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 | 1601 kWh | 641 kWh | 961 kWh | £173 | £96 | £269 | £4,069 | 15.1 yrs | £1,319 |
| 3 kW | 2402 kWh | 961 kWh | 1441 kWh | £260 | £144 | £404 | £6,104 | 15.1 yrs | £1,979 |
| 4 kW | 3203 kWh | 1281 kWh | 1922 kWh | £347 | £192 | £539 | £8,138 | 15.1 yrs | £2,638 |
| 5 kW | 4003 kWh | 1601 kWh | 2402 kWh | £433 | £240 | £674 | £10,173 | 15.1 yrs | £3,298 |
| 6 kW | 4804 kWh | 1922 kWh | 2882 kWh | £520 | £288 | £808 | £12,207 | 15.1 yrs | £3,958 |
| 7 kW | 5605 kWh | 2242 kWh | 3363 kWh | £607 | £336 | £943 | £14,242 | 15.1 yrs | £4,617 |
| 8 kW | 6405 kWh | 2562 kWh | 3843 kWh | £693 | £384 | £1,078 | £16,276 | 15.1 yrs | £5,277 |
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: £810, 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 | 1601 kWh | 961 kWh | 641 kWh | £260 | £64 | £324 | £6,169 | 19.0 yrs | £312 |
| 3 kW | 2402 kWh | 1441 kWh | 961 kWh | £390 | £96 | £486 | £8,204 | 16.9 yrs | £1,518 |
| 4 kW | 3203 kWh | 1922 kWh | 1281 kWh | £520 | £128 | £648 | £10,238 | 15.8 yrs | £2,724 |
| 5 kW | 4003 kWh | 2402 kWh | 1601 kWh | £650 | £160 | £810 | £12,273 | 15.1 yrs | £3,930 |
| 6 kW | 4804 kWh | 2882 kWh | 1922 kWh | £780 | £192 | £972 | £14,307 | 14.7 yrs | £5,136 |
| 7 kW | 5605 kWh | 3363 kWh | 2242 kWh | £910 | £224 | £1,134 | £16,342 | 14.4 yrs | £6,342 |
| 8 kW | 6405 kWh | 3843 kWh | 2562 kWh | £1,040 | £256 | £1,296 | £18,376 | 14.2 yrs | £7,548 |
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: £878, Upfront: £13,673, Break-even: 15.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1601 kWh | 1121 kWh | 480 kWh | £303 | £48 | £351 | £7,569 | 21.5 yrs | £-542 |
| 3 kW | 2402 kWh | 1681 kWh | 721 kWh | £455 | £72 | £527 | £9,604 | 18.2 yrs | £938 |
| 4 kW | 3203 kWh | 2242 kWh | 961 kWh | £607 | £96 | £703 | £11,638 | 16.6 yrs | £2,417 |
| 5 kW | 4003 kWh | 2802 kWh | 1201 kWh | £758 | £120 | £878 | £13,673 | 15.6 yrs | £3,896 |
| 6 kW | 4804 kWh | 3363 kWh | 1441 kWh | £910 | £144 | £1,054 | £15,707 | 14.9 yrs | £5,375 |
| 7 kW | 5605 kWh | 3923 kWh | 1681 kWh | £1,062 | £168 | £1,230 | £17,742 | 14.4 yrs | £6,854 |
| 8 kW | 6405 kWh | 4484 kWh | 1922 kWh | £1,213 | £192 | £1,405 | £19,776 | 14.1 yrs | £8,334 |
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: £899, Upfront: £15,423, Break-even: 17.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1601 kWh | 1169 kWh | 432 kWh | £316 | £43 | £360 | £9,319 | 25.9 yrs | £-2,128 |
| 3 kW | 2402 kWh | 1753 kWh | 649 kWh | £474 | £65 | £539 | £11,354 | 21.1 yrs | £-567 |
| 4 kW | 3203 kWh | 2338 kWh | 865 kWh | £633 | £86 | £719 | £13,388 | 18.6 yrs | £995 |
| 5 kW | 4003 kWh | 2922 kWh | 1081 kWh | £791 | £108 | £899 | £15,423 | 17.2 yrs | £2,556 |
| 6 kW | 4804 kWh | 3507 kWh | 1297 kWh | £949 | £130 | £1,079 | £17,457 | 16.2 yrs | £4,117 |
| 7 kW | 5605 kWh | 4091 kWh | 1513 kWh | £1,107 | £151 | £1,258 | £19,492 | 15.5 yrs | £5,678 |
| 8 kW | 6405 kWh | 4676 kWh | 1729 kWh | £1,265 | £173 | £1,438 | £21,526 | 15.0 yrs | £7,239 |
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 | 1601 kWh | 1201 kWh | 400 kWh | £325 | £40 | £365 | £11,069 | 30.3 yrs | £-3,768 |
| 3 kW | 2402 kWh | 1802 kWh | 601 kWh | £487 | £60 | £548 | £13,104 | 23.9 yrs | £-2,153 |
| 4 kW | 3203 kWh | 2402 kWh | 801 kWh | £650 | £80 | £730 | £15,138 | 20.7 yrs | £-537 |
| 5 kW | 4003 kWh | 3003 kWh | 1001 kWh | £812 | £100 | £913 | £17,173 | 18.8 yrs | £1,079 |
| 6 kW | 4804 kWh | 3603 kWh | 1201 kWh | £975 | £120 | £1,095 | £19,207 | 17.5 yrs | £2,695 |
| 7 kW | 5605 kWh | 4204 kWh | 1401 kWh | £1,137 | £140 | £1,278 | £21,242 | 16.6 yrs | £4,311 |
| 8 kW | 6405 kWh | 4804 kWh | 1601 kWh | £1,300 | £160 | £1,460 | £23,276 | 15.9 yrs | £5,926 |
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: £926, 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 | 1601 kWh | 1233 kWh | 368 kWh | £334 | £37 | £370 | £13,519 | 36.5 yrs | £-6,109 |
| 3 kW | 2402 kWh | 1850 kWh | 552 kWh | £500 | £55 | £556 | £15,554 | 28.0 yrs | £-4,439 |
| 4 kW | 3203 kWh | 2466 kWh | 737 kWh | £667 | £74 | £741 | £17,588 | 23.7 yrs | £-2,768 |
| 5 kW | 4003 kWh | 3083 kWh | 921 kWh | £834 | £92 | £926 | £19,623 | 21.2 yrs | £-1,098 |
| 6 kW | 4804 kWh | 3699 kWh | 1105 kWh | £1,001 | £110 | £1,111 | £21,657 | 19.5 yrs | £573 |
| 7 kW | 5605 kWh | 4316 kWh | 1289 kWh | £1,168 | £129 | £1,297 | £23,692 | 18.3 yrs | £2,243 |
| 8 kW | 6405 kWh | 4932 kWh | 1473 kWh | £1,335 | £147 | £1,482 | £25,726 | 17.4 yrs | £3,913 |
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.