Solar energy can be divided into direct and indirect categories. Most energy sources on Earth are forms of indirect solar energy. Coal, oil and natural gas derive from ancient biological material which took its energy from the sun (via plant photosynthesis) millions of years ago. All the energy in wood and foodstuffs also comes from the sun. Movement of the wind (which causes waves at sea), and the evaporation of water to form rainfall which accumulates in rivers and lakes, are also powered by the sun. Therefore, hydroelectric power and wind and wave power are forms of indirect solar energy. Solar energy research and applications have been receiving increasing attention throughout the world as solar energy must play a much greater role in the energy mix in upcoming years. This book examines new research in this frontier field.