Power tower systems:
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) utilize molten nitrate salt because of its superior heat transfer
and energy storage capabilities. Individual commercial plants will be
sized to produce anywhere from 50 to 200 MW of electricity.
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
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.