I assume Ajith is smart enough NOT to apply 300 volts to his micro. At least not twice....

You are using the mathamtical definition to shoehorn your solution. At any instant, the instantaneous product of current x voltage always describes the energy being delivered. If you take enough samples, then over a full cycle of a reactive load, the total energy delivered is 0, because you will have negative current flow with positive voltage and positive current flow with negative voltage. The net energy flow is of course zero. The net power is zero, cos phi = 0 etc etc.

There is no need to MEASURE peak voltage and current and deduce the power factor, all you need is a real integration.

Steve