Solar water heaters are a well-established renewable energy technology that has been widely adopted outside of the United States. Here we propose to significantly improve the evacuated solar tube collectors (ETC) by utilizing the dry-drawable carbon nanotube (CNT) sheets for solar energy absorption and CNT multifunctional nanocomposites with functional layers of heat accumulators and heat transporters. The benefits of the proposed carbon nanotube based solar water heaters is the property of carbon nanotubes as a near blackbody absorber, allowing the absorption of & gt;98% of the solar energy. In addition the porous nature of the sheets and nanometer diameter of tubes, increases light scattering inside the selective layer, resulting in light trapping, decreased reflectivity and increased light absorption. In this project we will be using large scale dry-drawable CNT sheets as multifunctional Absorbance layer on ETC, improving it further by birolling into its porous network functional layers of heat accumulation phase change material (PCM) microspheres and heat transfer sub-layer. In addition to being excellent blackbody absorbers, carbon nanotube sheets are a fast source of Joule heating (upon transmission of electrical current) and can be utilized to heat electrically the solar collectors when sunlight is not sufficient. Electrical connections can be made to the preferentially sectioned copper buffer layer to define the surface area for Joule heating. Such improvement would entirely eliminate the need for a separate gas or electric booster water heating system, by incorporating electric heating directly into the solar collector. A critical part of the proposed solar collector tube is the absorbing layer that is composed of CNT sheets. Developed in University of Texas at Dallas and licensed to Solarno, CNTs are grown as vertically oriented forests on iron-coated silicon wafer using chemical vapor deposition (CVD). Our RF-inductrive controllable CVD method for MWNT growth can be easily scaled to commercial level and reduce the manufacturing cost to the cost of the CVD process gases. In addition, the added value and savings of using the carbon nanotube based solar heater without the additional booster hardware would significantly decrease the payback period. According to a major manufacturer of solar water heaters, the payback period for a solar water heater with the current 57.1% efficiency solar collector tubes is 4-5 years. Upon successful implementation of the carbon nanotube sheets as the collector material and improved efficiency, we strongly believe that the payback period will remain less than 5 years. The ultimate goal of our research is to increase the usage of solar water heaters SWH in USA and achieve fast return on highly effective evacuated tube collectors ETC of SWH by using nanomaterials for light absorbing, conversion to heat, heat accumulation and heat transfer layers in ETC. our preliminary results has proven the validity of PCM incorporation into CNT- based absorber. Also birolling graphene flakes has proven to be beneficial for high thermal conductivity of CNT-based coatings. Our commercial partners, Apricus Solar and Westech Solar have generously provided us with parts of ETC and components for testing, and will be evaluating further this new technology for licensing and commercialization. Moreover Solarno will create RF-CVD systems for upscaling the growth of CNT sheets for commercial scale testing of full length 7 ft ETC in SWH panels.
