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 890 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: £748, Upfront: £10,173, 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 | 1779 kWh | 712 kWh | 1067 kWh | £193 | £107 | £299 | £4,069 | 13.6 yrs | £1,917 |
| 3 kW | 2669 kWh | 1067 kWh | 1601 kWh | £289 | £160 | £449 | £6,104 | 13.6 yrs | £2,876 |
| 4 kW | 3558 kWh | 1423 kWh | 2135 kWh | £385 | £213 | £599 | £8,138 | 13.6 yrs | £3,834 |
| 5 kW | 4448 kWh | 1779 kWh | 2669 kWh | £481 | £267 | £748 | £10,173 | 13.6 yrs | £4,793 |
| 6 kW | 5337 kWh | 2135 kWh | 3202 kWh | £578 | £320 | £898 | £12,207 | 13.6 yrs | £5,751 |
| 7 kW | 6227 kWh | 2491 kWh | 3736 kWh | £674 | £374 | £1,048 | £14,242 | 13.6 yrs | £6,710 |
| 8 kW | 7116 kWh | 2846 kWh | 4270 kWh | £770 | £427 | £1,197 | £16,276 | 13.6 yrs | £7,668 |
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: £900, Upfront: £12,273, 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 | 1779 kWh | 1067 kWh | 712 kWh | £289 | £71 | £360 | £6,169 | 17.1 yrs | £1,031 |
| 3 kW | 2669 kWh | 1601 kWh | 1067 kWh | £433 | £107 | £540 | £8,204 | 15.2 yrs | £2,597 |
| 4 kW | 3558 kWh | 2135 kWh | 1423 kWh | £578 | £142 | £720 | £10,238 | 14.2 yrs | £4,162 |
| 5 kW | 4448 kWh | 2669 kWh | 1779 kWh | £722 | £178 | £900 | £12,273 | 13.6 yrs | £5,728 |
| 6 kW | 5337 kWh | 3202 kWh | 2135 kWh | £867 | £213 | £1,080 | £14,307 | 13.2 yrs | £7,293 |
| 7 kW | 6227 kWh | 3736 kWh | 2491 kWh | £1,011 | £249 | £1,260 | £16,342 | 13.0 yrs | £8,859 |
| 8 kW | 7116 kWh | 4270 kWh | 2846 kWh | £1,155 | £285 | £1,440 | £18,376 | 12.8 yrs | £10,424 |
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: £976, Upfront: £13,673, 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 | 1779 kWh | 1245 kWh | 534 kWh | £337 | £53 | £390 | £7,569 | 19.4 yrs | £238 |
| 3 kW | 2669 kWh | 1868 kWh | 801 kWh | £505 | £80 | £586 | £9,604 | 16.4 yrs | £2,107 |
| 4 kW | 3558 kWh | 2491 kWh | 1067 kWh | £674 | £107 | £781 | £11,638 | 14.9 yrs | £3,976 |
| 5 kW | 4448 kWh | 3113 kWh | 1334 kWh | £842 | £133 | £976 | £13,673 | 14.0 yrs | £5,845 |
| 6 kW | 5337 kWh | 3736 kWh | 1601 kWh | £1,011 | £160 | £1,171 | £15,707 | 13.4 yrs | £7,714 |
| 7 kW | 6227 kWh | 4359 kWh | 1868 kWh | £1,179 | £187 | £1,366 | £17,742 | 13.0 yrs | £9,583 |
| 8 kW | 7116 kWh | 4981 kWh | 2135 kWh | £1,348 | £213 | £1,561 | £19,776 | 12.7 yrs | £11,452 |
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: £999, Upfront: £15,423, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1779 kWh | 1299 kWh | 480 kWh | £351 | £48 | £399 | £9,319 | 23.3 yrs | £-1,330 |
| 3 kW | 2669 kWh | 1948 kWh | 721 kWh | £527 | £72 | £599 | £11,354 | 18.9 yrs | £630 |
| 4 kW | 3558 kWh | 2597 kWh | 961 kWh | £703 | £96 | £799 | £13,388 | 16.8 yrs | £2,590 |
| 5 kW | 4448 kWh | 3247 kWh | 1201 kWh | £879 | £120 | £999 | £15,423 | 15.4 yrs | £4,551 |
| 6 kW | 5337 kWh | 3896 kWh | 1441 kWh | £1,054 | £144 | £1,198 | £17,457 | 14.6 yrs | £6,511 |
| 7 kW | 6227 kWh | 4545 kWh | 1681 kWh | £1,230 | £168 | £1,398 | £19,492 | 13.9 yrs | £8,471 |
| 8 kW | 7116 kWh | 5195 kWh | 1921 kWh | £1,406 | £192 | £1,598 | £21,526 | 13.5 yrs | £10,431 |
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: £1,014, Upfront: £17,173, Break-even: 16.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1779 kWh | 1334 kWh | 445 kWh | £361 | £44 | £406 | £11,069 | 27.3 yrs | £-2,958 |
| 3 kW | 2669 kWh | 2001 kWh | 667 kWh | £542 | £67 | £608 | £13,104 | 21.5 yrs | £-938 |
| 4 kW | 3558 kWh | 2669 kWh | 890 kWh | £722 | £89 | £811 | £15,138 | 18.7 yrs | £1,083 |
| 5 kW | 4448 kWh | 3336 kWh | 1112 kWh | £903 | £111 | £1,014 | £17,173 | 16.9 yrs | £3,104 |
| 6 kW | 5337 kWh | 4003 kWh | 1334 kWh | £1,083 | £133 | £1,217 | £19,207 | 15.8 yrs | £5,125 |
| 7 kW | 6227 kWh | 4670 kWh | 1557 kWh | £1,264 | £156 | £1,419 | £21,242 | 15.0 yrs | £7,146 |
| 8 kW | 7116 kWh | 5337 kWh | 1779 kWh | £1,444 | £178 | £1,622 | £23,276 | 14.3 yrs | £9,166 |
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: £1,029, Upfront: £19,623, Break-even: 19.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1779 kWh | 1370 kWh | 409 kWh | £371 | £41 | £412 | £13,519 | 32.8 yrs | £-5,287 |
| 3 kW | 2669 kWh | 2055 kWh | 614 kWh | £556 | £61 | £617 | £15,554 | 25.2 yrs | £-3,205 |
| 4 kW | 3558 kWh | 2740 kWh | 818 kWh | £741 | £82 | £823 | £17,588 | 21.4 yrs | £-1,124 |
| 5 kW | 4448 kWh | 3425 kWh | 1023 kWh | £927 | £102 | £1,029 | £19,623 | 19.1 yrs | £958 |
| 6 kW | 5337 kWh | 4110 kWh | 1228 kWh | £1,112 | £123 | £1,235 | £21,657 | 17.5 yrs | £3,039 |
| 7 kW | 6227 kWh | 4795 kWh | 1432 kWh | £1,297 | £143 | £1,441 | £23,692 | 16.4 yrs | £5,121 |
| 8 kW | 7116 kWh | 5479 kWh | 1637 kWh | £1,483 | £164 | £1,646 | £25,726 | 15.6 yrs | £7,202 |
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.