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 933 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: £762, Upfront: £10,173, Break-even: 13.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1865 kWh | 746 kWh | 1119 kWh | £193 | £112 | £305 | £4,069 | 13.4 yrs | £2,025 |
| 3 kW | 2798 kWh | 1119 kWh | 1679 kWh | £289 | £168 | £457 | £6,104 | 13.4 yrs | £3,037 |
| 4 kW | 3730 kWh | 1492 kWh | 2238 kWh | £386 | £224 | £609 | £8,138 | 13.4 yrs | £4,049 |
| 5 kW | 4663 kWh | 1865 kWh | 2798 kWh | £482 | £280 | £762 | £10,173 | 13.4 yrs | £5,061 |
| 6 kW | 5595 kWh | 2238 kWh | 3357 kWh | £578 | £336 | £914 | £12,207 | 13.4 yrs | £6,074 |
| 7 kW | 6528 kWh | 2611 kWh | 3917 kWh | £675 | £392 | £1,066 | £14,242 | 13.4 yrs | £7,086 |
| 8 kW | 7460 kWh | 2984 kWh | 4476 kWh | £771 | £448 | £1,219 | £16,276 | 13.4 yrs | £8,098 |
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: £909, Upfront: £12,273, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1865 kWh | 1119 kWh | 746 kWh | £289 | £75 | £364 | £6,169 | 17.0 yrs | £1,106 |
| 3 kW | 2798 kWh | 1679 kWh | 1119 kWh | £434 | £112 | £546 | £8,204 | 15.0 yrs | £2,709 |
| 4 kW | 3730 kWh | 2238 kWh | 1492 kWh | £578 | £149 | £728 | £10,238 | 14.1 yrs | £4,312 |
| 5 kW | 4663 kWh | 2798 kWh | 1865 kWh | £723 | £187 | £909 | £12,273 | 13.5 yrs | £5,916 |
| 6 kW | 5595 kWh | 3357 kWh | 2238 kWh | £867 | £224 | £1,091 | £14,307 | 13.1 yrs | £7,519 |
| 7 kW | 6528 kWh | 3917 kWh | 2611 kWh | £1,012 | £261 | £1,273 | £16,342 | 12.8 yrs | £9,122 |
| 8 kW | 7460 kWh | 4476 kWh | 2984 kWh | £1,157 | £298 | £1,455 | £18,376 | 12.6 yrs | £10,725 |
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: £983, Upfront: £13,673, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1865 kWh | 1306 kWh | 560 kWh | £337 | £56 | £393 | £7,569 | 19.2 yrs | £297 |
| 3 kW | 2798 kWh | 1958 kWh | 839 kWh | £506 | £84 | £590 | £9,604 | 16.3 yrs | £2,196 |
| 4 kW | 3730 kWh | 2611 kWh | 1119 kWh | £675 | £112 | £787 | £11,638 | 14.8 yrs | £4,094 |
| 5 kW | 4663 kWh | 3264 kWh | 1399 kWh | £843 | £140 | £983 | £13,673 | 13.9 yrs | £5,993 |
| 6 kW | 5595 kWh | 3917 kWh | 1679 kWh | £1,012 | £168 | £1,180 | £15,707 | 13.3 yrs | £7,891 |
| 7 kW | 6528 kWh | 4569 kWh | 1958 kWh | £1,181 | £196 | £1,377 | £17,742 | 12.9 yrs | £9,790 |
| 8 kW | 7460 kWh | 5222 kWh | 2238 kWh | £1,349 | £224 | £1,573 | £19,776 | 12.6 yrs | £11,688 |
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: £1,005, Upfront: £15,423, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1865 kWh | 1361 kWh | 504 kWh | £352 | £50 | £402 | £9,319 | 23.2 yrs | £-1,276 |
| 3 kW | 2798 kWh | 2042 kWh | 755 kWh | £528 | £76 | £603 | £11,354 | 18.8 yrs | £711 |
| 4 kW | 3730 kWh | 2723 kWh | 1007 kWh | £704 | £101 | £804 | £13,388 | 16.6 yrs | £2,699 |
| 5 kW | 4663 kWh | 3404 kWh | 1259 kWh | £880 | £126 | £1,005 | £15,423 | 15.3 yrs | £4,686 |
| 6 kW | 5595 kWh | 4084 kWh | 1511 kWh | £1,055 | £151 | £1,206 | £17,457 | 14.5 yrs | £6,673 |
| 7 kW | 6528 kWh | 4765 kWh | 1762 kWh | £1,231 | £176 | £1,408 | £19,492 | 13.8 yrs | £8,660 |
| 8 kW | 7460 kWh | 5446 kWh | 2014 kWh | £1,407 | £201 | £1,609 | £21,526 | 13.4 yrs | £10,647 |
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: £1,020, Upfront: £17,173, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1865 kWh | 1399 kWh | 466 kWh | £361 | £47 | £408 | £11,069 | 27.1 yrs | £-2,908 |
| 3 kW | 2798 kWh | 2098 kWh | 699 kWh | £542 | £70 | £612 | £13,104 | 21.4 yrs | £-861 |
| 4 kW | 3730 kWh | 2798 kWh | 933 kWh | £723 | £93 | £816 | £15,138 | 18.5 yrs | £1,185 |
| 5 kW | 4663 kWh | 3497 kWh | 1166 kWh | £904 | £117 | £1,020 | £17,173 | 16.8 yrs | £3,231 |
| 6 kW | 5595 kWh | 4196 kWh | 1399 kWh | £1,084 | £140 | £1,224 | £19,207 | 15.7 yrs | £5,277 |
| 7 kW | 6528 kWh | 4896 kWh | 1632 kWh | £1,265 | £163 | £1,428 | £21,242 | 14.9 yrs | £7,324 |
| 8 kW | 7460 kWh | 5595 kWh | 1865 kWh | £1,446 | £187 | £1,632 | £23,276 | 14.3 yrs | £9,370 |
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: £1,035, Upfront: £19,623, Break-even: 19.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1865 kWh | 1436 kWh | 429 kWh | £371 | £43 | £414 | £13,519 | 32.7 yrs | £-5,239 |
| 3 kW | 2798 kWh | 2154 kWh | 643 kWh | £557 | £64 | £621 | £15,554 | 25.0 yrs | £-3,134 |
| 4 kW | 3730 kWh | 2872 kWh | 858 kWh | £742 | £86 | £828 | £17,588 | 21.2 yrs | £-1,029 |
| 5 kW | 4663 kWh | 3590 kWh | 1072 kWh | £928 | £107 | £1,035 | £19,623 | 19.0 yrs | £1,077 |
| 6 kW | 5595 kWh | 4308 kWh | 1287 kWh | £1,113 | £129 | £1,242 | £21,657 | 17.4 yrs | £3,182 |
| 7 kW | 6528 kWh | 5026 kWh | 1501 kWh | £1,299 | £150 | £1,449 | £23,692 | 16.4 yrs | £5,287 |
| 8 kW | 7460 kWh | 5744 kWh | 1716 kWh | £1,484 | £172 | £1,656 | £25,726 | 15.5 yrs | £7,393 |
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.