Carbon-Free, Site Independent Energy Storage for Grid Integration
D. Shively, Dr. J. Gardner, T. Haynes, Dr. J. Ferguson
Boise State University
Performance
Introduction
The inherent intermittency of the two fastest growing renewable energy sources, wind
and solar, presents a significant barrier to their widespread penetration and replacement
of fossil-fuel sourced electricity generation. These intermittencies range from short term
ramp events experienced by wind farms to the diurnal fluctuation of solar installations.
The goal of this research is to develop an energy storage technology that is capable of
meeting the challenges posed by renewable energy. This approach is similar to existing
Compressed Air Energy Storage but with two key differences: it avoids the requirement
of natural gas combustion that is mandatory in the traditional compressed air energy
storage systems and is not site specific. The proposed approach incorporates the most
attractive attributes from traditional CAES and pumped hydro energy storage systems
and eliminates some of their shortcomings. This system is not site-specific, does not
require natural gas, and has the potential to be very efficient.
Water discharge
reservoir
Water Turbine/
Electric
Generator
Air/Water
interface
Energy in, Energy out, and Efficiency as functions of alpha (ratio of initial to
final volume of air)
Compressed air storage
tanks (possibly tube trailers)
Compressor
One-Week Simulation
Artistic rendition of how the system may look.
Parameters:
Cycle
Four events are fundamental to the cycle
• Wind Power Input – anemometer data taken from site in southern Idaho
• Fourteen GE 1.5MW wind turbines = 21 MW
• Target compression pressure = 3000 psi
• Five 1MW pelton turbines for power output
20
Wind Power
Energy Storage Power Output
18
Fill
Existing Bulk Energy Storage
16
Power (MW)
14
Vent
Compressed
Pressurize
12
10
8
6
4
Air:
2
x Requires natural gas
x Site specific
0
0
1
2
3
4
5
6
7
Time (days)
Sinusoidal power output to approximate daily load curve
Extract
20
Wind Power
Energy Storage Power Output
18
16
Fill
Pumped Hydro:
x High capital cost
x Site specific
Power (MW)
14
The tank should be filled with water to an appropriate ratio of air to water:
V Initialvolumeof air
α= i =
Vf Finalvolumeof air
12
10
8
6
4
2
0
0
1
2
3
4
5
6
7
Time (days)
Constant power output
20
Wind Power
Seneca, PA
Energy Storage Power Output
18
16
Power (MW)
14
Proposed Energy Storage System
Dual Fluid Energy Storage:
Does NOT require natural gas
NOT site specific
High efficiency
12
10
8
6
4
2
Stored energy (normalized) as a function of alpha (ratio of initial to final volume of air).
Pressurize
0
0
1
2
3
4
5
6
7
Time (days)
Daily scheduled power output, such as to meet peak demand
Power is input to the compressor until the target pressure is reached
Extract
•Pressurized air exerts a spring-like force on the water; valve is opened allowing
water to drive an impulse turbine connected to a generator
•Power output from turbine controlled through variable diameter nozzle
Vent/Re-Fill
•After tank is empty of water, residual pressure (and thus energy) remains in the
tank
• If residual pressure is left in the tank, additional energy is required to pump
water back into tank
• Venting the residual pressure increases energy losses per cycle
• Using a two-tank venting algorithm, water can be moved back into the tank
while only venting a fraction of the residual energy
Mechanical diagram of energy storage system.
Further Research
• Investigate ways in which this system could benefit grid operators
• For desired power capacity, energy capacity, and time of storage, a
correctly sized system could be determined
• Applications and performance metrics can be adjusted to function in
various regions according to different grid requirements
• Investigate batch operation: multiple tanks within a correctly sized system
providing a continuous power output under variable input
• Determine how application, power capacity, and energy capacity influence
capital costs and payback periods