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 742 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: £624, Upfront: £10,173, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1485 kWh | 594 kWh | 891 kWh | £161 | £89 | £250 | £4,069 | 16.3 yrs | £926 |
| 3 kW | 2227 kWh | 891 kWh | 1336 kWh | £241 | £134 | £375 | £6,104 | 16.3 yrs | £1,389 |
| 4 kW | 2969 kWh | 1188 kWh | 1781 kWh | £321 | £178 | £500 | £8,138 | 16.3 yrs | £1,853 |
| 5 kW | 3711 kWh | 1485 kWh | 2227 kWh | £402 | £223 | £624 | £10,173 | 16.3 yrs | £2,316 |
| 6 kW | 4454 kWh | 1781 kWh | 2672 kWh | £482 | £267 | £749 | £12,207 | 16.3 yrs | £2,779 |
| 7 kW | 5196 kWh | 2078 kWh | 3118 kWh | £562 | £312 | £874 | £14,242 | 16.3 yrs | £3,242 |
| 8 kW | 5938 kWh | 2375 kWh | 3563 kWh | £643 | £356 | £999 | £16,276 | 16.3 yrs | £3,705 |
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: £751, Upfront: £12,273, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1485 kWh | 891 kWh | 594 kWh | £241 | £59 | £300 | £6,169 | 20.5 yrs | £-161 |
| 3 kW | 2227 kWh | 1336 kWh | 891 kWh | £362 | £89 | £451 | £8,204 | 18.2 yrs | £809 |
| 4 kW | 2969 kWh | 1781 kWh | 1188 kWh | £482 | £119 | £601 | £10,238 | 17.0 yrs | £1,779 |
| 5 kW | 3711 kWh | 2227 kWh | 1485 kWh | £603 | £148 | £751 | £12,273 | 16.3 yrs | £2,748 |
| 6 kW | 4454 kWh | 2672 kWh | 1781 kWh | £723 | £178 | £901 | £14,307 | 15.9 yrs | £3,718 |
| 7 kW | 5196 kWh | 3118 kWh | 2078 kWh | £844 | £208 | £1,051 | £16,342 | 15.5 yrs | £4,688 |
| 8 kW | 5938 kWh | 3563 kWh | 2375 kWh | £964 | £238 | £1,202 | £18,376 | 15.3 yrs | £5,657 |
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: £814, Upfront: £13,673, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1485 kWh | 1039 kWh | 445 kWh | £281 | £45 | £326 | £7,569 | 23.2 yrs | £-1,054 |
| 3 kW | 2227 kWh | 1559 kWh | 668 kWh | £422 | £67 | £489 | £9,604 | 19.7 yrs | £169 |
| 4 kW | 2969 kWh | 2078 kWh | 891 kWh | £562 | £89 | £651 | £11,638 | 17.9 yrs | £1,392 |
| 5 kW | 3711 kWh | 2598 kWh | 1113 kWh | £703 | £111 | £814 | £13,673 | 16.8 yrs | £2,615 |
| 6 kW | 4454 kWh | 3118 kWh | 1336 kWh | £844 | £134 | £977 | £15,707 | 16.1 yrs | £3,838 |
| 7 kW | 5196 kWh | 3637 kWh | 1559 kWh | £984 | £156 | £1,140 | £17,742 | 15.6 yrs | £5,061 |
| 8 kW | 5938 kWh | 4157 kWh | 1781 kWh | £1,125 | £178 | £1,303 | £19,776 | 15.2 yrs | £6,284 |
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: £833, Upfront: £15,423, 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 | 1485 kWh | 1084 kWh | 401 kWh | £293 | £40 | £333 | £9,319 | 28.0 yrs | £-2,652 |
| 3 kW | 2227 kWh | 1626 kWh | 601 kWh | £440 | £60 | £500 | £11,354 | 22.7 yrs | £-1,353 |
| 4 kW | 2969 kWh | 2167 kWh | 802 kWh | £587 | £80 | £667 | £13,388 | 20.1 yrs | £-54 |
| 5 kW | 3711 kWh | 2709 kWh | 1002 kWh | £733 | £100 | £833 | £15,423 | 18.5 yrs | £1,245 |
| 6 kW | 4454 kWh | 3251 kWh | 1203 kWh | £880 | £120 | £1,000 | £17,457 | 17.5 yrs | £2,544 |
| 7 kW | 5196 kWh | 3793 kWh | 1403 kWh | £1,026 | £140 | £1,167 | £19,492 | 16.7 yrs | £3,843 |
| 8 kW | 5938 kWh | 4335 kWh | 1603 kWh | £1,173 | £160 | £1,333 | £21,526 | 16.1 yrs | £5,141 |
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: £846, Upfront: £17,173, Break-even: 20.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1485 kWh | 1113 kWh | 371 kWh | £301 | £37 | £338 | £11,069 | 32.7 yrs | £-4,301 |
| 3 kW | 2227 kWh | 1670 kWh | 557 kWh | £452 | £56 | £508 | £13,104 | 25.8 yrs | £-2,951 |
| 4 kW | 2969 kWh | 2227 kWh | 742 kWh | £603 | £74 | £677 | £15,138 | 22.4 yrs | £-1,602 |
| 5 kW | 3711 kWh | 2784 kWh | 928 kWh | £753 | £93 | £846 | £17,173 | 20.3 yrs | £-252 |
| 6 kW | 4454 kWh | 3340 kWh | 1113 kWh | £904 | £111 | £1,015 | £19,207 | 18.9 yrs | £1,098 |
| 7 kW | 5196 kWh | 3897 kWh | 1299 kWh | £1,055 | £130 | £1,184 | £21,242 | 17.9 yrs | £2,447 |
| 8 kW | 5938 kWh | 4454 kWh | 1485 kWh | £1,205 | £148 | £1,354 | £23,276 | 17.2 yrs | £3,797 |
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: £859, Upfront: £19,623, Break-even: 22.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1485 kWh | 1143 kWh | 341 kWh | £309 | £34 | £343 | £13,519 | 39.4 yrs | £-6,650 |
| 3 kW | 2227 kWh | 1715 kWh | 512 kWh | £464 | £51 | £515 | £15,554 | 30.2 yrs | £-5,249 |
| 4 kW | 2969 kWh | 2286 kWh | 683 kWh | £619 | £68 | £687 | £17,588 | 25.6 yrs | £-3,849 |
| 5 kW | 3711 kWh | 2858 kWh | 854 kWh | £773 | £85 | £859 | £19,623 | 22.9 yrs | £-2,449 |
| 6 kW | 4454 kWh | 3429 kWh | 1024 kWh | £928 | £102 | £1,030 | £21,657 | 21.0 yrs | £-1,049 |
| 7 kW | 5196 kWh | 4001 kWh | 1195 kWh | £1,083 | £120 | £1,202 | £23,692 | 19.7 yrs | £352 |
| 8 kW | 5938 kWh | 4573 kWh | 1366 kWh | £1,237 | £137 | £1,374 | £25,726 | 18.7 yrs | £1,752 |
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.