The use of graphite foams for simultaneous collection and storage of concentrated solar energy

Abstract

Graphite foams of varying composition and density were prepared using a low cost, local pitch material and expandable graphite for use in solar energy capture. The foams have a high degree of graphitization but exhibit a fine mosaic texture. A small oxidative treatment (6% mass loss) was necessary to fully open the foam pores. As the density is reduced a large decrease in the foam surface area was observed. Despite this, an increase in solar energy capture efficiency was measured due to increased circulation through the foam. By varying foam geometry and the concentration ratio it was demonstrated that the receiver size can be reduced by 75% at the same efficiency. The foam with the lowest density was used to test the thermal performance of a simultaneous energy capture and storage concept using a phase change material. The melting time of the phase change material is reduced by 46% whilst only reducing the energy storage density by 18%. In addition it was found that the foam composite resulted in more ideal phase transition behaviour due to the elimination of incongruent melting. The composite can effectively capture, store and discharge thermal energy, at a constant temperature, without any additional requirements.