A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 1030 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: £856, Upfront: £10,173, 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 | 2060 kWh | 824 kWh | 1236 kWh | £219 | £124 | £342 | £4,069 | 11.9 yrs | £2,775 |
| 3 kW | 3090 kWh | 1236 kWh | 1854 kWh | £328 | £185 | £513 | £6,104 | 11.9 yrs | £4,163 |
| 4 kW | 4120 kWh | 1648 kWh | 2472 kWh | £437 | £247 | £684 | £8,138 | 11.9 yrs | £5,550 |
| 5 kW | 5150 kWh | 2060 kWh | 3090 kWh | £547 | £309 | £856 | £10,173 | 11.9 yrs | £6,938 |
| 6 kW | 6180 kWh | 2472 kWh | 3708 kWh | £656 | £371 | £1,027 | £12,207 | 11.9 yrs | £8,325 |
| 7 kW | 7210 kWh | 2884 kWh | 4326 kWh | £765 | £433 | £1,198 | £14,242 | 11.9 yrs | £9,713 |
| 8 kW | 8240 kWh | 3296 kWh | 4944 kWh | £874 | £494 | £1,369 | £16,276 | 11.9 yrs | £11,100 |
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: £1,026, Upfront: £12,273, Break-even: 12.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2060 kWh | 1236 kWh | 824 kWh | £328 | £82 | £410 | £6,169 | 15.0 yrs | £2,037 |
| 3 kW | 3090 kWh | 1854 kWh | 1236 kWh | £492 | £124 | £615 | £8,204 | 13.3 yrs | £4,106 |
| 4 kW | 4120 kWh | 2472 kWh | 1648 kWh | £656 | £165 | £821 | £10,238 | 12.5 yrs | £6,174 |
| 5 kW | 5150 kWh | 3090 kWh | 2060 kWh | £820 | £206 | £1,026 | £12,273 | 12.0 yrs | £8,243 |
| 6 kW | 6180 kWh | 3708 kWh | 2472 kWh | £984 | £247 | £1,231 | £14,307 | 11.6 yrs | £10,311 |
| 7 kW | 7210 kWh | 4326 kWh | 2884 kWh | £1,148 | £288 | £1,436 | £16,342 | 11.4 yrs | £12,380 |
| 8 kW | 8240 kWh | 4944 kWh | 3296 kWh | £1,312 | £330 | £1,641 | £18,376 | 11.2 yrs | £14,448 |
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: £1,111, 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 | 2060 kWh | 1442 kWh | 618 kWh | £383 | £62 | £444 | £7,569 | 17.0 yrs | £1,318 |
| 3 kW | 3090 kWh | 2163 kWh | 927 kWh | £574 | £93 | £667 | £9,604 | 14.4 yrs | £3,727 |
| 4 kW | 4120 kWh | 2884 kWh | 1236 kWh | £765 | £124 | £889 | £11,638 | 13.1 yrs | £6,136 |
| 5 kW | 5150 kWh | 3605 kWh | 1545 kWh | £956 | £154 | £1,111 | £13,673 | 12.3 yrs | £8,545 |
| 6 kW | 6180 kWh | 4326 kWh | 1854 kWh | £1,148 | £185 | £1,333 | £15,707 | 11.8 yrs | £10,954 |
| 7 kW | 7210 kWh | 5047 kWh | 2163 kWh | £1,339 | £216 | £1,555 | £17,742 | 11.4 yrs | £13,364 |
| 8 kW | 8240 kWh | 5768 kWh | 2472 kWh | £1,530 | £247 | £1,777 | £19,776 | 11.1 yrs | £15,773 |
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: £1,136, Upfront: £15,423, 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 | 2060 kWh | 1504 kWh | 556 kWh | £399 | £56 | £455 | £9,319 | 20.5 yrs | £-228 |
| 3 kW | 3090 kWh | 2256 kWh | 834 kWh | £598 | £83 | £682 | £11,354 | 16.7 yrs | £2,284 |
| 4 kW | 4120 kWh | 3008 kWh | 1112 kWh | £798 | £111 | £909 | £13,388 | 14.7 yrs | £4,795 |
| 5 kW | 5150 kWh | 3759 kWh | 1390 kWh | £997 | £139 | £1,136 | £15,423 | 13.6 yrs | £7,306 |
| 6 kW | 6180 kWh | 4511 kWh | 1669 kWh | £1,197 | £167 | £1,364 | £17,457 | 12.8 yrs | £9,817 |
| 7 kW | 7210 kWh | 5263 kWh | 1947 kWh | £1,396 | £195 | £1,591 | £19,492 | 12.3 yrs | £12,329 |
| 8 kW | 8240 kWh | 6015 kWh | 2225 kWh | £1,596 | £222 | £1,818 | £21,526 | 11.8 yrs | £14,840 |
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: £1,153, Upfront: £17,173, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2060 kWh | 1545 kWh | 515 kWh | £410 | £51 | £461 | £11,069 | 24.0 yrs | £-1,841 |
| 3 kW | 3090 kWh | 2317 kWh | 772 kWh | £615 | £77 | £692 | £13,104 | 18.9 yrs | £738 |
| 4 kW | 4120 kWh | 3090 kWh | 1030 kWh | £820 | £103 | £923 | £15,138 | 16.4 yrs | £3,317 |
| 5 kW | 5150 kWh | 3862 kWh | 1287 kWh | £1,025 | £129 | £1,153 | £17,173 | 14.9 yrs | £5,897 |
| 6 kW | 6180 kWh | 4635 kWh | 1545 kWh | £1,230 | £154 | £1,384 | £19,207 | 13.9 yrs | £8,476 |
| 7 kW | 7210 kWh | 5407 kWh | 1802 kWh | £1,435 | £180 | £1,615 | £21,242 | 13.2 yrs | £11,055 |
| 8 kW | 8240 kWh | 6180 kWh | 2060 kWh | £1,640 | £206 | £1,846 | £23,276 | 12.6 yrs | £13,635 |
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: £1,170, Upfront: £19,623, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2060 kWh | 1586 kWh | 474 kWh | £421 | £47 | £468 | £13,519 | 28.9 yrs | £-4,155 |
| 3 kW | 3090 kWh | 2379 kWh | 711 kWh | £631 | £71 | £702 | £15,554 | 22.1 yrs | £-1,508 |
| 4 kW | 4120 kWh | 3172 kWh | 948 kWh | £842 | £95 | £936 | £17,588 | 18.8 yrs | £1,140 |
| 5 kW | 5150 kWh | 3965 kWh | 1184 kWh | £1,052 | £118 | £1,170 | £19,623 | 16.8 yrs | £3,787 |
| 6 kW | 6180 kWh | 4759 kWh | 1421 kWh | £1,262 | £142 | £1,405 | £21,657 | 15.4 yrs | £6,435 |
| 7 kW | 7210 kWh | 5552 kWh | 1658 kWh | £1,473 | £166 | £1,639 | £23,692 | 14.5 yrs | £9,082 |
| 8 kW | 8240 kWh | 6345 kWh | 1895 kWh | £1,683 | £190 | £1,873 | £25,726 | 13.7 yrs | £11,729 |
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.