A typical commercial solar photovoltaic (PV) cell costs approximately $7 per wat

Question

A typical commercial solar photovoltaic (PV) cell costs approximately $7 per watt and requires 7.6 TJ of energy per million dollars to manufacture the solar cells. If the PV cell has a conversion efficiency of 9%, a performance efficiency of 80% and a lifetime of 30 years. How much electricity will a 10 m by 2 m PV panel generate over its lifetime, based on an average solar insolation of 1700kWh/m_2-yr? Estimate the cost of the PV panel in part (a). Assume daylight averages 12 hours per day at full output and neglect adjustments associated with the Standard Laboratory Test Condition (STC). Estimate: (i) the energy invested in manufacturing the PV panel in (a), (ii) the time (in years) required for the PV panal in (a) to return its initial energy investment. If electricity displaced by the solar cells would cost $0.10/kWh in the retail market, then what is the time that it would take for the PV panel in (a) to pay for its initial cost?

Explanation / Answer

a) annual solar insolation = 1700 kWh/m^2
annual solar insolation of 10m by 2m solar panel = 1700*20 = 34000 kWh
energy converted to electricity = 34000*9% = 3060 kWh
electricity supplied finally = 3060*80% = 2448 kWh
Electricity supplied in 30 years = 73,440 kWh

b) Average Power of solar panel = energy supplied in 30 years/ 30 years = 73440*1000/30*365*24 = 279.45 W
Power of panel = 279.45*24/12 = 558.9 W ( because the panel works for 12 hours a day)
Cost = 558.9*7 = $3912.328

c) Energy invested in a million dollars = 7.6*10^12 J
Energy invested in a) = 7.6*10^12*3912.328/10^6 = 29.733 GJ (giga joule)
Time to return to initial energy investment = 29.733*10^9/279.45 = 3.373 years

d) Cost = $0.1 / kWh
Money made in t hours = 0.1*34000t/365*24 = 0.3881t
Money spent initially = $3912.328
t = 3912.328/0.3881 = 1.15 years

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