The Nexus of Energy & Water
Ashlynn S. Stillwell
Rainwater Revival | Dripping Springs, TXOctober 8, 2011October 8, 2011
Energy and water are interrelatedgy
• We use water for energy– Cooling during power generation– Liquid fuels production
• We use energy for water– Treatment and disinfection– Distribution– Heating
Ashlynn S. StillwellEnergy and Water 2
October 8, 2011
Energy and water are interrelatedgy
Ashlynn S. StillwellEnergy and Water 3
October 8, 2011Source: EPRI
Energy and water are also the two looming gy gcrises of the 21st century…
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National Geographic 3/2008
The Energy-Water Nexus: Can we solve both gycrises together?
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(Image courtesy of Scientific American Earth 3.0, 9/2008)
The hydrological cycle is globaly g y g
Ashlynn S. StillwellEnergy and Water 6
October 8, 2011
The hydrological cycle is global
Ashlynn S. StillwellEnergy and Water 7
October 8, 2011[Oki & Kanae 2006]
Freshwater is a small part of the total supply
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October 8, 2011
[Boberg, RAND]
Four main points to rememberp1. Energy and water are interrelated
• we use energy for water and water for energygy gy
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• 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 waterenergy-intensity of water
4. There are different policy actions that can help• Policy engagement on energy/water nexus is warranted
Ashlynn S. StillwellEnergy and Water 9
October 8, 2011
y g g gy
The energy sector uses a lot of water
• Thermoelectric power sector is the largest user of water in the US– 48% of total water withdrawals
39% f f h t ithd l [USGS]– 39% of freshwater withdrawals
• Withdrawal: 0.2 - 42.5 gal/kWh
Michigan City, INCredit: M. Webber, 8/09
[USGS]
• Consumption: 0.1 - 0.8 gal/kWh
Also need water for production and refining of transportation fuelsrefining of transportation fuels…
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There are two main cooling approaches for power plantspower plants
Open-Loop Cooling Closed-Loop Cooling
Most ater that isMost water that is withdrawn is returned…but at a higher temperature
Most water that is withdrawn is consumed
p
Withdraws more, consumes less
Withdraws less, consumes more
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October 8, 2011
consumes less
[Stillwell et al. 2009]
Thermoelectric power is the largest user of water in the U.S.
Closed-Loop (cooling tower)
Open-Loop(cooling tower)
Fuel Withdrawals [gal/kWh]
Consumption[gal/kWh]
Withdrawals[gal/kWh]
Consumption[gal/kWh]
N l 1 0 0 7 42 5 0 4Nuclear 1.0 0.7 42.5 0.4
Solar CSP 0.8 0.8 N/A N/A
Coal 0 5 0 5 35 0 0 3Coal 0.5 0.5 35.0 0.3
Natural Gas (combined cycle)
0.23 0.18 13.8 0.1
Natural Gas(combustion turbine)
negligible negligible negligible negligible
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Consumption: ~0.1 to 0.8 gal/kWhWithdrawals: ~0.2 to 42.5 gal/kWh
[Stillwell et al. 2011]
We use water from a variety of sources for a variety of purposes with a variety of energyvariety of purposes with a variety of energy
requirements
Ashlynn S. StillwellEnergy and Water 13
October 8, 2011[Twomey & Webber 2011]
The water sector uses a lot of energygy• Energy is used to produce, move, heat, and treat water
– About 5% just for residential & commercial sectors– 250-300 MMT of CO2 emissions (~5% of total)
• California is an extreme example• California is an extreme example– CA spends ~19% of its electricity on water
• Primarily for end-usePrimarily for end use• SoCal uses a lot of energy for conveyance
– similar story wherever water is scarce
Ashlynn S. StillwellEnergy and Water 14
October 8, 2011[Twomey & Webber 2011, CEC 2005]
Water/wastewater collection, treatment, and distribution requires energy
Source/Treatment Type Energy [kWh/Mgal]
Surface Water 1 400
Wat
er
Surface Water 1,400
Groundwater 1,800
Brackish Groundwater 3 900 9 750W Brackish Groundwater 3,900-9,750
Seawater 9,780-16,500
ewat
er Trickling Filter 955
Activated Sludge 1,300
Was
te
Advanced Treatment w/o Nitrification 1,500
Advanced Treatment w/ Nitrification 1,900
Ashlynn S. StillwellEnergy and Water 15
October 8, 2011[Stillwell et al. 2011]
Wastewater treatment requires energyq gy
• Sanitation differentiates– Healthy & wealthy = sanitation
– Sick and poor = no sanitationSick and poor no sanitation
• Reclaimed water– Advanced treatment is less
energy-intensive than desalinationdesalination
– “toilet to tap” (Singapore, ISS,…)
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The energy-water relationship is already under gy p ystrain
Ashlynn S. StillwellEnergy and Water 17
October 8, 2011
The energy-water relationship is already under gy p ystrain
• Water Constraints Become Energy Constraints– Heat Waves: thermal pollution limits can
constrain power plant operationD ht t it hibit l t– Droughts: water scarcity can prohibit power plant operation or fuels production
• Energy Constraints Become Water Constraints– Blackouts disrupt water treatment & distribution
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October 8, 2011
The energy-water relationship is already under gy p ystrain
• Record heat wave in France in 2003 caused nuclear power plants to dial back because of water temperature limitsto dial back because of water temperature limits
• “Droughts could close nuclear power plants: Southeast water shortage a factor in huge cooling requirements”g g g q
• Power generation reductions for at least one Texas power plant due to falling cooling reservoir levels
[Associated Press, 1/23/08]
[Houston Chronicle, 8/25/11]
• Civil War Between Georgia and Tennessee? – “Georgians want access to Tennessee water”
move the border 1 mile north to give GA access to the– move the border 1 mile north to give GA access to the Nickajack Reservoir on the dammed Tennessee river
[The Tennessean, 2/8/08]
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October 8, 2011
“Las Vegas Running Out of Water Means Dimming Los Angeles Lights”Dimming Los Angeles Lights
Worst 10-year drought in recorded historyy
Hoover Dam provides electricity to 750,000
A white "bathtub ring" on canyon walls at Lake
people in LA[Bloomberg, 2/26/09]
• The surface of Lake Mead has dropped 100 feet in six years If it
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 )
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, 1/29/08]
Ashlynn S. StillwellEnergy and Water 20
October 8, 2011
Trends imply that strain in the energy-water p y gyrelationship will be exacerbated
Ashlynn S. StillwellEnergy and Water 21
October 8, 2011
Trends imply that strain in the energy-water p y gyrelationship will be exacerbated
• Population growth– drives up total demand for energy & water
• Economic growthg– 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
Ashlynn S. StillwellEnergy and Water 22
October 8, 2011
gy
We are moving towards more energy-intensive waterwater
• Stricter water/wastewater treatment standards Tampa Bay, FL
Credit: A. Stillwell, 2/10
• Deep aquifer production
• Desalination
,
Desalination– Worldwide capacity to double by 2025– Middle East, London, San Diego, TX
[Economist, 6/7/08]
• Long-haul pipelines and inter-basin transfer– China, India, Texas
• Desalination plus long-haul transfer
Ashlynn S. StillwellEnergy and Water 23
October 8, 2011
We are moving towards more water-intensive genergy
• Nuclear power, Solar CSP(Note: we are also choosing water-lean energy forms, like
solar PV, wind, natural gas)
• Future transportation fuels are especially thirsty– Unconventional fossil fuels (2-4x worse)– Natural Gas (better to 1-2x worse)– Electricity (2-3x worse)
• Good with wind/solar PV, worse with nuclear– Hydrogen (1-500x worse)
G d ith i d/ l PV ith lAshlynn S. Stillwell
Energy and Water 24October 8, 2011
• Good with wind/solar PV, worse with nuclear– Biofuels (1-1000x worse)
[King & Webber 2009]
Federal policy essentially mandates increases in water consumption for transportation fuels
3,000
water consumption for transportation fuels
Coal to Liquid (Diesel)Annual Energy Outlook 2008
2,000
2,500Irrigated Ethanol – E85 Cellulosic
Reference Case
1,500
2,000
Bga
l/yr
Irrigated Ethanol – E85 Corn Grain
500
1,000Irrigated Ethanol – E10 Corn Grain
02005 2010 2015 2020 2025 2030
Petroleum Gasoline
Ashlynn S. StillwellEnergy and Water 25
October 8, 2011[King et al. 2010]
The view from Texas is particularly interestingp y g
Ashlynn S. StillwellEnergy and Water 26
October 8, 2011
Rights to surface water in Texas vary with g ygeography
Municipal Water Rights (ac-ft/yr)
• Large cities and river authoritiesriver authorities hold large rights
• Availability for new water rights depends on existing allocations
Ashlynn S. StillwellEnergy and Water 27
October 8, 2011[Data from TCEQ]
Large power plants are large water usersg p p gGeneration Capacity (kW) Water Consumption (gal/kWh)
Texas consumes 157 billion gallons of water
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October 8, 2011
to produce 400 billion kWh annually (more than any other state)
[Data from TWDB]
Large wastewater treatment plants are near g plarge populations
Wastewater Treatment (MGD)• Wastewater• Wastewater
treatment alone requires 25% more energy per volume than water treatment and distributionand distribution combined
• Unit energy• Unit energy kWh/Mgal varies widely with plant size
Ashlynn S. StillwellEnergy and Water 29
October 8, 2011[Data from TCEQ, EPA]
Annual per capita energy consumption varies from 75 (global) to 560 (Texas) MMBTUfrom 75 (global) to 560 (Texas) MMBTU600
n
24 Million
400
500
sum
ptio
300
400
ergy
Con
sM
BTU
] 300 Million
200
pita
Ene [M
M
6.7 Billion
60 Million
0
100
Per C
a
Ashlynn S. StillwellEnergy and Water 30
October 8, 2011
0World UK USA Texas
Total energy consumption will increase if the world changes per capita consumption toworld changes per capita consumption to
match the UK, USA, or Texas
6000
7000
tion 2008 Population:
6 7 Billion2050 Population: 11 Billion
4000
5000
onsu
mpt
ds]
6.7 Billion 11 Billion
2000
3000
nerg
y C
o[Q
uad
0
1000
Tota
l E
Ashlynn S. StillwellEnergy and Water 31
October 8, 2011
02008 World
Like UK Like USA
Like Texas
2050 World
Like UK Like USA
Like Texas
We consume vast sums of energy on water
Public restrooms usually use high quality drinking water to flush the toilets
Dogs also get the highest quality drinking water
• Texans consume ~135-250
drinking water
gallons of drinking water per person per day
• Water is often free or cheap at point of use
Ashlynn S. StillwellEnergy and Water 32
October 8, 2011Credit: Evelyn Webber 2009
Rainwater harvesting is one way to reduce g ystrain on the energy-water relationship
• Offsets use of energy-intensive drinking water
• Reduces pumping costs byReduces pumping costs by providing a distributed water supply
• Can match intended use with water quality
• Reduces surface runoff and associated stormwater
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October 8, 2011
and associated stormwater treatment
Good news: energy conservation and water gyconservation are synonymous
• Conserving water will conserve energy
• Conserving energy will conserve waterwill conserve water
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October 8, 2011
Energy-Water Nexus in Texas reportgy p
http://www.edf.org/documents/9479 Energy-p g _ gyWaterNexusinTexasApr2009.pdf
Ashlynn S. StillwellEnergy and Water 35
October 8, 2011
Questions?Q
Ashlynn S. Stillwell NSF Graduate Research Fellow
Department of Civil, Architectural, and Environmental Engineering
The University of Texas at [email protected]
http://www.webberenergygroup.com
Ashlynn S. StillwellEnergy and Water 36
October 8, 2011