Solar Case

2.11.5 Major technical issues

A SEGS power plant is essentially a marriage between a new and unique technology for converting solar energy into usable thermal energy, and a more conventional technology for converting that thermal energy into electricity. Thus, it is likely that the major troubleshooting effort in a new plant of this nature will be associated with those systems that are based on new technology as opposed to those systems which have a proven commercial-scale track record.

The major technical issues associated with the 1988 performance of the SEGS Kramer Junction solar fields were effectiveness and frequency of mirror washing, Heat Collection Element (HCE) tube breakage, and operational considerations.

Mirror washing

Given that the cumulative mirror surface area contained in SEGS I-VI1 is 1,350,000 square meters (over 300 acres), the necessity of a cost-effective mirror washing program is a top priority. A new mirror has a reflectivity of 94 percent; the objective of the mirror washing program is to maintain an average solar field reflectivity of 88-90 percent. Performance data shows that a drop in average solar field reflectivity of 3 percent results in a drop in solar power output of about 4 percent.

Luz has undertaken extensive efforts over the last three years to develop the most cost-effective means of washing mirrors. The optimum system at present is use of a high-pressure jet of demineralized water to wash the mirrors on an approximate two-week cycle. That is, each mirror in the field gets washed about once every two weeks. Several tight trailers have been fabricated, each equipped with a 1900 liter (500 gallon) demineralized water storage tank and two high pressure pumps with hand-held spray wands. The trailers are pulled through the solar fields by small tractors.

HCE tube breakage

During the initial startup phase of SEGS Ill and IV in early 1987, a HCE tube breakage rate slightly higher than projected was observed, affecting up to 7 percent of the solar field. The breakage of the outer glass envelope of the HCE was caused by war page of the inner stainless steel receiver to the point where it impacted the glass envelope. If breakage occurs, the efficiency of that single HCE drops to 85 percent of its design value. Thus 7 percent breakage could result in a drop in overall performance of about 1 percent.

Operational considerations

Luz has gained considerable experience over the last two years in operating the solar fields under various conditions involving weather and solar insolation.

Changing desert weather conditions, particularly high wind conditions and rain, require unique solar field operational procedures to optimize field performance and protect equipment.

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