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 1052 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: £873, Upfront: £10,173, 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 | 2104 kWh | 841 kWh | 1262 kWh | £223 | £126 | £349 | £4,069 | 11.7 yrs | £2,912 |
| 3 kW | 3155 kWh | 1262 kWh | 1893 kWh | £334 | £189 | £524 | £6,104 | 11.7 yrs | £4,368 |
| 4 kW | 4207 kWh | 1683 kWh | 2524 kWh | £446 | £252 | £698 | £8,138 | 11.7 yrs | £5,823 |
| 5 kW | 5259 kWh | 2104 kWh | 3155 kWh | £557 | £316 | £873 | £10,173 | 11.7 yrs | £7,279 |
| 6 kW | 6311 kWh | 2524 kWh | 3787 kWh | £668 | £379 | £1,047 | £12,207 | 11.7 yrs | £8,735 |
| 7 kW | 7363 kWh | 2945 kWh | 4418 kWh | £780 | £442 | £1,222 | £14,242 | 11.7 yrs | £10,191 |
| 8 kW | 8415 kWh | 3366 kWh | 5049 kWh | £891 | £505 | £1,396 | £16,276 | 11.7 yrs | £11,647 |
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: £1,046, 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 | 2104 kWh | 1262 kWh | 841 kWh | £334 | £84 | £418 | £6,169 | 14.7 yrs | £2,198 |
| 3 kW | 3155 kWh | 1893 kWh | 1262 kWh | £501 | £126 | £628 | £8,204 | 13.1 yrs | £4,348 |
| 4 kW | 4207 kWh | 2524 kWh | 1683 kWh | £668 | £168 | £837 | £10,238 | 12.2 yrs | £6,497 |
| 5 kW | 5259 kWh | 3155 kWh | 2104 kWh | £836 | £210 | £1,046 | £12,273 | 11.7 yrs | £8,646 |
| 6 kW | 6311 kWh | 3787 kWh | 2524 kWh | £1,003 | £252 | £1,255 | £14,307 | 11.4 yrs | £10,795 |
| 7 kW | 7363 kWh | 4418 kWh | 2945 kWh | £1,170 | £295 | £1,464 | £16,342 | 11.2 yrs | £12,944 |
| 8 kW | 8415 kWh | 5049 kWh | 3366 kWh | £1,337 | £337 | £1,673 | £18,376 | 11.0 yrs | £15,094 |
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: £1,133, Upfront: £13,673, 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 | 2104 kWh | 1473 kWh | 631 kWh | £390 | £63 | £453 | £7,569 | 16.7 yrs | £1,492 |
| 3 kW | 3155 kWh | 2209 kWh | 947 kWh | £585 | £95 | £680 | £9,604 | 14.1 yrs | £3,988 |
| 4 kW | 4207 kWh | 2945 kWh | 1262 kWh | £780 | £126 | £906 | £11,638 | 12.8 yrs | £6,484 |
| 5 kW | 5259 kWh | 3681 kWh | 1578 kWh | £975 | £158 | £1,133 | £13,673 | 12.1 yrs | £8,979 |
| 6 kW | 6311 kWh | 4418 kWh | 1893 kWh | £1,170 | £189 | £1,359 | £15,707 | 11.6 yrs | £11,475 |
| 7 kW | 7363 kWh | 5154 kWh | 2209 kWh | £1,365 | £221 | £1,586 | £17,742 | 11.2 yrs | £13,971 |
| 8 kW | 8415 kWh | 5890 kWh | 2524 kWh | £1,560 | £252 | £1,812 | £19,776 | 10.9 yrs | £16,467 |
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: £1,159, Upfront: £15,423, Break-even: 13.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2104 kWh | 1536 kWh | 568 kWh | £407 | £57 | £463 | £9,319 | 20.1 yrs | £-50 |
| 3 kW | 3155 kWh | 2303 kWh | 852 kWh | £610 | £85 | £695 | £11,354 | 16.3 yrs | £2,550 |
| 4 kW | 4207 kWh | 3071 kWh | 1136 kWh | £813 | £114 | £927 | £13,388 | 14.4 yrs | £5,150 |
| 5 kW | 5259 kWh | 3839 kWh | 1420 kWh | £1,017 | £142 | £1,159 | £15,423 | 13.3 yrs | £7,749 |
| 6 kW | 6311 kWh | 4607 kWh | 1704 kWh | £1,220 | £170 | £1,390 | £17,457 | 12.6 yrs | £10,349 |
| 7 kW | 7363 kWh | 5375 kWh | 1988 kWh | £1,423 | £199 | £1,622 | £19,492 | 12.0 yrs | £12,949 |
| 8 kW | 8415 kWh | 6143 kWh | 2272 kWh | £1,627 | £227 | £1,854 | £21,526 | 11.6 yrs | £15,549 |
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: £1,176, Upfront: £17,173, Break-even: 14.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2104 kWh | 1578 kWh | 526 kWh | £418 | £53 | £470 | £11,069 | 23.5 yrs | £-1,662 |
| 3 kW | 3155 kWh | 2367 kWh | 789 kWh | £627 | £79 | £706 | £13,104 | 18.6 yrs | £1,008 |
| 4 kW | 4207 kWh | 3155 kWh | 1052 kWh | £836 | £105 | £941 | £15,138 | 16.1 yrs | £3,677 |
| 5 kW | 5259 kWh | 3944 kWh | 1315 kWh | £1,044 | £131 | £1,176 | £17,173 | 14.6 yrs | £6,346 |
| 6 kW | 6311 kWh | 4733 kWh | 1578 kWh | £1,253 | £158 | £1,411 | £19,207 | 13.6 yrs | £9,015 |
| 7 kW | 7363 kWh | 5522 kWh | 1841 kWh | £1,462 | £184 | £1,646 | £21,242 | 12.9 yrs | £11,685 |
| 8 kW | 8415 kWh | 6311 kWh | 2104 kWh | £1,671 | £210 | £1,881 | £23,276 | 12.4 yrs | £14,354 |
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: £1,193, Upfront: £19,623, Break-even: 16.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2104 kWh | 1620 kWh | 484 kWh | £429 | £48 | £477 | £13,519 | 28.3 yrs | £-3,973 |
| 3 kW | 3155 kWh | 2430 kWh | 726 kWh | £643 | £73 | £716 | £15,554 | 21.7 yrs | £-1,234 |
| 4 kW | 4207 kWh | 3240 kWh | 968 kWh | £858 | £97 | £955 | £17,588 | 18.4 yrs | £1,504 |
| 5 kW | 5259 kWh | 4050 kWh | 1210 kWh | £1,072 | £121 | £1,193 | £19,623 | 16.4 yrs | £4,243 |
| 6 kW | 6311 kWh | 4859 kWh | 1452 kWh | £1,287 | £145 | £1,432 | £21,657 | 15.1 yrs | £6,981 |
| 7 kW | 7363 kWh | 5669 kWh | 1693 kWh | £1,501 | £169 | £1,671 | £23,692 | 14.2 yrs | £9,720 |
| 8 kW | 8415 kWh | 6479 kWh | 1935 kWh | £1,716 | £194 | £1,909 | £25,726 | 13.5 yrs | £12,459 |
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.