Solar panels, battery and generator for home backup

Each ticked row is watts times hours, summed into kilowatt-hours per day. The hours are the time the device is actually drawing power. A fridge motor often runs about a third of the day, so the default is 8 hours, not 24.

Solar, the battery, and the generator each have a tick of their own. Untick one and it drops out of the sum. Solar can be entered as panel watts times how many panels, or as the whole array in kilowatt-peak. Daily solar energy is that kilowatt-peak times the sun-hour band you pick, keeping 75 percent for heat, dust, wiring, and the inverter. The bands are about 2.5 hours in a cloudy climate, 3.5 in a mixed climate, 4.5 in a sunny one, and 5.5 in a very sunny one. This is not a survey of your roof.

The battery line is how many days that battery would last on its own. Lithium iron phosphate is allowed to use 80 percent of its capacity. Lead-acid is allowed 50 percent. Another 10 percent is set aside for inverter loss. The generator line is the fuel you have stored, at about half a litre of gasoline per kilowatt-hour, 0.32 litres of diesel, or 0.4 kilograms of propane.

The diagram under the numbers paints a load green when it can start and its energy for the days you asked still fits. The rest stay grey. The defaults are a fridge, lights, a router, and phone charging, with solar and a battery on and the generator off. Heating and an electric water heater dwarf this list.