What size solar generator do I need?

Sizing a portable power station is different from sizing a standby generator. A standby unit is rated in running watts, and you size to the load. A power station is rated in two things that both matter: watts (what it can start and run at once) and kilowatt-hours (how long it runs). You need enough of both.

The two numbers

• Output in watts. This is what the inverter can deliver at once. It decides whether the unit can start a fridge compressor (a brief surge) and run your loads simultaneously. A 300 W unit runs a laptop and lights. A 2,000 W unit runs a fridge. A 6,000 W unit can back-feed a transfer switch.
• Capacity in kilowatt-hours. This is how much energy the battery stores. It decides how long the unit runs. A 1 kWh unit runs a fridge for several hours. A 3.8 kWh unit runs it for the better part of a day.

The runtime reference shows exactly how long a given capacity runs a given load, using the same typical appliance wattages behind the sizing calculator.

What you want to keep running

List the loads, the same way you would for a standby generator:

• Phone, laptop, lights, CPAP. Small, steady draws. A 0.5 to 1 kWh unit with a few hundred watts of output covers these for a night or a weekend.
• A fridge. A fridge compressor draws 600 to 800 W while running and surges higher to start. You want at least 1 kWh of capacity and around 1,000 W of output. A 1 to 2 kWh unit runs a fridge for several hours to a day.
• A furnace blower or a window AC. These are bigger motor loads. You need 1,500 to 3,000 W of output and 2 kWh or more of capacity. Check the starting watts on the data plate.
• Partial home backup. A 3 to 6 kWh unit with 3,000 to 6,000 W of output can back-feed a transfer switch and run essentials plus a fridge and a furnace blower.

How to use the runtime reference

The reference is a matrix of capacity tiers (512 Wh, 1,024 Wh, 2,048 Wh, 3,840 Wh) against common appliance loads. Pick the capacity you’re considering along the top and the appliance down the side, and the cell is the rough runtime from a full charge. It accounts for inverter losses and the gap between nameplate and usable capacity. A cycling load like a fridge runs about 2 to 3 times longer than the continuous figure shown, because the compressor only runs part of the time.

Solar recharge

If you recharge with panels during the day, a smaller battery can stretch across a longer outage, as long as there’s sun. The unit’s solar input in watts sets how fast it recharges. A 400 W panel input on a 2 kWh unit recharges it in roughly 5 to 6 hours of good sun, which extends the runtime across a multi-day outage if the sun cooperates. Without sun, the battery is all you have.

Pick the unit

Once you know the watts and the kWh:

1. Check the runtime reference with your biggest load to confirm the capacity you need.
2. Compare portable power stations by capacity and output.
3. See the best solar generators for ranked picks by use, from a compact camping unit to a 3.8 kWh home-backup machine.

A solar generator is a different tool from a gas standby generator, and the sizing question is different too: you’re matching a battery to how long you want it to last, not an engine to how much it can carry. Get both numbers right and the unit does the job you bought it for.