Thermodynamic Analysis of High‐Temperature Energy Storage Concepts Based on Liquid Metal Technology

Abstract

Within the thermal energy storage (TES) initiative NAtional Demonstrator for IseNtropic Energy storage (NADINE), three projects have been conducted, each focusing on TES at different temperature levels. Herein, technical concepts for using liquid metal technology in innovative high‐temperature TES systems are dealt with. This approach implies some challenges; first, the unit costs are relatively large which makes a reduction of the mass inventory necessary. Second, the high thermal diffusivity, which is beneficial in any heat exchanger unit, reduces the efficiency in a single‐tank TES due to the fast degradation of the thermocline. These limitations can be overcome using a nonexpensive solid filler material, and, if properly designed, similar performance as in state‐of‐the‐art molten salt systems can be obtained, while maintaining the advantage of operating at temperatures well beyond their upper limit. Optimization strategies are presented for a reference case including transient behavior of the whole system. The sensitivity of multiple parameters, e.g., porosity, particle size, and influence of storage capacity regarding the discharge efficiency, is investigated.

Adoption of CO2 blended with C6F6 as working fluid in CSP plants

“…The higher LCOE for the high temperature ST plants is mainly due to the choice of a direct two-tank TES which implies the use of sodium also as storage fluid: the lower density and specific heat of sodium, together with its higher unit cost with respect to solar salts (2.00 $/kg vs 0.80 $/kg) implies higher TES cost (see Figure 6). The storage cost can be reduced using a single tank TES with thermocline and filler material [17] or by considering an indirect twotank storage using high temperature chloride solar salts as storage fluid. The selected storage size for the high temperature ST plants is thus the minimum within the considered range (7h), while for the for solar salts configuration is 8h; these results directly impact on the number of equivalent hours which are higher for the two low temperature cases.…”

A brief review of liquid heat transfer materials used in concentrated solar power systems and thermal energy storage devices of concentrated solar power systems

“…The technical and economic feasibilities of the hybrid power system were evaluated. Laube et al 95 studied the effects of several packing‐medium parameters on the operation performance of liquid LBE thermocline TES tank. Jiang et al 96 conducted a performance comparison of TES tanks using different HTMs, including the binary nitrate salt, ternary nitrate salt and liquid LBE.…”

A perspective on high‐temperature heat storage using liquid metal as heat transfer fluid

“…Liquid metal thermal energy storage systems are capable of storing heat with a wide temperature range and have, thus, been investigated for liquid metal-based CSP systems 3,4 and in the recent past also been proposed for industrial processes with high temperature process heat. 5 Up until now, only publications on theoretical and experimental investigations on individual storage concepts using liquid metals as heat transfer fluids have been published. This publication, by contrast, will give an overview of the state of the art of liquid-metal based heat storage and propose pathways to future advances and application fields.…”

“…As an alternative solution, liquid metal‐based heat storage systems are proposed. Liquid metal thermal energy storage systems are capable of storing heat with a wide temperature range and have, thus, been investigated for liquid metal‐based CSP systems 3,4 and in the recent past also been proposed for industrial processes with high temperature process heat 5 …”