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 964 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £782, 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 | 1928 kWh | 771 kWh | 1157 kWh | £197 | £116 | £313 | £4,069 | 13.0 yrs | £2,186 |
| 3 kW | 2892 kWh | 1157 kWh | 1735 kWh | £296 | £174 | £469 | £6,104 | 13.0 yrs | £3,280 |
| 4 kW | 3857 kWh | 1543 kWh | 2314 kWh | £394 | £231 | £626 | £8,138 | 13.0 yrs | £4,373 |
| 5 kW | 4821 kWh | 1928 kWh | 2892 kWh | £493 | £289 | £782 | £10,173 | 13.0 yrs | £5,466 |
| 6 kW | 5785 kWh | 2314 kWh | 3471 kWh | £591 | £347 | £938 | £12,207 | 13.0 yrs | £6,559 |
| 7 kW | 6749 kWh | 2700 kWh | 4049 kWh | £690 | £405 | £1,095 | £14,242 | 13.0 yrs | £7,652 |
| 8 kW | 7713 kWh | 3085 kWh | 4628 kWh | £788 | £463 | £1,251 | £16,276 | 13.0 yrs | £8,746 |
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 | 1928 kWh | 1157 kWh | 771 kWh | £296 | £77 | £373 | £6,169 | 16.6 yrs | £1,286 |
| 3 kW | 2892 kWh | 1735 kWh | 1157 kWh | £443 | £116 | £559 | £8,204 | 14.7 yrs | £2,979 |
| 4 kW | 3857 kWh | 2314 kWh | 1543 kWh | £591 | £154 | £745 | £10,238 | 13.7 yrs | £4,672 |
| 5 kW | 4821 kWh | 2892 kWh | 1928 kWh | £739 | £193 | £932 | £12,273 | 13.2 yrs | £6,364 |
| 6 kW | 5785 kWh | 3471 kWh | 2314 kWh | £887 | £231 | £1,118 | £14,307 | 12.8 yrs | £8,057 |
| 7 kW | 6749 kWh | 4049 kWh | 2700 kWh | £1,035 | £270 | £1,305 | £16,342 | 12.5 yrs | £9,750 |
| 8 kW | 7713 kWh | 4628 kWh | 3085 kWh | £1,182 | £309 | £1,491 | £18,376 | 12.3 yrs | £11,443 |
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 | 1928 kWh | 1350 kWh | 578 kWh | £345 | £58 | £403 | £7,569 | 18.8 yrs | £485 |
| 3 kW | 2892 kWh | 2025 kWh | 868 kWh | £517 | £87 | £604 | £9,604 | 15.9 yrs | £2,478 |
| 4 kW | 3857 kWh | 2700 kWh | 1157 kWh | £690 | £116 | £805 | £11,638 | 14.4 yrs | £4,471 |
| 5 kW | 4821 kWh | 3375 kWh | 1446 kWh | £862 | £145 | £1,007 | £13,673 | 13.6 yrs | £6,464 |
| 6 kW | 5785 kWh | 4049 kWh | 1735 kWh | £1,035 | £174 | £1,208 | £15,707 | 13.0 yrs | £8,456 |
| 7 kW | 6749 kWh | 4724 kWh | 2025 kWh | £1,207 | £202 | £1,410 | £17,742 | 12.6 yrs | £10,449 |
| 8 kW | 7713 kWh | 5399 kWh | 2314 kWh | £1,380 | £231 | £1,611 | £19,776 | 12.3 yrs | £12,442 |
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 | 1928 kWh | 1408 kWh | 521 kWh | £360 | £52 | £412 | £9,319 | 22.6 yrs | £-1,085 |
| 3 kW | 2892 kWh | 2111 kWh | 781 kWh | £539 | £78 | £618 | £11,354 | 18.4 yrs | £998 |
| 4 kW | 3857 kWh | 2815 kWh | 1041 kWh | £719 | £104 | £823 | £13,388 | 16.3 yrs | £3,081 |
| 5 kW | 4821 kWh | 3519 kWh | 1302 kWh | £899 | £130 | £1,029 | £15,423 | 15.0 yrs | £5,163 |
| 6 kW | 5785 kWh | 4223 kWh | 1562 kWh | £1,079 | £156 | £1,235 | £17,457 | 14.1 yrs | £7,246 |
| 7 kW | 6749 kWh | 4927 kWh | 1822 kWh | £1,259 | £182 | £1,441 | £19,492 | 13.5 yrs | £9,329 |
| 8 kW | 7713 kWh | 5631 kWh | 2083 kWh | £1,439 | £208 | £1,647 | £21,526 | 13.1 yrs | £11,412 |
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: 16.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1928 kWh | 1446 kWh | 482 kWh | £370 | £48 | £418 | £11,069 | 26.5 yrs | £-2,715 |
| 3 kW | 2892 kWh | 2169 kWh | 723 kWh | £554 | £72 | £627 | £13,104 | 20.9 yrs | £-572 |
| 4 kW | 3857 kWh | 2892 kWh | 964 kWh | £739 | £96 | £835 | £15,138 | 18.1 yrs | £1,571 |
| 5 kW | 4821 kWh | 3616 kWh | 1205 kWh | £924 | £121 | £1,044 | £17,173 | 16.4 yrs | £3,713 |
| 6 kW | 5785 kWh | 4339 kWh | 1446 kWh | £1,109 | £145 | £1,253 | £19,207 | 15.3 yrs | £5,856 |
| 7 kW | 6749 kWh | 5062 kWh | 1687 kWh | £1,293 | £169 | £1,462 | £21,242 | 14.5 yrs | £7,999 |
| 8 kW | 7713 kWh | 5785 kWh | 1928 kWh | £1,478 | £193 | £1,671 | £23,276 | 13.9 yrs | £10,141 |
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 | 1928 kWh | 1485 kWh | 444 kWh | £379 | £44 | £424 | £13,519 | 31.9 yrs | £-5,045 |
| 3 kW | 2892 kWh | 2227 kWh | 665 kWh | £569 | £67 | £636 | £15,554 | 24.5 yrs | £-2,842 |
| 4 kW | 3857 kWh | 2970 kWh | 887 kWh | £759 | £89 | £847 | £17,588 | 20.8 yrs | £-639 |
| 5 kW | 4821 kWh | 3712 kWh | 1109 kWh | £948 | £111 | £1,059 | £19,623 | 18.5 yrs | £1,563 |
| 6 kW | 5785 kWh | 4454 kWh | 1331 kWh | £1,138 | £133 | £1,271 | £21,657 | 17.0 yrs | £3,766 |
| 7 kW | 6749 kWh | 5197 kWh | 1552 kWh | £1,328 | £155 | £1,483 | £23,692 | 16.0 yrs | £5,968 |
| 8 kW | 7713 kWh | 5939 kWh | 1774 kWh | £1,517 | £177 | £1,695 | £25,726 | 15.2 yrs | £8,171 |
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.