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 801 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: £674, Upfront: £10,173, 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 | 1603 kWh | 641 kWh | 962 kWh | £174 | £96 | £270 | £4,069 | 15.1 yrs | £1,325 |
| 3 kW | 2404 kWh | 962 kWh | 1443 kWh | £260 | £144 | £405 | £6,104 | 15.1 yrs | £1,987 |
| 4 kW | 3206 kWh | 1282 kWh | 1924 kWh | £347 | £192 | £539 | £8,138 | 15.1 yrs | £2,649 |
| 5 kW | 4007 kWh | 1603 kWh | 2404 kWh | £434 | £240 | £674 | £10,173 | 15.1 yrs | £3,311 |
| 6 kW | 4809 kWh | 1924 kWh | 2885 kWh | £521 | £289 | £809 | £12,207 | 15.1 yrs | £3,974 |
| 7 kW | 5610 kWh | 2244 kWh | 3366 kWh | £607 | £337 | £944 | £14,242 | 15.1 yrs | £4,636 |
| 8 kW | 6412 kWh | 2565 kWh | 3847 kWh | £694 | £385 | £1,079 | £16,276 | 15.1 yrs | £5,298 |
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: £811, Upfront: £12,273, 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 | 1603 kWh | 962 kWh | 641 kWh | £260 | £64 | £324 | £6,169 | 19.0 yrs | £318 |
| 3 kW | 2404 kWh | 1443 kWh | 962 kWh | £390 | £96 | £487 | £8,204 | 16.9 yrs | £1,528 |
| 4 kW | 3206 kWh | 1924 kWh | 1282 kWh | £521 | £128 | £649 | £10,238 | 15.8 yrs | £2,737 |
| 5 kW | 4007 kWh | 2404 kWh | 1603 kWh | £651 | £160 | £811 | £12,273 | 15.1 yrs | £3,946 |
| 6 kW | 4809 kWh | 2885 kWh | 1924 kWh | £781 | £192 | £973 | £14,307 | 14.7 yrs | £5,155 |
| 7 kW | 5610 kWh | 3366 kWh | 2244 kWh | £911 | £224 | £1,135 | £16,342 | 14.4 yrs | £6,364 |
| 8 kW | 6412 kWh | 3847 kWh | 2565 kWh | £1,041 | £256 | £1,297 | £18,376 | 14.2 yrs | £7,574 |
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: £879, Upfront: £13,673, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1603 kWh | 1122 kWh | 481 kWh | £304 | £48 | £352 | £7,569 | 21.5 yrs | £-535 |
| 3 kW | 2404 kWh | 1683 kWh | 721 kWh | £455 | £72 | £528 | £9,604 | 18.2 yrs | £948 |
| 4 kW | 3206 kWh | 2244 kWh | 962 kWh | £607 | £96 | £703 | £11,638 | 16.5 yrs | £2,431 |
| 5 kW | 4007 kWh | 2805 kWh | 1202 kWh | £759 | £120 | £879 | £13,673 | 15.5 yrs | £3,913 |
| 6 kW | 4809 kWh | 3366 kWh | 1443 kWh | £911 | £144 | £1,055 | £15,707 | 14.9 yrs | £5,396 |
| 7 kW | 5610 kWh | 3927 kWh | 1683 kWh | £1,063 | £168 | £1,231 | £17,742 | 14.4 yrs | £6,879 |
| 8 kW | 6412 kWh | 4488 kWh | 1924 kWh | £1,215 | £192 | £1,407 | £19,776 | 14.1 yrs | £8,361 |
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: £900, Upfront: £15,423, 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 | 1603 kWh | 1170 kWh | 433 kWh | £317 | £43 | £360 | £9,319 | 25.9 yrs | £-2,121 |
| 3 kW | 2404 kWh | 1755 kWh | 649 kWh | £475 | £65 | £540 | £11,354 | 21.0 yrs | £-556 |
| 4 kW | 3206 kWh | 2340 kWh | 866 kWh | £633 | £87 | £720 | £13,388 | 18.6 yrs | £1,009 |
| 5 kW | 4007 kWh | 2925 kWh | 1082 kWh | £792 | £108 | £900 | £15,423 | 17.1 yrs | £2,573 |
| 6 kW | 4809 kWh | 3510 kWh | 1298 kWh | £950 | £130 | £1,080 | £17,457 | 16.2 yrs | £4,138 |
| 7 kW | 5610 kWh | 4096 kWh | 1515 kWh | £1,108 | £151 | £1,260 | £19,492 | 15.5 yrs | £5,703 |
| 8 kW | 6412 kWh | 4681 kWh | 1731 kWh | £1,267 | £173 | £1,440 | £21,526 | 15.0 yrs | £7,268 |
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: £913, Upfront: £17,173, Break-even: 18.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1603 kWh | 1202 kWh | 401 kWh | £325 | £40 | £365 | £11,069 | 30.3 yrs | £-3,761 |
| 3 kW | 2404 kWh | 1803 kWh | 601 kWh | £488 | £60 | £548 | £13,104 | 23.9 yrs | £-2,142 |
| 4 kW | 3206 kWh | 2404 kWh | 801 kWh | £651 | £80 | £731 | £15,138 | 20.7 yrs | £-522 |
| 5 kW | 4007 kWh | 3006 kWh | 1002 kWh | £813 | £100 | £913 | £17,173 | 18.8 yrs | £1,097 |
| 6 kW | 4809 kWh | 3607 kWh | 1202 kWh | £976 | £120 | £1,096 | £19,207 | 17.5 yrs | £2,716 |
| 7 kW | 5610 kWh | 4208 kWh | 1403 kWh | £1,139 | £140 | £1,279 | £21,242 | 16.6 yrs | £4,336 |
| 8 kW | 6412 kWh | 4809 kWh | 1603 kWh | £1,301 | £160 | £1,462 | £23,276 | 15.9 yrs | £5,955 |
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: £927, Upfront: £19,623, 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 | 1603 kWh | 1234 kWh | 369 kWh | £334 | £37 | £371 | £13,519 | 36.5 yrs | £-6,102 |
| 3 kW | 2404 kWh | 1851 kWh | 553 kWh | £501 | £55 | £556 | £15,554 | 28.0 yrs | £-4,428 |
| 4 kW | 3206 kWh | 2469 kWh | 737 kWh | £668 | £74 | £742 | £17,588 | 23.7 yrs | £-2,754 |
| 5 kW | 4007 kWh | 3086 kWh | 922 kWh | £835 | £92 | £927 | £19,623 | 21.2 yrs | £-1,080 |
| 6 kW | 4809 kWh | 3703 kWh | 1106 kWh | £1,002 | £111 | £1,113 | £21,657 | 19.5 yrs | £595 |
| 7 kW | 5610 kWh | 4320 kWh | 1290 kWh | £1,169 | £129 | £1,298 | £23,692 | 18.3 yrs | £2,269 |
| 8 kW | 6412 kWh | 4937 kWh | 1475 kWh | £1,336 | £147 | £1,483 | £25,726 | 17.3 yrs | £3,943 |
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.