As you dive deeper into designing a solar system you need to model how system parameters will change based on the conditions you are seeing at your job site. For example, if you visit an inverter manufacturers website they will most likely have an inverter sizing program to determine how the solar module you selected will operate with their inverters. These programs are easy to use but they don’t teach you the fundamentals of system design. The pages that follow, will break out the equations needed to manually design a solar system. The best way to learn these is to use them either on paper or by creating your own excel sheet to do the calculations for you.