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18 pages, 6341 KiB

Open AccessArticle

Hybridization of CSP Plants: Characterization of a Molten Salt Heater for Binary and Ternary Nitrate Salt Mixtures Fueled with Gas/Biogas Heaters

by Alberto Giaconia, Irena Balog and Giampaolo Caputo

Energies 2021, 14(22), 7652; https://0-doi-org.brum.beds.ac.uk/10.3390/en14227652 - 16 Nov 2021

Cited by 5 | Viewed by 1649

Abstract

Hybridization of CSP plants with alternative energy sources (fuels) represents a means to improve flexibility of operation, power dispatchability and utilization factor of the plant. New generation CSP plants make use of molten salts as Heat Transfer Fluid (HTF) besides Thermal Energy Storage [...] Read more.

Hybridization of CSP plants with alternative energy sources (fuels) represents a means to improve flexibility of operation, power dispatchability and utilization factor of the plant. New generation CSP plants make use of molten salts as Heat Transfer Fluid (HTF) besides Thermal Energy Storage (TES) medium. Therefore, proper interfaces should be developed to effectively transfer the heat from the back-up source to the molten salt. This paper presents the results obtained in the experimental validation of an innovative gas-fueled Molten Salt Heater (MSH) prototype. The objective of this research is to validate the MSH design, where the specific properties of molten salts (compared to other HTFs, e.g., thermal oils) have to be taken into account. The developed reduced-scale MSH (90 kW thermal) consists of a heat exchanger with the molten salt flowing inside finned tubes cross-flowed with the hot flue gas generated in an upstream combustion chamber. LPG or a biogas-like mixture has been used as gas fuel. Experimental results have been obtained with two different molten salt mixtures: the “solar salt” binary mixture (NaNO₃/KNO₃, 60/40%w) typically used in CSP applications (up to 565 °C) and the ternary mixture known as Hitec XL^® containing sodium/potassium/calcium nitrates (NaNO₃/KNO₃/Ca(NO₃)₂, 15/43/42%w) characterized by lower freezing temperatures. Experimental tests have been carried out changing some operative parameters like the flow rate of the molten salt (0.45–0.94 kg/s), the inlet temperatures of the molten salt (303–445 °C) and of the hot gas (596–632 °C). For both molten salt mixtures, it was demonstrated that heat transfer correlations based on the Dittus-Boelter equation allow to predict experimental results with <10% deviation between experimental and theoretical values of the heat transfer coefficient. Full article

(This article belongs to the Special Issue Concentrating Solar Power Systems)

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20 pages, 4756 KiB

Open AccessArticle

Minimizing the Computational Effort to Optimize Solar Concentrators with the Open-Source Tools SunPATH and Tonatiuh++

by Manuel J. Blanco, Victor Grigoriev, Kypros Milidonis, George Tsouloupas, Miguel Larrañeta and Manuel Silva

Energies 2021, 14(15), 4412; https://0-doi-org.brum.beds.ac.uk/10.3390/en14154412 - 22 Jul 2021

Cited by 6 | Viewed by 2965

Abstract

Integrals that are of interest in the analysis, design, and optimization of concentrating solar thermal systems (CST), such as the annual optical efficiency of the light collection and concentration (LCC) subsystem, can be accurately computed or estimated in two distinct ways: on the [...] Read more.

Integrals that are of interest in the analysis, design, and optimization of concentrating solar thermal systems (CST), such as the annual optical efficiency of the light collection and concentration (LCC) subsystem, can be accurately computed or estimated in two distinct ways: on the time domain and on the spatial domain. This article explores these two ways, using a case study that is highly representative of the commercial CST systems being deployed worldwide. In the time domain, the computation of these integrals are explored using 1-min, 10-min, and 1-h solar DNI input data and using The Cyprus Institute (CyI)’s High-Performance Computing (HPC) system and an open-source ray tracer, Tonatiuh++, being actively developed at CyI. In the spatial domain, the computation of these integrals is explored using SunPATH, another open-source software tool being actively developed at CyI, in tandem with Tonatiuh++. The comparison between the time and spatial domain approach clearly indicate that the spatial domain approach using SunPATH is dramatically more computationally efficient than the time domain approach. According to the results obtained, at least for the case study analyzed in this article, to compute the annual energy delivered by the LCC subsystem with a relative error less than 0.1%, it is enough to provide SunPATH with 1-h DNI data as input, request from SunPATH the sun position and weights of just 30 points in the celestial sphere, and run Tonatiuh++ to simulate these 30 points using 15 million rays per run. As the test case is highly representative, it is expected that this approach will yield similar results for most CST systems of interest. Full article

(This article belongs to the Special Issue Concentrating Solar Power Systems)

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22 pages, 6076 KiB

Open AccessArticle

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

by Simon Kamerling, Valéry Vuillerme and Sylvain Rodat

Energies 2021, 14(13), 3731; https://doi.org/10.3390/en14133731 - 22 Jun 2021

Cited by 7 | Viewed by 1930

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Concentrating Solar Power Systems)

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19 pages, 7014 KiB

Open AccessArticle

Analysis of the Applicability of the Parabolic Trough Solar Thermal Power Plants in the Locations with a Temperate Climate

by Tomasz Janusz Teleszewski, Mirosław Żukowski, Dorota Anna Krawczyk and Antonio Rodero

Energies 2021, 14(11), 3003; https://0-doi-org.brum.beds.ac.uk/10.3390/en14113003 - 22 May 2021

Cited by 5 | Viewed by 1694

Abstract

Currently, intensive work is underway in Poland to increase the share of renewable energy sources in the overall energy balance. Therefore, this paper presents the possibilities of using concentrated solar power in zones with a temperate climate. A simplified model based on the [...] Read more.

Currently, intensive work is underway in Poland to increase the share of renewable energy sources in the overall energy balance. Therefore, this paper presents the possibilities of using concentrated solar power in zones with a temperate climate. A simplified model based on the energy balance in the solar collectors considering the main operating parameters of the typical solar power plant was developed. It should be noted here that the model does not take into account issues related to heat accumulation and electricity generation in a Solar Thermal Power Station. The simulation of forced convection inside the solar collector absorber was additionally included in the calculations to improve its accuracy. The model was verified using actual heat measurements at the outlet of the parabolic collector installation at a Solar Thermal Power Station located in the south of Spain. The heat generated by a similar solar collector system in a selected region with a temperate climate, the city of Bialystok (north-eastern Poland, geographic coordinates: 53°08′07″ N 23°08′44″ E) was determined by the developed simplified model for different months of the year. Based on the results of the analysis, it was found that the energy obtained from the same area of concentrated solar collectors located near Bialystok is eight times lower compared to the location in Cordoba depending on the variant of the power plant operation. Full article

(This article belongs to the Special Issue Concentrating Solar Power Systems)

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21 pages, 8343 KiB

Open AccessArticle

Thermal Analysis of a Solar External Receiver Tube with a Novel Component of Guide Vanes

by Zecan Tu, Daniela Piccioni Koch, Nenad Sarunac, Martin Frank and Junkui Mao

Energies 2021, 14(8), 2253; https://0-doi-org.brum.beds.ac.uk/10.3390/en14082253 - 16 Apr 2021

Cited by 6 | Viewed by 1553

Abstract

The heat transfer performance of a solar external receiver tube with guide vanes was numerically studied under non-uniform heat flux conditions. Models of the smooth tube and the tube with guide vanes were built. The distributions of the temperature, velocity, turbulence intensity, and [...] Read more.

The heat transfer performance of a solar external receiver tube with guide vanes was numerically studied under non-uniform heat flux conditions. Models of the smooth tube and the tube with guide vanes were built. The distributions of the temperature, velocity, turbulence intensity, and Nu predicted by these two models were compared to investigate the heat transfer enhancement and the mixing effect of the guide vanes. The effect of the Re and the α on the heat transfer enhancement was also studied. The results show that the guide vanes form spiraling flows, reduce the maximum tube and molten salt temperatures, and improve the heat transfer. In addition, a more uniform temperature distribution is achieved compared to the smooth tube, allowing the molten salt to work safely under higher heat flux conditions in the receiver tube with guide vanes. It was observed that a larger Re enhances the heat transfer on the tube wall and achieves a longer effective distance of enhanced heat transfer in the downstream region, while the spiraling flow, the heat transfer enhancement, and the mixing are stronger for a larger α. Full article

(This article belongs to the Special Issue Concentrating Solar Power Systems)

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21 pages, 5557 KiB

Open AccessArticle

Reversible Molten Catalytic Methane Cracking Applied to Commercial Solar-Thermal Receivers

by Scott C. Rowe, Taylor A. Ariko, Kaylin M. Weiler, Jacob T. E. Spana and Alan W. Weimer

Energies 2020, 13(23), 6229; https://0-doi-org.brum.beds.ac.uk/10.3390/en13236229 - 26 Nov 2020

Cited by 3 | Viewed by 2563

Abstract

When driven by sunlight, molten catalytic methane cracking can produce clean hydrogen fuel from natural gas without greenhouse emissions. To design solar methane crackers, a canonical plug flow reactor model was developed that spanned industrially relevant temperatures and pressures (1150–1350 Kelvin and 2–200 [...] Read more.

When driven by sunlight, molten catalytic methane cracking can produce clean hydrogen fuel from natural gas without greenhouse emissions. To design solar methane crackers, a canonical plug flow reactor model was developed that spanned industrially relevant temperatures and pressures (1150–1350 Kelvin and 2–200 atmospheres). This model was then validated against published methane cracking data and used to screen power tower and beam-down reactor designs based on “Solar Two,” a renewables technology demonstrator from the 1990s. Overall, catalytic molten methane cracking is likely feasible in commercial beam-down solar reactors, but not power towers. The best beam-down reactor design was 9% efficient in the capture of sunlight as fungible hydrogen fuel, which approaches photovoltaic efficiencies. Conversely, the best discovered tower methane cracker was only 1.7% efficient. Thus, a beam-down reactor is likely tractable for solar methane cracking, whereas power tower configurations appear infeasible. However, the best simulated commercial reactors were heat transfer limited, not reaction limited. Efficiencies could be higher if heat bottlenecks are removed from solar methane cracker designs. This work sets benchmark conditions and performance for future solar reactor improvement via design innovation and multiphysics simulation. Full article

(This article belongs to the Special Issue Concentrating Solar Power Systems)

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24 pages, 13231 KiB

Open AccessArticle

Thermodynamic and Cost Analysis of a Solar Dish Power Plant in Spain Hybridized with a Micro-Gas Turbine

by Judit García-Ferrero, Irene Heras, María Jesús Santos, Rosa Pilar Merchán, Alejandro Medina, Antonio González and Antonio Calvo Hernández

Energies 2020, 13(19), 5178; https://0-doi-org.brum.beds.ac.uk/10.3390/en13195178 - 05 Oct 2020

Cited by 10 | Viewed by 2448

Abstract

Small-scale hybrid parabolic dish concentrated solar power systems are a promising option to obtain distributed electricity. During the day, solar energy is used to produce electricity, and the absence of sunlight can be overwhelmed with fuel combustion. This study presents a thermo-economic survey [...] Read more.

Small-scale hybrid parabolic dish concentrated solar power systems are a promising option to obtain distributed electricity. During the day, solar energy is used to produce electricity, and the absence of sunlight can be overwhelmed with fuel combustion. This study presents a thermo-economic survey for a hybridized power plant in different regions of Spain, considering the local climatic conditions. The developed model considers the instant solar irradiance and ambient temperature dynamically, providing an estimation of the power output, the associated fuel consumption, and the most relevant pollutant emissions linked to combustion. Hybrid and combustion-only operating modes at selected geographical locations in Spain (with different latitudes, mean solar irradiances, and meteorological conditions) are analyzed. The levelized cost of electricity indicator is estimated as a function of investment, interest rate, maintenance, and fuel consumption actual costs in Spain. Values of about 124 €/MWhe are feasible. Fuel consumption and emissions in hybrid operation can be reduced above 30% with respect to those of the same turbine working in a pure combustion mode. This model shows the potential of hybrid solar dishes to become cost-competitive against non-renewable technologies from the point of view of costs and reduction in gas emission levels in regions with high solar radiation and low water resources. Full article

(This article belongs to the Special Issue Concentrating Solar Power Systems)

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Review

Jump to: Research

26 pages, 3452 KiB

Open AccessReview

State-of-the-Art Measurement Instrumentation and Most Recent Measurement Techniques for Parabolic Trough Collector Fields

by Alex Brenner, Tobias Hirsch, Marc Röger and Robert Pitz-Paal

Energies 2021, 14(21), 7166; https://0-doi-org.brum.beds.ac.uk/10.3390/en14217166 - 01 Nov 2021

Cited by 1 | Viewed by 1448

Abstract

The presented review gives reliable information about the currently used measurement instrumentation in parabolic trough fields and recent monitoring approaches. The usually built-in measurement equipment in the solar field, clamp-on systems for flexible measurements of temperature and flow, solar irradiance measurements, standard meteorological [...] Read more.

The presented review gives reliable information about the currently used measurement instrumentation in parabolic trough fields and recent monitoring approaches. The usually built-in measurement equipment in the solar field, clamp-on systems for flexible measurements of temperature and flow, solar irradiance measurements, standard meteorological equipment, laboratory devices for heat transfer fluid analyses and instruments related to the tracking of solar collector assemblies are presented in detail. The measurement systems are reported with their measurement uncertainty, approximate costs and usual installation location for the built-in instrumentation. Specific findings related to the installation and operation of the measurement devices are presented. The usually installed instrumentation delivers a lot of measurements all over the field at the expense of measurement accuracy, compared to special test facility equipment. Recently introduced measurement approaches can improve the standard instrumentation in terms of accuracy, frequency, spatial distribution or can even extend the amount of measurands. The information about available measurands is the basis for future operation and maintenance solutions based on data-driven approaches. Full article

(This article belongs to the Special Issue Concentrating Solar Power Systems)

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