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 892 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £729, Upfront: £10,173, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1785 kWh | 714 kWh | 1071 kWh | £184 | £107 | £292 | £4,069 | 14.0 yrs | £1,763 |
| 3 kW | 2677 kWh | 1071 kWh | 1606 kWh | £277 | £161 | £437 | £6,104 | 14.0 yrs | £2,644 |
| 4 kW | 3570 kWh | 1428 kWh | 2142 kWh | £369 | £214 | £583 | £8,138 | 14.0 yrs | £3,525 |
| 5 kW | 4462 kWh | 1785 kWh | 2677 kWh | £461 | £268 | £729 | £10,173 | 14.0 yrs | £4,407 |
| 6 kW | 5355 kWh | 2142 kWh | 3213 kWh | £553 | £321 | £875 | £12,207 | 14.0 yrs | £5,288 |
| 7 kW | 6247 kWh | 2499 kWh | 3748 kWh | £646 | £375 | £1,021 | £14,242 | 14.0 yrs | £6,169 |
| 8 kW | 7140 kWh | 2856 kWh | 4284 kWh | £738 | £428 | £1,166 | £16,276 | 14.0 yrs | £7,050 |
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: £870, Upfront: £12,273, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1785 kWh | 1071 kWh | 714 kWh | £277 | £71 | £348 | £6,169 | 17.7 yrs | £794 |
| 3 kW | 2677 kWh | 1606 kWh | 1071 kWh | £415 | £107 | £522 | £8,204 | 15.7 yrs | £2,240 |
| 4 kW | 3570 kWh | 2142 kWh | 1428 kWh | £553 | £143 | £696 | £10,238 | 14.7 yrs | £3,687 |
| 5 kW | 4462 kWh | 2677 kWh | 1785 kWh | £692 | £178 | £870 | £12,273 | 14.1 yrs | £5,134 |
| 6 kW | 5355 kWh | 3213 kWh | 2142 kWh | £830 | £214 | £1,044 | £14,307 | 13.7 yrs | £6,581 |
| 7 kW | 6247 kWh | 3748 kWh | 2499 kWh | £969 | £250 | £1,218 | £16,342 | 13.4 yrs | £8,027 |
| 8 kW | 7140 kWh | 4284 kWh | 2856 kWh | £1,107 | £286 | £1,393 | £18,376 | 13.2 yrs | £9,474 |
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: £941, Upfront: £13,673, Break-even: 14.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1785 kWh | 1249 kWh | 535 kWh | £323 | £54 | £376 | £7,569 | 20.1 yrs | £-41 |
| 3 kW | 2677 kWh | 1874 kWh | 803 kWh | £484 | £80 | £565 | £9,604 | 17.0 yrs | £1,688 |
| 4 kW | 3570 kWh | 2499 kWh | 1071 kWh | £646 | £107 | £753 | £11,638 | 15.5 yrs | £3,418 |
| 5 kW | 4462 kWh | 3124 kWh | 1339 kWh | £807 | £134 | £941 | £13,673 | 14.5 yrs | £5,147 |
| 6 kW | 5355 kWh | 3748 kWh | 1606 kWh | £969 | £161 | £1,129 | £15,707 | 13.9 yrs | £6,877 |
| 7 kW | 6247 kWh | 4373 kWh | 1874 kWh | £1,130 | £187 | £1,317 | £17,742 | 13.5 yrs | £8,606 |
| 8 kW | 7140 kWh | 4998 kWh | 2142 kWh | £1,291 | £214 | £1,506 | £19,776 | 13.1 yrs | £10,336 |
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: £962, Upfront: £15,423, Break-even: 16.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1785 kWh | 1303 kWh | 482 kWh | £337 | £48 | £385 | £9,319 | 24.2 yrs | £-1,621 |
| 3 kW | 2677 kWh | 1954 kWh | 723 kWh | £505 | £72 | £577 | £11,354 | 19.7 yrs | £193 |
| 4 kW | 3570 kWh | 2606 kWh | 964 kWh | £673 | £96 | £770 | £13,388 | 17.4 yrs | £2,007 |
| 5 kW | 4462 kWh | 3257 kWh | 1205 kWh | £842 | £120 | £962 | £15,423 | 16.0 yrs | £3,822 |
| 6 kW | 5355 kWh | 3909 kWh | 1446 kWh | £1,010 | £145 | £1,155 | £17,457 | 15.1 yrs | £5,636 |
| 7 kW | 6247 kWh | 4560 kWh | 1687 kWh | £1,178 | £169 | £1,347 | £19,492 | 14.5 yrs | £7,450 |
| 8 kW | 7140 kWh | 5212 kWh | 1928 kWh | £1,347 | £193 | £1,540 | £21,526 | 14.0 yrs | £9,264 |
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: £976, Upfront: £17,173, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1785 kWh | 1339 kWh | 446 kWh | £346 | £45 | £391 | £11,069 | 28.3 yrs | £-3,258 |
| 3 kW | 2677 kWh | 2008 kWh | 669 kWh | £519 | £67 | £586 | £13,104 | 22.4 yrs | £-1,387 |
| 4 kW | 3570 kWh | 2677 kWh | 892 kWh | £692 | £89 | £781 | £15,138 | 19.4 yrs | £483 |
| 5 kW | 4462 kWh | 3347 kWh | 1116 kWh | £865 | £112 | £976 | £17,173 | 17.6 yrs | £2,354 |
| 6 kW | 5355 kWh | 4016 kWh | 1339 kWh | £1,038 | £134 | £1,172 | £19,207 | 16.4 yrs | £4,225 |
| 7 kW | 6247 kWh | 4685 kWh | 1562 kWh | £1,211 | £156 | £1,367 | £21,242 | 15.5 yrs | £6,096 |
| 8 kW | 7140 kWh | 5355 kWh | 1785 kWh | £1,384 | £178 | £1,562 | £23,276 | 14.9 yrs | £7,967 |
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: £990, Upfront: £19,623, Break-even: 19.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1785 kWh | 1374 kWh | 411 kWh | £355 | £41 | £396 | £13,519 | 34.1 yrs | £-5,595 |
| 3 kW | 2677 kWh | 2062 kWh | 616 kWh | £533 | £62 | £594 | £15,554 | 26.2 yrs | £-3,668 |
| 4 kW | 3570 kWh | 2749 kWh | 821 kWh | £710 | £82 | £792 | £17,588 | 22.2 yrs | £-1,740 |
| 5 kW | 4462 kWh | 3436 kWh | 1026 kWh | £888 | £103 | £990 | £19,623 | 19.8 yrs | £187 |
| 6 kW | 5355 kWh | 4123 kWh | 1232 kWh | £1,065 | £123 | £1,189 | £21,657 | 18.2 yrs | £2,114 |
| 7 kW | 6247 kWh | 4810 kWh | 1437 kWh | £1,243 | £144 | £1,387 | £23,692 | 17.1 yrs | £4,042 |
| 8 kW | 7140 kWh | 5497 kWh | 1642 kWh | £1,421 | £164 | £1,585 | £25,726 | 16.2 yrs | £5,969 |
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.