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Appendix C
Comparison of Different Power-Generation Methods 277

perform useful tasks since the time of ancient China. A legend claims
that Archimedes used polished shields to concentrate sunlight on the
invading Roman fleet and repel them from Syracuse. Auguste Mouchout
used a parabolic trough to produce steam for the first solar steam engine
in 1866, and subsequent developments led to the use of concentrating
solar-powered devices for irrigation, refrigeration, and locomotion.
Concentrating Solar Power (CSP) systems use lenses or mirrors and
tracking systems to focus a large area of sunlight into a small beam. The
concentrated light is then used as a heat source for a conventional power
plant. A wide range of concentrating technologies exists; the most
developed are the solar trough, parabolic dish, and solar power tower.
These methods vary in the way they track the Sun and focus light. In all
these systems, a working fluid is heated by the concentrated sunlight
and is then used for power generation or energy storage.
The PS10 concentrates sunlight from a field of heliostats on a central
tower. A solar trough consists of a linear parabolic reflector that concen-
trates light onto a receiver positioned along the reflector’s focal line. The
reflector is made to follow the Sun during the daylight hours by track-
ptg
ing along a single axis. Trough systems provide the best land-use factor
of any solar technology. The SEGS plants in California and Acciona’s
Nevada Solar One near Boulder City, Nevada, are representatives of this
technology.
A parabolic dish system consists of a stand-alone parabolic reflector
that concentrates light onto a receiver positioned at the reflector’s focal
point. The reflector tracks the Sun along two axes. Parabolic dish sys-
tems give the highest efficiency among CSP technologies. The 50 kW
Big Dish in Canberra, Australia, is an example of this technology.
A solar power tower uses an array of tracking reflectors (heliostats) to
concentrate light on a central receiver atop a tower. Power towers are
less advanced than trough systems but offer higher efficiency and better
energy storage capability. The Solar Two in Barstow, California, and the
Planta Solar 10 in Sanlucar la Mayor, Spain, are representatives of this
technology.

Experimental Solar Power and Storage Methods

A solar updraft tower (also known as a solar chimney or solar tower)
consists of a large greenhouse that funnels into a central tower. As sun-
light shines on the greenhouse, the air inside is heated and expands. The