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 934 kWh per year on a south-facing roof. We value self-used electricity at 27.7p 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: £798, Upfront: £10,173, Break-even: 12.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1868 kWh | 747 kWh | 1121 kWh | £207 | £112 | £319 | £4,069 | 12.7 yrs | £2,316 |
| 3 kW | 2803 kWh | 1121 kWh | 1682 kWh | £311 | £168 | £479 | £6,104 | 12.7 yrs | £3,475 |
| 4 kW | 3737 kWh | 1495 kWh | 2242 kWh | £414 | £224 | £639 | £8,138 | 12.7 yrs | £4,633 |
| 5 kW | 4671 kWh | 1868 kWh | 2803 kWh | £518 | £280 | £798 | £10,173 | 12.7 yrs | £5,791 |
| 6 kW | 5605 kWh | 2242 kWh | 3363 kWh | £621 | £336 | £958 | £12,207 | 12.7 yrs | £6,949 |
| 7 kW | 6539 kWh | 2616 kWh | 3924 kWh | £725 | £392 | £1,117 | £14,242 | 12.7 yrs | £8,107 |
| 8 kW | 7474 kWh | 2989 kWh | 4484 kWh | £829 | £448 | £1,277 | £16,276 | 12.7 yrs | £9,265 |
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: £964, Upfront: £12,273, Break-even: 12.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1868 kWh | 1121 kWh | 747 kWh | £311 | £75 | £385 | £6,169 | 16.0 yrs | £1,541 |
| 3 kW | 2803 kWh | 1682 kWh | 1121 kWh | £466 | £112 | £578 | £8,204 | 14.2 yrs | £3,361 |
| 4 kW | 3737 kWh | 2242 kWh | 1495 kWh | £621 | £149 | £771 | £10,238 | 13.3 yrs | £5,181 |
| 5 kW | 4671 kWh | 2803 kWh | 1868 kWh | £777 | £187 | £964 | £12,273 | 12.7 yrs | £7,002 |
| 6 kW | 5605 kWh | 3363 kWh | 2242 kWh | £932 | £224 | £1,156 | £14,307 | 12.4 yrs | £8,822 |
| 7 kW | 6539 kWh | 3924 kWh | 2616 kWh | £1,088 | £262 | £1,349 | £16,342 | 12.1 yrs | £10,642 |
| 8 kW | 7474 kWh | 4484 kWh | 2989 kWh | £1,243 | £299 | £1,542 | £18,376 | 11.9 yrs | £12,463 |
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: £1,046, Upfront: £13,673, Break-even: 13.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1868 kWh | 1308 kWh | 561 kWh | £363 | £56 | £419 | £7,569 | 18.1 yrs | £803 |
| 3 kW | 2803 kWh | 1962 kWh | 841 kWh | £544 | £84 | £628 | £9,604 | 15.3 yrs | £2,954 |
| 4 kW | 3737 kWh | 2616 kWh | 1121 kWh | £725 | £112 | £837 | £11,638 | 13.9 yrs | £5,106 |
| 5 kW | 4671 kWh | 3270 kWh | 1401 kWh | £906 | £140 | £1,046 | £13,673 | 13.1 yrs | £7,257 |
| 6 kW | 5605 kWh | 3924 kWh | 1682 kWh | £1,088 | £168 | £1,256 | £15,707 | 12.5 yrs | £9,408 |
| 7 kW | 6539 kWh | 4578 kWh | 1962 kWh | £1,269 | £196 | £1,465 | £17,742 | 12.1 yrs | £11,560 |
| 8 kW | 7474 kWh | 5231 kWh | 2242 kWh | £1,450 | £224 | £1,674 | £19,776 | 11.8 yrs | £13,711 |
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: £1,071, Upfront: £15,423, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1868 kWh | 1364 kWh | 504 kWh | £378 | £50 | £429 | £9,319 | 21.7 yrs | £-749 |
| 3 kW | 2803 kWh | 2046 kWh | 757 kWh | £567 | £76 | £643 | £11,354 | 17.7 yrs | £1,502 |
| 4 kW | 3737 kWh | 2728 kWh | 1009 kWh | £756 | £101 | £857 | £13,388 | 15.6 yrs | £3,753 |
| 5 kW | 4671 kWh | 3410 kWh | 1261 kWh | £945 | £126 | £1,071 | £15,423 | 14.4 yrs | £6,004 |
| 6 kW | 5605 kWh | 4092 kWh | 1513 kWh | £1,134 | £151 | £1,286 | £17,457 | 13.6 yrs | £8,254 |
| 7 kW | 6539 kWh | 4774 kWh | 1766 kWh | £1,323 | £177 | £1,500 | £19,492 | 13.0 yrs | £10,505 |
| 8 kW | 7474 kWh | 5456 kWh | 2018 kWh | £1,512 | £202 | £1,714 | £21,526 | 12.6 yrs | £12,756 |
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: £1,088, Upfront: £17,173, 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 | 1868 kWh | 1401 kWh | 467 kWh | £388 | £47 | £435 | £11,069 | 25.4 yrs | £-2,366 |
| 3 kW | 2803 kWh | 2102 kWh | 701 kWh | £583 | £70 | £653 | £13,104 | 20.1 yrs | £-49 |
| 4 kW | 3737 kWh | 2803 kWh | 934 kWh | £777 | £93 | £870 | £15,138 | 17.4 yrs | £2,268 |
| 5 kW | 4671 kWh | 3503 kWh | 1168 kWh | £971 | £117 | £1,088 | £17,173 | 15.8 yrs | £4,585 |
| 6 kW | 5605 kWh | 4204 kWh | 1401 kWh | £1,165 | £140 | £1,305 | £19,207 | 14.7 yrs | £6,902 |
| 7 kW | 6539 kWh | 4904 kWh | 1635 kWh | £1,360 | £163 | £1,523 | £21,242 | 13.9 yrs | £9,219 |
| 8 kW | 7474 kWh | 5605 kWh | 1868 kWh | £1,554 | £187 | £1,741 | £23,276 | 13.4 yrs | £11,536 |
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: £1,104, Upfront: £19,623, Break-even: 17.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1868 kWh | 1439 kWh | 430 kWh | £399 | £43 | £442 | £13,519 | 30.6 yrs | £-4,684 |
| 3 kW | 2803 kWh | 2158 kWh | 645 kWh | £598 | £64 | £663 | £15,554 | 23.5 yrs | £-2,301 |
| 4 kW | 3737 kWh | 2877 kWh | 859 kWh | £798 | £86 | £884 | £17,588 | 19.9 yrs | £83 |
| 5 kW | 4671 kWh | 3597 kWh | 1074 kWh | £997 | £107 | £1,104 | £19,623 | 17.8 yrs | £2,466 |
| 6 kW | 5605 kWh | 4316 kWh | 1289 kWh | £1,196 | £129 | £1,325 | £21,657 | 16.3 yrs | £4,849 |
| 7 kW | 6539 kWh | 5035 kWh | 1504 kWh | £1,396 | £150 | £1,546 | £23,692 | 15.3 yrs | £7,232 |
| 8 kW | 7474 kWh | 5755 kWh | 1719 kWh | £1,595 | £172 | £1,767 | £25,726 | 14.6 yrs | £9,615 |
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.