Cyclic operation of molten-salt thermal energy storage in thermoclines for solar power plants

Yang, Zhen; Garimella, Suresh V.

doi:10.1016/j.apenergy.2012.09.043

Cited by 104 publications

(45 citation statements)

References 24 publications

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“…Figure 6 illustrates this deconstruction with a plot of molten-salt temperature profile inside the case 5 porous bed during a charge process. Below the solidus temperature, the salt exhibits a sigmoid-shaped temperature profile typical of quartzite-filled thermocline tanks [25,26]. Above this point, the salt exhibits a delayed step increase in temperature, corresponding to the slower travel rate of the melt front.…”

Section: Heat-exchange Regionmentioning

confidence: 99%

Latent heat augmentation of thermocline energy storage for concentrating solar power – A system-level assessment

Flueckiger¹,

Garimella²

2014

Applied Energy

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Molten-salt thermocline tanks are a low-cost energy storage option for concentrating solar power plants. Despite the potential economic advantage, the capacity of thermocline tanks to store sufficient amounts of high-temperature heat is limited by the low energy density of the constituent sensible-heat storage media. A promising design modification replaces conventional rock filler inside the tank with an encapsulated phase-change material (PCM), contributing a latent heat storage mechanism to increase the overall energy density. The current study presents a new finite-volume approach to simulate mass and energy transport inside a latent heat thermocline tank at low computational cost. This storage model is then integrated into a systemlevel model of a molten-salt power tower plant to inform tank operation with respect to realistic solar collection and power production. With this system model, PCMs with different melting temperatures and heats of fusion are evaluated for their viability in latent heat storage for solar plants.Thermocline tanks filled with a single PCM do not yield a substantial increase in annual storage or plant output over a conventional rock-filled tank of equal size. As the melting temperature and heat of fusion are increased, the ability of the PCM to support steam generation improves but the corresponding ability of the thermocline tank to utilize this available latent heat decreases. This trend results from an inherent deconstruction of the heat-exchange region inside the tank between sensible and latent heat transfer, preventing effective use of the added phase change for daily plant operations. This problem can be circumvented with a cascaded filler structure composed of multiple PCMs with their melting temperatures tuned along the tank height. However, storage benefits with these cascaded tank structures are shown to be highly sensitive to the proper selection of the PCM melting points relative to the thermocline tank operating temperatures.3

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Section: Heat-exchange Regionmentioning

confidence: 99%

Latent heat augmentation of thermocline energy storage for concentrating solar power – A system-level assessment

Flueckiger¹,

Garimella²

2014

Applied Energy

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“…Flueckiger et al recently investigated thermal ratcheting via a computational fluid dynamics (CFD) 1 simulation of a thermocline storage volume enclosed with a composite wall [4]. Heat exchange in the dual-media fillerbed was resolved with a two-temperature approach in which the thermal transport in the porous bed and the molten salt is treated separately (and not as a homogeneous mixture), similar to previous investigations [5][6][7]. The composite wall design considered in Ref.…”

Section: Introductionmentioning

confidence: 86%

Thermomechanical Simulation of the Solar One Thermocline Storage Tank

Flueckiger

Yang

Garimella

2012

Journal of Solar Energy Engineering

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The growing interest in large-scale solar power production has led to a renewed exploration of thermal storage technologies. In a thermocline storage system, heat transfer fluid (HTF) from the collection field is simultaneously stored at both excited and dead thermal states inside a single tank by exploiting buoyancy forces. A granulated porous medium included in the tank provides additional thermal mass for storage and reduces the volume of HTF required. While the thermocline tank offers a low-cost storage option, thermal ratcheting of the tank wall (generated by reorientation of the granular material from continuous thermal cycling) poses a significant design concern. A comprehensive simulation of the 170 MWh t thermocline tank used in conjunction with the Solar One pilot plant is performed with a multidimensional two-temperature computational fluid dynamics model to investigate ratcheting potential. In operation from 1982 to 1986, this tank was subject to extensive instrumentation, including multiple strain gages along the tank wall to monitor hoop stress. Temperature profiles along the wall material are extracted from the simulation results to compute hoop stress via finite element models and compared with the original gage data. While the strain gages experienced large uncertainty, the maximum predicted hoop stress agrees to within 6.8% of the maximum stress recorded by the most reliable strain gages.

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“…The system operated during the night using the stored energy in the thermal storage. Assuming 19.7% of the energy is lost in the thermal storage due to the loss [6] and the remaining stored energy is operated the system during the night almost between 6:00 pm to 6:00 am. The solar field considered in this model comprised of 148 collectors which are single axis tracking and aligned on a north-south line.…”

Section: Thermal Analysismentioning

confidence: 99%

“…Thermal storage system is considered one main advantage of concentrating solar power technology over other technologies such as photovoltaic. The thermocline molten salt/filler storage [6] is used as thermal storage in this model. The local climatic conditions found in Derna (Libya) were taken into account.…”

Section: Introductionmentioning

confidence: 99%

Exergy Modelling of an Organic Rankine Cycle Energized by Heat from Parabolic Trough Collector with Thermal Storage

Mathkor¹,

Agnew²,

Al-Weshahi³

et al. 2015

JOCET

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Abstract-A thermal assessment study of an Organic Rankine Cycle (ORC) energized by heat absorbed from a parabolic trough collectors (PTC) is presented in this paper. The IPSEpro software is used to model the system of ORC and PTC with thermal storage located in Derna, Libya. The system is examined using three modes of operation. They are low-solar radiation mode, high-solar radiation mode, and storage mode. The solar radiation is classified into low and high solar radiation according to times of the system operation during the day. Part of the absorbed solar energy by the collectors used to produce the power and the remaining energy is used to charge the thermal storage to operate the system during the storage mode in the night. The simulation results are used to assess the system performance using energy and exergy analysis. The study showed that PTC collector was the main contributor of the energy and exergy losses within the PTC system and the evaporator within in the ORC. At this specific weather conditions, the ORC was able to produce about 1.5 MW electrical power from the powered PTC heat with thermal storage during the day and night. Moreover, exergy efficiency of the overall system was 8.94%, 5.38% and 5.47% for low-solar radiation, high-solar radiation and storage mode respectively.Index Terms-Energy and exergy analysis, ORC, PTC, thermal storage.

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Cyclic operation of molten-salt thermal energy storage in thermoclines for solar power plants

Cited by 104 publications

References 24 publications

Latent heat augmentation of thermocline energy storage for concentrating solar power – A system-level assessment

Latent heat augmentation of thermocline energy storage for concentrating solar power – A system-level assessment

Thermomechanical Simulation of the Solar One Thermocline Storage Tank

Exergy Modelling of an Organic Rankine Cycle Energized by Heat from Parabolic Trough Collector with Thermal Storage

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