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 1006 kWh per year on a south-facing roof. We value self-used electricity at 26.8p 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: £841, Upfront: £10,173, Break-even: 12.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2011 kWh | 804 kWh | 1207 kWh | £216 | £121 | £336 | £4,069 | 12.1 yrs | £2,659 |
| 3 kW | 3017 kWh | 1207 kWh | 1810 kWh | £324 | £181 | £505 | £6,104 | 12.1 yrs | £3,989 |
| 4 kW | 4022 kWh | 1609 kWh | 2413 kWh | £431 | £241 | £673 | £8,138 | 12.1 yrs | £5,318 |
| 5 kW | 5028 kWh | 2011 kWh | 3017 kWh | £539 | £302 | £841 | £10,173 | 12.1 yrs | £6,648 |
| 6 kW | 6033 kWh | 2413 kWh | 3620 kWh | £647 | £362 | £1,009 | £12,207 | 12.1 yrs | £7,977 |
| 7 kW | 7039 kWh | 2815 kWh | 4223 kWh | £755 | £422 | £1,177 | £14,242 | 12.1 yrs | £9,307 |
| 8 kW | 8044 kWh | 3218 kWh | 4826 kWh | £863 | £483 | £1,346 | £16,276 | 12.1 yrs | £10,636 |
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: £1,010, Upfront: £12,273, Break-even: 12.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2011 kWh | 1207 kWh | 804 kWh | £324 | £80 | £404 | £6,169 | 15.3 yrs | £1,912 |
| 3 kW | 3017 kWh | 1810 kWh | 1207 kWh | £485 | £121 | £606 | £8,204 | 13.5 yrs | £3,918 |
| 4 kW | 4022 kWh | 2413 kWh | 1609 kWh | £647 | £161 | £808 | £10,238 | 12.7 yrs | £5,924 |
| 5 kW | 5028 kWh | 3017 kWh | 2011 kWh | £809 | £201 | £1,010 | £12,273 | 12.1 yrs | £7,930 |
| 6 kW | 6033 kWh | 3620 kWh | 2413 kWh | £971 | £241 | £1,212 | £14,307 | 11.8 yrs | £9,936 |
| 7 kW | 7039 kWh | 4223 kWh | 2815 kWh | £1,133 | £282 | £1,414 | £16,342 | 11.6 yrs | £11,943 |
| 8 kW | 8044 kWh | 4826 kWh | 3218 kWh | £1,294 | £322 | £1,616 | £18,376 | 11.4 yrs | £13,949 |
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: £1,095, Upfront: £13,673, Break-even: 12.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2011 kWh | 1408 kWh | 603 kWh | £378 | £60 | £438 | £7,569 | 17.3 yrs | £1,189 |
| 3 kW | 3017 kWh | 2112 kWh | 905 kWh | £566 | £90 | £657 | £9,604 | 14.6 yrs | £3,533 |
| 4 kW | 4022 kWh | 2815 kWh | 1207 kWh | £755 | £121 | £876 | £11,638 | 13.3 yrs | £5,877 |
| 5 kW | 5028 kWh | 3519 kWh | 1508 kWh | £944 | £151 | £1,095 | £13,673 | 12.5 yrs | £8,222 |
| 6 kW | 6033 kWh | 4223 kWh | 1810 kWh | £1,133 | £181 | £1,314 | £15,707 | 12.0 yrs | £10,566 |
| 7 kW | 7039 kWh | 4927 kWh | 2112 kWh | £1,321 | £211 | £1,533 | £17,742 | 11.6 yrs | £12,910 |
| 8 kW | 8044 kWh | 5631 kWh | 2413 kWh | £1,510 | £241 | £1,752 | £19,776 | 11.3 yrs | £15,255 |
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: £1,120, Upfront: £15,423, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2011 kWh | 1468 kWh | 543 kWh | £394 | £54 | £448 | £9,319 | 20.8 yrs | £-358 |
| 3 kW | 3017 kWh | 2202 kWh | 814 kWh | £591 | £81 | £672 | £11,354 | 16.9 yrs | £2,087 |
| 4 kW | 4022 kWh | 2936 kWh | 1086 kWh | £787 | £109 | £896 | £13,388 | 14.9 yrs | £4,533 |
| 5 kW | 5028 kWh | 3670 kWh | 1357 kWh | £984 | £136 | £1,120 | £15,423 | 13.8 yrs | £6,979 |
| 6 kW | 6033 kWh | 4404 kWh | 1629 kWh | £1,181 | £163 | £1,344 | £17,457 | 13.0 yrs | £9,425 |
| 7 kW | 7039 kWh | 5138 kWh | 1900 kWh | £1,378 | £190 | £1,568 | £19,492 | 12.4 yrs | £11,871 |
| 8 kW | 8044 kWh | 5872 kWh | 2172 kWh | £1,575 | £217 | £1,792 | £21,526 | 12.0 yrs | £14,316 |
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: £1,137, Upfront: £17,173, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2011 kWh | 1508 kWh | 503 kWh | £405 | £50 | £455 | £11,069 | 24.3 yrs | £-1,973 |
| 3 kW | 3017 kWh | 2262 kWh | 754 kWh | £607 | £75 | £682 | £13,104 | 19.2 yrs | £540 |
| 4 kW | 4022 kWh | 3017 kWh | 1006 kWh | £809 | £101 | £910 | £15,138 | 16.6 yrs | £3,054 |
| 5 kW | 5028 kWh | 3771 kWh | 1257 kWh | £1,011 | £126 | £1,137 | £17,173 | 15.1 yrs | £5,567 |
| 6 kW | 6033 kWh | 4525 kWh | 1508 kWh | £1,214 | £151 | £1,364 | £19,207 | 14.1 yrs | £8,081 |
| 7 kW | 7039 kWh | 5279 kWh | 1760 kWh | £1,416 | £176 | £1,592 | £21,242 | 13.3 yrs | £10,594 |
| 8 kW | 8044 kWh | 6033 kWh | 2011 kWh | £1,618 | £201 | £1,819 | £23,276 | 12.8 yrs | £13,108 |
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: £1,154, Upfront: £19,623, Break-even: 17.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2011 kWh | 1549 kWh | 463 kWh | £415 | £46 | £462 | £13,519 | 29.3 yrs | £-4,288 |
| 3 kW | 3017 kWh | 2323 kWh | 694 kWh | £623 | £69 | £692 | £15,554 | 22.5 yrs | £-1,707 |
| 4 kW | 4022 kWh | 3097 kWh | 925 kWh | £831 | £93 | £923 | £17,588 | 19.1 yrs | £874 |
| 5 kW | 5028 kWh | 3871 kWh | 1156 kWh | £1,038 | £116 | £1,154 | £19,623 | 17.0 yrs | £3,456 |
| 6 kW | 6033 kWh | 4646 kWh | 1388 kWh | £1,246 | £139 | £1,385 | £21,657 | 15.6 yrs | £6,037 |
| 7 kW | 7039 kWh | 5420 kWh | 1619 kWh | £1,454 | £162 | £1,615 | £23,692 | 14.7 yrs | £8,618 |
| 8 kW | 8044 kWh | 6194 kWh | 1850 kWh | £1,661 | £185 | £1,846 | £25,726 | 13.9 yrs | £11,199 |
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.