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 1036 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: £859, Upfront: £10,173, Break-even: 11.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2071 kWh | 829 kWh | 1243 kWh | £219 | £124 | £344 | £4,069 | 11.8 yrs | £2,805 |
| 3 kW | 3107 kWh | 1243 kWh | 1864 kWh | £329 | £186 | £516 | £6,104 | 11.8 yrs | £4,207 |
| 4 kW | 4143 kWh | 1657 kWh | 2486 kWh | £439 | £249 | £687 | £8,138 | 11.8 yrs | £5,610 |
| 5 kW | 5179 kWh | 2071 kWh | 3107 kWh | £549 | £311 | £859 | £10,173 | 11.8 yrs | £7,012 |
| 6 kW | 6214 kWh | 2486 kWh | 3729 kWh | £658 | £373 | £1,031 | £12,207 | 11.8 yrs | £8,415 |
| 7 kW | 7250 kWh | 2900 kWh | 4350 kWh | £768 | £435 | £1,203 | £14,242 | 11.8 yrs | £9,817 |
| 8 kW | 8286 kWh | 3314 kWh | 4971 kWh | £878 | £497 | £1,375 | £16,276 | 11.8 yrs | £11,219 |
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: £1,030, Upfront: £12,273, Break-even: 11.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2071 kWh | 1243 kWh | 829 kWh | £329 | £83 | £412 | £6,169 | 15.0 yrs | £2,070 |
| 3 kW | 3107 kWh | 1864 kWh | 1243 kWh | £494 | £124 | £618 | £8,204 | 13.3 yrs | £4,156 |
| 4 kW | 4143 kWh | 2486 kWh | 1657 kWh | £658 | £166 | £824 | £10,238 | 12.4 yrs | £6,241 |
| 5 kW | 5179 kWh | 3107 kWh | 2071 kWh | £823 | £207 | £1,030 | £12,273 | 11.9 yrs | £8,326 |
| 6 kW | 6214 kWh | 3729 kWh | 2486 kWh | £987 | £249 | £1,236 | £14,307 | 11.6 yrs | £10,411 |
| 7 kW | 7250 kWh | 4350 kWh | 2900 kWh | £1,152 | £290 | £1,442 | £16,342 | 11.3 yrs | £12,496 |
| 8 kW | 8286 kWh | 4971 kWh | 3314 kWh | £1,316 | £331 | £1,648 | £18,376 | 11.2 yrs | £14,581 |
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: £1,115, Upfront: £13,673, 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 | 2071 kWh | 1450 kWh | 621 kWh | £384 | £62 | £446 | £7,569 | 17.0 yrs | £1,353 |
| 3 kW | 3107 kWh | 2175 kWh | 932 kWh | £576 | £93 | £669 | £9,604 | 14.4 yrs | £3,780 |
| 4 kW | 4143 kWh | 2900 kWh | 1243 kWh | £768 | £124 | £892 | £11,638 | 13.0 yrs | £6,206 |
| 5 kW | 5179 kWh | 3625 kWh | 1554 kWh | £960 | £155 | £1,115 | £13,673 | 12.3 yrs | £8,633 |
| 6 kW | 6214 kWh | 4350 kWh | 1864 kWh | £1,152 | £186 | £1,338 | £15,707 | 11.7 yrs | £11,059 |
| 7 kW | 7250 kWh | 5075 kWh | 2175 kWh | £1,344 | £218 | £1,561 | £17,742 | 11.4 yrs | £13,486 |
| 8 kW | 8286 kWh | 5800 kWh | 2486 kWh | £1,536 | £249 | £1,784 | £19,776 | 11.1 yrs | £15,912 |
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: £1,141, Upfront: £15,423, 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 | 2071 kWh | 1512 kWh | 559 kWh | £400 | £56 | £456 | £9,319 | 20.4 yrs | £-192 |
| 3 kW | 3107 kWh | 2268 kWh | 839 kWh | £601 | £84 | £685 | £11,354 | 16.6 yrs | £2,337 |
| 4 kW | 4143 kWh | 3024 kWh | 1119 kWh | £801 | £112 | £913 | £13,388 | 14.7 yrs | £4,866 |
| 5 kW | 5179 kWh | 3780 kWh | 1398 kWh | £1,001 | £140 | £1,141 | £15,423 | 13.5 yrs | £7,395 |
| 6 kW | 6214 kWh | 4536 kWh | 1678 kWh | £1,201 | £168 | £1,369 | £17,457 | 12.8 yrs | £9,924 |
| 7 kW | 7250 kWh | 5293 kWh | 1958 kWh | £1,401 | £196 | £1,597 | £19,492 | 12.2 yrs | £12,453 |
| 8 kW | 8286 kWh | 6049 kWh | 2237 kWh | £1,602 | £224 | £1,825 | £21,526 | 11.8 yrs | £14,982 |
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: £1,158, Upfront: £17,173, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2071 kWh | 1554 kWh | 518 kWh | £411 | £52 | £463 | £11,069 | 23.9 yrs | £-1,806 |
| 3 kW | 3107 kWh | 2330 kWh | 777 kWh | £617 | £78 | £695 | £13,104 | 18.9 yrs | £792 |
| 4 kW | 4143 kWh | 3107 kWh | 1036 kWh | £823 | £104 | £926 | £15,138 | 16.3 yrs | £3,389 |
| 5 kW | 5179 kWh | 3884 kWh | 1295 kWh | £1,028 | £129 | £1,158 | £17,173 | 14.8 yrs | £5,986 |
| 6 kW | 6214 kWh | 4661 kWh | 1554 kWh | £1,234 | £155 | £1,390 | £19,207 | 13.8 yrs | £8,583 |
| 7 kW | 7250 kWh | 5438 kWh | 1813 kWh | £1,440 | £181 | £1,621 | £21,242 | 13.1 yrs | £11,181 |
| 8 kW | 8286 kWh | 6214 kWh | 2071 kWh | £1,646 | £207 | £1,853 | £23,276 | 12.6 yrs | £13,778 |
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: £1,175, Upfront: £19,623, Break-even: 16.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2071 kWh | 1595 kWh | 476 kWh | £422 | £48 | £470 | £13,519 | 28.8 yrs | £-4,119 |
| 3 kW | 3107 kWh | 2393 kWh | 715 kWh | £634 | £71 | £705 | £15,554 | 22.1 yrs | £-1,453 |
| 4 kW | 4143 kWh | 3190 kWh | 953 kWh | £845 | £95 | £940 | £17,588 | 18.7 yrs | £1,212 |
| 5 kW | 5179 kWh | 3988 kWh | 1191 kWh | £1,056 | £119 | £1,175 | £19,623 | 16.7 yrs | £3,878 |
| 6 kW | 6214 kWh | 4785 kWh | 1429 kWh | £1,267 | £143 | £1,410 | £21,657 | 15.4 yrs | £6,543 |
| 7 kW | 7250 kWh | 5583 kWh | 1668 kWh | £1,478 | £167 | £1,645 | £23,692 | 14.4 yrs | £9,209 |
| 8 kW | 8286 kWh | 6380 kWh | 1906 kWh | £1,689 | £191 | £1,880 | £25,726 | 13.7 yrs | £11,874 |
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.