Conversion of electromagnetic radiation from the sun into other forms of energy drives most processes on Earth. Plants generate chemical energy from sunlight during photosynthesis; the maximum efficiency of this process in terms of the energy recoverable from sugars versus the energy in the incident sunlight is about 2%, for sugarcane growing in the tropics.  Solar energy is also responsible for air movements that produce wind power and for the evaporation of water from Earth’s surface and its subsequent precipitation that are the bases of hydroelectric power. Solar power as a renewable energy source, however, usually refers to the conversion of electromagnetic energy into electricity directly through photovoltaic cells or indirectly through solar power plants. Additionally, it is also possible to transform sunlight into thermal (heat) energy.
Currently, less than 0.1% of the world’s energy derives from solar power. Use of this energy source is expanding rapidly, however, and by the middle of the century, solar power should meet nearly 1% of human requirements. Solar power has the advantage that some of the times and places with the highest peak electricity demands have some of the highest incident solar radiation. Disadvantages are that solar power is not available at night and is limited during cloudy weather conditions. It thus requires energy storage and/or a complementary power system.
 Taiz, L. and E. Zeiger (2006) Plant Physiology, 4th Edition. Sinauer Associates, Sunderland, MA.
This is an excerpt from the book Global Climate Change: Convergence of Disciplines by Dr. Arnold J. Bloom and taken from UCVerse of the University of California.
©2010 Sinauer Associates and UC Regents