Handbook of Energy Storage for Transmission or ... - W2agz.com

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as a base-load combustion turbine and, when necessary, to operate at increased power during
peak hours to supply intermediate/maximum peak power as needed. This plant concept is
particularly well suited for distributed power generation applications. At present, the only hybrid
plant configuration developed is based on the Rolls Royce Allison Company’s KM7 combustion
turbine [13]. As such, the following is a brief description of the major operating modes of the
hybrid concept sized using the KM7 turbine:
• Base load operation – The plant is operated as a conventional combustion turbine with 100%
of the expander flow provided by the compressor. The turbine supplies a net power output of
4.8 MW e at 11,700 Btu/kWh.
• Intermediate peak load operation -- The expander flow and power are increased because the
expander receives compressed air flow from the storage reservoir in addition to the full
airflow from the main compressor. It is estimated that, when 20% additional airflow comes
from the storage reservoir, the net output power will be 7.9 MW e for 3 hours at 8,300
Btu/kWh.
• Maximum peak load operation -- The compressor is disengaged, and the full flow of the
compressed air from the storage reservoir goes into the expander. The power output is
approximately 16 MW e at a heat rate of approximately 4,000 Btu/kWh.
• Storage-charging mode of operation --The off-peak power feeds both the motor-driven main
compressor and the separate motor-driven boost compressor. For the KM7, 12.2 MW e of
off-peak power is required to drive the compressors.
• Self-charging operation -- 78% of the main compressor’s flow is sent to the expander to
generate electric power to drive the booster compressor to fill the storage reservoir. This
requires about 3.5 hours of charging time, with no power going to or from the grid.
• Synchronous condenser mode of operation – By opening the clutch between the compressor
and the motor/generator, and between the expander and the motor/generator, the
motor/generator is synchronized to the grid and is operated as a synchronous condenser,
providing power factor correction. In this mode, the motor/generator works to stabilize line
voltage and frequency, ease grid power transitions, and provides reactive power to assist in
providing high quality electrical power to the grid.
Key Features and Limitations
The key features of compressed air energy storage offer several advantages over alternative
energy storage technologies.
• The CAES plant is the only technology that can provide significant energy storage (in the
thousands of MWhs) at relatively low costs (approximately $400 to $500/kW e ). The plant
has practically unlimited flexibility for providing significant load management at the utility
or regional levels.
• Commercial turboexpander units range in size from 10 MW e (Rolls Royce-Allison) to 135
MW e (Dresser-Rand) to 300-400 MW e (Alstom).
Compressed Air Energy Storage (CAES) Page 10