A modified method to quantify the photo-thermal conversion efficiency of shape-stable phase change materials

Abstract

Photo-thermal conversion phase change materials (PCMs), which can overcome the gap between the demand and supply of solar energy, have shown significant potential in solar energy utilization. The photo-thermal conversion efficiency is a critical factor in determining the photo-thermal conversion performance of PCMs. Most previous investigations only considered the latent heat stored by PCMs to determine the photo-thermal conversion efficiency. The sensible heat absorbed by PCMs before and after the phase transition process was neglected, which might overestimate the photo-thermal conversion performance of PCMs. As an improvement, a modified method, considering both sensible and latent heat absorption and the temperature difference within the PCMs, was proposed to determine the photo-thermal conversion efficiency of PCMs accurately. Shape-stable PCMs with polyethylene glycol (PEG), few-layers graphene (FLG), and melamine foam (MF) as the PCM, photo absorber, and supporting material, respectively, were prepared to test the reliability and effectiveness of the proposed method. Results showed that the actual efficiency of PCMs was less than 25%, which truly reflected the photo-thermal conversion performance of PCMs, demonstrating that more work should be conducted to enhance the photo-thermal conversion performance for efficient solar energy utilization.