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 989 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: £829, Upfront: £10,173, 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 | 1978 kWh | 791 kWh | 1187 kWh | £213 | £119 | £332 | £4,069 | 12.3 yrs | £2,565 |
| 3 kW | 2967 kWh | 1187 kWh | 1780 kWh | £320 | £178 | £498 | £6,104 | 12.3 yrs | £3,848 |
| 4 kW | 3956 kWh | 1583 kWh | 2374 kWh | £426 | £237 | £663 | £8,138 | 12.3 yrs | £5,130 |
| 5 kW | 4946 kWh | 1978 kWh | 2967 kWh | £533 | £297 | £829 | £10,173 | 12.3 yrs | £6,413 |
| 6 kW | 5935 kWh | 2374 kWh | 3561 kWh | £639 | £356 | £995 | £12,207 | 12.3 yrs | £7,695 |
| 7 kW | 6924 kWh | 2770 kWh | 4154 kWh | £746 | £415 | £1,161 | £14,242 | 12.3 yrs | £8,978 |
| 8 kW | 7913 kWh | 3165 kWh | 4748 kWh | £852 | £475 | £1,327 | £16,276 | 12.3 yrs | £10,261 |
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: £997, Upfront: £12,273, 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 | 1978 kWh | 1187 kWh | 791 kWh | £320 | £79 | £399 | £6,169 | 15.5 yrs | £1,804 |
| 3 kW | 2967 kWh | 1780 kWh | 1187 kWh | £479 | £119 | £598 | £8,204 | 13.7 yrs | £3,756 |
| 4 kW | 3956 kWh | 2374 kWh | 1583 kWh | £639 | £158 | £797 | £10,238 | 12.8 yrs | £5,708 |
| 5 kW | 4946 kWh | 2967 kWh | 1978 kWh | £799 | £198 | £997 | £12,273 | 12.3 yrs | £7,660 |
| 6 kW | 5935 kWh | 3561 kWh | 2374 kWh | £959 | £237 | £1,196 | £14,307 | 12.0 yrs | £9,612 |
| 7 kW | 6924 kWh | 4154 kWh | 2770 kWh | £1,118 | £277 | £1,395 | £16,342 | 11.7 yrs | £11,564 |
| 8 kW | 7913 kWh | 4748 kWh | 3165 kWh | £1,278 | £317 | £1,595 | £18,376 | 11.5 yrs | £13,516 |
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: £1,080, Upfront: £13,673, Break-even: 12.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1978 kWh | 1385 kWh | 593 kWh | £373 | £59 | £432 | £7,569 | 17.5 yrs | £1,073 |
| 3 kW | 2967 kWh | 2077 kWh | 890 kWh | £559 | £89 | £648 | £9,604 | 14.8 yrs | £3,360 |
| 4 kW | 3956 kWh | 2770 kWh | 1187 kWh | £746 | £119 | £864 | £11,638 | 13.5 yrs | £5,647 |
| 5 kW | 4946 kWh | 3462 kWh | 1484 kWh | £932 | £148 | £1,080 | £13,673 | 12.7 yrs | £7,934 |
| 6 kW | 5935 kWh | 4154 kWh | 1780 kWh | £1,118 | £178 | £1,296 | £15,707 | 12.1 yrs | £10,220 |
| 7 kW | 6924 kWh | 4847 kWh | 2077 kWh | £1,305 | £208 | £1,512 | £17,742 | 11.7 yrs | £12,507 |
| 8 kW | 7913 kWh | 5539 kWh | 2374 kWh | £1,491 | £237 | £1,728 | £19,776 | 11.4 yrs | £14,794 |
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: £1,105, Upfront: £15,423, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1978 kWh | 1444 kWh | 534 kWh | £389 | £53 | £442 | £9,319 | 21.1 yrs | £-476 |
| 3 kW | 2967 kWh | 2166 kWh | 801 kWh | £583 | £80 | £663 | £11,354 | 17.1 yrs | £1,911 |
| 4 kW | 3956 kWh | 2888 kWh | 1068 kWh | £778 | £107 | £884 | £13,388 | 15.1 yrs | £4,299 |
| 5 kW | 4946 kWh | 3610 kWh | 1335 kWh | £972 | £134 | £1,105 | £15,423 | 14.0 yrs | £6,686 |
| 6 kW | 5935 kWh | 4332 kWh | 1602 kWh | £1,166 | £160 | £1,326 | £17,457 | 13.2 yrs | £9,073 |
| 7 kW | 6924 kWh | 5054 kWh | 1869 kWh | £1,361 | £187 | £1,548 | £19,492 | 12.6 yrs | £11,460 |
| 8 kW | 7913 kWh | 5776 kWh | 2136 kWh | £1,555 | £214 | £1,769 | £21,526 | 12.2 yrs | £13,847 |
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: £1,122, Upfront: £17,173, 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 | 1978 kWh | 1484 kWh | 495 kWh | £399 | £49 | £449 | £11,069 | 24.7 yrs | £-2,092 |
| 3 kW | 2967 kWh | 2225 kWh | 742 kWh | £599 | £74 | £673 | £13,104 | 19.5 yrs | £362 |
| 4 kW | 3956 kWh | 2967 kWh | 989 kWh | £799 | £99 | £898 | £15,138 | 16.9 yrs | £2,816 |
| 5 kW | 4946 kWh | 3709 kWh | 1236 kWh | £999 | £124 | £1,122 | £17,173 | 15.3 yrs | £5,270 |
| 6 kW | 5935 kWh | 4451 kWh | 1484 kWh | £1,198 | £148 | £1,347 | £19,207 | 14.3 yrs | £7,724 |
| 7 kW | 6924 kWh | 5193 kWh | 1731 kWh | £1,398 | £173 | £1,571 | £21,242 | 13.5 yrs | £10,178 |
| 8 kW | 7913 kWh | 5935 kWh | 1978 kWh | £1,598 | £198 | £1,795 | £23,276 | 13.0 yrs | £12,633 |
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: £1,139, Upfront: £19,623, Break-even: 17.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1978 kWh | 1523 kWh | 455 kWh | £410 | £45 | £456 | £13,519 | 29.7 yrs | £-4,408 |
| 3 kW | 2967 kWh | 2285 kWh | 682 kWh | £615 | £68 | £683 | £15,554 | 22.8 yrs | £-1,887 |
| 4 kW | 3956 kWh | 3046 kWh | 910 kWh | £820 | £91 | £911 | £17,588 | 19.3 yrs | £634 |
| 5 kW | 4946 kWh | 3808 kWh | 1137 kWh | £1,025 | £114 | £1,139 | £19,623 | 17.2 yrs | £3,155 |
| 6 kW | 5935 kWh | 4570 kWh | 1365 kWh | £1,230 | £136 | £1,367 | £21,657 | 15.8 yrs | £5,676 |
| 7 kW | 6924 kWh | 5331 kWh | 1592 kWh | £1,435 | £159 | £1,594 | £23,692 | 14.9 yrs | £8,197 |
| 8 kW | 7913 kWh | 6093 kWh | 1820 kWh | £1,640 | £182 | £1,822 | £25,726 | 14.1 yrs | £10,718 |
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.