A typical roof here lands around 5.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 1125 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: £943, Upfront: £10,173, Break-even: 10.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2250 kWh | 900 kWh | 1350 kWh | £242 | £135 | £377 | £4,069 | 10.8 yrs | £3,477 |
| 3 kW | 3375 kWh | 1350 kWh | 2025 kWh | £363 | £203 | £566 | £6,104 | 10.8 yrs | £5,216 |
| 4 kW | 4500 kWh | 1800 kWh | 2700 kWh | £485 | £270 | £755 | £8,138 | 10.8 yrs | £6,954 |
| 5 kW | 5625 kWh | 2250 kWh | 3375 kWh | £606 | £338 | £943 | £10,173 | 10.8 yrs | £8,693 |
| 6 kW | 6750 kWh | 2700 kWh | 4050 kWh | £727 | £405 | £1,132 | £12,207 | 10.8 yrs | £10,431 |
| 7 kW | 7875 kWh | 3150 kWh | 4725 kWh | £848 | £473 | £1,321 | £14,242 | 10.8 yrs | £12,170 |
| 8 kW | 9001 kWh | 3600 kWh | 5400 kWh | £969 | £540 | £1,509 | £16,276 | 10.8 yrs | £13,908 |
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: £1,134, Upfront: £12,273, Break-even: 10.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2250 kWh | 1350 kWh | 900 kWh | £363 | £90 | £453 | £6,169 | 13.6 yrs | £2,900 |
| 3 kW | 3375 kWh | 2025 kWh | 1350 kWh | £545 | £135 | £680 | £8,204 | 12.1 yrs | £5,400 |
| 4 kW | 4500 kWh | 2700 kWh | 1800 kWh | £727 | £180 | £907 | £10,238 | 11.3 yrs | £7,900 |
| 5 kW | 5625 kWh | 3375 kWh | 2250 kWh | £909 | £225 | £1,134 | £12,273 | 10.8 yrs | £10,400 |
| 6 kW | 6750 kWh | 4050 kWh | 2700 kWh | £1,090 | £270 | £1,360 | £14,307 | 10.5 yrs | £12,900 |
| 7 kW | 7875 kWh | 4725 kWh | 3150 kWh | £1,272 | £315 | £1,587 | £16,342 | 10.3 yrs | £15,400 |
| 8 kW | 9001 kWh | 5400 kWh | 3600 kWh | £1,454 | £360 | £1,814 | £18,376 | 10.1 yrs | £17,900 |
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: £1,229, Upfront: £13,673, Break-even: 11.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2250 kWh | 1575 kWh | 675 kWh | £424 | £68 | £492 | £7,569 | 15.4 yrs | £2,261 |
| 3 kW | 3375 kWh | 2363 kWh | 1013 kWh | £636 | £101 | £737 | £9,604 | 13.0 yrs | £5,142 |
| 4 kW | 4500 kWh | 3150 kWh | 1350 kWh | £848 | £135 | £983 | £11,638 | 11.8 yrs | £8,023 |
| 5 kW | 5625 kWh | 3938 kWh | 1688 kWh | £1,060 | £169 | £1,229 | £13,673 | 11.1 yrs | £10,903 |
| 6 kW | 6750 kWh | 4725 kWh | 2025 kWh | £1,272 | £203 | £1,475 | £15,707 | 10.7 yrs | £13,784 |
| 7 kW | 7875 kWh | 5513 kWh | 2363 kWh | £1,484 | £236 | £1,720 | £17,742 | 10.3 yrs | £16,665 |
| 8 kW | 9001 kWh | 6300 kWh | 2700 kWh | £1,696 | £270 | £1,966 | £19,776 | 10.1 yrs | £19,546 |
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: £1,257, Upfront: £15,423, 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 | 2250 kWh | 1643 kWh | 608 kWh | £442 | £61 | £503 | £9,319 | 18.5 yrs | £740 |
| 3 kW | 3375 kWh | 2464 kWh | 911 kWh | £663 | £91 | £754 | £11,354 | 15.0 yrs | £3,735 |
| 4 kW | 4500 kWh | 3285 kWh | 1215 kWh | £884 | £122 | £1,006 | £13,388 | 13.3 yrs | £6,730 |
| 5 kW | 5625 kWh | 4107 kWh | 1519 kWh | £1,105 | £152 | £1,257 | £15,423 | 12.3 yrs | £9,725 |
| 6 kW | 6750 kWh | 4928 kWh | 1823 kWh | £1,327 | £182 | £1,509 | £17,457 | 11.6 yrs | £12,719 |
| 7 kW | 7875 kWh | 5749 kWh | 2126 kWh | £1,548 | £213 | £1,760 | £19,492 | 11.1 yrs | £15,714 |
| 8 kW | 9001 kWh | 6570 kWh | 2430 kWh | £1,769 | £243 | £2,012 | £21,526 | 10.7 yrs | £18,709 |
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: £1,276, Upfront: £17,173, 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 | 2250 kWh | 1688 kWh | 563 kWh | £454 | £56 | £511 | £11,069 | 21.7 yrs | £-858 |
| 3 kW | 3375 kWh | 2531 kWh | 844 kWh | £681 | £84 | £766 | £13,104 | 17.1 yrs | £2,213 |
| 4 kW | 4500 kWh | 3375 kWh | 1125 kWh | £909 | £113 | £1,021 | £15,138 | 14.8 yrs | £5,284 |
| 5 kW | 5625 kWh | 4219 kWh | 1406 kWh | £1,136 | £141 | £1,276 | £17,173 | 13.5 yrs | £8,355 |
| 6 kW | 6750 kWh | 5063 kWh | 1688 kWh | £1,363 | £169 | £1,532 | £19,207 | 12.5 yrs | £11,426 |
| 7 kW | 7875 kWh | 5907 kWh | 1969 kWh | £1,590 | £197 | £1,787 | £21,242 | 11.9 yrs | £14,497 |
| 8 kW | 9001 kWh | 6750 kWh | 2250 kWh | £1,817 | £225 | £2,042 | £23,276 | 11.4 yrs | £17,568 |
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: £1,295, Upfront: £19,623, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2250 kWh | 1733 kWh | 518 kWh | £466 | £52 | £518 | £13,519 | 26.1 yrs | £-3,156 |
| 3 kW | 3375 kWh | 2599 kWh | 776 kWh | £700 | £78 | £777 | £15,554 | 20.0 yrs | £-8 |
| 4 kW | 4500 kWh | 3465 kWh | 1035 kWh | £933 | £104 | £1,036 | £17,588 | 17.0 yrs | £3,139 |
| 5 kW | 5625 kWh | 4332 kWh | 1294 kWh | £1,166 | £129 | £1,295 | £19,623 | 15.1 yrs | £6,286 |
| 6 kW | 6750 kWh | 5198 kWh | 1553 kWh | £1,399 | £155 | £1,555 | £21,657 | 13.9 yrs | £9,433 |
| 7 kW | 7875 kWh | 6064 kWh | 1811 kWh | £1,632 | £181 | £1,814 | £23,692 | 13.1 yrs | £12,580 |
| 8 kW | 9001 kWh | 6930 kWh | 2070 kWh | £1,866 | £207 | £2,073 | £25,726 | 12.4 yrs | £15,728 |
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.