Good question!

According to the U.S. Department of Energy (DOE) vision 2020, in order for the solar energy to be cost competitive with the other conventional sources of electricity, the cost should be one dollar per Watt or equivalently 6 cents per kWh.

You can read more about DOE vision 2020 using the URL:

www.doe.gov

Hope this helps answer your question.

Professor Yehia Khalil, Yale University, USA

Fellow of the University of Oxford, UK

Thank you for your answer, it s quite useful, i check the link above.