A typical roof here lands around 3.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 1056 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: £877, Upfront: £10,173, Break-even: 11.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2113 kWh | 845 kWh | 1268 kWh | £224 | £127 | £351 | £4,069 | 11.6 yrs | £2,950 |
| 3 kW | 3169 kWh | 1268 kWh | 1901 kWh | £336 | £190 | £526 | £6,104 | 11.6 yrs | £4,425 |
| 4 kW | 4225 kWh | 1690 kWh | 2535 kWh | £448 | £254 | £702 | £8,138 | 11.6 yrs | £5,900 |
| 5 kW | 5282 kWh | 2113 kWh | 3169 kWh | £560 | £317 | £877 | £10,173 | 11.6 yrs | £7,375 |
| 6 kW | 6338 kWh | 2535 kWh | 3803 kWh | £673 | £380 | £1,053 | £12,207 | 11.6 yrs | £8,850 |
| 7 kW | 7394 kWh | 2958 kWh | 4436 kWh | £785 | £444 | £1,228 | £14,242 | 11.6 yrs | £10,325 |
| 8 kW | 8450 kWh | 3380 kWh | 5070 kWh | £897 | £507 | £1,404 | £16,276 | 11.6 yrs | £11,800 |
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: £1,052, Upfront: £12,273, Break-even: 11.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2113 kWh | 1268 kWh | 845 kWh | £336 | £85 | £421 | £6,169 | 14.7 yrs | £2,247 |
| 3 kW | 3169 kWh | 1901 kWh | 1268 kWh | £504 | £127 | £631 | £8,204 | 13.0 yrs | £4,420 |
| 4 kW | 4225 kWh | 2535 kWh | 1690 kWh | £673 | £169 | £842 | £10,238 | 12.2 yrs | £6,593 |
| 5 kW | 5282 kWh | 3169 kWh | 2113 kWh | £841 | £211 | £1,052 | £12,273 | 11.7 yrs | £8,767 |
| 6 kW | 6338 kWh | 3803 kWh | 2535 kWh | £1,009 | £254 | £1,262 | £14,307 | 11.3 yrs | £10,940 |
| 7 kW | 7394 kWh | 4436 kWh | 2958 kWh | £1,177 | £296 | £1,473 | £16,342 | 11.1 yrs | £13,114 |
| 8 kW | 8450 kWh | 5070 kWh | 3380 kWh | £1,345 | £338 | £1,683 | £18,376 | 10.9 yrs | £15,287 |
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: £1,139, Upfront: £13,673, 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 | 2113 kWh | 1479 kWh | 634 kWh | £392 | £63 | £456 | £7,569 | 16.6 yrs | £1,545 |
| 3 kW | 3169 kWh | 2218 kWh | 951 kWh | £588 | £95 | £684 | £9,604 | 14.0 yrs | £4,068 |
| 4 kW | 4225 kWh | 2958 kWh | 1268 kWh | £785 | £127 | £911 | £11,638 | 12.8 yrs | £6,590 |
| 5 kW | 5282 kWh | 3697 kWh | 1584 kWh | £981 | £158 | £1,139 | £13,673 | 12.0 yrs | £9,113 |
| 6 kW | 6338 kWh | 4436 kWh | 1901 kWh | £1,177 | £190 | £1,367 | £15,707 | 11.5 yrs | £11,635 |
| 7 kW | 7394 kWh | 5176 kWh | 2218 kWh | £1,373 | £222 | £1,595 | £17,742 | 11.1 yrs | £14,158 |
| 8 kW | 8450 kWh | 5915 kWh | 2535 kWh | £1,569 | £254 | £1,823 | £19,776 | 10.8 yrs | £16,681 |
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: £1,165, Upfront: £15,423, Break-even: 13.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2113 kWh | 1542 kWh | 570 kWh | £409 | £57 | £466 | £9,319 | 20.0 yrs | £5 |
| 3 kW | 3169 kWh | 2313 kWh | 856 kWh | £614 | £86 | £699 | £11,354 | 16.2 yrs | £2,632 |
| 4 kW | 4225 kWh | 3084 kWh | 1141 kWh | £818 | £114 | £932 | £13,388 | 14.4 yrs | £5,259 |
| 5 kW | 5282 kWh | 3855 kWh | 1426 kWh | £1,023 | £143 | £1,165 | £15,423 | 13.2 yrs | £7,887 |
| 6 kW | 6338 kWh | 4627 kWh | 1711 kWh | £1,227 | £171 | £1,399 | £17,457 | 12.5 yrs | £10,514 |
| 7 kW | 7394 kWh | 5398 kWh | 1996 kWh | £1,432 | £200 | £1,632 | £19,492 | 11.9 yrs | £13,141 |
| 8 kW | 8450 kWh | 6169 kWh | 2282 kWh | £1,637 | £228 | £1,865 | £21,526 | 11.5 yrs | £15,769 |
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: £1,183, Upfront: £17,173, 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 | 2113 kWh | 1584 kWh | 528 kWh | £420 | £53 | £473 | £11,069 | 23.4 yrs | £-1,606 |
| 3 kW | 3169 kWh | 2377 kWh | 792 kWh | £631 | £79 | £710 | £13,104 | 18.5 yrs | £1,092 |
| 4 kW | 4225 kWh | 3169 kWh | 1056 kWh | £841 | £106 | £946 | £15,138 | 16.0 yrs | £3,789 |
| 5 kW | 5282 kWh | 3961 kWh | 1320 kWh | £1,051 | £132 | £1,183 | £17,173 | 14.5 yrs | £6,486 |
| 6 kW | 6338 kWh | 4753 kWh | 1584 kWh | £1,261 | £158 | £1,420 | £19,207 | 13.5 yrs | £9,183 |
| 7 kW | 7394 kWh | 5546 kWh | 1849 kWh | £1,471 | £185 | £1,656 | £21,242 | 12.8 yrs | £11,880 |
| 8 kW | 8450 kWh | 6338 kWh | 2113 kWh | £1,681 | £211 | £1,893 | £23,276 | 12.3 yrs | £14,577 |
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: £1,200, Upfront: £19,623, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2113 kWh | 1627 kWh | 486 kWh | £432 | £49 | £480 | £13,519 | 28.2 yrs | £-3,916 |
| 3 kW | 3169 kWh | 2440 kWh | 729 kWh | £647 | £73 | £720 | £15,554 | 21.6 yrs | £-1,149 |
| 4 kW | 4225 kWh | 3253 kWh | 972 kWh | £863 | £97 | £960 | £17,588 | 18.3 yrs | £1,618 |
| 5 kW | 5282 kWh | 4067 kWh | 1215 kWh | £1,079 | £121 | £1,200 | £19,623 | 16.3 yrs | £4,385 |
| 6 kW | 6338 kWh | 4880 kWh | 1458 kWh | £1,295 | £146 | £1,440 | £21,657 | 15.0 yrs | £7,152 |
| 7 kW | 7394 kWh | 5693 kWh | 1701 kWh | £1,510 | £170 | £1,681 | £23,692 | 14.1 yrs | £9,919 |
| 8 kW | 8450 kWh | 6507 kWh | 1944 kWh | £1,726 | £194 | £1,921 | £25,726 | 13.4 yrs | £12,686 |
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.