Solar power is a very complicated power source. Here we will look at recreational power using solar for recharging batteries used for fridges, lights and basic accessories.
Step 1: Work out what your accessories use in a given 24 hour period. (Most campers will use approx 50AH, this being a 40L compressor driven fridge 35AH and some lighting 2x 12V lamps 10AH and perhaps a radio and a water pump.)
Step 2: How long will you stay in one place. Times the days with your power use. Lets say 4 days = 200AH.
Step 3: How big is your battery bank less 30% so you don’t over discharge the battery. Lets say a 120AH battery less 30% gives us 84AH of usable power.
Step 4: The short fall. 200AH less the battery capacity of 84AH gives us a shortfall of 116AH.
Step 5: Time. We can hope for good weather and average 8 hours of sun per day. 8 hours x 4 days camping is 32 hours of sun. To obtain 116AH in 32 hours we need 3.63A/hour.
Step 6: Panel size. 3.63A x 13.8V = 50W (This is in ideal weather and using the typical float voltage of a battery) We now add 40% for losses and other factors including battery type and condition. 50W + 40% = 70W
This is the minimum required and excludes any gains you may have from generators or running the vehicle if it charges the battery used for camping.
The above is a typical scenario and has suited 90% of our customers. Factors including ambient temperature, rain and battery type, size and condition will affect the results. Note that the battery will not be fully charged after 4 days and will require a charge to bring it up to 100%.