I’m working hard on the math for off-grid solar power right now. The system consists of several big pieces, solar panels, batteries, a generator, and a control piece that manages charging the batteries and converting battery power (DC) to AC. It also provides DC for the few things it makes sense to run on DC.
The first thing you need to do is figure out how much electricity you need in watt-hours per day. This is a lot of work. The refrigerator is the biggest consumer as well as the easiest to figurel it’s on all the time. Contrast that with a microwave. Let’s see, we have a 1200 watt microwave we use about five minutes a day or a garbage disposal.
For solar panels, it seems you figure on five six hours (I checked a chart for our area) of sunlight per day. You multiply that times the number of watts your solar panels can produce and that’s how much power you can generate.
For batteries, you multiply your daily watt-hour needs by three to give you a three day supply of power. You then multiply that number by two because you don’t want to discharge the batteries below fifty percent. (Routinely discharging the batteries below fifty percent shortens their life.)
We are going to have a generator which means that something odd like ten days of rain is not going to leave us in the dark. It also lessens the tendency to overbuild the solar power.
The big power draws:
- Refrigerator
- Washing machine
- Clothes Dryer
- Microwave
- Pressure pump
You might wonder what a pressure pump is. Our water tower is not nearly tall enough to create the water pressure you need to shower or run things like tankless water heaters. When getting information on how much power the pressure pump needs, I was told to first to figure out how much water we will use a day.
One piece of solar power that is already done is the water supply. It’s a perfect little functioning system. It has its own solar panels (no batteries) that run the pump when there’s sun. It pumps the water about twenty-five feet up and into the water tank (1250 gallon). My rough estimate is that the tank holds about at least weeks worth of water and could be completely refilled with one good day of sun.