A typical roof here lands around 3.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 990 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £822, Upfront: £10,173, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1980 kWh | 792 kWh | 1188 kWh | £210 | £119 | £329 | £4,069 | 12.4 yrs | £2,510 |
| 3 kW | 2970 kWh | 1188 kWh | 1782 kWh | £315 | £178 | £493 | £6,104 | 12.4 yrs | £3,765 |
| 4 kW | 3960 kWh | 1584 kWh | 2376 kWh | £420 | £238 | £658 | £8,138 | 12.4 yrs | £5,019 |
| 5 kW | 4950 kWh | 1980 kWh | 2970 kWh | £525 | £297 | £822 | £10,173 | 12.4 yrs | £6,274 |
| 6 kW | 5940 kWh | 2376 kWh | 3564 kWh | £630 | £356 | £987 | £12,207 | 12.4 yrs | £7,529 |
| 7 kW | 6930 kWh | 2772 kWh | 4158 kWh | £735 | £416 | £1,151 | £14,242 | 12.4 yrs | £8,784 |
| 8 kW | 7920 kWh | 3168 kWh | 4752 kWh | £841 | £475 | £1,316 | £16,276 | 12.4 yrs | £10,039 |
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: £986, Upfront: £12,273, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1980 kWh | 1188 kWh | 792 kWh | £315 | £79 | £394 | £6,169 | 15.6 yrs | £1,719 |
| 3 kW | 2970 kWh | 1782 kWh | 1188 kWh | £473 | £119 | £592 | £8,204 | 13.9 yrs | £3,628 |
| 4 kW | 3960 kWh | 2376 kWh | 1584 kWh | £630 | £158 | £789 | £10,238 | 13.0 yrs | £5,538 |
| 5 kW | 4950 kWh | 2970 kWh | 1980 kWh | £788 | £198 | £986 | £12,273 | 12.4 yrs | £7,447 |
| 6 kW | 5940 kWh | 3564 kWh | 2376 kWh | £946 | £238 | £1,183 | £14,307 | 12.1 yrs | £9,357 |
| 7 kW | 6930 kWh | 4158 kWh | 2772 kWh | £1,103 | £277 | £1,380 | £16,342 | 11.8 yrs | £11,266 |
| 8 kW | 7920 kWh | 4752 kWh | 3168 kWh | £1,261 | £317 | £1,578 | £18,376 | 11.6 yrs | £13,176 |
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: £1,068, Upfront: £13,673, Break-even: 12.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1980 kWh | 1386 kWh | 594 kWh | £368 | £59 | £427 | £7,569 | 17.7 yrs | £974 |
| 3 kW | 2970 kWh | 2079 kWh | 891 kWh | £552 | £89 | £641 | £9,604 | 15.0 yrs | £3,210 |
| 4 kW | 3960 kWh | 2772 kWh | 1188 kWh | £735 | £119 | £854 | £11,638 | 13.6 yrs | £5,447 |
| 5 kW | 4950 kWh | 3465 kWh | 1485 kWh | £919 | £149 | £1,068 | £13,673 | 12.8 yrs | £7,684 |
| 6 kW | 5940 kWh | 4158 kWh | 1782 kWh | £1,103 | £178 | £1,281 | £15,707 | 12.3 yrs | £9,921 |
| 7 kW | 6930 kWh | 4851 kWh | 2079 kWh | £1,287 | £208 | £1,495 | £17,742 | 11.9 yrs | £12,158 |
| 8 kW | 7920 kWh | 5544 kWh | 2376 kWh | £1,471 | £238 | £1,709 | £19,776 | 11.6 yrs | £14,394 |
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: £1,092, Upfront: £15,423, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1980 kWh | 1445 kWh | 535 kWh | £383 | £53 | £437 | £9,319 | 21.3 yrs | £-580 |
| 3 kW | 2970 kWh | 2168 kWh | 802 kWh | £575 | £80 | £655 | £11,354 | 17.3 yrs | £1,755 |
| 4 kW | 3960 kWh | 2891 kWh | 1069 kWh | £767 | £107 | £874 | £13,388 | 15.3 yrs | £4,090 |
| 5 kW | 4950 kWh | 3614 kWh | 1337 kWh | £959 | £134 | £1,092 | £15,423 | 14.1 yrs | £6,425 |
| 6 kW | 5940 kWh | 4336 kWh | 1604 kWh | £1,150 | £160 | £1,311 | £17,457 | 13.3 yrs | £8,760 |
| 7 kW | 6930 kWh | 5059 kWh | 1871 kWh | £1,342 | £187 | £1,529 | £19,492 | 12.7 yrs | £11,095 |
| 8 kW | 7920 kWh | 5782 kWh | 2139 kWh | £1,534 | £214 | £1,748 | £21,526 | 12.3 yrs | £13,430 |
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: £1,109, Upfront: £17,173, 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 | 1980 kWh | 1485 kWh | 495 kWh | £394 | £50 | £443 | £11,069 | 25.0 yrs | £-2,199 |
| 3 kW | 2970 kWh | 2228 kWh | 743 kWh | £591 | £74 | £665 | £13,104 | 19.7 yrs | £201 |
| 4 kW | 3960 kWh | 2970 kWh | 990 kWh | £788 | £99 | £887 | £15,138 | 17.1 yrs | £2,602 |
| 5 kW | 4950 kWh | 3713 kWh | 1238 kWh | £985 | £124 | £1,109 | £17,173 | 15.5 yrs | £5,002 |
| 6 kW | 5940 kWh | 4455 kWh | 1485 kWh | £1,182 | £149 | £1,330 | £19,207 | 14.4 yrs | £7,403 |
| 7 kW | 6930 kWh | 5198 kWh | 1733 kWh | £1,379 | £173 | £1,552 | £21,242 | 13.7 yrs | £9,803 |
| 8 kW | 7920 kWh | 5940 kWh | 1980 kWh | £1,576 | £198 | £1,774 | £23,276 | 13.1 yrs | £12,204 |
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: £1,125, Upfront: £19,623, 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 | 1980 kWh | 1525 kWh | 455 kWh | £405 | £46 | £450 | £13,519 | 30.0 yrs | £-4,518 |
| 3 kW | 2970 kWh | 2287 kWh | 683 kWh | £607 | £68 | £675 | £15,554 | 23.0 yrs | £-2,052 |
| 4 kW | 3960 kWh | 3049 kWh | 911 kWh | £809 | £91 | £900 | £17,588 | 19.5 yrs | £414 |
| 5 kW | 4950 kWh | 3812 kWh | 1139 kWh | £1,011 | £114 | £1,125 | £19,623 | 17.4 yrs | £2,880 |
| 6 kW | 5940 kWh | 4574 kWh | 1366 kWh | £1,214 | £137 | £1,350 | £21,657 | 16.0 yrs | £5,346 |
| 7 kW | 6930 kWh | 5336 kWh | 1594 kWh | £1,416 | £159 | £1,575 | £23,692 | 15.0 yrs | £7,811 |
| 8 kW | 7920 kWh | 6099 kWh | 1822 kWh | £1,618 | £182 | £1,800 | £25,726 | 14.3 yrs | £10,277 |
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.