Graphene-enhanced phase change material systems: Minimizing optical and thermal losses for solar thermal applications

Photothermal utilization systems with nano-enhanced phase change materials are encouraging due to their high cost-effectiveness, tunability, and sustainability. However, the optical and thermal losses, which have failed to be quantified and suppressed in most previous work, give rise to an intractable challenge for practical applications. Herein, we comprehensively quantify the energy flow during the photothermal conversion and storage processes and propose various strategies to suppress the optical and thermal losses for boosting solar energy utilization via experiments and numerical simulations. The results indicate that a 30 % optical loss is suppressed by introducing graphene into the phase change composite (PCC), leading to a 5.5 % increase in photothermal storage (PTS) efficiency. Compared with the graphene-doped one, the PCC achieves a 5.6 % reduction in conductive thermal loss and a 2.2 % enhancement in PTS efficiency via optimizing insulation materials. Besides, the convective loss is suppressed by employing a transparent aerogel cover, resulting in a 4.3 % increase in PTS efficiency. Furthermore, the radiant thermal loss is reduced by 21.2 % with a thermal mirror due to the reflection of infrared radiation, and thus the PTS efficiency is boosted by 9.5 %. This work's findings offer new insight into optical and thermal management for efficient solar thermal utilization.