Solar Collector Field Research Articles

Thermal performance attenuation characteristics of solar collector field in solar district heating system

In centralized solar district heating systems, the optical performance attenuation of the solar collector field significantly impacts the system’s heating efficiency and economics. However, accurate lifecycle models for the optical performance attenuation of solar collector fields are still needed. In this paper, the attenuation patterns of transmittance, absorption, and emissivity are systematically established through accelerated attenuation tests and calculation models. Based on this, a lifecycle model for optical performance attenuation was developed using TRNSYS and applied to a centralized solar heating system in Langkazi, XiZang. The results indicate that low inlet temperatures and high flow rates reduce optical performance attenuation, with ultraviolet damage of the glass cover being the main cause of performance attenuation, accounting for 74.5 % of heat loss. A 15-year lifecycle analysis shows that performance attenuation in the solar collector field results in a 16.7 % reduction in effective heat collection, a decrease in the solar fraction from 66.1 % to 55.1 %, and a 32.4 % increase in auxiliary heat supply. Increasing the heating area or thermal storage to collection area ratio helps mitigate optical attenuation. Based on this, from the perspective of mitigating the attenuation of collection efficiency, the thermal storage to collection area ratio should exceed 0.2 m3/m2, and the solar fraction is recommended to be kept below 0.7. Additionally, considering optical attenuation, the levelized cost of heat increases by over 0.03 CNY/kWh when the thermal storage to collection area ratio exceeds 0.2 m3/m2. The results provide a methodological basis for more accurate design of the solar heating system.

A way to macroporous and alveolar geopolymer foams elaboration: Influence of operating parameters on porosity characteristics

Alveolar cellular foams are widely used in a wide range of applications, from aeronautics and filtration systems to chemical and transformation processes. Their porous characteristics make them a prime candidate for reactions, radiative transfer and flow. Geopolymeric foams, which have their origins in civil engineering, are materials with promising potential in terms of mechanical, thermal and acoustic resistance. As they are mainly used in civil engineering, the structures currently being developed are mainly closed-pore matrices. However, if they are to invert the field of photocatalytic oxidation processes, solar collectors or concentrated solar power plants, the supports need to develop a high exchange surface area. Metal alveolar foams have been identified as ideal but very costly supports. Geopolymeric foams could meet these requirements, but their surface areas are currently too limited for photoreactors. In this study, it is proposed to develop and optimize the operating conditions for geopolymer foam synthesis in order to impart macroporous properties and an interconnected alveolar structure. Based on two well-established synthesis methods (direct foaming and replication), operating conditions such as foaming agent and surfactant content, and drying and calcination conditions, are studied. Geopolymer foams are produced with different macroporous characteristics. We aim to define the synthesis conditions required to produce interconnected macroporous alveolar foams with milimetric pores. In civil engineering, these materials have the advantage of being easy to design, use and shape according to the application.

Field measurements reveal insights into the impact of turbulent wind on loads experienced by parabolic trough solar collectors

To ensure efficient and reliable operation of a concentrating solar-thermal power (CSP) plant, its solar collector field needs to accurately focus sunlight. The optical efficiency and structural integrity of the solar collectors is significantly influenced by wind conditions in the field. In this study, we present insights into dynamic wind loading on parabolic trough CSP collectors. We derive novel conclusions by analyzing a first-of-a-kind measurement campaign of wind and structural loads, performed at an operational CSP plant. Previous research primarily relied on wind tunnel tests and simulations, leaving uncertainty about wind loading effects in operational settings. We demonstrate that the parabolic trough field significantly alters the turbulent wind field within the collector field, especially under winds perpendicular to the trough rows. Our measurements within the trough field show reduced wind speeds, changes in wind direction and turbulence properties, and vortex shedding from the trough assemblies. These modifications to the wind field directly impact both static and dynamic support structure loads. Our measurements reveal higher wind loads on trough assemblies compared to those observed previously in wind tunnel tests. The insights from this study offer a novel perspective on our understanding of wind-driven loads on CSP collectors. By informing the development of next-generation design tools and models, this research paves the way for enhanced structural integrity and improved optical performance in future parabolic trough systems.

Heat pipe solar collectors: A Review

Abstract In today’s world, the consumption of energy is quickly growing, and the exhaustion of non-renewable energy sources poses a significant risk to the entire human race. The importance of renewable energy sources emerged as a result of this, and solar energy is currently considered to be among the most promising and significant sources of clean and renewable energy. There has been a significant amount of work done in the field of solar radiation harvesting in order to make the most of it. This was accomplished by substituting the standard solar collectors, which are lacking in certain elements of performance and have a lower efficiency, with a modified solar collector that is superior to the normal collectors. Among the many modifications that can be made to the solar collector, the heat pipe is particularly significant. This review will present a variety of studies on the modification of heat pipe solar collectors (HPSCs) construction and integration within the systems, as well as an analysis of the performance enhancements that were made to it. Additionally, we provide a wide range of applications that make use of solar collectors that are shaped like heat pipes. In conclusion, we offered some suggestions for potential developments in the field of heat pipe solar collectors with regard to future trends.

An innovative variable flow control strategy and system performance analysis of a solar collector field

The dynamic changes in the environmental variables and the fluctuation characteristics of the thermal storage temperature have notable influences on the efficiency of solar collector fields. In addition, the optimal flow rate of solar collector fields varies under different combinations of variables and depends primarily on the collector scale and connection form. On this basis, it is imperative to carefully and comprehensively determine and adjust the optimal operating flow rate, considering the specific characteristics of the employed solar collector field under diverse variable combinations. To address this, this study proposes and develops a variable flow control strategy for solar collector fields based on maximizing net income. The presented strategy adjusts the operation flow according to environmental variables and the thermal storage tank temperature. The control principle of the proposed strategy and the corresponding method of obtaining the optimal flow are described. Based on this principle, the optimal flow optimization model is established, and the polynomial function of the optimal flow value is obtained by regression. Using the developed model, several conventional control methods are defined and simulated, and an analysis is performed to compare the collector’s performance under different scenarios. The results indicated that the variable flow control strategy proposed in this study can significantly improve the economic feasibility of solar collector fields. A 100 m2 series–parallel flat-plate solar collector field is considered as an example, and the proposed variable flow control strategy is implemented. As a result, a notable increase in the net income is reported compared to other conventional operation strategies, ranging from 6.70 % to 14.04 % in three different regions, namely Lhasa, Yinchuan, and Xi’an.

Economic and operational assessment of solar-assisted hybrid carbon capture system for combined cycle power plants

The paper presents a post-combustion CO2 capture process which involves two configurations for enhancing the CO2 separation driving force in the conventional amine-based Carbon Capture System (CCS): a multi-stage membrane module for selective exhaust gas recirculation (SEGR case) and the combination of turbine exhaust gas recirculation with SEGR (EGR + SEGR case). Furthermore, the stripper reboiler in both configurations is integrated with a parabolic trough solar collector field with a 4-h thermal energy storage to provide the required thermal duty for solvent regeneration. Various system components are designed, simulated, and integrated with an economic model to evaluate the system's techno-economic performance across a wide range of loads. The results show that the proposed designs have efficient part-load performance although efficiency degradation is inevitable during partial-loads. A stable supply of solar thermal energy results during the partial operation of NGCC even during night. The EGR + SEGR case represents the case with the lowest levelized cost of electricity and CO2 avoided cost, 81.43 $/MWh and 101.66 $/tonneCO2, among the CCS-equipped designs, which highlight the advantages of this design over baseline and SEGR case. The proposed hybrid system shows promise for significantly decarbonizing fossil-fuel power plants and increasing power sector flexibility.

Flat plate solar collector networks: Design and retrofit considering fouling effects

This study presents the thermohydraulic principles for retrofitting existing flat plate solar collector networks with the aim of increasing energy capture using the installed capacity. The arrangement of a solar collector field influences its thermohydraulic performance and pumping costs. In this study, factors such as scaling-induced fouling, solar radiation, and flow distribution are considered. The case of an existing plant consisting of a total of 40 collectors is examined. It is concluded that the optimal arrangement should include 8 collectors per line connected in series as a limit to enhance thermohydraulic performance and reduce overall operating costs. The annual savings due to reduced natural gas consumption in the original plant structure (4Lx5px2s) amount to $17,522.72 USD per year; however, modifying the structure to 4Lx10s, the savings increase to $19,818.64 USD per year. Under fouling conditions, the new structure reaches savings of $19,512.41 USD per year. This suggests that, in design, the network configuration should prioritise the number of collectors in series per line, only limited by the increase in pressure drop.

Temperature homogenization control of parabolic trough solar collector field based on hydraulic calculation and extended Kalman filter

Parabolic Trough Collector fields serve as the heat-absorbing components in large-scale commercial solar trough power plants. However, they frequently encounter challenges related to uneven spatial distribution of solar irradiation and heat transfer fluid flow. These disparities often lead to temperature inhomogeneity across the field, thereby jeopardizing both the safety and economic efficiency of the collector field. To address these issues, this study first introduces a proportional-integral and feedforward based flow control strategy designed to stabilize the fluid outlet temperature in the collector field. Subsequently, a flow allocation scheme aimed at achieving temperature uniformity across individual collector loops is presented. This scheme relies on the effective irradiation estimates for each collector loop, calculated using the extended Kalman filter algorithm and a suggested hydraulic model. Simulation results demonstrate that these control strategies not only stabilize the outlet temperature of the collector field at the desired set value but also significantly diminish temperature variances among individual collector loops, with reduced computational overhead. The maximum temperature difference between loops can be reduced from 126.3 °C to 12.7 °C under uneven radiation intensity, ranging from 563 W/m2 to 885 W/m2, by the proposed temperature homogenization control strategy.

Wind and structural loads data measured on parabolic trough solar collectors at an operational power plant

Wind loading is a primary contributor to structural design costs of concentrating solar-thermal power collectors, such as heliostats and parabolic troughs. These structures must resist the mechanical forces generated by turbulent wind, while the reflector surfaces must maintain optimal optical performance. Studying wind-driven loads at a full-scale, operational concentrating solar-thermal power plant provides insights into the wind impact on the solar collector field beyond the capabilities of wind tunnel tests or state-of-the-art simulations. We conducted comprehensive field measurements of the atmospheric turbulent wind conditions and the resulting structural wind loads on parabolic troughs at the Nevada Solar One plant over a two-year period. The measurement setup included meteorological masts and structural load sensors on four trough rows. Additionally, a lidar scanned the horizontal plane above the trough field. In this study, we describe the high-resolution dataset characterizing the complex flow field and resulting structural loads. This first-of-its-kind dataset will enhance the understanding of wind loading on collector structures and will help in designing the next-generation solar collectors and photovoltaic trackers.

In-field monitoring and numerical parametric analysis of a small size adsorption solar cooling plant in Italy

Solar cooling of small buildings represents a very interesting potential market, still underdeveloped and characterized by a wide range of uncertainties, both on the technological and the economical side. Actually, there are a few low size ready-to-market adsorption/absorption chillers and their costs are significantly higher than technically mature compression systems. The combination of solar thermal systems with solar assisted chillers needs a thorough design stage to be correctly optimized and this may turn out unaffordable for a low size project. A monitoring campaign has been carried on a new building (PUEEL – Prototipo Uffici ad Elevata Efficienza in Legno, High Efficiency Wooden Office Prototype) realized at the facilities of IPLA1 in Turin, Italy. The building has a wooden highly insulated envelope, controlled mechanical ventilation with thermodynamic heat recovery, radiant heating/cooling. A solar thermal collector field is integrated in the building roof (Fig.1), used both for the building heating and cooling demand, thanks to a 9kW adsorption chiller. Dynamic simulations of the system, using software Polysun © for solar cooling plant and EnergyPlus © for building demand assessment, have also been carried on and compared with in-field measurements. The validated model has been used for a parametric evaluation of the effects of the installation of different components and control strategies.

Robust Fractional Order PID Controller Coupled with a Nonlinear Filtered Smith Predictor for Solar Collector Fields

This work introduces a Fractional Order PID (FOPID) controller associated with a nonlinear Filtered Smith Predictor (FSP) to control a Solar Collector Field (SCF) system. The combined approach enhances the control performance by decoupling model uncertainties. First, the FOPID addresses linear model uncertainties through optimal robust design across the operational conditions, while the FSP compensator adeptly manages the system’s varying time delays. Rigorous tuning in the frequency domain considering closed-loop, robustness, and disturbance rejection performances is developed using a bi-level optimization approach to obtain the FOPID control parameters. Experimental results of the FOPID + nonlinear FSP demonstrate low rise time for reference tracking and robust stability across several operating conditions, even in the face of high-frequency disturbances in the solar irradiance due to passing clouds. Moreover, the nonlinear FSP effectively handles variations in time delays undergone by the water flow variation during the experiment. The achieved outcomes of the overall control structure, comprising the FOPID + FSP, demonstrate a promising approach for SCF system control, obtaining robust behavior in the presence of model uncertainties and disturbances while offering satisfactory reference tracking capabilities across an extensive range of plant operations.

Disturbance rejection model predictive control for solar collector fields based on fast Fourier transform

Stability of fluid temperature in the collector field guarantees for the safe operation of a trough solar power plant. As a control algorithm that handles process characteristics, the model predictive control (MPC) algorithm provides good effectiveness in temperature control of the collector field. In order to compensate for model errors and unmeasurable disturbances, this paper proposes a novel model predictive control algorithm based on the Fast Fourier Transform (FFT) to control the temperature of the collector field. During the control process, the dominant frequencies of model deviations and disturbances are acquired by the FFT. Then, the effects brought by these factors can be estimated and compensated in advance by the expansion of the prediction model and the calculation of the estimator. Simulation results show that the proposed FFT-based MPC algorithm has good disturbance rejection ability, especially for periodic disturbances.

Design of a Parabolic Trough Collector Solar Field for a Pilot CO2 Capture Plant from Natural Gas Combined Cycle Power Plant Flue Gas.

A parabolic trough collector solar field was designed to supply the heat needed to regenerate the CO2-rich monoethanolamine in a solar-assisted carbon capture system. Process design modeling was performed for 90% of the CO2 removal from 1% of the flue gas produced by a 255 MWe natural gas combined cycle power plant. Calculations with and without 24 h of thermal energy storage by increasing the solar collector size needed and providing a buffer vessel to store hot heat transfer fluid were performed. A dynamic analysis of the solar field using the hourly solar forecast was performed to investigate how heat transfer fluid mass flow changes during January and June to maintain the desired parabolic solar field outlet temperature needed for CO2 reboiler operation. The calculations provided here present an explicit method to calculate relevant solar field design parameters that can be scaled up and used in solar energy-assisted gas capture processes.

Improving Temperature Tracking Control for Solar Collector Fields Based on Reference Feedforward

Improving temperature reference tracking in solar collector fields is essential for enhancing the performance of solar thermal plants. Conventional control strategies are usually employed as static reference feedforwards (FFs) to reduce rise time when reference changes occur. Nevertheless, strict performance requirements may demand precise control behavior that classical reference FFs cannot deliver. Therefore, from theoretical analysis, this work proposes two different control strategies based on reference FF structure to accomplish a low rise time and avoid producing overshoot for temperature reference tracking, namely, a lead–lag and a nonlinear reference FF. The structures are studied for suitable implementation, assuming an adaptive control framework to keep the same control performance under different operating conditions. Simulation experiments are developed to investigate and compare the proposed strategies with the conventional static FF with and without a reference filter. Furthermore, the proposed strategies are successfully tested in an actual solar plant AQUASOL-II, located in the Plataforma Solar de Almería (PSA), Almería, Spain. The promising results have concluded that the lead–lag and nonlinear reference FF associated with the adaptive structure have attended the proposed control requirements of low rise time and no overshoot. Moreover, the results have demonstrated the compromise between the lead–lag and the nonlinear controller, where the final choice should be made as a tradeoff between performance and control effort.

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

Solar district heating system in Latvia: A case study

The ever growth of urban population has caused the increase of energy demand. This situation challenges the global public to find a way to produce energy in a secure, environmentally friendly, flexible, renewable and sustainable energy transformation system. One of the most promising technologies that can over-come most of the challenges is the district energy network. This paper focuses on best practice project in Latvia – fully renewable district heating system assisted by solar collector system with thermal storage tank and woodchip boilers. The article demonstrates solar impact to district heating system (DHS) in the framework of the current situation of DHS in Latvia by creating simulation in TRNSYS and validation with real system operation data. Real operational data show that the heat produced by solar collector system with thermal energy storage (TES) per year will cover up to 20% (10933,2 MWh) of the heating demand in under local climate conditions. The TRNSYS simulations concluded that the contribution of this type of solar system integrated into the DHS could be increased up to 50%, if the difference between consumption and heat produced by solar collectors were to be increased during the summer months, this could be achieved, for example, by increasing the solar collector field area.

Thermo-economic assessment of hybrid Kalina cycle and organic Rankine cycle system using a parabolic trough collector solar field

This study presents a solar powered hybrid power system consisting the Kalina cycle (KC) and a bottoming organic Rankine cycle (ORC). LS-2 parabolic trough collector (PTC) is modeled in solar field with two different kinds of working fluid: Syltherm 800 and MXene/Syltherm 800 nanofluid. MXene particle (Ti3C2) is used with 0.1 wt% due to their outstanding thermal absorption properties. The use of MXene-based nanofluid has shown remarkable thermophysical properties, resulting in a significant increase in the useful heat generated by 11.10%. The hybrid system utilizing the MXene-based nanofluid demonstrates a substantial improvement in work utilization. Moreover, the maximum energetic and exergetic efficiency achieved with the MXene-based nanofluid are 6.095% and 6.55%, respectively, indicating its superior performance in converting solar energy into usable power with greater efficiency. When considering the overall cost of the MXene-based solar field, it was found to be approximately 7.63% higher compared to the Syltherm 800-based parabolic trough collector system. However, the Levelized cost of electricity (LCOE) for the Syltherm 800-based solar field was calculated as 0.1351 $/kW-hour, while for the MXene/Syltherm 800-based solar field, it was slightly lower at 0.1324 $/kW-hour. Additionally, the Payback period was reported as 5 years and 9 months for the Syltherm 800-based solar field, and 5 years and 7 months for the MXene/Syltherm 800-based solar field.

Nonlinear and infinite gain scheduling neural predictive control of the outlet temperature in a parabolic trough solar field: A comparative study

Solar thermal plants have high nonlinearities and non-manipulated energy source which make their control task a very challenging work. Linear controllers cannot cope with undesirable deviations of the outlet temperature over all the operation range of the dynamics of this type of plants. Moreover, nonlinear predictive control relying on online nonlinear optimization have the drawback of time consuming and numerical calculus issues. In this paper, an infinite gain scheduling neural predictive control is designed and applied to control the temperature in a distributed parabolic trough solar collector field. The performance of both tracking and disturbance rejection of the proposed controller is compared to those of four nonlinear predictive control variants: Two unconstrained neural predictive control using the Levenberg–Marquardt and the Broyden–Fletcher–Goldfarb–Shanno algorithms, and two constrained nonlinear predictive control using interior point algorithm, one is based on a neural network model and the other one is based on a first principal model. The superiority of the proposed control strategy is well demonstrated through simulation results.

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.

Low-temperature solar thermal-power systems for residential electricity supply under various seasonal and climate conditions

In this work, the performance of low-temperature (<100 °C) solar thermal-power systems to satisfy residential electric loads was analyzed. The solar-driven system was designed to provide a fraction of the total electricity demand in a complementary operation with the electric grid. The analysis was conducted for an coperation during seven days each season, considering real solar and climate variables and residential loads at different climate zones in the United States. The efficiency of the system strongly depends on the solar radiation profile and the ambient temperature. Maximum efficiencies of around 9.5% were obtained in the cold and marine climate zones due to the high solar energy input and low heat dissipation temperatures. In these two zones, the system could supply more than 98% of the electricity demand all seasons. At mixed-humid and hot-humid regions, the system supplied around 50% of the electric load in three of the four seasons, but it only supplies about 27% of the electricity needs in the mixed-humid zone during summer and hot-humid zone during winter. The effect of the solar collector field area and the tank volume was also analyzed. In general, larger solar fields positively impact the efficiency. However, the impact of the tank volume varies depending on the solar radiation profile and the load requirements. Average efficiencies for the seven-day operation can be larger than 6% with a proper selection of the solar collector area and tank volume for an Organic Rankine Cycle with a capacity of about 2.6 kW. Finally, an economic analysis of the system was conducted, and the results were compared with a solar PV + battery system of similar capacity. It is expected that the cost for the analyzed solar-thermal system decreases in the coming years with the increased interest on low temperature applications.