A typical roof here lands around 3.0 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 26.5p 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: £821, Upfront: £10,173, 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 | 1977 kWh | 791 kWh | 1186 kWh | £210 | £119 | £328 | £4,069 | 12.4 yrs | £2,501 |
| 3 kW | 2966 kWh | 1186 kWh | 1780 kWh | £315 | £178 | £493 | £6,104 | 12.4 yrs | £3,751 |
| 4 kW | 3955 kWh | 1582 kWh | 2373 kWh | £420 | £237 | £657 | £8,138 | 12.4 yrs | £5,001 |
| 5 kW | 4943 kWh | 1977 kWh | 2966 kWh | £525 | £297 | £821 | £10,173 | 12.4 yrs | £6,252 |
| 6 kW | 5932 kWh | 2373 kWh | 3559 kWh | £630 | £356 | £985 | £12,207 | 12.4 yrs | £7,502 |
| 7 kW | 6921 kWh | 2768 kWh | 4152 kWh | £734 | £415 | £1,150 | £14,242 | 12.4 yrs | £8,752 |
| 8 kW | 7910 kWh | 3164 kWh | 4746 kWh | £839 | £475 | £1,314 | £16,276 | 12.4 yrs | £10,003 |
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: £985, Upfront: £12,273, Break-even: 12.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1977 kWh | 1186 kWh | 791 kWh | £315 | £79 | £394 | £6,169 | 15.7 yrs | £1,708 |
| 3 kW | 2966 kWh | 1780 kWh | 1186 kWh | £472 | £119 | £591 | £8,204 | 13.9 yrs | £3,612 |
| 4 kW | 3955 kWh | 2373 kWh | 1582 kWh | £630 | £158 | £788 | £10,238 | 13.0 yrs | £5,516 |
| 5 kW | 4943 kWh | 2966 kWh | 1977 kWh | £787 | £198 | £985 | £12,273 | 12.5 yrs | £7,420 |
| 6 kW | 5932 kWh | 3559 kWh | 2373 kWh | £944 | £237 | £1,182 | £14,307 | 12.1 yrs | £9,324 |
| 7 kW | 6921 kWh | 4152 kWh | 2768 kWh | £1,102 | £277 | £1,378 | £16,342 | 11.9 yrs | £11,228 |
| 8 kW | 7910 kWh | 4746 kWh | 3164 kWh | £1,259 | £316 | £1,575 | £18,376 | 11.7 yrs | £13,132 |
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: £1,066, Upfront: £13,673, Break-even: 12.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1977 kWh | 1384 kWh | 593 kWh | £367 | £59 | £427 | £7,569 | 17.7 yrs | £962 |
| 3 kW | 2966 kWh | 2076 kWh | 890 kWh | £551 | £89 | £640 | £9,604 | 15.0 yrs | £3,193 |
| 4 kW | 3955 kWh | 2768 kWh | 1186 kWh | £734 | £119 | £853 | £11,638 | 13.6 yrs | £5,424 |
| 5 kW | 4943 kWh | 3460 kWh | 1483 kWh | £918 | £148 | £1,066 | £13,673 | 12.8 yrs | £7,654 |
| 6 kW | 5932 kWh | 4152 kWh | 1780 kWh | £1,102 | £178 | £1,280 | £15,707 | 12.3 yrs | £9,885 |
| 7 kW | 6921 kWh | 4845 kWh | 2076 kWh | £1,285 | £208 | £1,493 | £17,742 | 11.9 yrs | £12,116 |
| 8 kW | 7910 kWh | 5537 kWh | 2373 kWh | £1,469 | £237 | £1,706 | £19,776 | 11.6 yrs | £14,347 |
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: £1,091, Upfront: £15,423, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1977 kWh | 1443 kWh | 534 kWh | £383 | £53 | £436 | £9,319 | 21.4 yrs | £-592 |
| 3 kW | 2966 kWh | 2165 kWh | 801 kWh | £574 | £80 | £655 | £11,354 | 17.3 yrs | £1,737 |
| 4 kW | 3955 kWh | 2887 kWh | 1068 kWh | £766 | £107 | £873 | £13,388 | 15.3 yrs | £4,066 |
| 5 kW | 4943 kWh | 3609 kWh | 1335 kWh | £957 | £133 | £1,091 | £15,423 | 14.1 yrs | £6,395 |
| 6 kW | 5932 kWh | 4330 kWh | 1602 kWh | £1,149 | £160 | £1,309 | £17,457 | 13.3 yrs | £8,724 |
| 7 kW | 6921 kWh | 5052 kWh | 1869 kWh | £1,340 | £187 | £1,527 | £19,492 | 12.8 yrs | £11,053 |
| 8 kW | 7910 kWh | 5774 kWh | 2136 kWh | £1,532 | £214 | £1,745 | £21,526 | 12.3 yrs | £13,382 |
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: £1,107, Upfront: £17,173, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1977 kWh | 1483 kWh | 494 kWh | £393 | £49 | £443 | £11,069 | 25.0 yrs | £-2,211 |
| 3 kW | 2966 kWh | 2225 kWh | 742 kWh | £590 | £74 | £664 | £13,104 | 19.7 yrs | £183 |
| 4 kW | 3955 kWh | 2966 kWh | 989 kWh | £787 | £99 | £886 | £15,138 | 17.1 yrs | £2,577 |
| 5 kW | 4943 kWh | 3708 kWh | 1236 kWh | £984 | £124 | £1,107 | £17,173 | 15.5 yrs | £4,972 |
| 6 kW | 5932 kWh | 4449 kWh | 1483 kWh | £1,180 | £148 | £1,329 | £19,207 | 14.5 yrs | £7,366 |
| 7 kW | 6921 kWh | 5191 kWh | 1730 kWh | £1,377 | £173 | £1,550 | £21,242 | 13.7 yrs | £9,760 |
| 8 kW | 7910 kWh | 5932 kWh | 1977 kWh | £1,574 | £198 | £1,772 | £23,276 | 13.1 yrs | £12,155 |
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: £1,124, Upfront: £19,623, Break-even: 17.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1977 kWh | 1523 kWh | 455 kWh | £404 | £45 | £449 | £13,519 | 30.1 yrs | £-4,531 |
| 3 kW | 2966 kWh | 2284 kWh | 682 kWh | £606 | £68 | £674 | £15,554 | 23.1 yrs | £-2,071 |
| 4 kW | 3955 kWh | 3045 kWh | 910 kWh | £808 | £91 | £899 | £17,588 | 19.6 yrs | £389 |
| 5 kW | 4943 kWh | 3806 kWh | 1137 kWh | £1,010 | £114 | £1,124 | £19,623 | 17.5 yrs | £2,848 |
| 6 kW | 5932 kWh | 4568 kWh | 1364 kWh | £1,212 | £136 | £1,348 | £21,657 | 16.1 yrs | £5,308 |
| 7 kW | 6921 kWh | 5329 kWh | 1592 kWh | £1,414 | £159 | £1,573 | £23,692 | 15.1 yrs | £7,768 |
| 8 kW | 7910 kWh | 6090 kWh | 1819 kWh | £1,616 | £182 | £1,798 | £25,726 | 14.3 yrs | £10,228 |
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.