Balancing energy harvesting and crop production in a nanofluid spectral splitting covering for an active solar greenhouse

This work represents a nanofluid spectral splitting (NSS) covering applied to the greenhouse roof to achieve the co-production of crops and energy harvesting. NSS is a hollow structure composed of highly light-transmissive rigid materials with 10 mm thick 0.005 vol% ATO-WO3 nanofluids circulating in the hollow layer with a flow rate of 400 L/h. To study the growth response of plants in the NSS greenhouse (NSS-G), plant cultivation ex-periments and photothermal tests were carried out. The energy analysis and performance estimation of NSS-G were proved. The results show that NSS-G can absorb 77.9% of the solar energy within 800-1500 nm wave-lengths to generate heat. Compared with the conventional hollow covering greenhouse (Air-G), NSS-G can reduce the temperature of indoor air and plant leaves by 6.3 degrees C and 8.7 degrees C, respectively. Meanwhile, 76.6% of sunlight within 300-800 nm wavelengths is transmitted to plants for photosynthesis. The results of plant growth experiments showed that, in comparison with Air-G, the photosynthetic rate in NSS-G reduced by 6.5%, but plant dry weight was increased by 4.3% and there was no significant difference in biochemical component contents. It proved that it is feasible to use NSS as the covering of the greenhouse roofs, and the total solar energy utilization efficiency in NSS-G was more than 55%.