Photovoltaic thermal system combined with adsorption cooling achieves 75% efficiency
Researchers from IBM Zurich research laboratory combined photovoltaic (PV) and solar thermal techniques in a high-concentration PV thermal (HCPVT) system to achieve efficient electrical cooling output without the need for extra cells.
Their approach employs waste heat for cooling, using a adsorption chiller and water desalination, making the system highly efficient.
PV cells and solar thermal systems generally exploit only 25% of the sun’s rays. In order to increase output, triple junction PV cells convert solar radiation into power at three different wavelengths, thanks to three separate stacked semiconductor junctions, allowing for higher efficiency, albeit an expensive solution.
IBM Lab mounted a hot-water cooled multichip receiver in the focal point of a parabolic concentrator to generate both heat and electricity.
PV thermal concentrators operate at an efficiency rate of 25%. Approximately 50% of the remaining heat can be used for heating, desalination or adsorption cooling, raising the overall system efficiency to around 75%. The use of a 2000-fold concentrator reduces the number of PV cells required, but high concentration, requires active water-based cooling solutions.
Hot-water cooled silicon microchannel coolers with extremely low thermal resistance, allowing for the cooling of PV cells at 100°C with water at 90°C and at a concentration of up to 2000 suns, thus protecting the device. HCPVT systems are thus more effective with increased solar concentration thanks to the direct use of heat for cooling and desalination.
IBM requires that they will soon be able to generate power at a price equal to electricity from the grid or lower and cheap storage of low-grade heat, by means of a layered hot water tank, enables a predictable output of heating, cooling and desalinated water. Plans are underway to enhance the system by incorporating an efficient low-cost 100 m² faceted mirror with a 500 cm² receiver, using concrete, steel and silicon.