Prototype design of a low-concentration roof-mounted solar thermal collector for industrial heat production

Low- and medium-temperature industrial process heat demand represents a significant proportion of the total energy consumed within Australia. Currently, the overwhelming majority of this heat is generated via the combustion of natural gas, with a smaller contribution by electric resistance heating and heat pumps. In order to reduce fossil fuel consumption a renewable alternative process heat supply is highly desirable. Compound Parabolic Concentrators (CPCs) are low-optical-concentration non-imaging solar collectors which are capable of concentrating solar radiation over a broad range of acceptance angles. For this reason, CPCs lend themselves well to non-tracking, roof mounted applications for the generation of low- and medium-temperature thermal energy. The authors have presented a second paper describing an ab initio CPC design, however this presents a number of manufacturing challenges: precise geometric tolerances must be met in order to ensure high optical efficiency; a reflector substrate was required to meet the geometric specification while achieving a high-quality surface finish to maximize mirror reflectance; and a new evacuated tube absorber was developed to address the specific geometric and hydraulic needs. This paper presents the refinement of a CPC design for prototype manufacturability. Optical simulation is used to understand the sensitivity of the design to a range of manufacturing deviations, and this knowledge is applied to assess a number of candidate materials and manufacturing processes. Learnings from the prototype's development are considered in guiding the longer-term design for scale manufacturing. A prototype collector is currently in production and will be tested in the latter months of 2016 at the RMIT University solar test laboratory in Melbourne.