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 789 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: £663, Upfront: £10,173, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1577 kWh | 631 kWh | 946 kWh | £171 | £95 | £265 | £4,069 | 15.3 yrs | £1,238 |
| 3 kW | 2366 kWh | 946 kWh | 1420 kWh | £256 | £142 | £398 | £6,104 | 15.3 yrs | £1,857 |
| 4 kW | 3154 kWh | 1262 kWh | 1893 kWh | £341 | £189 | £531 | £8,138 | 15.3 yrs | £2,476 |
| 5 kW | 3943 kWh | 1577 kWh | 2366 kWh | £427 | £237 | £663 | £10,173 | 15.3 yrs | £3,095 |
| 6 kW | 4732 kWh | 1893 kWh | 2839 kWh | £512 | £284 | £796 | £12,207 | 15.3 yrs | £3,714 |
| 7 kW | 5520 kWh | 2208 kWh | 3312 kWh | £598 | £331 | £929 | £14,242 | 15.3 yrs | £4,333 |
| 8 kW | 6309 kWh | 2524 kWh | 3785 kWh | £683 | £379 | £1,061 | £16,276 | 15.3 yrs | £4,952 |
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: £798, Upfront: £12,273, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1577 kWh | 946 kWh | 631 kWh | £256 | £63 | £319 | £6,169 | 19.3 yrs | £214 |
| 3 kW | 2366 kWh | 1420 kWh | 946 kWh | £384 | £95 | £479 | £8,204 | 17.1 yrs | £1,372 |
| 4 kW | 3154 kWh | 1893 kWh | 1262 kWh | £512 | £126 | £638 | £10,238 | 16.0 yrs | £2,529 |
| 5 kW | 3943 kWh | 2366 kWh | 1577 kWh | £640 | £158 | £798 | £12,273 | 15.4 yrs | £3,686 |
| 6 kW | 4732 kWh | 2839 kWh | 1893 kWh | £768 | £189 | £958 | £14,307 | 14.9 yrs | £4,843 |
| 7 kW | 5520 kWh | 3312 kWh | 2208 kWh | £896 | £221 | £1,117 | £16,342 | 14.6 yrs | £6,000 |
| 8 kW | 6309 kWh | 3785 kWh | 2524 kWh | £1,024 | £252 | £1,277 | £18,376 | 14.4 yrs | £7,158 |
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: £865, Upfront: £13,673, Break-even: 15.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1577 kWh | 1104 kWh | 473 kWh | £299 | £47 | £346 | £7,569 | 21.9 yrs | £-647 |
| 3 kW | 2366 kWh | 1656 kWh | 710 kWh | £448 | £71 | £519 | £9,604 | 18.5 yrs | £779 |
| 4 kW | 3154 kWh | 2208 kWh | 946 kWh | £598 | £95 | £692 | £11,638 | 16.8 yrs | £2,205 |
| 5 kW | 3943 kWh | 2760 kWh | 1183 kWh | £747 | £118 | £865 | £13,673 | 15.8 yrs | £3,631 |
| 6 kW | 4732 kWh | 3312 kWh | 1420 kWh | £896 | £142 | £1,038 | £15,707 | 15.1 yrs | £5,058 |
| 7 kW | 5520 kWh | 3864 kWh | 1656 kWh | £1,046 | £166 | £1,211 | £17,742 | 14.6 yrs | £6,484 |
| 8 kW | 6309 kWh | 4416 kWh | 1893 kWh | £1,195 | £189 | £1,384 | £19,776 | 14.3 yrs | £7,910 |
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: £885, Upfront: £15,423, 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 | 1577 kWh | 1151 kWh | 426 kWh | £312 | £43 | £354 | £9,319 | 26.3 yrs | £-2,236 |
| 3 kW | 2366 kWh | 1727 kWh | 639 kWh | £467 | £64 | £531 | £11,354 | 21.4 yrs | £-729 |
| 4 kW | 3154 kWh | 2303 kWh | 852 kWh | £623 | £85 | £708 | £13,388 | 18.9 yrs | £778 |
| 5 kW | 3943 kWh | 2878 kWh | 1065 kWh | £779 | £106 | £885 | £15,423 | 17.4 yrs | £2,285 |
| 6 kW | 4732 kWh | 3454 kWh | 1278 kWh | £935 | £128 | £1,062 | £17,457 | 16.4 yrs | £3,792 |
| 7 kW | 5520 kWh | 4030 kWh | 1490 kWh | £1,090 | £149 | £1,240 | £19,492 | 15.7 yrs | £5,299 |
| 8 kW | 6309 kWh | 4606 kWh | 1703 kWh | £1,246 | £170 | £1,417 | £21,526 | 15.2 yrs | £6,806 |
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: £899, Upfront: £17,173, Break-even: 19.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1577 kWh | 1183 kWh | 394 kWh | £320 | £39 | £360 | £11,069 | 30.8 yrs | £-3,878 |
| 3 kW | 2366 kWh | 1774 kWh | 591 kWh | £480 | £59 | £539 | £13,104 | 24.3 yrs | £-2,318 |
| 4 kW | 3154 kWh | 2366 kWh | 789 kWh | £640 | £79 | £719 | £15,138 | 21.1 yrs | £-757 |
| 5 kW | 3943 kWh | 2957 kWh | 986 kWh | £800 | £99 | £899 | £17,173 | 19.1 yrs | £804 |
| 6 kW | 4732 kWh | 3549 kWh | 1183 kWh | £960 | £118 | £1,079 | £19,207 | 17.8 yrs | £2,365 |
| 7 kW | 5520 kWh | 4140 kWh | 1380 kWh | £1,120 | £138 | £1,258 | £21,242 | 16.9 yrs | £3,926 |
| 8 kW | 6309 kWh | 4732 kWh | 1577 kWh | £1,280 | £158 | £1,438 | £23,276 | 16.2 yrs | £5,486 |
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: £912, Upfront: £19,623, Break-even: 21.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1577 kWh | 1214 kWh | 363 kWh | £329 | £36 | £365 | £13,519 | 37.0 yrs | £-6,221 |
| 3 kW | 2366 kWh | 1822 kWh | 544 kWh | £493 | £54 | £547 | £15,554 | 28.4 yrs | £-4,606 |
| 4 kW | 3154 kWh | 2429 kWh | 726 kWh | £657 | £73 | £730 | £17,588 | 24.1 yrs | £-2,992 |
| 5 kW | 3943 kWh | 3036 kWh | 907 kWh | £822 | £91 | £912 | £19,623 | 21.5 yrs | £-1,377 |
| 6 kW | 4732 kWh | 3643 kWh | 1088 kWh | £986 | £109 | £1,095 | £21,657 | 19.8 yrs | £238 |
| 7 kW | 5520 kWh | 4251 kWh | 1270 kWh | £1,150 | £127 | £1,277 | £23,692 | 18.5 yrs | £1,852 |
| 8 kW | 6309 kWh | 4858 kWh | 1451 kWh | £1,315 | £145 | £1,460 | £25,726 | 17.6 yrs | £3,467 |
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.