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Question 7.1: Assuming the solar constant to be 1370 W/m²  and the radius ......

Assuming the solar constant to be 1370 W/m²  and the radius of the earth (supposed to be a sphere) R = 6370 km, calculate the power arriving at the top of the atmosphere and the energy received per day and per year. Electricity production was 1.8\times10^{4}\mathrm{TWh} in 2005. Compare that number to the solar energy arriving each day on top of the atmosphere.

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The earth is seen from the sun as a disk of radius R . The power received is 1370\times\pi\times R^{2}=1.75\times10^{17}\mathrm{W}. The earth receives 4.2\times10^{15}\mathrm{kWh}/\mathrm{day} or 1.5\times10^{18}\mathrm{kWh}/\mathrm{year}. Each day the earth receives 4.2\times10^{15}\mathrm{kWh}=4.2\times10^{6}\mathrm{TWh}. This is 233 times the annual electricity consumption.

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