This book will be of interest to those students who are interested in energy sources besides coal and nuclear. Oil and natural gas are obviously not suitable long term solutions to our energy requirements, and coal and nuclear energy face severe environmental obstacles. This means that the so-called alternative energy sources may well become primary sources over the next few decades. At the present time wind, solar photovoltaic, and solar thermal systems appear to be the main contenders for supplying a substantial fraction of the energy requirements of the United States and much of the remainder of the world as well.