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 1013 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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 | 2025 kWh | 810 kWh | 1215 kWh | £215 | £122 | £336 | £4,069 | 12.1 yrs | £2,660 |
| 3 kW | 3038 kWh | 1215 kWh | 1823 kWh | £322 | £182 | £505 | £6,104 | 12.1 yrs | £3,990 |
| 4 kW | 4051 kWh | 1620 kWh | 2430 kWh | £430 | £243 | £673 | £8,138 | 12.1 yrs | £5,320 |
| 5 kW | 5063 kWh | 2025 kWh | 3038 kWh | £537 | £304 | £841 | £10,173 | 12.1 yrs | £6,650 |
| 6 kW | 6076 kWh | 2430 kWh | 3646 kWh | £645 | £365 | £1,009 | £12,207 | 12.1 yrs | £7,980 |
| 7 kW | 7089 kWh | 2835 kWh | 4253 kWh | £752 | £425 | £1,178 | £14,242 | 12.1 yrs | £9,310 |
| 8 kW | 8101 kWh | 3241 kWh | 4861 kWh | £860 | £486 | £1,346 | £16,276 | 12.1 yrs | £10,640 |
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: £1,009, Upfront: £12,273, Break-even: 12.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2025 kWh | 1215 kWh | 810 kWh | £322 | £81 | £403 | £6,169 | 15.3 yrs | £1,899 |
| 3 kW | 3038 kWh | 1823 kWh | 1215 kWh | £484 | £122 | £605 | £8,204 | 13.6 yrs | £3,899 |
| 4 kW | 4051 kWh | 2430 kWh | 1620 kWh | £645 | £162 | £807 | £10,238 | 12.7 yrs | £5,898 |
| 5 kW | 5063 kWh | 3038 kWh | 2025 kWh | £806 | £203 | £1,009 | £12,273 | 12.2 yrs | £7,898 |
| 6 kW | 6076 kWh | 3646 kWh | 2430 kWh | £967 | £243 | £1,210 | £14,307 | 11.8 yrs | £9,897 |
| 7 kW | 7089 kWh | 4253 kWh | 2835 kWh | £1,128 | £284 | £1,412 | £16,342 | 11.6 yrs | £11,897 |
| 8 kW | 8101 kWh | 4861 kWh | 3241 kWh | £1,290 | £324 | £1,614 | £18,376 | 11.4 yrs | £13,896 |
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: £1,092, 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 | 2025 kWh | 1418 kWh | 608 kWh | £376 | £61 | £437 | £7,569 | 17.3 yrs | £1,169 |
| 3 kW | 3038 kWh | 2127 kWh | 911 kWh | £564 | £91 | £655 | £9,604 | 14.7 yrs | £3,503 |
| 4 kW | 4051 kWh | 2835 kWh | 1215 kWh | £752 | £122 | £874 | £11,638 | 13.3 yrs | £5,837 |
| 5 kW | 5063 kWh | 3544 kWh | 1519 kWh | £940 | £152 | £1,092 | £13,673 | 12.5 yrs | £8,172 |
| 6 kW | 6076 kWh | 4253 kWh | 1823 kWh | £1,128 | £182 | £1,311 | £15,707 | 12.0 yrs | £10,506 |
| 7 kW | 7089 kWh | 4962 kWh | 2127 kWh | £1,316 | £213 | £1,529 | £17,742 | 11.6 yrs | £12,840 |
| 8 kW | 8101 kWh | 5671 kWh | 2430 kWh | £1,505 | £243 | £1,748 | £19,776 | 11.3 yrs | £15,175 |
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: £1,117, 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 | 2025 kWh | 1478 kWh | 547 kWh | £392 | £55 | £447 | £9,319 | 20.9 yrs | £-380 |
| 3 kW | 3038 kWh | 2218 kWh | 820 kWh | £588 | £82 | £670 | £11,354 | 16.9 yrs | £2,054 |
| 4 kW | 4051 kWh | 2957 kWh | 1094 kWh | £784 | £109 | £894 | £13,388 | 15.0 yrs | £4,489 |
| 5 kW | 5063 kWh | 3696 kWh | 1367 kWh | £981 | £137 | £1,117 | £15,423 | 13.8 yrs | £6,924 |
| 6 kW | 6076 kWh | 4435 kWh | 1641 kWh | £1,177 | £164 | £1,341 | £17,457 | 13.0 yrs | £9,359 |
| 7 kW | 7089 kWh | 5175 kWh | 1914 kWh | £1,373 | £191 | £1,564 | £19,492 | 12.5 yrs | £11,794 |
| 8 kW | 8101 kWh | 5914 kWh | 2187 kWh | £1,569 | £219 | £1,788 | £21,526 | 12.0 yrs | £14,228 |
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: £1,134, 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 | 2025 kWh | 1519 kWh | 506 kWh | £403 | £51 | £454 | £11,069 | 24.4 yrs | £-1,997 |
| 3 kW | 3038 kWh | 2279 kWh | 760 kWh | £604 | £76 | £680 | £13,104 | 19.3 yrs | £505 |
| 4 kW | 4051 kWh | 3038 kWh | 1013 kWh | £806 | £101 | £907 | £15,138 | 16.7 yrs | £3,007 |
| 5 kW | 5063 kWh | 3798 kWh | 1266 kWh | £1,007 | £127 | £1,134 | £17,173 | 15.1 yrs | £5,509 |
| 6 kW | 6076 kWh | 4557 kWh | 1519 kWh | £1,209 | £152 | £1,361 | £19,207 | 14.1 yrs | £8,010 |
| 7 kW | 7089 kWh | 5317 kWh | 1772 kWh | £1,410 | £177 | £1,588 | £21,242 | 13.4 yrs | £10,512 |
| 8 kW | 8101 kWh | 6076 kWh | 2025 kWh | £1,612 | £203 | £1,815 | £23,276 | 12.8 yrs | £13,014 |
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: £1,151, Upfront: £19,623, Break-even: 17.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2025 kWh | 1560 kWh | 466 kWh | £414 | £47 | £460 | £13,519 | 29.4 yrs | £-4,313 |
| 3 kW | 3038 kWh | 2339 kWh | 699 kWh | £621 | £70 | £690 | £15,554 | 22.5 yrs | £-1,744 |
| 4 kW | 4051 kWh | 3119 kWh | 932 kWh | £827 | £93 | £921 | £17,588 | 19.1 yrs | £825 |
| 5 kW | 5063 kWh | 3899 kWh | 1165 kWh | £1,034 | £116 | £1,151 | £19,623 | 17.1 yrs | £3,394 |
| 6 kW | 6076 kWh | 4679 kWh | 1397 kWh | £1,241 | £140 | £1,381 | £21,657 | 15.7 yrs | £5,962 |
| 7 kW | 7089 kWh | 5458 kWh | 1630 kWh | £1,448 | £163 | £1,611 | £23,692 | 14.7 yrs | £8,531 |
| 8 kW | 8101 kWh | 6238 kWh | 1863 kWh | £1,655 | £186 | £1,841 | £25,726 | 14.0 yrs | £11,100 |
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.