How the numbers work
Every number on the calculator comes from four simple steps. Nothing is hidden and nothing is tuned to sell a bigger battery.
1. Energy per day
For each appliance: watts × hours switched on × share of time it actually runs. A fridge draws about 150 W while its compressor runs, but the compressor is only on about a third of the time, so it uses roughly 1.3 kWh a day, not 3.6.
2. Output and surge
The output figure adds up everything you picked, as if it all ran at the same moment. The surge figure adds the extra start-up draw of the hungriest motor on top. Pumps, compressors and fans can pull 2 to 3 times their running watts for a fraction of a second. A station that cannot deliver that surge shuts off, even if its battery is full.
3. Battery losses
Converting battery power to wall power loses energy. We assume 85% of the rated capacity reaches your outlets. That is conservative for the lithium iron phosphate (LFP) stations we list; real results vary with the load and temperature.
4. Solar recharge
A panel rarely delivers its rated watts. We count 4 hours of sun at 75% of the rating, which is a fair average for much of the US. Winter and cloudy days give far less, so the battery still has to carry the first night on its own.
What the calculator cannot know
- Your exact appliances. The label or a plug-in watt meter beats any typical value.
- Whether your house needs 240 V for a well pump or central air. Those need a transfer switch and an electrician.
- How cold it gets. Batteries give less in freezing temperatures and most will not charge below freezing.