Solar transparent and thermally insulated silica aerogel for efficiency improvement of photovoltaic/thermal collectors

Photovoltaic/thermal (PV/T) utilization has been regarded as a promising technique to efficiently harvest solar energy, but its thermal efficiency highly degrades in cold seasons because of remarkable heat loss. Although various methods, such as using air or vacuum gap, have been used to reduce heat loss of the PV/T, heat radiative loss still exists. In addition, unlike selective solar absorbers, the current PV/T absorber behaves like an infrared blackbody, showing great radiative heat loss. To overcome this drawback, a novel aerogel PV/T (referred to as "A-PV/T" hereinafter) collector based on solar transparent and thermally insulated silica aerogel is proposed, which can reduce the heat loss from both the non-radiative and radiative heat transfer modes. Experimental testing demonstrates that the thermal efficiency improvement of 25.1%-348% can be achieved for PV/T within the collecting temperature range of 35-70 degrees C when silica aerogel is introduced, indicating a significant efficiency enhancement. Compared with traditional PV/T (referred to as "T-PV/T" hereinafter) collector, the stagnation temperatures of the A-PV/T collector are 96.7 degrees C and 103.1 degrees C in outdoor and indoor environments, which are 27.4 degrees C and 25.8 degrees C greater, respectively, indicating a heat loss suppression of the aerogel. Moreover, simulation reveals that useful heat can hardly be provided by the T-PV/T collector in cold seasons, but the A-PV/T still exists a high solar thermal performance, showing good seasonal and regional applicability.