Centre Field Trip - March, 1999
Field Trip to SolarII
Yes it is all done by mirrors
Author: IEE Member - Mr. Julian Harvey
An extremely successful field trip took place in March to visit SolarII, a CSP (Concentrating Solar Power) power generation research facility at Daggett, California, in the Mojave Desert.
The project signboard lists the many participants of the Solar II consortium.
A group of 10 members and guests left Culver City in the early morning and arrived at Daggett, CA at about 11:00 AM. A very comprehensive 3 hour tour of the facility was given by Southern California Edison and Sandia Labs employees.
A detailed overview of the technology was given before the tour commenced.
The group learnt a bit about the history of Solar II and the underlying principles of "power towers" (or central-receiver systems). Solar II was developed from Solar I, that had operated successfully from 1982 to 1988. :Solar II was connected to the utility grid in 1996. These systems use many (in the case of Solar II - >1900) sun-tracking mirrors (heliostats), to reflect the sun's energy to a single receiver mounted atop the tower.
Solar I used water/steam as the heat transfer fluid to directly power a conventional Rankine cycle steam turbine. For Solar II the working fluid was replaced by a heat transfer/storage system using molten salt. This material (60% sodium nitraate/40% potassium nitrate) melts at 220 deg. C and is maintain in the molten state (at 290 deg. C) in the "cold" storage tank. The fluid is pumped to the receiver atop the tower where it is heated to 565 deg. C. and then flows to the "hot" storage tank. The hot storage tank has enough capacity to power the turbine for up to three hours.
Each heliostat consisted of twelve mirrors mounted on a central support column and driven by a simple DC motor. A digital control system focuses the heliostats precisely onto the receiver as they track the sun across the sky.
Our group was allowed to study the heliostats at close quarters, and learnt about the lightweight support structure for the mirror surface.
The receiver consists of a series of panels (each made from 32 thin walled stainless steel tubes) through which the molten salt flows in a serpentine path. The panels form a cylindrical shell surrounding piping, supports and control equipment. The external surfaces of the tubes are coated with a black robust, high temperature paint.
The white panel(s) below the receiver are used for initial beam setting for the heliostats.
The "hot" storage tank consists of an 875,000 liter externally insulated stainless steel tank. Natural convection cooling is used in the foundation of each tank to minimize overheating of the surrounding soil.
The "cold" storage tank, also of 875,000 liter capacity, is externally insulated and constructed from carbon steel. Thermal capacity of the system is 100 MWh.
The steam generator powers a 10 MW conventional Rankine cycle marine turbine coupled to a generator.
The group was fortunate to visit the facility before it was decommissioned at the end of March. Parts of Solar II are to be used for a gamma ray observatory, so the project will continue to provide useful data to the scientific community.
Many thanks are due to the employees of Southern California Edison and Sandia Labs
that made this field trip possible.
Document last updated: February 14, 2004