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 925 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £748, Upfront: £10,173, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1850 kWh | 740 kWh | 1110 kWh | £188 | £111 | £299 | £4,069 | 13.6 yrs | £1,916 |
| 3 kW | 2776 kWh | 1110 kWh | 1665 kWh | £282 | £167 | £449 | £6,104 | 13.6 yrs | £2,874 |
| 4 kW | 3701 kWh | 1480 kWh | 2221 kWh | £376 | £222 | £599 | £8,138 | 13.6 yrs | £3,832 |
| 5 kW | 4626 kWh | 1850 kWh | 2776 kWh | £471 | £278 | £748 | £10,173 | 13.6 yrs | £4,790 |
| 6 kW | 5551 kWh | 2221 kWh | 3331 kWh | £565 | £333 | £898 | £12,207 | 13.6 yrs | £5,749 |
| 7 kW | 6477 kWh | 2591 kWh | 3886 kWh | £659 | £389 | £1,047 | £14,242 | 13.6 yrs | £6,707 |
| 8 kW | 7402 kWh | 2961 kWh | 4441 kWh | £753 | £444 | £1,197 | £16,276 | 13.6 yrs | £7,665 |
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: £891, Upfront: £12,273, 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 | 1850 kWh | 1110 kWh | 740 kWh | £282 | £74 | £356 | £6,169 | 17.3 yrs | £958 |
| 3 kW | 2776 kWh | 1665 kWh | 1110 kWh | £424 | £111 | £535 | £8,204 | 15.3 yrs | £2,487 |
| 4 kW | 3701 kWh | 2221 kWh | 1480 kWh | £565 | £148 | £713 | £10,238 | 14.4 yrs | £4,017 |
| 5 kW | 4626 kWh | 2776 kWh | 1850 kWh | £706 | £185 | £891 | £12,273 | 13.8 yrs | £5,546 |
| 6 kW | 5551 kWh | 3331 kWh | 2221 kWh | £847 | £222 | £1,069 | £14,307 | 13.4 yrs | £7,075 |
| 7 kW | 6477 kWh | 3886 kWh | 2591 kWh | £988 | £259 | £1,247 | £16,342 | 13.1 yrs | £8,604 |
| 8 kW | 7402 kWh | 4441 kWh | 2961 kWh | £1,129 | £296 | £1,425 | £18,376 | 12.9 yrs | £10,133 |
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: £962, Upfront: £13,673, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1850 kWh | 1295 kWh | 555 kWh | £329 | £56 | £385 | £7,569 | 19.7 yrs | £129 |
| 3 kW | 2776 kWh | 1943 kWh | 833 kWh | £494 | £83 | £577 | £9,604 | 16.6 yrs | £1,944 |
| 4 kW | 3701 kWh | 2591 kWh | 1110 kWh | £659 | £111 | £770 | £11,638 | 15.1 yrs | £3,759 |
| 5 kW | 4626 kWh | 3238 kWh | 1388 kWh | £824 | £139 | £962 | £13,673 | 14.2 yrs | £5,573 |
| 6 kW | 5551 kWh | 3886 kWh | 1665 kWh | £988 | £167 | £1,155 | £15,707 | 13.6 yrs | £7,388 |
| 7 kW | 6477 kWh | 4534 kWh | 1943 kWh | £1,153 | £194 | £1,347 | £17,742 | 13.2 yrs | £9,203 |
| 8 kW | 7402 kWh | 5181 kWh | 2221 kWh | £1,318 | £222 | £1,540 | £19,776 | 12.8 yrs | £11,017 |
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: £984, Upfront: £15,423, Break-even: 15.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1850 kWh | 1351 kWh | 500 kWh | £344 | £50 | £393 | £9,319 | 23.7 yrs | £-1,449 |
| 3 kW | 2776 kWh | 2026 kWh | 749 kWh | £515 | £75 | £590 | £11,354 | 19.2 yrs | £451 |
| 4 kW | 3701 kWh | 2702 kWh | 999 kWh | £687 | £100 | £787 | £13,388 | 17.0 yrs | £2,351 |
| 5 kW | 4626 kWh | 3377 kWh | 1249 kWh | £859 | £125 | £984 | £15,423 | 15.7 yrs | £4,252 |
| 6 kW | 5551 kWh | 4053 kWh | 1499 kWh | £1,031 | £150 | £1,180 | £17,457 | 14.8 yrs | £6,152 |
| 7 kW | 6477 kWh | 4728 kWh | 1749 kWh | £1,202 | £175 | £1,377 | £19,492 | 14.2 yrs | £8,052 |
| 8 kW | 7402 kWh | 5403 kWh | 1999 kWh | £1,374 | £200 | £1,574 | £21,526 | 13.7 yrs | £9,953 |
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: £998, Upfront: £17,173, Break-even: 17.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1850 kWh | 1388 kWh | 463 kWh | £353 | £46 | £399 | £11,069 | 27.7 yrs | £-3,085 |
| 3 kW | 2776 kWh | 2082 kWh | 694 kWh | £529 | £69 | £599 | £13,104 | 21.9 yrs | £-1,128 |
| 4 kW | 3701 kWh | 2776 kWh | 925 kWh | £706 | £93 | £798 | £15,138 | 19.0 yrs | £830 |
| 5 kW | 4626 kWh | 3470 kWh | 1157 kWh | £882 | £116 | £998 | £17,173 | 17.2 yrs | £2,787 |
| 6 kW | 5551 kWh | 4164 kWh | 1388 kWh | £1,059 | £139 | £1,198 | £19,207 | 16.0 yrs | £4,745 |
| 7 kW | 6477 kWh | 4858 kWh | 1619 kWh | £1,235 | £162 | £1,397 | £21,242 | 15.2 yrs | £6,702 |
| 8 kW | 7402 kWh | 5551 kWh | 1850 kWh | £1,412 | £185 | £1,597 | £23,276 | 14.6 yrs | £8,660 |
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: £1,012, Upfront: £19,623, Break-even: 19.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1850 kWh | 1425 kWh | 426 kWh | £362 | £43 | £405 | £13,519 | 33.4 yrs | £-5,421 |
| 3 kW | 2776 kWh | 2137 kWh | 638 kWh | £544 | £64 | £607 | £15,554 | 25.6 yrs | £-3,406 |
| 4 kW | 3701 kWh | 2850 kWh | 851 kWh | £725 | £85 | £810 | £17,588 | 21.7 yrs | £-1,392 |
| 5 kW | 4626 kWh | 3562 kWh | 1064 kWh | £906 | £106 | £1,012 | £19,623 | 19.4 yrs | £623 |
| 6 kW | 5551 kWh | 4275 kWh | 1277 kWh | £1,087 | £128 | £1,215 | £21,657 | 17.8 yrs | £2,637 |
| 7 kW | 6477 kWh | 4987 kWh | 1490 kWh | £1,268 | £149 | £1,417 | £23,692 | 16.7 yrs | £4,652 |
| 8 kW | 7402 kWh | 5699 kWh | 1702 kWh | £1,449 | £170 | £1,620 | £25,726 | 15.9 yrs | £6,666 |
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.