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 914 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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: £737, Upfront: £10,173, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1828 kWh | 731 kWh | 1097 kWh | £185 | £110 | £295 | £4,069 | 13.8 yrs | £1,829 |
| 3 kW | 2742 kWh | 1097 kWh | 1645 kWh | £278 | £165 | £442 | £6,104 | 13.8 yrs | £2,744 |
| 4 kW | 3656 kWh | 1463 kWh | 2194 kWh | £370 | £219 | £590 | £8,138 | 13.8 yrs | £3,659 |
| 5 kW | 4570 kWh | 1828 kWh | 2742 kWh | £463 | £274 | £737 | £10,173 | 13.8 yrs | £4,574 |
| 6 kW | 5485 kWh | 2194 kWh | 3291 kWh | £556 | £329 | £885 | £12,207 | 13.8 yrs | £5,488 |
| 7 kW | 6399 kWh | 2559 kWh | 3839 kWh | £648 | £384 | £1,032 | £14,242 | 13.8 yrs | £6,403 |
| 8 kW | 7313 kWh | 2925 kWh | 4388 kWh | £741 | £439 | £1,180 | £16,276 | 13.8 yrs | £7,318 |
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: £877, Upfront: £12,273, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1828 kWh | 1097 kWh | 731 kWh | £278 | £73 | £351 | £6,169 | 17.6 yrs | £850 |
| 3 kW | 2742 kWh | 1645 kWh | 1097 kWh | £417 | £110 | £526 | £8,204 | 15.6 yrs | £2,326 |
| 4 kW | 3656 kWh | 2194 kWh | 1463 kWh | £556 | £146 | £702 | £10,238 | 14.6 yrs | £3,801 |
| 5 kW | 4570 kWh | 2742 kWh | 1828 kWh | £695 | £183 | £877 | £12,273 | 14.0 yrs | £5,276 |
| 6 kW | 5485 kWh | 3291 kWh | 2194 kWh | £834 | £219 | £1,053 | £14,307 | 13.6 yrs | £6,751 |
| 7 kW | 6399 kWh | 3839 kWh | 2559 kWh | £972 | £256 | £1,228 | £16,342 | 13.3 yrs | £8,227 |
| 8 kW | 7313 kWh | 4388 kWh | 2925 kWh | £1,111 | £293 | £1,404 | £18,376 | 13.1 yrs | £9,702 |
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: £947, Upfront: £13,673, 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 | 1828 kWh | 1280 kWh | 548 kWh | £324 | £55 | £379 | £7,569 | 20.0 yrs | £11 |
| 3 kW | 2742 kWh | 1920 kWh | 823 kWh | £486 | £82 | £568 | £9,604 | 16.9 yrs | £1,766 |
| 4 kW | 3656 kWh | 2559 kWh | 1097 kWh | £648 | £110 | £758 | £11,638 | 15.4 yrs | £3,522 |
| 5 kW | 4570 kWh | 3199 kWh | 1371 kWh | £810 | £137 | £947 | £13,673 | 14.4 yrs | £5,277 |
| 6 kW | 5485 kWh | 3839 kWh | 1645 kWh | £972 | £165 | £1,137 | £15,707 | 13.8 yrs | £7,033 |
| 7 kW | 6399 kWh | 4479 kWh | 1920 kWh | £1,135 | £192 | £1,326 | £17,742 | 13.4 yrs | £8,788 |
| 8 kW | 7313 kWh | 5119 kWh | 2194 kWh | £1,297 | £219 | £1,516 | £19,776 | 13.0 yrs | £10,544 |
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: £969, Upfront: £15,423, Break-even: 15.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1828 kWh | 1335 kWh | 494 kWh | £338 | £49 | £387 | £9,319 | 24.1 yrs | £-1,571 |
| 3 kW | 2742 kWh | 2002 kWh | 740 kWh | £507 | £74 | £581 | £11,354 | 19.5 yrs | £269 |
| 4 kW | 3656 kWh | 2669 kWh | 987 kWh | £676 | £99 | £775 | £13,388 | 17.3 yrs | £2,108 |
| 5 kW | 4570 kWh | 3336 kWh | 1234 kWh | £845 | £123 | £969 | £15,423 | 15.9 yrs | £3,948 |
| 6 kW | 5485 kWh | 4004 kWh | 1481 kWh | £1,014 | £148 | £1,162 | £17,457 | 15.0 yrs | £5,787 |
| 7 kW | 6399 kWh | 4671 kWh | 1728 kWh | £1,183 | £173 | £1,356 | £19,492 | 14.4 yrs | £7,627 |
| 8 kW | 7313 kWh | 5338 kWh | 1974 kWh | £1,352 | £197 | £1,550 | £21,526 | 13.9 yrs | £9,467 |
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: £983, Upfront: £17,173, Break-even: 17.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1828 kWh | 1371 kWh | 457 kWh | £347 | £46 | £393 | £11,069 | 28.2 yrs | £-3,209 |
| 3 kW | 2742 kWh | 2057 kWh | 686 kWh | £521 | £69 | £590 | £13,104 | 22.2 yrs | £-1,313 |
| 4 kW | 3656 kWh | 2742 kWh | 914 kWh | £695 | £91 | £786 | £15,138 | 19.3 yrs | £582 |
| 5 kW | 4570 kWh | 3428 kWh | 1143 kWh | £868 | £114 | £983 | £17,173 | 17.5 yrs | £2,478 |
| 6 kW | 5485 kWh | 4113 kWh | 1371 kWh | £1,042 | £137 | £1,179 | £19,207 | 16.3 yrs | £4,374 |
| 7 kW | 6399 kWh | 4799 kWh | 1600 kWh | £1,216 | £160 | £1,376 | £21,242 | 15.4 yrs | £6,269 |
| 8 kW | 7313 kWh | 5485 kWh | 1828 kWh | £1,389 | £183 | £1,572 | £23,276 | 14.8 yrs | £8,165 |
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: £997, Upfront: £19,623, Break-even: 19.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1828 kWh | 1408 kWh | 420 kWh | £357 | £42 | £399 | £13,519 | 33.9 yrs | £-5,547 |
| 3 kW | 2742 kWh | 2112 kWh | 631 kWh | £535 | £63 | £598 | £15,554 | 26.0 yrs | £-3,595 |
| 4 kW | 3656 kWh | 2815 kWh | 841 kWh | £713 | £84 | £797 | £17,588 | 22.1 yrs | £-1,643 |
| 5 kW | 4570 kWh | 3519 kWh | 1051 kWh | £891 | £105 | £997 | £19,623 | 19.7 yrs | £308 |
| 6 kW | 5485 kWh | 4223 kWh | 1261 kWh | £1,070 | £126 | £1,196 | £21,657 | 18.1 yrs | £2,260 |
| 7 kW | 6399 kWh | 4927 kWh | 1472 kWh | £1,248 | £147 | £1,395 | £23,692 | 17.0 yrs | £4,212 |
| 8 kW | 7313 kWh | 5631 kWh | 1682 kWh | £1,426 | £168 | £1,594 | £25,726 | 16.1 yrs | £6,163 |
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.