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 987 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: £820, Upfront: £10,173, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1974 kWh | 790 kWh | 1184 kWh | £209 | £118 | £328 | £4,069 | 12.4 yrs | £2,490 |
| 3 kW | 2961 kWh | 1184 kWh | 1777 kWh | £314 | £178 | £492 | £6,104 | 12.4 yrs | £3,734 |
| 4 kW | 3948 kWh | 1579 kWh | 2369 kWh | £419 | £237 | £656 | £8,138 | 12.4 yrs | £4,979 |
| 5 kW | 4935 kWh | 1974 kWh | 2961 kWh | £524 | £296 | £820 | £10,173 | 12.4 yrs | £6,224 |
| 6 kW | 5922 kWh | 2369 kWh | 3553 kWh | £628 | £355 | £984 | £12,207 | 12.4 yrs | £7,469 |
| 7 kW | 6909 kWh | 2764 kWh | 4146 kWh | £733 | £415 | £1,148 | £14,242 | 12.4 yrs | £8,714 |
| 8 kW | 7896 kWh | 3158 kWh | 4738 kWh | £838 | £474 | £1,312 | £16,276 | 12.4 yrs | £9,958 |
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: £983, Upfront: £12,273, Break-even: 12.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1974 kWh | 1184 kWh | 790 kWh | £314 | £79 | £393 | £6,169 | 15.7 yrs | £1,695 |
| 3 kW | 2961 kWh | 1777 kWh | 1184 kWh | £471 | £118 | £590 | £8,204 | 13.9 yrs | £3,592 |
| 4 kW | 3948 kWh | 2369 kWh | 1579 kWh | £628 | £158 | £786 | £10,238 | 13.0 yrs | £5,490 |
| 5 kW | 4935 kWh | 2961 kWh | 1974 kWh | £786 | £197 | £983 | £12,273 | 12.5 yrs | £7,387 |
| 6 kW | 5922 kWh | 3553 kWh | 2369 kWh | £943 | £237 | £1,180 | £14,307 | 12.1 yrs | £9,285 |
| 7 kW | 6909 kWh | 4146 kWh | 2764 kWh | £1,100 | £276 | £1,376 | £16,342 | 11.9 yrs | £11,182 |
| 8 kW | 7896 kWh | 4738 kWh | 3158 kWh | £1,257 | £316 | £1,573 | £18,376 | 11.7 yrs | £13,079 |
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: £1,065, Upfront: £13,673, Break-even: 12.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1974 kWh | 1382 kWh | 592 kWh | £367 | £59 | £426 | £7,569 | 17.8 yrs | £947 |
| 3 kW | 2961 kWh | 2073 kWh | 888 kWh | £550 | £89 | £639 | £9,604 | 15.0 yrs | £3,171 |
| 4 kW | 3948 kWh | 2764 kWh | 1184 kWh | £733 | £118 | £852 | £11,638 | 13.7 yrs | £5,395 |
| 5 kW | 4935 kWh | 3455 kWh | 1481 kWh | £917 | £148 | £1,065 | £13,673 | 12.8 yrs | £7,619 |
| 6 kW | 5922 kWh | 4146 kWh | 1777 kWh | £1,100 | £178 | £1,277 | £15,707 | 12.3 yrs | £9,842 |
| 7 kW | 6909 kWh | 4836 kWh | 2073 kWh | £1,283 | £207 | £1,490 | £17,742 | 11.9 yrs | £12,066 |
| 8 kW | 7896 kWh | 5527 kWh | 2369 kWh | £1,466 | £237 | £1,703 | £19,776 | 11.6 yrs | £14,290 |
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: £1,089, Upfront: £15,423, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1974 kWh | 1441 kWh | 533 kWh | £382 | £53 | £436 | £9,319 | 21.4 yrs | £-607 |
| 3 kW | 2961 kWh | 2162 kWh | 799 kWh | £573 | £80 | £653 | £11,354 | 17.4 yrs | £1,715 |
| 4 kW | 3948 kWh | 2882 kWh | 1066 kWh | £765 | £107 | £871 | £13,388 | 15.4 yrs | £4,037 |
| 5 kW | 4935 kWh | 3603 kWh | 1332 kWh | £956 | £133 | £1,089 | £15,423 | 14.2 yrs | £6,358 |
| 6 kW | 5922 kWh | 4323 kWh | 1599 kWh | £1,147 | £160 | £1,307 | £17,457 | 13.4 yrs | £8,680 |
| 7 kW | 6909 kWh | 5044 kWh | 1865 kWh | £1,338 | £187 | £1,525 | £19,492 | 12.8 yrs | £11,001 |
| 8 kW | 7896 kWh | 5764 kWh | 2132 kWh | £1,529 | £213 | £1,742 | £21,526 | 12.4 yrs | £13,323 |
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: £1,105, Upfront: £17,173, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1974 kWh | 1481 kWh | 494 kWh | £393 | £49 | £442 | £11,069 | 25.0 yrs | £-2,226 |
| 3 kW | 2961 kWh | 2221 kWh | 740 kWh | £589 | £74 | £663 | £13,104 | 19.8 yrs | £161 |
| 4 kW | 3948 kWh | 2961 kWh | 987 kWh | £786 | £99 | £884 | £15,138 | 17.1 yrs | £2,548 |
| 5 kW | 4935 kWh | 3701 kWh | 1234 kWh | £982 | £123 | £1,105 | £17,173 | 15.5 yrs | £4,934 |
| 6 kW | 5922 kWh | 4442 kWh | 1481 kWh | £1,178 | £148 | £1,326 | £19,207 | 14.5 yrs | £7,321 |
| 7 kW | 6909 kWh | 5182 kWh | 1727 kWh | £1,375 | £173 | £1,547 | £21,242 | 13.7 yrs | £9,708 |
| 8 kW | 7896 kWh | 5922 kWh | 1974 kWh | £1,571 | £197 | £1,769 | £23,276 | 13.2 yrs | £12,095 |
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: £1,122, Upfront: £19,623, Break-even: 17.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1974 kWh | 1520 kWh | 454 kWh | £403 | £45 | £449 | £13,519 | 30.1 yrs | £-4,546 |
| 3 kW | 2961 kWh | 2280 kWh | 681 kWh | £605 | £68 | £673 | £15,554 | 23.1 yrs | £-2,094 |
| 4 kW | 3948 kWh | 3040 kWh | 908 kWh | £807 | £91 | £897 | £17,588 | 19.6 yrs | £359 |
| 5 kW | 4935 kWh | 3800 kWh | 1135 kWh | £1,008 | £114 | £1,122 | £19,623 | 17.5 yrs | £2,811 |
| 6 kW | 5922 kWh | 4560 kWh | 1362 kWh | £1,210 | £136 | £1,346 | £21,657 | 16.1 yrs | £5,263 |
| 7 kW | 6909 kWh | 5320 kWh | 1589 kWh | £1,411 | £159 | £1,570 | £23,692 | 15.1 yrs | £7,715 |
| 8 kW | 7896 kWh | 6080 kWh | 1816 kWh | £1,613 | £182 | £1,795 | £25,726 | 14.3 yrs | £10,167 |
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.