Factors need to be considered:

1. Where the solar power system will be used? How is the local sunlight radiation?

2. What are the loads? The rated power and starting power of the loads.
 
3. Will the system be grid-connected or off-grid?
 
4. What is the output voltage of they system? AC or DC?
 
5. What is the max number of consecutive cloudy weather days expected where the system will be used.
 
6. How many these systems are needed?
 [MorningSolar Design Guide.PDF]    If need excel, please send us email