The years since the 1973 spurt in oil prices have witnessed a growing interest in renewable energy sources. Increased attention has been paid to the development of technologies using new and renewable sources of energy, such as solar, wind, tidal, biomass, and hydropower. These sources are all the more important in developing countries with scarce conventional sources of energy like coal and oil. The new and renewable energy resource systems offer attractive prospects because they are pollution-free, unlimited, and often cheap. They can also help preserve ecosystems and retard degradation of the environment. Moreover, renewable energy resources can be developed extraordinarily rapidly, as shown by the experience with wood fuel in United States, small hydropower and biogas in the PRC, and energy crops in Brazil. In some countries technical advances have brought wind machines, solar cells, and biogas close to commercialization for heating and electricity generation. Thus far, over 3 million solar water heaters have been sold in Japan and over 5 million wood stoves in the United States.
