Solar power sizing can be tricky. You have to figure out how many solar panels it will take to run your application while also keeping costs down. Here is how you can size your off grid solar power system to perform year round under any condition the world wants to throw at you.
First thing you need to do is figure out your load. How much energy (amps) is needed in a single day to power whatever it is you need to power (home, business, camera, light, etc.). This can be found by looking at the specifications of the item or following a chart of usage over time. For this example: let’s say your application draws 2.08 Amps and it runs 24 hours a day. This would require a total of 50 Amp hours per day. This number can change depending on the number of run hours your system actually requires.
Second thing is what is the amperage of the solar panel you want to use? This can be found on the solar panel specification page. You then take the total amps provided by a single solar panel and multiply it by the number of sun hours available in your area. Make sure to look at the worst month (December for above the equator). This information is available on NREL's Photovoltaic Solar Resource Map. Once you have figured out this you can start to figure out how many panels you will need to run your system reliably. For this example we will use 4 sun hours with a panel that produces 5 amps per hour.
Basically, if you need 50 Amp hours per day to run your application and you have a total of 4 sun hours available, you need a total of 15 amps (adding 20% overage) provided by your solar power system, or in this case 3 solar panels at 5 amps each. This also gives you a much needed overage for times of less than 4 hours sun. Seems easy so far, but there is a little more.
Battery backup is what you need for an off grid solar application. Making sure you have enough battery storage is essential for cloudy / stormy days. If you need a total of 50 Amp hours for a single day, making sure you have adaquate days storage will help get you through those not so sunny days. Multiply the total Amp hours by the desired days of storage, we recommend 4 – 5 days storage to ensure reliability and long term performance. 50 Amp hours times 5 days equals 250 amp hours which will power the applicaton for 5 full 24 hour days with zero sun.
Well that's about it. If you make sure you have enough solar to create 50 amps of energy every day and a battery system that holds 250 amp hours total, your system will not run out of power and will run reliably for years.