Do I need a generator if I have solar?
Answered by day three, not by day one · 2026-09-11
The first day of a blackout almost any sensible system answers «no». The battery came out of the night full and it holds. The third day says something else, because by then the battery starts the day half empty and the panels still have no sun. Measured: with one a/c at night with 6 panels and 16 kWh does not start the generator on day one and runs it 10 hours on day three. Same house, same gear, same sky.
Generator hours — first overcast day with no grid
| The house | 6 panels 16 kWh | 10 panels 32 kWh | 14 panels 32 kWh | 18 panels 48 kWh |
|---|---|---|---|---|
| The essentials | — | — | — | — |
| With one A/C at night | — | — | — | — |
| How people actually live | 20 h | 16 h | 3 h | — |
The same houses, third overcast day in a row
This is the one that matters after a hurricane, and it is the one nobody runs.
| The house | 6 panels 16 kWh | 10 panels 32 kWh | 14 panels 32 kWh | 18 panels 48 kWh |
|---|---|---|---|---|
| The essentials | — | — | — | — |
| With one A/C at night | 10 h | — | — | — |
| How people actually live | 20 h | 16 h | 14 h | 8 h |
A dash means the generator never starts. Hours are what the engine counts; what those hours cost in gasoline depends on your unit — multiply by its own gallons per hour, which is on its plate.
Sizing is the lever, not the generator
On the hardest house, going from 10 panels to 14 takes the first day from 16 hours to 3. Four panels cost less than most generators, and they work every other day of the year too.
There is a second lever that costs nothing: the living-room A/C. The house that never needs a generator in either table is the one running a bedroom unit at night — the same finding as the days with no grid page.
If you do keep a generator, running it few hours at full load beats running it all night at half: a generator at half load burns nearly what it burns at full. That is what an AC battery charger is for — it fills the battery fast so you can shut the generator off, instead of trickling into the house until morning.
Work out your own, hour by hour →
Free, no card and no sign-up. Your appliances, your town's sun, and the hour the generator would have to come in.
Run with 585 W panels, a 12 kW hybrid inverter and a 7 kW generator, overcast sky, no grid, in the central valley. The battery keeps a 20 % floor. Your own number will differ with your consumption and your equipment.