Solar Thermal Production Research Articles

Synthesis of low-cost refractory cordierite for solar thermal storage: Characterization of mechanical, thermal and physical stability during thermal shock cycles

To guarantee the efficiency of solar thermal energy production, the thermal storage material must have exceptional resistance to thermal shock to withstand prolonged thermal cycles. In addition, it must have specific properties tailored to the requirements of this field. In this study, we developed a refractory cordierite for solar thermal storage, characterized by very high thermophysical properties, from an initial formulation containing 20 % of abundant clays. The properties of materials sintered at 900 °C, 1000 °C, 1100 °C, 1200 °C and 1250 °C were assessed by a series of analyses including X-ray diffraction (XRD), mass loss, volumetric shrinkage, bulk density, and porosity, scanning electron microscopy (SEM), thermal conductivity, thermal diffusivity, thermal storage capacity, chemical resistance, and mechanical testing. The incorporation of natural clays, rich in sintering aid elements, facilitated the formation of 74 % α-cordierite at 1200 °C and 92 % at 1250 °C, significantly enhancing the material's densification. Materials sintered at 1250 °C and containing 92 % refractory cordierite were subjected to 50 thermal shock cycles from 500 °C to 0 °C. The obtained materials showed excellent mechanical properties, including compressive strength of 398 MPa, low porosity of 0.21 %, density of 2.52 g/cm3, zero mass loss in acidic and basic environments for 30 days, and very high values of heat capacity (3429.80 J/(kg·K)), thermal conductivity (2.08 W/(m·K)) and thermal diffusivity (0.84 mm2/s) at room temperature.

A holistic methodology for designing novel flat plate evacuated solar thermal collectors: Modelling and experimental assessment

This paper presents a comprehensive analysis of the design, implementation, experimentation, and optimization of a novel evacuated flat-plate solar thermal collector characterized by a vacuum level between the glass cover and the absorber plate. The paper addresses different research themes, primarily focusing on developing a low-cost evacuated solar thermal collector with a high innovation level. Additionally, it introduces a comprehensive approach for the conceptualization, design, fabrication, testing, and optimization of solar thermal collectors. Specifically, this study aims to highlight the characteristics of a vacuum-enhanced solar thermal collector and demonstrate a step-by-step process involved in its design, fabrication, testing, and optimization. The proposed methodology is based on the adoption of two software tools and an extensive experimental analysis: the commercial software ANSYS is utilized for structural analysis, while MatLab is employed to develop a suitable mathematical tool for assessing the energy performance of the system and optimizing it. The outcomes show the reliability of the methodology and the performance of the low-cost evacuated solar thermal collector under different vacuum levels, providing insights into energy, economic, and environmental aspects. This work innovates by presenting a thorough analysis covering all solar thermal collector production phases, from conceptualization to optimization. The conclusions highlight the production of a reliable approach, and proof-of-concept results demonstrate how increasing the vacuum level enhances the thermal efficiency of a solar collector.

Modelling of Solar Thermal Electricity Plants in the POSYTYF Research Project for an Extensive Integration of Renewable Energy Sources

This article presents a simplified simulation model of a concentrated solar thermal power plant developed in the framework of the European research project POSYTYF (POwering SYstem flexibiliTY in the Future through RES). Increasing the share of Renewable Energy Sources (RES) in modern power grids is of critical importance for the transformation of the energy markets worldwide. However, the stability of the grid and the limited participation in ancillary services of RES limit their use, especially when high penetration is expected from them. A solution to overcome these issues is to increase the share of so-called dispatchable RES (hydropower, biomass, concentrating solar thermal power). The main objective of the POSYTYF project is to group several renewable and non-renewable energy sources into a Dynamic Virtual Power Plant (DVPP). The simplified simulation model of a parabolic-trough solar thermal power plant developed consists of sub-models for the solar field, thermal energy storage system and power block and it has been validated with real DNI profiles and production data of a commercial STE plant in Spain. The differences between the simulation and real data of daily net production for the days analysed are lower than 1%. Parts of this paper were published as journal article “Using time-windowed solar radiation profiles to assess the daily uncertainty of solar thermal electricity production forecasts”, Journal of Cleaner Production, Volume 379, Part 2, 2022. Mario Biencinto, Lourdes González, Loreto Valenzuela (https://doi.org/10.1016/j.jclepro.2022.134821).

Synergistic solar energy integration for enhanced biomass chemical looping hydrogen production: Thermodynamics and techno-economic analyses

The concept of solar-assisted biomass chemical looping hydrogen (H2) production (BCLHP), wherein solar energy is directly integrated into the thermochemical H2 production process, was proposed. The mechanism behind the increased H2 production due to solar assistance was elucidated. Subsequently, a system design was proposed based on this principle, accompanied by strategies for managing solar energy fluctuations during system operation. Thermodynamics and techno-economic analyses were then conducted. The results indicate that the key principle behind the increased H2 production in solar-assisted BCLHP lies in substituting solar energy for the direct oxidation of the oxygen carrier, enabling full utilization of the oxygen carrier for H2 production without the need to maintain thermal balance. The integrated system based on this principle achieves a high solar-to-H2 exergy efficiency, with a theoretical maximum exceeding 30%, outperforming the exergy efficiencies of photovoltaic (PV) and solar thermal H2 production methods, while increasing the molar ratio of H2 to CO2 from 1.31 to 1.74. The economic viability of solar-assisted BCLHP systems and systems combining PV-based H2 production with BCLHP depends on a comprehensive assessment of local PV panel costs, heliostat costs, H2 selling prices, and solar conditions. This research presents a novel approach to enhance solar-to-H2 efficiency.

Equivalent Breakeven Installed Cost

Technoeconomic analysis (TEA) is commonly used to determine economic viability of power-generating technologies, including concentrating solar power (CSP) and thermal (CST) production plants. Levelized cost of electricity (LCOE) and analogous measures provide an estimate of long-term costs for operating power plants over their designed lifetimes by accounting for revenues and costs in a time-discounted manner. While these measures are effective when assessing a technology’s total lifecycle costs and productivity under various designs, TEA of candidate incremental technology improvements from the lens of LCOE can be limited when required investment and LCOE impacts are small. In this work, we propose a novel metric for TEA of a plant component technology that recasts relative changes in levelized system costs into component-specific capital cost budgets. This measure, which we refer to as the equivalent breakeven installed cost, is the maximum budget for the technology component that leads to improved levelized costs. We illustrate the usefulness of this metric using the example of candidate heliostat improvements for a CSP tower plant. Here, the results suggest that a reduction in mirror washing costs yield a total plant O&M cost of $37/kWe-yr, which is a breakeven proposition if the average reflectance is reduced from 0.90 to 0.85 as a result of the cost savings.

Performance study of a thermochemical energy storage reactor embedded with a microchannel tube heat exchanger for water heating

Thermochemical energy storage (TCES) provides a promising solution to addressing the mismatch between solar thermal production and heating demands in buildings. However, existing air-based open TCES systems face practical challenges in integrating with central water heating systems and controlling the supply temperature. To overcome these limitations, a novel water-based TCES-HEX-HRU system is proposed in this study, which integrates a water-to-air microchannel tube heat exchanger (HEX) and an air-to-air heat recovery unit (HRU). A comprehensive evaluation of the TCES-HEX-HRU system is conducted numerically using a COMSOL model, including a comparative assessment for different TCES system configurations. The results demonstrate that the TCES-HEX-HRU system achieves an overall thermal efficiency of 82.35 %, marking a substantial 69 percentage points improvement over the TCES-HEX system. Although slightly lower than the typical air-based TCES system without HEX and HRU by 15.44 percentage points, the TCES-HEX-HRU system can be a practically promising and viable choice for applications in central heating systems. Numerical investigations indicate that the thermal performance of the system is influenced by the inlet conditions of airflow and waterflow. Moreover, increasing the number of water channels in the HEX of the TCES-HEX-HRU system enhances heat transfer but reduces the amount of heat released by TCES composite materials, resulting in a maximum overall thermal efficiency of 92.09 % with 35 channels and a peak outlet water temperature of 33.67 °C at with 30 channels. However, further increases in the number of channels lead to a decline in overall thermal efficiency and outlet water temperature. Changes in the width of water channels in the HEX have a minor impact on the highest outlet water temperature and overall thermal efficiency, while affecting the volume of the TCES composite materials.

Exploring a novel tubular-type modular reactor for solar-driven thermochemical energy storage

Thermochemical energy storage (TCES) has gained extensive attention as a potential solution to address the mismatch between solar thermal energy production and demand. In this study, a novel tubular-type modular TCES reactor is introduced. COMSOL modelling of the system is developed and experimentally validated using a laboratory-scale TCES system. Both types of reactors show similar temperature increases, intensifying with higher inlet relative humidity. Their maximum temperature lifts exceeding 26 °C at 90 % RH. Tubular designs offer better axial flexural strength and dispersion of TCES composite materials compared to plate structures. This property of tubular structures beneficial reducing bed thickness and pressure drop and enhancing equivalent thermal efficiency. Simulations show tubular-type modular reactors reduce pressure drop by 4–5 times compared to plate-type modular reactors, increasing equivalent thermal efficiency by nearly 7% points. Increasing the number of reactor beds and inner tube radius improves equivalent thermal efficiency due to reduced bed thickness and pressure drop. As the number of matrix rows and columns in the reactor bed increases from 2 to 10, bed thickness decreases from 0.058 m to 0.012 m, reducing pressure drop from 845.53 Pa to 38 Pa and increasing equivalent thermal efficiency from 78.82 % to 96.61 %.

A Review of Solar-Coupled Phase Change Materials in Buildings.

Buildings use a significant percentage of the total energy consumed worldwide. Striving for energy conservation within buildings is of prime concern for researchers. Hence, scientists are aggressively exploring new energy storage and supply methods to reduce exorbitantly fluctuating energy demands and increase the share of renewable energy in building energy consumption. Solar systems that incorporate phase change materials (PCMs) for thermal storage have significant potential to serve in this context. These systems are not yet able to endure the significant energy demands, but they are being continually improved. The aim of this paper is to explore the existing solar PCM systems that are being studied or that are installed for use in indoor heating/cooling. As per the outcome of this systematic review, it has been observed that when coupled with solar thermal energy, the configuration of PCMs can either use passive or active techniques. Passive techniques are usually less efficient and more costly to implement in a building structure, resulting in active heat exchangers being widely implemented with better technical and economic results. At the same time, it has been observed that for most domestic buildings, organic PCMs with phase change temperatures of up to 42 °C and thermal conductivities of up to 0.56 W/m.K are most suitable for integration in solar thermal energy production. Hybrid systems are also commonly used for larger commercial buildings, in which the solar PCM system (SPCMS) provides a fraction of the total load. Additionally, the Stefan number is the most common technical parameter that is used to assess this performance, along with the effective thermal conductivity of the PCM after using enhancement techniques. The key economic indicator is annual savings per year, with most SPCMSs having a payback period of between 6 to 30 years. This review provides designers and researchers with key insights in terms of formulating a basis in the domain of coupling PCMs with solar thermal energy, especially within non-industrial buildings.

Results from a survey of life cycle assessment-aligned socioenvironmental priorities in US and Australian communities hosting oil, natural gas, coal, and solar thermal energy production

Large energy infrastructure is often socially and environmentally disruptive, even as it provides services that people have come to depend on. Residents of areas affected by energy development often note both negative and positive impacts. This reflects the multicategory nature of socioenvironmental outcomes and emphasizes the importance of careful, community-oriented decision making about major infrastructural transitions for processes like decarbonization. Quantitative tools like life cycle assessment (LCA) seek to collect and report comprehensive impact data, but even when successful, their value for decision support is limited by a lack of mechanisms to systematically engage with values-driven tradeoffs across noncommensurable categories. Sensitivity analyses designed to help decision makers and interested parties make sense of data are common in LCA and similar tools, but values are rarely explicitly addressed. This lack of attention to values—arguably the most meaningful set of decision inputs in such tools—can lead to overreliance on single issue (e.g. climate change impact) or proxy (e.g. monetized cost) outputs that reduce the value of holistic evaluations. This research presents results from preregistered hypotheses for a survey of residents of energy-producing communities in the United States (US) and Australia, with the goal of with the goal of uncovering energy transition-relevant priorities by collecting empirical, quantitative data on people’s priorities for outcomes aligned with LCA. The survey was designed to identify diverse value systems, with the goal of making it easier for users to identify and consider value conflicts, potentially highlighting needs for further data collection, system redesign, or additional engagement. Notably, results reveal remarkably consistent priority patterns across communities and subgroups, suggesting that the common LCA practice of equal prioritization might be masking decision-relevant information. Although this effort was designed specifically to support research on energy transitions, future work could easily be extended more broadly.

Thermally integrated pumped thermal energy storage for multi-energy districts: Integrated modelling, assessment and comparison with batteries

Integrating large shares of renewables into energy systems requires energy storage technologies able to efficiently dispatch and convert different energy vectors at a local level (multi-energy storage). The paper investigates the performance of multi-energy storage based on the Thermally Integrated Pumped Energy Storage (TIPTES) technology. TIPTES stores electric energy as thermal exergy at temperatures higher or lower than the environment but also exploits additional low-temperature thermal sources, commonly from renewables or waste heat recovery, to boost the charging or discharging phases. In the paper, two different multi-energy TIPTES (mTIPTES) systems are modelled and simulated in three residential case studies where electric and thermal vectors are present, together with solar electric and thermal production. The mTIPTES annual operation is optimised via mixed-integer linear programming, linearising the operating characteristics of mTIPTES components (heat pumps, chillers, organic Rankine cycles and thermal energy storage). Finally, mTIPTES was compared against lithium-ion batteries, a benchmark for residential energy storage. The comparison is based on thermodynamic and economic figures, with the mTIPTES capital cost estimated based on cost models from the literature. The results showed that mTIPTES perform better than the battery from a thermodynamic point of view, reducing the curtailment of renewables. In economic terms, for large penetrations of renewables, this translated into an operating cost reduction of up to around 15 % compared to a system without storage, which is five percentage points lower than what was achieved with batteries. Similar results were found for CO2 emissions and primary energy consumption, for which reductions larger than batteries and up to 20 %, compared to a case without storage, can be found. Despite the operating cost reduction, the mTIPTES total annualised cost (including capital costs) is around double compared to BES, and, for the investigated configurations, mTIPTES could not achieve financial feasibility.

Editorial: Forecasting solar radiation, photovoltaic power and thermal energy production applications

Editorial: Forecasting solar radiation, photovoltaic power and thermal energy production applications

Low emissivity thin film coating to enhance the thermal conversion efficiency of selective solar absorber in high vacuum flat plate collectors

Industrial heat and cooling applications are an essential fraction of the overall energy demand, mainly produced by fossil fuels. Solar thermal energy production can satisfy such a need by adopting the High Vacuum Flat Plate Collectors (HVFPCs) and increasing their efficiency. The absorptance and emittance of Selective Solar Absorbers (SSAs) determine the thermal efficiency of HVFPCs. Being the absorptance already maximized, the thermal emittance of the absorber should be minimized to increase further the operating temperature of the collector and its efficiency. This research aims to reduce the thermal emittance of commercially available Selective Solar Absorber by depositing a thin silver film on the aluminium substrate. So, in this work, the thermal stability of a silver coating has been investigated, and a diffusion barrier layer has been adopted to stabilize the coating performance up to 360 °C. The low-emissive layer of Ag and a diffusion barrier of CrOx guarantees a decrease of 11% in thermal emittance at 200 °C of commercially available SSA deposited on aluminium. Further emittance reduction can be obtained by depositing a thin Ag film on both sides of the aluminium substrate before the SSA deposition, proving to be a promising way to enhance the efficiency of HVFPCs.

Using time-windowed solar radiation profiles to assess the daily uncertainty of solar thermal electricity production forecasts

This work is aimed at analysing the impact of real-time weather forecasting on the simulation of solar thermal electricity plants. A novel method is presented that allows generating random solar radiation profiles to assess the uncertainty of forecasting solar thermal electricity production. Rather than a weather prediction model, this work proposes a fast and simple method for the generation of synthetic solar radiation data that focuses on the dynamics relevant for electricity production, not requiring long historical data series or meteorological details. Variable window lengths are used to reproduce the growing uncertainty of forecasts with longer time horizons. In addition, a simplified model of solar thermal power plant is described and implemented in MATLAB®. Both the solar profile generator and the plant model are used to simulate massive cases for four representative days with eight forecasting hours based on electricity markets. The results show uncertainty values for day-ahead predictions from 15% to 60% in cloudy days and from 2% to 40% in sunny days, with decreasing ranges for intra-day forecasts.

Assessment of the off-design performance of a solar thermally-integrated pumped-thermal energy storage

Long-duration storage (i.e., 6 + h) could foster the power sector transitions towards renewable energy sources. Pumped thermal energy Storage (PTES) recently gained much attention. Thermally-Integrated PTES (TI-PTES) exploiting additional thermal energy sources to boost electric roundtrip efficiency are promising and can exploit low-temperature heat sources, including solar thermal energy. Since the solar resource availability substantially varies along the year, assessing the yearly system performance is mandatory to estimate the solar TI-PTES practical potential. The paper studies a solar TI-PTES plant based on low-concentration Solar Thermal Collectors (STC), a High-Temperature Heat Pump (HTHP), and an Organic Rankine Cycle (ORC). In the paper, the HTHP and ORC off-design performance are mapped for a set of representative conditions through an off-design model. Such maps are used to simulate the system operation when coupled with a solar thermal energy production profile for some periods considered representative of the whole year. Results show that the average round trip efficiency is always between 0.85 and 0.87, and the system can operate in various conditions, even in the cold seasons. While the system performance is almost constant over the year, the operating charging and discharging hours and the stored energy are more than doubled from January to July.

Solar–Thermal Production of Graphitic Carbon and Hydrogen via Methane Decomposition

Contemporary carbon and hydrogen production processes release significant CO2 emissions with negative consequences for the Earth’s climate. Here we report a process in which concentrated irradiation from a simulated solar source converts methane to high-value graphitic carbon and hydrogen gas. Methane flows within a photothermal reactor through pores of a thin substrate, with the process reaching steady-state conditions from room temperature within the first minute of irradiation by several thousand suns. Methane decomposes primarily into hydrogen while depositing highly graphitic carbon that grows conformally over ligaments in the substrate. The localized solar heating serves to capture solid carbon into a readily extractable form while maintaining active deposition site density with persistent catalytic activity until the ligaments coalesce to block the flow. Even with a large flow area through regions of lower irradiation and temperature, methane conversions and hydrogen yields of approximately 70% are achieved, and 58% of the inlet carbon is fully captured in graphitic form.

Techno‐economic analysis of a hybrid solar‐geothermal power plant integrated with a desalination system

This paper proposes the use of a hybrid 5 MW power generation system combining concentrated solar thermal and solar photovoltaic technology where the efficiency of the power block is increased by taking advantage of hot water from a low-temperature geothermal source. Aiming at a case study for Winton in Queensland the pertinent meteorological data are used for our simulations. In addition, the paper analyzes the feasibility of including a thermal desalination technology that uses the waste heat from the power block for producing clean water from wastewater. Our design replaces the traditional dry cooling system with a water-cooled heat exchanger to remove the waste heat from the power block. Finally, this work explores the ratio of concentrated solar thermal and photovoltaic electricity production that optimizes the levelized cost of electricity and water production. the results indicate that the incorporation of the desalination system does not produce a significant increase in this value, and the optimal ratio of electricity production is obtained when the photovoltaic system contributes to 27.5% of the total electricity generation. Our water production cost can be as low as 40 ₵/m3 while for the combined system our minimum levelized cost of electricity figures out at 12.4 ₵/kWh to generate the base load with thermal storage.

Study, simulation and modulation of solar thermal domestic hot water production systems

Study, simulation and modulation of solar thermal domestic hot water production systems

Thermal production and heat cost analysis of the potential of solar concentrators for industrial process applications: A case study in six sites in Morocco

Industrial Process Heat (IPH) represents a promising sector of application for solar concentration technologies – the Linear Fresnel Reflectors (LFR) as an alternative to the conventional source of thermal energy. Morocco is endowed with an abundant solar resource as other countries in the MENA region, with high level of DNI available over the year especially in the southeast, mid-south, and the south (Moroccan Sahara Desert). The main objective of this work is to assess the potential of solar thermal production of industrial process heat considering six different sites in Morocco. The evaluation has been done with respect to the Levelized Cost of Heat (LCoH), representing the whole production cost structure. This study includes as well a comparison of the same application in Stellenbosch (South Africa) and Andasol (Spain). The results show that the annual thermal production is 7.2 GWh-th/year in Zagora, 6.4 GWh-th/year in Missour, and around 6.3 GWh-th/year in Ben-Guerir and Erfoud. As expected, the Moroccan sites show, in general, higher thermal energy production with +1.4 GWh-th/year in Zagora compared to the Andasol site, and +2.9 GWh-th/year compared to Stellenbosch. The cheapest LCoH has been found to be 2.47 c$/kWh-th in Zagora, whereas it was 4.02 c$/kWh-th in Stellenbosch and 3.04 c$/kWh-th in Andasol, with a difference of +62.75% and +23.1% respectively.

Annual Evaluation of a Model Predictive Controller in an Integrated Thermal-Electrical Renewable Energy System Using Clustering Technique

Abstract Whitebox model in a model predictive controller (MPC) for energy systems, though does help in developing an accurate system model, requires a long time for optimization. In this article, an adaptation of the clustering technique used in hardware-in-the-loop testbench is proposed for evaluation of the MPC on an annual scale with selected six representative days in a year for that particular system and location. Initially, the various input parameters for clustering (algorithm, distance metric, and datapoint input dimensions) are studied for the selected thermal-electrical integrated renewable energy system (with solar thermal collectors, auxiliary gas boiler, stratified thermal storage, micro fuel cell combined heat and power (FC-CHP), photovoltaic system, a lithium-ion battery) for a Sonnenhaus standard single-family residential building. Finally, the proposed methodology is used to compare the annual derived energy values and key performance indicators (KPIs) for an MPC implementation with a status quo controller as a reference. Also, extreme exemplary weather days are investigated as the selected representative days were only average days in each season. Despite the conflict of using the FC-CHP on cold sunny days, instead of utilizing the battery and increased gas boiler energy input, a 9% increase in decentral system fraction is reported. Via the use of MPC instead of status quo controllers, the results indicate −18% space heating (SH) demand; +30% solar thermal energy production; −29% gas boiler energy supply; −52% power-to-heat thermal energy supply; −52% electrical fuel cell production; +240 kWh battery utilization; and −52% reduced grid import at the expense of 1.2% of the electrical load demand as grid import.

Design and thermoeconomic analysis of a solar parabolic trough – ORC – Biomass cooling plant for a commercial center

Hybrid renewable polygeneration systems are regarded as key solutions for the sustainable energy supply of buildings. While solar heating and cooling comprises a wide range of technologies, there has been limited research on the combined production of power and cooling only, with little or no heat demand. This study designs and analyzes a hybrid solar–biomass ORC-based polygeneration system from energy, economic, and environmental viewpoints. The polygeneration system is designed to cover the electricity and cooling demands of a commercial center located in Zaragoza, Spain. A parabolic trough collector field coupled with thermal energy storage, and an auxiliary biomass boiler supply heat to an Organic Rankine Cycle (ORC), which generates electricity to cover electrical demands and to produce cooling in mechanical chillers. The biomass boiler supports the solar thermal production to ensure a stable and reliable heat supply to the ORC. The system is connected to the electric grid, so that electricity purchases and sales are possible. The equipment sizing is performed with the goal of achieving a high renewable fraction in the total electricity consumed by the commercial center. The analysis of the proposed plant includes the hourly operation throughout the year, complemented by an economic assessment, considering investment and operation costs, and an estimate of the environmental benefits of the plant. Also, a thermoeconomic analysis is developed to determine the cost formation process of the internal flows and final products of the plant. The unit cost of each flow is broken down into investment and operation cost components. Sensitivity analyses of the investment cost, interest rate, biomass price, and electricity selling price discount are made. The results show that, in economic terms, the system is not presently viable, since the cost of the electricity produced (279.07 €/MWh) is much higher than the electricity purchase price (126.70 €/MWh). In environmental terms, the system is capable of displacing 96.1% of the CO2 emissions and 85.6% of non-renewable primary energy consumption relative to a conventional system consuming grid electricity only.