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 1076 kWh per year on a south-facing roof. We value self-used electricity at 26.8p 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: £900, Upfront: £10,173, Break-even: 11.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2152 kWh | 861 kWh | 1291 kWh | £231 | £129 | £360 | £4,069 | 11.3 yrs | £3,129 |
| 3 kW | 3227 kWh | 1291 kWh | 1936 kWh | £346 | £194 | £540 | £6,104 | 11.3 yrs | £4,694 |
| 4 kW | 4303 kWh | 1721 kWh | 2582 kWh | £462 | £258 | £720 | £8,138 | 11.3 yrs | £6,258 |
| 5 kW | 5379 kWh | 2152 kWh | 3227 kWh | £577 | £323 | £900 | £10,173 | 11.3 yrs | £7,823 |
| 6 kW | 6455 kWh | 2582 kWh | 3873 kWh | £692 | £387 | £1,080 | £12,207 | 11.3 yrs | £9,388 |
| 7 kW | 7530 kWh | 3012 kWh | 4518 kWh | £808 | £452 | £1,260 | £14,242 | 11.3 yrs | £10,952 |
| 8 kW | 8606 kWh | 3442 kWh | 5164 kWh | £923 | £516 | £1,440 | £16,276 | 11.3 yrs | £12,517 |
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: £1,081, Upfront: £12,273, Break-even: 11.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2152 kWh | 1291 kWh | 861 kWh | £346 | £86 | £432 | £6,169 | 14.3 yrs | £2,477 |
| 3 kW | 3227 kWh | 1936 kWh | 1291 kWh | £519 | £129 | £648 | £8,204 | 12.7 yrs | £4,765 |
| 4 kW | 4303 kWh | 2582 kWh | 1721 kWh | £692 | £172 | £865 | £10,238 | 11.8 yrs | £7,054 |
| 5 kW | 5379 kWh | 3227 kWh | 2152 kWh | £866 | £215 | £1,081 | £12,273 | 11.4 yrs | £9,342 |
| 6 kW | 6455 kWh | 3873 kWh | 2582 kWh | £1,039 | £258 | £1,297 | £14,307 | 11.0 yrs | £11,630 |
| 7 kW | 7530 kWh | 4518 kWh | 3012 kWh | £1,212 | £301 | £1,513 | £16,342 | 10.8 yrs | £13,919 |
| 8 kW | 8606 kWh | 5164 kWh | 3442 kWh | £1,385 | £344 | £1,729 | £18,376 | 10.6 yrs | £16,207 |
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: £1,171, Upfront: £13,673, Break-even: 11.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2152 kWh | 1506 kWh | 645 kWh | £404 | £65 | £468 | £7,569 | 16.2 yrs | £1,801 |
| 3 kW | 3227 kWh | 2259 kWh | 968 kWh | £606 | £97 | £703 | £9,604 | 13.7 yrs | £4,451 |
| 4 kW | 4303 kWh | 3012 kWh | 1291 kWh | £808 | £129 | £937 | £11,638 | 12.4 yrs | £7,101 |
| 5 kW | 5379 kWh | 3765 kWh | 1614 kWh | £1,010 | £161 | £1,171 | £13,673 | 11.7 yrs | £9,751 |
| 6 kW | 6455 kWh | 4518 kWh | 1936 kWh | £1,212 | £194 | £1,405 | £15,707 | 11.2 yrs | £12,402 |
| 7 kW | 7530 kWh | 5271 kWh | 2259 kWh | £1,414 | £226 | £1,640 | £17,742 | 10.8 yrs | £15,052 |
| 8 kW | 8606 kWh | 6024 kWh | 2582 kWh | £1,616 | £258 | £1,874 | £19,776 | 10.6 yrs | £17,702 |
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: £1,198, Upfront: £15,423, Break-even: 12.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2152 kWh | 1571 kWh | 581 kWh | £421 | £58 | £479 | £9,319 | 19.4 yrs | £268 |
| 3 kW | 3227 kWh | 2356 kWh | 871 kWh | £632 | £87 | £719 | £11,354 | 15.8 yrs | £3,027 |
| 4 kW | 4303 kWh | 3141 kWh | 1162 kWh | £842 | £116 | £959 | £13,388 | 14.0 yrs | £5,785 |
| 5 kW | 5379 kWh | 3927 kWh | 1452 kWh | £1,053 | £145 | £1,198 | £15,423 | 12.9 yrs | £8,544 |
| 6 kW | 6455 kWh | 4712 kWh | 1743 kWh | £1,264 | £174 | £1,438 | £17,457 | 12.1 yrs | £11,303 |
| 7 kW | 7530 kWh | 5497 kWh | 2033 kWh | £1,474 | £203 | £1,678 | £19,492 | 11.6 yrs | £14,062 |
| 8 kW | 8606 kWh | 6283 kWh | 2324 kWh | £1,685 | £232 | £1,917 | £21,526 | 11.2 yrs | £16,821 |
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: £1,216, Upfront: £17,173, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2152 kWh | 1614 kWh | 538 kWh | £433 | £54 | £487 | £11,069 | 22.7 yrs | £-1,338 |
| 3 kW | 3227 kWh | 2421 kWh | 807 kWh | £649 | £81 | £730 | £13,104 | 18.0 yrs | £1,494 |
| 4 kW | 4303 kWh | 3227 kWh | 1076 kWh | £866 | £108 | £973 | £15,138 | 15.6 yrs | £4,325 |
| 5 kW | 5379 kWh | 4034 kWh | 1345 kWh | £1,082 | £134 | £1,216 | £17,173 | 14.1 yrs | £7,156 |
| 6 kW | 6455 kWh | 4841 kWh | 1614 kWh | £1,298 | £161 | £1,460 | £19,207 | 13.2 yrs | £9,987 |
| 7 kW | 7530 kWh | 5648 kWh | 1883 kWh | £1,515 | £188 | £1,703 | £21,242 | 12.5 yrs | £12,819 |
| 8 kW | 8606 kWh | 6455 kWh | 2152 kWh | £1,731 | £215 | £1,946 | £23,276 | 12.0 yrs | £15,650 |
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: £1,235, Upfront: £19,623, 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 | 2152 kWh | 1657 kWh | 495 kWh | £444 | £49 | £494 | £13,519 | 27.4 yrs | £-3,643 |
| 3 kW | 3227 kWh | 2485 kWh | 742 kWh | £666 | £74 | £741 | £15,554 | 21.0 yrs | £-739 |
| 4 kW | 4303 kWh | 3313 kWh | 990 kWh | £889 | £99 | £988 | £17,588 | 17.8 yrs | £2,164 |
| 5 kW | 5379 kWh | 4142 kWh | 1237 kWh | £1,111 | £124 | £1,235 | £19,623 | 15.9 yrs | £5,068 |
| 6 kW | 6455 kWh | 4970 kWh | 1485 kWh | £1,333 | £148 | £1,481 | £21,657 | 14.6 yrs | £7,972 |
| 7 kW | 7530 kWh | 5798 kWh | 1732 kWh | £1,555 | £173 | £1,728 | £23,692 | 13.7 yrs | £10,875 |
| 8 kW | 8606 kWh | 6627 kWh | 1979 kWh | £1,777 | £198 | £1,975 | £25,726 | 13.0 yrs | £13,779 |
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.