Performance evaluation of delta-nabla channel configuration in a solar absorber with thermal energy storage

A novel configuration of solar absorber containing water channels of triangular cross-section in a delta-nabla arrangement, has been experimentally investigated. Traditionally, the triangular channeled solar absorbers are in use for space heating, but their effectiveness in solar water heating systems is yet to be explored. In addition to the performance investigation of the absorber, the effect of an integrated phase change material (PCM) based thermal energy storage (TES) has also been examined under solar and off-solar conditions. The highest tem-perature of 80 degrees C is obtained on the right side of the absorber containing hot water outlet in contrast to the left side where the cold-water inlet is located. Moreover, the average temperature gradient exists along the surface normal from the channel contours to the outside glazing. Integration of paraffin-based TES provides 62 L of water above 30 degrees C during off solar conditions. The efficiency of TES increases with smaller delays after charging and for higher flow rates because of reduced heat losses from the storage to the atmosphere. A delta-nabla configuration comparison with a conventional flat plate type solar absorber shows a prominent improvement in the overall performance.