A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 910 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £736, 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 | 1820 kWh | 728 kWh | 1092 kWh | £185 | £109 | £294 | £4,069 | 13.8 yrs | £1,816 |
| 3 kW | 2729 kWh | 1092 kWh | 1638 kWh | £278 | £164 | £441 | £6,104 | 13.8 yrs | £2,725 |
| 4 kW | 3639 kWh | 1456 kWh | 2184 kWh | £370 | £218 | £589 | £8,138 | 13.8 yrs | £3,633 |
| 5 kW | 4549 kWh | 1820 kWh | 2729 kWh | £463 | £273 | £736 | £10,173 | 13.8 yrs | £4,541 |
| 6 kW | 5459 kWh | 2184 kWh | 3275 kWh | £555 | £328 | £883 | £12,207 | 13.8 yrs | £5,449 |
| 7 kW | 6369 kWh | 2547 kWh | 3821 kWh | £648 | £382 | £1,030 | £14,242 | 13.8 yrs | £6,357 |
| 8 kW | 7279 kWh | 2911 kWh | 4367 kWh | £740 | £437 | £1,177 | £16,276 | 13.8 yrs | £7,266 |
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: £876, 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 | 1820 kWh | 1092 kWh | 728 kWh | £278 | £73 | £350 | £6,169 | 17.6 yrs | £840 |
| 3 kW | 2729 kWh | 1638 kWh | 1092 kWh | £416 | £109 | £526 | £8,204 | 15.6 yrs | £2,309 |
| 4 kW | 3639 kWh | 2184 kWh | 1456 kWh | £555 | £146 | £701 | £10,238 | 14.6 yrs | £3,779 |
| 5 kW | 4549 kWh | 2729 kWh | 1820 kWh | £694 | £182 | £876 | £12,273 | 14.0 yrs | £5,249 |
| 6 kW | 5459 kWh | 3275 kWh | 2184 kWh | £833 | £218 | £1,051 | £14,307 | 13.6 yrs | £6,719 |
| 7 kW | 6369 kWh | 3821 kWh | 2547 kWh | £972 | £255 | £1,226 | £16,342 | 13.3 yrs | £8,188 |
| 8 kW | 7279 kWh | 4367 kWh | 2911 kWh | £1,111 | £291 | £1,402 | £18,376 | 13.1 yrs | £9,658 |
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: £946, 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 | 1820 kWh | 1274 kWh | 546 kWh | £324 | £55 | £379 | £7,569 | 20.0 yrs | £1 |
| 3 kW | 2729 kWh | 1911 kWh | 819 kWh | £486 | £82 | £568 | £9,604 | 16.9 yrs | £1,752 |
| 4 kW | 3639 kWh | 2547 kWh | 1092 kWh | £648 | £109 | £757 | £11,638 | 15.4 yrs | £3,502 |
| 5 kW | 4549 kWh | 3184 kWh | 1365 kWh | £810 | £136 | £946 | £13,673 | 14.4 yrs | £5,253 |
| 6 kW | 5459 kWh | 3821 kWh | 1638 kWh | £972 | £164 | £1,136 | £15,707 | 13.8 yrs | £7,003 |
| 7 kW | 6369 kWh | 4458 kWh | 1911 kWh | £1,134 | £191 | £1,325 | £17,742 | 13.4 yrs | £8,754 |
| 8 kW | 7279 kWh | 5095 kWh | 2184 kWh | £1,296 | £218 | £1,514 | £19,776 | 13.1 yrs | £10,504 |
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: £967, 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 | 1820 kWh | 1328 kWh | 491 kWh | £338 | £49 | £387 | £9,319 | 24.1 yrs | £-1,580 |
| 3 kW | 2729 kWh | 1993 kWh | 737 kWh | £507 | £74 | £580 | £11,354 | 19.6 yrs | £254 |
| 4 kW | 3639 kWh | 2657 kWh | 983 kWh | £676 | £98 | £774 | £13,388 | 17.3 yrs | £2,089 |
| 5 kW | 4549 kWh | 3321 kWh | 1228 kWh | £844 | £123 | £967 | £15,423 | 15.9 yrs | £3,924 |
| 6 kW | 5459 kWh | 3985 kWh | 1474 kWh | £1,013 | £147 | £1,161 | £17,457 | 15.0 yrs | £5,759 |
| 7 kW | 6369 kWh | 4649 kWh | 1720 kWh | £1,182 | £172 | £1,354 | £19,492 | 14.4 yrs | £7,593 |
| 8 kW | 7279 kWh | 5313 kWh | 1965 kWh | £1,351 | £197 | £1,548 | £21,526 | 13.9 yrs | £9,428 |
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: £981, 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 | 1820 kWh | 1365 kWh | 455 kWh | £347 | £45 | £393 | £11,069 | 28.2 yrs | £-3,218 |
| 3 kW | 2729 kWh | 2047 kWh | 682 kWh | £521 | £68 | £589 | £13,104 | 22.3 yrs | £-1,327 |
| 4 kW | 3639 kWh | 2729 kWh | 910 kWh | £694 | £91 | £785 | £15,138 | 19.3 yrs | £564 |
| 5 kW | 4549 kWh | 3412 kWh | 1137 kWh | £868 | £114 | £981 | £17,173 | 17.5 yrs | £2,455 |
| 6 kW | 5459 kWh | 4094 kWh | 1365 kWh | £1,041 | £136 | £1,178 | £19,207 | 16.3 yrs | £4,345 |
| 7 kW | 6369 kWh | 4777 kWh | 1592 kWh | £1,215 | £159 | £1,374 | £21,242 | 15.5 yrs | £6,236 |
| 8 kW | 7279 kWh | 5459 kWh | 1820 kWh | £1,388 | £182 | £1,570 | £23,276 | 14.8 yrs | £8,127 |
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: £995, 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 | 1820 kWh | 1401 kWh | 419 kWh | £356 | £42 | £398 | £13,519 | 34.0 yrs | £-5,556 |
| 3 kW | 2729 kWh | 2102 kWh | 628 kWh | £534 | £63 | £597 | £15,554 | 26.0 yrs | £-3,609 |
| 4 kW | 3639 kWh | 2802 kWh | 837 kWh | £713 | £84 | £796 | £17,588 | 22.1 yrs | £-1,662 |
| 5 kW | 4549 kWh | 3503 kWh | 1046 kWh | £891 | £105 | £995 | £19,623 | 19.7 yrs | £285 |
| 6 kW | 5459 kWh | 4203 kWh | 1256 kWh | £1,069 | £126 | £1,194 | £21,657 | 18.1 yrs | £2,232 |
| 7 kW | 6369 kWh | 4904 kWh | 1465 kWh | £1,247 | £146 | £1,394 | £23,692 | 17.0 yrs | £4,179 |
| 8 kW | 7279 kWh | 5604 kWh | 1674 kWh | £1,425 | £167 | £1,593 | £25,726 | 16.2 yrs | £6,126 |
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.