Solar Water Heating System with Phase Change Materials and Carbon Nanotube

Solar water heaters are a well-established renewable energy technology that has been widely adopted around the world. In this project we have significantly improved the evacuated solar tube collectors (ETC) by utilizing the "dry-drawable" carbon nanotube (CNT) sheets coatings for increasing solar energy absorption and paraffin phase change materials (PCMs) for increasing the heat accumulation and heat transfer layers in evacuated tube collectors. PCM by itself may not be effective due to the poor heat transfer rate and low thermal diffusivity and thermal conductivity of PCMs in general, particular in powder form. By combining CNT layers (with high thermal diffusivity and conductivity) as an excellent medium for PCM (in form of microcapsules), we are able to overcome the shortcomings of PCMs and design an innovative and efficient solar water heater. Such design enables heat storage directly on the collector for a more constant output even on a cloudy day and prolonged output of heat at night. In addition to being excellent blackbody absorbers, CNT sheets are also a fast source of Joule heating and can be utilized to heat electrically the solar collectors when sunlight is not sufficient. Such improvement would entirely eliminate the need for a separate gas or electric booster water heating system, by incorporating low power electric heating directly into the evacuated tube solar collector.