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 970 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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: £782, Upfront: £10,173, Break-even: 13.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1939 kWh | 776 kWh | 1164 kWh | £196 | £116 | £313 | £4,069 | 13.0 yrs | £2,188 |
| 3 kW | 2909 kWh | 1164 kWh | 1745 kWh | £295 | £175 | £469 | £6,104 | 13.0 yrs | £3,282 |
| 4 kW | 3879 kWh | 1552 kWh | 2327 kWh | £393 | £233 | £626 | £8,138 | 13.0 yrs | £4,376 |
| 5 kW | 4848 kWh | 1939 kWh | 2909 kWh | £491 | £291 | £782 | £10,173 | 13.0 yrs | £5,470 |
| 6 kW | 5818 kWh | 2327 kWh | 3491 kWh | £589 | £349 | £939 | £12,207 | 13.0 yrs | £6,565 |
| 7 kW | 6788 kWh | 2715 kWh | 4073 kWh | £688 | £407 | £1,095 | £14,242 | 13.0 yrs | £7,659 |
| 8 kW | 7758 kWh | 3103 kWh | 4655 kWh | £786 | £465 | £1,251 | £16,276 | 13.0 yrs | £8,753 |
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: £931, Upfront: £12,273, Break-even: 13.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1939 kWh | 1164 kWh | 776 kWh | £295 | £78 | £372 | £6,169 | 16.6 yrs | £1,277 |
| 3 kW | 2909 kWh | 1745 kWh | 1164 kWh | £442 | £116 | £558 | £8,204 | 14.7 yrs | £2,966 |
| 4 kW | 3879 kWh | 2327 kWh | 1552 kWh | £589 | £155 | £745 | £10,238 | 13.7 yrs | £4,655 |
| 5 kW | 4848 kWh | 2909 kWh | 1939 kWh | £737 | £194 | £931 | £12,273 | 13.2 yrs | £6,344 |
| 6 kW | 5818 kWh | 3491 kWh | 2327 kWh | £884 | £233 | £1,117 | £14,307 | 12.8 yrs | £8,032 |
| 7 kW | 6788 kWh | 4073 kWh | 2715 kWh | £1,032 | £272 | £1,303 | £16,342 | 12.5 yrs | £9,721 |
| 8 kW | 7758 kWh | 4655 kWh | 3103 kWh | £1,179 | £310 | £1,489 | £18,376 | 12.3 yrs | £11,410 |
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: £1,005, Upfront: £13,673, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1939 kWh | 1358 kWh | 582 kWh | £344 | £58 | £402 | £7,569 | 18.8 yrs | £472 |
| 3 kW | 2909 kWh | 2036 kWh | 873 kWh | £516 | £87 | £603 | £9,604 | 15.9 yrs | £2,458 |
| 4 kW | 3879 kWh | 2715 kWh | 1164 kWh | £688 | £116 | £804 | £11,638 | 14.5 yrs | £4,444 |
| 5 kW | 4848 kWh | 3394 kWh | 1455 kWh | £860 | £145 | £1,005 | £13,673 | 13.6 yrs | £6,430 |
| 6 kW | 5818 kWh | 4073 kWh | 1745 kWh | £1,032 | £175 | £1,206 | £15,707 | 13.0 yrs | £8,416 |
| 7 kW | 6788 kWh | 4751 kWh | 2036 kWh | £1,204 | £204 | £1,407 | £17,742 | 12.6 yrs | £10,402 |
| 8 kW | 7758 kWh | 5430 kWh | 2327 kWh | £1,375 | £233 | £1,608 | £19,776 | 12.3 yrs | £12,388 |
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: £1,027, Upfront: £15,423, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1939 kWh | 1416 kWh | 524 kWh | £359 | £52 | £411 | £9,319 | 22.7 yrs | £-1,100 |
| 3 kW | 2909 kWh | 2124 kWh | 785 kWh | £538 | £79 | £616 | £11,354 | 18.4 yrs | £976 |
| 4 kW | 3879 kWh | 2831 kWh | 1047 kWh | £717 | £105 | £822 | £13,388 | 16.3 yrs | £3,051 |
| 5 kW | 4848 kWh | 3539 kWh | 1309 kWh | £897 | £131 | £1,027 | £15,423 | 15.0 yrs | £5,126 |
| 6 kW | 5818 kWh | 4247 kWh | 1571 kWh | £1,076 | £157 | £1,233 | £17,457 | 14.2 yrs | £7,201 |
| 7 kW | 6788 kWh | 4955 kWh | 1833 kWh | £1,255 | £183 | £1,438 | £19,492 | 13.6 yrs | £9,276 |
| 8 kW | 7758 kWh | 5663 kWh | 2095 kWh | £1,434 | £209 | £1,644 | £21,526 | 13.1 yrs | £11,352 |
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: £1,042, Upfront: £17,173, Break-even: 16.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1939 kWh | 1455 kWh | 485 kWh | £368 | £48 | £417 | £11,069 | 26.5 yrs | £-2,731 |
| 3 kW | 2909 kWh | 2182 kWh | 727 kWh | £553 | £73 | £625 | £13,104 | 21.0 yrs | £-596 |
| 4 kW | 3879 kWh | 2909 kWh | 970 kWh | £737 | £97 | £834 | £15,138 | 18.2 yrs | £1,539 |
| 5 kW | 4848 kWh | 3636 kWh | 1212 kWh | £921 | £121 | £1,042 | £17,173 | 16.5 yrs | £3,673 |
| 6 kW | 5818 kWh | 4364 kWh | 1455 kWh | £1,105 | £145 | £1,251 | £19,207 | 15.4 yrs | £5,808 |
| 7 kW | 6788 kWh | 5091 kWh | 1697 kWh | £1,290 | £170 | £1,459 | £21,242 | 14.6 yrs | £7,943 |
| 8 kW | 7758 kWh | 5818 kWh | 1939 kWh | £1,474 | £194 | £1,668 | £23,276 | 14.0 yrs | £10,077 |
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: £1,057, Upfront: £19,623, 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 | 1939 kWh | 1493 kWh | 446 kWh | £378 | £45 | £423 | £13,519 | 32.0 yrs | £-5,062 |
| 3 kW | 2909 kWh | 2240 kWh | 669 kWh | £567 | £67 | £634 | £15,554 | 24.5 yrs | £-2,868 |
| 4 kW | 3879 kWh | 2987 kWh | 892 kWh | £757 | £89 | £846 | £17,588 | 20.8 yrs | £-673 |
| 5 kW | 4848 kWh | 3733 kWh | 1115 kWh | £946 | £112 | £1,057 | £19,623 | 18.6 yrs | £1,521 |
| 6 kW | 5818 kWh | 4480 kWh | 1338 kWh | £1,135 | £134 | £1,269 | £21,657 | 17.1 yrs | £3,715 |
| 7 kW | 6788 kWh | 5227 kWh | 1561 kWh | £1,324 | £156 | £1,480 | £23,692 | 16.0 yrs | £5,909 |
| 8 kW | 7758 kWh | 5973 kWh | 1784 kWh | £1,513 | £178 | £1,691 | £25,726 | 15.2 yrs | £8,103 |
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.