Improving efficiency of high-concentrator photovoltaics by cooling with two-phase forced convection

Abstract

SUMMARYThe potential of increasing high-concentrator photovoltaic cell efficiency by cooling with two-phase flow is analyzed.The governing energy equations were used to predict cell temperature distributions and cell efficiencies for aphotovoltaic cell under 100 suns’ concentration. Several design conditions were taken into consideration in the analysis,including cooling channel height, working fluid type (between water and R134a), working fluid inlet temperature,pressure, and mass flow rate. It was observed that the dominant parameter for increasing cell efficiency was the workingfluid saturation temperature, which itself is affected by a number of the aforementioned design parameters. The resultsshow R134a at low inlet pressures to be highly effective in this two-phase cooling design. Copyright r 2010 John Wiley& Sons, Ltd. KEY WORDS: high-concentrator photovoltaic efficiency; two-phase flow cooling applications 1. INTRODUCTIONThe demand for energy has led to a large effort tofind new energy resources in addition to developingand improving existing ones. Photovoltaics (PV)have become increasingly popular due to theirinherent cleanliness compared with fossil fuels, butcost remains a major obstacle to their widespreadadoption. High-concentrator PVs alleviate cost byusing mirrors and concentrating lenses to focusmore of the sun’s incident radiation onto a singlePV cell, thereby reducing the number of cellsrequired. Commercial PV cells typically have upperefficiency limits of about 25% [1]; the energy fromthe sun not directly converted into electricity ortransferred to the ambient largely manifests itself asthermal energy within the PV cell. Withoutadequate cooling, the highly concentrated solarradiation results in significant increases in celltemperature. From an energy balance, a PV cellwith a 100 sun input and only natural convectionand radiation cooling reaches temperatures ofabout 1200K. Subjecting PV cells to high tempera-tures is undesirable as it reduces efficiency almostlinearly with increasing temperature and can alsoresult in permanent cell damage [2]. Therefore, aprimary challenge becomes the removal of excessheat and maintaining higher efficiencies associated