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 711 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: £598, Upfront: £10,173, Break-even: 17.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1422 kWh | 569 kWh | 853 kWh | £154 | £85 | £239 | £4,069 | 17.0 yrs | £715 |
| 3 kW | 2132 kWh | 853 kWh | 1279 kWh | £231 | £128 | £359 | £6,104 | 17.0 yrs | £1,072 |
| 4 kW | 2843 kWh | 1137 kWh | 1706 kWh | £308 | £171 | £478 | £8,138 | 17.0 yrs | £1,429 |
| 5 kW | 3554 kWh | 1422 kWh | 2132 kWh | £385 | £213 | £598 | £10,173 | 17.0 yrs | £1,786 |
| 6 kW | 4265 kWh | 1706 kWh | 2559 kWh | £462 | £256 | £718 | £12,207 | 17.0 yrs | £2,144 |
| 7 kW | 4976 kWh | 1990 kWh | 2985 kWh | £539 | £299 | £837 | £14,242 | 17.0 yrs | £2,501 |
| 8 kW | 5687 kWh | 2275 kWh | 3412 kWh | £616 | £341 | £957 | £16,276 | 17.0 yrs | £2,858 |
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: £719, Upfront: £12,273, Break-even: 17.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1422 kWh | 853 kWh | 569 kWh | £231 | £57 | £288 | £6,169 | 21.4 yrs | £-415 |
| 3 kW | 2132 kWh | 1279 kWh | 853 kWh | £346 | £85 | £432 | £8,204 | 19.0 yrs | £427 |
| 4 kW | 2843 kWh | 1706 kWh | 1137 kWh | £462 | £114 | £575 | £10,238 | 17.8 yrs | £1,269 |
| 5 kW | 3554 kWh | 2132 kWh | 1422 kWh | £577 | £142 | £719 | £12,273 | 17.1 yrs | £2,112 |
| 6 kW | 4265 kWh | 2559 kWh | 1706 kWh | £692 | £171 | £863 | £14,307 | 16.6 yrs | £2,954 |
| 7 kW | 4976 kWh | 2985 kWh | 1990 kWh | £808 | £199 | £1,007 | £16,342 | 16.2 yrs | £3,797 |
| 8 kW | 5687 kWh | 3412 kWh | 2275 kWh | £923 | £227 | £1,151 | £18,376 | 16.0 yrs | £4,639 |
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: £780, Upfront: £13,673, Break-even: 17.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1422 kWh | 995 kWh | 426 kWh | £269 | £43 | £312 | £7,569 | 24.3 yrs | £-1,330 |
| 3 kW | 2132 kWh | 1493 kWh | 640 kWh | £404 | £64 | £468 | £9,604 | 20.5 yrs | £-245 |
| 4 kW | 2843 kWh | 1990 kWh | 853 kWh | £539 | £85 | £624 | £11,638 | 18.7 yrs | £840 |
| 5 kW | 3554 kWh | 2488 kWh | 1066 kWh | £673 | £107 | £780 | £13,673 | 17.5 yrs | £1,924 |
| 6 kW | 4265 kWh | 2985 kWh | 1279 kWh | £808 | £128 | £936 | £15,707 | 16.8 yrs | £3,009 |
| 7 kW | 4976 kWh | 3483 kWh | 1493 kWh | £943 | £149 | £1,092 | £17,742 | 16.2 yrs | £4,094 |
| 8 kW | 5687 kWh | 3981 kWh | 1706 kWh | £1,077 | £171 | £1,248 | £19,776 | 15.8 yrs | £5,179 |
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: £798, Upfront: £15,423, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1422 kWh | 1038 kWh | 384 kWh | £281 | £38 | £319 | £9,319 | 29.2 yrs | £-2,935 |
| 3 kW | 2132 kWh | 1557 kWh | 576 kWh | £421 | £58 | £479 | £11,354 | 23.7 yrs | £-1,777 |
| 4 kW | 2843 kWh | 2076 kWh | 768 kWh | £562 | £77 | £638 | £13,388 | 21.0 yrs | £-619 |
| 5 kW | 3554 kWh | 2595 kWh | 960 kWh | £702 | £96 | £798 | £15,423 | 19.3 yrs | £538 |
| 6 kW | 4265 kWh | 3113 kWh | 1152 kWh | £842 | £115 | £958 | £17,457 | 18.2 yrs | £1,696 |
| 7 kW | 4976 kWh | 3632 kWh | 1343 kWh | £983 | £134 | £1,117 | £19,492 | 17.4 yrs | £2,854 |
| 8 kW | 5687 kWh | 4151 kWh | 1535 kWh | £1,123 | £154 | £1,277 | £21,526 | 16.9 yrs | £4,011 |
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: £810, Upfront: £17,173, Break-even: 21.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1422 kWh | 1066 kWh | 355 kWh | £289 | £36 | £324 | £11,069 | 34.2 yrs | £-4,588 |
| 3 kW | 2132 kWh | 1599 kWh | 533 kWh | £433 | £53 | £486 | £13,104 | 27.0 yrs | £-3,382 |
| 4 kW | 2843 kWh | 2132 kWh | 711 kWh | £577 | £71 | £648 | £15,138 | 23.4 yrs | £-2,175 |
| 5 kW | 3554 kWh | 2666 kWh | 889 kWh | £721 | £89 | £810 | £17,173 | 21.2 yrs | £-969 |
| 6 kW | 4265 kWh | 3199 kWh | 1066 kWh | £866 | £107 | £972 | £19,207 | 19.8 yrs | £237 |
| 7 kW | 4976 kWh | 3732 kWh | 1244 kWh | £1,010 | £124 | £1,134 | £21,242 | 18.7 yrs | £1,443 |
| 8 kW | 5687 kWh | 4265 kWh | 1422 kWh | £1,154 | £142 | £1,296 | £23,276 | 18.0 yrs | £2,649 |
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: £822, Upfront: £19,623, Break-even: 23.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1422 kWh | 1095 kWh | 327 kWh | £296 | £33 | £329 | £13,519 | 41.1 yrs | £-6,941 |
| 3 kW | 2132 kWh | 1642 kWh | 490 kWh | £444 | £49 | £493 | £15,554 | 31.5 yrs | £-5,686 |
| 4 kW | 2843 kWh | 2189 kWh | 654 kWh | £592 | £65 | £658 | £17,588 | 26.7 yrs | £-4,431 |
| 5 kW | 3554 kWh | 2737 kWh | 817 kWh | £741 | £82 | £822 | £19,623 | 23.9 yrs | £-3,177 |
| 6 kW | 4265 kWh | 3284 kWh | 981 kWh | £889 | £98 | £987 | £21,657 | 21.9 yrs | £-1,922 |
| 7 kW | 4976 kWh | 3831 kWh | 1144 kWh | £1,037 | £114 | £1,151 | £23,692 | 20.6 yrs | £-667 |
| 8 kW | 5687 kWh | 4379 kWh | 1308 kWh | £1,185 | £131 | £1,316 | £25,726 | 19.6 yrs | £587 |
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.