In celebration of the 30th Anniversary of NASA Tech Briefs, our features in 2006 highlight a different technology category each month, tracing the past 30 years of the technology, and continuing with a glimpse into the future of where the technology is headed. Along the way, we include insights from industry leaders on the past, present, and future of each technology. This month, we take a look at the past 30 years of Power & Energy Technology.

One of the most debated issues today is power and energy, and the available resources for both. According to the U.S. Department of Energy (DOE), U.S. energy consumption is projected to increase by about 32 percent by 2020, and our nation’s dependence on foreign sources of oil is at an all-time high — and is expected to grow.

This wind turbine electrical power generation facility on San Clemente Island, CA, features turbines that begin producing power at 9 miles per hour (mph), and continue producing power up to 56 mph. (Warren Gretz, DOE/NREL)

The Energy Information Administration (EIA), which provides official energy statistics from the U.S. Government, predicts that carbon dioxide emissions from energy use will increase from 5.9 million metric tons (in 2004) to 7.6 million metric tons in 2025, an average annual increase of 1.2% per year. Renewable energy sources that provide alternatives to oil, coal, and other fossil fuels can significantly reduce or eliminate carbon dioxide emissions into the environment. These renewable sources include solar, wind, geothermal, and hydropower energy.

Over the past 30 years, the U.S. has significantly improved its energy efficiency through the use of renewable energy sources, but according to the DOE, even with considerable conservation, the U.S. will need more energy supplies of all types.

Solar Energy

Technologies to capture, store, and deploy solar energy have been around for decades, and although the use of these technologies continues to increase, widespread implementation has not happened, despite the proven advantages of energy efficiency, lower cost, and environmental friendliness associated with solar energy. Today, solar cells of various sizes are used to power everything from handheld calculators and watches, to road signs, homes, and commercial buildings. Harnessing the power of the sun is accomplished by technologies such as photovoltaic cells, concentrating solar power, and active and passive solar collection.

Photovoltaic (PV) cells — or solar cells — are electricity-producing devices made of semiconductor materials such as silicon, and convert sunlight directly into electricity. The PV cells are connected together to form modules that, in turn, are connected to form solar arrays. The size of an array depends on how much sunlight is available in a location and the amount of electricity demand.

Concentrating solar power (CSP) technology uses reflective materials to concentrate the sun’s heat energy, which drives a generator to produce electricity. CSP technologies include trough systems, power towers, and dishengine systems, which feature a large reflective dish that collects energy from the sun, concentrating it on a small area. A thermal receiver absorbs the concentrated beam of solar energy, converts it to heat, and transfers the heat to the generator.

Active and passive solar collectors also absorb the sun’s heat energy, but the heat is used directly for space heating or water heating in homes and industrial facilities. Passive solar collectors take advantage of warmth from the sun through design features such as south-facing windows, and wall and floor materials that absorb warmth during the day, and release it at night. Active systems collect and absorb solar radiation, and are combined with fans and pumps to transfer the collected heat. They usually incorporate an energy- storage system that provides heat when the sun is not shining.

This grid-tied, concentrator photovoltaic (CPV) system supplies electricity to the Arizona Public Service grid. Dual-axis tracking modules use small mirrors to focus sunlight on multijunction cells. Individual fins extend outward to cool each cell. (Arizona Public Service/DOE/NREL)

Geothermal Energy

While solar energy harnesses heat from the sun, geothermal energy captures heat from the Earth. Clean and sustainable, geothermal energy sources range from shallow ground to hot rock and water found miles beneath the Earth’s surface. Wells, similar to oil wells, are drilled into underground reservoirs to tap steam and extremely hot water that is brought to the surface and used to heat buildings, grow plants in greenhouses, and drive turbines for electricity generation. Currently, most geothermal reservoirs are located in the western United States, Alaska, and Hawaii.

In most locations, the upper ten feet of the Earth’s surface maintains a nearly constant temperature between 50 and 60°F. A geothermal heat pump with pipes buried in the shallow ground near a building can heat and cool the building all year. In winter, heat from the warmer ground goes through a heat exchanger into the building; in the summer, hot air from the house is pulled through the heat exchanger into the cooler ground. That removed heat can be used as a no-cost energy to heat water. This technology is also used by municipalities to melt snow and ice on sidewalks.


Hydropower is the fourth-largest source of U.S. electricity generation, producing nearly 10 percent of the country’s electricity, according to the DOE. In areas such as the Northwest and New York, hydropower makes an even larger contribution to electricity generation. Hydropower (or hydroelectric power) facilities generate enough power to supply 28 million households with electricity — the equivalent of nearly 500 million barrels of oil.

Hydropower is basically flowing water that creates energy, which is captured and turned into electricity. The most common type of hydropower plant uses a dam on a river to store water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, and activating a generator that produces electricity (see figure). But, surprisingly, only 2 percent of the dams in the U.S. produce electricity. According to the DOE, by adding hydroelectric projects to those dams where it is financially and environmentally feasible, the U.S. could increase its hydropower capacity by 17,000 MW.

The National Hydropower Association (NHA) estimates that today’s hydropower turbines can convert more than 90% of available energy into electricity, making them more efficient than any other form of generation.

The most common form of hydropower uses a dam to store water, which is released to meet

Wind Power

When the price of oil skyrocketed in the 1970s, so did interest in wind turbine generators. Wind turbine technology development in the 1980s introduced new ways of converting wind energy into power. These technologies were used to build “wind farms” or wind power plants — groups of turbines that feed electricity into the utility grid.

Wind turbines capture the wind’s energy with two or three propeller-like blades, which are mounted on a rotor, to generate electricity. The turbines sit on towers, taking advantage of the stronger and less turbulent wind at 100 feet or more above ground. Wind turbines can be used as standalone systems, or they can be connected to a utility power grid. Standalone turbines typically are used for water pumping, but farmers in windy areas also use them to generate electricity. Wind farms are used as utility-scale sources of wind energy.

Wind energy continues to be one of the world’s fastest-growing energy technologies. In 2005, the U.S. wind energy industry installed more than 2,300 megawatts of new wind energy capacity — or more than $3 billion worth of new generating equipment — in 22 states.

The United States has many areas with abundant winds, particularly in California, the Midwest, and the Great Plains. Researchers estimate that 50% of the U.S. has enough wind resources for small turbine development, and 60% of U.S. homes are located in those wind resource areas. Areas with good wind resources have the potential to supply up to 20% of the electricity consumption of the U.S.