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 944 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £768, 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 | 1889 kWh | 756 kWh | 1133 kWh | £194 | £113 | £307 | £4,069 | 13.3 yrs | £2,072 |
| 3 kW | 2833 kWh | 1133 kWh | 1700 kWh | £291 | £170 | £461 | £6,104 | 13.3 yrs | £3,108 |
| 4 kW | 3778 kWh | 1511 kWh | 2267 kWh | £387 | £227 | £614 | £8,138 | 13.3 yrs | £4,144 |
| 5 kW | 4722 kWh | 1889 kWh | 2833 kWh | £484 | £283 | £768 | £10,173 | 13.3 yrs | £5,180 |
| 6 kW | 5667 kWh | 2267 kWh | 3400 kWh | £581 | £340 | £921 | £12,207 | 13.3 yrs | £6,216 |
| 7 kW | 6611 kWh | 2644 kWh | 3967 kWh | £678 | £397 | £1,075 | £14,242 | 13.3 yrs | £7,252 |
| 8 kW | 7555 kWh | 3022 kWh | 4533 kWh | £775 | £453 | £1,228 | £16,276 | 13.3 yrs | £8,288 |
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: £915, Upfront: £12,273, 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 | 1889 kWh | 1133 kWh | 756 kWh | £291 | £76 | £366 | £6,169 | 16.8 yrs | £1,154 |
| 3 kW | 2833 kWh | 1700 kWh | 1133 kWh | £436 | £113 | £549 | £8,204 | 14.9 yrs | £2,781 |
| 4 kW | 3778 kWh | 2267 kWh | 1511 kWh | £581 | £151 | £732 | £10,238 | 14.0 yrs | £4,407 |
| 5 kW | 4722 kWh | 2833 kWh | 1889 kWh | £726 | £189 | £915 | £12,273 | 13.4 yrs | £6,034 |
| 6 kW | 5667 kWh | 3400 kWh | 2267 kWh | £872 | £227 | £1,098 | £14,307 | 13.0 yrs | £7,661 |
| 7 kW | 6611 kWh | 3967 kWh | 2644 kWh | £1,017 | £264 | £1,281 | £16,342 | 12.8 yrs | £9,288 |
| 8 kW | 7555 kWh | 4533 kWh | 3022 kWh | £1,162 | £302 | £1,465 | £18,376 | 12.5 yrs | £10,915 |
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: £989, Upfront: £13,673, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1889 kWh | 1322 kWh | 567 kWh | £339 | £57 | £396 | £7,569 | 19.1 yrs | £345 |
| 3 kW | 2833 kWh | 1983 kWh | 850 kWh | £509 | £85 | £594 | £9,604 | 16.2 yrs | £2,267 |
| 4 kW | 3778 kWh | 2644 kWh | 1133 kWh | £678 | £113 | £791 | £11,638 | 14.7 yrs | £4,189 |
| 5 kW | 4722 kWh | 3306 kWh | 1417 kWh | £848 | £142 | £989 | £13,673 | 13.8 yrs | £6,111 |
| 6 kW | 5667 kWh | 3967 kWh | 1700 kWh | £1,017 | £170 | £1,187 | £15,707 | 13.2 yrs | £8,034 |
| 7 kW | 6611 kWh | 4628 kWh | 1983 kWh | £1,187 | £198 | £1,385 | £17,742 | 12.8 yrs | £9,956 |
| 8 kW | 7555 kWh | 5289 kWh | 2267 kWh | £1,356 | £227 | £1,583 | £19,776 | 12.5 yrs | £11,878 |
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: £1,011, Upfront: £15,423, Break-even: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1889 kWh | 1379 kWh | 510 kWh | £354 | £51 | £405 | £9,319 | 23.0 yrs | £-1,228 |
| 3 kW | 2833 kWh | 2068 kWh | 765 kWh | £530 | £76 | £607 | £11,354 | 18.7 yrs | £783 |
| 4 kW | 3778 kWh | 2758 kWh | 1020 kWh | £707 | £102 | £809 | £13,388 | 16.5 yrs | £2,794 |
| 5 kW | 4722 kWh | 3447 kWh | 1275 kWh | £884 | £127 | £1,011 | £15,423 | 15.2 yrs | £4,804 |
| 6 kW | 5667 kWh | 4137 kWh | 1530 kWh | £1,061 | £153 | £1,214 | £17,457 | 14.4 yrs | £6,815 |
| 7 kW | 6611 kWh | 4826 kWh | 1785 kWh | £1,237 | £178 | £1,416 | £19,492 | 13.8 yrs | £8,826 |
| 8 kW | 7555 kWh | 5515 kWh | 2040 kWh | £1,414 | £204 | £1,618 | £21,526 | 13.3 yrs | £10,837 |
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: £1,026, Upfront: £17,173, Break-even: 16.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1889 kWh | 1417 kWh | 472 kWh | £363 | £47 | £410 | £11,069 | 27.0 yrs | £-2,860 |
| 3 kW | 2833 kWh | 2125 kWh | 708 kWh | £545 | £71 | £616 | £13,104 | 21.3 yrs | £-790 |
| 4 kW | 3778 kWh | 2833 kWh | 944 kWh | £726 | £94 | £821 | £15,138 | 18.4 yrs | £1,280 |
| 5 kW | 4722 kWh | 3542 kWh | 1181 kWh | £908 | £118 | £1,026 | £17,173 | 16.7 yrs | £3,350 |
| 6 kW | 5667 kWh | 4250 kWh | 1417 kWh | £1,090 | £142 | £1,231 | £19,207 | 15.6 yrs | £5,420 |
| 7 kW | 6611 kWh | 4958 kWh | 1653 kWh | £1,271 | £165 | £1,437 | £21,242 | 14.8 yrs | £7,490 |
| 8 kW | 7555 kWh | 5667 kWh | 1889 kWh | £1,453 | £189 | £1,642 | £23,276 | 14.2 yrs | £9,560 |
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: £1,041, 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 | 1889 kWh | 1454 kWh | 434 kWh | £373 | £43 | £416 | £13,519 | 32.5 yrs | £-5,192 |
| 3 kW | 2833 kWh | 2182 kWh | 652 kWh | £559 | £65 | £625 | £15,554 | 24.9 yrs | £-3,063 |
| 4 kW | 3778 kWh | 2909 kWh | 869 kWh | £746 | £87 | £833 | £17,588 | 21.1 yrs | £-934 |
| 5 kW | 4722 kWh | 3636 kWh | 1086 kWh | £932 | £109 | £1,041 | £19,623 | 18.9 yrs | £1,195 |
| 6 kW | 5667 kWh | 4363 kWh | 1303 kWh | £1,119 | £130 | £1,249 | £21,657 | 17.3 yrs | £3,324 |
| 7 kW | 6611 kWh | 5090 kWh | 1521 kWh | £1,305 | £152 | £1,457 | £23,692 | 16.3 yrs | £5,453 |
| 8 kW | 7555 kWh | 5818 kWh | 1738 kWh | £1,492 | £174 | £1,665 | £25,726 | 15.4 yrs | £7,583 |
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.