Natural circulating flat plate collectors : Investigations of a new material and performance simulations

Abstract

Solar energy can be utilized to heat water with the use of flat plate collectors. Effort is made to reduce the cost of solar water heating technology in order to make it economically competitive to conventional energy. An absorber material is tested on component level and performance related aspects are studied. The material has a lower price than the polymer materials currently used in glazed collectors, and therefore it has the potential to lower the cost of solar flat plate collectors. The performance related aspects are tested on a partially glazed, natural circulating flat plate collector, referred to as the Duo-Collector. The aim of letting the collector be partially glazed is to prevent the heat carrier from boiling. Samples cut from an extruded absorber sheet were exposed to 140 degrees Celsius and 150 degrees Celsius for different periods of time. These were used to map the mechanical properties of the material. The samples exposed to 150 degrees Celsius were used to map dimensional and optical changes. The results from the material-related studies on component level show that no failure occurs for any of the ageing periods which were realized in the time frame of the present work. The extruded absorber sheet has a sufficiently high absorptance and dimensional stability. These findings have strengthened the material's position as a candidate for use in solar thermal applications. The performance of the Duo-Collector has been simulated with MATLAB. It is found that the system is suitable as a method for preventing the fluid in the collector from boiling. The efficiency of such a system was also investigated. For low operating temperatures the efficiency of a Duo-Collector is approximately equal to the efficiency of a fully glazed or an unglazed collector. The efficiency of all the collectors decrease with increasing operating temperatures, and the efficiency of the Duo-Collector is between that of a fully glazed and that of an unglazed collector for all operating temperatures above approximately 10 degrees Celsius. Under certain circumstances the Duo-Collector can cool the water. This effect needs to be investigated further. Since only steady-state conditions are studied in this work, further analysis must be performed to compare how the Duo-Collector performs for different applications.