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This paper focuses on how the low-cost renewable H2 can change a process design configuration in solar fuel plant. As a case study, an industrial process is considered in detail at ANU to convert the algal biomass into Fischer–Tropsch liquid fuels via solar-powered supercritical water gasification (SCWG). The yield gases from the gasifier mainly contain methane, which is then converted into the suitable composition of syngas in the steam methane reforming (SMR) process. Two scenarios are evaluated here to balance the H2:CO ratio for the downstream process: (i) dumping a fraction of carbon in the form of CO2, (ii) supplying make-up H2 from PV-driven electrolysis unit. A detailed steady-state model of the SCWG-SMR and FT plants is developed in Aspen Plus software. The performance curves of gasification/FT units at design and off-design points together with a set of control logics is used to form an energy-based system-level dynamic model in OpenModelica. The levelised cost of fuel (LCOF) as a key parameter for system optimisation is calculated for the considered scenarios. It is revealed that the preferred process design choice of the whole plant is highly affected by the H2 price from a techno-economic standpoint. If the H2 cost falls by 42% (i.e. 5.6 AUD/kg), the SMR-H2 configuration is more economically feasible as compared to the SMR-dumping scenario.

In this study, Monte Carlo ray tracing (MCRT) is coupled with heat transfer models to analyse the efficiencies and energy losses of a cylindrical cavity receiver in a dish system. The progressive Monte Carlo evaluation (PMCE) method is used to determine good geometric designs with high receiver efficiencies. The spillage skirt, which consists of several coiled pipes outside the cavity inlet, is added and optimised to increase the receiver efficiency. Three different types of secondary reflectors, including conical, trumpet and compound parabolic concentrator (CPC) reflectors are also investigated to decrease the spillage loss. The results show that the spillage skirt helps in greatly decreasing the aperture size, while simultaneously reducing the spillage loss. The conical and trumpet reflectors can increase the efficiency by reflecting rays outside the cavity inlet into the receiver. CPC secondary reflectors experience more internal reflections which cause high secondary absorption loss and consequently cannot achieve the equivalent efficiency compared to other designs. With a combination of spillage skirt and conical or trumpet reflectors, the receivers obtain the highest efficiency, with a 1.0% increment in receiver efficiency and 12.9% relative reduction of losses compared to the best cylindrical receiver. Limitations of the current study are that the effects of skirt and reflectors on convective losses are not considered and that the primary concentrator design is fixed.

A system-level evaluation of a concentrating solar power (CSP) configuration, with high-temperature sodium boiler receiver, direct-contact NaCl phase change material (PCM) storage and a Stirling engine array at 1 MWe scale was performed using the modelling framework of SolarTherm to provide an estimate of system costs and comparison to a reference 100 MWe two-tank molten salt system. Assuming an allowable receiver peak flux limit of 1.75 MWth/m2 and a Stirling engine efficiency of 34.6%, a levelised cost of energy (LCOE) of 137 USD/MWhe is obtained via genetic optimisation of parameters including solar multiple, receiver size, and storage component geometry. For an optimistic power cycle efficiency at 75% of the Carnot limit, the calculated LCOE is 109 USD/MWhe. Assuming safety risks can be mitigated without major additional cost, this novel concept holds promise when compared to the reference case that has an LCOE of 123 USD/MWhe, especially for small-scale opportunities either off-grid or at the fringe-of-grid. As this concept operates at very high temperature, the thermal efficiency of the receiver is lower than for a conventional CSP plant, and the storage system is more expensive on a unit-cost basis due to the use of high strength alloys in the tank. However, these drawbacks are offset by the use of a low-cost steel lattice tower design which is feasible at small scale, and by high efficiency power conversion at ∼800°C.

In recent years, electricity costs in the Australian National Electric Market (NEM) have increased primarily due to the network costs associated with grid infrastructure upgrade and operation. Distributed power generation through small-scale concentrated solar power (CSP) can mitigate these network costs if deployed at critical points in the network where low capacity transmission lines most constrain transmission. This study identified cost-effective configurations of small-scale CSP plants, from 10 to 50 MWe, via levelised cost of electricity (LCOE) by adjusting the solar field layout and size, tower height, receiver dimensions and storage capacity. The model was implemented in SolarTherm, and parametric sweeps were carried out by varying solar multiple, storage capacity, and receiver size and tower height to determine the effect of these parameters in the LCOE. Also, two material options were considered for tower construction: reinforced concrete and steel truss. Results showed that the highest capacity factor is found at a 3.4 solar multiple and 15–16 hours of storage capacity at all CSP sizes, achieving an LCOE between 13.7–16.7 ¢USD/kWh depending on CSP size and assuming a 1.5 MW/m2 peak heat flux. Besides, if peak flux is reduced to 0.85 MW/m2, then LCOE ranges between 20.5–26.2 ¢USD/kWh. The use of steel towers is suitable for plant scales below 20 MWe, reducing the LCOE by 2.5–4.2% compared to concrete towers. Meanwhile, concrete construction is the best option for 30–50 MWe.

A bladed receiver concept, intended for use with conventional NaNO3:KNO3 solar salt, was developed and tested using a novel technique where water and air were used as working fluids, to estimate the losses that would be experienced with salt. The (hot) air and (cold) water tests allowed the optical and thermal losses to be separately observed. As well as the bladed receiver, tests were also conducted with an optimised flat receiver. Results showed the total efficiency (reflection, emission, convection losses) was 0.65% higher for the bladed vs. flat receiver, lower than the >2% improvement expected. The lower efficiency is tentatively attributed to lower flux, lower temperatures and windy conditions, compared to the design-point modelling.