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 951 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: £767, Upfront: £10,173, Break-even: 13.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1901 kWh | 760 kWh | 1141 kWh | £193 | £114 | £307 | £4,069 | 13.3 yrs | £2,065 |
| 3 kW | 2852 kWh | 1141 kWh | 1711 kWh | £289 | £171 | £460 | £6,104 | 13.3 yrs | £3,097 |
| 4 kW | 3802 kWh | 1521 kWh | 2281 kWh | £385 | £228 | £613 | £8,138 | 13.3 yrs | £4,129 |
| 5 kW | 4753 kWh | 1901 kWh | 2852 kWh | £482 | £285 | £767 | £10,173 | 13.3 yrs | £5,162 |
| 6 kW | 5703 kWh | 2281 kWh | 3422 kWh | £578 | £342 | £920 | £12,207 | 13.3 yrs | £6,194 |
| 7 kW | 6654 kWh | 2662 kWh | 3992 kWh | £674 | £399 | £1,073 | £14,242 | 13.3 yrs | £7,226 |
| 8 kW | 7604 kWh | 3042 kWh | 4563 kWh | £770 | £456 | £1,227 | £16,276 | 13.3 yrs | £8,258 |
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: £912, 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 | 1901 kWh | 1141 kWh | 760 kWh | £289 | £76 | £365 | £6,169 | 16.9 yrs | £1,130 |
| 3 kW | 2852 kWh | 1711 kWh | 1141 kWh | £433 | £114 | £547 | £8,204 | 15.0 yrs | £2,746 |
| 4 kW | 3802 kWh | 2281 kWh | 1521 kWh | £578 | £152 | £730 | £10,238 | 14.0 yrs | £4,361 |
| 5 kW | 4753 kWh | 2852 kWh | 1901 kWh | £722 | £190 | £912 | £12,273 | 13.5 yrs | £5,976 |
| 6 kW | 5703 kWh | 3422 kWh | 2281 kWh | £867 | £228 | £1,095 | £14,307 | 13.1 yrs | £7,591 |
| 7 kW | 6654 kWh | 3992 kWh | 2662 kWh | £1,011 | £266 | £1,277 | £16,342 | 12.8 yrs | £9,206 |
| 8 kW | 7604 kWh | 4563 kWh | 3042 kWh | £1,156 | £304 | £1,460 | £18,376 | 12.6 yrs | £10,821 |
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: £985, 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 | 1901 kWh | 1331 kWh | 570 kWh | £337 | £57 | £394 | £7,569 | 19.2 yrs | £313 |
| 3 kW | 2852 kWh | 1996 kWh | 855 kWh | £506 | £86 | £591 | £9,604 | 16.2 yrs | £2,220 |
| 4 kW | 3802 kWh | 2662 kWh | 1141 kWh | £674 | £114 | £788 | £11,638 | 14.8 yrs | £4,126 |
| 5 kW | 4753 kWh | 3327 kWh | 1426 kWh | £843 | £143 | £985 | £13,673 | 13.9 yrs | £6,033 |
| 6 kW | 5703 kWh | 3992 kWh | 1711 kWh | £1,011 | £171 | £1,182 | £15,707 | 13.3 yrs | £7,940 |
| 7 kW | 6654 kWh | 4658 kWh | 1996 kWh | £1,180 | £200 | £1,379 | £17,742 | 12.9 yrs | £9,846 |
| 8 kW | 7604 kWh | 5323 kWh | 2281 kWh | £1,348 | £228 | £1,576 | £19,776 | 12.5 yrs | £11,753 |
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: £1,007, 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 | 1901 kWh | 1388 kWh | 513 kWh | £352 | £51 | £403 | £9,319 | 23.1 yrs | £-1,262 |
| 3 kW | 2852 kWh | 2082 kWh | 770 kWh | £527 | £77 | £604 | £11,354 | 18.8 yrs | £732 |
| 4 kW | 3802 kWh | 2776 kWh | 1027 kWh | £703 | £103 | £806 | £13,388 | 16.6 yrs | £2,726 |
| 5 kW | 4753 kWh | 3469 kWh | 1283 kWh | £879 | £128 | £1,007 | £15,423 | 15.3 yrs | £4,720 |
| 6 kW | 5703 kWh | 4163 kWh | 1540 kWh | £1,055 | £154 | £1,209 | £17,457 | 14.4 yrs | £6,714 |
| 7 kW | 6654 kWh | 4857 kWh | 1797 kWh | £1,230 | £180 | £1,410 | £19,492 | 13.8 yrs | £8,708 |
| 8 kW | 7604 kWh | 5551 kWh | 2053 kWh | £1,406 | £205 | £1,611 | £21,526 | 13.4 yrs | £10,702 |
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: £1,022, 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 | 1901 kWh | 1426 kWh | 475 kWh | £361 | £48 | £409 | £11,069 | 27.1 yrs | £-2,895 |
| 3 kW | 2852 kWh | 2139 kWh | 713 kWh | £542 | £71 | £613 | £13,104 | 21.4 yrs | £-843 |
| 4 kW | 3802 kWh | 2852 kWh | 951 kWh | £722 | £95 | £817 | £15,138 | 18.5 yrs | £1,209 |
| 5 kW | 4753 kWh | 3565 kWh | 1188 kWh | £903 | £119 | £1,022 | £17,173 | 16.8 yrs | £3,262 |
| 6 kW | 5703 kWh | 4277 kWh | 1426 kWh | £1,083 | £143 | £1,226 | £19,207 | 15.7 yrs | £5,314 |
| 7 kW | 6654 kWh | 4990 kWh | 1663 kWh | £1,264 | £166 | £1,430 | £21,242 | 14.9 yrs | £7,366 |
| 8 kW | 7604 kWh | 5703 kWh | 1901 kWh | £1,445 | £190 | £1,635 | £23,276 | 14.2 yrs | £9,419 |
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: £1,036, Upfront: £19,623, Break-even: 18.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1901 kWh | 1464 kWh | 437 kWh | £371 | £44 | £415 | £13,519 | 32.6 yrs | £-5,229 |
| 3 kW | 2852 kWh | 2196 kWh | 656 kWh | £556 | £66 | £622 | £15,554 | 25.0 yrs | £-3,118 |
| 4 kW | 3802 kWh | 2928 kWh | 874 kWh | £742 | £87 | £829 | £17,588 | 21.2 yrs | £-1,008 |
| 5 kW | 4753 kWh | 3660 kWh | 1093 kWh | £927 | £109 | £1,036 | £19,623 | 18.9 yrs | £1,103 |
| 6 kW | 5703 kWh | 4391 kWh | 1312 kWh | £1,112 | £131 | £1,244 | £21,657 | 17.4 yrs | £3,214 |
| 7 kW | 6654 kWh | 5123 kWh | 1530 kWh | £1,298 | £153 | £1,451 | £23,692 | 16.3 yrs | £5,324 |
| 8 kW | 7604 kWh | 5855 kWh | 1749 kWh | £1,483 | £175 | £1,658 | £25,726 | 15.5 yrs | £7,435 |
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.