A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 880 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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: £709, Upfront: £10,173, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1759 kWh | 704 kWh | 1056 kWh | £178 | £106 | £284 | £4,069 | 14.3 yrs | £1,607 |
| 3 kW | 2639 kWh | 1056 kWh | 1583 kWh | £267 | £158 | £426 | £6,104 | 14.3 yrs | £2,410 |
| 4 kW | 3518 kWh | 1407 kWh | 2111 kWh | £356 | £211 | £568 | £8,138 | 14.3 yrs | £3,214 |
| 5 kW | 4398 kWh | 1759 kWh | 2639 kWh | £446 | £264 | £709 | £10,173 | 14.3 yrs | £4,017 |
| 6 kW | 5278 kWh | 2111 kWh | 3167 kWh | £535 | £317 | £851 | £12,207 | 14.3 yrs | £4,821 |
| 7 kW | 6157 kWh | 2463 kWh | 3694 kWh | £624 | £369 | £993 | £14,242 | 14.3 yrs | £5,624 |
| 8 kW | 7037 kWh | 2815 kWh | 4222 kWh | £713 | £422 | £1,135 | £16,276 | 14.3 yrs | £6,428 |
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: £844, Upfront: £12,273, 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 | 1759 kWh | 1056 kWh | 704 kWh | £267 | £70 | £338 | £6,169 | 18.3 yrs | £586 |
| 3 kW | 2639 kWh | 1583 kWh | 1056 kWh | £401 | £106 | £507 | £8,204 | 16.2 yrs | £1,929 |
| 4 kW | 3518 kWh | 2111 kWh | 1407 kWh | £535 | £141 | £675 | £10,238 | 15.2 yrs | £3,271 |
| 5 kW | 4398 kWh | 2639 kWh | 1759 kWh | £668 | £176 | £844 | £12,273 | 14.5 yrs | £4,614 |
| 6 kW | 5278 kWh | 3167 kWh | 2111 kWh | £802 | £211 | £1,013 | £14,307 | 14.1 yrs | £5,957 |
| 7 kW | 6157 kWh | 3694 kWh | 2463 kWh | £936 | £246 | £1,182 | £16,342 | 13.8 yrs | £7,300 |
| 8 kW | 7037 kWh | 4222 kWh | 2815 kWh | £1,069 | £281 | £1,351 | £18,376 | 13.6 yrs | £8,643 |
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: £912, Upfront: £13,673, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1759 kWh | 1231 kWh | 528 kWh | £312 | £53 | £365 | £7,569 | 20.8 yrs | £-275 |
| 3 kW | 2639 kWh | 1847 kWh | 792 kWh | £468 | £79 | £547 | £9,604 | 17.6 yrs | £1,338 |
| 4 kW | 3518 kWh | 2463 kWh | 1056 kWh | £624 | £106 | £729 | £11,638 | 16.0 yrs | £2,950 |
| 5 kW | 4398 kWh | 3079 kWh | 1319 kWh | £780 | £132 | £912 | £13,673 | 15.0 yrs | £4,563 |
| 6 kW | 5278 kWh | 3694 kWh | 1583 kWh | £936 | £158 | £1,094 | £15,707 | 14.4 yrs | £6,175 |
| 7 kW | 6157 kWh | 4310 kWh | 1847 kWh | £1,092 | £185 | £1,276 | £17,742 | 13.9 yrs | £7,788 |
| 8 kW | 7037 kWh | 4926 kWh | 2111 kWh | £1,248 | £211 | £1,459 | £19,776 | 13.6 yrs | £9,400 |
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: £932, Upfront: £15,423, Break-even: 16.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1759 kWh | 1284 kWh | 475 kWh | £325 | £47 | £373 | £9,319 | 25.0 yrs | £-1,863 |
| 3 kW | 2639 kWh | 1926 kWh | 712 kWh | £488 | £71 | £559 | £11,354 | 20.3 yrs | £-170 |
| 4 kW | 3518 kWh | 2568 kWh | 950 kWh | £651 | £95 | £746 | £13,388 | 18.0 yrs | £1,524 |
| 5 kW | 4398 kWh | 3211 kWh | 1187 kWh | £813 | £119 | £932 | £15,423 | 16.5 yrs | £3,217 |
| 6 kW | 5278 kWh | 3853 kWh | 1425 kWh | £976 | £142 | £1,118 | £17,457 | 15.6 yrs | £4,911 |
| 7 kW | 6157 kWh | 4495 kWh | 1662 kWh | £1,139 | £166 | £1,305 | £19,492 | 14.9 yrs | £6,604 |
| 8 kW | 7037 kWh | 5137 kWh | 1900 kWh | £1,301 | £190 | £1,491 | £21,526 | 14.4 yrs | £8,297 |
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: £945, Upfront: £17,173, Break-even: 18.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1759 kWh | 1319 kWh | 440 kWh | £334 | £44 | £378 | £11,069 | 29.3 yrs | £-3,505 |
| 3 kW | 2639 kWh | 1979 kWh | 660 kWh | £501 | £66 | £567 | £13,104 | 23.1 yrs | £-1,758 |
| 4 kW | 3518 kWh | 2639 kWh | 880 kWh | £668 | £88 | £756 | £15,138 | 20.0 yrs | £-11 |
| 5 kW | 4398 kWh | 3299 kWh | 1100 kWh | £836 | £110 | £945 | £17,173 | 18.2 yrs | £1,737 |
| 6 kW | 5278 kWh | 3958 kWh | 1319 kWh | £1,003 | £132 | £1,135 | £19,207 | 16.9 yrs | £3,484 |
| 7 kW | 6157 kWh | 4618 kWh | 1539 kWh | £1,170 | £154 | £1,324 | £21,242 | 16.0 yrs | £5,232 |
| 8 kW | 7037 kWh | 5278 kWh | 1759 kWh | £1,337 | £176 | £1,513 | £23,276 | 15.4 yrs | £6,979 |
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: £959, Upfront: £19,623, Break-even: 20.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1759 kWh | 1355 kWh | 405 kWh | £343 | £40 | £384 | £13,519 | 35.2 yrs | £-5,847 |
| 3 kW | 2639 kWh | 2032 kWh | 607 kWh | £515 | £61 | £575 | £15,554 | 27.0 yrs | £-4,046 |
| 4 kW | 3518 kWh | 2709 kWh | 809 kWh | £686 | £81 | £767 | £17,588 | 22.9 yrs | £-2,245 |
| 5 kW | 4398 kWh | 3386 kWh | 1012 kWh | £858 | £101 | £959 | £19,623 | 20.5 yrs | £-443 |
| 6 kW | 5278 kWh | 4064 kWh | 1214 kWh | £1,029 | £121 | £1,151 | £21,657 | 18.8 yrs | £1,358 |
| 7 kW | 6157 kWh | 4741 kWh | 1416 kWh | £1,201 | £142 | £1,343 | £23,692 | 17.6 yrs | £3,159 |
| 8 kW | 7037 kWh | 5418 kWh | 1618 kWh | £1,372 | £162 | £1,534 | £25,726 | 16.8 yrs | £4,960 |
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.