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 1133 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £940, Upfront: £10,173, Break-even: 10.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2266 kWh | 906 kWh | 1359 kWh | £240 | £136 | £376 | £4,069 | 10.8 yrs | £3,449 |
| 3 kW | 3398 kWh | 1359 kWh | 2039 kWh | £360 | £204 | £564 | £6,104 | 10.8 yrs | £5,173 |
| 4 kW | 4531 kWh | 1812 kWh | 2719 kWh | £480 | £272 | £752 | £8,138 | 10.8 yrs | £6,898 |
| 5 kW | 5664 kWh | 2266 kWh | 3398 kWh | £600 | £340 | £940 | £10,173 | 10.8 yrs | £8,622 |
| 6 kW | 6796 kWh | 2719 kWh | 4078 kWh | £720 | £408 | £1,128 | £12,207 | 10.8 yrs | £10,346 |
| 7 kW | 7929 kWh | 3172 kWh | 4758 kWh | £840 | £476 | £1,316 | £14,242 | 10.8 yrs | £12,071 |
| 8 kW | 9062 kWh | 3625 kWh | 5437 kWh | £960 | £544 | £1,504 | £16,276 | 10.8 yrs | £13,795 |
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: £1,126, Upfront: £12,273, Break-even: 10.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2266 kWh | 1359 kWh | 906 kWh | £360 | £91 | £451 | £6,169 | 13.7 yrs | £2,842 |
| 3 kW | 3398 kWh | 2039 kWh | 1359 kWh | £540 | £136 | £676 | £8,204 | 12.1 yrs | £5,313 |
| 4 kW | 4531 kWh | 2719 kWh | 1812 kWh | £720 | £181 | £901 | £10,238 | 11.4 yrs | £7,784 |
| 5 kW | 5664 kWh | 3398 kWh | 2266 kWh | £900 | £227 | £1,126 | £12,273 | 10.9 yrs | £10,256 |
| 6 kW | 6796 kWh | 4078 kWh | 2719 kWh | £1,080 | £272 | £1,352 | £14,307 | 10.6 yrs | £12,727 |
| 7 kW | 7929 kWh | 4758 kWh | 3172 kWh | £1,260 | £317 | £1,577 | £16,342 | 10.4 yrs | £15,198 |
| 8 kW | 9062 kWh | 5437 kWh | 3625 kWh | £1,440 | £362 | £1,802 | £18,376 | 10.2 yrs | £17,669 |
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: £1,220, Upfront: £13,673, Break-even: 11.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2266 kWh | 1586 kWh | 680 kWh | £420 | £68 | £488 | £7,569 | 15.5 yrs | £2,189 |
| 3 kW | 3398 kWh | 2379 kWh | 1019 kWh | £630 | £102 | £732 | £9,604 | 13.1 yrs | £5,033 |
| 4 kW | 4531 kWh | 3172 kWh | 1359 kWh | £840 | £136 | £976 | £11,638 | 11.9 yrs | £7,878 |
| 5 kW | 5664 kWh | 3965 kWh | 1699 kWh | £1,050 | £170 | £1,220 | £13,673 | 11.2 yrs | £10,722 |
| 6 kW | 6796 kWh | 4758 kWh | 2039 kWh | £1,260 | £204 | £1,464 | £15,707 | 10.7 yrs | £13,567 |
| 7 kW | 7929 kWh | 5550 kWh | 2379 kWh | £1,470 | £238 | £1,708 | £17,742 | 10.4 yrs | £16,411 |
| 8 kW | 9062 kWh | 6343 kWh | 2719 kWh | £1,680 | £272 | £1,952 | £19,776 | 10.1 yrs | £19,256 |
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: £1,248, Upfront: £15,423, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2266 kWh | 1654 kWh | 612 kWh | £438 | £61 | £499 | £9,319 | 18.7 yrs | £663 |
| 3 kW | 3398 kWh | 2481 kWh | 918 kWh | £657 | £92 | £749 | £11,354 | 15.2 yrs | £3,619 |
| 4 kW | 4531 kWh | 3308 kWh | 1223 kWh | £876 | £122 | £998 | £13,388 | 13.4 yrs | £6,576 |
| 5 kW | 5664 kWh | 4135 kWh | 1529 kWh | £1,095 | £153 | £1,248 | £15,423 | 12.4 yrs | £9,532 |
| 6 kW | 6796 kWh | 4961 kWh | 1835 kWh | £1,314 | £184 | £1,497 | £17,457 | 11.7 yrs | £12,489 |
| 7 kW | 7929 kWh | 5788 kWh | 2141 kWh | £1,533 | £214 | £1,747 | £19,492 | 11.2 yrs | £15,445 |
| 8 kW | 9062 kWh | 6615 kWh | 2447 kWh | £1,752 | £245 | £1,996 | £21,526 | 10.8 yrs | £18,402 |
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: £1,266, Upfront: £17,173, 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 | 2266 kWh | 1699 kWh | 566 kWh | £450 | £57 | £507 | £11,069 | 21.9 yrs | £-938 |
| 3 kW | 3398 kWh | 2549 kWh | 850 kWh | £675 | £85 | £760 | £13,104 | 17.2 yrs | £2,093 |
| 4 kW | 4531 kWh | 3398 kWh | 1133 kWh | £900 | £113 | £1,013 | £15,138 | 14.9 yrs | £5,125 |
| 5 kW | 5664 kWh | 4248 kWh | 1416 kWh | £1,125 | £142 | £1,266 | £17,173 | 13.6 yrs | £8,156 |
| 6 kW | 6796 kWh | 5097 kWh | 1699 kWh | £1,350 | £170 | £1,520 | £19,207 | 12.6 yrs | £11,187 |
| 7 kW | 7929 kWh | 5947 kWh | 1982 kWh | £1,575 | £198 | £1,773 | £21,242 | 12.0 yrs | £14,218 |
| 8 kW | 9062 kWh | 6796 kWh | 2266 kWh | £1,800 | £227 | £2,026 | £23,276 | 11.5 yrs | £17,249 |
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: £1,285, Upfront: £19,623, 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 | 2266 kWh | 1744 kWh | 521 kWh | £462 | £52 | £514 | £13,519 | 26.3 yrs | £-3,238 |
| 3 kW | 3398 kWh | 2617 kWh | 782 kWh | £693 | £78 | £771 | £15,554 | 20.2 yrs | £-133 |
| 4 kW | 4531 kWh | 3489 kWh | 1042 kWh | £924 | £104 | £1,028 | £17,588 | 17.1 yrs | £2,973 |
| 5 kW | 5664 kWh | 4361 kWh | 1303 kWh | £1,155 | £130 | £1,285 | £19,623 | 15.3 yrs | £6,079 |
| 6 kW | 6796 kWh | 5233 kWh | 1563 kWh | £1,386 | £156 | £1,542 | £21,657 | 14.0 yrs | £9,185 |
| 7 kW | 7929 kWh | 6106 kWh | 1824 kWh | £1,617 | £182 | £1,799 | £23,692 | 13.2 yrs | £12,291 |
| 8 kW | 9062 kWh | 6978 kWh | 2084 kWh | £1,848 | £208 | £2,056 | £25,726 | 12.5 yrs | £15,397 |
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.