Development of a commercial photovoltaic concentrator module
[report]
S.T. Saifee, G. Hutchison
1992
unpublished
The approach taken was to design, develop, and fabricate all components possible at Solar Kinetics, Inc. (SKI). The objective was to minimize costs in the fabrication and processing of the various components when possible. This helps to establish the fabrication issues and leads to identifying difficulties in the design. Fabrication of most cell assembly and module housing components requires precision sheet metal work. All such components were fabricated using SKI machinery. The solar cell
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... mbly consists of six components. They include the PV cell, the heat spreader, the bottom contact, the top contact, the SOE, and the SOE mounting tabs. An exploded view of the cell assembly as currently executed shows the various components in Figure 2 .1. Each component required fabrication and/or processing prior to assembly. -: The photovoltaic cell used is a N + on P/P + type single-crystalline silicon cell with efficiency varying from 15% to 19% at 300X (264 kW/m2) and 77 OF. A detailed specification of this PV cell manufactured by the Applied Solar Energy Corporation (ASEC) is included as Appendix A. The solar cells were visually inspected upon receipt. After various soldering tests, the following process was used. The backs were cleaned by wiping with an organic solvent. The cell back was fluxed, and the cell was placed face down on a cool soldering platen. Square solder preforms were cut to fit the area of the back of the cells. The preform was placed on the backside of the cell and the cell was transferred to a hot platen, causing the solder to flow, thus pretiMing the cell back. The cell and platen cooled, and the cell was transferred to in-process storage. HeatSDreader: The material for the heat spreader was received in sheet form. It was 0.060-inch-thick oxygen-free high-conductivity (OFHC) copper. In the first operation, the sheets were loaded onto a CNC turret punch. The control of the punch die stroke was such that the heat-spreader disk was not entirely separated from the sheet. It was sheared all the way around the perimeter, but the punch stroke stopped before the disk separated through the parent sheet. The sheet was taken off the press, and the parts manually separated from the sheet. This was done to prevent potential damage, such as nicking or bending that could occur if the press ejected the parts in the normal manner. The spreaders were manually deburred immediately after removal from the sheet. 'lSTRIBCfMON TH& ~~~~~~~~ IS UNLiMlTEB The next operation was flattening. Apress with a flat ram and platen squeezed the heat spreader to remove any bowing resulting from the stamping operation. Finally, the part was vapor degreased with l,l,l-Trichloroethane, acid etched in 15% nitric acid, rinsed, fluxed and pretinned on one side by a similar method as used on the cell. 3 Figure 2.1 Exploded View of Concentrating PV Cell Assembly. 4 Df SCLAIMER Portions of this document may be illegible electronic image products. images are produced from the best available original document. The copper used was O.O1O-inch-tkick, 1-inch wide ribbon of OFMC type. Tke copper for this component was received as flat coil stock. It wlits sheared to length and then formed in a custom die set in a single station press. Figwe 2.2 is the fabrication drawing of the bottom contact, Next, the part was acid etched, rinsed, fluxed, and pretinned. The first design of the bottom tab had no holes. After soldering, there was a significant voiding due to entrapment of flux gases. Small holes were drilled in the bottom tab to let the flw gases escape. These holes were also useful for visual inspection of the solder flow.
doi:10.2172/10183841
fatcat:skobwnksm5f3lcq4gwviks5bb4