The energy alternatives available to energy policy-makers are too numerous to consider in detail.
Below is a list of the major alternatives, notes on each, and a summary assessment.
1) Conservation or energy efficiency, while technically not a source of energy, is an alternative that avoids the increased use of other sources.
a. Forms: more efficient consumption of energy, for example, weatherization and energy saving industrial techniques; more efficient production and distribution of energy; consumption restraints, for example, higher efficiency standards for appliances and motor vehicles.
b. Strengths: the costs and risk are low; encourages sufficiency and appropriateness; flexibility is high; easily reversed.
c. Weaknesses: constraints on consumption could reduce employment; potential is limited in the long range.
d. Assessment: this option offers savings without a significant change in the quality of life. Conservation should be a top social priority and vigorously promoted by incentive programs and public and private investment.
2) Solar energy was the principle form of energy for centuries and now offers promise as a sustainable and appropriate fuel.
a. Forms: thermal applications, such as, the heating and cooling of buildings; biomass, such as, the burning of wood and alcohol from food grain; solar electric, such as, power towers, photovoltaics, wind, ocean thermal, and hydroelectric power.
b. Strengths: renewable and low risk; a variety of scales sets a standard for appropriateness; efficiency, as measured by fitting energy source to end use, and flexibility are high.
c. Weaknesses: many forms are not yet cost competitive, although this is improving; infrastructure is lacking; storage of energy is a problem; large tracts of land are needed for power towers; hydroelectric impacts species and ecosystems.
d. Assessment: along with conservation solar energy should be a priority for research and development and for public and private investment. Costs of most solar forms are becoming more competitive as technical innovation and economies of scale reduce to the price relative to other sources. Wind offers perhaps the most potential and is already cost competitive. Hydroelectric is inexpensive and does not cause air pollution but these benefits need to be measured against the costs it imposes on species and ecosystems.
3) Oil and natural gas while flexible, suffer from a fatal flaw as energy sources for the future. They are not renewable and supplies will become increasingly scarce.
a. Forms: oil, gasoline, various kinds of natural gas, oil shale, tar sands.
b. Strengths: flexibility; infrastructure in place; variety of end uses and scales; easily understood; low cost; gas is relatively clean burning; abundant if shale and tar sand resources are exploited.
c. Weaknesses: nonrenewable; cost will rise as oil becomes more scarce; air pollution; CO2 by-product causes global warming; dependency; geopolitical distribution is poor.
d. Assessment: Nonrenewability and contribution to global warming are the greatest weaknesses. Although exploitation of shale and tar sands would extend the supply of oil, to exploit these sources in Canada and the U.S. would be expensive, cause ecological damage, and be aesthetically disastrous. Efforts should be increased to reduce consumption of these very flexible fuels.
4) Nuclear is the most controversial and least understood of the alternatives.
a. Forms: conventional reactors (fission); breeder reactor (fission); fusion.
b. Strengths: Supplies would be long lasting with the breeder reactor and fusion; safety record is good; does not contribute to global warming; no air pollution.
c. Weaknesses: the possibility of major accidents and radioactive contamination; long term storage of radioactive wastes; vulnerability to terrorist attack; nuclear weapons proliferation; breeder reactor and fusion not developed and may never be developed; high cost; inappropriate in terms of scale, centralization, technical complexity, and participation; political sensitivity.
d. Assessment: the dilemmas posed by a major commitment to nuclear energy remain formidable. On the one hand the provision of basic needs, the availability of long lasting supplies, and the problems with the burning of coal make this energy system difficult to rule out. On the other hand are the factors that make this alternative incongruent with the ethic of ecological justice. Among these are the risks, real and perceived; the cost of making it reasonably safe and environmentally sound; the effects on future social institutions and values; the tying up of large amounts of capital; the threat of terrorist attack; and the constant threat of nuclear weapons proliferation.
5) Coal remains the chief source of energy to generate electrical power. Its attractiveness increases as nuclear costs rise and perceived dangers increase.
a. Forms: the direct combustion of coal; synthetic fuels.
b. Strengths: coal is in plentiful supply in the industrialized nations; costs are competitive; can be used in a number of appropriate scale burnings.
c. Weaknesses: the risk associated with the burning of coal, including mine accidents, black lung disease, air and water pollution, acid rain, land degradation with strip mining, global warming, and respiratory ailments; low on aesthetics; transportation is costly and cumbersome; resources are scarce in poor countries.
d. Assessment: coal and nuclear are often mentioned as the major fuels for a transition to sustainable futures. Neither is very attractive, although the provision of basic needs may dictate reliance on one or the other. It is a "messy" fuel even as millions are spent on cleaner power plants.
6) Hydrogen will probably be the primary source of fuel for motor vehicles in the long term. Development has begun but technological improvements and mass production are well in the future.1
a. Forms: using solar, wind, or other renewable sources of energy, hydrogen is separated from oxygen in water then recombined in a fuel cell to produce electricity, the by-product being steam. Also hydrogen can be produced from the reformation of natural gas.
b. Strengths: pollution free, long lasting, and a plentiful source.
c. Weaknesses: large quantities of energy are needed to separate hydrogen from oxygen; highly flammable; no infrastructure in place; not yet cost competitive; current technologies require use of platinum which is a rare metal; only in initial stages of development.
d. Assessment: Hydrogen as the primary source of fuel for motor vehicles is decades off, although the technology is developed enough to make prospects good. Since hydrogen is the most abundant element, supply will be no problem.
 Seth Dunn. "Decarbonizing the Energy Economy," in The Worldwatch Institute, State of the World 2001. New York: W.W. Norton & Company, pp. 84, 96 ff.; The Sierra Club. Sierra, July/August 2002, Vol. 87, no. 4, p. 32.