Solar Thermal Power Technology Research Articles

A Planar-Cavity Receiver Configuration for High-Temperature Solar Thermal Processes

Next-generation concentrating solar thermal power (CSP) technologies target a wide spectrum of applications including electricity generation, thermochemical processes, and industrial process heat for broad decarbonization potential. Many of these applications require higher temperatures than those of current commercial nitrate salt systems. Particulate materials are promising candidates for next-generation high-temperature heat transfer and low-cost storage media and can facilitate operation over a wide temperature range. However these materials necessitate novel receiver configurations to accept the high incident flux concentrations that enable high solar-to-thermal receiver efficiency. One option is a novel light-trapping planar cavity receiver configuration in which small cavity-like structures are formed from opaque planar surfaces such that a high incident flux concentration at the cavity aperture is reduced to a wall-absorbed solar flux concentration that is manageable within limited wall-to-particle heat transfer rates. The paper introduces the receiver configuration and provides calculated optical performance for a preliminary 50 MWt receiver design.

Energy cost optimization of Linear Fresnel Reflector (LFR) systems for different regions of installation

The Linear Fresnel Reflector (LFR) is a promising Concentrating Solar Thermal Power (CSP) technology due to its simplicity and cost-effectiveness. This paper presents a novel method for optimizing the Levelised Cost of Electricity (LCOE) for site-specific LFR systems. The method integrates ray tracing and a thermal model with a genetic algorithm to simulate and optimize LFR designs for three different annual solar irradiance profiles. For an LFR with a standard evacuated tube receiver with a 70 mm diameter, the optimal design variables are determined to be within the ranges of 8.9–9.2 m for receiver height, 18–22 for the number of mirrors, 0.63–0.81 m for mirror width and 0.10–0.13 m for mirror spacing. The results show that the optimized LFR design variables remain relatively consistent across different locations, allowing for the efficient use of one design in multiple locations. A sensitivity analysis shows that the LCOE is predominantly affected by receiver height. Comparing the optimized designs with recent commercial LFR installations reveals that, when 6 hours of thermal energy storage is used, LCOE savings of up to 20% are still achievable. Overall, the study demonstrates that there are still substantial LFR design improvements that can be made to reduce the cost of electricity from an LFR system and make it a cost-competitive solution for clean power generation.

Experimental and numerical investigation of the melting process of solar salt in a spherical capsule

Solar salt is commonly employed as phase change material in various industrial applications, particularly in latent heat-based thermal storage systems such as packed beds in solar thermal power technologies. Here, a series of experimental and numerical studies are conducted of the melting process of a binary nitrate salt inside a spherical capsule under a wide range of large Stefan numbers, specifically ranging from 0.56 to 1.12. For a deep understanding of the melting behavior inside the sphere and its heat transfer characteristics under different constant wall temperatures and sphere sizes, the visualized high-temperature phase change experiment along with a 2D axisymmetric numerical model are presented. To confirm modelling reliability, the numerical model well-realized the sinking phenomena visualized in the experiment with a suitable mushy-zone parameter value of 6*108 kg/(m3·s). Subsequently, the temperature field, flow field, melting front, total transfer rate and melting time are explored. Further, a detailed parametric investigation is applied, including the effects of dimensionless parameters such as Gr, Ste on the melting process. And finally, the dimensionless correlation is succeeded to be proposed for unconstrained melting process with 0.56 ≤ Ste ≤ 1.12 and 1.80E+04 ≤ Gr ≤ 2.02E+05.

A novel solar-driven Organic Rankine Cycle system based on the two-stage solar thermal collection and accumulation

Solar thermal power has attracted much attention because it is instrumental to solar energy storage and power grid peak shaving. Among the various solar thermal power technologies, the Organic Rankine Cycle stands out as a prevalent choice for low and intermediate-temperature (80 – 200 °C) solar thermal power generation applications. However, it is required of the concentrating solar collectors for medium temperature supply and its performance is greatly affected by the off-design operation owing to variable solar irradiance. In this paper, a novel solar-driven Organic Rankine Cycle system that consists of a two-stage solar thermal collection and accumulation design is proposed to solve the above issues. Two-stage non-concentrating solar plants are adopted to harvest global solar irradiance and regulate system operation. Two-stage energy accumulators can not only mitigate the influence of the solar irradiance fluctuation on the Organic Rankine Cycle off-design running but also enhance the temperature drop of thermal energy storage. Through the experimental test and numerical simulation, the results indicate that the influence of solar irradiance on the Organic Rankine Cycle steady operation has been weakened (reducing power output fluctuation range by approximately 70%), and the overall system efficiency has also been improved by 43.85%. Consequently, the solar Organic Rankine Cycle system proposed in this paper exhibits superior thermal performance compared to the conventional systems and is conducive to the advancement of the non-concentrating solar thermal power system.

Exergoeconomic Analysis of an Integrated Solar Combined Cycle in the Al-Qayara Power Plant in Iraq

Enhancing the sustainability and diversification of Iraq’s electricity system is a strategic objective. Achieving this goal depends critically on increasing the use of renewable energy sources (RESs). The significance of developing solar-powered technologies becomes essential at this point. Iraq, similar to other places with high average direct normal irradiation, is a good location for concentrated solar thermal power (CSP) technology. This study aims to recover the waste heat from the gas turbine cycle (GTC) in the Al-Qayara power plant in Iraq and integrate it with a solar power tower. A thermoeconomic analysis has been done to support the installation of an integrated solar combined cycle (ISCC), which uses concentrated solar tower technology. The results indicate that the examined power plant has a total capacity of 561.5 MW, of which 130.4 MW is due to the waste heat recovery of G.T.s, and 68 MW. is from CSP. Due to the waste heat recovery of GTC, the thermal and exergy efficiencies increase by 10.99 and 10.61%, respectively, and the overall unit cost of production is 11.43 USD/MWh. For ISCC, the thermal and exergy efficiencies increase by 17.96 and 17.34%, respectively, and the overall unit cost of production is 12.39 USD/MWh. The integrated solar combined cycle’s lowest monthly capacity was about 539 MW in September, while its highest monthly capacity was approximately 574.6 MW in April.

Multi-criteria decision making for different concentrated solar thermal power technologies

Solar thermal power technologies are promising renewable energy sources that could replace the conventional fossil fuel power plants. Parabolic trough collector (PTC), linear Fresnel reflector (LFR), solar power tower (SPT), and Solar power dish (SPD) are the commercial concentrated solar thermal power technologies. Technical, economical, and environmental aspects are varied from one technology to another. Deciding the best solar thermal power technology is quite important for the commercial applications. In order to decide the best technology, based on 22 criterions including the technical (9), economical (2), and environmental (11) aspects, different multi-criteria decision making (MCDM) models were applied. The main parameters of the MCDM model that determine the rating of alternatives include the choice of the method of normalization of the matrix of decisions, the choice of the method for evaluating the weights of the criteria and the choice of the method of aggregation of attributes when determining the indicator of the effectiveness of alternatives. Three different groups of MCDM methods are defined as a method for aggregating attributes in determining the performance indicator of alternatives: based on a weighted sum approach (WSM, WPM, WAPRAS), based on the concept of distance or distance from the desired object (TOPSIS, GRA, VIKOR), and based on the approach of aggregating local ratings based on setting the preference function (PROMETHEE-II). According to the results of all models, alternative A4 that represents the solar power dish technology is the best selection among the different solar technologies. A4 is winner (first rank I) for about 65% of considered cases followed by A3 that represents solar power tower technology. A3 is winner (first rank I) for about 35% of considered cases.

A performance evaluation of an integrated solar combined cycle power plant with solar tower in Saudi Arabia

• A 548.4 MW Integrated solar combined cycle power plant is proposed including 50 MW from solar tower technology. • A techno-economic analysis outcomes are incorporated with the weather characteristics of Saudi Arabia. • On-the-ground measured meteorological data is adopted for accurate simulations. • The hybridized solar tower field achieved efficiency ranging between 53 and 59% annually and a capacity factor of 49.9%. • The annual generation of the solar tower field is found to be at 220.89 GWh and the levelized cost of energy 12.71 cent/kWh. Improving the diversification and sustainability of Saudi Arabia’s national electricity grid is a strategic priority. In order for this objective to come to fruition, increasing the penetration of renewable energy resources (RESs) is of paramount importance. This is where the importance of improving solar powered technologies becomes crucial. Specifically, concentrated solar thermal power (CSP) technologies have significant potential in Saudi Arabia, as well as other locations with high averages of direct normal irradiation. In this research, a techno-economic analysis has been conducted for the adoption of an integrated solar combined cycle (ISCC) which utilizes solar tower (ST) technology in Saudi Arabia. The power plant under study has a total capacity of 548.4 MW, of which 50 MW is from CSP. The outputs of this model are compared with other conventional and renewable energy sources quantitively. The results show that the hybridized ST field can achieve efficiency ranging between 53 and 59% annually leading to a capacity factor of 49.9% which is higher than other RES technologies of similar intermittent nature. The solar field installed capacity represents 9.11% of the total power plant capacity, whereas its output represents up to 10.7% of the total output. The annual generation of the solar tower field is found to be at 220.89 GWh, net present value (NPV) 10.2 MSUD, and levelized cost of energy (LCOE) 12.71 cent/kWh. The results reflect that the hybridization of CSP with conventional combined cycle gas turbine (CCGT) results in enhanced annual generation, lower energy cost, and facilitates the transition to stand-alone CSP. The hybridization of ST ISCC helps to steadily build up the know-how of the operation and maintenance of a technology with great potential given the weather and demand characteristics of Saudi Arabia. Results of this research can facilitate decision-making in the early stages of penetrating CSP to the electricity mix in the Saudi national grid in order to achieve the desired sustainability of energy sources.

Design and analysis of an innovative concentrated solar power system using cascade organic Rankine cycle and two-tank water/steam storage

Direct steam generation (DSG) solar power systems have the potential to improve heat collection performance and reduce capital cost. One challenge of the DSG solar thermal power technology is the unsteadiness of steam generation and power conversion under fluctuating solar radiation. A novel concentrated solar power generation system is proposed. It has three features: two-phase water/steam as heat transfer fluid, two-tank water storage, and cascade organic Rankine cycle (CORC) with a mixing chamber as power block. Steam is produced in the solar field and condensed in a high temperature tank, while an organic fluid replaces water for power conversion. The system enables smooth cycle operation by resilient control strategy and can tackle the challenge associated with wet steam turbines. It can tolerate lower purity of water/steam that only serves as the heat transfer fluid, thereby reducing the technical requirement. Thermodynamic performance in the normal operation condition and heat discharge process are assessed. The influences of ORC working fluid and storage tank size are examined. Results indicate that the mixing chamber temperature plays a crucial role in thermal efficiencies of both charge and discharge processes, storage capacity, and overall performance. A CORC efficiency of about 27.4% is achievable. The equivalent heat-to-power efficiency ranges from 13.35% to 18.81%, depending on the ORC fluid and volume of the storage tank. The novel system has an efficiency comparable to a conventional DSG system while a lower technical requirement in heat collection and power generation.

Mapping concentrated solar power site suitability in Algeria

The investment in solar thermal power technologies has become increasingly attractive, despite their still perceived high costs. Algeria presented an ambitious plan for increasing the participation of renewable energy sources (RES) in the power system, with significant investments foreseen for solar power technologies. To achieve this objective, it is necessary to identify optimal sites for the implementation of these plants, as well as others where implementation is highly inadvisable from the economic, social, or environmental points of view. The main goal of this study is to present and apply a methodology to identify adequate locations for the installation of solar power plants in Algeria. The study addressed the particular case of concentrated solar power (CSP) and proposed a hybrid approach combining multi-criteria decision making and Geographic Information System. The approach allowed mapping and visualizing unfeasible areas and ranking the feasible sites. The results showed that more than 51% of the territory of the country is unfeasible for the implementation of CSP, mainly due to criteria related to topographic aspects, water availability, and distance to the grid. The results demonstrated that relying only on Direct Normal Irradiation (DNI) values may result in a reductionist vision for energy planning and thus other criteria can play a fundamental role in the decision process. The model allowed also to identify the best regions for CSP investment and opens routes for more detailed studies for the exact site selection.

Modeling, Simulation and Optimal Operation of Multi-Extraction Packed-Bed Thermal Storage Systems

Solar thermal power technologies require storage systems to mitigate the natural variability of solar irradiation. Packed bed thermal storage systems (PBTES) offer a cost-effective solution using air as heat transfer fluid and rocks as a storage medium. Compared to its alternatives, however, PBTES presents a limited flexibility of operation due to the conventional unidirectional flow, which involves the progressive reduction of the outlet temperature during discharge and thus lowers the thermodynamic efficiency of the power cycle. The present study summarizes the progress on the design and optimal operation of a novel multi-extraction PBTES, a project that aims at mitigating its typically poor operational flexibility for solar power applications. To this end, a one-dimensional model with a high spatial resolution of a PBTES was developed, which includes four intermediate outlet points along the axial direction to investigate the benefits of optimal extraction operation. In order to reduce the computational burden, a coarser model of the storage system is used in combination with non-linear model predictive control (NLMPC). Through the optimal manipulation of the extraction valves, the output temperature is maintained close to a prescribed temperature throughout the discharge. The control admits not only constant temperature targets, but also time-varying scheduled profiles. This work describes the limitation of such a design and control approach and sets the direction for the future, more detailed analyses needed to demonstrate its applicability.

Comparative Techno-Economic Study of Solar Thermal Power Plants with Various Capacities: A Case for the Northern Part of Cameroon

The purpose of this article is to evaluate the commercial use of different solar thermal power technologies in the northern part of Cameroon. For this, a techno-economic study highlighting the design of each technology using various capacities of the studied plant. The main objective was to carry out, technical, economic and financial parameters able to attract investors for the use of such kinds of technology to generate electricity in these provinces [G1] having a good direct normal irradiation estimated at 2145kWh/m2/year and meet at the energy demand of population living with less than 10% electrification rate in rural area. During this study, we considered some technical paramet[G2] ers as total annual DNI received by solar field, Field thermal output, thermal system transfer rated, overall energy efficiency and yearly electricity production. The last parameter was a key parameter for techno-economic analysis of the studied system.[G3] Some parameters as the payback period (PBP), internal rated return (IRR), net present value (NPV) and levelized cost of electricity (LCOE) have been found out during the economic analysis. The bonus carbon can be allowed to a company because of the good electricity generation has been applied during the calculation of these parameters. Other parameters as the initial investment and incentives from the government or financial named in this study have been considered also. The [G4] environmental and social impact assessment (ESIA) related to this purpose give a priority to criteria as grid, land and water access and use for electricity generating. Then, the ESIA study has been considered as a key parameter for Multi-Criteria Decision Maker. The studied systems had various range capacity starting from 5 MW to 100 MW and their analysis in the sub-Saharan region[G5] shown that, the cost of installed kW for concentrating solar technologies (CST) varies between 4550 – 6745 US Dollar , 5240 – 9365 US Dollar and 5100 - 6290 US Dollar and the levelized cost of electricity per kWh varies between 10.22-13.22 USD cents, 11.07-19.81 USD cents and 14.63-15.6 USD cents for Parabolic trough collector(PTC), Solar Tower (ST) and Linear Fresnel (LF) respectively. The solar tower technology can't be efficient compared to other techniques for the thermal power plant (TPP) under 10 MW[G6] [G7] [G8] e due to the initial investment. It important to add this, the cost of installed kW in the sub-Saharan region is higher[G9] than order region because of transportation fees, the lake of solar thermal manufactures for insulation and piping system, metal structure and expertise related to total indirect cost such as engineering procurement construction and advanced ESIA services in this area. The support of financial institution through CER/TAX and a similar approach in addition to existing subvention[G10] [G11] s for such technology can decrease considerably both payback period and feed-in-tariff (FİT) price of the studied system and contribute to developing the sector [G12] by creating an attractive market for investors.

A Research on Various Solar Thermal Power Technologies

Solar thermal electric systems are simplest and hold promise of viability. Solar thermal systems have great similitude with conventional power system. In this paper we present an overview of various solar thermal power technologies to evolve criteria for selection of best systems.

Conceptual design of a new thermal‐electric conversion device in lightweight concentrating solar thermal power system

AbstractConcentrating solar thermal power (CSTP) technology has become a hot issue in the present research because of its high conversion efficiency. However, traditional schemes cannot be widely applied due to their complex structure, low power density, and high cost. In view of this, based on a new type of lightweight cable mesh reflector structure and the Rankine cycle, a new conceptual design of thermal‐electric conversion device in CSTP system is proposed. The process of thermal‐electric conversion is actualized through smart and lightweight structural design; the performance estimation of the device is carried out through focusing performance analysis and thermodynamic analysis; the cycling feasibility is verified through multifield coupling simulation analysis. Compared with the existing thermal‐electric conversion devices, the device proposed in this paper has higher power‐to‐weight ratio. And the power generation system that combines the proposed device with the flexible cable net reflector has the characteristics of lightweight, portability, and small land area, which has a great significance for the popularization and application of distributed layout CSTP system.

Impact of ambient temperature on supercritical CO2 recompression Brayton cycle in arid locations: Finding the optimal design conditions

In this paper, we present a new method to determine the optimal design conditions of a supercritical CO2 recompression Brayton cycle with dry cooling based on plant location. These power cycles are gathering high interest in concentrated solar thermal power technologies, which are most likely to be deployed in arid areas where dry cooling is a strategic choice. However, the usual high ambient temperature associated with these locations affects negatively the cycle performance. The key selection of two design parameters, the recompression fraction and the compressor inlet temperature, can minimise this negative effect. The method presented here allows the adjustment of these two parameters maximising the annual generation of electricity and cycle efficiency simultaneously. The optimisation process analyses the drop in the cycle performance due to the yearly variation of ambient temperature at the specific location. To reduce the computational effort required, polynomial regressions extrapolate the results from a reduced set of design-point and off-design cycle simulations in a wide range of ambient and compressor inlet temperatures. As an example, the method is applied to three different locations demonstrating the existence of optimal design conditions and justifying the need to adjust these two key parameters for each specific location.

Dynamic Paths: Towards high frequency direct normal irradiance forecasts

Direct normal solar irradiance (DNI) series of high-frequency time resolution permit an accurate modeling and analysis of transient processes in concentrating solar thermal power (CSTP) technologies. Numerical weather prediction (NWP) models provide an overall understanding of solar forecasting, but they are unlikely to cover a local statistical representativeness of the DNI high frequency dynamics. On the contrary, local statistical information derived from site measurements can provide statistical behavior, but may not necessarily yield an explicit model for all of the physical relationships involved. In this work, we propose a novel locally-adapted procedure for high-frequency DNI forecasting that connects these two extremes, proposing a hybrid approach in which low frequency (3-h) NWP outcomes act as boundary conditions (assuring a physical consistency with site climatic behavior) and are supplemented with Dynamic Paths of local high frequency (1-min) DNI series (assuring a statistical reproduction of site high frequency dynamics). This methodology is tested with ground measurements in 4 locations situated in different climates, and compared with a forecast base case. The analyses are carried out by classifying each measured time series into 6 categories according to its daily clearness index. Finally, metrics for adequately compare high frequency DNI forecasts are discussed.

Thermal and Transport Properties of NaCl–KCl–ZnCl2 Eutectic Salts for New Generation High-Temperature Heat-Transfer Fluids

Three eutectic salts from a system of halide salts NaCl–KCl–ZnCl2 were chosen for detailed study of thermal and transport properties with the objective of developing a next generation high-temperature heat-transfer fluid (HTF) for concentrated solar thermal power (CSP) technology. The acceptable range of the working temperatures for the HTF is from below 250 °C to at least 800 °C. The tested properties are presented here for the three candidate eutectic salts, including melting point, heat of fusion, heat capacity, vapor pressure, viscosity, density, and thermal conductivity. Data-fitted equations are provided for all the measured properties for convenience in engineering application. It is concluded that the three eutectic salts can satisfy the needs for a high-temperature HTF and thus are recommended as a new generation high-temperature HTF.

A value tree for identification of evaluation criteria for solar thermal power technologies in developing countries

The diversification of electricity generation is necessary for the sustainable development of developing countries and to reduce greenhouse emissions. Solar thermal power technologies are advancing and expected to play a significant role in energy portfolios in the future. Accordingly, it is essential to identify comprehensive combination of criteria for assessing these technologies. Various researchers used different parameter combinations for multiple criteria evaluation in renewable energy portfolio planning. The novelty of the proposed approach lies in the structured deliberation and the following analysis to formulate a combination of assessment parameters for solar thermal power technologies based on data providers’ judgment. A generic value tree of evaluation parameters is therefore obtained for solar thermal power technologies in developing countries. Expert elicitation was conducted through the Delphi method, with a total of 140 data providers from multidisciplinary solar thermal power fields affiliated in educational institutes, research centers, governmental organizations, and industrial companies from 32 countries participating in the survey. Five impact categories and nineteen performance measures were combined following a comprehensive literature review to derive a preliminary value tree. Based on participants’ judgments, as expressed during two rounds of Delphi questionnaires, parameters with importance and consensus degrees>50% were incorporated into the final value tree. Each parameter had a variation coefficient of <29%. The output of the process is an aggregated value tree, consisting of 31 performance measures categorized under four main impact categories (technical, economic, environmental, and social). Technical and economic impact categories were rated as most important and achieved the highest degrees of consensus. At performance measures level, economic feasibility obtained the highest level of importance and consensus degrees, followed by reliability, capital cost, storage hours, and water consumption. The recommendations of this work can be utilized as a foundation for stakeholder assessment of regional solar thermal power utilities planning in developing countries.

Heat transfer to supercritical water in a vertical tube with concentrated incident solar heat flux on one side

A solar tower power plant with supercritical water as a heat-transfer medium in the central receiver is potentially one of the most promising solar thermal power technologies due to its high solar-to-electric efficiency. In this paper, the heat transfer of supercritical water in a vertical tube of a solar tower receiver has been investigated. A 3D mathematical model has been developed to investigate the distribution of heat flux in the circumferential direction of a circular tube heated by concentrated incident solar flux on one side. The RNG k–ε model with the standard wall function is employed to describe the turbulent flow of water from a liquid-like state to a gas-like state, and the results are validated with experimental data. For supercritical water in a tube heated on one side by concentrated incident solar heat flux, the maximum wall temperature is located on the sunward outside wall where the incident heat flux is at a maximum. In the pseudo-critical flow region, due to the drastic turbulent diffusion of supercritical water, the temperature distribution of the supercritical water in the tube is evenly distributed at the same flow cross section. To avoid deterioration in the heat transfer of supercritical water, the relation between the threshold incident solar heat flux and mass flux for the supercritical water has been provided. Furthermore, the Nusselt correlation which can be used to predict heat transfer coefficient of the vertical tube heated non-uniformly on one side by concentrated solar flux has been confirmed.

Perfortmance Evaluations of Concentrated Solar Thermal Power Technology

This review work consists of detailed description on various types of research in the field of solar thermal systems and various methods to improve the performance of the collector systems. Concentrated solar thermal systems are the highly advanced and large scale technology, which is used to generate the thermal energy and converted it in to electric energy through the application of power producing device coupled with the collector systems, therefore from the research point of view improvement in the working performance of the solar thermal system is highly important to achieve the better efficient device.

Performance of the solar hybrid STIG cycle with latent heat storage

Abstract The solar hybrid Steam Injection Gas turbine (STIG) cycle uses both recuperated heat and solar heat in order to generate steam at a low temperature and pressure, and inject it into the cycle in order to augment the power output. This work addresses the addition of thermal energy storage to allow operation from solar energy beyond the daylight hours. An annual performance analysis of the Solar STIG cycle with latent heat phase change material (PCM) storage is presented for the climatic conditions of Sede Boqer, Israel. We show that the heat transfer limitation present in a real PCM storage leads to a slight performance penalty only compared to an ideal storage. We also analyze the impact of shifting electricity generation from daytime to evening, which can lead to a surprisingly high contribution of the thermal storage. Results show annual solar fraction of up to 35.2%. The annual solar to electricity efficiency was 20.1% when using the recuperated Brayton cycle as reference, and 13.9% for an optimal conventional STIG cycle as reference. These values are similar to or higher than the annual efficiency of current solar thermal power technologies, even though the hybrid STIG cycle uses low-grade solar heat at 200–280 °C.