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 835 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: £682, Upfront: £10,173, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1669 kWh | 668 kWh | 1002 kWh | £173 | £100 | £273 | £4,069 | 14.9 yrs | £1,385 |
| 3 kW | 2504 kWh | 1002 kWh | 1502 kWh | £259 | £150 | £409 | £6,104 | 14.9 yrs | £2,077 |
| 4 kW | 3338 kWh | 1335 kWh | 2003 kWh | £345 | £200 | £545 | £8,138 | 14.9 yrs | £2,769 |
| 5 kW | 4173 kWh | 1669 kWh | 2504 kWh | £431 | £250 | £682 | £10,173 | 14.9 yrs | £3,462 |
| 6 kW | 5008 kWh | 2003 kWh | 3005 kWh | £518 | £300 | £818 | £12,207 | 14.9 yrs | £4,154 |
| 7 kW | 5842 kWh | 2337 kWh | 3505 kWh | £604 | £351 | £954 | £14,242 | 14.9 yrs | £4,846 |
| 8 kW | 6677 kWh | 2671 kWh | 4006 kWh | £690 | £401 | £1,091 | £16,276 | 14.9 yrs | £5,539 |
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: £814, 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 | 1669 kWh | 1002 kWh | 668 kWh | £259 | £67 | £326 | £6,169 | 18.9 yrs | £342 |
| 3 kW | 2504 kWh | 1502 kWh | 1002 kWh | £388 | £100 | £488 | £8,204 | 16.8 yrs | £1,563 |
| 4 kW | 3338 kWh | 2003 kWh | 1335 kWh | £518 | £134 | £651 | £10,238 | 15.7 yrs | £2,785 |
| 5 kW | 4173 kWh | 2504 kWh | 1669 kWh | £647 | £167 | £814 | £12,273 | 15.1 yrs | £4,006 |
| 6 kW | 5008 kWh | 3005 kWh | 2003 kWh | £776 | £200 | £977 | £14,307 | 14.6 yrs | £5,227 |
| 7 kW | 5842 kWh | 3505 kWh | 2337 kWh | £906 | £234 | £1,139 | £16,342 | 14.3 yrs | £6,448 |
| 8 kW | 6677 kWh | 4006 kWh | 2671 kWh | £1,035 | £267 | £1,302 | £18,376 | 14.1 yrs | £7,669 |
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: £880, 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 | 1669 kWh | 1168 kWh | 501 kWh | £302 | £50 | £352 | £7,569 | 21.5 yrs | £-529 |
| 3 kW | 2504 kWh | 1753 kWh | 751 kWh | £453 | £75 | £528 | £9,604 | 18.2 yrs | £957 |
| 4 kW | 3338 kWh | 2337 kWh | 1002 kWh | £604 | £100 | £704 | £11,638 | 16.5 yrs | £2,442 |
| 5 kW | 4173 kWh | 2921 kWh | 1252 kWh | £755 | £125 | £880 | £13,673 | 15.5 yrs | £3,928 |
| 6 kW | 5008 kWh | 3505 kWh | 1502 kWh | £906 | £150 | £1,056 | £15,707 | 14.9 yrs | £5,413 |
| 7 kW | 5842 kWh | 4090 kWh | 1753 kWh | £1,057 | £175 | £1,232 | £17,742 | 14.4 yrs | £6,899 |
| 8 kW | 6677 kWh | 4674 kWh | 2003 kWh | £1,208 | £200 | £1,408 | £19,776 | 14.0 yrs | £8,384 |
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 | 1669 kWh | 1219 kWh | 451 kWh | £315 | £45 | £360 | £9,319 | 25.9 yrs | £-2,120 |
| 3 kW | 2504 kWh | 1828 kWh | 676 kWh | £472 | £68 | £540 | £11,354 | 21.0 yrs | £-555 |
| 4 kW | 3338 kWh | 2437 kWh | 901 kWh | £630 | £90 | £720 | £13,388 | 18.6 yrs | £1,009 |
| 5 kW | 4173 kWh | 3046 kWh | 1127 kWh | £787 | £113 | £900 | £15,423 | 17.1 yrs | £2,574 |
| 6 kW | 5008 kWh | 3656 kWh | 1352 kWh | £945 | £135 | £1,080 | £17,457 | 16.2 yrs | £4,139 |
| 7 kW | 5842 kWh | 4265 kWh | 1577 kWh | £1,102 | £158 | £1,260 | £19,492 | 15.5 yrs | £5,704 |
| 8 kW | 6677 kWh | 4874 kWh | 1803 kWh | £1,259 | £180 | £1,440 | £21,526 | 15.0 yrs | £7,269 |
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 | 1669 kWh | 1252 kWh | 417 kWh | £323 | £42 | £365 | £11,069 | 30.3 yrs | £-3,765 |
| 3 kW | 2504 kWh | 1878 kWh | 626 kWh | £485 | £63 | £548 | £13,104 | 23.9 yrs | £-2,147 |
| 4 kW | 3338 kWh | 2504 kWh | 835 kWh | £647 | £83 | £730 | £15,138 | 20.7 yrs | £-529 |
| 5 kW | 4173 kWh | 3130 kWh | 1043 kWh | £809 | £104 | £913 | £17,173 | 18.8 yrs | £1,089 |
| 6 kW | 5008 kWh | 3756 kWh | 1252 kWh | £970 | £125 | £1,096 | £19,207 | 17.5 yrs | £2,706 |
| 7 kW | 5842 kWh | 4382 kWh | 1461 kWh | £1,132 | £146 | £1,278 | £21,242 | 16.6 yrs | £4,324 |
| 8 kW | 6677 kWh | 5008 kWh | 1669 kWh | £1,294 | £167 | £1,461 | £23,276 | 15.9 yrs | £5,942 |
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 | 1669 kWh | 1285 kWh | 384 kWh | £332 | £38 | £371 | £13,519 | 36.5 yrs | £-6,109 |
| 3 kW | 2504 kWh | 1928 kWh | 576 kWh | £498 | £58 | £556 | £15,554 | 28.0 yrs | £-4,438 |
| 4 kW | 3338 kWh | 2571 kWh | 768 kWh | £664 | £77 | £741 | £17,588 | 23.7 yrs | £-2,768 |
| 5 kW | 4173 kWh | 3213 kWh | 960 kWh | £830 | £96 | £926 | £19,623 | 21.2 yrs | £-1,097 |
| 6 kW | 5008 kWh | 3856 kWh | 1152 kWh | £996 | £115 | £1,112 | £21,657 | 19.5 yrs | £574 |
| 7 kW | 5842 kWh | 4499 kWh | 1344 kWh | £1,162 | £134 | £1,297 | £23,692 | 18.3 yrs | £2,244 |
| 8 kW | 6677 kWh | 5141 kWh | 1536 kWh | £1,328 | £154 | £1,482 | £25,726 | 17.4 yrs | £3,915 |
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.