Fusion is the uniting of two or more small nuclei to form a larger one, a process accompanied by the release of energy. But the research of fusion is still a long way from being commercially available. The forms of hydrogen needed to fuel the fusion reactor are abundant and could provide energy for millions of years. Fusion reactions occur at extremely high temperatures, the emissions of highly energetic neutrons from the fusion reaction would weaken metals and necessitate their replacement every 5 years. Metal fatigue might lead to rupture of the vessel and the release of radioactive materials or highly reactive lithium.
Solar energy is abundant, but it provides only a fraction of our energy needs. Passive solar systems are the simplest and most cost-effective. Buildings are designed to capture sunlight energy and store it within thermal mass, walls and floors. The stored heat is gradually released into the structure. Active solar systems rely on collectors that absorb sunlight and convert it into heat, which is then transferred to water or air flowing through them. Pumps generally move water or air to a storage unit, where heat can be drawn off as needed. Photovoltaics are made of silicon or other materials that emit electrons when struck by sunlight, thus producing electricity.
Solar systems provide many advantages over conventional power sources: The fuel is free, nondepletable, and clean. When operating, systems produce no pollution and pay back energy invested in their production. The major limitations are that the source is intermittent, making it necessary to store energy overnight or on cloudy days.
Winds can be tapped to generate electricity. The potential of wind energy is enormous. Wind energy offers many of the advantages of direct solar energy : It’s clean and renewable, uses only a small amount of land, and is safe to operate. Moreover, wind technologies do not preclude other land uses - wind farms can be grazed and planted. The disadvantages to wind systems are that the wind does not blow all the time, so backup systems and storage are needed. The other weaknesses are the visual impact, the noise and impairing of television reception and telephone communications.
Biomass, a form of indirect solar energy, has some potential. Biomass is the organic matter contained in plants. Useful biomass includes wood, wood residues, crop wastes, industrial wastes, manure, and urban waste.