A typical roof here lands around 5.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 841 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £708, Upfront: £10,173, 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 | 1682 kWh | 673 kWh | 1009 kWh | £182 | £101 | £283 | £4,069 | 14.4 yrs | £1,591 |
| 3 kW | 2523 kWh | 1009 kWh | 1514 kWh | £273 | £151 | £425 | £6,104 | 14.4 yrs | £2,387 |
| 4 kW | 3365 kWh | 1346 kWh | 2019 kWh | £364 | £202 | £566 | £8,138 | 14.4 yrs | £3,183 |
| 5 kW | 4206 kWh | 1682 kWh | 2523 kWh | £455 | £252 | £708 | £10,173 | 14.4 yrs | £3,979 |
| 6 kW | 5047 kWh | 2019 kWh | 3028 kWh | £546 | £303 | £849 | £12,207 | 14.4 yrs | £4,774 |
| 7 kW | 5888 kWh | 2355 kWh | 3533 kWh | £637 | £353 | £991 | £14,242 | 14.4 yrs | £5,570 |
| 8 kW | 6729 kWh | 2692 kWh | 4037 kWh | £728 | £404 | £1,132 | £16,276 | 14.4 yrs | £6,366 |
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: £851, Upfront: £12,273, 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 | 1682 kWh | 1009 kWh | 673 kWh | £273 | £67 | £340 | £6,169 | 18.1 yrs | £639 |
| 3 kW | 2523 kWh | 1514 kWh | 1009 kWh | £410 | £101 | £511 | £8,204 | 16.1 yrs | £2,009 |
| 4 kW | 3365 kWh | 2019 kWh | 1346 kWh | £546 | £135 | £681 | £10,238 | 15.0 yrs | £3,379 |
| 5 kW | 4206 kWh | 2523 kWh | 1682 kWh | £683 | £168 | £851 | £12,273 | 14.4 yrs | £4,749 |
| 6 kW | 5047 kWh | 3028 kWh | 2019 kWh | £819 | £202 | £1,021 | £14,307 | 14.0 yrs | £6,118 |
| 7 kW | 5888 kWh | 3533 kWh | 2355 kWh | £956 | £236 | £1,191 | £16,342 | 13.7 yrs | £7,488 |
| 8 kW | 6729 kWh | 4037 kWh | 2692 kWh | £1,093 | £269 | £1,362 | £18,376 | 13.5 yrs | £8,858 |
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: £923, Upfront: £13,673, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1682 kWh | 1178 kWh | 505 kWh | £319 | £50 | £369 | £7,569 | 20.5 yrs | £-187 |
| 3 kW | 2523 kWh | 1766 kWh | 757 kWh | £478 | £76 | £554 | £9,604 | 17.3 yrs | £1,470 |
| 4 kW | 3365 kWh | 2355 kWh | 1009 kWh | £637 | £101 | £738 | £11,638 | 15.8 yrs | £3,127 |
| 5 kW | 4206 kWh | 2944 kWh | 1262 kWh | £797 | £126 | £923 | £13,673 | 14.8 yrs | £4,784 |
| 6 kW | 5047 kWh | 3533 kWh | 1514 kWh | £956 | £151 | £1,107 | £15,707 | 14.2 yrs | £6,440 |
| 7 kW | 5888 kWh | 4122 kWh | 1766 kWh | £1,115 | £177 | £1,292 | £17,742 | 13.7 yrs | £8,097 |
| 8 kW | 6729 kWh | 4710 kWh | 2019 kWh | £1,275 | £202 | £1,476 | £19,776 | 13.4 yrs | £9,754 |
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: £944, Upfront: £15,423, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1682 kWh | 1228 kWh | 454 kWh | £332 | £45 | £378 | £9,319 | 24.7 yrs | £-1,764 |
| 3 kW | 2523 kWh | 1842 kWh | 681 kWh | £498 | £68 | £567 | £11,354 | 20.0 yrs | £-22 |
| 4 kW | 3365 kWh | 2456 kWh | 908 kWh | £665 | £91 | £755 | £13,388 | 17.7 yrs | £1,721 |
| 5 kW | 4206 kWh | 3070 kWh | 1136 kWh | £831 | £114 | £944 | £15,423 | 16.3 yrs | £3,464 |
| 6 kW | 5047 kWh | 3684 kWh | 1363 kWh | £997 | £136 | £1,133 | £17,457 | 15.4 yrs | £5,207 |
| 7 kW | 5888 kWh | 4298 kWh | 1590 kWh | £1,163 | £159 | £1,322 | £19,492 | 14.7 yrs | £6,950 |
| 8 kW | 6729 kWh | 4912 kWh | 1817 kWh | £1,329 | £182 | £1,511 | £21,526 | 14.2 yrs | £8,692 |
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: £959, Upfront: £17,173, Break-even: 17.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1682 kWh | 1262 kWh | 421 kWh | £341 | £42 | £383 | £11,069 | 28.9 yrs | £-3,400 |
| 3 kW | 2523 kWh | 1893 kWh | 631 kWh | £512 | £63 | £575 | £13,104 | 22.8 yrs | £-1,599 |
| 4 kW | 3365 kWh | 2523 kWh | 841 kWh | £683 | £84 | £767 | £15,138 | 19.7 yrs | £201 |
| 5 kW | 4206 kWh | 3154 kWh | 1051 kWh | £854 | £105 | £959 | £17,173 | 17.9 yrs | £2,001 |
| 6 kW | 5047 kWh | 3785 kWh | 1262 kWh | £1,024 | £126 | £1,150 | £19,207 | 16.7 yrs | £3,801 |
| 7 kW | 5888 kWh | 4416 kWh | 1472 kWh | £1,195 | £147 | £1,342 | £21,242 | 15.8 yrs | £5,601 |
| 8 kW | 6729 kWh | 5047 kWh | 1682 kWh | £1,366 | £168 | £1,534 | £23,276 | 15.2 yrs | £7,402 |
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: £973, Upfront: £19,623, Break-even: 20.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1682 kWh | 1295 kWh | 387 kWh | £351 | £39 | £389 | £13,519 | 34.7 yrs | £-5,735 |
| 3 kW | 2523 kWh | 1943 kWh | 580 kWh | £526 | £58 | £584 | £15,554 | 26.6 yrs | £-3,877 |
| 4 kW | 3365 kWh | 2591 kWh | 774 kWh | £701 | £77 | £778 | £17,588 | 22.6 yrs | £-2,020 |
| 5 kW | 4206 kWh | 3238 kWh | 967 kWh | £876 | £97 | £973 | £19,623 | 20.2 yrs | £-162 |
| 6 kW | 5047 kWh | 3886 kWh | 1161 kWh | £1,052 | £116 | £1,168 | £21,657 | 18.5 yrs | £1,696 |
| 7 kW | 5888 kWh | 4534 kWh | 1354 kWh | £1,227 | £135 | £1,362 | £23,692 | 17.4 yrs | £3,553 |
| 8 kW | 6729 kWh | 5181 kWh | 1548 kWh | £1,402 | £155 | £1,557 | £25,726 | 16.5 yrs | £5,411 |
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.