Solar Thermal Facility Research Articles

Improved Particle Heat Transfer by way of Bimodal Particle Distributions for High Temperature Solar Thermal Energy

High temperature solar thermal facilities are looking to increase operating temperatures through novel heat transfer media, one such being solid particles. These particles operating at high temperatures will require transferring their thermal energy into another working fluid like supercritical carbon dioxide which can be used in advanced power cycles. Achieving high heat transfer between the particles and supercritical carbon dioxide is essential to high efficiency and low-cost operation. Therefore, optimizing the thermal conductivity of these particles is one potential way to ensure high performance. Traditionally, unimodal particle distributions have been employed in high temperature particle solar power plants. However, ambient temperature testing of bimodal particle distributions has revealed a superior thermal conductivity when compared to its unimodal counterpart at the same temperature. This data was obtained by certified, off-the-shelf instruments that can effectively simulate the conditions a particle would be exposed to in a high temperature solar thermal system. Data obtained in this way suggests that the increased thermal conductively imputed by a bimodal particle distribution is significant at working temperatures in solar facilities. Furthermore, the thermal conductivity of these bimodal particle distributions peaks when the best combination of large and small particles is applied. At high temperatures, binary particle distributions are compared to monodispersed distributions of larger particles where heat transfer is more prolific due to the increased surface radiation. Various thermal conductivity, porosity and heat exchanger models are explored in conjunction with data acquired up to 700 C.

Coupled abrasion Erosion-Oxidation wear from particles in Concentrating solar thermal power facilities

Solid particles represent an attractive heat transfer and energy storage media for next generation solar thermal power facilities for their ability to operate at high temperatures without concerns for freezing or corrosion. A potential outstanding issue that still remains for particles as heat transfer media is the wear on components operating with particles flowing (sliding) in, along, or over them. Prior work has shown that even at the low velocities (∼1 cm/s to ∼ 1 m/s) expected in solar thermal facilities, material wear will still occur, and the lifetime and performance of components undergoing wear needs to be well understood. Abrasion erosion occurs when particles come into contact with containment materials at extremely shallow angles, and is likely to be seen in heat exchangers, storage bins, and flow control mechanisms. Additionally, because of the open nature of most of these systems to air, oxidation of metals is also of concern. Here, we show how critical the coupled erosion-oxidation mechanism is to understanding particle/material durability and therefore need for greater in-depth analysis. Abrasive wear experiments are conducted on metals such as SS316 (L and H grades), Inconel 740H, Haynes 230 with different particles (HSP 40/70, Wedload 430, and CarboMax HD) for different operating conditions. Results clearly indicate that oxide spallation and removal is critical to the overall wear seen at high temperatures.

Hydrogen production by isothermal thermochemical cycles using La0.8Ca0.2MeO3±δ (Me = Co, Ni, Fe and Cu) perovskites

Solar-driven thermochemical water splitting has the potential to transform concentrated solar energy into green hydrogen and other solar fuels. In this work, La0.8Ca0.2MeO3±δ (Me = Co, Ni, Fe and Cu) perovskites have been synthesised by a modified Pechini method and evaluated as materials for hydrogen production by two step thermochemical water splitting cycles. Performing the thermal reduction at temperatures of 1200 and 1000 °C, while the oxidation is done at 800 °C, allows a remarkable and stable hydrogen production after 5 consecutive cycles. However, the perovskites suffer changes in the structure after each redox cycle, with potential effects in the long-term cyclic operation. On the contrary, the isothermal thermochemical cycles at 800 °C produce a stable amount of hydrogen with each consecutive cycle maintaining the perovskite structure. This hydrogen production ranges from 3.60 cm3 STP/gmaterial·cycle for the material with the lowest productivity (La0.8Ca0.2FeO3±δ) to 5.02 cm3 STP/gmaterial·cycle for the one with the highest activity (La0.8Ca0.2NiO3±δ). Particularly the Ni-based material shows the highest H2 productivity accompanied by very good material stability after 15 consecutive cycles, being possible to combine with current solar thermal facilities based on concentrated solar power technologies like plants with central receivers.

Hierarchical control based on a hybrid nonlinear predictive strategy for a solar-powered absorption machine facility

This work presents a hierarchical framework to control a solar thermal facility aiming to provide the required operating conditions for an absorption chiller machine. The CIESOL thermal plant, located at the University of Almería (Spain), is proposed as a case study in which all subsystems and valves are considered in a trustworthy simulation environment. Herein, the thermal plant dynamic representation is completed by presenting the absorption chiller modeling, in which three distinct models, namely, a first principle lumped parameters, an AutoRegressive with eXogenous input (ARX), and a Nonlinear ARX (NLARX) models, are validated. Accordingly, by using these models, the hierarchical control based on a hybrid nonlinear predictive controller is formulated. Dwell-time and stress zone are embedded in the operating condition constraints of the hybrid control component of the upper layer to enhance robustness and performance. Moreover, a lower layer based on Proportional–Integral (PI) controllers is also designed to overcome the valve’s nonlinear dynamics and improve disturbance rejection on the regulatory layer. The results demonstrate that the hierarchical structure controls the solar plant around 115 min more in the operating time of the solar-powered absorption chiller, with less usage of fossil fuels sources compared to a conventional operation of the system.

Performance investigation of seawater desalination system powered by central receiver concentrated solar thermal plant

Seawater desalination using solar energy is a promising solution for addressing water scarcity in arid and semi- arid regions, as it not only provides a reliable source of fresh water, but also utilizes the abundant solar energy resources in the region to power the desalination process in a sustainable way. For this, the aim of this research is to investigate the performance and economic feasibility of a concentrated solar power plant coupled with a desalination unit for sustainable electricity and freshwater production. Six different coastal sites throughout the Middle East and North Africa region were considered, i.e., Agadir (Morocco), Algiers (Algeria), Sharm el-Sheikh (Egypt), Dammam (Saudi Arabia), Salalah (Oman), and Aden (Yemen). The concentrated solar power facility has a 100 MWe net output with two tanks of direct thermal energy storage using wet cooling with seawater as the cooling agent in the condenser; the solar tower model was validated using the Gemasolar power facility in Spain; and the desalination process include a direct-contact membrane distillation (DCMD) system numerically solved using the MATLAB software®, with experimental data used to validate the model. The findings indicate that large-scale central receiver concentrated solar thermal facilities are more competitive in Sharm el-Sheikh, where annual energy output and capacity factor are expected to be 586.28GWh and 67%, respectively, while the cooling water demand is expected to be 1,793,310 m3. The nominal levelized cost of electricity (LCOEnom) is 11.2 ¢/kWh. Furthermore, water production costs are <0.5 $/m3 in Aden, Damman, Sharm el-Sheikh, and Salalah, but >1.0 $ /m3 in Agadir and Algiers. The results obtained indicate that the combination of these two technologies can be a reliable source of power and fresh water for these locations.

Performances and control aspects of steam storage systems with PCM: Key learnings from a pilot-scale prototype

Medium and High temperature steam is used as Heat Transfer Fluid in a wide range of industrial processes. Steam storage is required when steam production or consumption is variable in time, like in solar thermal facilities or batch industrial processes. In introduction, this paper gives an extensive review of the PCM storage prototypes that were operated worldwide for steam applications between 120 and 400 °C. At CEA Grenoble, a PCM steam storage prototype was operated during >300 days during three tests campaigns from 2013 to 2019. 78 charge–discharge cycles were performed with the same PCM volume under a wide range of operating conditions. This paper aims at reporting some significant experimental results obtained from this prototype. Thermal performance indicators (storage capacity, utilization rate, storage efficiency, and exergy efficiency) are evaluated in detail for the first time for a pilot scale PCM steam storage. For a complete charging-discharging cycle at sliding pressure, constant mass flow, and from homogeneous temperatures in initial conditions, utilization rate is estimated at 81.9%, storage efficiency at 79.3%, and storage exergy efficiency at 76.2%. From 2013 to 2019, thermal testing of the storage prototype showed very repeatable results: in this paper, the authors demonstrate that heat transfers were not altered between 2013 and 2019. Beyond most commonly used operating modes for PCM steam storage (fixed pressure and sliding pressure), advanced control strategies are proposed. Two examples of advanced controls are described in this paper, showing an insight of the valuable services that a PCM storage system can provide to an industrial steam user (power cycle, industrial steam network,…).

A review on thermal application of metal foam

Heat exchangers embedded with metal foam are drawing increasing attention in the thermal application field, due to the performance of low density, large ratio of surface area to volume as well as high thermal conductivity. In these applications, compact heat exchanger, solar thermal facilities and thermal energy storage are the three core components. This paper focuses on the lasted advances in thermal applications, presenting a review of theoretical and experimental progress over metal foam in thermal application. The empirical and theoretical models for pressure drop, heat transfer coefficient and performance evaluation criteria of compact heat exchangers with metal foam are reviewed and discussed, especially different optimized configurations. There is a trade-off between heat transfer enhancement and increase of pressure drop. Some exploratory work performed by present authors are also introduced. The manufacturing, heat transfer and flow characteristics of tube bundle wrapped with metal foam are taken into account for optimization of heat exchanger. It is confirmed that the conversion mechanism of heat transfer is carried out that heat conduction is the dominative term at high dimension permeability. The correlations of heat transfer rate and pressure drop for staggered and single row tube bundle wrapped with metal foam are concluded, respectively. The effects of different bonding methods are revealed for point-contact in metal foam and base tube. The powder-sintering method can provide a stable and minimum-thickness bonding layer. Various types of solar thermal facilities utilized metal foam to improve the energy conversion efficiency from solar radiant energy to thermal energy are also reviewed and discussed, including solar collector for intermediate-low temperature utilization and solar receiver for high temperature utilization. The Last but not least, existing and future metal foam thermal application stations are overviewed.

Drivers of renewable technology adoption in the household sector

Using data from the German Socio-Economic Panel, we undertake a simultaneous assessment of the importance of factors that are individually found to be significant for the adoption of renewable energy systems by households but are not yet tested jointly. These are sociodemographic and housing characteristics, environmental concern, personality traits, and economic factors; i.e. the expected costs of and revenues from the investment. Our results suggest that household decisions to invest in photovoltaic systems and solar thermal facilities are mainly driven by economic factors. Taking account of sociodemographic and housing characteristics, environmental concern, or personality traits has comparatively little relevance, while the quantitative nexus between the decision to invest and returns on the investment is robust to their inclusion.

Highly Selective Solar Thermal Sprayable Coating Based on Carbon Nanotubes

A key component in solar thermal energy conversion system is the light collector that is coated with an absorbing material. Optimal performance is accomplished by high absorptance and low emittance. The best collectors are fabricated by vacuum deposition processes, which are limited to small size and flat objects. Here, the formation and performance of a new three-layer solar selective coating, which is formed by a simple wet-deposition process is reported. The solar absorbing layer is based on carbon nanotubes, which are considered the most absorbing material. This layer is coated by a second layer of ITO, which functions as an IR reflecting layer, followed by an AlOOH anti-reflective layer. The resulting CNT/ITO/AlOOH coating exhibited the best-reported spectral selectivity by wet deposition process, with high absorptance of 0.941 ± 0.004 and low emittance of 0.13 ± 0.02 at room temperature. Furthermore, the multilayer sprayable coating is stable at elevated temperature for a prolong time and therefore, shows promise for application in large scale and on-site solar thermal facilities.

Accelerating the deployment of low emission technology in Australia

Transforming the way Australia produces and uses energy must be a cornerstone of a national response to addressing greenhouse gas emissions. Natural gas can deliver significant greenhouse gas emission reductions at a fraction of the cost of alternative technologies. To drive this forward, industry is looking for policy certainty and a level playing field. Furthermore, there exists the opportunity to leverage other low emission technologies from gas—for example, the integration of natural gas combined cycle generation with a solar thermal array offers an opportunity to enable the early deployment of solar thermal technology in Australia. Integration can deliver a power outcome at lower cost and with higher conversion efficiencies than an equivalent stand-alone solar thermal facility.

Component developments for novel solar thermal facilities

The state of development for the important components of solar thermal facilities as well as the objectives for improving activities are shortly described. Most of these activities have been formulated as project plans ofthe IEA-SolarPACES Task III Solar Technology and Advanced Applications. The progress lines of development in collector technology will be reported for trough, heliostat and dish mirrors. The receiver trends will also be described for tube and volumetric absorber techniques. Special attention will be given to the advances of the parabolic trough technology (direct steam generation, improved/simplified components), to the newest results of American and Spanish/German heliostats, and to the Israeli high-flux closed cycle receiver as well as to German volumetric receiver advances.

Photocatalytic Destruction of Chlorinated Solvents in Water With Solar Energy

Sandia National Laboratories and the National Renewable Energy Laboratory are developing a photocatalytic process to destroy organic contaminants in water. Tests with common water pollutants have been conducted at Sandia’s Solar Thermal Facility using a near commercial scale, single-axis tracking parabolic trough system with a glass pipe reactor mounted at its focus. Experiments at this scale provide verification of laboratory studies and allow examination of design and operation issues at a real-life scale. The catalyst, titanium dioxide (TiO2), is a harmless material found in paint, cosmetics, and toothpaste. Experiments were conducted to determine the effects of key process parameters on destruction rates of chlorinated organic compounds that are common water pollutants. In this paper, we summarize the engineering-scale results of these experiments and analyses.

The Dual Medium Storage Tank at the IEA/SSPS Project in Almeria (Spain); Part I: Experimental Validation of the Thermodynamic Design Model

Efficient and reliable thermal storage is an important requirement for substituting conventional power systems with solar thermal facilities. Storage will synchronize the intermittent supply of solar radiation with the usually constant demand of technical thermal processes. The distributed collector system of the IEA/SSPS Project in Almeri´a (Spain) uses two different storage systems for the 100 to 295°C temperature range: a single thermocline vessel and a dual medium storage tank (DMST). In the first tank, thermal oil is used as the energy carrier as well as for energy storage; in the dual medium tank, the storage medium is cast iron, and the oil acts primarily as a heat transfer fluid. At the SSPS, this concept’s potential for future process heat applications has been assessed. Performance and operational restrictions of the DMST were systematically studied over a wide range of temperatures, and an existing simulation model was verified and adapted at the same time. The thermodynamic model of the DMST is presented and compared with the first results of the 1985 test program.