Page 265 - Alternative Energy Systems in Building Design

INNOVATIONS IN PASSIVE SOLAR POWER TECHNOLOGY 241

has contracted with Solargenix Energy to construct and provide the solar thermal technology
for the plant, which is expected to come online in April 2005. Solargenix, formerly Duke Solar,
is based out of Raleigh, North Carolina. Solargenix has partnered with Ormat, who will provide
the engine to convert the solar heat, collected by the Solargenix solar collectors, into electricity.
“The APS Saguaro Solar Trough Power Plant presents a unique opportunity to further expand
our renewable energy portfolio,” said Peter Johnston, manager of Technology Development for
APS. “We are committed to developing clean renewable energy sources today that will fuel
tomorrow’s economy. We believe solar-trough technology can be part of a renewable solution.”
The company’s solar-trough technology uses parabolic-shaped reflectors (or mirrors) to con-
centrate the sun’s rays to heat a mineral oil between 250 and 570 degrees. The fluid then enters
the Ormat engine, passing first through a heat exchanger to vaporize a secondary working fluid.
The vapor is used to spin a turbine, making electricity. It is then condensed back into a liquid
before being vaporized once again.
Historically, solar-trough technology has required tens of megawatts of plant installation to
produce steam from water to turn generation turbines. The significant first cost of multi-
megawatt power plants had precluded their use in the APS solar portfolio. This solar trough
system combines the relatively low cost of parabolic solar trough thermal technology with the
commercially available smaller turbines usually associated with low-temperature geothermal
generation plants, such as the Ormat unit being used for this project.
In addition to generating electricity for APS customers, the solar trough plant will help APS
meet the goals of the Arizona Corporation Commission’s Environmental Portfolio Standard,
which requires APS to generate 1.1 percent of its energy through renewable sources—60 percent
through solar—by 2007. APS owns and operates approximately 4.5 MW of photovoltaic solar
generation around the state and has partnered on a 3-MW biomass plant in Eager, which came
online in February, and a 15-megawatt wind farm to be constructed near St. Johns. APS,
Arizona’s largest and longest-serving electricity utility, serves about 902,000 customers in
11 of the state’s counties.

Innovations in Passive Solar Power

Technology

The following are a few innovations under development by Energy Innovations, a sub-
sidiary of IdeaLab, located in Pasadena, California.

STIRLING ENGINE SUNFLOWER
The Stirling Engine Sunflower is a radical concept because it does not use stationary PV
cell technology. Rather, it is constructed from lightweight, polished, and aluminized
plastic reflector petals that are each adjusted by a microprocessor-based motor controller,
enabling the petals to track the sun in an independent fashion. This heat engine is used to
produce hot water by concentrating solar rays onto a low-profile water chamber.
At present, the technology is being refined to produce higher-efficiency and more
cost-effective production models, and the company is working on bigger models for
use in large-scale solar water-heating installations. Figure 6.12 shows a prototype
Stirling Engine Sunflower.