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The sunshape and mirror surface slope error are two main factors that influence the characteristics of incoming and reflected solar beams in a solar concentrator. Different optical modelling tools, however, address these two factors with different methods and simplifications. In this study, simulation methods are reviewed in five optical modelling tools, namely SolTrace, Tonatiuh, Tracer, Heliosim and SolarPILOT. A series of simple test cases are simulated in each tool to compare and verify the implementation of sunshape and slope error models separately. This strategy has successfully identified discrepancies among the tools and contributed to a better understanding of their reasons. It has also uncovered few glitches in some of those tools and contributed to improve them. It is our hope that this study will help to resolve common misconceptions, to build confidence amongst CSP researches on the accuracy of tools with which they have less experience, and to ensure better agreement in optical modelling work in future.

The applicability of the cylindrical arrangement of vertical tube banks is evaluated for liquid sodium concentrating solar thermal receivers and compared with a molten salt reference case through a series of parametric studies. It is shown that sodium receivers experience less thermo-elastic stress load and can operate under higher flux which presents advantages in terms of size reduction and efficiency. While the cylindrical receiver configuration cannot reach the efficiency target of 91% in a high temperature configuration (480 °C to 640 °C), there is potential to improve efficiency by improving heliostat field optics. Flux limitations due to thermo-elastic stresses are less stringent due for sodium receivers due to the better heat transfer properties, and consequently better heliostat field optics would benefit sodium receiver concepts more than molten salts ones.

For commercial solar tower systems of relevant size, state of the art of light collection and concentration (LCC) subsystems (heliostat field plus receiver envelope) do not achieve annual optical efficiencies larger than 65%. Achieving optical efficiencies substantially higher than that requires departing from the traditional mono-tower design. Although multi-tower systems were identified long time ago as candidates to achieve high annual optical efficiencies, so far no multi-tower concept has emerged as a clear alternative to the mono-tower system. In this article, we introduce a variant of the multi-tower concept that combines the modularity and high land coverage of linear focusing technologies with the low thermal losses and high operating temperatures of solar tower technology, and overall represents a disruptive departure from the traditional mono-tower design.

In this work, we explore for the first time the viability and the annual performance of a solar plant which combines a sodium receiver, phase-change material (PCM) storage and supercritical CO2 (sCO2) power block. The simulation results suggest that the system is thermodynamically and economically viable, reducing the levelized cost of electricity (LCOE) compared with a conventional CST plant based on molten salts. The paper presents a new dynamic model of the novel plant configuration which is used for performing a storage sizing study obtaining the best plant investment.

A significant problem with conventional heliostats is off-axis astigmatism, which increases the spot size at the central receiver, limiting the temperature and efficiency of solar thermal systems. Inspired by low-cost mini-actuators used for car wing mirrors, we examine the economic feasibility of a heliostat with individually adjustable mini-facets to correct astigmatic effects, and we compare three alternative tracking configurations. Refereed/Peer-reviewed

A stochastic multi-objective optimisation method is used to determine receiver geometries with maximum second law efficiency, minimal average temperature and minimal surface area. The method is able to identify a set of Pareto optimal candidates that show advantageous geometrical features, mainly in being able to maximise the intercepted flux within the geometrical boundaries set. Receivers with first law thermal efficiencies ranging from 87% to 91% are also evaluated using the second law of thermodynamics and found to have similar efficiencies of over 60%, highlighting the influence that the geometry can play in the maximisation of the work output of receivers by influencing the distribution of the flux from the concentrator.

A new tubular cavity receiver for direct steam generation, 'SG4', has been built and tested on-sun based on integrated optical and thermal modelling. The new receiver achieved an average thermal efficiency of 97.1±2.1% across several hours of testing, and reduced the losses by more than half, compared to the modelled performance of the previous SG3 receiver and dish. Near-steady-state outlet steam temperatures up to 560°C were achieved during the tests.

Annual performance simulations provide a valuable tool for analysing the viability and overall impact of different concentrating solar power (CSP) component and system designs. However, existing tools work best with conventional systems and are difficult or impossible to adapt when novel components, configurations and operating strategies are of interest. SolarTherm is a new open source simulation tool that fulfils this need for the solar community. It includes a simulation framework and a library of flexible CSP components and control strategies that can be adapted or replaced with new designs to meet the special needs of end users. This paper provides an introduction to SolarTherm and a comparison of models for an energy-based trough system and a physical tower system to those in the well-established and widely-used simulator SAM. Differences were found in some components where the inner workings of SAM are undocumented or not well understood, while the other parts show strong agreement. These results help to validate the fundamentals of SolarTherm and demonstrate that, while at an early stage of development, it is already a useful tool for performing annual simulations.

Conversion of algal biomass into value added products, such as liquid fuels, using solar-assisted supercritical water gasification (SCWG) offers a promising approach for clean fuel production. SCWG has significant advantages over conventional gasification in terms of flexibility of feedstock, faster intrinsic kinetics and lower char formation. A relatively unexplored avenue in SCWG is the use of non-renewable source of energy for driving the endothermic gasification. The use of concentrated solar thermal to provide the process heat is attractive, especially in the case of expensive feedstocks such as algae. This study attempts to identify the key parameters and constraints in designing a solar cavity receiver/reactor for on-sun SCWG of algal biomass. A tubular plug-flow reactor, operating at 24 MPa and 400-600 °C with a solar input of 20MWth is modelled. Solar energy is utilized to increase the temperature of the reaction medium (10 wt.% algae solution) from 400 to 605 °C and simultaneously drive the gasification. The model additionally incorporates material constraints based on the allowable stresses for a commercially available Ni-based alloy (Inconel 625), and exergy accounting for the cavity reactor. A parametric evaluation of the steady state performance and quantification of the losses through wall conduction, external radiation and convection, internal convection, frictional pressure drop, mixing and chemical irreversibility, is presented.

For the prediction of convective heat loss from solar concentrating receiver cavities a number of empirical correlations exist. Geometry and the inclination angle determine the degree to which natural convection can infiltrate the cavity and remove stably stratified hot air out through the aperture. This makes the task of defining characteristic lengths for such Nusselt correlations difficult, neither does their use offer insight as to how one might reduce heat loss through the use of baffles, air curtains or small aperture-to-cavity-area ratios. Computational Fluid Dynamics (CFD) can assist in the design of better cavity receivers as long as the rules upon which it rests are respected. This paper is an exploration of the need for turbulence modelling in cavity receivers using some common linear eddy viscosity closure schemes. Good agreement was obtained with the CFD software OpenFOAMO® 3.0.1 for a deep cavity aperture but it under-predicted a shallow cavity. The experiments used for validation were in the Grashof region Gr ≈ 10 6 , well below the region for transition to turbulence between 10 8 < Gr < 10 9 .

Three high-temperature solar receiver design concepts are being evaluated as part of the Australian Solar Thermal Research Initiative (ASTRI): a flux-optimised sodium receiver, a falling particle receiver, and an expanding-vortex particle receiver. Preliminary results from performance modelling of each concept are presented. For the falling particle receiver, it is shown how particle size and flow rate have a significant influence on absorptance. For the vortex receiver, methods to reduce particle deposition on the window and increase particle residence time are discussed. For the sodium receiver, the methodology for geometry optimisation is discussed, as well as practical constraints relating to containment materials.

Bladed receivers use conventional receiver tube-banks rearranged into bladed/finned structures, and offer better light trapping, reduced radiative and convective losses, and reduced tube mass, based on the presented optical and thermal analysis. Optimising for optical performance, deep blades emerge. Considering thermal losses leads to shallower blades. Horizontal blades perform better, in both windy and no-wind conditions, than vertical blades, at the scales considered so far. Air curtains offer options to further reduce convective losses; high flux on blade-tips is still a concern.

An integrated model for an axisymmetric helical-coil tubular cavity receiver is presented, incorporating optical ray-tracing for incident solar flux, radiosity analysis for thermal emissions, computational fluid dynamics for external convection, and a one-dimensional hydrodynamic model for internal flow-boiling of water. A receiver efficiency of 98.7% is calculated, for an inlet/outlet temperature range of 60–500 °C, which is the ratio of fluid heating to receiver incident irradiance. The high-efficiency design makes effective use of non-uniform flux in its non-isothermal layout, matching lower temperature regions to areas of lower flux. Full-scale testing of the design will occur in late 2015.