A decision variable is a variable whose optimal value is determined during the course of the optimization process. An example is the size of the PV array. If you are specifying your own Size your own, HOMER considers each different PV array size you specify and finds the value that results in the least net present cost.
The decision variables in HOMER are:
•Size of the PV array
•Number of wind turbines
•Size of the hydro system
•Size of each generator
•Number of batteries
•Size of the converter
•Size of the electrolyzer
•Size of the hydrogen storage tank
•Maximum grid demand
Decision variables are also known as optimization variables.