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Work has been underway since 2001 in the use of concentrating solar dishes for electrical power generation. Originally, this consisted of two dish-Stirling systems: one marketed by SES (Stirling Energy Systems) and one marketed by SAIC (Science Applications International Corporation). The latter used a Stirling Thermal Motors (STM) engine. A picture of these two systems is shown in Figure 1. Each unit developed about 25 kW at maximum operational conditions, and the generated power fed into the Nevada Power grid. Nevada Power is cooperating with the project and furnished the interconnect equipment.

Each of the dishes shared some aspects in common with the other. Included was the fact that power was generated from a solar-driven Stirling engine which in turn powered an electrical generator. The overall power output of the two dishes was similar. Some distinct differences also existed. Probably the single most obvious one was that the SES unit used fixed-focus facets, while the SAIC unit used stretched membrane facets.

This project was funded by the U.S. Department of Energy, and it had several goals including the training of students in the theory and operation of dish systems, the improvement of reliability of these types of units, and making developments on the design and operational characteristics of the system. The original project ended in December 2002, and two new but related projects are being pursued. Both of the latter projects are being funded by the National Renewable Energy Laboratory.

SES Dish Modifications

In the first of these newer projects started in 2002, the operations of the SES system are being enhanced via a number of new aspects. One of these is the application of a closed feedback control system to the dish. Previously an open-loop control system was used. Other aspects include the investigation of the possibility of design modifications to accomplish a downward stow of the dish (it was designed to stow upward) when not in use to lessen the atmospheric dirt accumulation. SES is contemplating the installation of a 1-MWe system (40 dishes of the type shown here) in Southern Nevada, and this work is leading toward that goal.

SAIC Dish Modifications

Several modifications to the SAIC dish in 2003 included the replacement of the stretched membrane facets with a hexagonal fixed-facet design. The new configuration is shown in Figure 2.

In other modifications to this system, a photovoltaic (PV) receiver replaced the engine. From a distance this looks similar to the engine system, but the largest part of the volume replacing the engine was with an air-cooled radiator unit for heat removal. This cooling unit is used to draw heat from the PV receiver (in simple terms a flat plate with PV cells on one side and cooling tubes on the back). Originally it had been hoped that we could install triple junction cells, which would yield sun-to-electricity efficiencies in the high twenties percent. Because the initially anticipated cells were not ready for application at the needed time, the initial test is using high flux single junction cells, with proportionately lower efficiencies.

Amonix Integrated High Concentration Photovoltaic (IHCPV) System

In 2003 UNLV, in partnership with NSWEP, began working on the construction of a new solar power generating system. This system is very different from the other systems on UNLV campus because it is not a dish. This is an Integrated High Concentration Photovoltaic (IHCPV) system and is made by Amonix. It has a large flat visual appearance. Figure 3 is a picture of UNLV's system. This system produces power through its Megamodules™. A Megamodules™ is a large flat surface with about 1200 single junction silicon photovoltaic cells.

Each cell has its own Fresnel lens (like an acrylic magnifying glass) which magnifies the sunlight onto it.

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