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 627 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £528, Upfront: £10,173, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1254 kWh | 502 kWh | 753 kWh | £136 | £75 | £211 | £4,069 | 19.3 yrs | £151 |
| 3 kW | 1881 kWh | 753 kWh | 1129 kWh | £204 | £113 | £317 | £6,104 | 19.3 yrs | £227 |
| 4 kW | 2509 kWh | 1003 kWh | 1505 kWh | £272 | £151 | £422 | £8,138 | 19.3 yrs | £303 |
| 5 kW | 3136 kWh | 1254 kWh | 1881 kWh | £339 | £188 | £528 | £10,173 | 19.3 yrs | £378 |
| 6 kW | 3763 kWh | 1505 kWh | 2258 kWh | £407 | £226 | £633 | £12,207 | 19.3 yrs | £454 |
| 7 kW | 4390 kWh | 1756 kWh | 2634 kWh | £475 | £263 | £739 | £14,242 | 19.3 yrs | £530 |
| 8 kW | 5017 kWh | 2007 kWh | 3010 kWh | £543 | £301 | £844 | £16,276 | 19.3 yrs | £606 |
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: £635, Upfront: £12,273, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1254 kWh | 753 kWh | 502 kWh | £204 | £50 | £254 | £6,169 | 24.3 yrs | £-1,093 |
| 3 kW | 1881 kWh | 1129 kWh | 753 kWh | £305 | £75 | £381 | £8,204 | 21.5 yrs | £-589 |
| 4 kW | 2509 kWh | 1505 kWh | 1003 kWh | £407 | £100 | £508 | £10,238 | 20.2 yrs | £-85 |
| 5 kW | 3136 kWh | 1881 kWh | 1254 kWh | £509 | £125 | £635 | £12,273 | 19.3 yrs | £418 |
| 6 kW | 3763 kWh | 2258 kWh | 1505 kWh | £611 | £151 | £761 | £14,307 | 18.8 yrs | £922 |
| 7 kW | 4390 kWh | 2634 kWh | 1756 kWh | £713 | £176 | £888 | £16,342 | 18.4 yrs | £1,426 |
| 8 kW | 5017 kWh | 3010 kWh | 2007 kWh | £815 | £201 | £1,015 | £18,376 | 18.1 yrs | £1,929 |
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: £688, Upfront: £13,673, Break-even: 19.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1254 kWh | 878 kWh | 376 kWh | £238 | £38 | £275 | £7,569 | 27.5 yrs | £-2,065 |
| 3 kW | 1881 kWh | 1317 kWh | 564 kWh | £356 | £56 | £413 | £9,604 | 23.3 yrs | £-1,347 |
| 4 kW | 2509 kWh | 1756 kWh | 753 kWh | £475 | £75 | £550 | £11,638 | 21.1 yrs | £-629 |
| 5 kW | 3136 kWh | 2195 kWh | 941 kWh | £594 | £94 | £688 | £13,673 | 19.9 yrs | £88 |
| 6 kW | 3763 kWh | 2634 kWh | 1129 kWh | £713 | £113 | £826 | £15,707 | 19.0 yrs | £806 |
| 7 kW | 4390 kWh | 3073 kWh | 1317 kWh | £832 | £132 | £963 | £17,742 | 18.4 yrs | £1,523 |
| 8 kW | 5017 kWh | 3512 kWh | 1505 kWh | £950 | £151 | £1,101 | £19,776 | 18.0 yrs | £2,241 |
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: £704, Upfront: £15,423, Break-even: 21.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1254 kWh | 916 kWh | 339 kWh | £248 | £34 | £282 | £9,319 | 33.1 yrs | £-3,686 |
| 3 kW | 1881 kWh | 1373 kWh | 508 kWh | £372 | £51 | £422 | £11,354 | 26.9 yrs | £-2,905 |
| 4 kW | 2509 kWh | 1831 kWh | 677 kWh | £496 | £68 | £563 | £13,388 | 23.8 yrs | £-2,123 |
| 5 kW | 3136 kWh | 2289 kWh | 847 kWh | £619 | £85 | £704 | £15,423 | 21.9 yrs | £-1,341 |
| 6 kW | 3763 kWh | 2747 kWh | 1016 kWh | £743 | £102 | £845 | £17,457 | 20.7 yrs | £-559 |
| 7 kW | 4390 kWh | 3205 kWh | 1185 kWh | £867 | £119 | £986 | £19,492 | 19.8 yrs | £223 |
| 8 kW | 5017 kWh | 3662 kWh | 1355 kWh | £991 | £135 | £1,127 | £21,526 | 19.1 yrs | £1,005 |
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: £715, Upfront: £17,173, Break-even: 24.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1254 kWh | 941 kWh | 314 kWh | £255 | £31 | £286 | £11,069 | 38.7 yrs | £-5,351 |
| 3 kW | 1881 kWh | 1411 kWh | 470 kWh | £382 | £47 | £429 | £13,104 | 30.6 yrs | £-4,526 |
| 4 kW | 2509 kWh | 1881 kWh | 627 kWh | £509 | £63 | £572 | £15,138 | 26.5 yrs | £-3,702 |
| 5 kW | 3136 kWh | 2352 kWh | 784 kWh | £636 | £78 | £715 | £17,173 | 24.0 yrs | £-2,877 |
| 6 kW | 3763 kWh | 2822 kWh | 941 kWh | £764 | £94 | £858 | £19,207 | 22.4 yrs | £-2,052 |
| 7 kW | 4390 kWh | 3292 kWh | 1097 kWh | £891 | £110 | £1,001 | £21,242 | 21.2 yrs | £-1,228 |
| 8 kW | 5017 kWh | 3763 kWh | 1254 kWh | £1,018 | £125 | £1,144 | £23,276 | 20.4 yrs | £-403 |
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: £725, Upfront: £19,623, Break-even: 27.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1254 kWh | 966 kWh | 288 kWh | £261 | £29 | £290 | £13,519 | 46.6 yrs | £-7,715 |
| 3 kW | 1881 kWh | 1449 kWh | 433 kWh | £392 | £43 | £435 | £15,554 | 35.7 yrs | £-6,848 |
| 4 kW | 2509 kWh | 1932 kWh | 577 kWh | £523 | £58 | £580 | £17,588 | 30.3 yrs | £-5,980 |
| 5 kW | 3136 kWh | 2414 kWh | 721 kWh | £653 | £72 | £725 | £19,623 | 27.0 yrs | £-5,113 |
| 6 kW | 3763 kWh | 2897 kWh | 865 kWh | £784 | £87 | £871 | £21,657 | 24.9 yrs | £-4,245 |
| 7 kW | 4390 kWh | 3380 kWh | 1010 kWh | £915 | £101 | £1,016 | £23,692 | 23.3 yrs | £-3,378 |
| 8 kW | 5017 kWh | 3863 kWh | 1154 kWh | £1,045 | £115 | £1,161 | £25,726 | 22.2 yrs | £-2,511 |
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.