Solar generator size calculator
Find the watt-hours of portable power you need for your essentials, and the panels to recharge it, starting from your own bill.
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Size the station by what you run
A portable power station is rated in watt-hours (Wh), the amount of energy it stores, and in watts, the most it can deliver at once. You need both to be big enough. The watt-hours decide how long your devices run; the watts decide whether they start at all.
The formulas, with the constants
- energy needed (Wh) = device watts x hours of use, summed over devices
- essentials planning figure = 10 kWh a day, or 10,000 Wh
- with headroom = x 1.5, or 15,000 Wh
- panel watts to recharge = Wh / (sun hours x 0.75)
The 10,000 Wh essentials figure is a house-scale planning number used across this site. It is far above what a single portable station holds, and that is the point: it shows how much a home really uses. For a camper, a workshop or a short outage you will usually total your own device list instead, which is a few hundred to a few thousand Wh.
A quick example
A refrigerator averaging 60 W over a day uses about 1,440 Wh. A router at 10 W for 24 hours adds 240 Wh, and ten LED lights at 10 W for five hours adds 500 Wh. The total is roughly 2,200 Wh. With 1.5 times headroom, look for about 3,300 Wh. To refill 2,200 Wh in 5 sun hours with a 0.75 derate, you need about 590 W of panels. These device wattages are illustrative; measure your own with a plug-in watt meter.
Watts matter too
Motors, such as a fridge compressor, a well pump or a power tool, draw several times their running power for a moment on startup. Add up the watts of everything you might run at once and pick a station whose continuous rating exceeds it, with margin for the surge. If a station trips off, it was probably undersized in watts, not in watt-hours.
Before you buy
Prices change often, so we show none here. The links in your results search each brand's own store, and we may earn a commission if you buy through them; it does not change your price. Do not plug a portable station into a house outlet to back-feed your wiring. If you want it to power your panel, a licensed electrician must install a proper transfer switch.
Planning estimate. Permits, interconnection approval and a licensed electrician are required for grid-tied systems.
Questions
What is a solar generator?
It is a portable power station, a battery with an inverter in one box, paired with solar panels that recharge it. There is no fuel and no engine. It is sold under many brand names.
How many watt-hours do I need?
Add up the watts of each device times the hours you will run it. As a planning figure, essentials for a home are about 10,000 Wh a day, and most portable stations are much smaller, so decide what you really need to keep running.
Why add headroom?
Running a battery from full to flat shortens its life, inverters waste some energy, and demand rises when you add a device. The tool shows a figure with 1.5 times headroom for that reason.
Can a solar generator run a whole house?
Not a typical portable one. Whole-home backup needs far more storage and a proper transfer switch installed by a licensed electrician. Portable stations suit essentials, tools and camping.
How long to recharge from panels?
Divide the watt-hours you used by the panel watts times the usable sun hours and a loss factor. With a 0.75 derate, 400 W of panels in 5 sun hours gives about 1,500 Wh a day.