Energy Production and Water Usage
Water and Energy
Image Source: US Department of Energy
Although few are aware of the intricate relationship between water and energy, it is one that requires much attention. To attain energy, water must be used in various stages such as extraction, processing, and cooling just to name a few. Electricity production in the US is very inefficient; approximately twenty-five gallons of water are required for cooling of one kilowatt-hour of electricity (Glenn, J.C. & Gordon, T.J. 2006). Our inefficient use of energy and inefficient production of energy leads us to waste water. Thermoelectric energy alone accounted for an estimated 39% of groundwater withdrawals in 2000, almost as much as the 40% withdrawn for irrigation (US Department of Energy 2006). Thermoelectric power includes coal, oil, natural gas and nuclear energy--all which require water for production of energy. Power plants that do not use water are responsible for only one percent of the total energy production in the United States (Torcellini 2003). The need for water to produce energy presents a future problem when the already declining groundwater resources will no longer be enough to satisfy the public and agricultural sectors let alone the energy sector.
The world energy consumption in 2002 was approximately 411 Quadrillion BTU per year (NETL Department of Energy 2008). In 2003 the US energy consumption was estimated to be 98 Quadrillion BTU per year (NETL Department of Energy 2008); this highlights the large energy demands of the US. These numbers are predicted to increase 57% and 36% respectively by the year 2025 due to the trends in population growth (NETL Department of Energy 2008). The higher demand for energy will put a strain on the already stressed water supply. A current hot button issue has been the production of more energy nationally and reducing fossil fuel use through alternative energy, a step towards reducing carbon emissions. Although this is a seemingly environmentally friendly option it creates a higher demand for water when the alternative energy sources chosen are much more water intensive, such as biofuels. Biofuels, produced from corn or soy, require a large amount of water for growing and processing the corn and soy. According to the U.S. Department of Energy, 6,200 gallons of water are needed to grow about 27 kg of soy which produces only one gallon of biofuel. Similar to soy, corn requires 2,200 gallons of water to produce about 27 kg of corn that results in 2.7 to 4.7 gallons of biofuel. To lower the water intensity of energy, other forms of alternative energy must be considered.
Current sources of energy production are not as efficient as they could be. This is often due to the existence of outdated power plants that do not use water to its maximum efficiency. The majority of this water is used in the cooling process of these power plants. After burning fuels or running a nuclear process, steam is produced, the exhaust steam must be cooled and condensed into water. There are various ways this is accomplished, however, the majority use cooling water in some form or another. There are various other ways water is utilized within power plants; however, these uses are minimal compared to the amount of water used for cooling.
Another issue that must be addressed concerning energy and water is that of hydroelectric power, which provides about 19% of electric power in the US (9). Hydroelectric power is dependant on the amount of water in rivers stored behind dams. As the amount of water available depletes there will be a decrease in hydroelectric power produced.
Hydroelectric power is one of the most important alternative sources of energy utilized in the U.S. In 1995, it accounted for 95% of the total fuel fuel production from alternative energy in the country (Hydroelectric Power Water Use 2008). Currently, there are close to 75,00 dams in the U.S. The main benefits to using hydropower include the absence of fossil fuel burning or greenhouse gas emissions, relatively low maintenance costs, and reliability.
In order to harvest hydropower however, dams, structures that obstruct the natural flow of a river, must be built. There is also a need for reservoirs, or structures that store the captured water. Most water storage capacity in the U.S. was built from the 1940's - 1980's (Hydroelectric Power Water Use 2008). Since then, dam construction slowed. This is because the most appropriate locations for dams have already been exploited. These sites are deemed appropriate if the height and flow of the body of water are considerable, so as to harness significant potential energy. This energy is converted into mechanical energy through the movement of turbines, which in turn give way to an electric current that can be transmitted to consumers through power lines.
Although dams provide clean alternative energy, the actual structures have detrimental effects upon the surrounding ecosystems. Dams decrease river flow and create a stable temperature of the river water at
about 42 degrees Fahrenheit, much different from the natural rate of flow and temperature (Glen Canyon Dam 2000). The rivers' rate of flow and temperatures depend on the season and can have great variation throughout the year, the temperature can vary from 32 to 80 degrees Fahrenheit (Glen Canyon Dam 2000). Such constant conditions created by dams do not allow for reproduction of species that reproduce at very low or very high temperatures such as salmon (Glen Canyon Dam 2000). Over time these conditions have caused a decline in population of certain species, which in turn has decreased the biodiversity of river ecosystems, removing an integral section of the food chain. Another negative side effect created from the implementation of dams is that of trapped sediment along with other organic material (Glen Canyon Dam 2000). The sediment can no longer be spread throughout the river and therefore many animals and plants do not have the resources they naturally obtain from sediment and organic matter (Glen Canyon Dam 2000).
These changes in the environment often promote the growth, spread, and eventually invasion of exotic species. In the Glen Canyon Dam alone about 11% of the plants are nonnative (U.S. Department of the Interior 2007). These species pose a threat since they often use more resources than do native plants. For example, the Tamarisk, a nonnative tree in the Glen Canyon National Recreation Area, helps prevent erosion near the river bank. However, the tree also requires much more water than the native species of plants originally located there (U.S. Department of the Interior. Glen Canyon: Environmental Factors 2007)(Ligon, F.K.; Dietrich W.E.; Trush W.J. 1995). It is obvious that dams significantly alter the environment which causes the removal of dams to be difficult. Due to the large build up of sediment behind the dam when it is removed, the reintroduction of the sediment into the river can present a hazard to the ecology. In order to prevent these effects sediment is detected and removed before the dam is scheduled for demolition. It is difficult to detect all sediment and it is common that much sediment is reintroduced into the river all at once (Ligon, F.K.; Dietrich W.E.; Trush W.J. 1995). This is a problem that must be addressed when considering the removal of dams.
By 2020, 85% of the dams in the U.S. will be half a century old and in need of repairing. A report by the ASCE deemed 3,300 dams within the U.S. unsafe. The Association of State Dam Safety Officials estimate that total repairs across the U.S. will amount to $36.2 billion (Protecting Public Safety 2007). Repairing only the structures with most urgent conditions will cost an estimated $10.1 billion over the next 12 years. The Dam Rehabilitation and Repair Act was proposed in 2007 and is pending approval. If enacted, it would provide $200 million over five years to repair public dams. In certain cases, if repairing the dam is not cost-effective, it could be demolished. This can further disturb the surrounding ecosystem.
Cogeneration
Combined Heat and Power (CHP), or cogeneration, provides many benefits in terms of technology. By utilizing steam that would otherwise be wasted, it is possible to generate electricity, thus increasing efficiency and lowering energy costs as well as greenhouse gas emissions. In addition, cogeneration is a cost effective way to power desalination plants, thus producing usable water from energy that would otherwise be wasted. Cogeneration plants are not a new idea but present a possible solution for water use. In Southern California, desalination plants have been constructed in conjunction with cogeneration plants in order to produce potable water. Cogeneration-Desalination plants appear to be the most cost-effective option for desalinating water because they use energy that would otherwise be wasted. This provides a way to produce more fresh water and use fuel more efficiently, thus decreasing the amount of water needed to produce more fuel.
The one example of this is the cogeneration plant that was built in Carlsbad, CA which produced 66,378 kg/h exhaust flue gas at 948°F (509°C). This gas is ducted to a heat recovery steam generator. The steam output is 10,160 kg/h at 1.05 kg/cm cubed which is supplied to the desalination unit. The operation of the desalination system requires 9185 kg/h. The cost of water produced from this desalination plant is $1.6/cubic meter (Tadros, 1995).
The problem that must be addressed is how to implement the use of cogeneration in the United States, especially in the southwest. Policies designed in the early 1900's to regulate electricity are no longer relevant with new problems such as global warming and water shortages as well as new technologies that make producing energy on a smaller scale less expensive. While other types of plants that support centralized energy are subsidized, high start up costs make cogeneration plants less attractive and/or feasible (Casten, 2007). Also, in several states, only federal electric utilities can sell energy, so there are not many incentives for companies to utilize cogeneration. Likewise there are no subsidies or incentives for an investment in cogeneration, which can be costly. One suggestion to “level the playing field” is a 10-percent investment credit for qualified CHP and recycled energy systems up to 50 MW to make CHP more economically feasible (Casten, 2007). CHP in the long run is more economic because it saves investments in fuel and therefore the one-time investment would pay for itself over time.
One case study examines the barriers of a Cogenerating Gas Turbine Project in Texas. It utilizes Natural Gas, producing 21MW. Its major barriers are discount tariffs. The utility would lose revenue in the building of this cogeneration plant, so they offered confidential seven to ten year discount rate contracts, making it less affordable to use the cogeneration plant despite reductions in carbon dioxide and nitrogen oxides emissions, higher power reliability, and on-site generation of electricity and steam. The industrial customer payed one million dollars to allow the cogeneration plant to be payed, which may not be feasible in most places (Alderfer et al. 2000, p. 53).
Currently, the US is significantly less efficient than European Countries and Japan in using energy to produce electricity. More efficient countries can produce about 50% more electricity than the US using the same amount of energy resources (De Grauwe, 2007).This in turn uses more water to mine, refine among other things so reducing the use of oil can lead to less water use. Many countries in Europe are more efficient due to their use of cogeneration. One case study illustrates Denmark's transition to cogeneration. The transition took less than 2 decades; subsidies were required to overcome initial investments. Utilities earn more money the more electricity they sell; therefore there is no incentive to conserve so there need to be financial incentives to reduce the amount of energy used (Romm 2008). Strong government support and a restructuring of the energy utilities were necessary, as would be in the United States. Education would also be an important aspect because training, conferences, workshops and short courses would help spread the required knowledge and experience. With this idea, it is necessary to raise public awareness on the benefits of cogeneration so that it can be implemented. One note of caution though, in Denmark, low electricity prices but high gas prices arose as a result, but renewed networking is overcoming these effects (Klimstra). To give an idea of how much water could possibly be saved using cogeneration, thermoelectric power plants represent 39% of the water withdrawals in the United States, approximately 25 gallons per kWh (Pater, 2006). These plants generate 89% of the United States' energy. If existing cogeneration plants are about 66% (Guascor, 2006) efficient, and most coal plants are around 31% efficient (Schilling, 2005), then the United States could possible save 289 trillion gallons of water per year.
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