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The Energy-Water Nexus
Clean Energy and Water International Workshop
Porto de Galinhas, Recife - Brazil
Kelly M. Twomey
September 23, 2011
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Energy and Water Are the Two Critical
Aspects to Modern Civilization
• More critical than food:
– modern food production requires energy & water
• More critical than healthcare:
– top global public health problem: access to clean
water & sanitation (e.g. wastewater treatment)
• More critical than law & order:
– Katrina: lawlessness follows blackouts (food
spoilage) and lack of water availability
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Energy and Water Are Also the Two Looming
Crises of the 21st Century…
National Geographic 3/2008
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There Are Three Main Points to Remember
1. Energy and water are interrelated
• we use energy for water and water for energy
2. The energy and water relationship is already under strain
• constraints in one resource introduce constraints in the other
3. Trends imply these strains will be exacerbated
• Population growth increases total demand
• Economic growth increases per capita demand
• Global climate change intensifies the hydrological cycle
• Policy shifts towards increasing water-intensity of energy and
energy-intensity of water
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Energy and Water are Interrelated
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Energy and Water are Interrelated
[DOE]
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The Thermoelectric Power Sector is the
Largest User of Water in the US • 48% of total water withdrawals (39% of freshwater withdrawals)
• Withdrawal: 4-150 L/kWh Consumption: 0.9-4 L/kWh
[USGS]
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The Thermoelectric Power Sector Uses Water
for Cooling
Withdrawals
[L/kWh]
Consumption
[L/kWh]
Thermoelectric
(National Average)
80 2
Thermoelectric
(with once-through cooling)
151 0.9
Thermoelectric
(with cooling tower)
4 4
Hydroelectric 68 68
•Aggregate National Average consumption: 7.6 L/kWh
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The Water Sector Uses a Lot of Energy
• Energy is used to produce, move, heat and treat water
– ~ 3% of U.S. electricity for water/wastewater plants
– ~10%+ including end-use (heating, etc.)
• Largest energy user in most municipalities (~50%)
• most WWTPs are municipally-owned
• California is an extreme example
– CA spends ~19% of its electricity on water
• primarily for end-use
• SoCal uses a lot of energy for conveyance
– similar story wherever water is scarce
• Mexico, Egypt, China, Libya, etc.
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Water Production, Treatment and Distribution
Requires Energy
Source/Treatment Type Energy Use [kWh/ML]
Surface Water 370
Groundwater 480
Brackish Groundwater 1,030-2,580
Seawater 2,580-4,360
[Stillwell, 2009]
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Wastewater Treatment Requires Energy
Treatment Type Energy [kWh/ML]
Trickling Filter 250
Activated Sludge 340
Advanced Treatment
w/o Nitrification
400
Advanced Treatment
w/ Nitrification*
500
*Advanced treatment with nitrification, followed by water
treatment, is less energy-intensive than desalination
Reclaimed water: “toilet to tap” (Singapore, ISS,…)
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We estimate that the US uses 9 quads (9.2%) of
energy and 542 billion kWh (13.2%) of electricity
on water-related activities, annually
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The Energy-Water Relationship Is Already
Under Strain
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Energy Production, Distribution and Use Can
Impact Water Quality
6/2011
Multiple Oil Spills in China’s
Bohai Bay
4/20/2010
BP Deepwater Horizon Spill
11/11/07:
Oil Spills into the SF Bay
3/24/1989 :
Exxon Valdez Oil Spill Deepwater Horizon Spill; Source: Wikipedia
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Coal Spills, Too--It’s Not Just Oil Spills
• “Coal Ash Spill Revives Issue of Its Hazards”, NYT, 24 Dec 2008
– The spill released about 300 million gallons of sludge & water
– Much larger than Exxon Valdez
“…the spill reignited a debate over
whether the federal government should
regulate coal ash as a hazardous
material. Similar ponds and mounds of
ash exist at hundreds of coal plants
around the nation…<snip>…the Edison
Electric Institute estimated that the
industry would have to spend up to $5
billion in additional cleanup costs if the
substance were declared hazardous.”
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Electricity Production Often Requires
Large Amounts of Water for Cooling
Fukushima Reactor #3 days after
Tsunami hits Source: nytimes.com
Duke Energy’s Nuclear Reactor in NC during
2008 drought Source: dailytech.com
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“Las Vegas Running Out of Water Means
Dimming Los Angeles Lights”
• “The surface of Lake Mead has dropped 100 feet in six years. If it
drops 50 feet lower, Las Vegas could lose an intake that supplies 40
percent of its water. Simultaneously, "Hoover Dam stops generating
electricity”
– Denver Post, 1/29/2008
A white "bathtub ring" on canyon walls at Lake Mead National Recreation Area in July
shows mineral deposits left by higher levels of water near the Arizona Intake Towers at the Hoover Dam. (Ethan Miller, Getty Images )
Worst 10-year drought in recorded history
Hoover Dam provides electricity to
750,000 people in LA
Bloomberg.com, 2/26/09
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Hydraulic Fracturing Raises Water-quantity
and Water-quality Issues
• How much water
is needed?
• Will adjacent
water tables be
contaminated?
• What should be
done with the
residual
wastewater?
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Trends Imply That Strain in the Energy-Water
Relationship Will Be Exacerbated
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Trends Imply That Strain in the Energy-Water
Relationship Will Be Exacerbated • Population growth
– drives up total demand for energy & water
• Economic growth
– drives up per capita demand for energy & water
• might be counteracted by efficiency
• Climate change
• Policy choices
– movement towards energy-intensive water and water-intensive energy
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The Future of the Water-Energy Nexus
is Not Clear
• Some trends indicate more water-intensive
energy
– Nuclear power, Concentrating Solar Power (CSP),
Carbon Capture and Sequestration (CCS), Hydraulic
Fracturing
– Future transportation fuels are especially thirsty
• Electricity (2-3x worse)
• Unconventional fossil fuels (2-4x worse)
• Hydrogen (1-500x worse)
• Biofuels (1-1000x worse)
• Some trends indicate more water-efficient energy
– Wind, Solar PV, Natural Gas, Dry Cooling, etc.
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We Are Moving Towards More Energy-
Intensive Water
• Stricter water/wastewater treatment standards
• Deep aquifer production
• Desalination
– Worldwide capacity to double by 2025
– Middle East, London, San Diego, TX
• Long-haul pipelines and inter-basin transfer
– China, India, Texas
• Desalination plus long-haul transfer
Global Water Intelligence, Vol 9, Issue 8 (August 2008)
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Take-away: Implementing Advanced Efficiency
is the Key to the Sustainable Use of Both
Energy and Water
• Conserving water
will conserve
energy
• Conserving
energy will
conserve water
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Acknowledgements
• Associates:
– Dr. Michael Webber
– Dr. Carey King
– Mrs. Ashlynn Stillwell
– Ms. Melissa Lott
• Colleagues:
– Dr. Ian Duncan
– Ms. Amy Hardberger
• Sponsors:
– Texas State Energy
Conservation Office
– Texas Water Development
Board
– Environmental Defense Fund
– Energy Foundation
– National Science Foundation
– Environmental Protection
Agency
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Kelly M. Twomey
National Science Foundation Research Fellow Thermal Fluid Systems Mechanical Engineering
University of Texas at Austin
http://www.webberenergygroup.com