Topic Area: Solar Energy
Geographic Area: Barstow, California, United States
Focal Question: Are Solar "Power Towers" An Economically Viable Energy Alternative for Southern California?
(1) "Sandia Expertise, Experience Key Factors in Newly Dedicated Solar Two Power Tower." Sandia Lab News. June 21, 1996.
(2) "Sandia Labs Shares Major Solar Success with Industrial Consortium." Sandia National Laboratories News Release. June 5, 1996.
(3) "Solar Power Towers-Snap Shot."
(4) "Solar Two: A Solar Thermal Power Plant." PDD Net. (5) California Experiments with 300-Foot-Tall Solar 'Power Tower'."
Reviewer: Sunil H. Thakor, Colby College '99

In an effort to find a sustainable, clean, yet economically efficient source of electrical power, Southern California has turned to Solar "Power Towers" as one possible alternative. A consortium of ten companies and the United States Department of Energy commissioned a project to construct a large-scale solar power plant near Barstow, California capable of generating 10 megawatts of electricity. This is enough power to supply nearly 10,000 homes.

The "Power Tower" concept uses a radically different method for transforming the sun's power into electricity than has been used in the past. Until now, traditional methods have revolved around the use of photovoltaics to convert the sun's energy directly into electricity. The "Power Tower" on the other hand, consists of nearly 2,000 mirrors (called heliostats) that track the sun throughout the day, focusing its rays onto the top of a three hundred foot tower. This generates an enormous amount of heat which is used to create steam to drive a turbine that produces the electricity.

Solar One, the original "Power Tower" pilot project came on line in 1982 and was used to produce electricity until 1988. It was the first time that a public utility (Southern California Edison) was able to employ solar power as a significant source of its energy. Though it represented a huge step forward in solar technology, Solar One did not come free of drawbacks. Since the sunlight was used to heat water that was immediately converted to steam for the turbines, when there was no sun, no power could be generated. Thus, at nights and on cloudy days Solar One was unable to generate electricity.

In 1996, a redesigned "Power Tower", Solar Two, was connected to Southern California's utility grid. Capable of producing 10 megawatts of electricity, this $48.5 million project contained significant upgrades from Solar One. Most importantly, instead of using the sunlight to heat water, it was used to heat a molten salt solution. In addition to being environmentally friendly, the solution is capable of absorbing and retaining heat for long periods of time. Once the molten salt is heated, it is stored in large tanks at the base of the tower for later use. This allows the operators of the plant to tap into its stored heat when they need it, not just when the sun is shining. Consequently, Solar Two is capable of producing electricity during cloudy parts of the day, and well into the evening after the sun has set. With Solar Two's "on demand" energy production capabilities, it can now be counted on as a more reliable and thus more practical energy source.

While Solar Two has been a huge success, showing that it is indeed possible to use solar energy to generate electrical power both reliably and cost-effectively, few other utilities have seriously explored this alternative. The main reasons for this resistance are related to issues of cost and reliability. While Solar Two is efficient and more cost effective than other forms of solar, it is still a more expensive method of energy production than traditional means such as coal or gas. Solar Two generates power at a cost of 10-14 cents per kilowatt-hour while most fossil fuel plants produce electricity at 4-5 cents per kilowatt-hour. Additionally, the cost of building a plant such as Solar Two would be prohibitively expensive for most utilities. It is estimated that a "Power Tower" power plant would have to have a 2-mile wide field of mirrors and have a production capacity of 100-200 megawatts in order to be commercially competitive. A plant of this scale would come at an estimated cost of $140 million.

While the cost of the "Power Tower" technology is currently high, it still holds a great deal of promise for the future. Undoubtedly, as the state of technology advances, and solar gains wider acceptance as a viable energy source, the cost and reliability of this type of facility will only move lower. Additionally, as pollution from other forms of energy production mounts, consumers are sure to demand cleaner, more environmentally friendly power production. Furthermore, if the environmental costs of power production are internalized to both the producers and consumers of non-environmentally friendly sources of power, solar will become more competitive and widely used.

All things considered, the Solar Two "Power Tower" project is a huge success. It shows what can happen when the government and industry work hand in hand towards a common goal, while also demonstrating that the solar energy can be harnessed in an efficient and cost-effective manner.

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