The correct answer is **234 m ^{2}**.

Using the formula (area) = (power)/(flux), the answer is 18,000 W divided by 77 W/m^{2}.

This is the area of a rectangle 10 meters by 23.4 meters--too large for the top of a compact car. The area of the hood, cabin roof, and trunk of a typical compact car is only about 6 m^{2}.

**Question 8.**

Recall that in using averages, we are assuming that energy from a solar power collector is stored in a battery.

To try to make a solar powered car more feasible, take into account the fact that a typical car is used only part of the time.

Use the average power requirement of 18,000 W and the flux of 84 W/m^{2}, but assume that the car is run only 5% of the time (this would be 1.2 hours per day). Also assume that the battery's efficiency is 80% (i.e. of energy stored in the battery, only 80% can be usefully extracted.) How much collecting area is needed now?

(We will ignore the fact that adding batteries to the car will increase its weight considerably, and hence increase the power required.)

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© 2001-2002, 2005 by Wm. Robert Johnston.

Last modified 11 January 2005.

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