NEW LOW CONCENTRATION CPC TYPE COLLECTOR WITH CONVECTION CONTROLED BY A HONEYCOMB TIM MATERIAL: A COMPROMISE WITH STAGNATION TEMPERATURE CONTROL AND SURVIVAL OF CHEAP FABRICATION MATERIALS

摘要

Stationary non evacuated CPC collectors have the potential to perform close to evacuated tubular collectors at high temperatures, yet they can be manufactured with the simplicity and low cost of good flat plate collectors. However taking full advantage of the concentration factor achievable with CPCs without the use of more expensive materials is a real challenge, as there is always a risk of too high stagnation temperatures. But more and more applications come forward requiring operating temperatures around or above 100ºC, as, for instance, solar cooling or desalination. In this paper modifications on a standard CPC 1.12X collector were made in order to obtain efficiencies arround 50% at an inlet temperature above 100ºC. These modifications include the addition of honeycomb type TIM, calculated in order to comply with the following constraints: 1. be able to fit in the available space; 2. have the cell size and thickness which will achieve the desired convection reduction; 3. keep healthy distances from the hottest places in the collector; 4. produce a stagnation temperature not above the threshold for the survivability of the different collector components. This latest requirement is crucial. Its solution depends on many factors but advantage is taken of the fact that the CPC collector seems to have a stronger convection regime once the temperature of the absorber rises above a certain value. In the present paper the solution is presented and discussed. Collector test results are presented. This solution constitutes the basis for implementation of the solar collector field in the AQUASOL project, financed by the EU, and which will be installed at Plataforma Solar.