In Hawaii, three concentrating solar thermal projects, marked on Fig. 1, have gone through various stages of completion: solar repowering, a solar photovoltaic energy system; and a Small Community Solar Experiment at Molokai Electric Company. All were supported primarily by the
U. S. Department of Energy (USDOE), Hawaii state government, and through private costsharing.
The solar repowering project at Pioneer Sugar Mill Co., located in Lahaina on the leeward (dry side) lowlands of West Maui, called for a preliminary design of a solar power tower adjacent to the sugar factory. This concept featured a field of mirrors or heliostats directing sunlight to a centrally located receiver for steam production for use in the sugar milling process and power generation. The preliminary design was for an 8 MW system with about 568 heliostats directing sunlight to a 79 m tower. The area required for this system was about 0.24 km2. The overall cost was estimated to be about U. S. $40 million. The recommendation from this study called for third-party financing with a power sales agreement from the local utility (Amfac, 1983). The project has been put on hold until financial backing can be obtained (G. St. John, personal communication, 1987).
The G. N. Wilcox Memorial Hospital and Health Care Center, located in Lihue on Kauai, was the site of a parabolic concentrator photovoltaic/thermal solar system from 1982-83. The system was rated at 35 kw and designed to produce 22,000 net kWh of electricity and 2,350 kl of 82° C water (about 900 million Btu) annually. A field of 10 rows of eight parabolic collectors, each 1.83 m by
3.5 m in aperture, was used. The collectors tracked the sun by rotating about their north-south horizontal axes and concentrated the incident sunlight on photovoltaic cells mounted on the receivers at the collectors’ focal lines. For optimal system operation, the photovoltaic cells were cooled by water passing in series through the hollow centers of all 80 aluminum receivers. This water, part of a closed, continually recirculating system with an 11.4 m3 storage tank, took the excess thermal energy away from the photovoltaic cells and transferred the energy through a heat exchanger to the hospital’s hot water supply. The solar system at Wilcox Hospital did not perform well because of two factors: inclement weather (1982 was the wettest and least sunny year in the past 50) and photovoltaic cell deterioration. At the end of the project, the solar system was transferred to the Barking Sands Missile Range, outside Kekaha on the leeward side of Kauai.
The system is now providing thermal energy for the facility’s cafeteria (Yuen, Seki, and Curtis, 1983).
The third concentrating solar thermal project was the now-terminated Small Community Solar Experiment at Molokai Electric Company’s Cooke Generating Station in Palaau, a few miles outside Kaunakakai on Molokai. The system was designed for an output of 250 kw from five point-focus concentrating collectors. Each concentrating collector would have had about 400 separate mirrors focusing sunlight 18.3 m away. The working fluid was water, which would have been converted to steam at the collector receiver for transfer to a converted air-cooled, 4-cylinder, diesel engine. This unique system has been proven in White Cliffs, Australia, using a smaller converted diesel engine. This facility, originally scheduled for construction by 1989, apparently will not be built (R. Rogers and E. Bilodeau, personal communication, 1985).