Lowering the barriers to developing thermal renewable energy technologies

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.Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Mechanical Engineering, 201

The potential role of data-centres in enabling investment in geothermal energy

A techno-economic analysis is presented, of the potential for data-centres and fibre optic networks to drive investment in geothermal resources. The concept is attractive because of data-centres’ stable demand for electricity and refrigeration at a scale of <5MWe, corresponding to the output of a single well doublet; because the cost of establishing a fibre optic link is an order of magnitude less than augmenting an electricity transmission network; and because it offers an opportunity for geothermal systems to compete with the retail price of electricity. A comparison of energy delivery outcomes was performed for both engineered geothermal systems (EGS) and hot sedimentary aquifer (HSA) reservoirs to identify the minimum conditions that could make the concept economically attractive. For the high temperature EGS, a single and dual pressure binary organic Rankine cycle (EGS-ORC, EGS-2×ORC), a single stage flash (EGS-flash) and a hybrid flash-binary system (EGS-hybrid) were studied. The HSA system investigated the direct use (HSA-DU) of the geo-fluid in an absorption chiller for refrigeration and the use of coincidental natural gas resources to deliver electricity via an internal combustion engine. The technical performance of these systems was assessed for a range of well-head pressure (EGS only) and geo-fluid flow rate scenarios. The economic performance of the combined set of investments in optical fibre and energy infrastructure was examined by estimating the expected internal rate of return (E[IRR]). The HSA-DU option yielded an E[IRR] of 14%, following the installation of energy capacity equivalent to the output of one well-doublet assuming the displacement of the Australian retail price of electricity; and 12% for the US retail price. In comparison, the EGS-hybrid was found to have an E[IRR] of 8%, if the Australian retail price were displaced and 4% if the US retail price were displaced. The EGS-flash, ORC and 2×ORC scenarios were found to be progressively less attractive than the EGS-hybrid. To identify the conditions under which the concept could satisfy commercial hurdle rates, the sensitivity of the E[IRR] was investigated for the cost of an optical fibre link; the EGS resource depth; the retail price of electricity displaced; and a data-centres’ energy consumption profile. Credits for CO2 emissions abatement at $23/ton were found to have only a marginal influence on the economic performance of the EGS and HSA scenarios examined.Ashok A. Kaniyal, Graham J. Nathan and Jonathan J. Pincu

Dynamic modeling of the coproduction of liquid fuels and electricity from a hybrid solar gasifier with various fuel blends

Ashok A. Kaniyal, Philip J. van Eyk and Graham J. Natha

Storage capacity assessment of liquid fuels production by solar gasification in a packed bed reactor using a dynamic process model

Abstract not availableAshok A. Kaniyal, Philip J. van Eyk, Graham J. Natha

Polygeneration of liquid fuels and electricity by the atmospheric pressure hybrid solar gasification of coal

An analysis of system operation and performance has been undertaken, for the first time, of a solar-hybrid coal-to-liquids polygeneration facility incorporating solar resource variability. The energetic and environmental performance of a coal-to-liquids process that is integrated with a solar hybridized, oxygen blown, atmospheric pressure gasifier (CTLsol) is compared with that of a reference, nonsolar, autothermal, pressurized gasification integrated, CTLref configuration. To allow the plant to respond to solar resource transience, pressurized storage of upgraded syngas and oxygen is incorporated into the proposed CTLsol system. The CTLsol process is simulated using a dynamic model that assumes pseudosteady state operation at each time-step, for a 12-month, hourly averaged solar insolation time-series. Both the CTLsol and CTLref systems were modeled using AspenPlus and Aspen HYSYS (v 7.1) software. The analysis of the CTLsol system’s performance showed an annually averaged improvement of 21% to the total energetic output and a reduction of 30% in the mine-to-tank greenhouse gas emissions relative to the CTLref system assuming equilibrium gasification conditions of 1400 °C and 1 bar-a. The integration of a pressurized syngas storage facility was shown to enable the CTLsol system to allow the variation in throughput of each unit of process equipment to be maintained within normal operational ranges despite the fluctuations in the transient solar input to the solar-hybrid coal gasification process.Ashok A. Kaniyal, Philip J. van Eyk, Graham J. Nathan, Peter J. Ashman and Jonathan J. Pincu

Polygeneration of Fischer-Tropsch fuels and electricity by hybridised solar gasification of coal - a pseudo-dynamic process model

Presented is a comparative energetic and environmental performance analysis of a solar hybridised gasification, coal to liquids polygeneration system and a non-solar reference. Using AspenPlus and HYSYS software, the reference system was configured, assuming the integration of a pressurised, Shell entrained flow gasifier with a Fischer Tropsch liquids (FTL) polygeneration facility. The hybrid plant assumes the feasibility of integrating an atmospheric, continuously operational, directly irradiated, oxygen blown hybrid solar reactor with this polygeneration facility. To mitigate the diurnal and stochastic impacts of the solar-boosted production of syngas, the hybrid polygeneration model was also assumed to be configured with a pressurised syngas storage plant. Here, the dynamic operation of the polygeneration system was modeled using a pseudo-steady state approximation for two, six day time-series of validated solar insolation model data. The two time-series were selected to represent a period in 'summer' characterised by a steady, low cloud period of solar insolation, and a period in 'winter' marked by intermittent solar insolation and high cloud. Using these data, a MATLAB model was used to predict the maximum steady rate of liquids that could be produced for the given solar insolation scenario. For the summer time series, the hybrid solar gasification system was shown to improve the steady rate of liquids production by 32% and decrease the source-to-wheel (STW) GHG emissions per GJ FTL by 26%, relative to the reference. For the winter time-series, only a marginal improvement in liquids production was predicted .This result followed from the assumed difference in gasification temperatures between the hybrid system and the reference. On a total energetic output basis, GHG emissions were shown to decrease relative to the reference by 17-21 percentage points for the summer-time series, but increase by 18 percentage points for the winter time-series. This increase in GHG emissions follows the large parasitic impact of SG compression on the hybrid system's net electrical output. Additional sensitivity analyses identified the potentially significant energetic and environmental value of either operating the hybrid gasifier at just 2 bar-g instead of 1 bar-g or incorporating an O2 storage system to reduce the parasitic load of the hybrid system's ASU. Importantly, the present analysis found the difference in the steady output from the FT reactor and electricity generating plant between the summer and winter time-series to be within the feasible operational limits of the respective plant components. This provides assurance as to the feasibility of developing a solar hybridised C2L polygeneration facility using commercially available plant components.Ashok A Kaniyal, Philip J van Eyk, Graham J Nathan, Peter J Ashman, Jonathan J Pincu