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 938 kWh per year on a south-facing roof. We value self-used electricity at 27.7p 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: £802, 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 | 1876 kWh | 751 kWh | 1126 kWh | £208 | £113 | £321 | £4,069 | 12.7 yrs | £2,344 |
| 3 kW | 2815 kWh | 1126 kWh | 1689 kWh | £312 | £169 | £481 | £6,104 | 12.7 yrs | £3,515 |
| 4 kW | 3753 kWh | 1501 kWh | 2252 kWh | £416 | £225 | £641 | £8,138 | 12.7 yrs | £4,687 |
| 5 kW | 4691 kWh | 1876 kWh | 2815 kWh | £520 | £281 | £802 | £10,173 | 12.7 yrs | £5,859 |
| 6 kW | 5629 kWh | 2252 kWh | 3377 kWh | £624 | £338 | £962 | £12,207 | 12.7 yrs | £7,031 |
| 7 kW | 6567 kWh | 2627 kWh | 3940 kWh | £728 | £394 | £1,122 | £14,242 | 12.7 yrs | £8,202 |
| 8 kW | 7505 kWh | 3002 kWh | 4503 kWh | £832 | £450 | £1,283 | £16,276 | 12.7 yrs | £9,374 |
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: £968, Upfront: £12,273, 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 | 1876 kWh | 1126 kWh | 751 kWh | £312 | £75 | £387 | £6,169 | 15.9 yrs | £1,574 |
| 3 kW | 2815 kWh | 1689 kWh | 1126 kWh | £468 | £113 | £581 | £8,204 | 14.1 yrs | £3,410 |
| 4 kW | 3753 kWh | 2252 kWh | 1501 kWh | £624 | £150 | £774 | £10,238 | 13.2 yrs | £5,247 |
| 5 kW | 4691 kWh | 2815 kWh | 1876 kWh | £780 | £188 | £968 | £12,273 | 12.7 yrs | £7,084 |
| 6 kW | 5629 kWh | 3377 kWh | 2252 kWh | £936 | £225 | £1,161 | £14,307 | 12.3 yrs | £8,921 |
| 7 kW | 6567 kWh | 3940 kWh | 2627 kWh | £1,092 | £263 | £1,355 | £16,342 | 12.1 yrs | £10,757 |
| 8 kW | 7505 kWh | 4503 kWh | 3002 kWh | £1,248 | £300 | £1,549 | £18,376 | 11.9 yrs | £12,594 |
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: £1,051, Upfront: £13,673, Break-even: 13.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1876 kWh | 1313 kWh | 563 kWh | £364 | £56 | £420 | £7,569 | 18.0 yrs | £838 |
| 3 kW | 2815 kWh | 1970 kWh | 844 kWh | £546 | £84 | £631 | £9,604 | 15.2 yrs | £3,008 |
| 4 kW | 3753 kWh | 2627 kWh | 1126 kWh | £728 | £113 | £841 | £11,638 | 13.8 yrs | £5,177 |
| 5 kW | 4691 kWh | 3284 kWh | 1407 kWh | £910 | £141 | £1,051 | £13,673 | 13.0 yrs | £7,346 |
| 6 kW | 5629 kWh | 3940 kWh | 1689 kWh | £1,092 | £169 | £1,261 | £15,707 | 12.5 yrs | £9,515 |
| 7 kW | 6567 kWh | 4597 kWh | 1970 kWh | £1,274 | £197 | £1,471 | £17,742 | 12.1 yrs | £11,685 |
| 8 kW | 7505 kWh | 5254 kWh | 2252 kWh | £1,456 | £225 | £1,682 | £19,776 | 11.8 yrs | £13,854 |
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: £1,076, Upfront: £15,423, 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 | 1876 kWh | 1370 kWh | 507 kWh | £380 | £51 | £430 | £9,319 | 21.7 yrs | £-712 |
| 3 kW | 2815 kWh | 2055 kWh | 760 kWh | £570 | £76 | £646 | £11,354 | 17.6 yrs | £1,557 |
| 4 kW | 3753 kWh | 2739 kWh | 1013 kWh | £759 | £101 | £861 | £13,388 | 15.6 yrs | £3,826 |
| 5 kW | 4691 kWh | 3424 kWh | 1267 kWh | £949 | £127 | £1,076 | £15,423 | 14.3 yrs | £6,095 |
| 6 kW | 5629 kWh | 4109 kWh | 1520 kWh | £1,139 | £152 | £1,291 | £17,457 | 13.5 yrs | £8,364 |
| 7 kW | 6567 kWh | 4794 kWh | 1773 kWh | £1,329 | £177 | £1,506 | £19,492 | 12.9 yrs | £10,633 |
| 8 kW | 7505 kWh | 5479 kWh | 2026 kWh | £1,519 | £203 | £1,721 | £21,526 | 12.5 yrs | £12,902 |
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: £1,092, Upfront: £17,173, Break-even: 15.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1876 kWh | 1407 kWh | 469 kWh | £390 | £47 | £437 | £11,069 | 25.3 yrs | £-2,329 |
| 3 kW | 2815 kWh | 2111 kWh | 704 kWh | £585 | £70 | £655 | £13,104 | 20.0 yrs | £6 |
| 4 kW | 3753 kWh | 2815 kWh | 938 kWh | £780 | £94 | £874 | £15,138 | 17.3 yrs | £2,342 |
| 5 kW | 4691 kWh | 3518 kWh | 1173 kWh | £975 | £117 | £1,092 | £17,173 | 15.7 yrs | £4,677 |
| 6 kW | 5629 kWh | 4222 kWh | 1407 kWh | £1,170 | £141 | £1,311 | £19,207 | 14.7 yrs | £7,013 |
| 7 kW | 6567 kWh | 4925 kWh | 1642 kWh | £1,365 | £164 | £1,529 | £21,242 | 13.9 yrs | £9,348 |
| 8 kW | 7505 kWh | 5629 kWh | 1876 kWh | £1,560 | £188 | £1,748 | £23,276 | 13.3 yrs | £11,684 |
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: £1,109, Upfront: £19,623, 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 | 1876 kWh | 1445 kWh | 432 kWh | £400 | £43 | £444 | £13,519 | 30.5 yrs | £-4,646 |
| 3 kW | 2815 kWh | 2167 kWh | 647 kWh | £601 | £65 | £665 | £15,554 | 23.4 yrs | £-2,244 |
| 4 kW | 3753 kWh | 2890 kWh | 863 kWh | £801 | £86 | £887 | £17,588 | 19.8 yrs | £158 |
| 5 kW | 4691 kWh | 3612 kWh | 1079 kWh | £1,001 | £108 | £1,109 | £19,623 | 17.7 yrs | £2,560 |
| 6 kW | 5629 kWh | 4334 kWh | 1295 kWh | £1,201 | £129 | £1,331 | £21,657 | 16.3 yrs | £4,962 |
| 7 kW | 6567 kWh | 5057 kWh | 1510 kWh | £1,402 | £151 | £1,553 | £23,692 | 15.3 yrs | £7,364 |
| 8 kW | 7505 kWh | 5779 kWh | 1726 kWh | £1,602 | £173 | £1,775 | £25,726 | 14.5 yrs | £9,766 |
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.