Development of a Molten-Salt Thermocline Thermal Storage System for Parabolic Trough Plants

2002 ◽  
Vol 124 (2) ◽  
pp. 153-159 ◽  
Author(s):  
James E. Pacheco ◽  
Steven K. Showalter ◽  
William J. Kolb
Keyword(s):  
Molten Salt ◽  
Thermal Gradient ◽  
Power Plants ◽  
Low Cost ◽  
Storage System ◽  
Thermal Storage ◽  
Pilot Scale ◽  
Heat Transfer Fluid ◽  
Parabolic Trough ◽  
Molten Salt System

Thermal storage improves the dispatchability and marketability of parabolic trough power plants allowing them to produce electricity on demand independent of solar collection. One such thermal storage system, a thermocline, uses a single tank containing a fluid with a thermal gradient running vertically through the tank, where hotter fluid (lower density) is at the top of the tank and colder fluid is at the base of the tank. The thermal gradient separates the two temperature potentials. A low-cost filler material provides the bulk of the thermal capacitance of the thermal storage, prevents convective mixing, and reduces the amount of fluid required. In this paper, development of a thermocline system that uses molten-nitrate salt as the heat transfer fluid is described and compared to a two-tank molten salt system. Results of isothermal and thermal cycling tests on candidate materials and salt safety tests are presented as well as results from a small pilot-scale (2.3 MWh) thermocline.

Development of a Molten-Salt Thermocline Thermal Storage System for Parabolic Trough Plants

2001 ◽  
Author(s):  
James E. Pacheco ◽  
Steven K. Showalter ◽  
William J. Kolb
Keyword(s):  
Molten Salt ◽  
Thermal Gradient ◽  
Power Plants ◽  
Low Cost ◽  
Storage System ◽  
Thermal Storage ◽  
Pilot Scale ◽  
Heat Transfer Fluid ◽  
Parabolic Trough ◽  
Molten Salt System

Abstract Thermal storage improves the dispatchability and marketability of parabolic trough power plants allowing them to produce electricity on demand independent of solar collection. One such thermal storage system, a thermocline, uses a single tank containing a fluid with a thermal gradient running vertically through the tank, where hotter fluid (lower density) is at the top of the tank and colder fluid is at the base of the tank. The thermal gradient separates the two temperature potentials. A low-cost filler material provides the bulk of the thermal capacitance of the thermal storage, prevents convective mixing, and reduces the amount of fluid required. In this paper, development of a thermocline system that uses molten-nitrate salt as the heat transfer fluid is described and compared to a two-tank molten salt system. Results of isothermal and thermal cycling tests on candidate materials and salt safety tests are presented as well as results from a small pilot-scale (2.3 MWh) thermocline.

Comparison of Two-Tank Indirect Thermal Storage Designs for Solar Parabolic Trough Power Plants

2009 ◽  
Author(s):  
Joseph Kopp ◽  
R. F. Boehm
Keyword(s):  
Power Generation ◽  
Molten Salt ◽  
Heat Exchangers ◽  
Power Plants ◽  
Thermal Storage ◽  
Heat Transfer Fluid ◽  
Base Case ◽  
Parabolic Trough ◽  
Trade Offs ◽  
Solar Field

The performance of a solar thermal parabolic trough plant with thermal storage is dependent upon the arrangement of the heat exchangers that ultimately transfer energy from the sun into steam. An indirect two-tank molten salt storage system that only transfers heat with the solar field heat transfer fluid is the most commercially acceptable thermal storage design. Annual electricity generation from two differing indirect two-tank molten salt storage designs and a base case with no thermal storage were modeled. Four components were characterized in a quasi-steady state analysis dependent upon key ambient and operational parameters: solar field, storage, heat exchangers, and power block. The parameters for the collector field remained constant for all models and were based on the SEGS VI plant. The results of net power generation favor storage though the design that maximizes annual output depends on whether maximum power generation or power generation during the evening peak demand hours is desired. Additionally, the economic trade offs are discussed for the three arrangements.

Optimal Design of a Molten Salt Thermal Storage Tank for Parabolic Trough Solar Power Plants

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
R. Gabbrielli ◽  
C. Zamparelli
Keyword(s):  
Optimal Design ◽  
Molten Salt ◽  
Storage Tank ◽  
Power Plants ◽  
Storage System ◽  
Thermal Storage ◽  
Parabolic Trough ◽  
Investment Cost ◽  
Total Investment ◽  
Solar Power Plants

This paper presents an optimal design procedure for internally insulated, carbon steel, molten salt thermal storage tanks for parabolic trough solar power plants. The exact size of the vessel and insulation layers and the shape of the roof are optimized by minimizing the total investment cost of the storage system under three technical constraints: remaining within the maximum allowable values of both temperature and stress in the steel structure, and avoiding excessive cooling and consequent solidification of the molten salt during long periods of no solar input. The thermal, mechanical and economic aspects have been integrated into an iterative step-by-step optimization procedure, which is shown to be effective through application to the case study of a 600MWh thermal storage system. The optimal design turns out to be an internally insulated, carbon steel storage tank characterized by a maximum allowable height of 11m and a diameter of 22.4m. The total investment cost is about 20% lower than that of a corresponding AISI 321H stainless steel storage tank without internal protection or insulation.

Experimental Exploration of a Small Scale Pneumatically Pumped Thermal Storage System

2016 ◽  
Author(s):  
Inri Rodriguez ◽  
Jesus Cerda ◽  
Daniel S. Codd
Keyword(s):  
High Temperature ◽  
Storage Tank ◽  
Pulse Width Modulation ◽  
Low Cost ◽  
Storage System ◽  
Heat Engine ◽  
Thermal Storage ◽  
Heat Transfer Fluid ◽  
Small Scale ◽  
Constant Frequency

A prototype water-glycerol two tank storage system was designed to simulate the fluidic properties of a high temperature molten salt system while allowing for room temperature testing of a low cost, small scale pneumatically pumped thermal storage system for use in concentrated solar power (CSP) applications. Pressurized air is metered into a primary heat transfer fluid (HTF) storage tank; the airflow displaces the HTF through a 3D printed prototype thermoplate receiver and into a secondary storage tank to be dispatched in order to drive a heat engine during peak demand times. A microcontroller was programmed to use pulse-width modulation (PWM) to regulate air flow via an air solenoid. At a constant frequency of 10Hz, it was found that the lowest pressure drops and the slowest flowrates across the receiver occurred at low duty cycles of 15% and 20% and low inlet air pressures of 124 and 207 kPa. However, the data also suggested the possibility of slug flow. Replacement equipment and design modifications are suggested for further analysis and high temperature experiments. Nevertheless, testing demonstrated the feasibility of pneumatic pumping for small systems.

Assessment of a Molten Salt Heat Transfer Fluid in a Parabolic Trough Solar Field

2003 ◽  
Vol 125 (2) ◽  
pp. 170-176 ◽  
Author(s):  
D. Kearney ◽  
U. Herrmann ◽  
P. Nava ◽  
B. Kelly ◽  
R. Mahoney ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Molten Salt ◽  
Mojave Desert ◽  
Storage System ◽  
Eutectic Mixture ◽  
Heat Transfer Fluid ◽  
Diphenyl Oxide ◽  
Parabolic Trough ◽  
Electricity Cost ◽  
Solar Field

An evaluation was carried out to investigate the feasibility of utilizing a molten salt as the heat transfer fluid (HTF) and for thermal storage in a parabolic trough solar field to improve system performance and to reduce the levelized electricity cost. The operating SEGS (Solar Electric Generating Systems located in Mojave Desert, California) plants currently use a high temperature synthetic oil consisting of a eutectic mixture of biphenyl/diphenyl oxide. The scope of this investigation included examination of known critical issues, postulating solutions or possible approaches where potential problems exist, and the quantification of performance and electricity cost using preliminary cost inputs. The two leading candidates were the so-called solar salt (a binary salt consisting of 60% NaNO3 and 40% KNO3) and a salt sold commercially as HitecXL (a ternary salt consisting of 48% CaNO32, 7% NaNO3, and 45% KNO3). Assuming a two-tank storage system and a maximum operation temperature of 450°C, the evaluation showed that the levelized electricity cost can be reduced by 14.2% compared to a state-of-the-art parabolic trough plant such as the SEGS plants. If higher temperatures are possible, the improvement may be as high as 17.6%. Thermocline salt storage systems offer even greater benefits.

Experimental Study of a Novel Thermal Storage System Using Sands With High-Conductive Fluids Occupying the Pores

2014 ◽  
Author(s):  
Jingxiao Han ◽  
Ben Xu ◽  
Peiwen Li ◽  
Anurag Kumar ◽  
Yongping Yang
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Low Cost ◽  
Storage System ◽  
Solid Material ◽  
Thermal Storage ◽  
Heat Transfer Fluid ◽  
Large Capacity ◽  
Conductive Fluid ◽  
Media System

Because of the capability of large capacity thermal storage, concentrated solar power (CSP) technology is getting more attentions in the recent years. The energy storage allows power generation using solar energy during the late afternoon and evening time. For a large capacity of thermal energy storage, a dual-media system is typically adopted for reducing the use of the heat transfer fluid (HTF), which is usually expensive. In a dual-media system, the solid material must have large heat capacity and be inexpensive. One type of configuration for a dual-media system is that HTF flowing in pipes which are imbedded into the solid material. The present study considers sands, a major component of concrete, as low-cost solid thermal storage materials. The novel approach is that the sand is saturated with high thermal conductive fluid. Compared to using concrete for thermal storage, this method avoids issues of heat transfer degradation associated with the mismatch of thermal expansion of pipes and concrete. Since only sands are porous materials and the heat transfer performance is low, a high conductive fluid (XCELTHERM® 600 hot oil) was used to saturate sands, which then forms a new thermal storage material that can have better heat transfer. Results of thermal storage process with sands only and with the oil-saturated sands are presented and discussed.

scholarly journals Demonstration and analysis of a steam reforming process driven with solar heat using molten salts as heat transfer fluid

2022 ◽  
Vol 334 ◽  
pp. 01004
Author(s):  
Alberto Giaconia ◽  
Giampaolo Caputo ◽  
Primo Di Ascenzi ◽  
Giulia Monteleone ◽  
Luca Turchetti
Keyword(s):  
Heat Transfer ◽  
Molten Salt ◽  
Steam Reforming ◽  
Molten Salts ◽  
Experimental Validation ◽  
Low Cost ◽  
Water Electrolysis ◽  
Pilot Scale ◽  
Heat Transfer Fluid ◽  
Hydrogen Availability

Solar reforming of biogas or biomethane represents an example hydrogen production from the combination of renewable sources such as biomass and solar energy. Thanks to its relatively low-cost and flexibility, solar-reforming can represent a complementary source of hydrogen where/when the demand exceeds the green hydrogen availability from water electrolysis powered by PV or wind. Molten salts can be used as heat transfer fluid and heat storage medium in solar-driven steam reforming. The main units of the process have been developed at the pilot scale and experimentally tested in a molten salt experimental loop at ENEA-Casaccia research center: a molten salt heater and a molten salt membrane reformer. After experimental validation, techno-economic studies have been carried out to assess the solar reforming technology on commercial scale and exploitation opportunities have been analysed.

Survey of Thermal Energy Storage for Parabolic Trough Power Plants

2002 ◽  
Vol 124 (2) ◽  
pp. 145-152 ◽  
Author(s):  
Ulf Herrmann ◽  
David W. Kearney
Keyword(s):  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Power Plants ◽  
Storage Capacity ◽  
State Of The Art ◽  
Storage System ◽  
Heat Transfer Fluid ◽  
Parabolic Trough ◽  
Tank Storage

A literature review was carried out to critically evaluate the state of the art of thermal energy storage applied to parabolic trough power plants. This survey briefly describes the work done before 1990 followed by a more detailed discussion of later efforts. The most advanced system is a 2-tank-storage system where the heat transfer fluid (HTF) also serves as storage medium. This concept was successfully demonstrated in a commercial trough plant (13.8MWe SEGS I plant; 120MWht storage capacity) and a demonstration tower plant (10MWe Solar Two; 105MWht storage capacity). However, the HTF used in state-of-the-art parabolic trough power plants 30-80MWe is expensive, dramatically increasing the cost of larger HTF storage systems. Other promising storage concepts are under development, such as concrete storage, phase change material storage, and chemical storage. These concepts promise a considerable cost reduction compared to the direct 2-tank system, but some additional R&D is required before those systems can be used in commercial solar power plants. An interesting and likely cost-effective near-term option for thermal energy storage for parabolic trough power plants is the use of an indirect 2-tank-storage, where another (less expensive) liquid medium such as molten salt is utilized rather than the HTF itself.

scholarly journals High-Temperature Chloride-Carbonate Phase Change Material: Thermal Performances and Modelling of a Packed Bed Storage System for Concentrating Solar Power Plants

Energies ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5339
Author(s):  
Giovanni Salvatore Sau ◽  
Valerio Tripi ◽  
Anna Chiara Tizzoni ◽  
Raffaele Liberatore ◽  
Emiliana Mansi ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Heat Exchange ◽  
Phase Change ◽  
Power Plants ◽  
Solar Power ◽  
Storage System ◽  
Ternary Eutectic ◽  
Thermal Storage ◽  
Packed Bed ◽  
Heat Transfer Fluid

Molten salts eutectics are promising candidates as phase change materials (PCMs) for thermal storage applications, especially considering the possibility to store and release heat at high temperatures. Although many compounds have been proposed for this purpose in the scientific literature, very few data are available regarding actual applications. In particular, there is a lack of information concerning thermal storage at temperatures around 600 °C, necessary for the coupling with a highly efficient Rankine cycle powered by concentrated solar power (CSP) plants. In this contest, the present work deals with a thermophysical behavior investigation of a storage heat exchanger containing a cost-effective and safe ternary eutectic, consisting of sodium chloride, potassium chloride, and sodium carbonate. This material was preliminarily and properly selected and characterized to comply with the necessary melting temperature and latent enthalpy. Then, an indirect heat exchanger was considered for the simulation, assuming aluminum capsules to confine the PCM, thus obtaining the maximum possible heat exchange surface and air at 5 bar as heat transfer fluid (HTF). The modelling was carried out setting the inlet and outlet air temperatures at, respectively, 290 °C and 550 °C, obtaining a realistic storage efficiency of around 0.6. Finally, a conservative investment cost was estimated for the storage system, demonstrating a real possible economic benefit in using these types of materials and heat exchange geometries, with the results varying, according to possible manufacturing prices, in a range from 25 to 40 EUR/kWh.

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