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 836 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: £683, Upfront: £10,173, 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 | 1672 kWh | 669 kWh | 1003 kWh | £173 | £100 | £273 | £4,069 | 14.9 yrs | £1,393 |
| 3 kW | 2508 kWh | 1003 kWh | 1505 kWh | £259 | £150 | £410 | £6,104 | 14.9 yrs | £2,089 |
| 4 kW | 3343 kWh | 1337 kWh | 2006 kWh | £346 | £201 | £546 | £8,138 | 14.9 yrs | £2,785 |
| 5 kW | 4179 kWh | 1672 kWh | 2508 kWh | £432 | £251 | £683 | £10,173 | 14.9 yrs | £3,482 |
| 6 kW | 5015 kWh | 2006 kWh | 3009 kWh | £518 | £301 | £819 | £12,207 | 14.9 yrs | £4,178 |
| 7 kW | 5851 kWh | 2340 kWh | 3511 kWh | £605 | £351 | £956 | £14,242 | 14.9 yrs | £4,874 |
| 8 kW | 6687 kWh | 2675 kWh | 4012 kWh | £691 | £401 | £1,092 | £16,276 | 14.9 yrs | £5,571 |
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: £815, Upfront: £12,273, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1672 kWh | 1003 kWh | 669 kWh | £259 | £67 | £326 | £6,169 | 18.9 yrs | £352 |
| 3 kW | 2508 kWh | 1505 kWh | 1003 kWh | £389 | £100 | £489 | £8,204 | 16.8 yrs | £1,578 |
| 4 kW | 3343 kWh | 2006 kWh | 1337 kWh | £518 | £134 | £652 | £10,238 | 15.7 yrs | £2,804 |
| 5 kW | 4179 kWh | 2508 kWh | 1672 kWh | £648 | £167 | £815 | £12,273 | 15.1 yrs | £4,030 |
| 6 kW | 5015 kWh | 3009 kWh | 2006 kWh | £778 | £201 | £978 | £14,307 | 14.6 yrs | £5,256 |
| 7 kW | 5851 kWh | 3511 kWh | 2340 kWh | £907 | £234 | £1,141 | £16,342 | 14.3 yrs | £6,482 |
| 8 kW | 6687 kWh | 4012 kWh | 2675 kWh | £1,037 | £267 | £1,304 | £18,376 | 14.1 yrs | £7,707 |
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: £881, Upfront: £13,673, 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 | 1672 kWh | 1170 kWh | 502 kWh | £302 | £50 | £353 | £7,569 | 21.5 yrs | £-519 |
| 3 kW | 2508 kWh | 1755 kWh | 752 kWh | £454 | £75 | £529 | £9,604 | 18.2 yrs | £972 |
| 4 kW | 3343 kWh | 2340 kWh | 1003 kWh | £605 | £100 | £705 | £11,638 | 16.5 yrs | £2,463 |
| 5 kW | 4179 kWh | 2925 kWh | 1254 kWh | £756 | £125 | £881 | £13,673 | 15.5 yrs | £3,954 |
| 6 kW | 5015 kWh | 3511 kWh | 1505 kWh | £907 | £150 | £1,058 | £15,707 | 14.9 yrs | £5,444 |
| 7 kW | 5851 kWh | 4096 kWh | 1755 kWh | £1,058 | £176 | £1,234 | £17,742 | 14.4 yrs | £6,935 |
| 8 kW | 6687 kWh | 4681 kWh | 2006 kWh | £1,209 | £201 | £1,410 | £19,776 | 14.0 yrs | £8,426 |
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: £901, Upfront: £15,423, Break-even: 17.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1672 kWh | 1220 kWh | 451 kWh | £315 | £45 | £360 | £9,319 | 25.9 yrs | £-2,110 |
| 3 kW | 2508 kWh | 1830 kWh | 677 kWh | £473 | £68 | £541 | £11,354 | 21.0 yrs | £-539 |
| 4 kW | 3343 kWh | 2441 kWh | 903 kWh | £631 | £90 | £721 | £13,388 | 18.6 yrs | £1,031 |
| 5 kW | 4179 kWh | 3051 kWh | 1128 kWh | £788 | £113 | £901 | £15,423 | 17.1 yrs | £2,601 |
| 6 kW | 5015 kWh | 3661 kWh | 1354 kWh | £946 | £135 | £1,081 | £17,457 | 16.1 yrs | £4,171 |
| 7 kW | 5851 kWh | 4271 kWh | 1580 kWh | £1,104 | £158 | £1,262 | £19,492 | 15.4 yrs | £5,741 |
| 8 kW | 6687 kWh | 4881 kWh | 1805 kWh | £1,261 | £181 | £1,442 | £21,526 | 14.9 yrs | £7,311 |
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: £914, Upfront: £17,173, Break-even: 18.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1672 kWh | 1254 kWh | 418 kWh | £324 | £42 | £366 | £11,069 | 30.3 yrs | £-3,754 |
| 3 kW | 2508 kWh | 1881 kWh | 627 kWh | £486 | £63 | £549 | £13,104 | 23.9 yrs | £-2,131 |
| 4 kW | 3343 kWh | 2508 kWh | 836 kWh | £648 | £84 | £732 | £15,138 | 20.7 yrs | £-507 |
| 5 kW | 4179 kWh | 3134 kWh | 1045 kWh | £810 | £104 | £914 | £17,173 | 18.8 yrs | £1,116 |
| 6 kW | 5015 kWh | 3761 kWh | 1254 kWh | £972 | £125 | £1,097 | £19,207 | 17.5 yrs | £2,739 |
| 7 kW | 5851 kWh | 4388 kWh | 1463 kWh | £1,134 | £146 | £1,280 | £21,242 | 16.6 yrs | £4,362 |
| 8 kW | 6687 kWh | 5015 kWh | 1672 kWh | £1,296 | £167 | £1,463 | £23,276 | 15.9 yrs | £5,985 |
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: £928, Upfront: £19,623, Break-even: 21.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1672 kWh | 1287 kWh | 384 kWh | £333 | £38 | £371 | £13,519 | 36.4 yrs | £-6,098 |
| 3 kW | 2508 kWh | 1931 kWh | 577 kWh | £499 | £58 | £557 | £15,554 | 27.9 yrs | £-4,422 |
| 4 kW | 3343 kWh | 2574 kWh | 769 kWh | £665 | £77 | £742 | £17,588 | 23.7 yrs | £-2,746 |
| 5 kW | 4179 kWh | 3218 kWh | 961 kWh | £832 | £96 | £928 | £19,623 | 21.2 yrs | £-1,070 |
| 6 kW | 5015 kWh | 3862 kWh | 1153 kWh | £998 | £115 | £1,113 | £21,657 | 19.5 yrs | £607 |
| 7 kW | 5851 kWh | 4505 kWh | 1346 kWh | £1,164 | £135 | £1,299 | £23,692 | 18.2 yrs | £2,283 |
| 8 kW | 6687 kWh | 5149 kWh | 1538 kWh | £1,330 | £154 | £1,484 | £25,726 | 17.3 yrs | £3,959 |
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.