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 927 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £749, Upfront: £10,173, 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 | 1853 kWh | 741 kWh | 1112 kWh | £189 | £111 | £300 | £4,069 | 13.6 yrs | £1,925 |
| 3 kW | 2780 kWh | 1112 kWh | 1668 kWh | £283 | £167 | £450 | £6,104 | 13.6 yrs | £2,888 |
| 4 kW | 3707 kWh | 1483 kWh | 2224 kWh | £377 | £222 | £599 | £8,138 | 13.6 yrs | £3,850 |
| 5 kW | 4633 kWh | 1853 kWh | 2780 kWh | £471 | £278 | £749 | £10,173 | 13.6 yrs | £4,813 |
| 6 kW | 5560 kWh | 2224 kWh | 3336 kWh | £566 | £334 | £899 | £12,207 | 13.6 yrs | £5,776 |
| 7 kW | 6486 kWh | 2595 kWh | 3892 kWh | £660 | £389 | £1,049 | £14,242 | 13.6 yrs | £6,738 |
| 8 kW | 7413 kWh | 2965 kWh | 4448 kWh | £754 | £445 | £1,199 | £16,276 | 13.6 yrs | £7,701 |
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: £892, Upfront: £12,273, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1853 kWh | 1112 kWh | 741 kWh | £283 | £74 | £357 | £6,169 | 17.3 yrs | £969 |
| 3 kW | 2780 kWh | 1668 kWh | 1112 kWh | £424 | £111 | £535 | £8,204 | 15.3 yrs | £2,504 |
| 4 kW | 3707 kWh | 2224 kWh | 1483 kWh | £566 | £148 | £714 | £10,238 | 14.3 yrs | £4,038 |
| 5 kW | 4633 kWh | 2780 kWh | 1853 kWh | £707 | £185 | £892 | £12,273 | 13.8 yrs | £5,573 |
| 6 kW | 5560 kWh | 3336 kWh | 2224 kWh | £848 | £222 | £1,071 | £14,307 | 13.4 yrs | £7,107 |
| 7 kW | 6486 kWh | 3892 kWh | 2595 kWh | £990 | £259 | £1,249 | £16,342 | 13.1 yrs | £8,642 |
| 8 kW | 7413 kWh | 4448 kWh | 2965 kWh | £1,131 | £297 | £1,428 | £18,376 | 12.9 yrs | £10,176 |
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: £964, Upfront: £13,673, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1853 kWh | 1297 kWh | 556 kWh | £330 | £56 | £386 | £7,569 | 19.6 yrs | £141 |
| 3 kW | 2780 kWh | 1946 kWh | 834 kWh | £495 | £83 | £578 | £9,604 | 16.6 yrs | £1,961 |
| 4 kW | 3707 kWh | 2595 kWh | 1112 kWh | £660 | £111 | £771 | £11,638 | 15.1 yrs | £3,782 |
| 5 kW | 4633 kWh | 3243 kWh | 1390 kWh | £825 | £139 | £964 | £13,673 | 14.2 yrs | £5,602 |
| 6 kW | 5560 kWh | 3892 kWh | 1668 kWh | £990 | £167 | £1,157 | £15,707 | 13.6 yrs | £7,423 |
| 7 kW | 6486 kWh | 4541 kWh | 1946 kWh | £1,155 | £195 | £1,349 | £17,742 | 13.1 yrs | £9,243 |
| 8 kW | 7413 kWh | 5189 kWh | 2224 kWh | £1,320 | £222 | £1,542 | £19,776 | 12.8 yrs | £11,064 |
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: £985, Upfront: £15,423, Break-even: 15.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1853 kWh | 1353 kWh | 500 kWh | £344 | £50 | £394 | £9,319 | 23.6 yrs | £-1,437 |
| 3 kW | 2780 kWh | 2029 kWh | 751 kWh | £516 | £75 | £591 | £11,354 | 19.2 yrs | £469 |
| 4 kW | 3707 kWh | 2706 kWh | 1001 kWh | £688 | £100 | £788 | £13,388 | 17.0 yrs | £2,375 |
| 5 kW | 4633 kWh | 3382 kWh | 1251 kWh | £860 | £125 | £985 | £15,423 | 15.7 yrs | £4,281 |
| 6 kW | 5560 kWh | 4059 kWh | 1501 kWh | £1,032 | £150 | £1,182 | £17,457 | 14.8 yrs | £6,188 |
| 7 kW | 6486 kWh | 4735 kWh | 1751 kWh | £1,204 | £175 | £1,379 | £19,492 | 14.1 yrs | £8,094 |
| 8 kW | 7413 kWh | 5412 kWh | 2002 kWh | £1,376 | £200 | £1,576 | £21,526 | 13.7 yrs | £10,000 |
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: £999, Upfront: £17,173, 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 | 1853 kWh | 1390 kWh | 463 kWh | £353 | £46 | £400 | £11,069 | 27.7 yrs | £-3,073 |
| 3 kW | 2780 kWh | 2085 kWh | 695 kWh | £530 | £69 | £600 | £13,104 | 21.9 yrs | £-1,110 |
| 4 kW | 3707 kWh | 2780 kWh | 927 kWh | £707 | £93 | £800 | £15,138 | 18.9 yrs | £854 |
| 5 kW | 4633 kWh | 3475 kWh | 1158 kWh | £884 | £116 | £999 | £17,173 | 17.2 yrs | £2,817 |
| 6 kW | 5560 kWh | 4170 kWh | 1390 kWh | £1,060 | £139 | £1,199 | £19,207 | 16.0 yrs | £4,781 |
| 7 kW | 6486 kWh | 4865 kWh | 1622 kWh | £1,237 | £162 | £1,399 | £21,242 | 15.2 yrs | £6,744 |
| 8 kW | 7413 kWh | 5560 kWh | 1853 kWh | £1,414 | £185 | £1,599 | £23,276 | 14.6 yrs | £8,708 |
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: £1,014, Upfront: £19,623, Break-even: 19.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1853 kWh | 1427 kWh | 426 kWh | £363 | £43 | £406 | £13,519 | 33.3 yrs | £-5,409 |
| 3 kW | 2780 kWh | 2141 kWh | 639 kWh | £544 | £64 | £608 | £15,554 | 25.6 yrs | £-3,388 |
| 4 kW | 3707 kWh | 2854 kWh | 853 kWh | £726 | £85 | £811 | £17,588 | 21.7 yrs | £-1,367 |
| 5 kW | 4633 kWh | 3568 kWh | 1066 kWh | £907 | £107 | £1,014 | £19,623 | 19.4 yrs | £653 |
| 6 kW | 5560 kWh | 4281 kWh | 1279 kWh | £1,089 | £128 | £1,217 | £21,657 | 17.8 yrs | £2,674 |
| 7 kW | 6486 kWh | 4995 kWh | 1492 kWh | £1,270 | £149 | £1,419 | £23,692 | 16.7 yrs | £4,695 |
| 8 kW | 7413 kWh | 5708 kWh | 1705 kWh | £1,452 | £171 | £1,622 | £25,726 | 15.9 yrs | £6,715 |
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.