You can use PVWatts to find solar harvest estimates for a particular place, month, array size, etc. You can use this info to

- find out how much power your

First, pick a location using the search bar:

We need to make a couple changes here

• your array size in kW. A kilowatt is 1,000w, so a 200w = 0.2kW (zero-point-two)¹⁾
• accept the default losses for MPPT systems. PWM systems should use something like 30%
• if your panels are flat (most are) adjust tilt to zero

The first column is kWh/square meter/day, AKA Hours of Full Sun Equivalent (FSE).

The second column is kWh harvested per month. To find average maximal harvest per day divide this figure by the number of days in that month.

Example: In January in this location the system could make 17kWh. 17 divided by 31 days = 0.548kWh/day, (548Wh/day).

Note: the 2nd column is rounded to whole numbers. This makes little difference with large residential installs but can distort the result with our small systems. You can use the FSE number to do the math for your setup directly:

FSE x array wattage x ((100 - system losses) / 100)

…which gives a more precise 605Wh/day. You may want to plug that formula into a spreadsheet for easy re-use.The system losses will be 14.08 or 30.0 as above, depending on the controller.

This is simpler because you can pick your location as above then accept the defaults. We only care about Hours of FSE, the 2nd column which is called “Solar Radiation”. Since we want to know the worst-case scenario, pick the month with the lowest FSE when you will be camping. For full-timers this usually means December.

The formula is

  Wh required / FSE / overall system efficiency

System efficiency will be 0.85 for MPPT and 0.7 for PWM.

You need 900Wh/day. You live in Stuttgart, Germany and the lowest FSE in a month you will be camping is 2.37 hours of FSE in October.

So 900Wh / 2.37 / 0.85 = 446.76w of flat-mounted panel.