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 842 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: £709, Upfront: £10,173, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1683 kWh | 673 kWh | 1010 kWh | £183 | £101 | £284 | £4,069 | 14.4 yrs | £1,601 |
| 3 kW | 2525 kWh | 1010 kWh | 1515 kWh | £274 | £151 | £425 | £6,104 | 14.4 yrs | £2,402 |
| 4 kW | 3366 kWh | 1347 kWh | 2020 kWh | £365 | £202 | £567 | £8,138 | 14.4 yrs | £3,203 |
| 5 kW | 4208 kWh | 1683 kWh | 2525 kWh | £456 | £252 | £709 | £10,173 | 14.4 yrs | £4,003 |
| 6 kW | 5050 kWh | 2020 kWh | 3030 kWh | £548 | £303 | £851 | £12,207 | 14.4 yrs | £4,804 |
| 7 kW | 5891 kWh | 2356 kWh | 3535 kWh | £639 | £353 | £992 | £14,242 | 14.4 yrs | £5,604 |
| 8 kW | 6733 kWh | 2693 kWh | 4040 kWh | £730 | £404 | £1,134 | £16,276 | 14.4 yrs | £6,405 |
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: £853, Upfront: £12,273, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1683 kWh | 1010 kWh | 673 kWh | £274 | £67 | £341 | £6,169 | 18.1 yrs | £653 |
| 3 kW | 2525 kWh | 1515 kWh | 1010 kWh | £411 | £101 | £512 | £8,204 | 16.0 yrs | £2,030 |
| 4 kW | 3366 kWh | 2020 kWh | 1347 kWh | £548 | £135 | £682 | £10,238 | 15.0 yrs | £3,406 |
| 5 kW | 4208 kWh | 2525 kWh | 1683 kWh | £684 | £168 | £853 | £12,273 | 14.4 yrs | £4,783 |
| 6 kW | 5050 kWh | 3030 kWh | 2020 kWh | £821 | £202 | £1,023 | £14,307 | 14.0 yrs | £6,160 |
| 7 kW | 5891 kWh | 3535 kWh | 2356 kWh | £958 | £236 | £1,194 | £16,342 | 13.7 yrs | £7,536 |
| 8 kW | 6733 kWh | 4040 kWh | 2693 kWh | £1,095 | £269 | £1,364 | £18,376 | 13.5 yrs | £8,913 |
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: £925, Upfront: £13,673, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1683 kWh | 1178 kWh | 505 kWh | £319 | £50 | £370 | £7,569 | 20.5 yrs | £-171 |
| 3 kW | 2525 kWh | 1767 kWh | 757 kWh | £479 | £76 | £555 | £9,604 | 17.3 yrs | £1,494 |
| 4 kW | 3366 kWh | 2356 kWh | 1010 kWh | £639 | £101 | £740 | £11,638 | 15.7 yrs | £3,158 |
| 5 kW | 4208 kWh | 2946 kWh | 1262 kWh | £799 | £126 | £925 | £13,673 | 14.8 yrs | £4,823 |
| 6 kW | 5050 kWh | 3535 kWh | 1515 kWh | £958 | £151 | £1,110 | £15,707 | 14.2 yrs | £6,488 |
| 7 kW | 5891 kWh | 4124 kWh | 1767 kWh | £1,118 | £177 | £1,295 | £17,742 | 13.7 yrs | £8,152 |
| 8 kW | 6733 kWh | 4713 kWh | 2020 kWh | £1,278 | £202 | £1,480 | £19,776 | 13.4 yrs | £9,817 |
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: £946, Upfront: £15,423, 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 | 1683 kWh | 1229 kWh | 454 kWh | £333 | £45 | £379 | £9,319 | 24.6 yrs | £-1,748 |
| 3 kW | 2525 kWh | 1843 kWh | 682 kWh | £500 | £68 | £568 | £11,354 | 20.0 yrs | £3 |
| 4 kW | 3366 kWh | 2457 kWh | 909 kWh | £666 | £91 | £757 | £13,388 | 17.7 yrs | £1,754 |
| 5 kW | 4208 kWh | 3072 kWh | 1136 kWh | £833 | £114 | £946 | £15,423 | 16.3 yrs | £3,505 |
| 6 kW | 5050 kWh | 3686 kWh | 1363 kWh | £999 | £136 | £1,136 | £17,457 | 15.4 yrs | £5,256 |
| 7 kW | 5891 kWh | 4301 kWh | 1591 kWh | £1,166 | £159 | £1,325 | £19,492 | 14.7 yrs | £7,007 |
| 8 kW | 6733 kWh | 4915 kWh | 1818 kWh | £1,332 | £182 | £1,514 | £21,526 | 14.2 yrs | £8,758 |
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: £961, Upfront: £17,173, Break-even: 17.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1683 kWh | 1262 kWh | 421 kWh | £342 | £42 | £384 | £11,069 | 28.8 yrs | £-3,383 |
| 3 kW | 2525 kWh | 1894 kWh | 631 kWh | £513 | £63 | £576 | £13,104 | 22.7 yrs | £-1,574 |
| 4 kW | 3366 kWh | 2525 kWh | 842 kWh | £684 | £84 | £769 | £15,138 | 19.7 yrs | £234 |
| 5 kW | 4208 kWh | 3156 kWh | 1052 kWh | £856 | £105 | £961 | £17,173 | 17.9 yrs | £2,043 |
| 6 kW | 5050 kWh | 3787 kWh | 1262 kWh | £1,027 | £126 | £1,153 | £19,207 | 16.7 yrs | £3,852 |
| 7 kW | 5891 kWh | 4418 kWh | 1473 kWh | £1,198 | £147 | £1,345 | £21,242 | 15.8 yrs | £5,660 |
| 8 kW | 6733 kWh | 5050 kWh | 1683 kWh | £1,369 | £168 | £1,537 | £23,276 | 15.1 yrs | £7,469 |
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: £975, Upfront: £19,623, Break-even: 20.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1683 kWh | 1296 kWh | 387 kWh | £351 | £39 | £390 | £13,519 | 34.7 yrs | £-5,718 |
| 3 kW | 2525 kWh | 1944 kWh | 581 kWh | £527 | £58 | £585 | £15,554 | 26.6 yrs | £-3,851 |
| 4 kW | 3366 kWh | 2592 kWh | 774 kWh | £703 | £77 | £780 | £17,588 | 22.5 yrs | £-1,985 |
| 5 kW | 4208 kWh | 3240 kWh | 968 kWh | £878 | £97 | £975 | £19,623 | 20.1 yrs | £-119 |
| 6 kW | 5050 kWh | 3888 kWh | 1161 kWh | £1,054 | £116 | £1,170 | £21,657 | 18.5 yrs | £1,747 |
| 7 kW | 5891 kWh | 4536 kWh | 1355 kWh | £1,230 | £135 | £1,365 | £23,692 | 17.4 yrs | £3,613 |
| 8 kW | 6733 kWh | 5184 kWh | 1549 kWh | £1,405 | £155 | £1,560 | £25,726 | 16.5 yrs | £5,480 |
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.