The amount of energy the United States consumes increases every year and this growth in energy consumption outpaces energy production. To fill this gap, the U.S. imports 35% of its energy. More importantly, the U.S. imports over 60% of its total oil consumption. Added to this, 70% of this energy is from non-renewable sources.

Renewable energy sources have proven to be energy efficient, cost effective, and environmentally friendly. The military is adopting many types of renewable energy sources and the results are impressive.

Renewable energy consumption by major sources, including biomass sources of wood, biofuels such as ethanol and biodiesel, and waste sources such as landfills and agricultural bioproducts.

Green energy includes renewable energy sources, and provides a means to reduce reliance on imports, wean the U.S. off oil, and bring costs under control.

There are several viable renewable energy sources: biomass, hydropower, geothermal, wind, solar, and nuclear. Geography limits some renewable energy sources, like hydropower, while others, like nuclear power, are limited by the length of time it takes to build and certify the power plant. Nevertheless, all renewable energy sources have potential for growth.

The Federal Government has taken steps to encourage and regulate green energy through various laws and initiatives. The National Energy Policy (NEP), published in 2001, provides the basis for the current legal and regulatory framework surrounding green energy. In compliance with legislative mandates, the military is expanding its implementation of green energy.

Renewable Energy Sources

Biomass is man’s oldest source of fuel. Today, power is generated from a variety of biomass sources. In addition to wood, biomass sources include landfill gases and energy crops such as corn and grasses. Still, 75% of current biomass production comes from wood. In 2005, renewable energy sources contributed 7% of the nation’s energy and biomass accounted for 48% of the renewable energy consumed in the U.S. (not including nuclear power).

Biomass resources are primarily located in the eastern half of the country and on the West Coast. Today, the U.S. only produces 190 million dry tons of biomass. The use of biomass has the potential to reduce greenhouse emissions from between 52 to 86%. An added benefit of biomass crops is they create a carbon sink. Plants require carbon dioxide to grow and the physical production of biomass crops directly reduces the amount of greenhouse gases. Energy produced from biomass is as inexpensive as six cents per kilowatt-hour and is in line with other renewable sources of energy.

While biomass is the oldest form of renewable energy, hydropower is the most successful. Hydropower uses water to create electricity, usually through a dam. Water flow, regulated by the dam, turns turbines, which turn generators and create electricity. With a dam, water flow is available and controlled, producing a high, consistent flow of electricity. As an example, the Hoover Dam produces on average 4.4 billion kilowatt hours per year — enough to serve 1.3 million people. Overall, hydropower produces 42% of the nation’s renewable energy and is the second leading producer — recently surpassed by biomass.

Geothermal technologies use steam and hot water generated from the earth to produce power. Steam or hot water extracted from the ground turns a turbine linked to a generator that produces electricity. Geothermal power plants produce energy efficiently for five cents per kilowatt-hour and are almost emission- free.

A typical hydropower system uses water to create electricity, usually through a dam. Water flow, regulated by the dam, turns turbines, which turn generators and create electricity. With a dam, waterflow is available and controlled, producing a high, consistent flow of electricity.

Wind power is a growing source of alternative energy. In 2005, the U.S. installed more new wind farms than any other country in the world. Wind power is renewable, creates no emissions and requires no sources of oil. Wind-generated energy is also inexpensive, costing between four and six cents per kilowatthour. Today, the U.S. generates over 11,600 megawatts from wind farms — enough electricity to power over 2.3 million households.

Wind power is actually a form of solar energy, since the Sun creates wind. The wind generates electricity by turning a blade that connects to a shaft that turns a generator. The size of the windmill determines the potential power generation, which can range anywhere from 100 kilowatts to several megawatts. Multiply a single windmill output by the number of windmills in a wind farm and the power generation is significant. Because the wind must blow to generate power, creating a stable supply of electricity is a challenge for wind power. Batteries can store the energy generated or a complementary source of power can augment the system.

The Sun provides renewable energy in several manners. The two most mature and common forms of solar power include photovoltaics, a semiconductor material that converts sunlight directly to electricity and solar heating, where the Sun’s energy directly heats water or building interiors. Two areas of ongoing solar research include concentrating solar power (CSP) and solar lighting. CSP is the process where the Sun’s heat energy is concentrated through mirrors and drives a generator that produces electricity.

Solar heating provides heat to both water and space. For water heating, the Sun heats water or a heat transferring liquid. The water is then stored in a collection tank (or the heat transferring liquid heats the water). Conventional heating systems provide any additional heat. For heat or air conditioning, the air routes through a solar collector and the collector adds or removes heat depending on the season.

Seventeen percent of renewable energy electricity generation is from geothermal activities. This map indicates the potential U.S. resources. The DOE considers geothermal resources above 200°C (shown in red) as excellent sites, and those with 150°C (orange) as having good potential.

Nuclear power is another alternative energy source. It is renewable and domestically produced. In a nuclear power plant, the reactor core heats the water and produces steam, which turns a turbine generator and produces electricity. This process is extremely effective and efficient; nuclear reactors currently generate about 8% of the U.S. electricity usage. The greatest challenge of nuclear power is the disposal of radioactive waste.

Potential Battlefield Uses

The military operates in two distinct situations — home and deployed. When considering green energy for military uses, it is important to understand the difference. While a military unit is at its home base, the unit is primarily engaged in training operations. Additionally, the military can acquire energy from a stable source. In a deployed environment, the military cannot rely on a stable energy source or a stable energy distribution network.

The green energy application must meet, or even exceed, mission requirements. Next, the green energy application must improve the environment. Renewable energy sources must provide the same amount and duration of power as its counterparts, and must not put the soldier in more danger or require additional logistics support.

Green energy for the battlefield has the potential to reduce the logistics tail and improve mission effectiveness. Several renewable energy sources immediately rule themselves out for potential use on the battlefield. These sources require very large fixed structures, long lead times to build, and often use hazardous materials. Hydropower requires the battlefield be close to a large water source. Geothermal sources also require time to drill and place pipes into the earth. Wind power is extremely location specific. Nuclear power requires even more time to build the plant, not to mention the energy source is inherently dangerous, especially in a war zones. On the other hand, one shining potential candidate for battlefield use is solar power. Biomass also shows potential.

Green energy has great potential to benefit the soldier on the battlefield. Up to this point, the acquisition and application of this technology has been haphazard. In some instances, technologies already exist and are being applied. Green energy offers a solution to the energy crisis, improving national security, reducing emissions, and controlling costs. Furthermore, green energy for the battlefield potentially improves the effectiveness of the individual soldier and the U.S. military as a whole.

This article was written by Major Stephanie D. Halcrow of the U.S. Air Force. For more information, click here .

NASA Tech Briefs Magazine

This article first appeared in the July, 2008 issue of NASA Tech Briefs Magazine.

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