History

Organized, large-scale development of solar collectors began in the U.S. in the mid-1970s under the Energy Researc h and Development Administration (ERDA) and continued with the establishment of the U.S. Department of Energ y (DOE) in 1978. Parabolic trough collectors capable of generating temperatures greater than 500°C (932°F) were initially developed for industrial process heat (IPH) applications. Much of the early development was conducted b y or sponsored through Sandia National Laboratories in Albuquerque, New Mexico. Numerous process heat applications, ranging in size from a few hundred to about 5000 m2 of collector area, were put into service. Acurex, SunTec, and Solar Kinetics were the key parabolic trough manufacturers in the United States during this period.

Parabolic trough development was also taking place in Europe and culminated with the construction of the IEA Smal l Solar Power Systems Project/Distributed Collector System (SSPS/DCS) in Tabernas, Spain, in 1981. This facilit y consisted of two parabolic trough solar fields with a total mirror aperture area of 7602 m2. The fields used the single-axis tracking Acurex collectors and the double-axis tracking parabolic trough collectors developed by M.A.N. o f Munich, Germany. In 1982, Luz International Limited (Luz) developed a parabolic trough collector for IP H applications that was based largely on the experience that had been gained by DOE/Sandia and the SSPS projects.

Although several parabolic trough developers sold IPH systems in the 1970s and 1980's, they generally found tw o barriers to successful marketing of their technologies. First, there was a relatively high marketing and engineerin g effort required for even small projects. Second, most potential industrial customers had cumbersome decision-making processes which often resulted in a negative decision after considerable effort had already been expended.

In 1983, Southern California Edison (SCE) signed an agreement with Acurex Corporation to purchase power from a solar electric parabolic trough power plant. Acurex was unable to raise financing for the project. Consequently, Lu z negotiated similar power purchase agreements with SCE for the Solar Electric Generating System (SEGS) I and II plants. Later, with the advent of the California Standard Offer (SO) power purchase contracts for qualifying facilities under the Public Utility Regulatory Policies Act (PURPA), Luz was able to sign a number of SO contracts with SC E that led to the development of the SEGS III through SEGS IX projects. Initially, the plants were limited by PURP A to 30 MW in size; later this limit was raised to 80 MW. Table 1 shows the characteristics of the nine SEGS plants built by Luz.

In 1991, Luz filed for bankruptcy when it was unable to secure construction financing for its tenth plant (SEGS X) . Though many factors contributed to the demise of Luz, the basic problem was that the cost of the technology was to o high to compete in the power market. Lotker [5] describes the events that enabled Luz to successfully compete in th e power market between 1984 and 1990 and many of the institutional barriers that contributed to their eventual downfall. It is important to note that all of the SEGS plants were sold to investor groups as independent power projects and continue to operate today.

Table 1. Characteristics of SEGS I through IX [4].

SEGS

1st Year of

Net

Solar Field

Solar Field

Solar

Fossil

Annual

Plant

Operation

Output

Outlet Temp.

Area

Turbine

Turbine

Output

(MWe)

(°C/°F)

(m2)

Eff. (%)

Eff. (%)

(MWh)

I

1985

13.8

307/585

82,960

31.5

-

30,100

II

1986

30

316/601

190,338

29.4

37.3

80,500

III & IV

1987

30

349/660

230,300

30.6

37.4

92,780

V

1988

30

349/660

250,500

30.6

37.4

91,820

VI

1989

30

390/734

188,000

37.5

39.5

90,850

VII

1989

30

390/734

194,280

37.5

39.5

92,646

VIII

1990

80

390/734

464,340

37.6

37.6

252,750

IX

1991

80

390/734

483,960

37.6

37.6

256,125

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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