More efficient energy use, together with a greater reliance on renewable sources, could reduce or even eliminate our dependence on fossil fuels and nuclear energy.
One of the best ways to relieve environmental problems resulting from our energy use is to simply use less. There are many opportunities to conserve energy through greater efficiencies in lighting, space and water heating, insulation, better industrial motors and controls, and simply turning off appliances when not in use. Cogeneration of heat and electricity can double the efficiency of home or business energy use. Affordable systems provide stable, efficient backup energy for many applications.
Transportation is one of our biggest energy uses as well as a great opportunity for conservation. Raising the average mileage of U.S. automobiles and light trucks by 3 mpg would save consumers about $25 billion per year, reduce CO2 emissions by 140 tons annually, and save more oil every year than the maximum expected flow from the Arctic National Wildlife Refuge. Hybrid gasoline-electric vehicles have the highest efficiency rating and lowest emissions of any commercially available option.
Solar energy is a vast resource. People have used passive space heating for thousands of years. Active solar systems collect and store solar energy, and move it mechanically to where it's needed. One of the most promising solar technologies is photovoltaic cells that convert sunlight into electricity. Prices of these cells have come down dramatically, and they are now competitive with other electrical sources in many remote locations. A rooftop array could provide all the power you need without any moving parts. Storage of this energy can be a problem. For homes connected to a utility grid, the best solution may be to sell surplus energy to the utility and then buy back what's needed when the sun doesn't shine. For remote, large-scale solar arrays, the best way to transport energy may be to use it to generate hydrogen gas that can be shipped to markets via underground pipelines.
Fuel cells are devices that use electrochemical reactions and semipermeable membranes to generate an electrical current. Ideally, their only waste product is clean water. A number of different fuel cell designs are available and several are now available at competitive prices.
Biomass has long been used as a fuel for heat and light. In many places, this has led to deforestation and air pollution. Supplies are becoming scarce for the billions of people who depend on biomass. Firewood, dung, and charcoal are the main forms of biomass used in most places. More efficient stoves or digesters that convert dung to methane could help conserve energy.
Hydropower once produced most electricity in the world, but has largely been replaced by fossil fuels. Large hydropower resources remain untapped, but there are severe social and environmental problems associated with many large dam projects. Small-scale, run-of-the-river turbines may offer a better solution in some cases.
Wind power is the fastest growing energy source in the world and offers a huge potential for clean, renewable power. Wind farms already supply about 35,000 MW, and this capacity is expected to double in 5 years. Wind could easily supply all the electricity we need and free us from the economic, social, and environmental problems associated with fossil fuels and nuclear power.
Geothermal energy is a valuable resource in places like Iceland and New Zealand that have large geothermal features. Nearly everywhere, the constant temperature of the earth a few meters below the surface can provide a useful heat sink for heating or cooling. Tidal and wave energy and steep ocean temperature gradients also can be a valuable resource in some locations.
Although none of the renewable sources discussed in this chapter are likely to completely replace fossil fuels in the near future, a combination of alternative approaches could make a significant difference in our energy uses.
