Lowering the barriers to developing thermal renewable energy technologies

Abstract

Impediments to investment in renewable energy resources arise in five areas, namely, infrastructure access, technological and resource uncertainty, competition from established fossil fuel alternatives, asset financing and public policy. Together these can lead to large capital cost penalties and poor resource productivity that reduce the viability of projects. Presented here are system-wide analyses of two novel pathways to generate new investment in concentrated solar thermal and in geothermal energy resources. The pathways are designed to reduce the minimum capital outlay required for the development of renewable energy resources, by identifying synergies with established energy and non-energy infrastructure and technologies. The endothermic, thermochemical processing of fossil, waste and biomass using concentrated solar energy has been demonstrated, at experimental scales between 3-500 kWth, to upgrade the calorific value of syngas relative to the feedstock by ~30%, depending on the reactor technology employed and the fuel that is processed. However, no process modeling analysis has previously been presented of the impacts of diurnal, seasonal and cloud-induced solar resource availability on the operational limits of commercially available Fischer-Tropsch (FT) liquids syngas processing infrastructure. Presented here, are process modeling analyses of the relative performance of two solar gasification reactor systems and the operational impacts of their integration with a coal-to-liquids polygeneration facility. The reactor designs assessed were the batch process, indirectly irradiated solar packed bed gasifier that operates with solar input alone and a hybridised configuration of the solar vortex reactor that is assumed to integrate combustion to account for solar resource transience and thus enable a continuous non-zero syngas throughput. To address the impacts of solar resource transience, the process modeling analyses showed that the packed bed solar reactor requires syngas storage equivalent to >30 days of gas flow to maintain feasible operation of unit operations downstream of the gasifier. In comparison, the hybrid solar vortex reactor was shown to require only ~8 hours of syngas storage. A dynamic process modeling study of integrating a hybrid solar vortex coal gasifier with a FT liquids polygeneration system was shown to improve the overall energetic productivity by 24% and to reduce mine-to-tank CO2 emissions by 28%. This is the first comprehensive system analysis of a solar hybridised coal-to-liquids process that has assessed all the impacts of solar resource transience on the unit operations that comprise a FT liquids polygeneration system. Geothermal resources can face barriers to investment arising from their remoteness—in particular, distance from established electricity transmission lines—uncertainty in the cost of establishing well infrastructure and uncertainty in the scale of the recoverable resource. To address these challenges, presented here is a comprehensive system evaluation of the potential of high-value energy load data-centres to reduce the cost of developing geothermal resources. This potential arises from the data-centres’ modularity, their stable load for both electricity and refrigeration, and because their energy demand can be scaled commensurate to geothermal resource availability. Moreover, they can be connected to market by fibre optic network infrastructure, which is at least two orders of magnitude less expensive than electricity transmission. System analyses of this concept showed that a hybrid energy system that integrates low-temperature geothermal resources to meet data-centres’ refrigeration load, and natural gas to meet the electrical load, could generate expected returns of 25% and reduce the cost of developing geothermal resources by >30 times. The systems modelled in this thesis have shown that, compared with stand-alone development, the hybridised development of renewable energy resources with fossil fuel energy technologies offers a lower cost pathway.