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 698 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: £587, Upfront: £10,173, Break-even: 17.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1396 kWh | 559 kWh | 838 kWh | £151 | £84 | £235 | £4,069 | 17.3 yrs | £630 |
| 3 kW | 2095 kWh | 838 kWh | 1257 kWh | £227 | £126 | £352 | £6,104 | 17.3 yrs | £945 |
| 4 kW | 2793 kWh | 1117 kWh | 1676 kWh | £302 | £168 | £470 | £8,138 | 17.3 yrs | £1,260 |
| 5 kW | 3491 kWh | 1396 kWh | 2095 kWh | £378 | £209 | £587 | £10,173 | 17.3 yrs | £1,574 |
| 6 kW | 4189 kWh | 1676 kWh | 2514 kWh | £453 | £251 | £705 | £12,207 | 17.3 yrs | £1,889 |
| 7 kW | 4888 kWh | 1955 kWh | 2933 kWh | £529 | £293 | £822 | £14,242 | 17.3 yrs | £2,204 |
| 8 kW | 5586 kWh | 2234 kWh | 3352 kWh | £605 | £335 | £940 | £16,276 | 17.3 yrs | £2,519 |
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: £706, Upfront: £12,273, Break-even: 17.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1396 kWh | 838 kWh | 559 kWh | £227 | £56 | £283 | £6,169 | 21.8 yrs | £-517 |
| 3 kW | 2095 kWh | 1257 kWh | 838 kWh | £340 | £84 | £424 | £8,204 | 19.4 yrs | £274 |
| 4 kW | 2793 kWh | 1676 kWh | 1117 kWh | £453 | £112 | £565 | £10,238 | 18.1 yrs | £1,065 |
| 5 kW | 3491 kWh | 2095 kWh | 1396 kWh | £567 | £140 | £706 | £12,273 | 17.4 yrs | £1,857 |
| 6 kW | 4189 kWh | 2514 kWh | 1676 kWh | £680 | £168 | £848 | £14,307 | 16.9 yrs | £2,648 |
| 7 kW | 4888 kWh | 2933 kWh | 1955 kWh | £794 | £196 | £989 | £16,342 | 16.5 yrs | £3,440 |
| 8 kW | 5586 kWh | 3352 kWh | 2234 kWh | £907 | £223 | £1,130 | £18,376 | 16.3 yrs | £4,231 |
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: £766, Upfront: £13,673, Break-even: 17.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1396 kWh | 978 kWh | 419 kWh | £265 | £42 | £306 | £7,569 | 24.7 yrs | £-1,441 |
| 3 kW | 2095 kWh | 1466 kWh | 628 kWh | £397 | £63 | £460 | £9,604 | 20.9 yrs | £-411 |
| 4 kW | 2793 kWh | 1955 kWh | 838 kWh | £529 | £84 | £613 | £11,638 | 19.0 yrs | £618 |
| 5 kW | 3491 kWh | 2444 kWh | 1047 kWh | £661 | £105 | £766 | £13,673 | 17.8 yrs | £1,648 |
| 6 kW | 4189 kWh | 2933 kWh | 1257 kWh | £794 | £126 | £919 | £15,707 | 17.1 yrs | £2,678 |
| 7 kW | 4888 kWh | 3421 kWh | 1466 kWh | £926 | £147 | £1,072 | £17,742 | 16.5 yrs | £3,707 |
| 8 kW | 5586 kWh | 3910 kWh | 1676 kWh | £1,058 | £168 | £1,226 | £19,776 | 16.1 yrs | £4,737 |
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: £784, Upfront: £15,423, Break-even: 19.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1396 kWh | 1019 kWh | 377 kWh | £276 | £38 | £314 | £9,319 | 29.7 yrs | £-3,048 |
| 3 kW | 2095 kWh | 1529 kWh | 566 kWh | £414 | £57 | £470 | £11,354 | 24.1 yrs | £-1,947 |
| 4 kW | 2793 kWh | 2039 kWh | 754 kWh | £552 | £75 | £627 | £13,388 | 21.3 yrs | £-846 |
| 5 kW | 3491 kWh | 2549 kWh | 943 kWh | £690 | £94 | £784 | £15,423 | 19.7 yrs | £255 |
| 6 kW | 4189 kWh | 3058 kWh | 1131 kWh | £828 | £113 | £941 | £17,457 | 18.6 yrs | £1,356 |
| 7 kW | 4888 kWh | 3568 kWh | 1320 kWh | £965 | £132 | £1,097 | £19,492 | 17.8 yrs | £2,458 |
| 8 kW | 5586 kWh | 4078 kWh | 1508 kWh | £1,103 | £151 | £1,254 | £21,526 | 17.2 yrs | £3,559 |
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: £796, Upfront: £17,173, Break-even: 21.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1396 kWh | 1047 kWh | 349 kWh | £283 | £35 | £318 | £11,069 | 34.8 yrs | £-4,703 |
| 3 kW | 2095 kWh | 1571 kWh | 524 kWh | £425 | £52 | £477 | £13,104 | 27.4 yrs | £-3,554 |
| 4 kW | 2793 kWh | 2095 kWh | 698 kWh | £567 | £70 | £637 | £15,138 | 23.8 yrs | £-2,405 |
| 5 kW | 3491 kWh | 2618 kWh | 873 kWh | £709 | £87 | £796 | £17,173 | 21.6 yrs | £-1,256 |
| 6 kW | 4189 kWh | 3142 kWh | 1047 kWh | £850 | £105 | £955 | £19,207 | 20.1 yrs | £-108 |
| 7 kW | 4888 kWh | 3666 kWh | 1222 kWh | £992 | £122 | £1,114 | £21,242 | 19.1 yrs | £1,041 |
| 8 kW | 5586 kWh | 4189 kWh | 1396 kWh | £1,134 | £140 | £1,273 | £23,276 | 18.3 yrs | £2,190 |
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: £808, Upfront: £19,623, Break-even: 24.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1396 kWh | 1075 kWh | 321 kWh | £291 | £32 | £323 | £13,519 | 41.8 yrs | £-7,057 |
| 3 kW | 2095 kWh | 1613 kWh | 482 kWh | £436 | £48 | £485 | £15,554 | 32.1 yrs | £-5,861 |
| 4 kW | 2793 kWh | 2151 kWh | 642 kWh | £582 | £64 | £646 | £17,588 | 27.2 yrs | £-4,665 |
| 5 kW | 3491 kWh | 2688 kWh | 803 kWh | £727 | £80 | £808 | £19,623 | 24.3 yrs | £-3,468 |
| 6 kW | 4189 kWh | 3226 kWh | 964 kWh | £873 | £96 | £969 | £21,657 | 22.3 yrs | £-2,272 |
| 7 kW | 4888 kWh | 3763 kWh | 1124 kWh | £1,018 | £112 | £1,131 | £23,692 | 21.0 yrs | £-1,075 |
| 8 kW | 5586 kWh | 4301 kWh | 1285 kWh | £1,164 | £128 | £1,292 | £25,726 | 19.9 yrs | £121 |
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.