A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 858 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £701, Upfront: £10,173, Break-even: 14.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1716 kWh | 686 kWh | 1030 kWh | £177 | £103 | £280 | £4,069 | 14.5 yrs | £1,537 |
| 3 kW | 2574 kWh | 1030 kWh | 1544 kWh | £266 | £154 | £420 | £6,104 | 14.5 yrs | £2,306 |
| 4 kW | 3432 kWh | 1373 kWh | 2059 kWh | £355 | £206 | £561 | £8,138 | 14.5 yrs | £3,074 |
| 5 kW | 4290 kWh | 1716 kWh | 2574 kWh | £443 | £257 | £701 | £10,173 | 14.5 yrs | £3,843 |
| 6 kW | 5148 kWh | 2059 kWh | 3089 kWh | £532 | £309 | £841 | £12,207 | 14.5 yrs | £4,611 |
| 7 kW | 6006 kWh | 2402 kWh | 3603 kWh | £621 | £360 | £981 | £14,242 | 14.5 yrs | £5,380 |
| 8 kW | 6864 kWh | 2745 kWh | 4118 kWh | £709 | £412 | £1,121 | £16,276 | 14.5 yrs | £6,148 |
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: £837, Upfront: £12,273, Break-even: 14.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1716 kWh | 1030 kWh | 686 kWh | £266 | £69 | £335 | £6,169 | 18.4 yrs | £524 |
| 3 kW | 2574 kWh | 1544 kWh | 1030 kWh | £399 | £103 | £502 | £8,204 | 16.3 yrs | £1,836 |
| 4 kW | 3432 kWh | 2059 kWh | 1373 kWh | £532 | £137 | £669 | £10,238 | 15.3 yrs | £3,149 |
| 5 kW | 4290 kWh | 2574 kWh | 1716 kWh | £665 | £172 | £837 | £12,273 | 14.7 yrs | £4,461 |
| 6 kW | 5148 kWh | 3089 kWh | 2059 kWh | £798 | £206 | £1,004 | £14,307 | 14.3 yrs | £5,773 |
| 7 kW | 6006 kWh | 3603 kWh | 2402 kWh | £931 | £240 | £1,171 | £16,342 | 14.0 yrs | £7,085 |
| 8 kW | 6864 kWh | 4118 kWh | 2745 kWh | £1,064 | £275 | £1,339 | £18,376 | 13.7 yrs | £8,397 |
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: £905, Upfront: £13,673, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1716 kWh | 1201 kWh | 515 kWh | £310 | £51 | £362 | £7,569 | 20.9 yrs | £-332 |
| 3 kW | 2574 kWh | 1802 kWh | 772 kWh | £466 | £77 | £543 | £9,604 | 17.7 yrs | £1,252 |
| 4 kW | 3432 kWh | 2402 kWh | 1030 kWh | £621 | £103 | £724 | £11,638 | 16.1 yrs | £2,836 |
| 5 kW | 4290 kWh | 3003 kWh | 1287 kWh | £776 | £129 | £905 | £13,673 | 15.1 yrs | £4,420 |
| 6 kW | 5148 kWh | 3603 kWh | 1544 kWh | £931 | £154 | £1,086 | £15,707 | 14.5 yrs | £6,004 |
| 7 kW | 6006 kWh | 4204 kWh | 1802 kWh | £1,086 | £180 | £1,266 | £17,742 | 14.0 yrs | £7,588 |
| 8 kW | 6864 kWh | 4804 kWh | 2059 kWh | £1,241 | £206 | £1,447 | £19,776 | 13.7 yrs | £9,172 |
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: £925, Upfront: £15,423, Break-even: 16.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1716 kWh | 1253 kWh | 463 kWh | £324 | £46 | £370 | £9,319 | 25.2 yrs | £-1,919 |
| 3 kW | 2574 kWh | 1879 kWh | 695 kWh | £486 | £69 | £555 | £11,354 | 20.5 yrs | £-254 |
| 4 kW | 3432 kWh | 2505 kWh | 927 kWh | £647 | £93 | £740 | £13,388 | 18.1 yrs | £1,412 |
| 5 kW | 4290 kWh | 3131 kWh | 1158 kWh | £809 | £116 | £925 | £15,423 | 16.7 yrs | £3,077 |
| 6 kW | 5148 kWh | 3758 kWh | 1390 kWh | £971 | £139 | £1,110 | £17,457 | 15.7 yrs | £4,743 |
| 7 kW | 6006 kWh | 4384 kWh | 1622 kWh | £1,133 | £162 | £1,295 | £19,492 | 15.1 yrs | £6,408 |
| 8 kW | 6864 kWh | 5010 kWh | 1853 kWh | £1,295 | £185 | £1,480 | £21,526 | 14.5 yrs | £8,074 |
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: £939, Upfront: £17,173, Break-even: 18.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1716 kWh | 1287 kWh | 429 kWh | £333 | £43 | £375 | £11,069 | 29.5 yrs | £-3,560 |
| 3 kW | 2574 kWh | 1930 kWh | 643 kWh | £499 | £64 | £563 | £13,104 | 23.3 yrs | £-1,840 |
| 4 kW | 3432 kWh | 2574 kWh | 858 kWh | £665 | £86 | £751 | £15,138 | 20.2 yrs | £-121 |
| 5 kW | 4290 kWh | 3217 kWh | 1072 kWh | £831 | £107 | £939 | £17,173 | 18.3 yrs | £1,599 |
| 6 kW | 5148 kWh | 3861 kWh | 1287 kWh | £998 | £129 | £1,126 | £19,207 | 17.1 yrs | £3,319 |
| 7 kW | 6006 kWh | 4504 kWh | 1501 kWh | £1,164 | £150 | £1,314 | £21,242 | 16.2 yrs | £5,039 |
| 8 kW | 6864 kWh | 5148 kWh | 1716 kWh | £1,330 | £172 | £1,502 | £23,276 | 15.5 yrs | £6,759 |
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: £952, Upfront: £19,623, Break-even: 20.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1716 kWh | 1321 kWh | 395 kWh | £341 | £39 | £381 | £13,519 | 35.5 yrs | £-5,902 |
| 3 kW | 2574 kWh | 1982 kWh | 592 kWh | £512 | £59 | £571 | £15,554 | 27.2 yrs | £-4,127 |
| 4 kW | 3432 kWh | 2642 kWh | 789 kWh | £683 | £79 | £762 | £17,588 | 23.1 yrs | £-2,353 |
| 5 kW | 4290 kWh | 3303 kWh | 987 kWh | £854 | £99 | £952 | £19,623 | 20.6 yrs | £-579 |
| 6 kW | 5148 kWh | 3964 kWh | 1184 kWh | £1,024 | £118 | £1,143 | £21,657 | 19.0 yrs | £1,195 |
| 7 kW | 6006 kWh | 4624 kWh | 1381 kWh | £1,195 | £138 | £1,333 | £23,692 | 17.8 yrs | £2,969 |
| 8 kW | 6864 kWh | 5285 kWh | 1579 kWh | £1,366 | £158 | £1,523 | £25,726 | 16.9 yrs | £4,744 |
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.