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 990 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: £803, Upfront: £10,173, Break-even: 12.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1981 kWh | 792 kWh | 1188 kWh | £202 | £119 | £321 | £4,069 | 12.7 yrs | £2,356 |
| 3 kW | 2971 kWh | 1188 kWh | 1783 kWh | £304 | £178 | £482 | £6,104 | 12.7 yrs | £3,534 |
| 4 kW | 3961 kWh | 1584 kWh | 2377 kWh | £405 | £238 | £643 | £8,138 | 12.7 yrs | £4,712 |
| 5 kW | 4951 kWh | 1981 kWh | 2971 kWh | £506 | £297 | £803 | £10,173 | 12.7 yrs | £5,890 |
| 6 kW | 5942 kWh | 2377 kWh | 3565 kWh | £607 | £357 | £964 | £12,207 | 12.7 yrs | £7,068 |
| 7 kW | 6932 kWh | 2773 kWh | 4159 kWh | £708 | £416 | £1,124 | £14,242 | 12.7 yrs | £8,246 |
| 8 kW | 7922 kWh | 3169 kWh | 4753 kWh | £810 | £475 | £1,285 | £16,276 | 12.7 yrs | £9,424 |
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: £957, Upfront: £12,273, 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 | 1981 kWh | 1188 kWh | 792 kWh | £304 | £79 | £383 | £6,169 | 16.1 yrs | £1,488 |
| 3 kW | 2971 kWh | 1783 kWh | 1188 kWh | £455 | £119 | £574 | £8,204 | 14.3 yrs | £3,282 |
| 4 kW | 3961 kWh | 2377 kWh | 1584 kWh | £607 | £158 | £766 | £10,238 | 13.4 yrs | £5,076 |
| 5 kW | 4951 kWh | 2971 kWh | 1981 kWh | £759 | £198 | £957 | £12,273 | 12.8 yrs | £6,870 |
| 6 kW | 5942 kWh | 3565 kWh | 2377 kWh | £911 | £238 | £1,149 | £14,307 | 12.5 yrs | £8,664 |
| 7 kW | 6932 kWh | 4159 kWh | 2773 kWh | £1,063 | £277 | £1,340 | £16,342 | 12.2 yrs | £10,458 |
| 8 kW | 7922 kWh | 4753 kWh | 3169 kWh | £1,214 | £317 | £1,531 | £18,376 | 12.0 yrs | £12,252 |
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: £1,034, Upfront: £13,673, Break-even: 13.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1981 kWh | 1386 kWh | 594 kWh | £354 | £59 | £414 | £7,569 | 18.3 yrs | £704 |
| 3 kW | 2971 kWh | 2080 kWh | 891 kWh | £531 | £89 | £620 | £9,604 | 15.5 yrs | £2,806 |
| 4 kW | 3961 kWh | 2773 kWh | 1188 kWh | £708 | £119 | £827 | £11,638 | 14.1 yrs | £4,908 |
| 5 kW | 4951 kWh | 3466 kWh | 1485 kWh | £886 | £149 | £1,034 | £13,673 | 13.2 yrs | £7,010 |
| 6 kW | 5942 kWh | 4159 kWh | 1783 kWh | £1,063 | £178 | £1,241 | £15,707 | 12.7 yrs | £9,112 |
| 7 kW | 6932 kWh | 4852 kWh | 2080 kWh | £1,240 | £208 | £1,448 | £17,742 | 12.3 yrs | £11,214 |
| 8 kW | 7922 kWh | 5546 kWh | 2377 kWh | £1,417 | £238 | £1,655 | £19,776 | 12.0 yrs | £13,315 |
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: £1,057, Upfront: £15,423, Break-even: 14.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1981 kWh | 1446 kWh | 535 kWh | £369 | £53 | £423 | £9,319 | 22.0 yrs | £-861 |
| 3 kW | 2971 kWh | 2169 kWh | 802 kWh | £554 | £80 | £634 | £11,354 | 17.9 yrs | £1,333 |
| 4 kW | 3961 kWh | 2892 kWh | 1070 kWh | £739 | £107 | £846 | £13,388 | 15.8 yrs | £3,527 |
| 5 kW | 4951 kWh | 3615 kWh | 1337 kWh | £924 | £134 | £1,057 | £15,423 | 14.6 yrs | £5,722 |
| 6 kW | 5942 kWh | 4337 kWh | 1604 kWh | £1,108 | £160 | £1,269 | £17,457 | 13.8 yrs | £7,916 |
| 7 kW | 6932 kWh | 5060 kWh | 1872 kWh | £1,293 | £187 | £1,480 | £19,492 | 13.2 yrs | £10,110 |
| 8 kW | 7922 kWh | 5783 kWh | 2139 kWh | £1,478 | £214 | £1,692 | £21,526 | 12.7 yrs | £12,305 |
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: £1,073, Upfront: £17,173, Break-even: 16.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1981 kWh | 1485 kWh | 495 kWh | £380 | £50 | £429 | £11,069 | 25.8 yrs | £-2,488 |
| 3 kW | 2971 kWh | 2228 kWh | 743 kWh | £569 | £74 | £644 | £13,104 | 20.4 yrs | £-232 |
| 4 kW | 3961 kWh | 2971 kWh | 990 kWh | £759 | £99 | £858 | £15,138 | 17.6 yrs | £2,024 |
| 5 kW | 4951 kWh | 3714 kWh | 1238 kWh | £949 | £124 | £1,073 | £17,173 | 16.0 yrs | £4,280 |
| 6 kW | 5942 kWh | 4456 kWh | 1485 kWh | £1,139 | £149 | £1,287 | £19,207 | 14.9 yrs | £6,536 |
| 7 kW | 6932 kWh | 5199 kWh | 1733 kWh | £1,328 | £173 | £1,502 | £21,242 | 14.1 yrs | £8,791 |
| 8 kW | 7922 kWh | 5942 kWh | 1981 kWh | £1,518 | £198 | £1,716 | £23,276 | 13.6 yrs | £11,047 |
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: £1,088, Upfront: £19,623, 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 | 1981 kWh | 1525 kWh | 456 kWh | £390 | £46 | £435 | £13,519 | 31.1 yrs | £-4,815 |
| 3 kW | 2971 kWh | 2288 kWh | 683 kWh | £584 | £68 | £653 | £15,554 | 23.8 yrs | £-2,497 |
| 4 kW | 3961 kWh | 3050 kWh | 911 kWh | £779 | £91 | £870 | £17,588 | 20.2 yrs | £-180 |
| 5 kW | 4951 kWh | 3813 kWh | 1139 kWh | £974 | £114 | £1,088 | £19,623 | 18.0 yrs | £2,138 |
| 6 kW | 5942 kWh | 4575 kWh | 1367 kWh | £1,169 | £137 | £1,306 | £21,657 | 16.6 yrs | £4,455 |
| 7 kW | 6932 kWh | 5338 kWh | 1594 kWh | £1,364 | £159 | £1,523 | £23,692 | 15.6 yrs | £6,773 |
| 8 kW | 7922 kWh | 6100 kWh | 1822 kWh | £1,559 | £182 | £1,741 | £25,726 | 14.8 yrs | £9,090 |
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.