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 958 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: £777, Upfront: £10,173, Break-even: 13.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1916 kWh | 766 kWh | 1149 kWh | £196 | £115 | £311 | £4,069 | 13.1 yrs | £2,146 |
| 3 kW | 2874 kWh | 1149 kWh | 1724 kWh | £294 | £172 | £466 | £6,104 | 13.1 yrs | £3,219 |
| 4 kW | 3832 kWh | 1533 kWh | 2299 kWh | £392 | £230 | £621 | £8,138 | 13.1 yrs | £4,292 |
| 5 kW | 4790 kWh | 1916 kWh | 2874 kWh | £489 | £287 | £777 | £10,173 | 13.1 yrs | £5,365 |
| 6 kW | 5747 kWh | 2299 kWh | 3448 kWh | £587 | £345 | £932 | £12,207 | 13.1 yrs | £6,438 |
| 7 kW | 6705 kWh | 2682 kWh | 4023 kWh | £685 | £402 | £1,088 | £14,242 | 13.1 yrs | £7,511 |
| 8 kW | 7663 kWh | 3065 kWh | 4598 kWh | £783 | £460 | £1,243 | £16,276 | 13.1 yrs | £8,584 |
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: £926, Upfront: £12,273, 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 | 1916 kWh | 1149 kWh | 766 kWh | £294 | £77 | £370 | £6,169 | 16.7 yrs | £1,238 |
| 3 kW | 2874 kWh | 1724 kWh | 1149 kWh | £441 | £115 | £555 | £8,204 | 14.8 yrs | £2,906 |
| 4 kW | 3832 kWh | 2299 kWh | 1533 kWh | £587 | £153 | £741 | £10,238 | 13.8 yrs | £4,575 |
| 5 kW | 4790 kWh | 2874 kWh | 1916 kWh | £734 | £192 | £926 | £12,273 | 13.3 yrs | £6,244 |
| 6 kW | 5747 kWh | 3448 kWh | 2299 kWh | £881 | £230 | £1,111 | £14,307 | 12.9 yrs | £7,913 |
| 7 kW | 6705 kWh | 4023 kWh | 2682 kWh | £1,028 | £268 | £1,296 | £16,342 | 12.6 yrs | £9,581 |
| 8 kW | 7663 kWh | 4598 kWh | 3065 kWh | £1,175 | £307 | £1,481 | £18,376 | 12.4 yrs | £11,250 |
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: £1,000, Upfront: £13,673, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1916 kWh | 1341 kWh | 575 kWh | £343 | £57 | £400 | £7,569 | 18.9 yrs | £433 |
| 3 kW | 2874 kWh | 2012 kWh | 862 kWh | £514 | £86 | £600 | £9,604 | 16.0 yrs | £2,400 |
| 4 kW | 3832 kWh | 2682 kWh | 1149 kWh | £685 | £115 | £800 | £11,638 | 14.5 yrs | £4,367 |
| 5 kW | 4790 kWh | 3353 kWh | 1437 kWh | £857 | £144 | £1,000 | £13,673 | 13.7 yrs | £6,333 |
| 6 kW | 5747 kWh | 4023 kWh | 1724 kWh | £1,028 | £172 | £1,200 | £15,707 | 13.1 yrs | £8,300 |
| 7 kW | 6705 kWh | 4694 kWh | 2012 kWh | £1,199 | £201 | £1,400 | £17,742 | 12.7 yrs | £10,267 |
| 8 kW | 7663 kWh | 5364 kWh | 2299 kWh | £1,371 | £230 | £1,600 | £19,776 | 12.4 yrs | £12,233 |
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: £1,023, Upfront: £15,423, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1916 kWh | 1399 kWh | 517 kWh | £357 | £52 | £409 | £9,319 | 22.8 yrs | £-1,138 |
| 3 kW | 2874 kWh | 2098 kWh | 776 kWh | £536 | £78 | £614 | £11,354 | 18.5 yrs | £918 |
| 4 kW | 3832 kWh | 2797 kWh | 1035 kWh | £715 | £103 | £818 | £13,388 | 16.4 yrs | £2,974 |
| 5 kW | 4790 kWh | 3496 kWh | 1293 kWh | £893 | £129 | £1,023 | £15,423 | 15.1 yrs | £5,030 |
| 6 kW | 5747 kWh | 4196 kWh | 1552 kWh | £1,072 | £155 | £1,227 | £17,457 | 14.2 yrs | £7,086 |
| 7 kW | 6705 kWh | 4895 kWh | 1810 kWh | £1,251 | £181 | £1,432 | £19,492 | 13.6 yrs | £9,142 |
| 8 kW | 7663 kWh | 5594 kWh | 2069 kWh | £1,429 | £207 | £1,636 | £21,526 | 13.2 yrs | £11,198 |
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: £1,038, Upfront: £17,173, Break-even: 16.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1916 kWh | 1437 kWh | 479 kWh | £367 | £48 | £415 | £11,069 | 26.7 yrs | £-2,769 |
| 3 kW | 2874 kWh | 2155 kWh | 718 kWh | £551 | £72 | £623 | £13,104 | 21.0 yrs | £-653 |
| 4 kW | 3832 kWh | 2874 kWh | 958 kWh | £734 | £96 | £830 | £15,138 | 18.2 yrs | £1,463 |
| 5 kW | 4790 kWh | 3592 kWh | 1197 kWh | £918 | £120 | £1,038 | £17,173 | 16.6 yrs | £3,578 |
| 6 kW | 5747 kWh | 4311 kWh | 1437 kWh | £1,101 | £144 | £1,245 | £19,207 | 15.4 yrs | £5,694 |
| 7 kW | 6705 kWh | 5029 kWh | 1676 kWh | £1,285 | £168 | £1,453 | £21,242 | 14.6 yrs | £7,809 |
| 8 kW | 7663 kWh | 5747 kWh | 1916 kWh | £1,468 | £192 | £1,660 | £23,276 | 14.0 yrs | £9,925 |
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: £1,052, 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 | 1916 kWh | 1475 kWh | 441 kWh | £377 | £44 | £421 | £13,519 | 32.1 yrs | £-5,100 |
| 3 kW | 2874 kWh | 2213 kWh | 661 kWh | £565 | £66 | £631 | £15,554 | 24.6 yrs | £-2,924 |
| 4 kW | 3832 kWh | 2950 kWh | 881 kWh | £754 | £88 | £842 | £17,588 | 20.9 yrs | £-749 |
| 5 kW | 4790 kWh | 3688 kWh | 1102 kWh | £942 | £110 | £1,052 | £19,623 | 18.6 yrs | £1,426 |
| 6 kW | 5747 kWh | 4426 kWh | 1322 kWh | £1,131 | £132 | £1,263 | £21,657 | 17.1 yrs | £3,601 |
| 7 kW | 6705 kWh | 5163 kWh | 1542 kWh | £1,319 | £154 | £1,473 | £23,692 | 16.1 yrs | £5,777 |
| 8 kW | 7663 kWh | 5901 kWh | 1763 kWh | £1,508 | £176 | £1,684 | £25,726 | 15.3 yrs | £7,952 |
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.