A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 915 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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: £738, Upfront: £10,173, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1830 kWh | 732 kWh | 1098 kWh | £185 | £110 | £295 | £4,069 | 13.8 yrs | £1,835 |
| 3 kW | 2745 kWh | 1098 kWh | 1647 kWh | £278 | £165 | £443 | £6,104 | 13.8 yrs | £2,753 |
| 4 kW | 3660 kWh | 1464 kWh | 2196 kWh | £371 | £220 | £590 | £8,138 | 13.8 yrs | £3,671 |
| 5 kW | 4575 kWh | 1830 kWh | 2745 kWh | £464 | £274 | £738 | £10,173 | 13.8 yrs | £4,588 |
| 6 kW | 5490 kWh | 2196 kWh | 3294 kWh | £556 | £329 | £886 | £12,207 | 13.8 yrs | £5,506 |
| 7 kW | 6405 kWh | 2562 kWh | 3843 kWh | £649 | £384 | £1,033 | £14,242 | 13.8 yrs | £6,424 |
| 8 kW | 7320 kWh | 2928 kWh | 4392 kWh | £742 | £439 | £1,181 | £16,276 | 13.8 yrs | £7,341 |
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: £878, Upfront: £12,273, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1830 kWh | 1098 kWh | 732 kWh | £278 | £73 | £351 | £6,169 | 17.6 yrs | £857 |
| 3 kW | 2745 kWh | 1647 kWh | 1098 kWh | £417 | £110 | £527 | £8,204 | 15.6 yrs | £2,336 |
| 4 kW | 3660 kWh | 2196 kWh | 1464 kWh | £556 | £146 | £703 | £10,238 | 14.6 yrs | £3,815 |
| 5 kW | 4575 kWh | 2745 kWh | 1830 kWh | £695 | £183 | £878 | £12,273 | 14.0 yrs | £5,294 |
| 6 kW | 5490 kWh | 3294 kWh | 2196 kWh | £834 | £220 | £1,054 | £14,307 | 13.6 yrs | £6,772 |
| 7 kW | 6405 kWh | 3843 kWh | 2562 kWh | £973 | £256 | £1,230 | £16,342 | 13.3 yrs | £8,251 |
| 8 kW | 7320 kWh | 4392 kWh | 2928 kWh | £1,112 | £293 | £1,405 | £18,376 | 13.1 yrs | £9,730 |
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: £948, Upfront: £13,673, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1830 kWh | 1281 kWh | 549 kWh | £324 | £55 | £379 | £7,569 | 20.0 yrs | £19 |
| 3 kW | 2745 kWh | 1921 kWh | 824 kWh | £487 | £82 | £569 | £9,604 | 16.9 yrs | £1,778 |
| 4 kW | 3660 kWh | 2562 kWh | 1098 kWh | £649 | £110 | £759 | £11,638 | 15.3 yrs | £3,537 |
| 5 kW | 4575 kWh | 3202 kWh | 1372 kWh | £811 | £137 | £948 | £13,673 | 14.4 yrs | £5,296 |
| 6 kW | 5490 kWh | 3843 kWh | 1647 kWh | £973 | £165 | £1,138 | £15,707 | 13.8 yrs | £7,056 |
| 7 kW | 6405 kWh | 4484 kWh | 1922 kWh | £1,136 | £192 | £1,328 | £17,742 | 13.4 yrs | £8,815 |
| 8 kW | 7320 kWh | 5124 kWh | 2196 kWh | £1,298 | £220 | £1,518 | £19,776 | 13.0 yrs | £10,574 |
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: £969, Upfront: £15,423, Break-even: 15.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1830 kWh | 1336 kWh | 494 kWh | £338 | £49 | £388 | £9,319 | 24.0 yrs | £-1,563 |
| 3 kW | 2745 kWh | 2004 kWh | 741 kWh | £508 | £74 | £582 | £11,354 | 19.5 yrs | £280 |
| 4 kW | 3660 kWh | 2672 kWh | 988 kWh | £677 | £99 | £776 | £13,388 | 17.3 yrs | £2,124 |
| 5 kW | 4575 kWh | 3340 kWh | 1235 kWh | £846 | £124 | £969 | £15,423 | 15.9 yrs | £3,967 |
| 6 kW | 5490 kWh | 4008 kWh | 1482 kWh | £1,015 | £148 | £1,163 | £17,457 | 15.0 yrs | £5,811 |
| 7 kW | 6405 kWh | 4676 kWh | 1729 kWh | £1,184 | £173 | £1,357 | £19,492 | 14.4 yrs | £7,654 |
| 8 kW | 7320 kWh | 5344 kWh | 1976 kWh | £1,354 | £198 | £1,551 | £21,526 | 13.9 yrs | £9,497 |
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: £984, Upfront: £17,173, 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 | 1830 kWh | 1372 kWh | 458 kWh | £348 | £46 | £393 | £11,069 | 28.1 yrs | £-3,201 |
| 3 kW | 2745 kWh | 2059 kWh | 686 kWh | £521 | £69 | £590 | £13,104 | 22.2 yrs | £-1,301 |
| 4 kW | 3660 kWh | 2745 kWh | 915 kWh | £695 | £92 | £787 | £15,138 | 19.2 yrs | £598 |
| 5 kW | 4575 kWh | 3431 kWh | 1144 kWh | £869 | £114 | £984 | £17,173 | 17.5 yrs | £2,498 |
| 6 kW | 5490 kWh | 4118 kWh | 1372 kWh | £1,043 | £137 | £1,180 | £19,207 | 16.3 yrs | £4,397 |
| 7 kW | 6405 kWh | 4804 kWh | 1601 kWh | £1,217 | £160 | £1,377 | £21,242 | 15.4 yrs | £6,297 |
| 8 kW | 7320 kWh | 5490 kWh | 1830 kWh | £1,391 | £183 | £1,574 | £23,276 | 14.8 yrs | £8,196 |
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: £998, Upfront: £19,623, Break-even: 19.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1830 kWh | 1409 kWh | 421 kWh | £357 | £42 | £399 | £13,519 | 33.9 yrs | £-5,539 |
| 3 kW | 2745 kWh | 2114 kWh | 631 kWh | £535 | £63 | £599 | £15,554 | 26.0 yrs | £-3,583 |
| 4 kW | 3660 kWh | 2818 kWh | 842 kWh | £714 | £84 | £798 | £17,588 | 22.0 yrs | £-1,627 |
| 5 kW | 4575 kWh | 3523 kWh | 1052 kWh | £892 | £105 | £998 | £19,623 | 19.7 yrs | £328 |
| 6 kW | 5490 kWh | 4227 kWh | 1263 kWh | £1,071 | £126 | £1,197 | £21,657 | 18.1 yrs | £2,284 |
| 7 kW | 6405 kWh | 4932 kWh | 1473 kWh | £1,249 | £147 | £1,397 | £23,692 | 17.0 yrs | £4,239 |
| 8 kW | 7320 kWh | 5636 kWh | 1684 kWh | £1,428 | £168 | £1,596 | £25,726 | 16.1 yrs | £6,195 |
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.