Could be compared to energy economy made by non use of fossile energy or electricity. And thus  cost reduction per hour of use can divide the manufacturing cost or selling price.

You obtain the duration to payback...

We know that the sun is capable of delivering 3.5 to 7 KWh of energy per day(depending on the region). On the other hand we know the fuel consumption for cooking per day in a home of 5 people. if the energy used per day be equated to the joules of energy used for cooking (based on the efficiency of heat transfer in the cooking method) if the same amount of energy can be tapped with a parabolic concentrator from the sun.

Now the cost of the solar concentrator can be compared to the fuel cost as the solar cooker should be in par with what the existing technology or better to drive the change to solar.

This is the approach based on Joules that is used for the compassion.

Getting the payback period is very simple. First you should sum up the total cost incurred in constructing the collector. Then sum up the savings in fuel cost you benefit from not using the collector over one year and call it the annual savings. Then divide the total costs by the annual savings and get the payback period in years.

As far as I know there is only comparison estimation method to calculate payback period. U can only estimate how much fuel u save by the use of solar cooker.

Piyushkumar,

This is a problem that depends on: (a) Location of your PCSC and performance curve of the equipment; (b) Capital Cost; (c) O&M costs; (d) cost of conventional fuel and technology you´ll need to use otherwise. With all these parameters + use-load + cost of money + inflation + escalation rate of conventional fuel and some other minor ingredients in this cocktail, you´ll be able to find if this technology is viable for the given application.

I suggest you to download RETScreen (www.retscreen.net) a free software that will help you to perform calculations in a very simple and comprehensive manner, including tips. It will allow you also to figure sensitivity-risk analysis and GHG emission reduction obtained by your project.

I hope it helps!

Luis