Energy Excursions

Why is the Water-Energy Nexus Important?

In the previous lesson, you explored how vital water is for human livelihood, and you learned about the risks that come with inadequate water supply to meet municipal needs. However, what we have not touched on is the importance of water for energy production and electricity generation. Without water, we would not be able to turn the lights on or drive a car. Energy also allows us to access safe drinking water from our own homes, affording us the means to treat and transport water long distances. Water and other natural resources used to power and energize  our world are all interconnected. This is the premise behind the “water-energy nexus.” 

Water-Energy Nexus

The water-energy nexus represents the point where two essential ingredients—water and energy—overlap. By running a tap or turning on the lights, you participate in the water-energy nexus, a relationship between the water needed to produce and consume energy and the energy required to produce and transport water supplies or treat and convey waste water.1Vasquez, S., Bare , R., Wilcox , A., & Dillingham , G. (n.d.). Texas Energy-Water Nexus. arcgis.com. https://www.arcgis.com/apps/Cascade/index.html?appid=2c271d2352974566825c44e456acfda8 You will hear people also speak of the energy-water nexus. The terms are interchangeable, and one is often used over the other to emphasize one element or the other.

Power Generation

Water is used to cool thermoelectric power plants that generate electricity through heat, from natural resources such as coal, natural gas, solar, geothermal, and nuclear.2Stillwell, A., King , C., Webber , M., Duncan , I., & Hardberger , A. (2009, April). Energy‐Water Nexus in Texas. http://texaslivingwaters.org/wp-content/uploads/2013/04/energy-and-water-in-tx09.pdf Water is also used at hydroelectric power plants, using running water at dams to turn turbines that generate power. For natural gas alone, a generous amount of water is needed in order to extract hydrocarbons at the surface, before it can be sent to nearby power plants for electricity generation. Highly saline “produced water,” also comes to the surface along with natural gas extraction, typically concentrated with harmful minerals and chemicals for human consumption or untreated disposal. This produced water must be managed. You will have an opportunity to learn more about produced water throughout the remainder of this course, an important issue facing Texans today. 

Power vs. Energy

In the field of energy generation and storage, there can be confusion between two related, but different, physical quantities: energy and power. Let’s briefly explore the difference.

Energy

Energy is the capacity to do work. Energy can be stored and measured in many forms. The unit of measurement in the International System of Units (SI) of energy is the joule, but for this discussion of energy we will use another measure: the watt-hour (Wh). A watt-hour (Wh) is equal to the energy of one watt steadily supplied to, or taken from, an electric circuit for one hour.

Although we often talk about energy consumption, energy is never really destroyed. It is just transferred from one form to another, doing work in the process. When we talk about energy consumption, we are really talking about the extraction of energy resources, such as coal, oil, and natural gas. Although energy measures the total quantity of work done, it doesn’t indicate how fast you can get the work done. 

Power

If you wanted to move a heavy sofa across your living room, two Olympic weight-lifting competitors could likely push it across the room much faster than two of your typical family members. Although both groups of people would exert the same energy, one group accomplishes the work much faster. We might even say that the weight-lifters are ‘more powerful’. Power is defined as the rate of producing or consuming energy.

Power, Energy and Electricity

The standard unit of electrical power is the watt, which is defined as a current of one ampere, pushed by a voltage of one volt

volts × amps = watts

The standard wall socket in the United States delivers 120 volts (=difference in electric potential). If you plug in a light bulb and find that a current of ½ amp (=unit of constant electrical current) is flowing through it, you know that the power of the bulb is:

120 volts × ½ amp = 60 watts [your typical 60-watt bulb]

How much energy is the bulb using? That depends on how long we leave it burning.

  • A 60-watt bulb burning for one hour will consume 60 watt-hours of energy.
  • Ten bulbs burning for ten hours would consume 10 x 60 x 10, or 6,000 watt-hours, which we can write as 6 kWh.
  • A thousand households all doing this would consume 6,000 kWh, which equals 6 megawatt-hours, or 6 MWh (because 1,000,000 watts = 1,000 kilowatts = 1 megawatt).3Lewis, R. (2015, February 2) The Great “Power Vs. Energy” Confusion. Clean Technica.

How Much Water?

In the United States, to generate a single kilowatt-hour of energy, roughly 19 gallons of water are needed.4Vasquez, S., Bare , R., Wilcox , A., & Dillingham , G. (n.d.). Texas Energy-Water Nexus. arcgis.com. https://www.arcgis.com/apps/Cascade/index.html?appid=2c271d2352974566825c44e456acfda8 That single kilowatt-hour can be used to run your air conditioner for ~ twenty minutes or keep a 100-kilowatt light bulb turned on for about ten hours. The nineteen gallons for powering the single lightbulb for ten hours was used to cool the thermoelectric power plant where that electricity was generated. Texas uses roughly 157,000 million gallons of water just for the purpose of cooling power plants annually.5Stillwell, A., King, C., Webber, M., Duncan, I., & Hardberger, A. (2009, April). Energy‐Water Nexus in Texas. http://texaslivingwaters.org/wp-content/uploads/2013/04/energy-and-water-in-tx09.pdf Drilling a single hydraulically fractured well, for the purpose of natural gas extraction, requires an average of 15 million gallons of water in the Texas Permian Basin.6Scanlon, B. R., Ikonnikova, S., Yang, Q., & Reedy, R. C. (2020). Will Water Issues Constrain Oil and Gas Production in the United States? Environmental Science & Technology, 54(6), 3510-3519. These wells are common in Texas, and actual water use in each hydraulic fracturing job depends on geology and a number of other factors.

How Much Energy?

Conversely, electricity is used for water too, such as extracting, treating, and transporting water for drinking, irrigation, etc. Moving water for these purposes often requires pumping at a point along the way, requiring electricity to power the pump—for example, groundwater pumping for irrigation use.7Tidwell, V. C., Moreland, B. D., & Zemlick, K. (2014, June 25). Geographic Footprint of Electricity Use for Water Services in the Western U.S. Environmental Science and Technology. https://www.osti.gov/servlets/purl/1182984 A study completed by the Sandia National Laboratories looked at the geographic footprint of electricity use for water services in the western region of the United States. The study region consisted of 17 states, and the results found that, “when considered in the context of state electricity use, most states expended about 5% or more on water services.8Tidwell, V. C., Moreland, B. D., & Zemlick, K. (2014, June 25). Geographic Footprint of Electricity Use for Water Services in the Western U.S. Environmental Science and Technology. https://www.osti.gov/servlets/purl/1182984

Collection, transportation, disposal, and treatment of wastewater requires electricity. While the electricity consumption for water collection and wastewater treatment is significantly lower than other areas of consumption, it is still important to understand the synergy between energy and water. University of Texas San Antonio researchers report that up to 1.2% of the state’s total electricity generation is consumed for the purpose of wastewater treatment.9Dimmick, I. (2020, January 31). Energy/Water Nexus: Policy, Partnerships to Lead the Way. San Antonio Report. https://sanantonioreport.org/energywater-nexus-policy-partnerships-to-lead-the-way/

The Water-Energy Nexus involves a number of complex sources, treatment techniques, and recovery methods for various applications as seen here.

Population growth, urban development, societal advancements, and economic growth all contribute to increasing demand for energy. The U.S. Energy Information Administration (EIA) projects that global energy demand will nearly double by 2050, heavily relying on increased demand for fossil fuels, renewable energy, and water for greater electricity generation.10U.S. Energy Information Administration. (n.d.). U.S. Energy Information Administration – EIA – Independent Statistics and Analysis. EIA projects nearly 50% increase in world energy usage by 2050, led by growth in Asia – Today in Energy – U.S. Energy Information Administration (EIA). https://www.eia.gov/todayinenergy/detail.php?id=41433 On a global scale, do you think we will have enough energy supply to meet this demand? 

Global energy consumption (2010 to 2050) by source measured in British thermal units (BTU). A BTU is a measurement of heat, 1 BTU = 1℉ increase per pound of water. 1 quadrillion = 1015

Texas alone offers a very diverse range of energy sources used for electricity production and consumption. According to the EIA, Texas is the leading state in both electricity production and consumption.11Accounts, T. C. of P. (n.d.). Texas’ Electricity Resources. https://comptroller.texas.gov/economy/fiscal-notes/2020/august/ercot.php. Power plants supply electricity to our homes using resources such as natural gas, nuclear, coal, wind, and solar. Many of these resources are derived from within the state (intrastate resources), but some are brought in from other states (for example, some coal with a higher BTU rating is brought in for mixing at coal-fired power plants in Texas). However, the underlying resource to allow all of this generation to occur is water. As Texas becomes vulnerable to landscape and climate change over time, our water will be impacted too. How will this affect our power supply? 

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