Sources of values
Solar constant:
"The solar energy reaching the periphery of the earth's atmosphere is considered to be constant for all practical purposes, and is known as the solar constant. Because of the difficulty in achieving accurate measurements, the exact value of the solar constant is not known with certainty but is believed to be between 1,353 and 1,395 W/m2 (approximately 1.4 kW/m2, or 2.0 cal/cm2/min). The solar constant value is estimated on the basis of the solar radiation received on a unit area exposed perpendicularly to the rays of the sun at an average distance between the sun and the earth. "
[http://almashriq.hiof.no/lebanon/600/610/614/solar-water/unesco/21-23.html]
Radius of the Earth:
Value of 6371 km used here is the Volumic Radius, ie the value giving a fairly exact value for the Earth's volume by the usual formula for a true sphere. Because the Earth is actually an oblate spheroid, other radii have been calculated, see reference.
[http://en.wikipedia.org/wiki/Earth_radius]
Albedo:
"Astronomers have determined the visual albedos of our planets. From NASA’s planetary sites, the brightest is Venus with an albedo of 0.65. That means 65% of incoming sunlight is reflected from the cloud-covered planet. The remaining 35% contributes to the heat energy of Venus. Mercury, at 0.11, has the lowest planetary albedo. Earth’s albedo is 0.37; Mars is 0.15; Jupiter, 0.52; Saturn, 0.47; Uranus, 0.51; Neptune 0.41. Pluto’s albedo varies from 0.5 to 0.7. Our Moon’s average albedo is 0.12.
It should be pointed out that these planetary albedos are averages. Taking Earth as an example, clouds vary from 0.4 to 0.8, snow varies from 0.4 to 0.85, forests vary from 0.04 to 0.1, grass is about 0.15, and water varies from 0.02 with the Sun directly overhead to 0.8 at low levels of incidence. So the Earth’s albedo varies, and depends on the extent of cloudiness, snowfall, and the Sun’s angle of incidence on the oceans. With an average albedo of 0.37, 63% of incoming solar energy contributes to the warmth of our planet. It’s obvious that if cloud cover were to decrease significantly, the Earth’s surface temperature would increase, contributing to other factors of global warming such as the amounts of greenhouse gasses."
[http://www.asterism.org/tutorials/tut26-1.htm]
World energy generation/consumption:
"Global energy production in 1993 reached 338 exajoules (1 exajoule = 10**18 joules, or ~163 million barrels of oil).
The long upward trend in global commercial energy production and consumption continued through 1993, the most recent year for which data are available. Global energy production in 1993 reached 338 exajoules (1 exajoule = 10**18 joules, or ~163 million barrels of oil), which is 40% greater than that in 1973. Total energy consumption rose to 326 exajoules, which is 49% greater than that in 1973. The energy consumption of Europe in 1993 was 93 exajoules, which indicates that Europe accounted for almost 30% of the global energy consumption."
[http://hypertextbook.com/facts/1998/MarvinRusinek.shtml]
Calculations
Taking the solar constant to be 1.4 kW/m2, and the Earth's radius to be 6371 km, the cross-sectional area of the Earth is pi*r^2, ie 3.142*((6371*10^3)^2)=1.2753E14 sq m.
With the Earth at its average distance from the Sun, total energy received (ignoring atmosphere etc) is 1.785E14 KW. This is equal to 1.785E8 GW (gigawatts), ie 178,500,000 GW. (For population ca 6 billion, solar energy per person= ca 30MW.)
1 year=365.25*24 hr =8766 hr. Total solar energy received/yr = 8766*1.785E14 KW-hrs = 1.564731 * 1018 KW-hrs = 5.6330316 * 1024 joules.
Global energy production in 1993 reached 338 exajoules (1 exajoule = 10**18 joules)
= 3.38 * 1020 joules. Therefore man's production over solar imput = <1/10,000.
1 kilowatt hour = 3 600 000 joules = 3.6E6 joules. 1 kilowatt = 1.0 x 10-6 gigawatts
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