Intermediate Tank Layout for Thermoelectric Heat Storage Efficiency
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Solution Overview
Problem
Thermoelectric energy storage systems face limitations in round-trip efficiency due to thermodynamic irreversibilities, particularly in heat transfer over large temperature differences, leading to high capital costs and inefficiencies in existing solutions like large heat exchangers or phase change materials.
Innovation Solution
A thermoelectric energy storage system employing a transcritical process with a heat exchanger and thermal storage medium circuit that includes hot, intermediate, and cold storage tanks, where the flow rate of the thermal storage medium is modified to minimize temperature differences between the working fluid and thermal storage medium, using an internal stream splitter to optimize heat exchange during both charging and discharging cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If large heat exchangers are used to transfer heat over large temperature differences, then heat transfer capability is improved, but capital cost increases
Solution Approach 1:
The thermal storage system is divided into multiple temperature zones (hot, intermediate, cold storage tanks) rather than using a single large heat exchanger. This segmentation allows heat transfer to occur across smaller temperature differences in each zone, reducing the overall heat exchanger size and capital cost while maintaining heat transfer capability.
Solution Approach 2:
An intermediate temperature storage tank is introduced as a mediator between the hot and cold storage tanks. This intermediate zone facilitates heat transfer by breaking down the large temperature difference into smaller steps, thereby reducing the required heat exchanger area and capital investment.
2Quantity of substance
If phase change materials are used to store thermal energy, then energy density is improved, but system complexity and cost increase
Solution Approach 1:
The system uses sensible heat storage with fluid thermal storage media instead of phase change materials. By changing the storage parameter from latent heat (phase change) to sensible heat (temperature change), the system achieves sufficient energy density while avoiding the complexity associated with phase change material management, encapsulation, and heat transfer interfaces.
3Productivity
If heat transfer over large temperature differences is used to improve heat pump performance, then charging efficiency is improved, but thermodynamic reversibility decreases
Solution Approach 1:
The heat transfer process is segmented into multiple smaller temperature difference steps by using intermediate storage tanks. This allows the heat pump to operate with smaller temperature differences during each heat transfer step, improving thermodynamic reversibility and reducing energy losses while maintaining acceptable charging efficiency.
Solution Approach 2:
The system dynamically adjusts the flow rates of thermal storage medium in and out of the intermediate storage tank to optimize heat transfer. By varying flow rates based on operating conditions, the system balances charging efficiency with thermodynamic reversibility, minimizing energy losses during heat transfer.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances round-trip efficiency by reducing temperature differences and minimizing thermal storage medium requirements, thereby lowering capital costs and improving the system's overall energy conversion efficiency.
Implementation Method 1
heat transfer in the heat exchanger
Implementation Method 2
the working fluid undergoes a transcritical process during heat transfer in the heat exchanger
Implementation Method 3
Thermal energy can be stored in the form of sensible heat via a change in temperature
Data Source
AI summary
A system and method are provided for storing electric energy in the form of thermal energy. A thermoelectric energy storage system includes a working fluid circuit for circulating a working fluid through a heat exchanger, and a thermal storage medium circuit for circulating a thermal storage medium. The thermal storage medium circuit includes at least one hot storage tank, an intermediate temperature storage tank, and a cold storage tank connected together via the heat exchanger. A proportion of the storage medium is redirected to or from the intermediate storage tank from or to the hot or cold storage tank, joining another proportion which flows directly between the cold and hot storage tank.