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 877 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £713, Upfront: £10,173, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1754 kWh | 701 kWh | 1052 kWh | £180 | £105 | £285 | £4,069 | 14.3 yrs | £1,632 |
| 3 kW | 2630 kWh | 1052 kWh | 1578 kWh | £270 | £158 | £428 | £6,104 | 14.3 yrs | £2,448 |
| 4 kW | 3507 kWh | 1403 kWh | 2104 kWh | £360 | £210 | £570 | £8,138 | 14.3 yrs | £3,264 |
| 5 kW | 4384 kWh | 1754 kWh | 2630 kWh | £450 | £263 | £713 | £10,173 | 14.3 yrs | £4,080 |
| 6 kW | 5261 kWh | 2104 kWh | 3156 kWh | £540 | £316 | £855 | £12,207 | 14.3 yrs | £4,896 |
| 7 kW | 6137 kWh | 2455 kWh | 3682 kWh | £629 | £368 | £998 | £14,242 | 14.3 yrs | £5,713 |
| 8 kW | 7014 kWh | 2806 kWh | 4209 kWh | £719 | £421 | £1,140 | £16,276 | 14.3 yrs | £6,529 |
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: £850, Upfront: £12,273, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1754 kWh | 1052 kWh | 701 kWh | £270 | £70 | £340 | £6,169 | 18.1 yrs | £629 |
| 3 kW | 2630 kWh | 1578 kWh | 1052 kWh | £405 | £105 | £510 | £8,204 | 16.1 yrs | £1,994 |
| 4 kW | 3507 kWh | 2104 kWh | 1403 kWh | £540 | £140 | £680 | £10,238 | 15.1 yrs | £3,358 |
| 5 kW | 4384 kWh | 2630 kWh | 1754 kWh | £674 | £175 | £850 | £12,273 | 14.4 yrs | £4,723 |
| 6 kW | 5261 kWh | 3156 kWh | 2104 kWh | £809 | £210 | £1,020 | £14,307 | 14.0 yrs | £6,088 |
| 7 kW | 6137 kWh | 3682 kWh | 2455 kWh | £944 | £245 | £1,190 | £16,342 | 13.7 yrs | £7,452 |
| 8 kW | 7014 kWh | 4209 kWh | 2806 kWh | £1,079 | £281 | £1,360 | £18,376 | 13.5 yrs | £8,817 |
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: £918, Upfront: £13,673, 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 | 1754 kWh | 1227 kWh | 526 kWh | £315 | £53 | £367 | £7,569 | 20.6 yrs | £-222 |
| 3 kW | 2630 kWh | 1841 kWh | 789 kWh | £472 | £79 | £551 | £9,604 | 17.4 yrs | £1,417 |
| 4 kW | 3507 kWh | 2455 kWh | 1052 kWh | £629 | £105 | £735 | £11,638 | 15.8 yrs | £3,055 |
| 5 kW | 4384 kWh | 3069 kWh | 1315 kWh | £787 | £132 | £918 | £13,673 | 14.9 yrs | £4,694 |
| 6 kW | 5261 kWh | 3682 kWh | 1578 kWh | £944 | £158 | £1,102 | £15,707 | 14.3 yrs | £6,333 |
| 7 kW | 6137 kWh | 4296 kWh | 1841 kWh | £1,102 | £184 | £1,286 | £17,742 | 13.8 yrs | £7,972 |
| 8 kW | 7014 kWh | 4910 kWh | 2104 kWh | £1,259 | £210 | £1,469 | £19,776 | 13.5 yrs | £9,611 |
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: £939, Upfront: £15,423, Break-even: 16.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1754 kWh | 1280 kWh | 473 kWh | £328 | £47 | £376 | £9,319 | 24.8 yrs | £-1,808 |
| 3 kW | 2630 kWh | 1920 kWh | 710 kWh | £492 | £71 | £563 | £11,354 | 20.2 yrs | £-87 |
| 4 kW | 3507 kWh | 2560 kWh | 947 kWh | £656 | £95 | £751 | £13,388 | 17.8 yrs | £1,634 |
| 5 kW | 4384 kWh | 3200 kWh | 1184 kWh | £821 | £118 | £939 | £15,423 | 16.4 yrs | £3,356 |
| 6 kW | 5261 kWh | 3840 kWh | 1420 kWh | £985 | £142 | £1,127 | £17,457 | 15.5 yrs | £5,077 |
| 7 kW | 6137 kWh | 4480 kWh | 1657 kWh | £1,149 | £166 | £1,314 | £19,492 | 14.8 yrs | £6,798 |
| 8 kW | 7014 kWh | 5120 kWh | 1894 kWh | £1,313 | £189 | £1,502 | £21,526 | 14.3 yrs | £8,519 |
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: £953, Upfront: £17,173, Break-even: 18.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1754 kWh | 1315 kWh | 438 kWh | £337 | £44 | £381 | £11,069 | 29.0 yrs | £-3,448 |
| 3 kW | 2630 kWh | 1973 kWh | 658 kWh | £506 | £66 | £572 | £13,104 | 22.9 yrs | £-1,672 |
| 4 kW | 3507 kWh | 2630 kWh | 877 kWh | £674 | £88 | £762 | £15,138 | 19.9 yrs | £104 |
| 5 kW | 4384 kWh | 3288 kWh | 1096 kWh | £843 | £110 | £953 | £17,173 | 18.0 yrs | £1,880 |
| 6 kW | 5261 kWh | 3946 kWh | 1315 kWh | £1,012 | £132 | £1,143 | £19,207 | 16.8 yrs | £3,656 |
| 7 kW | 6137 kWh | 4603 kWh | 1534 kWh | £1,180 | £153 | £1,334 | £21,242 | 15.9 yrs | £5,432 |
| 8 kW | 7014 kWh | 5261 kWh | 1754 kWh | £1,349 | £175 | £1,524 | £23,276 | 15.3 yrs | £7,208 |
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: £966, Upfront: £19,623, Break-even: 20.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1754 kWh | 1350 kWh | 403 kWh | £346 | £40 | £387 | £13,519 | 35.0 yrs | £-5,788 |
| 3 kW | 2630 kWh | 2025 kWh | 605 kWh | £519 | £60 | £580 | £15,554 | 26.8 yrs | £-3,958 |
| 4 kW | 3507 kWh | 2700 kWh | 807 kWh | £692 | £81 | £773 | £17,588 | 22.8 yrs | £-2,127 |
| 5 kW | 4384 kWh | 3376 kWh | 1008 kWh | £866 | £101 | £966 | £19,623 | 20.3 yrs | £-296 |
| 6 kW | 5261 kWh | 4051 kWh | 1210 kWh | £1,039 | £121 | £1,160 | £21,657 | 18.7 yrs | £1,535 |
| 7 kW | 6137 kWh | 4726 kWh | 1412 kWh | £1,212 | £141 | £1,353 | £23,692 | 17.5 yrs | £3,366 |
| 8 kW | 7014 kWh | 5401 kWh | 1613 kWh | £1,385 | £161 | £1,546 | £25,726 | 16.6 yrs | £5,197 |
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.