A 200W solar panel does not make 200 watts all day. That number is measured in a lab under standard test conditions: bright, direct light at a set cell temperature. Out in your yard, what you actually collect depends on how much strong sun your area gets and how much gets lost along the way.
Start with peak sun hours
A peak sun hour is one hour of sunlight at 1,000 watts per square meter, the same intensity panels are rated at. Your daily sun gets converted into that unit. Using NREL solar data, Unbound Solar lists state averages such as about 6.5 peak sun hours a day in Arizona, 5.6 in California, 5.3 in Texas and Florida, 4.0 in New York and Michigan, and 3.8 in Washington. Those are yearly averages; winter days are shorter and weaker.
Then take off the losses
NREL’s PVWatts calculator uses a default of 14% for system losses like dirt, wiring, connections and mismatch. Portable panels can do worse than that in practice, because they sit at one angle on the ground instead of being aimed perfectly, and they get warm, which lowers output.
The rough math
Rated watts x peak sun hours x 0.86 gives a reasonable daily estimate. A 200W panel in a 4-sun-hour location: 200 x 4 x 0.86 is about 690Wh a day. A 350W panel like the BLUETTI PV350 in the same spot: about 1,200Wh. That means a single 200W panel would need about three good days, before charging losses, to refill a 2kWh power station like the Jackery HomePower 2000 Plus v2.
How to get your own number
Plug your address into NREL’s free PVWatts calculator, enter your panel wattage as the system size, and it will estimate monthly output from NREL’s long-term weather data for your location. Use your worst month, not the yearly average, if you are sizing for winter outages.
Want to see how much a panel would refill your battery during an outage? Our Whole-Home Energy Calculator lets you pick a panel and a power station, then shows the daily refill, how long your essentials would run and which cable the pair needs.