Development of solar water heating system using multi-layer photo-thermal conversion material

Abstract

Solar thermal technologies, which convert solar energy into heat, have received increasing interest during the past few decades and are considered to be a promising candidate because of their high energy storage density and high energy conversion efficiency in many emerging applications such as solar collectors for heating and cooling systems, solar cookers, solar-heated clothes and steam generators. In this study, we fabricate the metal/dielectric based solar absorber on various substrate such as glass, fabric, thermoelectric etc. The sample, consisting of a layered titanium (Ti) and magnesium fluoride (MgF2) film multi-layers structure, were fabricated using electron beam evaporator at room temperature. The absorbers showed a high absorption of approximately 85% over a wavelength range of 0.2−4.0 μm, and the selective absorption can be tuned by the thickness of each layer. Under 1 sun illumination, the light absorber on various stretchable substrates increased the substrate temperature to approximately 60°C. The thermoelectric generator (TEG) with the absorber on the top surface also showed an enhanced output power of 60%, compared with that without the absorber. A solar water heating system was fabricated using a solar absorber with this absorption characteristic. Under 40 sun condensation, the surface temperature of the absorber on aluminum (Al) substrate of 1.5 cm x 1.5 cm area increased up to 92°C and the water temperature increased by 5°C. Although absorber is small area, water temperature increase. Moreover, the heat transfer and antireflection technology of absorber is also investigated for optimized solar absorption. This work should play an important role distillation water purification technology using a multi-layer thin-film photo-thermal conversion material for decentralized water supply.