The roofs of many homes in the United States are covered with photovoltaic (PV)

Question

The roofs of many homes in the United States are covered with photovoltaic (PV) solar cells that resemble roof tiles, generating electricity quietly from solar energy. An article stated that over its projected 30-year service life, a 4-KW roof PV system in California will reduce the production of CO2 that causes global warming by 433,000 lbm, sulfates that cause acid rain by 2900 lbm, and nitrates that cause smog by 1660 lbm. The article also claims that a PV roof will save 253,000 lbm of coal, 21,000 gallons of oil, and 27 million ft3 of natural gas. Making reasonable assumptions for incident solar radiation, efficiency, and emissions, evaluate these claims and make corrections if necessary.

Explanation / Answer

Because of earths its spherical shape incoming solar radiation is not equally distributed over the planet. At each point on the earth surface the sun lights only half of the planet's surface, with maximum radiation coming in during noon and less in other times of the day.The atmosphere of the earth exhibits absorptance that varies drastically with wavelength. Radiation represents the upper limit to the amount of radiation that a real substance may emit at a given temperature. Emissivity is a measure of how strongly a body radiates at a given wavelength; it ranges between zero and one for all real substances. Solar energy and gravitational energy are the fundamental sources of energy for the Earth's climate system. The Earth's axis of rotation tilts at a 23.5° away from the plane of rotation around the sun, that makes the poles point towards the sun during solstice time. This is the reason for the seasons. During solstice, the pole pointing to the sun and the surrounding area receive radiation during all 24 hours of the day while the opposite pole does not receive any solar energy. This has the potential for making the poles as warm or warmer than the equator in their respective summer time if it were not for the large albedo of the Polar Regions.The total daily radiation decreases from equator to the poles.Thus the earth near the equator is warmer than at the poles.

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