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 684 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: £576, Upfront: £10,173, Break-even: 17.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1369 kWh | 548 kWh | 821 kWh | £148 | £82 | £230 | £4,069 | 17.7 yrs | £537 |
| 3 kW | 2053 kWh | 821 kWh | 1232 kWh | £222 | £123 | £345 | £6,104 | 17.7 yrs | £805 |
| 4 kW | 2738 kWh | 1095 kWh | 1643 kWh | £296 | £164 | £461 | £8,138 | 17.7 yrs | £1,074 |
| 5 kW | 3422 kWh | 1369 kWh | 2053 kWh | £370 | £205 | £576 | £10,173 | 17.7 yrs | £1,342 |
| 6 kW | 4106 kWh | 1643 kWh | 2464 kWh | £444 | £246 | £691 | £12,207 | 17.7 yrs | £1,610 |
| 7 kW | 4791 kWh | 1916 kWh | 2875 kWh | £519 | £287 | £806 | £14,242 | 17.7 yrs | £1,879 |
| 8 kW | 5475 kWh | 2190 kWh | 3285 kWh | £593 | £329 | £921 | £16,276 | 17.7 yrs | £2,147 |
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: £692, Upfront: £12,273, Break-even: 17.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1369 kWh | 821 kWh | 548 kWh | £222 | £55 | £277 | £6,169 | 22.3 yrs | £-629 |
| 3 kW | 2053 kWh | 1232 kWh | 821 kWh | £333 | £82 | £415 | £8,204 | 19.7 yrs | £106 |
| 4 kW | 2738 kWh | 1643 kWh | 1095 kWh | £444 | £110 | £554 | £10,238 | 18.5 yrs | £842 |
| 5 kW | 3422 kWh | 2053 kWh | 1369 kWh | £556 | £137 | £692 | £12,273 | 17.7 yrs | £1,577 |
| 6 kW | 4106 kWh | 2464 kWh | 1643 kWh | £667 | £164 | £831 | £14,307 | 17.2 yrs | £2,313 |
| 7 kW | 4791 kWh | 2875 kWh | 1916 kWh | £778 | £192 | £969 | £16,342 | 16.9 yrs | £3,048 |
| 8 kW | 5475 kWh | 3285 kWh | 2190 kWh | £889 | £219 | £1,108 | £18,376 | 16.6 yrs | £3,783 |
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: £751, Upfront: £13,673, Break-even: 18.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1369 kWh | 958 kWh | 411 kWh | £259 | £41 | £300 | £7,569 | 25.2 yrs | £-1,562 |
| 3 kW | 2053 kWh | 1437 kWh | 616 kWh | £389 | £62 | £451 | £9,604 | 21.3 yrs | £-593 |
| 4 kW | 2738 kWh | 1916 kWh | 821 kWh | £519 | £82 | £601 | £11,638 | 19.4 yrs | £376 |
| 5 kW | 3422 kWh | 2395 kWh | 1027 kWh | £648 | £103 | £751 | £13,673 | 18.2 yrs | £1,345 |
| 6 kW | 4106 kWh | 2875 kWh | 1232 kWh | £778 | £123 | £901 | £15,707 | 17.4 yrs | £2,314 |
| 7 kW | 4791 kWh | 3354 kWh | 1437 kWh | £907 | £144 | £1,051 | £17,742 | 16.9 yrs | £3,283 |
| 8 kW | 5475 kWh | 3833 kWh | 1643 kWh | £1,037 | £164 | £1,201 | £19,776 | 16.5 yrs | £4,252 |
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: £768, Upfront: £15,423, Break-even: 20.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1369 kWh | 999 kWh | 370 kWh | £270 | £37 | £307 | £9,319 | 30.3 yrs | £-3,172 |
| 3 kW | 2053 kWh | 1499 kWh | 554 kWh | £406 | £55 | £461 | £11,354 | 24.6 yrs | £-2,133 |
| 4 kW | 2738 kWh | 1998 kWh | 739 kWh | £541 | £74 | £615 | £13,388 | 21.8 yrs | £-1,094 |
| 5 kW | 3422 kWh | 2498 kWh | 924 kWh | £676 | £92 | £768 | £15,423 | 20.1 yrs | £-55 |
| 6 kW | 4106 kWh | 2998 kWh | 1109 kWh | £811 | £111 | £922 | £17,457 | 18.9 yrs | £984 |
| 7 kW | 4791 kWh | 3497 kWh | 1294 kWh | £946 | £129 | £1,076 | £19,492 | 18.1 yrs | £2,023 |
| 8 kW | 5475 kWh | 3997 kWh | 1478 kWh | £1,082 | £148 | £1,229 | £21,526 | 17.5 yrs | £3,062 |
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: £780, Upfront: £17,173, Break-even: 22.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1369 kWh | 1027 kWh | 342 kWh | £278 | £34 | £312 | £11,069 | 35.5 yrs | £-4,829 |
| 3 kW | 2053 kWh | 1540 kWh | 513 kWh | £417 | £51 | £468 | £13,104 | 28.0 yrs | £-3,743 |
| 4 kW | 2738 kWh | 2053 kWh | 684 kWh | £556 | £68 | £624 | £15,138 | 24.3 yrs | £-2,657 |
| 5 kW | 3422 kWh | 2567 kWh | 856 kWh | £695 | £86 | £780 | £17,173 | 22.0 yrs | £-1,571 |
| 6 kW | 4106 kWh | 3080 kWh | 1027 kWh | £833 | £103 | £936 | £19,207 | 20.5 yrs | £-486 |
| 7 kW | 4791 kWh | 3593 kWh | 1198 kWh | £972 | £120 | £1,092 | £21,242 | 19.5 yrs | £600 |
| 8 kW | 5475 kWh | 4106 kWh | 1369 kWh | £1,111 | £137 | £1,248 | £23,276 | 18.6 yrs | £1,686 |
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: £792, Upfront: £19,623, Break-even: 24.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1369 kWh | 1054 kWh | 315 kWh | £285 | £31 | £317 | £13,519 | 42.7 yrs | £-7,185 |
| 3 kW | 2053 kWh | 1581 kWh | 472 kWh | £428 | £47 | £475 | £15,554 | 32.7 yrs | £-6,053 |
| 4 kW | 2738 kWh | 2108 kWh | 630 kWh | £570 | £63 | £633 | £17,588 | 27.8 yrs | £-4,920 |
| 5 kW | 3422 kWh | 2635 kWh | 787 kWh | £713 | £79 | £792 | £19,623 | 24.8 yrs | £-3,788 |
| 6 kW | 4106 kWh | 3162 kWh | 944 kWh | £856 | £94 | £950 | £21,657 | 22.8 yrs | £-2,655 |
| 7 kW | 4791 kWh | 3689 kWh | 1102 kWh | £998 | £110 | £1,108 | £23,692 | 21.4 yrs | £-1,523 |
| 8 kW | 5475 kWh | 4216 kWh | 1259 kWh | £1,141 | £126 | £1,267 | £25,726 | 20.3 yrs | £-391 |
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.