Exploring Heat Transfer Efficiency Enhancement for Hybrid PV/Thermal Systems

A. Cauchon, M. Anderson, J. Druzynski
Icarus RT, Inc.,
United States

Keywords: hybrid photovoltaic/thermal, heat transfer


Reduced cost of photovoltaic (PV) panels and increased engagement towards combatting climate change have renewed interest in developing a hybrid system that harvests waste heat from PV panels while improving the performance of the PV panels through temperature regulation and cogenerating hot water. Maximization of efficiency in transfer of waste heat between the PV panel and the heat extractor is therefore crucial to the operation of successful systems. Organic additives such as carboxymethyl cellulose (CMC) as well as inorganics have been shown to increase the specific heat capacity of water when present in solution. Heat extraction using a CMC (or other) solution as a working fluid in place of water would have the same thermal transfer capacity with a lower liquid volume, allowing for a smaller and more efficient system. Commercial products are also available, developed for use in automobile engines and industrial boilers, which minimize the contact angle of water and improve the heat transfer coefficient. If applied to hybrid PV panel heat extraction systems, these would enhance the transference of heat across the barrier of the heat extractor. A similar effect can be achieved using a coating on the inside of the extractor; this thin layer of inorganic material (e.g., alumina or zinc oxide), can substantially improve the heat flux. The presence of a coating can also alter the substrate’s radiative properties, augmenting the heat flow through the surface. Before physical experimentation, the new heat extractor systems will be modeled for simulation in Pipeflow, Solidworks and other methods to compare results with and without modification and predict the outcomes. For heat capacity additives, the target is a 10% increase in specific heat capacity of the working fluid. The objective for surfactants and other additives is likewise a 10% increase in the heat transfer coefficient. This paper will explore new methods of improving heat transfer in hybrid solar/thermal systems with several main avenues of inquiry: traditional or nanoadditives to increase specific heat capacity of the working fluid, or to improve its surface contact with the extractor; traditional or nanocoatings on the extractor surface to improve or modify emissivity, reflectivity, or absorption, or to improve the contact angle with the working fluid; and other potential changes to features of the system such as flow rate or flow pattern with the introduction of fins or other structures.