In: Physics
The power of sunlight reaching each square meter of the Earth's surface on a clear day in the tropics is close to 1 000 W. On a winter day in Manitoba, the power concentration of sunlight can be 100 W/m2. Many human activities are described by a power per unit area on the order of 102 W/m2 or less.
(a) Consider, for example, a family of four paying $66 to the
electric company every 30 days for 615 kWh of energy carried by
electrical transmission to their house, which has floor dimensions
of 13.0 m by 9.50 m. Compute the power per unit area used by the
family.
W/m2
(b) Consider a car 2.19 m wide and 4.90 m long traveling at 55.0
mi/h using gasoline having "heat of combustion" 44.0 MJ/kg with
fuel economy 25.0 mi/gal. One gallon of gasoline has a mass of 2.54
kg. Find the power per unit area used by the car.
W/m2
(c) Explain why direct use of solar energy is not practical for
running a conventional automobile.
(d) What are some uses of solar energy that are more practical?