Thermo-Mechanical Energy Storage with Solid Heat Media
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Solution Overview
Problem
Existing energy storage systems using Brayton and Rankine cycles face inefficiencies due to low combined efficiency, second law losses, and variable heat capacity issues, particularly in gas compression and expansion processes, as well as external heat exchanger dependencies.
Innovation Solution
A thermo-mechanical energy storage system utilizing a closed loop with solid heat storage media, incorporating a reversible transcritical, trilateral, or Rankine thermodynamic cycle, which includes separate high and low pressure heat storage devices with a working fluid that adjusts to temperature variations, minimizing external losses and avoiding external heat exchangers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If Brayton cycle is used for energy storage, then extended temperature range is achieved, but combined efficiency is low due to two gas compression and two gas expansion processes
Solution Approach 1:
The system divides the heat storage process into two separate devices: a high-pressure heat storage device for high-temperature storage and a low-pressure heat storage device for low-temperature storage. This segmentation allows the working fluid to undergo only one gas compression and one gas expansion process per cycle, eliminating the inefficiency of dual compression/expansion processes while maintaining extended temperature range coverage.
2Power
If reversible Rankine cycle is used for energy storage, then mechanical energy storage is achieved, but second law losses occur due to superheat in charging mode and gradient preheating in discharging mode
Solution Approach 1:
The system changes the thermodynamic parameters by using a transcritical cycle instead of a conventional Rankine cycle. The working fluid undergoes isothermal heat exchange at constant temperature during phase change, eliminating superheat losses. The cycle operates between a high-pressure side and low-pressure side with the fluid transitioning between liquid, gas, and supercritical states, avoiding gradient preheating losses through optimized heat exchange processes.
3Use of energy by moving object
If transcritical cycle is used for energy storage, then efficient heat exchange is achieved, but losses occur due to variable heat capacity of working fluid versus constant heat capacity of storage fluid
Solution Approach 1:
The system employs dynamic adaptation where the working fluid's variable heat capacity is matched to the storage fluid's constant heat capacity through flow rate adjustments. The mass flow rate of the working fluid is dynamically controlled to compensate for heat capacity variations during different phases of the cycle, ensuring efficient heat exchange between the transcritical working fluid and the isothermal storage media in both high-pressure and low-pressure heat storage devices.
4Use of energy by moving object
If external heat exchangers are used in conventional systems, then heat transfer is achieved, but system complexity and external losses increase
Solution Approach 1:
The system merges the heat storage function directly into the cycle by using the working fluid itself as the heat transfer medium in integrated heat storage devices. The high-pressure and low-pressure heat storage devices contain the working fluid circulating through internal heat exchange pathways, eliminating the need for separate external heat exchangers and reducing system complexity while maintaining effective 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
The system achieves reduced second law losses, extended temperature range, and efficient compression and expansion processes, enabling effective storage and retrieval of mechanical energy as heat with small temperature differences between the working fluid and storage media.
Implementation Method 1
The working fluid transfers or exchanges heat with the solid heat storage material(s) occur along the pipes in the high and low pressure heat storage devices or sections
Implementation Method 2
storing and/or retrieving mechanical energy as heat
Implementation Method 3
The working fluid is in the liquid phase in the low pressure liquid connection and the high-pressure liquid connection, and in the gas phase in the high pressure gas connection and the low-pressure gas connection
Implementation Method 4
use both latent heat from the liquid air and sensible heat from the solid media
Implementation Method 5
use both latent heat from the liquid air and sensible heat from the solid media
Data Source
AI summary
Systems and methods for storing and retrieving thermo-mechanical energy are disclosed. The systems and methods generally include a thermodynamic loop or cycle (e.g., a reversible transcritical, trilateral, or Rankine/vapor compression cycle) that works as a heat pump in a charging mode and as a heat engine in a discharging mode. The thermodynamic loop or cycle includes a gas pressure changing device, a liquid pressure changing device, and a working fluid. The system further includes one or more heat storage devices with solid heat storage material(s). Heat is transferred between the working fluid and the solid heat storage material(s) in the high and low pressure sides of the thermodynamic cycle, respectively.