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 1123 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £941, 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 | 2246 kWh | 898 kWh | 1347 kWh | £242 | £135 | £377 | £4,069 | 10.8 yrs | £3,462 |
| 3 kW | 3368 kWh | 1347 kWh | 2021 kWh | £363 | £202 | £565 | £6,104 | 10.8 yrs | £5,192 |
| 4 kW | 4491 kWh | 1796 kWh | 2695 kWh | £484 | £269 | £753 | £8,138 | 10.8 yrs | £6,923 |
| 5 kW | 5614 kWh | 2246 kWh | 3368 kWh | £604 | £337 | £941 | £10,173 | 10.8 yrs | £8,654 |
| 6 kW | 6737 kWh | 2695 kWh | 4042 kWh | £725 | £404 | £1,130 | £12,207 | 10.8 yrs | £10,385 |
| 7 kW | 7859 kWh | 3144 kWh | 4716 kWh | £846 | £472 | £1,318 | £14,242 | 10.8 yrs | £12,115 |
| 8 kW | 8982 kWh | 3593 kWh | 5389 kWh | £967 | £539 | £1,506 | £16,276 | 10.8 yrs | £13,846 |
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: £1,131, Upfront: £12,273, 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 | 2246 kWh | 1347 kWh | 898 kWh | £363 | £90 | £453 | £6,169 | 13.6 yrs | £2,881 |
| 3 kW | 3368 kWh | 2021 kWh | 1347 kWh | £544 | £135 | £679 | £8,204 | 12.1 yrs | £5,372 |
| 4 kW | 4491 kWh | 2695 kWh | 1796 kWh | £725 | £180 | £905 | £10,238 | 11.3 yrs | £7,863 |
| 5 kW | 5614 kWh | 3368 kWh | 2246 kWh | £907 | £225 | £1,131 | £12,273 | 10.8 yrs | £10,353 |
| 6 kW | 6737 kWh | 4042 kWh | 2695 kWh | £1,088 | £269 | £1,358 | £14,307 | 10.5 yrs | £12,844 |
| 7 kW | 7859 kWh | 4716 kWh | 3144 kWh | £1,269 | £314 | £1,584 | £16,342 | 10.3 yrs | £15,335 |
| 8 kW | 8982 kWh | 5389 kWh | 3593 kWh | £1,451 | £359 | £1,810 | £18,376 | 10.2 yrs | £17,825 |
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: £1,226, Upfront: £13,673, Break-even: 11.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2246 kWh | 1572 kWh | 674 kWh | £423 | £67 | £491 | £7,569 | 15.4 yrs | £2,241 |
| 3 kW | 3368 kWh | 2358 kWh | 1010 kWh | £635 | £101 | £736 | £9,604 | 13.1 yrs | £5,112 |
| 4 kW | 4491 kWh | 3144 kWh | 1347 kWh | £846 | £135 | £981 | £11,638 | 11.9 yrs | £7,982 |
| 5 kW | 5614 kWh | 3930 kWh | 1684 kWh | £1,058 | £168 | £1,226 | £13,673 | 11.1 yrs | £10,853 |
| 6 kW | 6737 kWh | 4716 kWh | 2021 kWh | £1,269 | £202 | £1,472 | £15,707 | 10.7 yrs | £13,724 |
| 7 kW | 7859 kWh | 5502 kWh | 2358 kWh | £1,481 | £236 | £1,717 | £17,742 | 10.3 yrs | £16,594 |
| 8 kW | 8982 kWh | 6287 kWh | 2695 kWh | £1,693 | £269 | £1,962 | £19,776 | 10.1 yrs | £19,465 |
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: £1,255, Upfront: £15,423, Break-even: 12.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2246 kWh | 1639 kWh | 606 kWh | £441 | £61 | £502 | £9,319 | 18.6 yrs | £719 |
| 3 kW | 3368 kWh | 2459 kWh | 909 kWh | £662 | £91 | £753 | £11,354 | 15.1 yrs | £3,704 |
| 4 kW | 4491 kWh | 3278 kWh | 1213 kWh | £883 | £121 | £1,004 | £13,388 | 13.3 yrs | £6,688 |
| 5 kW | 5614 kWh | 4098 kWh | 1516 kWh | £1,103 | £152 | £1,255 | £15,423 | 12.3 yrs | £9,673 |
| 6 kW | 6737 kWh | 4918 kWh | 1819 kWh | £1,324 | £182 | £1,506 | £17,457 | 11.6 yrs | £12,658 |
| 7 kW | 7859 kWh | 5737 kWh | 2122 kWh | £1,544 | £212 | £1,757 | £19,492 | 11.1 yrs | £15,642 |
| 8 kW | 8982 kWh | 6557 kWh | 2425 kWh | £1,765 | £243 | £2,008 | £21,526 | 10.7 yrs | £18,627 |
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: £1,274, Upfront: £17,173, 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 | 2246 kWh | 1684 kWh | 561 kWh | £453 | £56 | £510 | £11,069 | 21.7 yrs | £-879 |
| 3 kW | 3368 kWh | 2526 kWh | 842 kWh | £680 | £84 | £764 | £13,104 | 17.1 yrs | £2,182 |
| 4 kW | 4491 kWh | 3368 kWh | 1123 kWh | £907 | £112 | £1,019 | £15,138 | 14.9 yrs | £5,242 |
| 5 kW | 5614 kWh | 4210 kWh | 1403 kWh | £1,133 | £140 | £1,274 | £17,173 | 13.5 yrs | £8,303 |
| 6 kW | 6737 kWh | 5052 kWh | 1684 kWh | £1,360 | £168 | £1,529 | £19,207 | 12.6 yrs | £11,363 |
| 7 kW | 7859 kWh | 5894 kWh | 1965 kWh | £1,587 | £196 | £1,783 | £21,242 | 11.9 yrs | £14,424 |
| 8 kW | 8982 kWh | 6737 kWh | 2246 kWh | £1,813 | £225 | £2,038 | £23,276 | 11.4 yrs | £17,485 |
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: £1,293, Upfront: £19,623, 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 | 2246 kWh | 1729 kWh | 516 kWh | £465 | £52 | £517 | £13,519 | 26.1 yrs | £-3,177 |
| 3 kW | 3368 kWh | 2594 kWh | 775 kWh | £698 | £77 | £776 | £15,554 | 20.1 yrs | £-40 |
| 4 kW | 4491 kWh | 3458 kWh | 1033 kWh | £931 | £103 | £1,034 | £17,588 | 17.0 yrs | £3,096 |
| 5 kW | 5614 kWh | 4323 kWh | 1291 kWh | £1,164 | £129 | £1,293 | £19,623 | 15.2 yrs | £6,233 |
| 6 kW | 6737 kWh | 5187 kWh | 1549 kWh | £1,396 | £155 | £1,551 | £21,657 | 14.0 yrs | £9,369 |
| 7 kW | 7859 kWh | 6052 kWh | 1808 kWh | £1,629 | £181 | £1,810 | £23,692 | 13.1 yrs | £12,506 |
| 8 kW | 8982 kWh | 6916 kWh | 2066 kWh | £1,862 | £207 | £2,068 | £25,726 | 12.4 yrs | £15,643 |
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.