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 844 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £690, Upfront: £10,173, Break-even: 14.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1689 kWh | 676 kWh | 1013 kWh | £175 | £101 | £276 | £4,069 | 14.7 yrs | £1,449 |
| 3 kW | 2533 kWh | 1013 kWh | 1520 kWh | £262 | £152 | £414 | £6,104 | 14.7 yrs | £2,173 |
| 4 kW | 3378 kWh | 1351 kWh | 2027 kWh | £349 | £203 | £552 | £8,138 | 14.7 yrs | £2,898 |
| 5 kW | 4222 kWh | 1689 kWh | 2533 kWh | £436 | £253 | £690 | £10,173 | 14.7 yrs | £3,622 |
| 6 kW | 5067 kWh | 2027 kWh | 3040 kWh | £524 | £304 | £828 | £12,207 | 14.7 yrs | £4,346 |
| 7 kW | 5911 kWh | 2364 kWh | 3547 kWh | £611 | £355 | £966 | £14,242 | 14.7 yrs | £5,071 |
| 8 kW | 6755 kWh | 2702 kWh | 4053 kWh | £698 | £405 | £1,104 | £16,276 | 14.7 yrs | £5,795 |
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: £823, Upfront: £12,273, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1689 kWh | 1013 kWh | 676 kWh | £262 | £68 | £329 | £6,169 | 18.7 yrs | £419 |
| 3 kW | 2533 kWh | 1520 kWh | 1013 kWh | £393 | £101 | £494 | £8,204 | 16.6 yrs | £1,678 |
| 4 kW | 3378 kWh | 2027 kWh | 1351 kWh | £524 | £135 | £659 | £10,238 | 15.5 yrs | £2,938 |
| 5 kW | 4222 kWh | 2533 kWh | 1689 kWh | £655 | £169 | £823 | £12,273 | 14.9 yrs | £4,197 |
| 6 kW | 5067 kWh | 3040 kWh | 2027 kWh | £786 | £203 | £988 | £14,307 | 14.5 yrs | £5,457 |
| 7 kW | 5911 kWh | 3547 kWh | 2364 kWh | £916 | £236 | £1,153 | £16,342 | 14.2 yrs | £6,716 |
| 8 kW | 6755 kWh | 4053 kWh | 2702 kWh | £1,047 | £270 | £1,318 | £18,376 | 13.9 yrs | £7,976 |
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: £890, Upfront: £13,673, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1689 kWh | 1182 kWh | 507 kWh | £305 | £51 | £356 | £7,569 | 21.3 yrs | £-446 |
| 3 kW | 2533 kWh | 1773 kWh | 760 kWh | £458 | £76 | £534 | £9,604 | 18.0 yrs | £1,081 |
| 4 kW | 3378 kWh | 2364 kWh | 1013 kWh | £611 | £101 | £712 | £11,638 | 16.3 yrs | £2,608 |
| 5 kW | 4222 kWh | 2956 kWh | 1267 kWh | £764 | £127 | £890 | £13,673 | 15.4 yrs | £4,135 |
| 6 kW | 5067 kWh | 3547 kWh | 1520 kWh | £916 | £152 | £1,068 | £15,707 | 14.7 yrs | £5,662 |
| 7 kW | 5911 kWh | 4138 kWh | 1773 kWh | £1,069 | £177 | £1,247 | £17,742 | 14.2 yrs | £7,189 |
| 8 kW | 6755 kWh | 4729 kWh | 2027 kWh | £1,222 | £203 | £1,425 | £19,776 | 13.9 yrs | £8,716 |
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: £910, Upfront: £15,423, Break-even: 16.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1689 kWh | 1233 kWh | 456 kWh | £319 | £46 | £364 | £9,319 | 25.6 yrs | £-2,036 |
| 3 kW | 2533 kWh | 1849 kWh | 684 kWh | £478 | £68 | £546 | £11,354 | 20.8 yrs | £-428 |
| 4 kW | 3378 kWh | 2466 kWh | 912 kWh | £637 | £91 | £728 | £13,388 | 18.4 yrs | £1,179 |
| 5 kW | 4222 kWh | 3082 kWh | 1140 kWh | £796 | £114 | £910 | £15,423 | 16.9 yrs | £2,786 |
| 6 kW | 5067 kWh | 3699 kWh | 1368 kWh | £956 | £137 | £1,093 | £17,457 | 16.0 yrs | £4,393 |
| 7 kW | 5911 kWh | 4315 kWh | 1596 kWh | £1,115 | £160 | £1,275 | £19,492 | 15.3 yrs | £6,000 |
| 8 kW | 6755 kWh | 4931 kWh | 1824 kWh | £1,274 | £182 | £1,457 | £21,526 | 14.8 yrs | £7,608 |
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: £924, Upfront: £17,173, Break-even: 18.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1689 kWh | 1267 kWh | 422 kWh | £327 | £42 | £370 | £11,069 | 30.0 yrs | £-3,679 |
| 3 kW | 2533 kWh | 1900 kWh | 633 kWh | £491 | £63 | £554 | £13,104 | 23.6 yrs | £-2,018 |
| 4 kW | 3378 kWh | 2533 kWh | 844 kWh | £655 | £84 | £739 | £15,138 | 20.5 yrs | £-357 |
| 5 kW | 4222 kWh | 3167 kWh | 1056 kWh | £818 | £106 | £924 | £17,173 | 18.6 yrs | £1,304 |
| 6 kW | 5067 kWh | 3800 kWh | 1267 kWh | £982 | £127 | £1,109 | £19,207 | 17.3 yrs | £2,964 |
| 7 kW | 5911 kWh | 4433 kWh | 1478 kWh | £1,146 | £148 | £1,293 | £21,242 | 16.4 yrs | £4,625 |
| 8 kW | 6755 kWh | 5067 kWh | 1689 kWh | £1,309 | £169 | £1,478 | £23,276 | 15.7 yrs | £6,286 |
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: £937, Upfront: £19,623, Break-even: 20.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1689 kWh | 1300 kWh | 388 kWh | £336 | £39 | £375 | £13,519 | 36.1 yrs | £-6,022 |
| 3 kW | 2533 kWh | 1951 kWh | 583 kWh | £504 | £58 | £562 | £15,554 | 27.7 yrs | £-4,307 |
| 4 kW | 3378 kWh | 2601 kWh | 777 kWh | £672 | £78 | £750 | £17,588 | 23.5 yrs | £-2,593 |
| 5 kW | 4222 kWh | 3251 kWh | 971 kWh | £840 | £97 | £937 | £19,623 | 20.9 yrs | £-879 |
| 6 kW | 5067 kWh | 3901 kWh | 1165 kWh | £1,008 | £117 | £1,125 | £21,657 | 19.3 yrs | £835 |
| 7 kW | 5911 kWh | 4551 kWh | 1360 kWh | £1,176 | £136 | £1,312 | £23,692 | 18.1 yrs | £2,550 |
| 8 kW | 6755 kWh | 5202 kWh | 1554 kWh | £1,344 | £155 | £1,499 | £25,726 | 17.2 yrs | £4,264 |
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.