Alternative Energy, Overview

Alternative energy is derived from sources that are renewable, do not use up natural resources or harm the environment, or can replace fossil fuels such as coal, natural gas, and oil. Alternative energy is generated for electricity and heating from sources such as moving water, the sun, wind, geothermal energy from the earth's heat, biomass from vegetative or waste material, and biogas from anaerobic digestion. Given the looming energy crisis facing much of the world, alternative energy is destined to become an even more important area for science communicators.

Renewable energy sources can restore themselves over short periods of time and do not diminish. Green power, a subset of renewable energy, is clean technology that provides the highest environmental benefit. Green energy sources produce electricity with less impact on the environment than conventional power technologies and produce no anthropogenic greenhouse gas emissions. Brown energy sources, the nonrenewable or polluting energy sources, generally consume water; require mining, drilling, or extraction; or emit greenhouse gases and air pollution during combustion. Categorization of nuclear energy is debatable because it emits no greenhouse gases yet requires mining, extraction, and long-term radioactive waste storage.

Concerns about skyrocketing oil prices, world energy security, and impacts of greenhouse gases have driven growth in multiple renewable energy industries. By mid-2007, investments in more than 140 publicly traded renewable energy companies exceeded $100 billion. Key business initiatives include green tags, which represent proof that 1 megawatt-hour of electricity was generated from an eligible renewable energy resource, and the Leadership in Energy and Environmental Design (LEED) green building rating system.

The commercialization of renewable energy over the last century has involved three generations of technologies. First-generation technologies, already economically competitive, include biomass, hydroelectricity, and geothermal heat and power. Second-generation technologies, market ready and currently deployed, include solar heating, photovoltaics (PVs), and new forms of bioenergy. Third-generation technologies, which require continued research and development efforts to make significant contributions, include advanced biomass gasification, biorefinery technologies, solar thermal power stations, hot dry rock geo-thermal power, and ocean energy.

Net energy analysis, which indicates the efficiency of an energy technology, compares the amount of energy a technology delivers to society to the total energy required to find, extract, process, deliver, and otherwise upgrade that energy to a useful form. One net energy measure, energy return on investment, is the ratio of energy delivered to energy costs. Another measure, life cycle cost analysis, compares the electricity generated to the amount of energy needed in the manufacture, transport, construction, operation, and other stages of a technology's life cycle.