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 768 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £646, Upfront: £10,173, Break-even: 15.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1535 kWh | 614 kWh | 921 kWh | £166 | £92 | £258 | £4,069 | 15.8 yrs | £1,096 |
| 3 kW | 2303 kWh | 921 kWh | 1382 kWh | £249 | £138 | £387 | £6,104 | 15.8 yrs | £1,644 |
| 4 kW | 3070 kWh | 1228 kWh | 1842 kWh | £332 | £184 | £517 | £8,138 | 15.8 yrs | £2,193 |
| 5 kW | 3838 kWh | 1535 kWh | 2303 kWh | £415 | £230 | £646 | £10,173 | 15.8 yrs | £2,741 |
| 6 kW | 4605 kWh | 1842 kWh | 2763 kWh | £498 | £276 | £775 | £12,207 | 15.8 yrs | £3,289 |
| 7 kW | 5373 kWh | 2149 kWh | 3224 kWh | £582 | £322 | £904 | £14,242 | 15.8 yrs | £3,837 |
| 8 kW | 6140 kWh | 2456 kWh | 3684 kWh | £665 | £368 | £1,033 | £16,276 | 15.8 yrs | £4,385 |
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: £777, Upfront: £12,273, Break-even: 15.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1535 kWh | 921 kWh | 614 kWh | £249 | £61 | £311 | £6,169 | 19.9 yrs | £44 |
| 3 kW | 2303 kWh | 1382 kWh | 921 kWh | £374 | £92 | £466 | £8,204 | 17.6 yrs | £1,116 |
| 4 kW | 3070 kWh | 1842 kWh | 1228 kWh | £498 | £123 | £621 | £10,238 | 16.5 yrs | £2,188 |
| 5 kW | 3838 kWh | 2303 kWh | 1535 kWh | £623 | £154 | £777 | £12,273 | 15.8 yrs | £3,260 |
| 6 kW | 4605 kWh | 2763 kWh | 1842 kWh | £748 | £184 | £932 | £14,307 | 15.4 yrs | £4,332 |
| 7 kW | 5373 kWh | 3224 kWh | 2149 kWh | £872 | £215 | £1,087 | £16,342 | 15.0 yrs | £5,403 |
| 8 kW | 6140 kWh | 3684 kWh | 2456 kWh | £997 | £246 | £1,243 | £18,376 | 14.8 yrs | £6,475 |
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: £842, Upfront: £13,673, Break-even: 16.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1535 kWh | 1075 kWh | 461 kWh | £291 | £46 | £337 | £7,569 | 22.5 yrs | £-832 |
| 3 kW | 2303 kWh | 1612 kWh | 691 kWh | £436 | £69 | £505 | £9,604 | 19.0 yrs | £501 |
| 4 kW | 3070 kWh | 2149 kWh | 921 kWh | £582 | £92 | £674 | £11,638 | 17.3 yrs | £1,835 |
| 5 kW | 3838 kWh | 2686 kWh | 1151 kWh | £727 | £115 | £842 | £13,673 | 16.2 yrs | £3,169 |
| 6 kW | 4605 kWh | 3224 kWh | 1382 kWh | £872 | £138 | £1,010 | £15,707 | 15.5 yrs | £4,503 |
| 7 kW | 5373 kWh | 3761 kWh | 1612 kWh | £1,018 | £161 | £1,179 | £17,742 | 15.0 yrs | £5,837 |
| 8 kW | 6140 kWh | 4298 kWh | 1842 kWh | £1,163 | £184 | £1,347 | £19,776 | 14.7 yrs | £7,170 |
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: £862, Upfront: £15,423, Break-even: 17.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1535 kWh | 1121 kWh | 414 kWh | £303 | £41 | £345 | £9,319 | 27.0 yrs | £-2,425 |
| 3 kW | 2303 kWh | 1681 kWh | 622 kWh | £455 | £62 | £517 | £11,354 | 22.0 yrs | £-1,013 |
| 4 kW | 3070 kWh | 2241 kWh | 829 kWh | £606 | £83 | £689 | £13,388 | 19.4 yrs | £399 |
| 5 kW | 3838 kWh | 2802 kWh | 1036 kWh | £758 | £104 | £862 | £15,423 | 17.9 yrs | £1,812 |
| 6 kW | 4605 kWh | 3362 kWh | 1243 kWh | £910 | £124 | £1,034 | £17,457 | 16.9 yrs | £3,224 |
| 7 kW | 5373 kWh | 3922 kWh | 1451 kWh | £1,061 | £145 | £1,206 | £19,492 | 16.2 yrs | £4,637 |
| 8 kW | 6140 kWh | 4482 kWh | 1658 kWh | £1,213 | £166 | £1,379 | £21,526 | 15.6 yrs | £6,049 |
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: £875, Upfront: £17,173, Break-even: 19.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1535 kWh | 1151 kWh | 384 kWh | £312 | £38 | £350 | £11,069 | 31.6 yrs | £-4,070 |
| 3 kW | 2303 kWh | 1727 kWh | 576 kWh | £467 | £58 | £525 | £13,104 | 25.0 yrs | £-2,606 |
| 4 kW | 3070 kWh | 2303 kWh | 768 kWh | £623 | £77 | £700 | £15,138 | 21.6 yrs | £-1,141 |
| 5 kW | 3838 kWh | 2878 kWh | 959 kWh | £779 | £96 | £875 | £17,173 | 19.6 yrs | £324 |
| 6 kW | 4605 kWh | 3454 kWh | 1151 kWh | £935 | £115 | £1,050 | £19,207 | 18.3 yrs | £1,789 |
| 7 kW | 5373 kWh | 4030 kWh | 1343 kWh | £1,090 | £134 | £1,225 | £21,242 | 17.3 yrs | £3,253 |
| 8 kW | 6140 kWh | 4605 kWh | 1535 kWh | £1,246 | £154 | £1,400 | £23,276 | 16.6 yrs | £4,718 |
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: £888, Upfront: £19,623, Break-even: 22.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1535 kWh | 1182 kWh | 353 kWh | £320 | £35 | £355 | £13,519 | 38.1 yrs | £-6,416 |
| 3 kW | 2303 kWh | 1773 kWh | 530 kWh | £480 | £53 | £533 | £15,554 | 29.2 yrs | £-4,899 |
| 4 kW | 3070 kWh | 2364 kWh | 706 kWh | £640 | £71 | £710 | £17,588 | 24.8 yrs | £-3,381 |
| 5 kW | 3838 kWh | 2955 kWh | 883 kWh | £800 | £88 | £888 | £19,623 | 22.1 yrs | £-1,864 |
| 6 kW | 4605 kWh | 3546 kWh | 1059 kWh | £960 | £106 | £1,065 | £21,657 | 20.3 yrs | £-347 |
| 7 kW | 5373 kWh | 4137 kWh | 1236 kWh | £1,119 | £124 | £1,243 | £23,692 | 19.1 yrs | £1,170 |
| 8 kW | 6140 kWh | 4728 kWh | 1412 kWh | £1,279 | £141 | £1,421 | £25,726 | 18.1 yrs | £2,687 |
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.