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 753 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: £634, Upfront: £10,173, Break-even: 16.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1507 kWh | 603 kWh | 904 kWh | £163 | £90 | £253 | £4,069 | 16.1 yrs | £1,001 |
| 3 kW | 2260 kWh | 904 kWh | 1356 kWh | £245 | £136 | £380 | £6,104 | 16.1 yrs | £1,501 |
| 4 kW | 3013 kWh | 1205 kWh | 1808 kWh | £326 | £181 | £507 | £8,138 | 16.1 yrs | £2,001 |
| 5 kW | 3767 kWh | 1507 kWh | 2260 kWh | £408 | £226 | £634 | £10,173 | 16.1 yrs | £2,502 |
| 6 kW | 4520 kWh | 1808 kWh | 2712 kWh | £489 | £271 | £760 | £12,207 | 16.1 yrs | £3,002 |
| 7 kW | 5273 kWh | 2109 kWh | 3164 kWh | £571 | £316 | £887 | £14,242 | 16.1 yrs | £3,503 |
| 8 kW | 6027 kWh | 2411 kWh | 3616 kWh | £652 | £362 | £1,014 | £16,276 | 16.1 yrs | £4,003 |
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: £762, Upfront: £12,273, Break-even: 16.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1507 kWh | 904 kWh | 603 kWh | £245 | £60 | £305 | £6,169 | 20.2 yrs | £-71 |
| 3 kW | 2260 kWh | 1356 kWh | 904 kWh | £367 | £90 | £457 | £8,204 | 17.9 yrs | £943 |
| 4 kW | 3013 kWh | 1808 kWh | 1205 kWh | £489 | £121 | £610 | £10,238 | 16.8 yrs | £1,958 |
| 5 kW | 3767 kWh | 2260 kWh | 1507 kWh | £612 | £151 | £762 | £12,273 | 16.1 yrs | £2,972 |
| 6 kW | 4520 kWh | 2712 kWh | 1808 kWh | £734 | £181 | £915 | £14,307 | 15.6 yrs | £3,987 |
| 7 kW | 5273 kWh | 3164 kWh | 2109 kWh | £856 | £211 | £1,067 | £16,342 | 15.3 yrs | £5,001 |
| 8 kW | 6027 kWh | 3616 kWh | 2411 kWh | £979 | £241 | £1,220 | £18,376 | 15.1 yrs | £6,016 |
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: £827, Upfront: £13,673, 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 | 1507 kWh | 1055 kWh | 452 kWh | £285 | £45 | £331 | £7,569 | 22.9 yrs | £-957 |
| 3 kW | 2260 kWh | 1582 kWh | 678 kWh | £428 | £68 | £496 | £9,604 | 19.4 yrs | £314 |
| 4 kW | 3013 kWh | 2109 kWh | 904 kWh | £571 | £90 | £661 | £11,638 | 17.6 yrs | £1,586 |
| 5 kW | 3767 kWh | 2637 kWh | 1130 kWh | £713 | £113 | £827 | £13,673 | 16.5 yrs | £2,857 |
| 6 kW | 4520 kWh | 3164 kWh | 1356 kWh | £856 | £136 | £992 | £15,707 | 15.8 yrs | £4,129 |
| 7 kW | 5273 kWh | 3691 kWh | 1582 kWh | £999 | £158 | £1,157 | £17,742 | 15.3 yrs | £5,400 |
| 8 kW | 6027 kWh | 4219 kWh | 1808 kWh | £1,142 | £181 | £1,322 | £19,776 | 15.0 yrs | £6,672 |
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: £846, Upfront: £15,423, 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 | 1507 kWh | 1100 kWh | 407 kWh | £298 | £41 | £338 | £9,319 | 27.5 yrs | £-2,553 |
| 3 kW | 2260 kWh | 1650 kWh | 610 kWh | £446 | £61 | £507 | £11,354 | 22.4 yrs | £-1,204 |
| 4 kW | 3013 kWh | 2200 kWh | 814 kWh | £595 | £81 | £677 | £13,388 | 19.8 yrs | £144 |
| 5 kW | 3767 kWh | 2750 kWh | 1017 kWh | £744 | £102 | £846 | £15,423 | 18.2 yrs | £1,493 |
| 6 kW | 4520 kWh | 3300 kWh | 1220 kWh | £893 | £122 | £1,015 | £17,457 | 17.2 yrs | £2,842 |
| 7 kW | 5273 kWh | 3850 kWh | 1424 kWh | £1,042 | £142 | £1,184 | £19,492 | 16.5 yrs | £4,190 |
| 8 kW | 6027 kWh | 4400 kWh | 1627 kWh | £1,191 | £163 | £1,353 | £21,526 | 15.9 yrs | £5,539 |
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: £859, Upfront: £17,173, Break-even: 20.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1507 kWh | 1130 kWh | 377 kWh | £306 | £38 | £343 | £11,069 | 32.2 yrs | £-4,200 |
| 3 kW | 2260 kWh | 1695 kWh | 565 kWh | £459 | £57 | £515 | £13,104 | 25.4 yrs | £-2,800 |
| 4 kW | 3013 kWh | 2260 kWh | 753 kWh | £612 | £75 | £687 | £15,138 | 22.0 yrs | £-1,400 |
| 5 kW | 3767 kWh | 2825 kWh | 942 kWh | £764 | £94 | £859 | £17,173 | 20.0 yrs | £0 |
| 6 kW | 4520 kWh | 3390 kWh | 1130 kWh | £917 | £113 | £1,030 | £19,207 | 18.6 yrs | £1,400 |
| 7 kW | 5273 kWh | 3955 kWh | 1318 kWh | £1,070 | £132 | £1,202 | £21,242 | 17.7 yrs | £2,800 |
| 8 kW | 6027 kWh | 4520 kWh | 1507 kWh | £1,223 | £151 | £1,374 | £23,276 | 16.9 yrs | £4,200 |
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: £871, Upfront: £19,623, Break-even: 22.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1507 kWh | 1160 kWh | 347 kWh | £314 | £35 | £349 | £13,519 | 38.8 yrs | £-6,547 |
| 3 kW | 2260 kWh | 1740 kWh | 520 kWh | £471 | £52 | £523 | £15,554 | 29.7 yrs | £-5,096 |
| 4 kW | 3013 kWh | 2320 kWh | 693 kWh | £628 | £69 | £697 | £17,588 | 25.2 yrs | £-3,644 |
| 5 kW | 3767 kWh | 2900 kWh | 866 kWh | £785 | £87 | £871 | £19,623 | 22.5 yrs | £-2,193 |
| 6 kW | 4520 kWh | 3480 kWh | 1040 kWh | £942 | £104 | £1,046 | £21,657 | 20.7 yrs | £-741 |
| 7 kW | 5273 kWh | 4061 kWh | 1213 kWh | £1,099 | £121 | £1,220 | £23,692 | 19.4 yrs | £710 |
| 8 kW | 6027 kWh | 4641 kWh | 1386 kWh | £1,256 | £139 | £1,394 | £25,726 | 18.4 yrs | £2,161 |
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.