Optimization of Solar Thermal and Solar Photovoltaic Systems for Medium Temperature Industrial Applications

Abstract

Solar-derived industrial heat could be derived from the solar resource available on factory rooftops from either solar thermal (ST) collectors, which can generate heat directly, or from solar photovoltaic modules (PV), which can indirectly generate heat through heat pumps or resistance heaters. At present, there is no mature solar technology exists which integrates both for medium temperature outputs, although this has certainly been the subject of a lot of recent research. Based on this assumption, this thesis investigates the potential of using ST and PV solar collectors in a side-by-side configuration for industry rooftops, ranging from 100% PV to 100% ST. Thus, the central question for this thesis is: What is the best ‘mix’ of solar technologies for factories around the world? To answer this, a simulation-based method was developed and applied, which considered several objective functions, including economic (levelized cost of energy), technical (overall performance) and environmental (embodied energy and emissions), and multi-objective combinations of these objectives. The economic function is dependent on the local cost parameters, thus, the levelized cost of energy was determined in several geographic locations. The technical function is also local and was determined through determining the annual transient performance of each technology for the proposed application. Additionally, the environmental function requires knowledge of the embodied energy and embodied greenhouse gas emissions that are associated with these solar technologies during their manufacturing stage. Global geographical locations were also analyzed to determine the equivalent carbon dioxide impact for the primary energy mix that the solar production offsets. Several parameters/ factors were analyzed to investigate their impacts on the system performance such as the load profile, load temperature, and various solar technologies. Sensitivity analyses were also conducted for the coefficient of performance and PV efficiency to analyze the impact of changing these parameters. The results revealed that these parameters are significant on the system output and can vary the optimum solar mix by up to 17%. The results indicate that the ST collector has a lower energy payback time (i.e. EPBT<1.2 years) in high direct normal irradiation locations and that a mix of technologies provides the fastest EBPT. The cost function was reduced using the solar mix (i.e. by up to 9.8% compared to ST alone). In terms of the greenhouse gas emission payback time (GHGe PBT), the findings do not reveal a conclusive verdict for or against ST versus PV technologies. Lastly, global maps were produced to present the optimum ‘mix’ and embodied impacts based upon the findings of these results. This thesis is significant as it presents a better way to make decisions about which solar technology to use, potentially enabling industrial customers to achieve better cost, performance and emissions outcomes from their operations