O. Demirel, M.G. Anderson, E. Gonzalez
Icarus RT, Inc.,
United States
Keywords: PV cells, heat recovery, thermal conductivity, polymers, graphite additives
Summary:
Photovoltaic (PV) solar cells are a viable renewable energy technology, yet their inadequate conversion efficiency remains a steadfast problem. At the standard test condition temperature of 25°C, PV cells convert a typical maximum of 21% of incident solar energy into usable power. Additionally, when panel temperatures increase, their efficiency declines further. As PV panel temperatures reach ~70°C, their output efficiency drops to 16% or lower. Icarus RT, Inc. is developing a heat extractor that will attach to the back of a PV panel and cool the panel to boost its power performance. Icarus’ heat extractors will be made of innovative composites, which will advance material sustainability, scalability, thermal conductivity, weight, and cost. Although metals such as aluminum and copper are among most thermally conductive, their weight and cost are over-bearing for scalable application and thus are not viable. Most plastics on the other hand are lightweight and more cost effective but have inherently low thermal and electrical conductivity. Two of the most widely available plastics are high density polyethylene (HDPE) and low density polyethylene (LDPE). HDPE is not suitable for our application due to its low thermal conductivity of 0.52 W/m-K, and an operating temperature of 70°C, which is lower than our standard working temperature of 80 °C. LDPE has a higher working temperature of 85 °C but has a lower thermal conductivity of 0.3 W/m-K which is inadequate for this application. Since standard commercial plastics are not a sufficient solution for PV heat extraction, Icarus proposes using thermally conductive additive filled polymers as a composite material to fabricate its proprietary PV heat extractors. Embedding polymers with additives such as carbon nanotubes, graphite fibers or ceramics has the potential to improve their thermal conductivity by many orders of magnitude. Graphite fibers are among the most thermally conductive, cost effective and lightweight additives. Previous studies have shown that the thermal conductivity of graphite polymer composites such as 60wt% graphite/40wt% LDPE is up to 23 times higher than that of pure LDPE. Additionally, these composites increase the structural strength of a polymer, leading to higher environmental resistance and longer lasting application. Homogeneous graphite-polymer composites can be fabricated using the environmentally friendly, cost effective and easily scalable melt-intercalation process. These composites can then easily be injection molded into desired heat extractor layout. This paper will investigate various compositions of additives and polymers to optimize energy harvesting, particularly in solar waste heat applications. These materials will be analyzed based on ease of scalability, improvement in thermal conductivity, resistance to the environment and cost. The main objective of this paper is to determine the most suitable composite materials for PV thermal applications and explore how nanotechnology will enable Icarus to broaden its applications to develop and improve solar energy solutions.