Alternative Fuels

In the United States, national security, environmental, and economic concerns drive an interest in alternatives to petroleum that are domestic, low-carbon, and sustainable. Fuels that receive significant policy support include corn-based ethanol, natural gas, methanol, or electricity. However, many alternative fuels are more water-intensive than conventional petroleum-based fuels such as gasoline and diesel.1C. W. King and M. E. Webber, “Water Intensity of Transportation,” Environmental Science and Technology 42 (2008), 7866–7872.  For example, more electric vehicles on roads indirectly increases water use for power plant cooling. In 2005, petroleum-based gasoline required about 950 billion liters (250 billion gallons) of water to produce 530 billion liters (140 billion gallons) of fuel. Switching to ethanol from corn—with just 15% of the crop requiring irrigation—requires over 3.75 trillion liters (1 trillion gallons) of water per year within two decades.2C. W. King, M. E. Webber, and I. J. Duncan, “The Water Needs for LDV Transportation in the United States,” Energy Policy 38 (2010), 1157–1167.  Just a small irrigated fraction of the biofuels mandate will increase water consumption for light-duty transportation by a factor of four or more.

Adding expectations for other fuels such as cellulosic ethanol, coal-to-liquids, and other sources, requires another 3.75 trillion liters (1 trillion gallons) of water. Because annual water consumption in the United States is about 136 trillion liters (36 trillion gallons), an additional 7.5 trillion liters (2 trillion gallons) or more per year significantly increases water consumption. The Environmental Protection Agency’s Renewable Fuel Standard program and incentives for electric vehicles are examples of energy policymaking that ignores water impacts.

Image Credits: Alf Ribeiro/Shutterstock.com.

Feedback Loops

Feedback that amplifies or increases change is known as positive feedback. It leads to exponential deviation away from equilibrium. Unfortunately, the interactions between the energy sector, the hydrologic cycle, and climate change form a positive feedback loop. Energy consumption causes climate change, which affects the hydrologic cycle, triggering investments in energy-intensive water solutions, exacerbating climate change, and so forth. As another example, the higher temperatures of a warming planet reduce the global photosynthetic efficiency and require more energy-intensive irrigation, fertilizing, and harvesting to overcome impacts on efficiency.

Climate change might reduce the amount of energy produced by emissions-free hydropower. California, Oregon, and Washington contribute more than half of the hydroelectric energy generated in the United States. This region is also particularly sensitive to climate change because changes to snowmelt and precipitation patterns impact water availability. For a large basin such as that of the Colorado River, small changes in precipitation cause major droughts, which can dramatically reduce power output from a series of hydroelectric dams. Every 1% decrease in precipitation causes a 2% to 3% drop in streamflow, and every 1% decrease in streamflow in the Colorado River Basin yields a 3% drop in power generation.1U.S. National Oceanic and Atmospheric Administration, Global Climate Change Impacts in the United States (New York: Cambridge University Press, 2009).  

Boulder City, Hoover Dam (formerly Boulder dam) and Lake Mead is in the Black Canyon of the Colorado River on the border of Arizona and Nevada, it was build between 1931 and 1939.

At the same time, many millions of people depend on the basin’s water for irrigation, drinking, commercial activity, industrial processes, and power production. Higher temperatures increase rates of evaporation, reducing water stored in reservoirs. The reduced hydropower in California during the multiyear drought from 2011 to 2015 increased consumers’ electric costs. As hydropower dropped from 18% to 12% of the fuel mix, utilities spent extra money purchasing natural gas to make up the difference.2Felicity Barringer, “Troubling Interdependency of Water and Power,” New York Times, April 22, 2015. Alternatively, higher snowmelt from rising temperatures could initially increase hydroelectric generation.3B. Boehlert, et al., “Climate change impacts and greenhouse gas mitigation effects on U.S. hydropower generation,” Environmental Research Letters 7 (2015), 1326-1338, accessed August 30, 2016, doi: 10.1002/2014MS000400.

Hydroelectric generation in California dropped more than 65% during the multi-year drought from 2011 to 2015.

Image Credits: James Mattil/Shutterstock.com; spiritofamerica/stock.adobe.com.

Climate Change

Climate change exacerbates strains at the energy-water nexus because climate change manifests in changes to the hydrologic cycle. Elevated ocean levels, elevated ocean temperatures, more frequent and intensive flooding, more frequent and intensive droughts, and distorted snowmelt patterns are different effects of climate change.

Elevated ocean levels threaten 40% of the world’s population, which lives within 100 kilometers (62 miles) of the coastline. Higher ocean levels raise the risk for erosion of coastlines, submersion of valuable properties and infrastructure, and saltwater intrusion into freshwater aquifers. Elevated ocean temperatures impact systems as diverse as fisheries, aquaculture, and power plant cooling. More frequent and intensive flooding creates more cumulative damage, and greater intensity means individual floods cause more damage more suddenly. Responding to rising ocean levels will cost a significant amount of money. Possible solutions include moving buildings out of expanded floodplains or shoring up levees, protecting land that can absorb the water, or building reservoirs that are intended to capture excess water during flooding.

The Coast Guard responds to search and rescue requests in response to Hurricane Harvey in the Beaumont, Texas, area Aug. 30, 2017.

Alternatively, more frequent and intensive droughts accompany increased flooding. Mitigating droughts requires expensive infrastructure for storing water, long-haul pipelines to move water farther, and more powerful pumps for raising water from deeper wells as surface water sources dry up and overextraction from nonrenewable groundwater sources increases.

Distorted snowmelt patterns are another consequence of climate change. Snowpack that is thinner and melts earlier affects the rhythms of water availability, irrigation, crop rotation, and other historical patterns. Of the world’s 7 billion people, approximately 1.5 billion rely on snowmelt from the Himalayas alone. As population grows, those living on snowmelt from the Rockies, Andes, and other major mountain ranges will grow. Villages around Mount Kilimanjaro in eastern Africa are particularly vulnerable. On May 29, 2015, government officials reported zero snowpack in California, placing at risk the source of water for tens of millions of people and the majority of U.S. fruit, nut, and vegetable growth.1Kai Ryssdal, “California’s snowpack has run out,” Marketplace, May 29, 2015. Managing these shifting patterns might spawn impactful, expensive, and energy-intensive investments in large-scale water storage infrastructure such as reservoirs to hold the water over a greater span of time.

These images captured by NASA’s Aqua satellite show the difference between snow cover in 2010—the last year with average winter snowfall in the region—and 2015 across the Sierra Nevada Mountains. (Swipe sideways to compare.)

These impacts can be mitigated through investing in new infrastructure, changing industrial and agricultural mixes of the impacted societies, or by moving entire societies to other locations with better odds to survive significant climatic shifts. All of these options have their drawbacks and some of those choices, because of their energy requirements, might exacerbate the situation in the long-term. At the same time, the negative effects often fall hardest on the poorest societies. For example, emissions from the richest members of the globe will cause expensive problems that the poorest will bear. The inequality in the emissions (mostly by the rich) and the suffering (mostly by the poor) presents a key quandary for the world to resolve.

Image Credits: cowardlion/Shutterstock.com; Brandon Giles/U.S. Coast Guard.

Water Temperature

Thermal pollution standards from the U.S. Clean Water Act and other international regulations limit the maximum temperature allowable for water returned to water bodies from a power plant's cooling system. To prevent ecosystem damage and harm to aquatic life, regulations either set maximum allowable exit temperatures (at a fixed absolute value) or limit the relative differential between the inlet and outlet water temperatures. When heat waves increase the temperature of incoming water, power plant operators sometimes decrease production to avoid exceeding their thermal pollution threshold.

For example, during a countrywide heat wave in France in 2003, when power demand spiked as customers sought cooling, 17 of 58 power plants reduced capacity or shut down to avoid violating thermal pollution regulations.1H. Forster and J. Lilliestam “Modeling thermoelectric power generation in view of climate change,” Regional Environmental Change 10 (2010), 327-338, doi: 10.1007/s10113-009-0104-x; M. Poumadere, C. Mays, S. L. Mer, and R. Blong, “The 2003 Heat Wave in France: Dangerous Climate Change Here and Now,” Risk Analysis 25 (2005), 1483-1494, doi: 10.1111/j.1539-6924.2005.00694.x; and M. Hightower and S. A. Pierce, “The Energy Challenge.” Nature 452 (2008), 285-286, doi: 10.1038/452285a.  High river temperatures and low river levels endangered the entire electricity system. Électricité de France (EDF) requested and received exemptions from European regulators to keep operating so that demand for air conditioning could protect human health without causing the grid to fail. Unfortunately, despite these efforts, the weather caused 15,000 to 20,000 heat-related deaths in the country.2Jean-Marie Robine, et al., “Death toll exceeded 70,000 in Europe during the summer of 2003,” Comptes Rendus Biologies 331 (2008), 171-178, doi: 10.1016/j.crvi.2007.12.001; M. Poumadere, C. Mays, S. L. Mer, and R. Blong, “The 2003 Heat Wave in France: Dangerous Climate Change Here and Now,” Risk Analysis 25 (2005), 1483-1494, doi: 10.1111/j.1539-6924.2005.00694.x; and P. Lagadec, “Understanding the French 2003 Heat Wave Experience: Beyond the heat, a Multi-Layered Challenge,” Journal of Contingencies and Crisis Management 12 (2004), 160-169, doi: 10.1111/j.0966-0879.2004.00446.x.  As climate change intensifies, regulators and policy makers will encounter an ethical dilemma between protecting aquatic environments and saving human lives unless the systems are designed differently.

Image courtesy Reto Stockli and Robert Simmon, based upon data provided by the MODIS Land Science Team. NASA, 2003.

Image courtesy Reto Stockli and Robert Simmon, based upon data provided by the MODIS Land Science Team. NASA, 2003.

Compared to July 2001, temperatures in July 2003 were much hotter than normal. This image shows the differences in day time land surface temperatures collected in the two years by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite.

Cold conditions and freezing water also threaten the reliability of the electricity sector in winter months. For example, water freezing within coal-fired power plants in Texas caused a cascade of failures, which plunged the state into varying degrees of darkness in February 2011.3Federal Energy Regulatory Commission and North American Electric Reliability Corporation, Outages and Curtailments During the Southwest Cold Weather Event of February 1–5, 2011 (Federal Energy Regulatory Commission, 2011), accessed August 27, 2016, link; E. Souder, S. Gwynne, and G. Jacobson, “Freeze knocked out coal plants and natural gas supplies, leading to blackouts,” Dallas Morning News, February 6, 2011; and E. Souder, G. Jacobson, and S. Gwynne, “Texas electric grid operator's rolling blackouts during freeze bring political scrutiny,” Dallas Morning News, February 12, 2011.  First, frozen water caused multiple fossil fuel power plants to turn off when instrumentation and sensing lines were no longer operable because water could no longer flow through them. At the same time, because of the cold temperatures, Texans were using natural gas to heat their homes and buildings, making natural gas less available for power plant backup. Consequently, the power went out in portions of the state, which turned off electrical equipment and gas compressors along gas pipelines, causing gas pressures to drop and straining the system further.4K. Galbraith, “The Rolling Chain of Events Behind Texas Blackouts,” Texas Tribune, February 3, 2011.  Ultimately, between February 1 and 4, 2011, more than two hundred individual generating units within the Texas grid experienced an outage, derating, or failure for a total loss of 4,000 megawatts (MW) of capacity.5Federal Energy Regulatory Commission and North American Electric Reliability Corporation, Outages and Curtailments During the Southwest Cold Weather Event of February 1–5, 2011 (Federal Energy Regulatory Commission, 2011), accessed August 27, 2016, link. This anecdote of small water lines producing statewide blackouts demonstrates the degree to which the power sector depends on water and its vulnerability to minor changes in water temperature and availability.

In February 2011, gas pipeline operators in the southwestern United States got a taste of what this Russian facility handles every winter when unseasonably cold weather led to natural gas curtailments for more than 50,000 customers in New Mexico, Arizona, and Texas.

Image Credits: zhangyang13576997233/Shutterstock.com; ZoranOrcik/Shutterstock.com.

Thermal Power Plants

Water indirectly enables power generation by cooling power plants that use heat to make steam that drives a steam turbine. These thermoelectric facilities make up about 75% of the world’s power plants. Water cooling is used to protect equipment and to increase efficiency. Overall, the power sector is the single largest user of water in the United States, responsible for nearly half of all water withdrawals (more than 606 billion liters (161 billion gallons) per day, including seawater), primarily from surface water.1M.A. Maupin et al., “Estimated use of water in the United States in 2010,” U.S. Geological Survey Circular 1405, November 5, 2014, accessed August 26, 2016, doi: 10.3133/cir1405. When we consider only freshwater withdrawals, then power plants and agriculture each withdraw roughly 435 billion liters (115 billion gallons) per day. Agriculture uses significantly more groundwater for irrigation. The mining sector, which includes extraction for fuels production, requires another 19 billion liters (5 billion gallons) per day, and the industrial sector, which includes refineries and other facilities for upgrading fuels, is responsible for another 61 billion liters (16 billion gallons) per day of withdrawals.

Most of the water withdrawn for power plants is returned to the source, though at a different temperature and quality. The amount of water that is withdrawn and consumed by thermal power plants is driven by a mix of factors including the fuel (coal, gas, nuclear, etc.), turbine design, cooling technology, and local weather. Nuclear power plants require more water because unlike power plants fueled by coal or natural gas, they cannot shed any waste heat into the atmosphere through smokestacks. The benefit of this scenario is that nuclear power plants lack emissions, but the disadvantage is that waterways absorb their waste heat.

The three most common cooling methods are open-loop, closed-loop, and air-cooling. On average, about 57 liters (15 gallons) of water are withdrawn and just under 4 liters (1 gallon) is consumed for every kilowatt-hour (kWh) of electricity generated in the United States. Because typical U.S. homes use between 10 and 40 kWh of electricity each day, electric generation alone requires 1,100 to 2,300 liters (300 to 600 gallons) of cooling water per day. That same home might consume an additional 570 liters (150 gallons) per day for washing, cooking, drinking, and landscaping. That means we indirectly use two to four times more water at home for our lights and outlets than directly for our faucets and shower heads.

Open-loop (once-through) cooling withdraws large volumes of fresh or saline surface water, passes it through the power plant one time, and returns nearly all the water to the source with small quantities consumed along the way due to evaporation. While open-loop cooling is energy efficient and has low infrastructure and operational costs, discharged water is warmer than ambient water, causing thermal pollution, which can harm aquatic ecosystems. As a result, environmental agencies regulate discharge temperatures, taking into account a water body’s heat dissipation capacity. If power plant operators return the water above their approved temperature, they incur a fine and can be forced to curtail operations. Furthermore, water intake systems at power plants can entrain and impinge aquatic life.

Prior to closing at the end of 2014, Vermont Yankee’s discharge permit allowed them to raise the temperature of the river by as much as 7°C (13°F) during winter months and as much as 3°C (5°F) in the summer and fall. The plant was able to discharge up to 2 billion liters (543 million gallons) of heated water a day, some of it as hot as 41°C (105°F). That heated plume of water could extend as far as 89 kilometers (55 miles) downstream.
closed-loop cooling tower

The stereotypical image of a closed-loop cooling tower is a concrete inverse parabola with white clouds of water vapor escaping to the atmosphere. Cooling towers withdraw water and then recirculate the water until it evaporates, which has a cooling effect. Because evaporation induces cooling, closed-loop cooling towers consume the water they take in.

As of 2005, 43% of U.S. thermal power plants were large power facilities with generation capacity of over 100 MW. Of these large power plants, 42% used closed-loop cooling towers and just over 14% used cooling reservoirs. The remaining 43% of these large power plants use once-through cooling, and just under 1% use dry cooling, which is also known as air cooling.2C. W. King, A. S. Stillwell, K. T. Sanders, and M. E. Webber, “Coherence between water and energy policies,” Natural Resources Journal 117 (2013); and National Energy Technology Laboratory, Estimating Freshwater Needs to Meet Future Thermoelectric Generation Requirements (U.S. Department of Energy National Energy Technology Lab, 2008), DOE/NETL-400/2008/1391. Most of those plants with once-through cooling systems were built before the Clean Water Act legislation was passed in the 1970s. Many of them also avoided strict emissions controls because they were constructed before the legislation regulating air pollution from power plants became law. Whether older, dirtier, and thirstier power plants close in exchange for newer, cleaner, leaner plants remains a hotly contested public policy debate.

Because of environmental concerns, the California State Lands Commission proposed a moratorium on construction of new power plants with open-loop cooling systems on the coast. However, this proposal clashes with a separate effort to push new power plants to coastal regions where open-loop cooling can use seawater rather than inland freshwater.3Proposed Resolution by the California State Lands Commission Regarding Once-Through Cooling in California Power Plants (Sacramento: California State Lands Commission, 2006), accessed August 27, 2016, link. In other words, environmental concerns about oceanic wildlife are in direct conflict with environmental concerns about inland freshwater supply. It is possible, however, for conservation, efficiency, and the use of alternative, water-lean options to meet competing environmental objectives simultaneously.

The San Onofre Nuclear Generating Station outside of San Diego, California, used water from the Pacific Ocean for cooling its systems. The plant’s owner permanently retired the facility in 2013.

More water-efficient cooling technologies exist; however, these systems have drawbacks. Dry-cooled systems operate like radiators in automobiles by circulating a coolant within a series of closed pipes coupled with air blowing over the system to cool the pipes. Air-cooled systems withdraw and consume less than 10% of the water of wet-cooled systems.4C. Kutscher et al. “Hybrid Wet-Dry Cooling for Power Plants,” (presnted at the Parabolic Trough Technology Workshop, Incline Village, Nevada, Feburary 14-16, 2006).  However, dry-cooling systems have higher capital costs, and reduce overall efficiency of the plant, which increases costs and emissions per unit of electricity generated. Because the heat capacity of air is so much lower than water, air-cooled systems require much more air to equal the cooling achieved by water. Hence, dry cooling systems require much larger facilities to create the larger cooling surfaces, which dramatically increases capital costs. Furthermore, a power plant with dry cooling can experience a 1% loss in efficiency for each degree increase of temperature, limiting the capacity of power generation when it is hot outside.

A dry-cooled system like this condenser unit does not require water but is more expensive to build and to operate than a traditional open- or closed-loop wet cooling system.

Because they include both closed-loop wet systems and dry-cooling equipment, hybrid wet-dry cooling systems provide a compromise between wet and dry cooling systems.5The hybrid power plant cooling system by Johnson Controls, Inc. is one notable example of a hybrid design that reduces water use, see: Electric Power Research Institute, “Technology Insights Brief: Thermosyphon Cooler Hybrid System for Water Savings in Power Plants,” Technology Insights: A Report from EPRI’s Innovation Scouts (Palo Alto, Electric Power Research Institute, 2012). Hybrid wet-dry cooling systems can consume low volumes of water for much of the year by operating primarily in dry mode with the flexibility to operate more efficiently in wet mode during the hottest times of the year when extra cooling boosts power output from the plant. Unfortunately, water resources are typically less available during these peak demand times. Although dry-cooling and hybrid wet‑dry cooling systems are proven technologies, they are typically more expensive. However, in water-constrained regions where water is not available for cooling, dry-cooling is often the only alternative. In such cases, the up-front capital costs and reduction in the power plant’s efficiency are more readily justifiable.

Almost all early thermoelectric power plants used open-loop cooling. However, during the 1960s and 1970s, environmental concerns about water usage by the power sector increased, kicking off an era of regulatory pressure to reduce water use at power plants. One of the key pieces of legislation was the Clean Water Act, which established the framework for regulating discharges of chemical and thermal pollution into the waters of the United States.6“History of the Clean Water Act,” U.S. Environmental Protection Agency, accessed October 27, 2012, link; and “Summary of the Clean Water Act: 33 U.S.C. §1251 et seq. (1972)”, U.S. Environmental Protection Agency, accessed October 27, 2012, link.

The Clean Water Act outlawed the unpermitted discharge of any pollutant from a point source into navigable waters. While the legislation regulated point sources—discrete locations such as pipes or man-made ditches—it ignored broader sources of pollution such as runoff over a wide area including farms and other agricultural operations. Although homes do not generally need a permit for their wastewater flows into sewers or septic systems, industrial, municipal, and other non-domestic facilities must obtain permits for discharges flowing to surface waterways. The law also sets regulations for intake requirements at power plants. Subsequently, power plants built since 1972 have almost exclusively used closed-loop designs with cooling towers as a way to serve many environmental interests by greatly reducing the entrainment and impingement of aquatic wildlife and reducing thermal pollution by limiting hot water returns.

Image Credits: zhangyang13576997233/Shutterstock.com; Jeffrey M.Phillips/Webber Energy Group; Vaclav Volrab/Shutterstock.com; iofoto/Shutterstock.com; Brisbane/Shutterstock.com.

Math of Pumping Water

The energy that is needed to raise water by overcoming potential energy is essentially the reverse of how hydroelectric dams extract the potential energy of falling water:

where ρ is the density of the water (1,000 kilograms per cubic meter (kg/m3)), V is the volume of water raised, g is the acceleration due to Earth’s gravity (9.8 meters per second squared (m/s2)), and h is the net or cumulative change in height (in m). Raising a 10-liter (2.75-gallon) bucket of water through a distance of about 100 meters (330 feet) requires approximately 10,000 joules (10 British thermal units (Btu)) of energy. Pumping the water up only 10 m (33 feet), for example by raising the water from a river to the top of a nearby riverbank, requires 1,000 joules (1 Btu) of energy.

For continuous flows, it is more useful to look at the power required for pumping, which is the energy required over time:

For this equation, the term P is the change in potential energy per unit time (or the pumping power needed), ηp is the efficiency of the pump (approximately 80% or 0.8), and Q is the volumetric flow rate (m3/s). The other terms are the same as the prior equation. Pumping 100 liters per second—enough water for 1,900 average Americans—out of an aquifer 100 meters below the ground requires a pump with about 100 kW of pumping power. Keep in mind that a typical house needs 1 to 3 kW of power on average to run the whole place, so a pump that size consumes the same power as approximately 30 to 100 homes.

Pumps must also overcome friction within pipelines. The water industry terms the losses from friction “head losses,” which is analogous to the additional “head” or elevation that must be overcome for pumping. These losses can be described for turbulent flow by the Darcy-Weisbach equation:

where hf is the head loss due to friction (in meters, m), f is the unitless friction factor specific to physical parameters of the pipe, ΔL is the length of pipe through which the water is piped (m), v is the velocity of the fluid on average (m/s), and D is the diameter of the inside of the pipe. The gravitational constant g is the same as before.

Image Credits: benjamas154/Shutterstock.com.

Moving Water Across California

To overcome water scarcity in the southern part of the state and to increase agricultural production through the twentieth century, an intricate water infrastructure grew across the state of California. Different federal, state, and municipal agencies built and maintain a network of reservoirs, aqueducts, canals, pumping stations, and power plants to transport water from water-rich to water-poor regions. For example, the State Water Project moves water from rivers in Northern California all the way to the San Diego Aqueduct under the supervision of the California Department of Water Resources. The total length of the pipeline infrastructure is about 1,100 kilometers (km) (700 miles), including the world's largest water pumps at the Edmondson Pumping Plant that lift water 600 meters (2,000 feet) over the Tehachapi Mountains.

The Dos Amigos Pumping Plant on the California Aqueduct lifts water coming from the north 36 m (118 feet) to flow by gravity 265 km (164 miles) south to the next pumping station. The State Water Project consumes approximately 3.7 kWh/m³ (14,000 kWh per million gallons) to transport water from the Sierra Nevada Mountains to San Diego.

Over 25 million people receive access to clean freshwater through this project, which consumes 5.1 terawatt-hours (TWh) each year, between 2% and 3% of the entire state’s electricity capacity.1Ronnie Cohen, Barry Nelson, and Gary Wolff, Energy Down The Drain: The Hidden Costs of California’s Water Supply (Oakland: National Resources Defense Council and Pacific Institute, 2004). The State Water Project shares many facilities with the Central Valley Project, which alone has about 800 km (500 miles) of canals. Transporting the water consumes 1 TWh annually, but 11 hydroelectric power plants in the system harness electricity from the snowmelt. Additionally, the Metropolitan Water District of Southern California operates the Colorado River Aqueduct, which transports water from Lake Havasu on the Arizona-California border to the Santa Ana Mountains for the Los Angeles and San Diego metropolitan areas.

This map from the Public Policy Institute of California (PPIC) shows how the state’s elaborate network of conveyance and storage infrastructure is controlled by federal, state, and local agencies. Download the entire publication for free.

Although many people benefit from the improved infrastructure, the projects remain a source of contention within California. For example, the Central Valley Project ended salmon migration in the Sacramento, American, and Stanislaus Rivers.2John Williams, “Appendix A: Major Salmon Streams,” San Francisco Estuary and Watershed Science 4 (2006). Also, many agricultural operations made possible by irrigation increase stress on the already strained system. For example, tree nut production consumes 4 liters (1.1 gallons) per nut grown.3Erin Brodwin and Samantha Lee, “Chart shows how some of your favorite foods could be making California's drought worse,” Business Insider, April 8, 2015, accessed August 30, 2016, link.

The documentary Cadillac Desert offers a deeper look at the history of water in California and the State Water Project.

Image Credits: Tom/stock.adobe.com; Aaron Kohr/Shutterstock.com.

Pumping

Though abundant globally, water is often out of reach. When water is far away, energy is used to transport it. And, because of its density—water weighs 1,000 kg/m3 (8.34 pounds per gallon)—the energy required to raise water is significant. The total energy needed for pumping water depends on the height to which the water is raised, the rate at which it is raised, pipe diameter, friction, and other factors. Whether raising water from a well or pumping water over a mountain, the total energy required must overcome the force of gravity exerted on that volume of water.

The ancient Egyptians used Archimedes’ screw, which is a clever device that converts the manual turning of a screw into a process that elevates water. The tight coil of connected blades raises water as long as it is continually operated. Its invention is attributed to Archimedes in the third century BCE, but might have been in use earlier. Thousands of years later, modern water-lifting stations at amusement parks, water treatment plants, and elsewhere still make use of the design.

Schlitterbahn Waterpark in New Braunfels, Texas, uses an Archimedes’ screw to lift 36,000 gallons (136 m3) of water per minute to power The Falls, billed as “the world’s longest tubing adventure.”1John Boyd, “35 fun facts about Schlitterbahn on its 35th anniversary,” My San Antonio, March 5, 2014, accessed August 29, 2016, link; and Winter Prosapio, “Schlitterbahn New Braunfels Waterpark Fact Sheet 2016,” Schlitterbahn Newsroom, February 18, 2015, accessed August 29, 2016, link.

A medium-sized U.S. city with one million residents might need 570 million liters (150 million gallons) of water per day. Raising that water from surface sources to elevated water treatment plants over a height of 100 meters requires a little more than 6 megawatts (MW) of pumping power. Massive wind turbines generate approximately 1 MW each, so the city would need 6 turbines running at full capacity exclusively for pumping water to the treatment and storage facility at the top of the hill, after which it can flow downhill to customers. The energy intensity of pumping is one of the reasons why people prefer shallow wells and surface water sources. Deeper, dirtier sources require even more energy and are usually only deployed when less energy-intensive options are available.

Using local surface water for agricultural applications requires less energy than transporting water from the Colorado River Aqueduct for treatment and distribution to residences where the water is subsequently heated.

Image Credits: Peter Turner Photography/Shutterstock.com.

Modern Thermodynamics

The field of thermodynamics is the underlying science of energy. The word thermodynamics itself reveals its component parts.

The components of the word thermodynamics are derived from the Greek words θέρμη therme, meaning “heat,” and δύναμις dynamis, meaning “power.” The term thermo-dynamic was first used in January 1849 by William Thomson, later Lord Kelvin, in the phrase “a perfect thermo-dynamic engine” to describe Sadi Carnot’s heat engine.

Energy contained in fuels such as coal, oil, wood, or gas can be converted into useful functions such as mechanical work for moving a car or crushing rock and can be used for thermal activities such as warming and cooking. But, before that energy in the fuels can be harnessed, it must be transformed. These transformations are governed by the laws of thermodynamics. While these fuels enable useful services, they also cause pollution and waste.

The laws of thermodynamics provide the key scientific principles or physical laws by which society harnesses (and wastes) energy. The science of thermodynamics developed in the 1800s from the desire to increase the performance of early steam engines. These engines were increasingly valuable in Britain just after the Industrial Revolution because they provided mechanical power at factories and mills.

Iron and Coal, 1855–60, by William Bell Scott illustrates the rise of coal and iron working in the Industrial Revolution and the heavy engineering projects they made possible.

The development of more efficient steam engines benefited from the emergence of the scientific method. Inventors and scientists tested hypotheses against empirical evidence, leading to a truly scientific understanding of the phenomena they witnessed. As factory workers and inventors developed iterative models of early engines, early scientists, such as Thompson, Carnot, Watt, and Joule, began to generalize evidence from the field into theory, producing the laws of thermodynamics.

Both scientists and engineers contribute to the world of human knowledge, but in different ways. Scientists use the scientific method to make testable explanations and predictions about the world. Engineers use the engineering design process to create solutions to problems.

As prominent science historian Bruce Hunt noted, it is not clear who helped whom the most. While the modern paradigm for innovation suggests that discoveries in the lab lead to better engineering design in the field, the historical relationship of thermodynamics and the steam engine may be reversed. Rather than going from fundamental science to a better engine, the tinkerers inventing and improving engines in mines and factories advanced the science of thermodynamics more than the theoretical scientists improved the engines. Engineers converted heat into motion before scientific theory could explain the phenomenon.

Image Credits: Baptist/Shutterstock.com; Jeffrey M. Phillips/Webber Energy Group.