Navajo Generating Station

Another page on the Web discusses the economic consequences of the closing of the Navajo Generating Station. It has been said by proponents of draining Lake Powell that the Navajo Generating Station could continue to be the major generating facility that it is if the Lake was drained.

The Navajo Generating Station has a maximum capacity of 2,250 MW. The ownership is:

U.S.Bureau of Reclamation 24.3%
SRP 21.7%
Los Angeles Dept. of Water & Power 21.2%
Arizona Public Service Company 14.0%
Nevada Power 11.3%
Tucson Electric Power 7.5%

The Navajo plant uses approximately 28,000 acre-feet of water a year. The majority of the water is used to "make up" the water lost to evaporation from the six cooling towers which provide cooling water to condense the steam exhausting from the turbines (which turn the generators, which provide the electricity).

Two arguments have been made. One is that the river water could still be used for the cooling water requirements. This would require another small dam across the Colorado River. A 25' dam across the river near Antelope Point would provide approximately a one year supply for the power plant. This dam would back water up the channel for 25 miles, upstream of the "Crossing of the Fathers". It is doubtful that the proponents of draining the lake would find this acceptable. The operations would require continuous dredging. The construction of the pumping plant would cost millions of dollars. (The information on the amount of water backed behind the small dam was taken from "Lake Powell, Virgin flow to Dynamo" University of New Mexico Press, 1989.The book documents the findings of the Lake Powell Research Project, a study conducted by investigators from Arizona State University, Dartmouth College, John Muir Institute, Northern Arizona Society of Science and Art, University of Arizona, University of California-Los Angeles, University of California-Santa Barbara, University of New Mexico, and University of Rochester, as well as investigators from other institutions.)

But as explained below this is probably the only economically viable alternative for condensing the steam exhausting from the Navajo Generating Station turbines if Lake Powell were drained.

The second "proposal" is alluded to by David Wegner in an article in the Canyon Country Zephyr, based in Moab, Utah. "There has also been concern that the coal fired power plant outside Page, the Navajo Generation Station, will have to close down. The power plant is not dependent on the reservoir except for cooling water. The cooling could be accomplished by other means. It does not depend or need Glen Canyon dam to survive. Its existence is there because the people decided in 1968 that they did not want more dams in the Grand Canyon. Its location is defined by its access to Black Mesa coal and the electrical distribution market to Central Arizona. That will not change."

First let me address the location decision. Coal is transported over 270 miles from the Black Mesa to the Mohave plant in Laughlin, Nevada by slurry pipeline. The Navajo plant transports coal 70 miles from the Black Mesa. Coal fired power plants in the Midwest burn coal shipped by rail from Wyoming. If fuel was the most important factor all plants would have been built next to mines (this is only the case when sufficient water is also available near a mine or when fuel costs are so low that "dry" cooling technologies are economically feasible). As to the transmission system, new transmission lines were constructed between the Navajo plant and its customer regions. There was no existing transmission capability in the area for the amount of power that would be generated by this plant prior to the plant construction. None of the transmission lines that were in the area prior to the plant's construction are used to transmit Navajo plant generation. Also the majority of the power does not go to central Arizona (defined as the Phoenix metropolitan area). Power is also delivered to Las Vegas, Nevada; Los Angeles, California; Tucson, Arizona; and to the Central Arizona Project.

The plant was built where it now stands was because there was a supply of water and an established town nearby - period!

Now as to "The cooling could be accomplished by other means.". I can only assume he is referring to "dry cooling towers" or "air cooled condensers". While the technologies seemed attractive 20 years ago, the installation of these type of devices have significant draw backs. They are being installed on small "combined cycle" plants and there installations in South Africa on larger coal fired power plants. The use of this type of cooling should be addressed during the initial design phase of a power plant. Both types increase the temperature and pressure at the exhaust of the turbines compared with a wet tower given the same ambient conditions, and are much more expensive. This has the result of reducing the thermal efficiency of a power plant. In the case of the "air cooled condenser", in areas with ambient conditions similar to Page, Arizona, the exhaust pressures which result are generally in excess of most turbines in service today including the Navajo turbines.

Assuming "dry cooling towers" were to be used, the Navajo plant could only generate power at less than 70% of current capacity, and water would still be needed for auxiliary equipment cooling, and to make up for system losses. This would result in even more* new capacity (approximately 700 MW) to be built to meet the peak needs in the Southwest. The costs of building the new capacity and the new cooling systems would exceed half a billion dollars. Combined with new air quality regulations and the associated costs that are expected in the next ten years the owners of the Navajo Generating Station could easily find that abandoning the Navajo Generating Station and buying capacity from another party (which would still have to be built and paid for by someone) would be the more attractive alternative in the the new competitive electrical power industry. (see Technical Discussion)

There is one significant power plant in the U.S. that uses air cooled condensers. The Wyodak plant in northern Wyoming is less than one sixth the size of the Navajo plant. Even with the obviously different ambient summer temperatures this plant's turbines operate with a "backpressure" of up to 15 inches of Mercury (initially designed for this because of the air cooled condensers). The Navajo turbine's maximum "backpressure" is 5 inches of Mercury to protect the turbine blading. The Wyodak plant can profitably produce power (even with the lower efficiency) because its coal costs are less than half of the coal costs for the Navajo plant. (This has to do with the very different types of coal veins in the mines supplying the two plants, royalties, etc.)

There are air cooled condensers in the world on "large" Units. None have the ambient conditions combined with the backpressure requirements of the Navajo Generation Station. Discussions with engineers with a company, which builds these type of condensers around the world, led to the realization that this type of retrofit could easily cost half a billion dollars also (and none exist that are of the size that would be required for the Navajo Generation Station). Again in the new world of electrical deregulation this cost could not be passed on to the rate payers and the owners of the Navajo Generating Station could very well decide to abandon the plant. (see Technical Discussion)

The bottom line is that converting to a "dry" type cooling system would lead to costs that the owners of the Navajo Generating Station would find as unacceptable. This would lead to the need for additional capacity in the Southwest and would lead to the economic results on the linked page.

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