Solar Heat Storage Using Compressed Gas and Solid Beds
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Solution Overview
Problem
Conventional solar power plants face limitations in thermal efficiency due to the use of expensive, flammable, and temperature-limited heat transfer fluids, which restrict the maximum operating temperature and lead to operational issues such as solidification of molten salts at night, and existing storage methods have low efficiency and high energy losses.
Innovation Solution
A system using compressed, non-flammable gases like air or CO2 as the heat transfer medium, passed through a series of solar thermal collectors at high velocity, with heat storage in tanks filled with high-temperature resistant solids, allowing for efficient heat storage and recovery over a wide temperature range, up to 3000°F, and enabling flexible load scheduling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional heat transfer fluids (Dowtherm-like fluids or molten salts) are used in solar thermal collectors, then the system can operate at elevated temperatures, but the thermal efficiency is limited because these fluids cannot withstand temperatures above 800°F to 1050°F
Solution Approach 1:
The invention changes the fundamental parameter of the heat transfer medium from liquid (Dowtherm or molten salt) to compressed gas (air or CO2). This parameter change enables operation at temperatures up to 3000°F, dramatically increasing the thermal efficiency of the power plant while eliminating the temperature limitations of conventional fluids.
2Temperature
If molten salts are used for heat storage, then higher temperatures (up to 1050°F) can be accommodated, but the salts solidify as they cool at night requiring heat tracing and causing operational problems
Solution Approach 1:
The invention changes the phase parameter of the storage medium from liquid (molten salt) to solid (heat-resistant solid filling such as ceramic beads or rocks). This eliminates the solidification problem entirely since the solid filling remains stable across the operating temperature range, improving reliability without requiring heat tracing systems.
3Loss of energy
If a large number of solar thermal collectors are arranged in a row and gas is passed through them at high velocity, then the heat transfer coefficient increases and thermal efficiency improves, but the pressure drop through the system increases
Solution Approach 1:
The invention changes the pressure parameter by operating the compressed gas system at elevated pressures (e.g., 10-100 atm). This allows the gas to maintain high velocity through the collector train for improved heat transfer while the compression system compensates for pressure drops, enabling longer collector trains and higher overall efficiency.
4Loss of energy
If excess hot gas is passed through heat storage tanks filled with heat resistant solid filling, then heat can be stored efficiently with storage efficiency exceeding 90%, but the system complexity increases
Solution Approach 1:
The invention uses pneumatic flow of compressed gas through the solid filling beds for heat storage and retrieval. The gas flows through distributors at the ends of horizontal storage vessels, absorbing or releasing heat as it passes through the solid medium. This pneumatic approach achieves high storage efficiency with relatively simple equipment compared to liquid-based thermal storage systems.
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 solution enhances thermal efficiency, reduces energy losses, and allows for cost-effective operation at higher temperatures, providing a robust and efficient method for storing heat in solar power plants, capable of meeting variable electricity demands with high storage efficiency exceeding 90%.
Implementation Method 1
A large number of solar thermal collectors can be arranged in a row and the gas is passed through them at high velocity
Implementation Method 2
the heated gas from the solar thermal collectors is passed to the power plant
Implementation Method 3
Any excess hot gas not needed in the power plant is passed through one or more heat storage tanks that are filled with a heat resistant solid filling
Implementation Method 4
efficient heat storage, which is equivalent to storage of electricity
Implementation Method 5
The invention uses a compressed, preferably non-flammable gas, e.g., air or carbon dioxide (CO2), as the heat transfer medium
Implementation Method 6
the gas is passed through them at high velocity
Data Source
AI summary
A method for storing heat from a solar collector CSTC in Concentrating Solar Power plants and delivering the heat to the power plant PP when needed. The method uses a compressed gas such as carbon dioxide or air as a heat transfer medium in the collectors CSTC and transferring the heat by depositing it on a bed of heat-resistant solids and later, recovering the heat by a second circuit of the same compressed gas. The storage system HSS is designed to allow the heat to be recovered at a high efficiency with practically no reduction in temperature. Unlike liquid heat transfer media, our storage method itself can operate at very high temperatures, up to 3000° F., a capability which can lead to greater efficiency. Due to material constraints and cost considerations in the rest of the system the maximum temperature is presently limited to between 1700° F. and 2000° F. The method can be applied to all current solar collector designs. This Abstract is not intended to define the invention disclosed in the specification, nor intended to limit the scope of the invention in any way.