Energy Efficiency through the Years

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The Sun has supplied the Earth with a never-ending source of energy since time began. As human life developed, the Sun remained the only energy source for human use unless a lightning strike happened to cause fire. The earliest humans probably ran from fires with other animals, but at some point in history they began to appreciate the heat that came from it. Fires caused by lightning strikes ran their course, burned out, and left humans again in darkness and cold, waiting for the next strike to rekindle the phenomenon. Perhaps humans learned to anticipate the next strike with the knowledge that light and warmth would return with it.

Humans’ ability to start fires on their own represented a tremendous step in civilization because people had harnessed energy for the first time. Early humans started fire by rubbing two pieces of flint together, and they kept the fire going with the easiest fuel at hand—wood. A constant and controlled fire enabled people to live a less nomadic life, and small settlements congregated around fires for heat, light, and cooking. Meanwhile, residents of these settlements used the energy supplied by flowing water in streams and rivers to carry away wastes.

After mastering fire and making use of water’s energy, Phoenician sailors 3,500 years ago learned to harness the wind to power their ships. Two thousand years later people combined waterpower and wind power to develop waterwheels and windmills to grind grain and run sawmills. As the centuries unfolded, oils that bubbled up from the sea, coal, and natural gas all served as fuels for heat and making light. Though these fuels dominate the industrialized world today, until about 150 years ago wood remained the main source of energy, as it still is in many underdeveloped parts of the world.

Throughout the 20th century and the early years of the 21st, oil, coal, and natural gas served as society’s leading sources of energy. But prolonged use of these fossil fuels has led to water and air pollution, destruction of habitat, and global warming. The 21st century will make greater use of six energy sources that avoid the use of fossil fuels: solar, wind, wave and tidal action, geothermal, hydrogen, and biomass. Of these energy sources, solar energy has provided the first breakthroughs in shifting a fossil fuel–based society to one that depends on nonfossil fuels. The California sustainability expert Geof Syphers said of the new solar communities on the rise, “This is really about lifestyle. We want to make sustainable living easy for people. We want to make it appealing.” Like fire, wind, and water harnessed by the ancients, steam engines and combustion in the Industrial Revolution, and modern nuclear energy, new energy sources are always appealing because they enable technology to take a major step forward.

Solar communities like that described by Syphers and other renewable energy sources have been supplying an increasing portion of total energy consumption in the United States, but these alternative energies still account for only 7 percent of total energy consumption. (Petroleum supplies 40 percent, natural gas supplies 23 percent, coal accounts for 22 percent, and nuclear energy supplies the remaining 8 percent of total U.S. energy consumption.)

The solar power industry divides its business into two segments: photovoltaic power, which converts sunlight to electricity, and thermal solar power, which turns sunlight into heat. Photovoltaic systems have grown rapidly in the industry for the past 10 to 15 years, and they make up a large portion of renewable energy’s 3 percent annual increase in growth. Thermal solar power rose for the 10 years up to 2006 as oil prices increased, then declined as oil prices declined. The outlook for the global solar industry continues to be encouraging, especially because many new solar technologies have been emerging for the purpose of increasing solar power’s efficiency and decreasing its cost.