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Solar energy calculations

Could you please explain what formula and step are involved and please provide (example) problem if possible

Assume that due to dwindling supplies of crude oil and natural gas, the US embarks on a plan to implement the "hydrogen economy" for which hydrogen will be generated by electrolysis of water. The source of electricity is from photovoltaic (PV) conversion of sunlight in the southwestern US.

(a) Assume that a flat plate PV system is used, with a solar conversion efficiency of 25 percent and a hydrogen production efficiency of 95 percent. Assume the average annual insolation in the southwest is 270 watts per square meter. Calculate the annual electrical energy produced in kJ/sq. meter. Calculate the weight of hydrogen (kg/sq. meter) produced per year.

(b) The US consumed 38 EJ of petroleum in 2000. How many square meters of PV collectors would be needed to supply the equivalent amount of energy in hydrogen?

Solution Preview

Solar panels convert sunlight into electricity, which is then used to generate hydrogen. We know we are only getting 25% of that energy out of the PV collectors. For each square meter of solar panel, therefore, we get 270 watts x .25 = 67.5 watts of electricity. Now you just need to convert this to annual joules per square ...