Energy plays a vital role in our everyday lives. A country’s standard of living is con­sidered to be proportional to the energy consumption by the people of that country. Energy is one of the vital inputs to the socioeconomic development of any coun­try. The abundance of energy around us can be stored, converted, and amplified for our use in a variety of ways. Energy production has always been a concern for researchers as well as policymakers.

Global energy sources are classified into two groups, fossil and renewable. Pri­mary energy sources can be divided into nonrenewables and renewables. Nonre­newable energy sources include coal, petroleum, gas, gas hydrate, and fissile mate­rial, while renewable energy sources include biomass, hydro, geothermal, solar, and wind energy. The main fissile energy sources are uranium and thorium.

An energy source can also be classified according to its depletion rate. While biomass energy can be depleted, solar and wind energy are nondepletable. In real­ity the energy availability from nonrenewable sources is limited, and beyond that, the exploration, processing, and use of energy involve considerable impacts on the environment. Fossil fuels have been the prime sources of energy for the purpose of transportation, power generation, and agriculture, as well as in commercial, res­idential, and industrial activity for more than a century. The world’s energy re­quirements are currently satisfied by fossil fuels, which serve as the primary energy source.

Because of the increase in petroleum prices, especially after the oil crisis in 1973 and then the Gulf war in 1991, in addition to the geographically reduced availability of petroleum and more stringent governmental regulations on exhaust emissions, researchers have studied alternative fuels and alternative solutions.

Interestingly, renewable energy resources are more evenly distributed than fossil or nuclear resources. Today’s energy system is unsustainable because of equity is­sues as well as environmental, economic, and geopolitical concerns that will have implications far into the future. Hence, sustainable renewable energy sources such as biomass, hydro, wind, solar (both thermal and photovoltaic), geothermal, and ma­rine energy sources will play an important role in the world’s future energy supply.

Developing renewable sources of energy has become necessary due to the limited supply of fossil fuels. Global environmental concerns and decreasing resources of crude oil have prompted demand for alternative fuels. Global climate change is also the major environmental issue of our time. Global warming, the Kyoto Protocol, the emission of greenhouse gases, and the depletion of fossil fuels are the topics of environmental concern worldwide. Due to rapidly increasing energy requirements along with technological development around the world, research and development activities have perforce focused on new and renewable energy.

The major sources of alternative energy are biorenewables, hydro, solar, wind, geothermal, and other forms of energy, each of them having their own advantages and disadvantages, including political, economic, and practical issues. Renewable energy is a promising alternative solution because it is clean and environmentally safe. Sources of renewable energy also produce lower or negligible levels of green­house gases and other pollutants as compared with the fossil energy sources they replace.