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Upper reservoir of Raccoon Mountain pumped storage plant. Image courtesy TVA.

Dead Center in the Energy Debate

The world's energy needs are growing. Projections from the World Energy Council indicate that energy usage will double by 2050. Predictions from Shell triple this usage.

Much of the energy in the United States is generated by fossil fuels. Their finite supply and environmental issues limit our ability to rely on them to meet future demand. Attention has been given to nuclear power as a substitute to fossil fuels, but this is a political hot topic for many people.

Fossil fuels also use between 14.2 and 28.4 liters of water for each kilowatt hour generated while nuclear uses between 31 and 74.9 liters for each kwh generated.

But other sources of energy also utilize water.

Energy companies drill for natural gas, deep into the rock layers in a process called "fracking.” This process uses water, sand, and chemicals at high pressure to fracture rocks and release the gas. The fracking solution is extracted and has to be cleaned. The process uses fresh water and increases the need for treatment. Plus, this method has generated concern about groundwater contamination.

An article in Scientific American suggests that wind, water, and solar can provide for our future needs. In this article, the authors group hydroelectric, wave, and geothermal energy under the category of water. Hydroelectric systems, for the most part, remove energy from water as it is flowing in a river. Thus it does not consume water. Wave power comes from kinetic energy and does not remove water from the supply. Similarly, geothermal power can be a closed loop, resulting in minimal long-term impact on water use. The authors also talk about wind and solar. These sources have limits because wind and sunlight are not always available. There are ways to overcome this drawback.

The article does not discuss two other techniques: splitting water molecules and elevated storage plants. In the former, energy is used to split water molecules into hydrogen and oxygen. The molecules are then recombined in a fuel cell to generate electricity when it is needed. Since the water can be repeatedly split and recombined, this will have a minimal impact on longer term water use. With the latter, wind and solar energy is utilized to pump water to a high-elevation storage facility. The water runs downhill through turbines to generate power when needed. Elevated or pumped storage plants, like Raccoon Mountain in Tennessee, remove water from a river or other source, reducing available water for utilities. Of course, over time the storage facility will return most of that water (minus evaporation) to the river, but this may not be convenient for the water utility. Furthermore, drought conditions can place competing demands between the storage facility and downstream water utilities. Currently, these types of facilities are somewhat rare so their impact on water availability is small. However, if wind and solar power are used in this way, then many pump storage facilities will need to be built. This will then have a cumulative impact on water usage.

Many wastewater facilities use their solids digesters for methane gas to generate electricity. A newer method, an electrogenic bioreactor, extracts electrons directly from bacteria in wastewater, providing energy that can be channeled out of the reactor. The process also produces hydrogen gas, which can be combined with oxygen in a fuel cell to generate more electricity. With 1.1 trillion kwhs of energy in wastewater, this provides a significant new source of energy.

As we can see, these technologies will push the water and wastewater field dead center into debate over the future of power generation. Thus, we will once again become the center of attention.

Posted by Grant Van Hemert, P.E., Schneider Electric Water Wastewater Competency Center on Mar 02, 2011