The Water/Energy Nexus for 

Arizona and the West 

 

 

 

LASC 195a Colloquium 2 Water Resources in 

the Tucson Basin: Student Research Report 

 

 

 

 

 

Spring 2010 

Instructor: James J. Riley   

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Note: This is a report prepared by students in a one‐unit 

First Year Colloquia class taught in spring 2010  entitled: 

“Water Resources in the Tucson Basin”.  The enrolled 

students are not experts in water resources, so the 

report should be read with that in mind. This report is 

posted on the class web site: 

www.cals.arizona.edu/swes/tucwater2 

We wish to express our appreciation to Ms. Jeanne L. 

Pfander and Leslie A. Sult, Associate Librarians with the 

University of Arizona Libraries for their support and 

guidance in assisting the students in their research.  

 

J.J.Riley, Associate Professor, Soil, Water and 

Environmental Science Department 

jjriley@ag.arizona.edu   

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The Most Effective Solar Energy Method Mark Jacobson, Katie Miles, Andrea Lawson, &Viraj Patel Abstract: Arizona is facing two major issues dealing with getting solar

energy. The first is how to find alternate energy. The second is how to utilize water in the most efficient manner. These two goals are contradictory of each other, because the most efficient energy source is solar panels, and they also consume a large amount of water. A solution to this was found after doing research which lies in concentrate solar power (CSP). The CSP focused on is the dish/engine system. We focused our report on this system to prove our point on how it would be a better product to use when conducting energy in Arizona, which has very little supply of water. We started our argument with an introduction that introduced the problem and the dish/engine system. Next all the materials were introduced on how we gathered all the necessary information on the topic. The results and discussion came next and describes our findings in a greater detail. Lastly we state our conclusion which wraps up our argument and states our boldest points. The dish/engine system is very unique one that has a lot of information to back it up.

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The Most Effective Solar Energy Method

Introduction:

Our group researched and composed a paper on the relationship between solar

energy and water consumption. However, it is important to introduce the idea of

alternate energy. As of today, burning fossil fuels is a primary source of energy.

Fossil fuels supply more than 85% of the energy used around the world

(Alternative Energy Sources). As for the United States, two-thirds of the

electricity is generated from fossil fuels such as coal, gas, and oil (Alternative

Energy Sources). Since the world has depended on fossil fuels for such a long

time, the reserves are now limited and these fossil fuels are nonrenewable

resources. Not only are they limited, but also they are not environment friendly.

According to the US Department of Energy, the burning of fossil fuels pumped

more than 27 billion metric tons of carbon dioxide into the atmosphere in the year

2004 alone (Alternative Energy Sources).

Therefore, the traditional major energy sources have been recognized as

having many drawbacks to the environment and the need of an alternative form of

energy is desired. The traditional major energy sources include the following: oil,

natural gas, coal, uranium, and hydroelectric power. With fossil fuels diminishing

and the dependence on foreign oil increasing, the experimenting with alternative

energy source has begun.

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The search for alternative energy sources is funded by private and federal

funds. Some examples of alternative energy sources are as follows: nuclear power,

wind power, water power, geothermal power, and solar power (Alternative Energy

Sources). Solar energy is the source that has made a breakthrough.

Sunlight has been used as a powerful source of energy since early times. For

example, “burning glasses” (magnifying lens that could concentrate the sun’s rays

to start a fire) were found at the ruins of Nineva dating back to 7 BC (Solar

Energy). Earth absorbs about 4 quadrillion kilowatts of energy from the sun (Solar

Energy). Solar energy is free, nonpolluting energy from the sun. It is ideal as an

alternative energy source because it is a continuously renewable source and has the

least environmental and safety hazards (Solar energy handbook: , 1979).

However, many solar-energy technologies require large amounts of water,

more than coal and nuclear power plants. The solar panels use the sun’s energy to

produce steam that generates electricity. Water is used to generate the steam and

to cool down the solar panels. Unfortunately, most of the water is lost to

evaporation. The ideal place for solar panel farms is sunny, open areas. It is not a

surprise that Arizona is one of the hot spots for solar panel locations. However,

Arizona is a desert with limited water supply. Solar energy developers have

mapped out five areas that are suitable for solar panel farms. One of the five areas

happens to be outside of Tucson (McKinnon, 2010). In Tucson, there is enough

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water for residents and businesses, but a problem may surface if water is handed

out in large quantities to solar energy developers. The debate comes down to the

higher demand of two important resources: energy and water supply. Solar energy

developers are coming up with different engineered solar panels to work with the

water overconsumption.

Materials and Methods:

All the materials used throughout this informational project were from the internet,

books, and journals. Along with the great help of being able to contact the

librarians and to have them guide you in the right direction of where you can find

these recourses. The books were found at the University of Arizona library, to

guide us in the direction of where to find these books we had to use the computers

located on the second floor. Typing in all the general information about a certain

book that we were looking for, like title or author, in the computer is able to direct

us where in the five story library those types of books are located. The book source

was defiantly our best investment of time. Along with books the report consumes

of information from journals entries of projects that they have done with the topic

of solar panels and cooling off mechanisms. It was a great source to use when

conducting a report on a future aspect. It gave well knowledgeable information to

planners about what could eventually take place.

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Along with books and journals, the internet was a great source to use when

conducting a research project. We went to the world known search engine, like

Google.com, and put the words that related to what we were looking for. The key

words we used were, “solar panels without water” and “rotating solar

panels.”Many websites turned up and many were not ones that we wanted to use,

and others we used a great deal of information from. We were careful when

choosing our information if it sounds sketchy or not right, it is always

recommended to find our information somewhere else.

After using all the resources were gathered about our information about our

project, we had to source all the information used. If we were to fail to do so, it

would have been considered plagiarism, which can lead our group to failing this

assignment. To correctly site our work we used easybib.com and other sites that

can help us site our work correctly. After we site we have completed our part of

gathering all the information, now it is the time to sit down and write out our report

based on all this information.

Results:

Due to the large amounts of solar resource available in the Southwest United

States, utilities are showing an increasing interest in the development of

concentrating solar power, or called CSP, plants to meet the requirements of state

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renewable portfolio standards. This development of all these plants will be

developed through a 30% investment in tax credit. The type of CSP plants that we

are focusing on is the Dish/Engine systems. “This concept uses a field of

individual parabolic-shaped dish reflectors that each focus sunlight onto an

engine/generator that uses the Sterling thermodynamic cycle to directly produce

electricity without producing steam” (Department of Energy, 10). Due to this

device being able to track the sun in two axes, it is capable of capturing the

maximum amount of direct beam of solar radiation throughout the day. This

system has a higher efficiency, along with being able to convert 30% of the

sunlight to electrical energy. Another advantage of this system is that the engines

are air-cooled; the high operating temperatures allow high efficiencies without

water cooling, meaning no water is needed for more than for mirror cleaning. From

a state like Arizona, the dishes are well suited for this area due to the major

droughts the states go through. Below is a picture of what these solar panels would

look like in the setting of the desert.

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http://susty.com/image/suncatcher‐solar‐thermal‐technology‐power‐conversion‐unit‐pcu‐dish‐controller‐mirror‐facet‐

elevation‐drive‐pcu‐boom‐azimuth‐drive‐main‐beam‐box‐trusses‐pedestal‐ses‐stirling‐energy‐systems‐photo.jpg

These plants can be built at any size and do not require to be on even ground. The

only disadvantage to this plant is the technology does not easily lend itself to

thermal storage, and so these systems are designed to only give electricity when

the sun is shining. Luckily the area that the government is looking to place this

plant is located in the desert, for example Arizona. Below is the area map of where

the government is looking to put these solar plants, like this one.

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http://news.cnet.com/i/bto/20090701/BLM_Solar_Energy_Study_Areas_Arizona_.jpg

In Arizona, they are looking to build this plant near the southwest border of the

state. There is much desert that any kind of solar plant would be compatible. The

only problem is solar energy plants that require water or steam as their cooling

mechanism, will suffer from the lack of water. Concluding that the state of Arizona

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will also have a huge loss of water that they barely have now, and that is why

Arizona should invest their time, money, and desert to the Dish/Engine systems.

Discussion:

There are several different types of ways to collect solar energy. In fact there are

four different types that are commercially used. The four methods are Parabolic

Troughs, Linear Fresnel, Power Towers, and Dish/Engine Systems. In the United

States there are only certain kinds of solar energy collection methods. There is not

a single Dish/Engine solar collection method in America. All these types have

different rates of water consumption.

“The majority of new fossil power plants use evaporative water

cooling to reject the steam cycle heat. A typical coal plant or nuclear

plant consumes 500 gallons of water per M(gal/MWh) of electricity

generated. This is similar to the water consumption by a power tower.

A combined-cycle natural gas plant consumes about 200 gal/MWh. A

water-cooled parabolic trough plant consumes about 800 gal/MWh.

Of this, 2% is used for mirror washing. Dish/engine systems only

require water for mirror washing (approximately 20 gal/MWh).”

Based off these finding the best method would be the Dish/Engine Method. This is

true because they have the highest amount of energy to water ratio. They do this by

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turning the dishes throughout the day towards the sun which creates a focal point

on one spot. This creates high heat and because of the extreme structure they do

not need water to cool it off. Using air as a dry cool works effectively because the

temperature is so high where as with other methods they need water because it

takes too long to cool it off to an appropriate temperature. Only water or a hybrid

works because the other methods need to be at cooler temperatures to continue

working. This is the only method of the four that does not use steam engines to

create power. It creates electricity using the Sterling engine and can transfer 30%

of solar beams into energy. The only water that this method needs is to clean the

dishes. Also these dishes can be installed on uneven ground which is an advantage

that the other methods do not have. The only problem is there is no way to store

thermal energy when the sun goes down. So this method is unusable in the evening

which is one of the highest times for energy demand.

The other methods use a much higher amount of water because they need water to

cool down all the machinery. Even the turbines that use steam as power can

overheat and use high amounts of water. The different types of water cooling are

such; once-through cooling, evaporative cooling, dry cooling, and hybrid cooling.

Once-through cooling may appear to be the most effective because they recollect

the water after it is used and route it back to the water source it was taken from.

This however creates a higher temperature in the ground water or stream that it

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was taken from. This is bad for the ecosystem and also increases evaporation in the

water source. There is much concern about the impact this method has.

Evaporative cooling is simply letting the water that is used to cool enter the

atmosphere. This is the highest amount of water used because none of it is

returned. It simply escapes and is no longer usable. Dry cooling uses air as a

cooling method but most of the time fans are needed to create wind flow. This

requires energy, takes longer to cool, and lowers efficiency around 10%. Finally

there is the hybrid which uses a mix of all of these methods to try and lower water

consumption but also maximize efficiency.

With the dish method of solar energy no water is required to cool down the

apparatus. Therefore this system has the highest energy to water ratio of all the

methods. All desert habitats should look into the dish method that is trying to

create greener energy plants. The plants can be put on any terrain because they can

turn and focus the energy on to one point. As long as they have the proper angles at

all times, the dishes can create energy all throughout the day. There has to be some

system that creates energy at night though because the dish/engine method cannot

store thermal energy. That is the only downside to the dish/engine system.

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Conclusion:

The dish/engine system is clearly the obvious choice when it comes to

saving water, but since it is useless at night a hybrid of the dish/engine system and

other systems would be optimal in both saving water and saving energy. This

system would greatly benefit the Tucson area because it is a desert thus has

massive empty land plots and is prime location for solar plants, but is very dry in

water resources. This would save the most water and thus be most beneficial to

Tucson.

References:

1 . "Alternative energy sources." UXL Encyclopedia of Science. Ed. Rob Nagel.

2nd ed. Detroit: U*X*L, 2007. Discovering Collection. Gale. Collinsville High

School.25Mar.2010.

<http://find.galegroup.com/srcx/infomark.do?&contentSet=GSRC&type=retrieve

&tabID=T001&prodId=DC&docId=EJ2644300053&source=gale&srcprod=DISC

&userGroupName=coll72001&version=1.0>.

2. McKinnon, S. (2010, January 17). Amid state's push for solar

power, water-supply worries arise. Retrieved from

http://www.azcentral.com/private/cleanprint/?1264092014441

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3. Solar energy handbook: theory and applications. (1979). Ontario,

Canada: Chilton.

4. "Solar Energy." Experiment Central. Ed. John T. Tanacredi and John Loret.

Vol. 4. Detroit: UXL, 2000. Discovering Collection. Gale. Collinsville High

School. 25 Mar. 2010

<http://find.galegroup.com/srcx/infomark.do?&contentSet=GSRC&type=retrieve

&tabID=T001&prodId=DC&docId=EJ2121000038&source=gale&srcprod=DISC

&userGroupName=coll72001&version=1.0>.

5.  Us Department of Energy. "Dish/Engine Systems." Concentrating Solar Power

Commercial Application Study: Reducing Water Consumption of Concentrating

Solar Power Electricity Generation (2009): 1-24. Print.

 

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The Central Arizona Project (CAP) versus

Groundwater:

A Comprehensive Look at Arizona’s Water-Energy

Nexus Between the Two Systems

Daniel Basubas, Robbie Horvath, Monica Malapit,

and Anu Venkatesh

Abstract: The arid region of southern Arizona gets its water from two main sources, the Central Arizona Project and from pumping groundwater. The C.A.P. is a canal that runs from Parker, AZ all the way to south of Tucson and requires 688,000 MWh per year to pump 215,000 acre feet of water to make the distance. There are numerous groundwater wells and facilities in southern Arizona that help satisfy Tucson’s water needs; pumping 135,000 acre feet of water requires 162,000 MWh per year. Using articles, books, websites, and online journals we composed these results to conclude that in Tucson, pumping groundwater is about 50% more efficient than using water from the C.A.P. The C.A.P. isn’t as economically sustainable as pumping groundwater, but it is more environmentally sustainable.

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The Central Arizona Project (CAP) versus Groundwater:

A Comprehensive Look at Arizona’s Water-Energy Nexus Between the Two Systems

Introduction:

Water is a scarcity in Arizona and due to the depleting amounts of water

being fed from the Colorado River, its importance to Tucson is more prevalent

now than ever. The Central Arizona Project (C.A.P.) is vital to the state of Arizona,

which provides 55% of the state’s water. It diverts water from the Colorado River

and runs it through 14 pumping plants, 39 radial gates, 50 turnouts, and 1

generating plant. The remaining 45% of Arizona’s water comes from groundwater

as stated in the Arroyo article produced by the Water Resources Research Center at

the University of Arizona. These percentages are refutable because it is also

claimed that 80% of Arizona’s water is provided by the C.A.P. (http://www.cap-

az.com/public-information/ngs/). Since there are many areas of Arizona that water

doesn’t run through, the C.A.P. and groundwater are both important functions of

getting water to Arizona residents. Tucson is located in southern Arizona and relies

mostly on water from the C.A.P. Since the C.A.P. starts in Parker, the water must

travel over 336 miles and be elevated over 2900 feet over that course to finally get

to Tucson. The C.A.P. also recharges reservoirs in several areas near the channel,

in which the groundwater has yet to be used where it sits in case of emergency.

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39% of water in Tucson comes from groundwater. Although the groundwater is

already in the southern Arizona region, factors such as pumping, collection,

distribution, and treatment must be taken into account. All of these processes use

energy, which is becoming a bigger and bigger issue in regards to water. The

water-energy nexus in Arizona is the relationship between the amount of water

used to create energy and the amount of energy required to acquire water. With no

immediate renewable water sources near the southern Arizona region, it takes a lot

of energy to extract and treat that water. Topics that will be discussed include: the

amount of energy it takes to extract groundwater in Tucson, the amount of energy

it takes to transport water to Tucson via the C.A.P., the amount of energy it takes

to treat and distribute that water, which form of water acquisition is most

economically plausible for southern Arizona residents, and which source will be

able to sustain water sources for the future.

Methods and Materials:

The assignment was split into sections between group members, researching

the water-energy nexus of the C.A.P. and the water-energy nexus between

groundwater. Each group came together with their information, which was then

combined to make the report. For groundwater research, the materials were found

primarily using the University of Arizona’s Library. The Science and Engineering

library as well as the Main library provided relevant sources of information. The

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library database WorldCat, proved to be a useful search engine for locating online

sources and digitalized resources that were for the research paper. Two interlibrary

loans were completed thorough the ILL office at the U of A library to obtain two

books, one of which was borrowed from the University of Arkansas. The

information for C.A.P. was gathered using the Internet, C.A.P. videos, C.A.P.

pamphlets, and the online University of Arizona library and cited by

www.refworks.com. Dr. Riley provided the C.A.P. videos and pamphlets, which

can also be found at the nearest C.A.P. site in west Tucson. As for any problems

encountered, there was only one problem for the groundwater research. Some of

the books and articles found were dated materials that were sometimes older than

10 years. The subject they address and the information they provided can still be

used effectively for this research paper, it is just important to note that there was

some difficulty in finding more recent sources.

Results:

The Central Arizona Project provides water for over 50% of Arizona’s

population. Its only pump generating plant lies at the border between Arizona and

California at Parker Dam, where the four generators produce 30,000 kWh each

amassing to a 120,000 kWhs energy output. The C.A.P. also gets power from the

Navajo Generating Station, which it owns a 24% share of the station’s 2250 MW

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energy output (Arroyo article). The high number of turnouts and radial gates means

that there are many recipients that depend on this water.

Figure 1

Source: http://www.cap-az.com/operations/

To get water from the beginning of the C.A.P. in Parker all the way to

Tucson, it takes 9.8 kWh of energy to transport 1,000 gallons of water. There are

325,851 gallons of water in an acre foot, which means that it takes about 3200

kWh to transport an acre foot of water to Tucson. The average amount of energy it

takes to transport water from the C.A.P. is 5.5 kWh per 1000 gallons, or 1792 kWh

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per acre foot. The reason Tucson’s energy requirement is so much higher is due to

its elevation.

Figure 2

Source: http://ag.arizona.edu/azwater/files/Arroyo_2010.pdf

As shown in the figure above, the route that the C.A.P. takes begins with a

slight incline, and then moves to an exponential incline. This has a direct

correlation with the amount of energy it takes to transport the water. As previously

stated, there are 14 pumping plants that elevate the C.A.P. water over 2900 feet

over the 336 mile course. It only makes sense that the amount of energy it takes to

transport water to the Mark Wilmer pumping station in northern Arizona would be

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significantly less than the amount of energy it takes to transport that same water to

the Black Mountain pumping station south of Tucson in southern Arizona (figure

2). The C.A.P. distributes 215,000 acre feet of C.A.P. water to Tucson every year,

with 38,300 acre feet of that water going to the Native American Reservations.

This means that it takes 688,000 MWh to transport all of Tucson’s C.A.P. water to

Tucson annually.

Figure 3

Source: http://ag.arizona.edu/azwater/files/Arroyo_2010.pdf

The figure above indicates the amount of energy in kWh per acre foot it

takes to deal with the water in Phoenix and Tucson. The important parts of Figure

3 include pumping, water treatment, and water distribution. In four out of the six

categories, Tucson uses less energy for its water needs compared to Phoenix.

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Conveyance refers to the C.A.P., which requires more energy in Tucson than in

Phoenix because it is elevated higher. The energy required to treat water from

Tucson is more than in Phoenix because Tucson suffers from groundwater

contaminated with TCE (trichloroethylene) that dates back to the early 20th

century. Adding up the required energies for pumping, water treatment, and

distribution, it takes about 1200 kWh per acre foot to fully convert the groundwater

and transport to it to destinations.

Figure 4

Tucson consumes 135,000 acre feet of groundwater per year. Figure 4 above

shows where this groundwater is distributed to with most of it going to central

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Tucson. The majority of groundwater wells in Tucson are located in central

Tucson, however there are a number of wells that are far away, almost 100 miles

from Tucson, that transport groundwater to the area. This contributes to a higher

overall use of energy in MWh of groundwater and could be reduced if conveyance

measures were most efficient. With Tucson consuming 135,000 acre feet of

groundwater per year, according to the Energy Intensity by Water Use Stage graph,

Tucson consumes 162,000 MWh annually to pump, treat, and distribute the

groundwater. According to our results, it takes the C.A.P. 688,000 MWh to

transport 215,000 acre feet of water annually while pumping groundwater takes

162,000 MWh to transport 135,000 acre feet of water annually. This means that in

Tucson, pumping groundwater is 52% more efficient than using the C.A.P. for

fresh water.

Discussion:

The C.A.P. allows millions of people the chance to have clean water,

without having to pump it from a local well. However, the amount of energy used

to get water from the C.A.P. is far more than the amount of energy it takes to pump

water from the ground. The energy used for ground water is more efficient because

the only energy required is to pump, clean, and transport. Though the C.A.P. water

also needs to be transported and cleaned, the amount of energy it takes to pump

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and transport that water from an elevation of 423 ft. in Parker to 2,389 ft. in

Tucson is massive.

Groundwater is mainly used for agriculture and irrigation and the uses of

groundwater are not limited to just that; they may equally overlap the uses of water

that are utilized from the C.A.P. Groundwater is relied on as a long-term source to

fill in any shortcomings by the C.A.P, thus it can be concluded that both resources

are necessary to sustain Arizona’s water resources long term. Although C.A.P.

water is easier to access as the tools for transportation have been laid out, pumping

groundwater is closer and overall requires less energy. The C.A.P. does deliver

more water than groundwater is pumped, however pumping groundwater in

Tucson is a far more efficient method of obtaining water.

Conclusion:

Pumping groundwater is a more energy-efficient and economical source of

water for Tucson. The long distance and difference of elevation between the start

of the C.A.P. in Parker and Tucson is too much of obstacle to be an efficient form

of obtaining water for southern Arizona residents. This is not to say that the C.A.P.

should be abandoned, however. The C.A.P. offers hundreds of jobs to many

Arizona residents, thus stimulating Arizona’s economy while providing a

necessary resource to southern Arizona. Despite the economical disadvantages of

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transporting water using the C.A.P., it is vital that Arizona utilizes both of these

resources in order to supply its ever growing population with clean, pure water.

References/Works Cited

1. Booker, James F. "Economic and Hydrological Impacts of

Groundwater Management for Arizona." Effects of Human-

Induced Changes on Hydrological Systems. (1994): 781-790.

Print.

2. Fox, Kel M., Peter F. Ffolliott, Malchus B. Baker, Jr., and Leonard

F. Debano. More Water for Arizona: A History of the Arizona

Watershed Program and the Arizona Water Resources

Committee. 1st ed,. Phoenix, Arizona: Primer Publishers,

2000. 70-74. Print.

3. Stone, Andrew W. . "Groundwater for Household Water supply in

Rural America: Private wells or Public systems?." Gambling

with Groundwater-Physical, Chemical, and Biological

Aspects of Aquifer-Stream Relations. 227-232. Print.

4. Hanemann, W. Michael. The Central Arizona Project.

[Berkeley]: California Agricultural Experiment Station,

Giannini Foundation of Agricultural Economics, 2002.

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5. Hoffmann, J. P., Leake, S. A., Arizona. Dept. of Water Resources., Geological Survey

(U.S.). Ground-water Resources Program. & Geological Survey (U.S.). (2005).

Simulated water-level responses, ground-water fluxes, and storage changes for

recharge scenarios along Rillito Creek, Tucson, Arizona. Online source.

6. Robinson, D.W. "Construction and Operating Costs of Groundwater Pumps

for Irrigation in the Riverine Plain."CSIRO. CSIRO land and water,

January 2002. Web. 9 Mar 2010. <http://www.clw.csiro.au/publicatio

ons/technical2002/tr20-02.pdf>

7. Dwyer, Colleen. "Parker Dam and Powerplant." U.S Bureau of Reclamation. U.S Bureau of Reclamation, 07/2003. Web. 8 Apr 2010. <http:/ /www.usbr.gov/lc/region/pao/parker.html>.

8. Lamberton, Melissa; Newman, David; Eden, Susanna; Gelt , Joe. “The Water-Energy Nexus.” Sharon Megdal. The University of Arizona, 2010. 20 April 2010. <http:/ /ag.arizona.edu/azwater/fi les/Arroyo_2010.pdf>

9. May, Kyle. “Navajo Generating Station.” The Central Arizona Project. Phoenix, AZ October 30, 2008. 20 April 2010. <http://www.cap-az.com/public-information/ngs/>

 

 

 

 

   

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Arizona Water- Energy Nexus:

Evaluating Wind Energy and Bio fuels

Chelsea Hanen, Christina Duffala, Rochelle Reuter, and Clifford Jones 

 

 

 

Abstract   

The essential goal of this paper is to compare and contrast the alternative energy sources in the Tucson Basin. We are specifically comparing wind energy and the bio fuel Ethanol by researching how each energy source is produced and importantly the water used to making each source. With that in mind, we researched both wind energy and the production of Ethanol to determine which energy source consumes the least amount of water. As a result, we found out that wind energy requires a substantially less amount of water than the production and harvesting of Ethanol.

 

 

 

 

 

 

 

 

 

 

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Arizona Water- Energy Nexus: Evaluating Wind Energy and Bio Fuels

Introduction

  Water resources in the arid west have always been a main concern for the

people who inhabit it. Unlike the east, there are very little natural water sources

and rain fall that can sustain a massive population. Therefore, the people who have

settled in the west have devised ways to capture what little water is available and

use it to sustain most of the west coast. The west’s most important water supply is

the Hoover Dam, formerly known as Boulder Dam, which utilizes the Colorado

River to distribute water to its inhabitants (2). Following the Hoover Dam there

have been many smaller dams to assist with the massive project. The Hoover Dam

not only supplies water to the west, it also provides much of the electricity that is

distributed to the west coast. By using water as a source for electricity, many can

see that many problems can arise from this particular strategy. If a severe drought

was to occur in the west, not only would the west would lose most of its water

supply, the power supply would also disappear. As one could imagine, that would

be detrimental to the west, therefore, energy alternatives must be found to prevent

this from happening. Among the states in the arid west that receives the benefits

from Hoover Dam, is Arizona. Arizona is an especially dry state that receives

much less rainfall and has very little natural resources than the other states that

share the precious water source, placing the state in a stressful situation if a severe

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drought was to occur. With that constant threat, it is important that alternative

energy resources be implemented in Arizona to preserve the precious water supply.

There are many different energy alternatives that can be researched and applied to

the west. In particular, we are going to compare and contrast the bio fuel, Ethanol,

and wind turbines. These two energy resources are important alternatives to using

water in energy production. Wind turbines harness the wind’s power to generate

useable energy. On the other hand, Ethanol is made from crops to produce an

alternative fuel for fossil fuels. By thoroughly investigating each alternative, we

will determine which alternative energy source would be beneficial to the Tucson

Basin.

Materials and Methods

For the report we had to find books, magazines/ journals, special databases,

and grey literature, but we also found information on websites. We found these

resources in the library, on the library website, and on the internet. When we were

in the library we would use the quick lookup guide to find where we needed to go

to find the materials that were needed, then we would go find them and check them

out of the library. When were on the library website, we would look up the items

that we needed that had the key words that we were searching for, and they would

have an online copy for us to view. Lastly, when we were on the internet looking

31  

 

for information we would use Google to start us out on our search for information.

We would then pick and choose what materials we wanted to use in our report

from our research results.

Results 

After completing the necessary research, we found that each alternative

energy source is much different than the other, and that 80% of the cost of water is

related to energy (7). Wind turbines are devices that generate energy from the wind

that occurs naturally in the environment. They are mostly made up of steel and

fiberglass, or wood proxy (8). Once the windmills are up they require no energy

and occasional maintenance, but only in dry arid conditions they require water (8).

They only need a small amount of water to occasionally clean the blades of the

turbine to prevent the material from warping under the severe weather. In the event

that the wind turbines blades are compromised, they will no longer work efficiently

and will need to be completely replaced. If the turbine is located where heat would

not warp the blades, then they do not require water for cleaning. Wind turbines can

range from 250 watts to 5 megawatts and each can generate different amounts of

energy. For example, a 10 kilowatt wind turbine can produce up to 10,000

kilowatt-hours with an average of 12 miles per hour wind speed, which is not

enough to power the average household because one household uses on average

10,655 kilowatt-hours (kWh) per year (8). On a larger scale, more energy can be

32  

 

produced on wind farms than individual wind turbines (1). The power that is

created on varies on how many and how big the wind turbines are. Generally, wind

farms require a minimum of 13 miles per hour wind average to be beneficial (1).

Specifically, Arizona has 18 prime locations that can be utilized for wind farms

(9).

Another alternative energy source that was researched was Ethanol.

Ethanol is an alcohol that is produced from the sugar of plants, such as corn, switch

grass, and sugar cane (4). First, the plants that are going to be made into Ethanol

must be grown, but this requires mass amounts of water. The water that is required

to water the plants as they grow varies from state, but in Arizona the use of water

would be massive (7). Once the plants are harvested, they are ground to expose the

starch (3). Then, water is added to the ground grain, cooked briefly and enzymes

are added to covert the starch to sugar using a chemical reaction called hydrolysis

(3). Yeast is then added to ferment the sugar to Ethanol, later the Ethanol is taken

out of the mixture by distillation and the water is removed by dehydration (3).

Adding to the water that is required to produce the plants, the production adds on

about 4 gallons of water to every one gallon of Ethanol produced (4).

33  

 

Figure 1 represents the 

possible areas where 

wind farms can be 

placed in Arizona (9). 

34  

 

Figure 3 shows the 

planned ethanol plats 

and their estimated 

water use in gallons 

per day (5). 

Figure 2 represents 

the increased 

amount of Ethanol 

production (6). 

35  

 

Discussion

Looking at both wind energy and bio fuels, specifically Ethanol, one can

understand that both create alternative energy sources for daily usages. They both

contribute to the ability to create energy without depleting non- renewable

resources such as fossil fuels. They are great ways to have energy by using

renewable resources as opposed to non- renewable resources. However, when

looking at the water consumption used in the creation of energy one can clearly see

that wind energy is a better alternative.

Ethanol uses massive amounts of water as opposed to wind energy that

uses very little to none. To create ethanol colossal amounts of water need to be

used just to create it as shown in Figure 3. In general, it takes about four gallons of

water to create one gallon of ethanol. With this statistic, the question arises if

benefits really outweigh the costs.

Ethanol is a great alternative fuel but the consumption of water can be

detrimental. Ethanol is a great and efficient alternative fuel source for cars because

it reduces the carbon emissions and reduce the demand for fossil fuels. However,

looking at Figure 2 it can be seen that the production of ethanol has risen over the

years. With the production rising, at this rate it appears that the usage of water

would not be a great alternative in the long run and using that much water makes

the costs to outweigh the benefits, causing it not to be as efficient as wind energy.

36  

 

The numbers show that wind energy is the way to go and in the long run prove that

wind energy is a better alternative energy source than that of ethanol, especially in

the arid southwest and specifically Arizona where water resources are limited.

Although wind energy would be beneficial to the west, it can only deliver energy

to houses and buildings. However, ethanol is a more transferable energy source

and it is more commonly used.

What about wind energy? Looking at wind energy the amount of water is

miniscule compared to that used in the production of ethanol. The amount of water

needed would only be used for the condition of the wind turbine. Water would be

used to keep the blades from warping and most places have ideal environments that

would prevent the need for regular cleaning. However, in the arid southwest we

would need to use water to clean the blades because of the dry weather that would

cause the blade to warp. Overall, wind turbines require much less water and only

use it for regular maintenance.

Looking at the comparison of ethanol to water, it is apparent that wind

energy would be the best alternative for the arid southwest and specifically

Arizona, because our water sources are limited. There is little thought about wind

energy in Arizona because it is a dry, hot environment with little wind. To create

wind energy, wind speeds must average at least 13 MPH to create a sufficient

amount of energy that is useful. However, in Arizona there are places that enable

37  

 

wind energy to be a possibility. Looking at Figure 1, there are 18 locations that

wind farms could be placed to create energy. In particular, San Xavier is the

closest location that could be highly beneficial to the area.

Conclusion

The prime source of water derives from the Colorado River and with an

increase of population in the Phoenix and Tucson areas; it will only be a matter of

time before our water resources will soon run out. The demand for alternative

energy sources is increasing. Wind turbines and the bio fuel ethanol, are important

sources to Arizona’s energy but differ greatly. One of the benefits of having a wind

farm is that it requires very minimal water and creates large amounts of energy.

Because of the lack of wind in the Tucson area, wind farms are not applicable to

Tucson but San Xavier would provide energy to Tucson instead. Ethanol, although

it is considered a safer energy source, the water demanded for the energy source is

significantly higher than others. The harvesting alone requires more than 325,000

gallons of water per acre of land. In addition to the water used for harvesting the

plants used for Ethanol, the water used for the actual production of ethanol is

demanding as well. For every 1-gallon of Ethanol produced, approximately 4

gallons of water is needed for production. Ethanol and Wind farms are safer and

more environmentally friendly sources of energy. However, one can infer that the

water demanded for sources like Ethanol are incomparable. Although wind farms

38  

 

are highly efficient and the most renewable, Arizona cannot rely on wind power

alone to generate energy. With today’s increase in technology and the rapid

decline of water, we can only hope to find more renewable energy sources with

little demand for water use.

 

 

 

 

 

 

 

 

 

 

 

 

 

39  

 

References 

1. Ackermann, Thomas. Wind Power in Power Systems. Chichester, West

Sussex, England: John Wiley, 2009. 25-195. Print.

2. Eden, Susanna, and Sharon B. Megdal. "Water and Growth." Special

Databases. University of Arizona. Web. Mar. 2010.

3. "Ethanol and Water Use." Web. Mar. 2010.

4. Kaltenbach, Colin. Arizona Bio fuels. 2010. Pima Associations of

Government. PowerPoint. Mar.2010.

5. "November 2007." Watercrunch. Web. Mar. 2010.

6. "Morehead State University - Richard Bloomfield - Ethanol Technology."

Morehead State University - The People Publisher. Web. Mar. 2010.

7. "The Water- Energy Nexus." Arroyo (2010). Water Resources Research

Center, Department of Agriculture, The University of Arizona. Print.

Mar. 2010.

8. "Wind Energy Basics." American Wind Energy Association. Web. Mar.

2010.

9. "Wind Powering America: Arizona 50-Meter Wind Resource Map." Wind

and Water Power Program: Wind Powering America. Web. Mar.

2010.

   

40  

 

 

Nuclear Power and the Water-Energy Nexus:

Palo Verde Nuclear Generating Station

 

Bernardo Jimenez, John F Kodatt, & Tom R. Taylor

 

 

 

 

Abstract:

The Southwest has experienced an unprecedented growth in population that created a need for power. Taking into consideration the impact on the water-energy nexus, the Palo Verde Nuclear Generating Station was built. We explored the costs, benefits, and consequences of this action and found evidence for it. The impact on the environment was not as pronounced as other forms of producing energy. The water use a relatively insignificant issue because 99 percent of the water used is effluent that comes from the 91st Avenue treatment plant in Phoenix, minimizing the pumping of groundwater for plant use. Compared to the other alternatives, such as coal burning plants, or natural gas plants, the nuclear power plant was the best choice based on kWhrs produced vs. water used.

 

 

41  

 

Nuclear Power and the Water-Energy Nexus: Palo Verde Nuclear

Generating Station

Introduction:

With the increase of population in the arid Southwest, the demand for water

and electricity has increased. We explored the impact, positive or negative, that a

nuclear power plant can have on the water-energy nexus. Because the Palo Verde

Nuclear Generating Station is the largest nuclear power plant in the United States

and is located right here in Arizona, we specifically focused on it. Nuclear energy

should be of interest to Tucson as the city grows and requires more water and

electricity due to the small amount of water used in the energy production. The

water it takes to power the massive reactors at Palo Verde is about the same as a

small city for an entire year, about 20 billion gallons. The plant produces enough

power for millions of people to have electricity, 4,000 megawatts, but how much

water does it cost the state of Arizona in its allotment of water each year? The

ideas and basis of this paper is a comparison between the amount of water it takes,

to the amount of energy it produces. The amount of coal and other styles of

producing energy are common and everyone knows more about how they work,

but little is known about the advantages and disadvantages of nuclear since the last

one built was in the late 70's (Keay).

42  

 

Materials and Methods:

Information was found through the library one way or another. We searched

key terms in the University of Arizona Library’s online catalog. Terms such as

“nuclear power” and “Palo Verde power plant” were typed into the search box and

got results for several texts. By reading the description of each book, we could

decide if it was worth a look. Once it was decided a book was worth looking at in

person, the call number was recorded. After browsing through all the results, a trip

was made to the library to check out the books in person. This method saved time

since the search for existing texts could be made anywhere with a computer. The

only trip required to the library was to check out the books.

Another method we used was searching the internet itself for information.

Using a search engine such as Google, typing in relevant terms such as “nuclear

power” and “Palo Verde power plant” yielded multiple results. Once the search

results popped up, we had to discern whether or not a particular source was useful.

Relevance to our topic, author, and writing style were all considered.

Working as a group proved to be a challenge. Hectic work and school

schedules were a challenge to deal with. Meeting online and through other

technology aided in the communication that did exist.

43  

 

Results:

The Palo Verde Nuclear Generating Station is located about 55 miles west

of Phoenix; it has been the largest power producer of any kind in the United States

since 1992. Its three units are capable of generating nearly 4,000 megawatts of

electricity and recycles about 20 billion gallons of waste water each year, 99

percent of its total water usage (Nuclear Reactor Commission). A nuclear power

plant does not expel CO2 emissions from fossil fuels. The waste is minimal. If the

waste produced by nuclear facilities to power someone for their entire life was

added up, it would add up to a regular size can of soup. This waste is then disposed

of through carefully regulated measures. (PNM).

Each unit has 2 reactor cooling loops, each with a 2 reactor cooling pump

and a single steam generator. (Virtual Nuclear Tourist)

44  

 

Because of its desert location, Palo Verde is the only nuclear plant in the United

States that does not sit on a large body of water. Instead, it uses treated effluent

from several area municipalities to meet its cooling water needs, the main provider

of water being the 91st Avenue treatment plant. (APS)

Palo Verde, the largest single commercial taxpayer in Arizona, is operated

by APS and is owned by a consortium of seven utilities in the Southwest. APS

owns 29.1 percent of the plant.

45  

 

The given graph represents the amount of energy that comes from nuclear reactors

and also from other forms of materials. As we can see, nuclear is not the highest,

but is in the top three when it comes to how much energy comes from that

substance.

The site of the Palo Verde is located in a semi-arid desert in Arizona.

Summers are hot, rainfall is low, and there is a big range of daily temperatures.

Highs over 40 degrees Celsius are normal during the summer. Temperatures can

drop to zero degrees Celsius at night in the winter (APS).

The sources of water for the plant are onsite wells and effluent from the City

of Phoenix 91st Avenue municipal sewage treatment plant. Almost 99 percent of

the water used is effluent from the sewage plant while one percent is from the

wells. Water use is mainly for heat transfer in the primary cooling systems for,

steam production in the turbine systems, and cooling water for the condenser

cooling water systems. The pumped groundwater is only for domestic use, utilities,

and air conditioning. Reclaimed water is utilized for all other purposes. About

60,180 gpm of effluent is the maximum flow from Phoenix to the Palo Verde

station. At the plant, there is a local treatment facility to prepare the water for use.

Almost 15,750 gpm are sent to each unit of the condenser cooling-water systems.

The cooling towers use an average 14,700 gpm per unit in evaporation. These

values will later be discussed as how it pertains to the water energy nexus, and also

46  

 

how this relates to the water used to produce unit of electricity. (Nuclear Reactor

Commission).

During the construction of the power plant, there had to be some impact on

the surrounding area. The construction did not impact any surface bodies of water

because none existed in the area. As a result, groundwater had to be pumped for

construction. Pumping for construction resulted in a drawdown of the water table

of 1 ft/yr. Yet, irrigation in the area caused a drawdown four times as large

(Nuclear Reactor Commission).

Water at the site is also affected during operation of the plant. While there

are no surface waters in the vicinity, a reservoir does exist onsite. Furthermore, the

drawdown of groundwater is the same as during construction. The water vapor

plumes emitted by the cooling towers can have certain weather effects. Water

droplets may form and fall to the ground. The vapor plumes can descend and create

fog, and even increase humidity by 50 percent. (Nuclear Reactor Commission).

Compared to many different power sources, nuclear energy is one of, if not

the most efficient. In theory, solar energy seems like a great alternative, especially

in Arizona where there is so much sunlight; however, it is not economically

advantageous enough to use mass amounts of solar panels. While they are

improving, solar cells do not do a well enough job of creating electricity from the

47  

 

sun. Geothermal is another alternative energy source. Harnessing the power of the

Earth seems difficult and dangerous such as the volcanoes that erupt at Pompeii .

Yet, it is not well exploited. Very little production comes out of this type of

energy. In addition, hydroelectric power is clean and effective, but not feasible.

The Colorado River is all dammed up and no new dams will be constructed.

Virtually all the hydroelectric power possible is currently being squeezed out of the

Colorado River. Similarly, while wind energy is as clean as one can get, Arizona

simply does not have enough wind to consistently churn big turbines. For such a

massive power demand, nuclear power was the best choice.

Table 1: Water Consumption of PNM Power Plants

(Christensen)

48  

 

These are all power plants that the Public Service Company of New Mexico

(PNM) uses to provide electricity to the state, designed by the engineering firm

JLR. The San Juan plant is a coal plant that has one of the worst Gals/kwh there is,

this means it uses a lot of water while producing minimal energy. The Reeves plant

is a natural gas plant that has a ratio close to 1.0, which tells us it, uses almost as

much water as energy it produces. Afton and Lordsburg both are natural gas that

have ratios which are nothing to be ashamed about but could not hurt to try and

make better the overall ratio is fairly small. As for the Four Corner plants, they are

coal driven and are comprised of 5 units and has an overall water to energy ratio

that is higher than the Palo Verde. (PNM). The Palo Verde is a nuclear plant and as

you know has a great ratio of only 0.028, which beats all the other natural resource

plants beside wind, which uses no water at all. As mentioned before the Wind

Farms plant uses no water and still generates a large amount of electricity, which

makes that plant the “greenest of them all”. Last the Delta Person plant, which is

natural gas, which produces a small amount of electricity and doesn’t use that

much water when compared. (Christensen). This is freshwater usage such as

groundwater and river water. The Palo Verde plant is the best at not consuming

these limited quantities by recycling effluent water (APS).

49  

 

Discussion:

As we can see from the results, it takes about 20 billion gallons a year to run

the Palo Verde plant. Calculating to see if the amount of water it uses subtracted

from the recycled water should be done to see how much water is really being used

in the plants process of make nuclear energy (APS). Water is a key ingredient in

making power whether you’re a nuclear station or not. The amount of water

consumed must be justified in how much energy being produced is compared to

the water intake. Seeing that coal is the most widely used element in the production

of energy, nuclear should be taken into consideration and seeing if the amount of

electricity being produced by nuclear compares to that of coal. Although nuclear

energy has a bad reputation of being too dangerous we can see by the results that

the number of nuclear accidents has gone down. By determining if nuclear is safe

enough or not we can see that no new nuclear reactors have been built since 1979.

Conclusion:

What you have read is a paper about the Palo Verde is that it uses a lot of

water and makes a lot of electricity, but is it effective in what it does? The plant

delivers power to millions of customers across the state that uses more than 4,000

Megawatts per year. For the plant to run smooth and efficiently, we have to make

sure that the plant has enough water and cools down the reactors. To make sure

50  

 

they have enough water they use minimal wells and rely mostly on the 91st Ave.

treatment plant. Not only is the plant the largest nuclear reactor in the world it has

a ratio (0.028) of gallons per kilowatt-hour that makes us one of the best out there

despite the wind farm that uses no water but produces little to no energy in

Arizona. Although looking at the Four Corners plant that only uses a ratio of

(0.010) gallons per kilowatt-hour, if you average that with the other Four Corners

plant you can see that the Palo Verde plant is still the lowest. The data and research

we have collected all leads us to say that although the plant uses billions of gallons

a year to run it produces enough energy to make up for it.

51  

 

References Cited

1. APS. “Power Plants.” <http://www.aps.com/general_info/AboutAPS_18.html> 

 

2. Christensen, Marc. “Industry and Water Quality: Electric Power.” New Mexico

Water Resources Research Institute. October 2006.

<http://wrri.nmsu.edu/publish/watcon/proc51/christensen.pdf>

3. Keay, Colin. “A perspective on Nuclear Energy.” World Nuclear Association,  

London, February 2002.  <http://www.world‐nuclear.org/opinion/razorfeb02.htm> 

 

4. PNM. “Power Plants.” <http://www.pnm.com/systems/plants.htm> 

 

5. The Virtual Nuclear Tourist. “PWR Cycle.” 2009. Revised: April 12, 2009. 

    <http://www.nucleartourist.com/type/pwr_cycle.htm> 

 

6. United States. Department of Energy. “Energy Explained: Electricity in the   

United States.” Update: 2 Feb. 2010. 

<http://tonto.eia.doe.gov/energyexplained/index.cfm?page=electricity_in_the_united_states> 

 

7. United States. Office of Nuclear Reactor Regulation. Final Environmental  

Statement Related to Construction of Palo Verde Nuclear Generating Station, Units 1,2 & 3. 

1975.  

   

52  

 

Exploring the Water-Energy Nexus:

Sustainability of Thermal Solar Power Plants

Courtney Campbell, Adrian Maracinaru, Vanda Ngo & Ngoc Hue Nguyen

  

 

ABSTRACT

Water is necessary to life on earth; the energy that creates electricity is essential to our lifestyle. The two are inherently related. As the Water-Energy Nexus comes to the forefront of discussion in areas such as the arid Southwest and Arizona, attention is brought to the importance of conserving resources and utilizing methods that minimize water use, while maximizing energy production. Through extensive research and careful comparison of several methods of energy production, it was determined that solar thermal power is much more sustainable than other methods of electrical generation, in the sense that energy production can be maximized on minimal water usage.

 

 

 

 

53  

 

Exploring the Water-Energy Nexus: Sustainability of Thermal Solar Power Plants

INTRODUCTION

Water is a necessity of life. As such, it is important to effectively manage and

conserve water, especially in the arid Southwest. As the push towards clean,

renewable, and efficiently produced energy intensifies, Arizona has become a focal

point for the development of solar thermal power plants. Plants such as these have

already been implemented in the Mojave Desert of California, and have achieved

great success in the generation of energy using the solar thermal method. The

technology used in solar thermal power uses heat from the sun to create steam,

which turns turbines to generate energy. Water is often utilized as the fluid which

is boiled to create steam. It is also used as a cooling method, in some cases. While

the Arizona desert serves as the ideal location for such plants, a problem arises in

the lack of water to contribute to the generation of solar thermal energy.

Fortunately, the water usage in solar thermal power plants is considerably lower in

comparison to other methods of energy generation.

 MATERIALS AND METHODS

We familiarized ourselves with the topic by researching the multiple facets of the

Water-Energy Nexus, as it relates to the Arid Southwest and the city of Tucson.

Once groups were established, we chose to set our focus on the environmental

54  

 

sustainability and cost efficiency of solar thermal energy production. We explored

the relationship between water usage and energy production in order to determine

if this method of energy production actually maximizes the energy produced while

minimizing water usage. Utilizing search tools provided to us by the University of

Arizona library, simple Google searches, and lots of online exploration, we

garnered information pertinent to the subject matter. Due to Tucson's lack of

thermal solar power plants, our analysis is not entirely focused on the Tucson

basin, but rather demonstrates how solar thermal technology can benefit the entire

state of Arizona and the arid Southwest, as a whole. By compiling data from

existing plants in California and plans for new plants in Arizona, we were able to

find enough information which was applicable to the Water-Energy Nexus in

Arizona. Relevant research shows that the solar thermal power plants are

distinguished according to either air or water cooling. In this report, the air cooling

data was used to represent solar thermal power plants in comparison to other

energy production technologies.

RESULTS

As both energy and water demands continue to increase, it is imperative that the

residents of the arid Southwest, including Tucson, AZ, explore methods of energy

generation which find a balance between water usage and electric production. One

method which has already been implemented in California's Mojave Desert, as

55  

 

well as in other areas around the world, is the creation of solar thermal power

plants. These solar thermal power plants already constitute the vast majority of the

world's solar power plants, and they rely on water for energy production. Majority

of solar power plants are what is called concentrating solar power system (CSP). In

essence, the solar radiation is used to heat water and create steam, producing

electricity through turbine generators (5). In some cases, water is also utilized to

cool the solar panels, when air cooling is either nor effective enough or too costly.

The solar thermal energy production method is similar to the way traditional fossil

fuel power plants operate. The difference is in the source of the energy. Solar

energy production relies on clean and renewable solar radiation, whereas

traditional fossil fuel power plants rely largely on coal and natural gas. There are

three main types of concentrating solar technology which are used in solar thermal

power plants: power tower, linear concentrator, and the dish-engine system. They

all use some kind of heat transfer fluid to collect the sun’s energy reflected by the

mirrors but themselves fluid could be water or certain kind of oil or salt. It depends

on the specific plants for which type of fluid they use.

Solar Thermal Technology 1: The Power Tower

The first and most prevalent type of solar thermal power plant is the power tower

model. These power plants consists of a series of large, flat mirrors called

heliostats that focus the sunlight on to a receiver at the top of a tower, which is

56  

 

centrally focused within the framework of these mirrors. Inside, the receiver is

filled with a heat transfer fluid. The different heat transfer fluids used include

water, oil, and molten salt. This fluid is heated and then used to heat the water, thus

creating steam and powering the turbines, which allows electricity to be generated

(4). According the study done by National Renewable Energy Laboratory, the

water consumption of the power tower using the dry cooling method is estimated

to use about 90 gal/MWh (5). This approach is one that can be explored further as

solar thermal energy production is expanded within the Southwest region.

Presently, water is the most utilized fluid. Given recent trends, however, molten

salt is actually becoming more ideal for the power tower because it is a more

efficient heat transfer fluid. Molten salt also has the ability to store thermal energy,

which allows the solar plant, such as the Solar Two in California, to generate

electricity when it is nighttime or in sunless weather. Water will still be needed to

run the turbine generator but less water will be consumed when it is not used as a

heat transfer fluid.

  

 

57  

 

 

 

 

Figure 1: Example of the Power Tower System. (U.S. Department of Energy)

Solar Thermal Technology 2: The Linear Concentrator

The second type of thermal solar power plant is the linear concentrator, which has

two different designs. The more common one is called the parabolic trough system.

The shape of the troughs focuses the sun energy at a horizontal tube running

parallel to the trough, which contains the heat transfer fluid—in some cases, water.

Like other CSP methods, the fluid is used to heat water create steam to drive the

turbine generator. The other type of linear concentrator is a linear Fresnel reflector

system (4). In this case, mirrors are set to reflect sunlight into tubes placed above

the mirrors, though both types work according to similar principles. That system is

probably the least efficient as far as its water use of 1000 gal/MWh (5). Assuming

58  

 

that the air cooling method is used, the average parabolic trough plant consumes

only 78 gal/MWh of electricity produced (5). According to a recent report

published by the US Department of Energy, air cooling for solar thermal power

plants is sufficient even in extremely high temperature climates due to the higher

operating temperatures of these power plants which do rely on concentration of

heat and the subsequent production of steam. A majority of the CSP systems in

development or proposed in Arizona are the parabolic trough type. The Solana

Generating Station in Maricopa County is set to become one of the largest solar

plants and said to use “85% less water than current agricultural land use” (11). At

this particular plant uses molten salt storage tanks for heat so the plant can operate

during cloudy days or after sunset.

  

  

 

 

 

 

Figure 2: Diagram of the Parabolic Trough System. (U.S. Department of Energy)

59  

 

 

 

  

 

 

Figure 3: Diagram of the Linear Fresnel Reflector System. (U.S. Department of

Energy)

Solar Thermal Technology 3: The Dish-Engine System

The final type of thermal solar power plant is a dish-engine system, though it

should be noted that this is the least utilized model. The system utilizes a series of

large dishes to collect incoming solar energy and concentrate it onto a beam which

is directed at a thermal receiver in the power conversion unit. Tubes of both

cooling and heat transfer fluid are in the receiver, and the fluid is heated and

transferred to the engine. In a Stirling engine, the receiver heats up the fluid and

the fluid is used to move pistons to create mechanical energy (4). The energy goes

through a generator to produce electricity. That system is air cooled, so there is no

additional need for water except for cleaning which is about 20 gal/MWh (5).

60  

 

  

 

 

 

 

 

Figure 4: Example of the Dish/Engine System. (U.S. Department of Energy)

Existing Solar Thermal Power Plants in the Arid Southwest

Due to the immense amount of sun light, as well as hundreds of miles of empty

space available in the desert regions of Southern California and Arizona, California

has produced numerous solar power plants in the Mojave Desert region in the last

three decades. A total of nine solar power plants built in the1980s in the Mojave

Desert of California are given the name Solar Energy Generating Systems (SEGS)

by Sun Lab, which works under the U.S. Department of Energy (13). SEGS uses

trough systems to produce a total capacity of 354 MW to generate electricity for

approximately 500,000 people near Barstow, California, where the Mojave Desert

is located. These trough systems are believed to be able to concentrate the heat

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from the sun and intensify it 30-60 times more. The receiver then heats synthetic

oil, which reaches temperatures as high as 735 degrees Farenheit. This then creates

steam that turns the turbine to create electricity. However, on cloudy days, SEGS

plants are relying on natural gas for operation, which provides a total of 25% of

SEGS output (13). Within the SEGS plants in the Mojave Desert region, The U.S.

Department of Energy has built two solar power towers (5). The U.S. Department

of Energy upgraded Solar One to Solar Two, which uses "molten nitrate salt as a

heat transfer fluid in the receiver and a heat storage media" (3). Solar Two operated

from 1996 to 1999, during which it had a capacity of producing up to 10MW of

power. By switching away from water as the heat-transfer fluid, water usage was

further minimized (5).

Recently, the state of California has added the Abengoa Solar Project to join the

nine older solar power plants in the Mojave Desert. According to the California

Energy Commission, the Abengoa Solar Project was proposed to the state of

California on August 10, 2009, and it has been said to be located approximately

halfway between Barstow and Karmer Junction (2). This project will be using the

parabolic trough system to trap sunlight then transfer heat to generate steam. The

steam turns turbines which create electricity from two independent operated solar

fields, each feeding a 125-MW power island. The California Energy Commission

also indicates that the Abengoa Solar Project will be using solely sunlight as its

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energy source and no other substitutes like natural gas will be used for producing

energy (2). The Abengoa Solar Project will use approximately 5,239 acre-feet of

water per year, 2,160 of which will be use in order to cool down the facility (1).

This is equivalent to approximately 780 gal/MWh, a number that is relatively high

in comparison to other solar thermal plants due to the wet cooling technology.

The Solar Millennium Blythe Plant, located approximately 8 miles west of the

city of Blythe, California, is another solar power plant produced by joint forces

from both the Solar Millennium, LLC and Chevron Energy Solutions. This 7,030

acre project will use solar parabolic trough technology and will generate 1,000

MW of total capacity of electricity (12). According to the Federal Register website,

the plant needs will use 600 acre-feet of water annually for full operation, which is

approximately 20 gal/MWh (9).

New Development of Solar Thermal Power Plants in Arizona

Ultimately, Arizona serves as the ideal place for the construction of solar thermal

power plants, being the place which gets the most solar radiation exposure

anywhere in the United States. This arid, radiation-rich desert landscape provides

the perfect environment for the construction of solar thermal power plants. The

planning for construction of large-scale solar thermal power plants in Arizona has

already begun. In April of 2009, the Arizona Department of Commerce and

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Albiasa Solar of Spain announced their intent to construct a $1 billion, 200 MW

solar plant in Kingman, AZ (10). While the exact location of the plant will not be

made public for some time, the company secured over 1,400 acres upon which to

build it. This plant will be the third of its type to be constructed in Arizona. When

it opens in 2013, it will generate enough power to supply up to 50,000 homes,

which will make it one of the largest solar power plants in the world. The plant

intends to minimize water usage by using molten salt as the heat transfer fluid for

energy generation and thermal storage (10).

More recently, Mohave Sun Power, LLC proposed the construction of a 340 MW

plant in May of 2009. The plant will use parabolic trough technology, which has

been utilized in America since the early 1980s and has been proved efficient (8).

On average, plants that operate using this technology utilize between 78-800

gal/MWh (5). The location of this plant will be about 25 miles north of Kingman

and 100 miles south of Las Vegas, and when constructed, it will be the largest

plant of its kind in the world-- taking up over 4,000 acres of land and costing over

$2 billion. The Kingman plant will also utilize molten salts as the heat transfer

fluid. The project will utilize the wet cooling method, but is projected to use as

little as 2000 acre-feet of water per year, which is equivalent to about 200

gal/MWh (8). This value is within the expected range of water usage for parabolic

troughs, but due to the wet cooling technology is higher than most other water

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usage. Despite this, the energy generated from this large-scale parabolic trough

power plant will be up to 75% cheaper than electricity generated using

photovoltaic technology, which uses the light from the sun to generate energy, is

popular in many other solar plants. Additionally, the plants water usage will

account for less than half of the available water allocated to that area of land (8). In

conjunction with the relatively low water usage, this plant is expected to help

reduce the cost of energy for Arizona residents.

 

 

 

 

Figure 5: Site rendering of solar thermal power plant. (Mohave Sun Power LLC)

 

 

 

 

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Comparison of Solar Thermal to Other Energy production Technologies 

 

 

 

 

 

 

 

 

 

Figure 6: Comparison chart of the amount of water used by the different types of

electricity generators. (National Renewable Energy Laboratory)  

 

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In comparison to other methods of energy production and types of power plants,

such as the traditional coal or natural gas steam power plant, solar thermal plants

are both sustainable and cost efficient. Power plants which utilize coal and nuclear

power plants generally use upwards of 500 gal/MWh and can consume as much as

25,000 gal/MWh (5). Some plants such as natural gas power plants utilizing a

combined-cycle, re-circulating design are able to use as little as 200 gal/WMWh,

but this value is still relatively high in comparison to solar thermal plants that

utilize air cooling technology.

 

Figure 7: Pie chart displaying the breakdown of Arizona's energy production

according to fuel source. (U.S. Department of Energy) 

Despite the plans for the development of solar thermal power plants, this type of

energy production has yet to be harvested on a large scale in Arizona. Most solar

power generation and use has been developed for private or individual use, with

very little solar-generated electricity entering the power grid. Arizona currently

generates 43% of its electricity from coal (which requires a minimal of 200

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gal/MWh of electricity), 23% from natural gas (which also requires a minimal of

200 gal/MWh generated), and 28% from nuclear (which consumes a minimum of

500 gal/MWh) (7). These alternate methods of energy production cause both an

intensification of the problem of the Water-Energy Nexus and pose environmental

threats.

DISCUSSION

According to our research and evaluation of data, solar thermal power plants prove

to be the best method for maximizing energy production while minimizing water

usage. Solar energy is a renewable, clean energy source. Other energy production

methods such as coal, oil, and natural gas are limited in quantity and will therefore

continue to become more expensive to recover and difficult to work with. As the

discussion of the Water-Energy Nexus intensifies, especially here in Arizona, it is

important to address the need for renewable, sustainable energy. The results clearly

demonstrate that water consumption by solar thermal power plants which utilize air

cooling is up to 122% less than the significant values for other types of energy

production. These solar thermal power plants rely on a maximum of 90 gal/MWh.

As demonstrated in Figure 6 of the Results section, other types of power plants—

such as coal or nuclear plants—consume considerably more water. In contrast,

solar thermal power plants could consume as little as 78 gal/MWh, if dry cooling

technology was utilized.

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Currently, most of Arizona’s power is generated through coal, natural gas, and

nuclear, with only 0.7% of Arizona’s total energy production originating from

renewable sources, very little of which is solar power. Therefore, over 94% of

Arizona’s total energy needs are generated at the water consumption rate of 200

gal/MWh—at a minimum. Replacing these three types of power plants with solar

thermal energy will result in water savings up to 122%, which translates into

conservation of a minimum of 110 gal/mWh. This allows for the generation of up

to twice the amount of energy, while still conserving water. Given this data, not

only would solar thermal power plants be sustainable in Arizona, but such power

plants would be ideal for Arizona given its geographic topography and climate. By

utilizing dry cooling technology, solar thermal power plants in Arizona would be

able to minimize water usage, maximize energy production, and reduce both cost

and wastes.

CONCLUSION

Water is a precious resource, especially within the dry, arid desert of Arizona. By

analyzing the data, it was concluded that if solar thermal power plants were used to

produce all of the energy for the state of Arizona, the water consumption rate could

be reduced by up to 55%, saving hundreds of thousands of gallons of water. Given

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current water consumption in electric generation, switching almost exclusively to

solar thermal solar generation would allow us to produce double the energy while

still conserving water. In addition, switching to solar thermal would not only

reduce the water cost, but it would also considerably cut down on harmful

pollutants and carbon dioxide emissions. Taking into account the high amount of

solar radiation which Arizona receives, and pairing that with increased solar

efficiency, the conclusion reached can only be that solar thermal power plants

would be sustainable within Arizona given today’s parameters.

REFERENCES

1. "Abengoa Solar Thermal Project Nears Finish Line." California Current.

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2. "Abengoa Mojave Solar Project, Docket # 2009-AFC-05." California

Energy Commission Home Page. Web. 07 Apr. 2010.

<http://www.energy.ca.gov/sitingcases/abengoa/index.html>.

3. Boer, K. Advances in Solar Energy: An Annual Review of Research and

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<http://www.nrel.gov/learning/re_csp.html>.

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<http://apps1.eere.energy.gov/states/electricity.cfm/state=AZaf>.

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<http://hualapaivalleysolar.com/faq.html>.

9. Norris, Karla. "FR Doc 2010-7666." The Federal Register » Daily Rule

Changes, Proposed Rules and Notices of the Federal Government.

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<http://www.thefederalregister.com/d.p/2010-04-06-2010-7666>.

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<http://www.azcentral.com/business/articles/2009/04/19/20090419biz -

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