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 824 kWh per year on a south-facing roof. We value self-used electricity at 0.0p 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: £247, Upfront: £10,173, Break-even: 41.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1648 kWh | 659 kWh | 989 kWh | £0 | £99 | £99 | £4,069 | 41.1 yrs | £-2,091 |
| 3 kW | 2473 kWh | 989 kWh | 1484 kWh | £0 | £148 | £148 | £6,104 | 41.1 yrs | £-3,136 |
| 4 kW | 3297 kWh | 1319 kWh | 1978 kWh | £0 | £198 | £198 | £8,138 | 41.1 yrs | £-4,182 |
| 5 kW | 4121 kWh | 1648 kWh | 2473 kWh | £0 | £247 | £247 | £10,173 | 41.1 yrs | £-5,227 |
| 6 kW | 4945 kWh | 1978 kWh | 2967 kWh | £0 | £297 | £297 | £12,207 | 41.1 yrs | £-6,273 |
| 7 kW | 5770 kWh | 2308 kWh | 3462 kWh | £0 | £346 | £346 | £14,242 | 41.1 yrs | £-7,318 |
| 8 kW | 6594 kWh | 2638 kWh | 3956 kWh | £0 | £396 | £396 | £16,276 | 41.1 yrs | £-8,363 |
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: £165, Upfront: £12,273, Break-even: 74.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1648 kWh | 989 kWh | 659 kWh | £0 | £66 | £66 | £6,169 | 93.6 yrs | £-4,850 |
| 3 kW | 2473 kWh | 1484 kWh | 989 kWh | £0 | £99 | £99 | £8,204 | 82.9 yrs | £-6,225 |
| 4 kW | 3297 kWh | 1978 kWh | 1319 kWh | £0 | £132 | £132 | £10,238 | 77.6 yrs | £-7,600 |
| 5 kW | 4121 kWh | 2473 kWh | 1648 kWh | £0 | £165 | £165 | £12,273 | 74.4 yrs | £-8,976 |
| 6 kW | 4945 kWh | 2967 kWh | 1978 kWh | £0 | £198 | £198 | £14,307 | 72.3 yrs | £-10,351 |
| 7 kW | 5770 kWh | 3462 kWh | 2308 kWh | £0 | £231 | £231 | £16,342 | 70.8 yrs | £-11,726 |
| 8 kW | 6594 kWh | 3956 kWh | 2638 kWh | £0 | £264 | £264 | £18,376 | 69.7 yrs | £-13,101 |
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: £124, Upfront: £13,673, Break-even: 110.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1648 kWh | 1154 kWh | 495 kWh | £0 | £49 | £49 | £7,569 | 153.1 yrs | £-6,580 |
| 3 kW | 2473 kWh | 1731 kWh | 742 kWh | £0 | £74 | £74 | £9,604 | 129.5 yrs | £-8,120 |
| 4 kW | 3297 kWh | 2308 kWh | 989 kWh | £0 | £99 | £99 | £11,638 | 117.7 yrs | £-9,660 |
| 5 kW | 4121 kWh | 2885 kWh | 1236 kWh | £0 | £124 | £124 | £13,673 | 110.6 yrs | £-11,200 |
| 6 kW | 4945 kWh | 3462 kWh | 1484 kWh | £0 | £148 | £148 | £15,707 | 105.9 yrs | £-12,740 |
| 7 kW | 5770 kWh | 4039 kWh | 1731 kWh | £0 | £173 | £173 | £17,742 | 102.5 yrs | £-14,280 |
| 8 kW | 6594 kWh | 4616 kWh | 1978 kWh | £0 | £198 | £198 | £19,776 | 100.0 yrs | £-15,820 |
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: £111, Upfront: £15,423, Break-even: 138.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1648 kWh | 1203 kWh | 445 kWh | £0 | £45 | £45 | £9,319 | 209.4 yrs | £-8,429 |
| 3 kW | 2473 kWh | 1805 kWh | 668 kWh | £0 | £67 | £67 | £11,354 | 170.1 yrs | £-10,018 |
| 4 kW | 3297 kWh | 2407 kWh | 890 kWh | £0 | £89 | £89 | £13,388 | 150.4 yrs | £-11,608 |
| 5 kW | 4121 kWh | 3008 kWh | 1113 kWh | £0 | £111 | £111 | £15,423 | 138.6 yrs | £-13,197 |
| 6 kW | 4945 kWh | 3610 kWh | 1335 kWh | £0 | £134 | £134 | £17,457 | 130.7 yrs | £-14,787 |
| 7 kW | 5770 kWh | 4212 kWh | 1558 kWh | £0 | £156 | £156 | £19,492 | 125.1 yrs | £-16,376 |
| 8 kW | 6594 kWh | 4814 kWh | 1780 kWh | £0 | £178 | £178 | £21,526 | 120.9 yrs | £-17,965 |
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: £103, Upfront: £17,173, Break-even: 166.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1648 kWh | 1236 kWh | 412 kWh | £0 | £41 | £41 | £11,069 | 268.6 yrs | £-10,245 |
| 3 kW | 2473 kWh | 1855 kWh | 618 kWh | £0 | £62 | £62 | £13,104 | 212.0 yrs | £-11,867 |
| 4 kW | 3297 kWh | 2473 kWh | 824 kWh | £0 | £82 | £82 | £15,138 | 183.7 yrs | £-13,490 |
| 5 kW | 4121 kWh | 3091 kWh | 1030 kWh | £0 | £103 | £103 | £17,173 | 166.7 yrs | £-15,112 |
| 6 kW | 4945 kWh | 3709 kWh | 1236 kWh | £0 | £124 | £124 | £19,207 | 155.4 yrs | £-16,734 |
| 7 kW | 5770 kWh | 4327 kWh | 1442 kWh | £0 | £144 | £144 | £21,242 | 147.3 yrs | £-18,357 |
| 8 kW | 6594 kWh | 4945 kWh | 1648 kWh | £0 | £165 | £165 | £23,276 | 141.2 yrs | £-19,979 |
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: £95, Upfront: £19,623, Break-even: 207.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1648 kWh | 1269 kWh | 379 kWh | £0 | £38 | £38 | £13,519 | 356.6 yrs | £-12,761 |
| 3 kW | 2473 kWh | 1904 kWh | 569 kWh | £0 | £57 | £57 | £15,554 | 273.5 yrs | £-14,416 |
| 4 kW | 3297 kWh | 2539 kWh | 758 kWh | £0 | £76 | £76 | £17,588 | 231.9 yrs | £-16,071 |
| 5 kW | 4121 kWh | 3173 kWh | 948 kWh | £0 | £95 | £95 | £19,623 | 207.0 yrs | £-17,727 |
| 6 kW | 4945 kWh | 3808 kWh | 1137 kWh | £0 | £114 | £114 | £21,657 | 190.4 yrs | £-19,382 |
| 7 kW | 5770 kWh | 4443 kWh | 1327 kWh | £0 | £133 | £133 | £23,692 | 178.5 yrs | £-21,038 |
| 8 kW | 6594 kWh | 5077 kWh | 1517 kWh | £0 | £152 | £152 | £25,726 | 169.6 yrs | £-22,693 |
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.