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 971 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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: £783, Upfront: £10,173, Break-even: 13.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1942 kWh | 777 kWh | 1165 kWh | £197 | £117 | £313 | £4,069 | 13.0 yrs | £2,197 |
| 3 kW | 2913 kWh | 1165 kWh | 1748 kWh | £295 | £175 | £470 | £6,104 | 13.0 yrs | £3,295 |
| 4 kW | 3884 kWh | 1554 kWh | 2331 kWh | £394 | £233 | £627 | £8,138 | 13.0 yrs | £4,394 |
| 5 kW | 4855 kWh | 1942 kWh | 2913 kWh | £492 | £291 | £783 | £10,173 | 13.0 yrs | £5,492 |
| 6 kW | 5826 kWh | 2331 kWh | 3496 kWh | £590 | £350 | £940 | £12,207 | 13.0 yrs | £6,591 |
| 7 kW | 6797 kWh | 2719 kWh | 4078 kWh | £689 | £408 | £1,097 | £14,242 | 13.0 yrs | £7,689 |
| 8 kW | 7768 kWh | 3107 kWh | 4661 kWh | £787 | £466 | £1,253 | £16,276 | 13.0 yrs | £8,788 |
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: £932, Upfront: £12,273, Break-even: 13.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1942 kWh | 1165 kWh | 777 kWh | £295 | £78 | £373 | £6,169 | 16.5 yrs | £1,288 |
| 3 kW | 2913 kWh | 1748 kWh | 1165 kWh | £443 | £117 | £559 | £8,204 | 14.7 yrs | £2,982 |
| 4 kW | 3884 kWh | 2331 kWh | 1554 kWh | £590 | £155 | £746 | £10,238 | 13.7 yrs | £4,676 |
| 5 kW | 4855 kWh | 2913 kWh | 1942 kWh | £738 | £194 | £932 | £12,273 | 13.2 yrs | £6,370 |
| 6 kW | 5826 kWh | 3496 kWh | 2331 kWh | £885 | £233 | £1,119 | £14,307 | 12.8 yrs | £8,064 |
| 7 kW | 6797 kWh | 4078 kWh | 2719 kWh | £1,033 | £272 | £1,305 | £16,342 | 12.5 yrs | £9,758 |
| 8 kW | 7768 kWh | 4661 kWh | 3107 kWh | £1,181 | £311 | £1,491 | £18,376 | 12.3 yrs | £11,451 |
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: £1,007, Upfront: £13,673, 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 | 1942 kWh | 1359 kWh | 583 kWh | £344 | £58 | £403 | £7,569 | 18.8 yrs | £483 |
| 3 kW | 2913 kWh | 2039 kWh | 874 kWh | £517 | £87 | £604 | £9,604 | 15.9 yrs | £2,475 |
| 4 kW | 3884 kWh | 2719 kWh | 1165 kWh | £689 | £117 | £805 | £11,638 | 14.5 yrs | £4,467 |
| 5 kW | 4855 kWh | 3399 kWh | 1457 kWh | £861 | £146 | £1,007 | £13,673 | 13.6 yrs | £6,458 |
| 6 kW | 5826 kWh | 4078 kWh | 1748 kWh | £1,033 | £175 | £1,208 | £15,707 | 13.0 yrs | £8,450 |
| 7 kW | 6797 kWh | 4758 kWh | 2039 kWh | £1,205 | £204 | £1,409 | £17,742 | 12.6 yrs | £10,442 |
| 8 kW | 7768 kWh | 5438 kWh | 2331 kWh | £1,377 | £233 | £1,610 | £19,776 | 12.3 yrs | £12,433 |
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: £1,029, Upfront: £15,423, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1942 kWh | 1418 kWh | 524 kWh | £359 | £52 | £412 | £9,319 | 22.6 yrs | £-1,088 |
| 3 kW | 2913 kWh | 2127 kWh | 787 kWh | £539 | £79 | £617 | £11,354 | 18.4 yrs | £993 |
| 4 kW | 3884 kWh | 2835 kWh | 1049 kWh | £718 | £105 | £823 | £13,388 | 16.3 yrs | £3,074 |
| 5 kW | 4855 kWh | 3544 kWh | 1311 kWh | £898 | £131 | £1,029 | £15,423 | 15.0 yrs | £5,155 |
| 6 kW | 5826 kWh | 4253 kWh | 1573 kWh | £1,077 | £157 | £1,235 | £17,457 | 14.1 yrs | £7,236 |
| 7 kW | 6797 kWh | 4962 kWh | 1835 kWh | £1,257 | £184 | £1,440 | £19,492 | 13.5 yrs | £9,317 |
| 8 kW | 7768 kWh | 5671 kWh | 2097 kWh | £1,436 | £210 | £1,646 | £21,526 | 13.1 yrs | £11,398 |
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: £1,044, Upfront: £17,173, Break-even: 16.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1942 kWh | 1457 kWh | 486 kWh | £369 | £49 | £418 | £11,069 | 26.5 yrs | £-2,719 |
| 3 kW | 2913 kWh | 2185 kWh | 728 kWh | £553 | £73 | £626 | £13,104 | 20.9 yrs | £-578 |
| 4 kW | 3884 kWh | 2913 kWh | 971 kWh | £738 | £97 | £835 | £15,138 | 18.1 yrs | £1,562 |
| 5 kW | 4855 kWh | 3641 kWh | 1214 kWh | £922 | £121 | £1,044 | £17,173 | 16.5 yrs | £3,703 |
| 6 kW | 5826 kWh | 4370 kWh | 1457 kWh | £1,107 | £146 | £1,253 | £19,207 | 15.3 yrs | £5,843 |
| 7 kW | 6797 kWh | 5098 kWh | 1699 kWh | £1,291 | £170 | £1,461 | £21,242 | 14.5 yrs | £7,984 |
| 8 kW | 7768 kWh | 5826 kWh | 1942 kWh | £1,476 | £194 | £1,670 | £23,276 | 13.9 yrs | £10,124 |
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: £1,059, Upfront: £19,623, Break-even: 18.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1942 kWh | 1495 kWh | 447 kWh | £379 | £45 | £423 | £13,519 | 31.9 yrs | £-5,050 |
| 3 kW | 2913 kWh | 2243 kWh | 670 kWh | £568 | £67 | £635 | £15,554 | 24.5 yrs | £-2,850 |
| 4 kW | 3884 kWh | 2991 kWh | 893 kWh | £758 | £89 | £847 | £17,588 | 20.8 yrs | £-650 |
| 5 kW | 4855 kWh | 3739 kWh | 1117 kWh | £947 | £112 | £1,059 | £19,623 | 18.5 yrs | £1,550 |
| 6 kW | 5826 kWh | 4486 kWh | 1340 kWh | £1,136 | £134 | £1,270 | £21,657 | 17.0 yrs | £3,750 |
| 7 kW | 6797 kWh | 5234 kWh | 1563 kWh | £1,326 | £156 | £1,482 | £23,692 | 16.0 yrs | £5,950 |
| 8 kW | 7768 kWh | 5982 kWh | 1787 kWh | £1,515 | £179 | £1,694 | £25,726 | 15.2 yrs | £8,151 |
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.