | £-811 |
| 3 kW | 2310 kWh | 1617 kWh | 693 kWh | £438 | £69 | £507 | £9,604 | 18.9 yrs | £533 |
| 4 kW | 3080 kWh | 2156 kWh | 924 kWh | £583 | £92 | £676 | £11,638 | 17.2 yrs | £1,878 |
| 5 kW | 3850 kWh | 2695 kWh | 1155 kWh | £729 | £115 | £845 | £13,673 | 16.2 yrs | £3,222 |
| 6 kW | 4620 kWh | 3234 kWh | 1386 kWh | £875 | £139 | £1,014 | £15,707 | 15.5 yrs | £4,567 |
| 7 kW | 5390 kWh | 3773 kWh | 1617 kWh | £1,021 | £162 | £1,183 | £17,742 | 15.0 yrs | £5,911 |
| 8 kW | 6160 kWh | 4312 kWh | 1848 kWh | £1,167 | £185 | £1,352 | £19,776 | 14.6 yrs | £7,256 |
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: £864, Upfront: £15,423, Break-even: 17.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1540 kWh | 1124 kWh | 416 kWh | £304 | £42 | £346 | £9,319 | 27.0 yrs | £-2,403 |
| 3 kW | 2310 kWh | 1686 kWh | 624 kWh | £456 | £62 | £519 | £11,354 | 21.9 yrs | £-980 |
| 4 kW | 3080 kWh | 2248 kWh | 832 kWh | £608 | £83 | £692 | £13,388 | 19.4 yrs | £443 |
| 5 kW | 3850 kWh | 2810 kWh | 1039 kWh | £761 | £104 | £864 | £15,423 | 17.8 yrs | £1,866 |
| 6 kW | 4620 kWh | 3373 kWh | 1247 kWh | £913 | £125 | £1,037 | £17,457 | 16.8 yrs | £3,290 |
| 7 kW | 5390 kWh | 3935 kWh | 1455 kWh | £1,065 | £146 | £1,210 | £19,492 | 16.1 yrs | £4,713 |
| 8 kW | 6160 kWh | 4497 kWh | 1663 kWh | £1,217 | £166 | £1,383 | £21,526 | 15.6 yrs | £6,136 |
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: £878, 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 | 1540 kWh | 1155 kWh | 385 kWh | £313 | £38 | £351 | £11,069 | 31.5 yrs | £-4,048 |
| 3 kW | 2310 kWh | 1732 kWh | 577 kWh | £469 | £58 | £527 | £13,104 | 24.9 yrs | £-2,573 |
| 4 kW | 3080 kWh | 2310 kWh | 770 kWh | £625 | £77 | £702 | £15,138 | 21.6 yrs | £-1,097 |
| 5 kW | 3850 kWh | 2887 kWh | 962 kWh | £781 | £96 | £878 | £17,173 | 19.6 yrs | £379 |
| 6 kW | 4620 kWh | 3465 kWh | 1155 kWh | £938 | £115 | £1,053 | £19,207 | 18.2 yrs | £1,855 |
| 7 kW | 5390 kWh | 4042 kWh | 1347 kWh | £1,094 | £135 | £1,229 | £21,242 | 17.3 yrs | £3,331 |
| 8 kW | 6160 kWh | 4620 kWh | 1540 kWh | £1,250 | £154 | £1,404 | £23,276 | 16.6 yrs | £4,807 |
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: £891, Upfront: £19,623, Break-even: 22.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1540 kWh | 1186 kWh | 354 kWh | £321 | £35 | £356 | £13,519 | 37.9 yrs | £-6,393 |
| 3 kW | 2310 kWh | 1779 kWh | 531 kWh | £481 | £53 | £534 | £15,554 | 29.1 yrs | £-4,865 |
| 4 kW | 3080 kWh | 2372 kWh | 708 kWh | £642 | £71 | £713 | £17,588 | 24.7 yrs | £-3,337 |
| 5 kW | 3850 kWh | 2964 kWh | 885 kWh | £802 | £89 | £891 | £19,623 | 22.0 yrs | £-1,808 |
| 6 kW | 4620 kWh | 3557 kWh | 1063 kWh | £963 | £106 | £1,069 | £21,657 | 20.3 yrs | £-280 |
| 7 kW | 5390 kWh | 4150 kWh | 1240 kWh | £1,123 | £124 | £1,247 | £23,692 | 19.0 yrs | £1,249 |
| 8 kW | 6160 kWh | 4743 kWh | 1417 kWh | £1,283 | £142 | £1,425 | £25,726 | 18.1 yrs | £2,777 |
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.