Exploitable results
The objective of this project was to build a prototype solar thermal power plant using a fixed hemispherical mirror and a tracking gas turbine. A target price of $0.10/kWh was set for solar electricity produced from this technology.
Early in the project it was established that the original concept of 1 MW size systems was not viable due to the non availability of suitably priced gas turbines. Project activities covered the following:
- Mirror selection. Back silvered thin glass at a cost of $7/m2 was selected as the best option. A low micro concrete hexagonal substrate of area 1 m2 was selected as the building block for the fixed mirror. The mirror is bonded to the concrete. Production costs for the mirror and substrate are $25/m2.
- Receiver selection and design. A volumetric receiver concept designed by DLR was selected. The solar absorber had to be redesigned for the fixed mirror optical system and a new absorber made and installed in the receiver.
- Turbine selection. A 35 kW turbine made by Bowman Power Systems was selected. An in-line configuration was the optimum providing a new combustor was designed for hybrid operation and safety valves installed in the case of total failure. These components were designed and installed in the turbine.
- System Optimization. The Phase 1 design was optimized to reduce mirror area by 25%. The final mirror size specified has a radius of curvature of 30 metres. It has a 47 degree cut out in the north south direction and a 60 degree cut out in the east west direction.
- The power train was designed to integrate into the tower and tracking system. Testing of the power train took place in the UK prior to shipment to the Crete test site.
- System Design. Two options were considered for the primary mirror - a space frame above ground or an excavated concrete mirror. The latter was chosen on cost grounds. The final tower and tracking design based on least cost, durability, reliability and achievement of required accuracy is a tripod tower with a "swingometer" that tracks on a ground mounted truss in the north-south direction. The truss tracks on rails to the north and south of the mirror. A hydraulic tracking system was designed.
- System Construction. The phase 1 system was completed in October 1998 and commissioned during the period October to March 1999. The solar-has turbine system worked successfully - the first such integration at this scale.
- Performance Monitoring. Limited performance monitoring has taken place. At low power outputs the system can make up to 90% solar contribution. At higher outputs the maximum obtained to date is 60%. The maximum output of the solar system is 60 kW thermal against a design objective of 110 kW thermal. This lower output is due to degradation on the mirrors and to misalignment of some of the mirror segments.
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