The correct answers are:
South Texas: 92 W/m2
northern U.S.: 77 W/m2
northern U.S. (winter): 35 W/m2

These are the results of multiplying each answer from part 5 by 30%.

Notice that these values, the maximum useful solar energy, are far less than the flux originally reaching the Earth from the Sun--only 2.6% to 6.7%, specifically.

We have ignored weather: on cloudy days useful flux will be further reduced (same for days with significant haze or dust in the air). Accounting for weather would reduce our results by another 35% on average, in fact.

The following questions will be based on available solar energy for the northern U.S.: 77 W/m2. (You can, of course, repeat all the following calculations on your own using another choice.)

Question 6.

Use the above value of flux to find how much collecting area is needed for a typical U.S. household. Average household power needs are 3,200 W.

(Note that this is an average power consumption for the household and the average power available in the northern U.S. We are effectively assuming we can store the energy with perfect efficiency in a battery, which is not feasible, and over long periods of time, which is not currently practical. Do you think power demands are high when available sunlight is at its most, or its least?)

(Also note: this figure refers to all household power use, which currently averages 38% from electricity and 62% from fossil fuel or wood burning within the home.)

Click here to check your answers and continue...

© 2001-2002, 2005 by Wm. Robert Johnston.
Last modified 11 January 2005.
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