Stress in Shaped Glass Evacuated Collectors

Abstract

Shaped glass evacuated collectors have the lower vacuum envelope formed with a CPC shape. The internal surface is silvered. This surface concentrates solar radiation onto an internal absorbing tube. The upper part of the vacuum envelope is a window to pass the solar radiation in to the absorbing tube. A computer program using analytical equations is used to design these collectors while keeping the glass tensile stress arising from evacuation below acceptable limits. A finite element computer program is used to test the accuracy of the stress calculated analytically. The calculations agree within about 1 MPa. Wind and thermal stresses in the glass are lower than the stresses caused by evacuation.