The correct answers are: 1.04 x 108 MW for the total power needs, and 1,350,000 km2 for the needed collection area.
To get the total power needs, first get the average power consumption per American: 3.29x106 MW / 291,000,000 = 0.0113 MW (or 11,300 W) per person. Then multiply by the assumed world population: 0.0113 MW * 9,200,000,000 = 1.04 x 108 MW.
Finally, use the formula (area) = (power)/(flux): the answer is 1.04x108 MW divided by 77 MW/km2.
This is the area of Texas, California, and Minnesota combined.
Solar power can and does meet energy needs best in certain specialized situations. However, solar energy is too dilute to meet all the energy needs of an industrial society. This is not because technology hasn't yet met the challenge, and it is not because governments are not funding solar energy sufficiently. As you have just demonstrated in this exercise, solar energy cannot power society because of physics: it is impossible, by the same laws of physics that determine how you harness solar energy, to get that much energy from the Sun unless you have very large collecting surfaces. Do you think that the same environmentalists that promote solar energy would allow areas of the Earth's surface equivalent to several states to be completely covered by solar collectors? Of course not!
Those that think that government subsidies will improve solar power do not understand economics. If solar power really were cheap, it would already have been done by profiteers that realized they could undercut the oil and coal companies and make a fortune. In reality, tax money must be sunk into an uncompetive venture--solar energy--to give the illusion of comparable cost to conventional energy sources.
The central point is that solar energy is dilute. Dr. Petr Beckmann illustrated it as such: A large tree might have a very large collecting area of leaves which gather solar energy for a century. If the tree is buried and converted to coal, this stored energy may be concentrated into a small lump of coal. When we burn this lump of coal, this accumulated energy is released in a few minutes to produce industrially useful power. Solar energy is dilute and is only industrially useful if highly concentrated in time (by the tree in this illustration) or over area (by very large collecting surfaces, as in these exercises).
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© 2001-2002, 2005 by Wm. Robert Johnston.
Last modified 11 January 2005.
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