click to return to the Renewable Energy page
Return to Renewable Energy Page

Solar Power Towers Deliver Energy Solutions

What is a Power Tower and How Does it Work?

A power tower converts sunshine into clean electricity for the world’s electricity grids. The technology utilizes many large, sun-tracking mirrors (heliostats) to focus sunlight on a receiver at the top of a tower. A heat transfer fluid heated in the receiver is used to generate steam, which, in turn, is used in a conventional turbine-generator to produce electricity. Early power towers (such as the Solar One plant) utilized steam as the heat transfer fluid; current designs (including Solar Two, pictured at the right) utilize molten nitrate salt because of its superior heat transfer and energy storage capabilities.

 

What are the Benefits of Power Towers?

Solar power towers offer large-scale, distributed solutions to our nation’s energy needs, particularly for peaking power. Like all solar technologies, they are fueled by sunshine and do not release greenhouse gases. They are unique among solar electric technologies in their ability to efficiently store solar energy and dispatch electricity to the grid when needed—even at night or during cloudy weather. A single 100-megawatt power tower with 12 hours of storage needs only 1000 acres of otherwise non-productive land to supply enough electricity for 50,000 homes. Throughout the sunny Southwest, millions of acres are available with solar resources that could easily produce solar power at the scale of hydropower in the Northwest U. S.

What is the Status of Power Tower Technology?

Power towers enjoy the benefits of two successful, large-scale demonstration plants. The 10-MW Solar One plant near Barstow, CA, demonstrated the viability of power towers, producing over 38 million kilowatt-hours of electricity during its operation from 1982 to 1988. The Solar Two plant was a retrofit of Solar One to demonstrate the advantages of molten salt for heat transfer and thermal storage. Utilizing its highly efficient molten-salt energy storage system, Solar Two successfully demonstrated efficient collection of solar energy and dispatch of electricity, including the ability to routinely produce electricity during cloudy weather and at night. In one demonstration, it delivered power to the grid 24 hours per day for nearly 7 straight days before cloudy weather interrupted operation.

The successful conclusion of Solar Two sparked worldwide interest in power towers. As Solar Two completed operations, an international consortium, led by U. S. industry including Bechtel and Boeing (with technical support from Sandia National Laboratories), formed to pursue power tower plants worldwide, especially in Spain (where special solar premiums make the technology cost-effective), but also in Egypt, Morocco, and Italy. Their first commercial power tower plant is planned to be four times the size of Solar Two (about 40 MW equivalent, utilizing storage to power a 15MW turbine up to 24 hours per day).

This industry is also actively pursuing opportunities to build a similar plant in our desert Southwest, where a 30 to 50 MW plant would take advantage of the Spanish design and production capacity to reduce costs, while providing much needed peaking capacity for the Western grid. The first such plant would cost in the range of $100M and produce power for about 15¢/kWh. While still somewhat higher in cost than conventional technologies in the peaking market, the cost differential could be made up with modest green power subsidies and political support, jump-starting this technology on a path to 7¢/kWh power with the economies of scale and engineering improvements of the first few plants. It would, at that point, provide clean power as economically as more conventional technologies.

What are the Benefits of a Power Tower at WIPP?

The Waste Isolation Pilot Plant (WIPP) is located in southeastern New Mexico about 26 miles east of Carlsbad. The underground repository for disposal of transuranic waste was chosen as a unique site to help clean-up nuclear waste and as such the actual disposal area is at a depth of 2150 feet on a 16 square mile tract that is permanently withdrawn and owned by the U.S. Department of Energy. To capitalize on the taxpayers’ investment in extensive infrastructure and land (16 square miles) and an operating life of at least 35 years the WIPP site offers great potential for testing, demonstrating and deploying technologies like solar power. The following are some of the principal reasons why establishing a renewable energy (Solar power design and demonstration) project is beneficial:

  • WIPP averages 360 solar days with and is located in a very good solar resource region estimated to be 6-7kWh/m2/day
  • WIPP is located on relatively flat topography and has approximately 10,240 acres permanently withdrawn and owned by the government which could potentially be used for solar power projects
  • WIPP has a commitment to ensure its energy consumption is 5% green (renewable) by 2005
  • WIPP is located in a community that has a history of supporting national needs
  • WIPP has a unique relationship with local community and the local cooperative electrical groups and an agreement could be attained that could provide excess energy to the Western grid.
  • WIPP has a successful history of establishing rapport and trust with local community
  • WIPP has proven success in working with the national laboratories and industry leaders in addressing national issues by utilizing the brightest minds and cutting-edge technology
  • WIPP legal and regulatory basis provide avenues to pursue alternative missions

To implement a solar project would best be addressed by a two-phase approach: First phase would consist of conducting an engineering design and development project. The outcome of phase one would provide the basis and technological approach for phase two which would consist of a demonstration or construction of a prototype commercial plant utilizing new or existing solar power technology to support the WIPP commitment to acquire 5% renewable energy and in establishing a mechanism to provide excess energy to the Western grid in support of the pending energy requirements of the west.

What Legal/Regulatory Processes must DOE undertake to install a Solar Tower at WIPP

Under DOE regulations implementing the National Environmental Policy Act an environmental assessment (EA) would be required for the construction of the solar tower if it would produce less than 50 MW, and an environmental impact statement (EIS) would be required if it would produce 50 MW or more. Likely issues that would be addressed in the context of the EA or EIS would include, impacts of construction of the tower and associated structures including indirect impacts like disposal of construction debris and any waste generated by operation of the tower, impacts on existing grazing leases and other existing land uses, impacts on archeological and biological resources, and the impacts of construction of any associated transmission lines.

Return to Science@WIPP