ME 258
Johann Karkheck
• The ability to store energy has become a necessity due to the
intermittency of renewable energy sources that are gaining
presence on the grid.
• Various technologies exist to accommodate a wide variety of
storage needs.
• CAES is capable of high power output with long discharge
times.
• Issues with CAES
• Existing configurations are not very efficient
• 321 MW Huntorf, Germany ~ 42%
• 110 MW McIntosh, Alabama ~ 50%
• Storage Vessel
• Energy Losses
• Modeled each system
component separately to
achieve a modular
layout
• Analyze different CAES configurations to achieve maximum
efficiency
• Configuration 1 – Single-stage turbo machinery components with
polytropic processes
• Configuration 2 – Double-stage compression and heat exchangers
• Configuration 3 – Triple-stage compression and heat exchangers
• Configuration 4 – Single-stage turbo machinery w/isentropic
compression/expansion and ideal motor and generator
• Inter and after-cooling have the most detrimental effect on
system efficiency
• The highest efficiency, 52-62% depending on heating and
cooling load, is achieved in a two-stage adiabatic CAES
configuration
• If cooling is done via a natural source (i.e. river) an efficiency of
60% is realistic and would not require supplemental fuel
• The key element to improve efficiency is development of a high
temperature thermal storage (>600°C) and temperature
resistant compressor materials
• CAES can be implemented to
mitigate the intermittency of
renewable energy sources
• Thermal energy storage
coupled with CAES eliminates
the need for fossil fuel in
reheating
• Evaluate the effect of thermal
storage on the efficiency of
CAES using thermodynamic
modeling
• Initial parameters were used
to study the effect of thermal
storage on CAES
• Inlet temperature of
compressor and expander has
greatest effect on thermal and
power efficiency
• The ratio of high storage
pressure to the ambient
pressure effects all work and
heat transfer parameters
• Number of charge/discharge
cycles does not effect these
parameters
• Selection of appropriate
pressure limits can raise power
and thermal efficiency
• Charge and discharge processes induce
fluctuations in the pressure and
temperature within the storage cavern
• Predictions of these fluctuations are
required for proper cavern design and
selection of turbo-machinery
• Numerical and approximate analytical
solutions were used to model the T&P of
the air cavern
• Sensitivity analysis was conducted to
determine the dominant parameters that
affect the T&P fluctuations and the
required storage volume.
• Heat transfer through cavern walls
greatly effects T&P variations
• Preference should be given to
caverns with high rock effusivity
• Losses can be reduced through
reducing the injected air
temperature
• Longer durations of charge and
discharge can also aid in reducing
losses
• Numerical modeling was performed on coupled thermodynamic,
multiphase fluid flow and heat transfer associated with CAES in
lined rock caverns
• Using concrete lined caverns at a relatively shallow depth can
reduce construction and operational costs if air tightness and
stability can be assured
• Numerical modeling was
performed on coupled
thermodynamic,
multiphase fluid flow and
heat transfer associated
with CAES in lined rock
caverns
• Using concrete lined
caverns at a relatively
shallow depth can reduce
construction and
operational costs if air
tightness and stability can
be assured
• Models of both tight and
leaky caverns show that the
leakage rate increases over
time resulting in increasing gas
saturation of the lining and
cavern wall
• Leaky storage caverns
continue to diminish the
achievable storage pressure
over time
• Use of lined rock caverns at a shallow depth is only feasible if air
tightness and stability can be assured
• The key parameter to assure long term air tightness is the
permeability of the concrete and surrounding rock
• Increasing the moisture content of the lining can also decrease air
leakage
• Keeping the injection temperature close to the ambient cavern
temperature can nearly eliminate thermal losses through the cavern
walls
• To avoid the deterioration of the
cavern over time, configurations of a
constant pressure water-compensated
CAES system was studied
• The constant pressure system with a
compensating water column requires a
very deep air storage cavern to
produce the required pressure,
resulting in high construction costs
• Using a hydraulic pump rather than
elevation difference reduces
necessary storage depth, but the
pump consumes approximately 15%
of the generated power
• Coupled compressed air and
hydraulic storage tanks allow the
compressed air to remain at constant
pressure and energy to be produced
by both CAES and hydraulic storage
• System is independent of storage
depth
• Exergy loss of the air in
hydraulic storage during discharge
can be reduced by spraying water
into the air to achieve a quasiisothermal process
• Thermal storage improves CAES system efficiency and can
negate the need for supplemental fuel during expansion
• Research is needed to find high temperature (>600°C) thermal
storage and compressor materials
• Keeping the cavern inlet temperature near the storage
temperature reduces losses due to heat transfer
• Air tightness of storage cavern is essential to retain long term
system efficiency
• CAES coupled with hydraulic storage can make the depth of
the storage cavern irrelevant and improve start up time of
discharge cycle
1. The thermodynamic effect of thermal energy storage on compressed air energy storage system
Zhang, Yuan (Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China); Yang, Ke; Li,
Xuemei; Xu, Jianzhong Source: Renewable Energy, v 50, p 227-235, February 2013
Database: Compendex
2. Operating characteristics of constant-pressure compressed air energy storage (CAES) system combined with
pumped hydro storage based on energy and exergy analysis
Kim, Y.M. (ECO Machinery Division, Korea Institute of Machinery and Materials, 171 Jang-dong, Yuseong-gu, Daejeon
305-343, Korea, Republic of); Shin, D.G.; Favrat, D. Source: Energy, v 36, n 10, p 6220-6233, October 2011
Database: Compendex
3. Exploring the concept of compressed air energy storage (CAES) in lined rock caverns at shallow depth: A
modeling study of air tightness and energy balance
Kim, Hyung-Mok (Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon 305-350, Korea, Republic of);
Rutqvist, Jonny; Ryu, Dong-Woo; Choi, Byung-Hee; Sunwoo, Choon; Song, Won-Kyong Source: Applied Energy, v 92, p
653-667, April 2012
Database: Compendex
4. Temperature and pressure variations within compressed air energy storage caverns
Kushnir, R. (School of Mechanical Engineering, Tel Aviv University, Tel Aviv 69978, Israel); Dayan, A.; Ullmann, A. Source:
International Journal of Heat and Mass Transfer, v 55, n 21-22, p 5616-5630, October 2012
Database: Compendex
5. Simulation and analysis of different adiabatic Compressed Air Energy Storage plant configurations
Hartmann, Niklas (University of Stuttgart, Institute of Energy Economics and the Rational Use of Energy (IER), Hebrühlstr.
49a, 70565 Stuttgart, Germany); Vöhringer, O.; Kruck, C.; Eltrop, L. Source: Applied Energy, v 93, p 541-548, May 2012
Database: Compendex