Sizing solar system

How did we know how many solar panels, batteries, and what size inverter and charge controller we needed?

We didn't know anything about solar power or RV solar systems and started researching different websites for solar calculators to use to help determine what we needed.  We found a few on vendor sites like and some on blog sites like

These calculators each had features we liked, but weren't something we could include in our blog.  So I made my own with a few adjustments based on what we've seen over time in our van.

We knew we wanted 12 volt lithium batteries, flexible solar panels, mppt charge controller, and a pure sine wave inverter, so we factored these specific elements into our calculator.

We researched each electric appliance for our van to determine the number of amps or watts generated by each device.  For instance, a 700 Watt microwave is AC powered and may have a peak wattage slightly higher than specified for the product.  Or, should we or should we not get a water heater for our shower (and for the record, it was the big one at 1440 Watts and takes 30 minutes to heat 4 gallons of water).  It might be something as simple as a 2 Amp DC charger to charge our mobile devices.  If your devices are listed with Amps, then use the calculation Amps * Volts = Watts.  A 2 Amp DC charger would then be 2*12=24 Watts.

We put each device in a small list.

Device Watts Hours AC/DC
Fridge 25 24 DC
Heater 24 8 DC
Water pump 50 .5 DC
Fan 13 8 DC
LED Lights 15 1 DC
Phone Charger 24 2 DC
Microwave 900 .5 AC
TV 80 2 AC
Induction Plate 800 .5 AC
Water Heater 1440 .5 AC



If we only use the water heater on specific days, and don't use the microwave or induction plate at the same time, we can get away with 200Ah of battery power, a 40 Amp charge controller, 320 Watts of solar, and a 2000 Watt inverter.

However, if we want to use the water heater, microwave, induction plate and all the DC devices at the same time...  We're going to need 300Ah of battery power, a 60 amp charge controller, 450 Watts of solar, and a 3000 Watt inverter.

 Solar System Calculator

Device Watts Hours AC/DC Result  
Daily Watt Hours
12V Battery Required
Minimum Solar Required
Charge Controller
Minimum Inverter


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