I am challenged by rate of return and pay back analysis

HOMER does calculate payback and other comparison metrics like IRR.  When you double click on a system configuration in the Optimization Results list, the Simulation Results window will appear. On the Cost Summary tab, click Compare. Now you can choose a system configuration to use as a base case, and HOMER will compare the cash flow sequences for the two system configurations and calculate the payback, IRR, and so on.