Solar Thermal Field Research Articles

Improving solar HVAC performance by incorporating sutterby SiO2–Cu/C3H8O2 hybrid nanofluid flow via a collocation based Gegenbauer wavelets technique: Effects of electromagnetic control and Smoluchowksi's temperature slippage

AbstractThe utilization of solar energy in heating, ventilation, and air conditioning (HVAC) systems has gained significant attention as a sustainable and environmentally friendly solution to meet the increasing energy demands. Therefore, this research work introduces a novel engineering study that explores solar‐HVAC systems. However, the study utilized hybrid nanofluids (HNFs) consisting of silicon dioxide and copper nanoparticles, with propylene glycol serving as the base fluid. Furthermore, this exploration features a magnetohydrodynamics (MHD) driven rotating flow with activation energy to enhance the heat transfer performance of solar‐HVAC systems. To increase the model novelty, 3D mathematical models were developed to characterize boundary conditions, which include the speed slippery and Smoluchowski temperature slippage. The partial differential equations in the model are transformed into ordinary differential equations (ODEs) through the use of similarity transformations. The Wavelets and Gegenbauer wavelets method in Mathematica was utilized to solve ODEs and investigate physical attributes such as plate friction, Nusselt number, Sherwood number, and mass flux. The findings show that the solar thermal radiation and magnetic field improve the thermal transfer efficiency of solar‐HVAC. Therefore, the findings of the research have practical applications in solar energy for HVAC systems and can contribute to technological improvements in the manufacturing industry.

Optimal model-free adaptive control based on reinforcement Q-Learning for solar thermal collector fields

Optimal model-free adaptive control based on reinforcement Q-Learning for solar thermal collector fields

A novel bio-waste-driven multigeneration cycle integrated with a solar thermal field and atmospheric water harvesting cycle: An effort to mitigate the environmental impacts of the wastewater treatment plants

Poor management in the municipal waste disposal is a serious crisis for the health of the ecosystem and society. The implementation of the waste-to-energy projects can simultaneously recover the available energy in waste and significantly mitigate the environmental impacts of releasing waste into the environment. In this article, a novel bio-waste-driven multigeneration cycle (BW-MGC) integrated with a solar thermal field for the production of various valuable products from sewage sludge is introduced and evaluated (from thermodynamic, environmental and economic points of view). Herein, the biogas and syngas are obtained through the anaerobic digestion and gasification processes, respectively. Besides that, hydrogen energy and water production cycles are based on the water-gas shift reaction and atmospheric water harvesting cycle (AWHC) units, respectively. In the offered project, the heating capacity and a part of the electricity are obtained through the waste heat recovery system. The offered project provides a new process with a novel structure and configuration to produce useful products. Moreover, it can jointly address the simultaneous issues of energy, water, and environment. The offered plant can produce 18.1 MW of electricity, 18.72 l/h of water, and 0.9 kg/s of hydrogen fuel. The energy efficiency of the system in such design conditions was calculated as 36.12%, while the exergy efficiency was 40.9%. Further, the exergy sustainability factor, total products unit cost, and levelized total CO2 emissions are calculated as 0.5281, 0.05168 USD/kWh, and 0.2124 kg/kWh, respectively.

Modeling and Performance Evaluation of Hybrid Solar Cooling Systems Driven by Photovoltaic and Solar Thermal Collectors—Case Study: Greenhouses of Andalusia

Sustainable greenhouses have gained relevance in recent years due to their potential to reduce the carbon footprint of the agricultural sector by being integrated with renewable systems, contributing to the decarbonization of energy. Although solar technologies tend to be more accessible to cover the system’s energy demands, greenhouses are subject to installation area restrictions, limiting their energy potential. This research evaluates the energy advantages of hybridizing solar thermal collector fields with photovoltaic module fields to cover a greenhouse’s cooling and heating demands. For this purpose, the solar thermal field and the photovoltaic solar system were simulated with TRNSYS and MATLAB, respectively, while a method was developed to simulate the performance of a single-effect absorption chiller that was validated using the temperature measurements of a chiller in operation. The results show that the general method maintains differences between measurements and simulation smaller than 5% with set temperatures between 5.5 and 12 degrees Celsius. The hybrid system, with an air-to-water chiller as the main machine and absorption chiller, reached a solar fraction of 0.85 and a fractional energy saving of 83%. This represents a 27% reduction in area concerning an individual solar thermal system. This research highlights that the solar hybrid configuration reduces fossil energy consumption by improving the global efficiency of energy conversion, thereby reducing the area of the solar field.

Solar-assisted district heating networks: Development and experimental validation of a novel simulation tool for the energy optimization

Due to the growing interest in 4th and 5th generation district heating systems, characterized by lower working fluid temperatures compared to the past, poligenerative solar-assisted networks are experiencing increasing attention from the research community. In this framework, the adoption of large solar-based thermal systems will become more common for such applications. Therefore, optimising the design and operation of each solar field servicing a specific network will be crucial to improving its overall performance. In this context, the objective of the current research is to develop a method to maximise the performance of solar-assisted poligenerative district heating networks by optimising each associated solar system separately. To this end, a novel dynamic simulation tool for solar thermal field design and optimization has been developed and experimentally calibrated in the Simulink/Simscape environment. The tool is capable of investigating innovative control logics, and accurately assessing both the thermal and hydraulic behaviour of the systems. The latter is one of its novelty, as ignoring the hydronic behaviour of the system can lead to the adoption of flawed design or control logic. The resulting tool will enable accurate optimization of the design and management of each solar field servicing a given district heating network, thereby improving the efficiency of the system as a whole. In order to demonstrate the viability of the proposed method and the capabilities of the developed simulation tool, a proof-of-concept analysis is conducted on an existing solar thermal field serving the Geneva district heating network. Diverse control logics (including Rule-Based and Model Predictive Control) are evaluated for the selected case study. The performed analysis demonstrates that the proposed method has the potential to accomplish significant primary energy reductions (up to 10.3%) and CO2 emissions avoidance (up to 10.9 tCO2/year).

9E analysis of a flat plate solar collector system implementation: A new approach based on digital twin model coupled with global sensitivity analysis and multi-objective optimization

Flat plate solar collectors are technology with the most solar thermal energy field applications, and different studies based on artificial intelligence have been used to model these systems. This research study presents a 9E analysis based on a digital twin model coupled with global sensitivity analysis and multi-objective optimization of a solar system integrated with an array of flat plate solar collectors to satisfy residential hot water demand that represents a case study with different applications. A model based on artificial neural networks was trained, and a global sensitivity analysis using the Sobol method and a multi-objective optimization study using a genetic algorithm were also implemented. The main outcomes revealed that the digital twin model presented a high correlation above 0.99, and the 9E analysis reported a maximum value of 25.18% for thermal efficiency and 0.266% for exergetic efficiency. Also, a value of 1798.5 kgCO2/year was obtained for the amount of CO2 mitigated, $1342.9 USD for net present value, $0.0104 USD/kWh for levelized cost of energy, and 92.62, 0.519 kgCO2/year, $3.43, $1.34, and $0.00752 USD/year for energoenvironmental, exergoenvironmental, enviroeconomic energoenviroeconomic, and exergoenviroeconomic indicators, respectively. The methodology and the 9E analysis results provide a comprehensive approach that determines the optimal choice by analyzing the system's viability with different assessments and goes beyond the conventional analyses currently presented in the literature as it shows an untapped market potential for the best decision-making.

Numerical study of thermal enhancement in ZnO-SAE50 nanolubricant over a spherical magnetized surface influenced by Newtonian heating and thermal radiation

ApplicationsThermal conductivity of nanomaterials potentially contributes in heat transport applications. Due to heat absorbing and cooling characteristics, nanoparticles broadly use in environmental engineering, solar plates, computational chemistry, chemical engineering and thermal engineering etc. Thus, it is substantial to identify the nanomaterials with effective heat generating or absorbing properties which have variety of applications in mechanical engineering. Purposeand Methodology: The main focus of this study are to introduce a nanofluid model using ZnO-SAE50 nanolubricant under additional effects of solar thermal radiations, magnetic field and resistive heating. This parametric study will help to maintain the temperature under various ranges of physical parameters which has broad applications in many engineering disciplines. The achieved model analyzed through numerical approach and comprehensive analysis provided in the view of furnished results. Major findingsInvestigation of the results provided that the heat transport is maximize using ZnO-SAE50 nanolubricant while; conventional SAE50 is not good to achieve desired heat transfer rate. Solar thermal radiations and dissipation effects positively act on the temperature role of ZnO-SAE50.

Solar Thermal Treatment: Case Study for Cashew Juice Pasteurization

Energy and food are very intertwined and important in human life. Cashew juice is a very abundant product in southern Senegal. Unfortunately, due to lack of processing and conservation, this product cannot last 24 hours without being fermented. The aim of this study is to study the heat treatment processes of agri-food products, particularly the pasteurization of cashew fruit juices. Pasteurization often uses heat from fossil fuels. In this heat treatment process of cashew juice, we are interested in the energy source. Thus thermal solar energy is used in this heat treatment. A solar thermal collector with an area of 17.9 m² and a hot water storage tank with a capacity of 0.1 m³ are used. With the pasteurization model used, the juice circulates in a copper coil immersed in hot water coming from the solar thermal field or the hot water storage tank. A numerical simulation program has been developed on Ansys Fluent 2020 R1 to study the evolution of the temperature of the juice from the inlet to the outlet of the coil. The results obtained give outlet temperatures varying from 70 to 80°C depending on the speed of circulation of the juice. We can also achieve outlet temperatures of 100°C. This means that our system can operate in sterilizer mode.

A Design Tool for Solar Thermal Remediation Using Borehole Heat Exchangers.

Low temperature heating of the subsurface (increases of about 5-20 °C) can substantially increase rates of biotic and abiotic destruction of dissolved contaminants such as chlorinated solvents. Low-temperature heating can be sustainably and cost-effectively achieved using solar thermal collectors coupled with closed-loop borehole heat exchangers. This technology has been implemented at several sites in the United States and abroad with favorable results. The design of a solar thermal remediation system requires a quantitative understanding of heat transfer from the array of borehole heat exchangers. We present an easy-to-use design tool that is based on a transient three-dimensional analytical heat transfer solution and is programmed in Visual Basic in Excel. This tool can be used to quickly explore the effect of design variables on the forecast temperature field. Typical design variables would include the site-specific average and monthly solar insolation data, solar collector configuration, borehole heat exchanger geometry and spacing, and the effects of environmental variables such as groundwater velocity, background subsurface temperature, and thermal conductivity. The design tool has been verified by comparisons with the TOUGH2 multiphase heat transfer code for a three-dimensional multi-heater system with seasonally variable thermal power rates. The code has been validated by comparisons to observed temperatures measured at a solar thermal field remediation application at a site in Colorado.

Life Cycle Assessment for a solar cooling plant

This work aims to evaluate the environmental loads of a hypothetical solar cooling plant making a Life Cycle Assessment (LCA) analysis. In this study, an LCA of a solar cooling plant for a cold room installed in a fruit and vegetable company is performed. The plant is equipped with an absorption chiller of 150 kW and an auxiliary boiler of 50 kW. The hot water storage tank is 5000 l as the cold water one. The solar thermal field is 250 m2 using evacuated tube collectors. The functional unit of the study is the entire plant. The entire life cycle is evaluated assuming that the lifetime is equal to 20 years. The Ecoinvent v3.8 database is used to collect data and SimaPro v.9 software is used to perform the analysis. IPCC 2013 and ReCiPe 2016 are chosen as impact assessment methods and their results are evaluated. The results show that the total CO2 equivalent emissions that are given by the Global Warming Potential evaluation using IPCC 2013 method increase when solar fraction decrease. Therefore, reducing gas consumption and, also, improving plant solar fraction is the most important way to reduce the total emission. However, the solar plant emissions are related to the installation, maintenance and use phases.

A brief review of liquid heat transfer materials used in concentrated solar power systems and thermal energy storage devices of concentrated solar power systems

AbstractSolar power generation is an effective approach to promote the achievement of carbon neutrality. Heat transfer materials (HTMs) are important for concentrated solar power (CSP) systems and their accessary thermal energy storage (TES) devices. The performances of HTMs can influence the operation behaviors of CSP systems and TES devices. On the whole, the HTMs can be divided into three categories according to their physical states, which are the liquid, gaseous, and solid HTMs, respectively. This article presents a brief review of research works on liquid HTMs used in CSP systems and TES devices of CSP systems, mainly including different kinds of molten salts, heat transfer oils, nanofluids, liquid metals, and water. Some typical practical applications, experimental and simulation studies on different kinds of liquid HTMs used in CSP and TES systems are introduced, and the advantages, disadvantages, and further research and development work prospects of different kinds of HTMs are briefly summarized. This article aims to providing a reference for researchers in solar thermal power field.

Review on Nano-Fluids Applications and Heat Transfer Enhancement Techniques in Different Enclosures

Nano-fluid applications span such a broad range of topics in the practical field that they demand their own review articles. In this review paper, the use of magnetic fields, porous media, and Nano-fluids in different heat transfer applications is discussed mainly in the solar thermal field. It has been proven that the employment of these techniques provides significant enhancement results for convective flows especially when they are combined, also the mathematical equations used to model this type of flow are summarized. In addition, different studies reported that the geometrical parameters of the enclosures can also effect the flow. In this context, recently scholars maintained many investigations on complex shaped cavities and their impact on heat transfer. These studies showed promising results for the use of this type of geometries especially for the trapezoidal ones. As reviewed in this paper, trapezoidal geometries and their properties strongly effect the convective flow in a great way leading to considerable enhancement. Overall, this review aims to present an insightful vision on different heat transfer improvement techniques and values the use of these methods in trapezoidal geometries for solar heat transfer applications.

Optimisation strategies for solar assisted heat pumps coupled to traditional thermal fields

The advantages of the solar assisted heat pumps are well-known but their diffusion on the market is still very limited. One of the main causes is associated to their complexity and almost always working under transient regime which can lead to frequent blocks especially when a low level of control and automatization is present. From the point of view of conceptual design, solar assisted heat pumps tend to be more subjected to blocks due to their serial asset. The present work illustrates the case study of the solar assisted heat pump pilot plant at Palacus, Genoa, equipped with a heat pump bypass which can directly connect the solar thermal field to either the domestic hot water or the space heating systems when the temperature in the circuit exceeds a fixed set point. This configuration allows therefore the use of the solar field either independently from the heat pump or interfaced with it, according to the external conditions. A numerical model within TRNSYS environment has been developed basing on the information collected on the pilot plant by the data acquisition system. A simulation of the working of the pilot plant along a typical year has been performed, evaluating its increased performance and optimisation thanks to the bypass.

A Forward Feedback Control Scheme for a Solar Thermochemical Moving Bed Counter-Current Flow Reactor

Abstract Pelletized thermochemical energy storage media has a potential for long-duration energy storage. Production of solid-state energy storage media can be done within a cavity chemical reactor that captures concentrated solar radiation from a solar thermal field. The temperature stability of a solar reactor is directly influenced by the solar flux intercepted. This paper presents a low-order physical model to simulate the dynamic response of temperature inside a tubular plug-flow reactor prototype. Solid granular particles are fed to the reactor from the top whereas a counter-current flowing gas enters the reactor from the bottom. An in-house code was developed to model transient heat transfer of the reactor wall, gas, and moving particles. The model was preliminarily validated with packed beds for different temperature ranges and two gas flowrates. Dynamic response of the reactor temperature is simulated for different input power and gas/particle flowrates. The results show that the system response can be controlled efficiently by utilizing input power (solar flux) as a control parameter. A conventional proportional integral (PI) controller is designed to control the temperature inside the reactor and to maintain it during the solar flux intermittency. The controller parameters are tuned using the Ziegler–Nichols method to ensure optimal system response. The results show that the feedback control model is successful in tracking different reference reactor temperatures within a reasonable settling time of 30 min and eliminated overshoot. This study can be extended to include a hybrid reactor with a multi-input, multi-output variable system.

Heat transfer enhancement for U-pipe evacuated tube solar absorber by high-emissivity coating on metal fin

In the solar thermal field, the U-pipe evacuated tube collector has been widely used to provide hot water for domestic usage and space heating, or integrated with concentrating reflector to deliver thermal power in higher temperature range. Enhancing heat transfer process inside the U-pipe evacuated tube has significant effect on improving the overall thermal efficiency of the collector. However, the current heat transfer enhancement methods require either structure modification or material property change, and are therefore difficult to be promoted for commercial use. Herein, we proposed an easy and feasible method of depositing a high-emissivity coating on a metal fin to enhance the interior heat transfer. The effect of applying this method on the U-pipe evacuated tube with and without compound parabolic concentrator integration was investigated by numerical simulation. We found that this method exerts elevating improvement effect with an increasing operating temperature of the collector. The proposed method yields a maximum improvement of 2.7% for a single U-pipe evacuated tube operating up to 150 °C. Higher optimization effect was achieved in the case of compound parabolic concentrator integration. By employing this method, we found an 8.4% performance improvement when the tube is combined with a concentrator with concentration ratio of 6.0 at an operation temperature of 200 °C. At the background that the structure of the U-pipe has been mature and commercialized for a long time, the proposed method with easy-feasibility and low cost is expected to have potential for implementation.

Performance of Solar-driven Ejector Refrigeration System (SERS) as pre-cooling system for air handling units in warm climates

Europe is encouraging new buildings to minimize their primary energy dependence to be considered, from 2021, Nearly Zero Energy Buildings (NZEB). In this regard, solar thermal energy is being extensively used as a renewable source to produce Domestic Hot Water (DHW). However, solar thermal energy fields may be oversized during the warmest season of the year, rejecting the waste heat to the ambient while increasing the air conditioning demand. The Solar-driven Ejector Refrigeration System (SERS) may be a solution for solar cooling. Nevertheless, the SERS performance is constrained when low to medium temperature solar thermal collectors, commonly installed for DHW production, are used in warm climates. Consequently, this paper reformulates the SERS application as a novel fresh air pre-cooling system for air handling units. Thereby, greater evaporating temperatures that enable the SERS adoption in NZEB are explored. In doing so, the seasonal performance under severe operating conditions is analyzed considering the two-phase flow ejector geometry, as well as refrigerants with low global warming potential. Main results demonstrate a maximum seasonal COP of 0.37 by using R717. Moreover, an average cooling capacity of 28.3 kW could be produced per kW of electricity if an optimized multi-ejector solution with R600 is adopted.

Demand-Side Optimal Sizing of a Solar Energy–Biomass Hybrid System for Isolated Greenhouse Environments: Methodology and Application Example

The water–energy–food nexus has captured the attention of many researchers and policy makers for the potential synergies between those sectors, including the development of self-sustainable solutions for agriculture systems. This paper poses a novel design approach aimed at balancing the trade-off between the computational burden and accuracy of the results. The method is based on the combination of static energy hub models of the system components and rule-based control to simulate the operational costs over a one-year period as well as a global optimization algorithm that provides, from those results, a design that maximizes the solar energy contribution. The presented real-world case study is based on an isolated greenhouse, whose water needs are met due to a desalination facility, both acting as heat consumers, as well as a solar thermal field and a biomass boiler that cover the demand. Considering the Almerian climate and 1 ha of tomato crops with two growing seasons, the optimal design parameters were determined to be (with a solar fraction of 16% and a biomass fraction of 84%): 266 m2 for the incident area of the solar field, 425 kWh for the thermal storage system, and 4234 kW for the biomass-generated power. The Levelized Cost of Heat (LCOH) values obtained for the solar field and biomass boiler were 0.035 and 0.078 €/kWh, respectively, and the discounted payback period also confirmed the profitability of the plant for fuel prices over 0.05 €/kWh. Thus, the proposed algorithm is useful as an innovative decision-making tool for farmers, for whom the burden of transitioning to sustainable farming systems might increase in the near future.

Solar Field Output Temperature Optimization Using a MILP Algorithm and a 0D Model in the Case of a Hybrid Concentrated Solar Thermal Power Plant for SHIP Applications

Using solar power for industrial process heat is an increasing trend to fight against climate change thanks to renewable heat. Process heat demand and solar flux can both present intermittency issues in industrial systems, therefore solar systems with storage introduce a degree of freedom on which optimization, on a mathematical basis, can be performed. As the efficiency of solar thermal receivers varies as a function of temperature and solar flux, it seems natural to consider an optimization on the operating temperature of the solar field. In this paper, a Mixed Integer Linear Programming (MILP) algorithm is developed to optimize the operating temperature in a system consisting of a concentrated solar thermal field with storage, hybridized with a boiler. The MILP algorithm optimizes the control trajectory on a time horizon of 48 h in order to minimize boiler use. Objective function corresponds to the boiler use, for completion of the heat from the solar field, whereas the linear constraints are a simplified representation of the system. The solar field mass flow rate is the optimization variable which is directly linked to the outlet temperature of the solar field. The control trajectory consists of the solar field mass flow rate and outlet temperature, along with the auxiliary mass flow rate going directly to the boiler. The control trajectory is then injected in a 0D model of the plant which performs more detailed calculations. For the purpose of the study, a Linear Fresnel system is investigated, with generic heat demand curves and constant temperature demand. The value of the developed algorithm is compared with two other control approaches: one operating at the nominal solar field output temperature, and the other one operating at the actual demand mass flow rate. Finally, a case study and a sensitivity analysis are presented. The MILP’s control shows to be more performant, up to a relative increase of the annual solar fraction of 4% at 350 °C process temperature. Novelty of this work resides in the MILP optimization of temperature levels presenting high non-linearities, applied to a solar thermal system with storage for process heat applications.

Experimental operation of a solar‐driven climate system with thermal energy storages using mixed‐integer nonlinear model predictive control

AbstractThis work presents the results of experimental operation of a solar‐driven climate system using mixed‐integer nonlinear model predictive control (MPC). The system is installed in a university building and consists of two solar thermal collector fields, an adsorption cooling machine with different operation modes, a stratified hot water storage with multiple inlets and outlets as well as a cold water storage. The system and the applied modeling approach is described and a parallelized algorithm for mixed‐integer nonlinear MPC and a corresponding implementation for the system are presented. Finally, we show and discuss the results of experimental operation of the system and highlight the advantages of the mixed‐integer nonlinear MPC application.

Analysis of Chemically Reactive Hydromagnetic Maxwell Fluid Conveying Tiny Particles Due to Navier Partial Slip

The analysis of nanofluids in the solar thermal system is very fascinating owing to its important engineering applications (i.e., solar collectors). Aside from these the non-Newtonian boundary layer fluid flow has experienced considerable attention due to uprising engineering applications in the solar thermal field. This work investigates the analysis of chemically reactive hydromagnetic Maxwell fluid conveying tiny particles due to Navier partial slip. The governing equations that model the transport phenomena were transformed using suitable similarity variables. The boundary value problem of the corresponding coupled nonlinear ordinary differential equations was solved numerically using the shooting technique together with the fourth-order Runge-Kutta integration scheme and in-built bvp4c package of MATLAB. The effects of various controlling parameters on velocity, temperature, and concentration distributions were presented graphically and studied theoretically. Furthermore, the study reveals that the Navier slip parameter (δ) increases as the velocity distribution decreases, while it enhances both the temperature and concentration distributions, increase in the radiation parameter (Nr) enhances the temperature distribution, and the chemical reaction (γ) increment leads to decrease in concentration distribution.