Experimental Testing of Greenhouse-Integrated Vanadium-Titanium Black Ceramic Solar Absorbers

As a solution for solar heating, the low-cost and long-life vanadium-titanium black ceramic solar absorbers have been used in rural construction. However, in contrast to its high absorptance(0.93-0.97), ceramic also has high emissivity(approximately 90%) and low thermal conductivity(1.3 W/(m·K)). Without a glaze covering, ceramic absorbers cannot meet the industrial standard. This paper assumes that glaze covering can be substituted by insulation film in a solar greenhouse. To verify this assumption, field experiments were conducted. First, a traditional greenhouse in the Tacheng Basin, a severely cold area in China, was renovated to improve its passive thermal performance. Then, 90 m^(2) of ceramic absorbers and floor coils as well as a water tank were installed inside the greenhouse, which made the entire construction act as an integrated solar collector. This heat collection and release system moderately increased the indoor air temperature(0.9℃-22.4℃) and substantially increased the soil temperature(15.5℃-31.2℃). The average daily useful heat gain under a daily solar insolation value of 17 MJ/m^(2) was 13.8 MJ, and the mean value of the collection efficiency was 0.81. Furthermore, the payback time of the project(7 years) is short, which is principally due to the low cost of ceramic materials and the financial savings of the shared construction components(e.g., transparent cover, metal frame and extra insulation). In conclusion, the main contribution of this study is the verification that it is feasible to replace glaze covering with insulation film in a novel greenhouse-integrated vanadium-titanium black ceramic solar system.