Solar thermal systems operate by using sunlight to raise the temperature of an oil medium as high as 400°F or a molten salt to temperatures exceeding 1,800°F. The energy captured in this process is stored in the form of heat that can later be used in a number of applications ranging from large-scale electric power generation to simply heating water for home use. This capacity to store energy at a lower relative cost is a key advantage that solar thermal systems have over photovoltaic systems.
With support from the California Energy Commission PIER Program, the solar technology research team at UC Merced successfully designed, developed and demonstrated an innovative low-cost, high temperature, non-tracking solar thermal collector system. Called an External Compound Parabolic Concentrator (XCPC), this system is able to operate with a solar thermal efficiency of 50% at temperatures up to 200ºC (400ºF). Previously, only tracking solar thermal collector systems could achieve this temperature.
The XCPC system consists of a series of evacuated solar thermal absorbers paired with non-imaging reflectors that gather and concentrate both direct and indirect sunlight. Unlike tracking solar thermal systems, which are expensive to install and complex to operate and maintain, the XCPC system’s lightweight design enables it to be mounted on rooftops or even walls. It also performs well in diffuse (hazy or dusty) conditions, where other solar concentrators produce little or no heat.
XCPC systems can augment or replace natural gas driven systems, and they produce no greenhouse gases. Their numerous potential applications include solar heating, cooling, desalination, oil extraction, electricity generation, and food processing.
UC Merced researchers have constructed a 25kW thermal test array that powers a commercially-produced 6.5 ton double-effect absorption cooling system. The UC Merced Solar Cooling Demonstration Project is the first of its kind (non-tracking collectors/double-effect chiller), and it demonstrates solar-powered air conditioning in a real-world setting.