A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 1012 kWh per year on a south-facing roof. We value self-used electricity at 26.8p 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: £846, Upfront: £10,173, Break-even: 12.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2023 kWh | 809 kWh | 1214 kWh | £217 | £121 | £338 | £4,069 | 12.0 yrs | £2,700 |
| 3 kW | 3035 kWh | 1214 kWh | 1821 kWh | £326 | £182 | £508 | £6,104 | 12.0 yrs | £4,050 |
| 4 kW | 4046 kWh | 1619 kWh | 2428 kWh | £434 | £243 | £677 | £8,138 | 12.0 yrs | £5,400 |
| 5 kW | 5058 kWh | 2023 kWh | 3035 kWh | £543 | £303 | £846 | £10,173 | 12.0 yrs | £6,750 |
| 6 kW | 6070 kWh | 2428 kWh | 3642 kWh | £651 | £364 | £1,015 | £12,207 | 12.0 yrs | £8,100 |
| 7 kW | 7081 kWh | 2833 kWh | 4249 kWh | £760 | £425 | £1,185 | £14,242 | 12.0 yrs | £9,450 |
| 8 kW | 8093 kWh | 3237 kWh | 4856 kWh | £868 | £486 | £1,354 | £16,276 | 12.0 yrs | £10,800 |
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: £1,016, Upfront: £12,273, 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 | 2023 kWh | 1214 kWh | 809 kWh | £326 | £81 | £407 | £6,169 | 15.2 yrs | £1,961 |
| 3 kW | 3035 kWh | 1821 kWh | 1214 kWh | £488 | £121 | £610 | £8,204 | 13.5 yrs | £3,992 |
| 4 kW | 4046 kWh | 2428 kWh | 1619 kWh | £651 | £162 | £813 | £10,238 | 12.6 yrs | £6,022 |
| 5 kW | 5058 kWh | 3035 kWh | 2023 kWh | £814 | £202 | £1,016 | £12,273 | 12.1 yrs | £8,053 |
| 6 kW | 6070 kWh | 3642 kWh | 2428 kWh | £977 | £243 | £1,220 | £14,307 | 11.7 yrs | £10,084 |
| 7 kW | 7081 kWh | 4249 kWh | 2833 kWh | £1,140 | £283 | £1,423 | £16,342 | 11.5 yrs | £12,114 |
| 8 kW | 8093 kWh | 4856 kWh | 3237 kWh | £1,302 | £324 | £1,626 | £18,376 | 11.3 yrs | £14,145 |
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: £1,101, Upfront: £13,673, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2023 kWh | 1416 kWh | 607 kWh | £380 | £61 | £441 | £7,569 | 17.2 yrs | £1,242 |
| 3 kW | 3035 kWh | 2124 kWh | 910 kWh | £570 | £91 | £661 | £9,604 | 14.5 yrs | £3,613 |
| 4 kW | 4046 kWh | 2833 kWh | 1214 kWh | £760 | £121 | £881 | £11,638 | 13.2 yrs | £5,984 |
| 5 kW | 5058 kWh | 3541 kWh | 1517 kWh | £950 | £152 | £1,101 | £13,673 | 12.4 yrs | £8,354 |
| 6 kW | 6070 kWh | 4249 kWh | 1821 kWh | £1,140 | £182 | £1,322 | £15,707 | 11.9 yrs | £10,725 |
| 7 kW | 7081 kWh | 4957 kWh | 2124 kWh | £1,329 | £212 | £1,542 | £17,742 | 11.5 yrs | £13,096 |
| 8 kW | 8093 kWh | 5665 kWh | 2428 kWh | £1,519 | £243 | £1,762 | £19,776 | 11.2 yrs | £15,467 |
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: £1,127, Upfront: £15,423, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2023 kWh | 1477 kWh | 546 kWh | £396 | £55 | £451 | £9,319 | 20.7 yrs | £-304 |
| 3 kW | 3035 kWh | 2215 kWh | 819 kWh | £594 | £82 | £676 | £11,354 | 16.8 yrs | £2,169 |
| 4 kW | 4046 kWh | 2954 kWh | 1093 kWh | £792 | £109 | £901 | £13,388 | 14.9 yrs | £4,642 |
| 5 kW | 5058 kWh | 3692 kWh | 1366 kWh | £990 | £137 | £1,127 | £15,423 | 13.7 yrs | £7,115 |
| 6 kW | 6070 kWh | 4431 kWh | 1639 kWh | £1,188 | £164 | £1,352 | £17,457 | 12.9 yrs | £9,588 |
| 7 kW | 7081 kWh | 5169 kWh | 1912 kWh | £1,386 | £191 | £1,578 | £19,492 | 12.4 yrs | £12,061 |
| 8 kW | 8093 kWh | 5908 kWh | 2185 kWh | £1,584 | £219 | £1,803 | £21,526 | 11.9 yrs | £14,534 |
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: £1,144, Upfront: £17,173, 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 | 2023 kWh | 1517 kWh | 506 kWh | £407 | £51 | £458 | £11,069 | 24.2 yrs | £-1,918 |
| 3 kW | 3035 kWh | 2276 kWh | 759 kWh | £610 | £76 | £686 | £13,104 | 19.1 yrs | £623 |
| 4 kW | 4046 kWh | 3035 kWh | 1012 kWh | £814 | £101 | £915 | £15,138 | 16.5 yrs | £3,164 |
| 5 kW | 5058 kWh | 3794 kWh | 1265 kWh | £1,017 | £126 | £1,144 | £17,173 | 15.0 yrs | £5,705 |
| 6 kW | 6070 kWh | 4552 kWh | 1517 kWh | £1,221 | £152 | £1,373 | £19,207 | 14.0 yrs | £8,246 |
| 7 kW | 7081 kWh | 5311 kWh | 1770 kWh | £1,424 | £177 | £1,601 | £21,242 | 13.3 yrs | £10,787 |
| 8 kW | 8093 kWh | 6070 kWh | 2023 kWh | £1,628 | £202 | £1,830 | £23,276 | 12.7 yrs | £13,328 |
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: £1,161, Upfront: £19,623, 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 | 2023 kWh | 1558 kWh | 465 kWh | £418 | £47 | £464 | £13,519 | 29.1 yrs | £-4,232 |
| 3 kW | 3035 kWh | 2337 kWh | 698 kWh | £627 | £70 | £697 | £15,554 | 22.3 yrs | £-1,623 |
| 4 kW | 4046 kWh | 3116 kWh | 931 kWh | £836 | £93 | £929 | £17,588 | 18.9 yrs | £986 |
| 5 kW | 5058 kWh | 3895 kWh | 1163 kWh | £1,045 | £116 | £1,161 | £19,623 | 16.9 yrs | £3,596 |
| 6 kW | 6070 kWh | 4674 kWh | 1396 kWh | £1,253 | £140 | £1,393 | £21,657 | 15.5 yrs | £6,205 |
| 7 kW | 7081 kWh | 5453 kWh | 1629 kWh | £1,462 | £163 | £1,625 | £23,692 | 14.6 yrs | £8,814 |
| 8 kW | 8093 kWh | 6232 kWh | 1861 kWh | £1,671 | £186 | £1,857 | £25,726 | 13.9 yrs | £11,423 |
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.