Energy Storage and The Integration of Renewable Energy
Into The Grid
University of Colorado at Boulder
Department of Electrical, Computer, and Energy Engineering
Energy Storage Research Group
Frank S Barnes
frank.barnes@colorado.edu
303.492.8225
http://www.colorado.edu/engineering/energystorage/
Acknowledgements
The work leading to this talk was conducted by
•
•
•
•
•
•
•
Jonah Levine
Michelle Lim
Mohit Chhabra
Brad Lutz
Greg Martin
Muhammad Awan
Taha Harnesswala
• Richard Moutoux
• Camelia Bouf
• Kimberly Newman
2
Outline of Our Work
1. Potential Location of Pumped
Hydroelectric Storage in Colorado
2. Issues in Compressed Air Storage at
1500m in Eastern Colorado
3. The use of battery storage for frequency
control and voltage regulation
4. Feed In Angle for Solar Power
5. The Optimization of Energy Use in Water
Systems.
6. Detection of Power Theft
7. Optimization of Energy Use in Water
3
Obstacles to Integration of
Wind and Solar Energy
The Variability of Wind, Solar and Hydroelectric
Power and Mismatch to the Loads
2. The Integration and Control of a Large Number of
Distributed Sources in to the Grid
3. Lack of low cost convenient energy storage systems
1.
4
San Luis Valley Solar Data (09/11/2010) Good Day [1]
5
San Luis Valley Solar Data (09/12/2010) Bad Day [1]
6
Intermittent Wind Generation
7
7
Simplified System Model
Steam
Generator
+
Gas Generator
Wind
Generators
Energy Storage
System (ESS)
Load
Reference: [2]-[4]
Δfrequency
Σ
+
-
+
Σ
+
Network
Electric
System
Sbase= 600 MVA
Load (4-hr)
Value
(MWh)
Winter
~1500
Summer
~1640
8
Input Data
Sbase = 600 MVA
11th Jan 2011: 1 pm
9th June 2011: 1 pm
Wind Power in the Summer
Wind Power in the Winter
0.6
0.6
Power(pu)
Power(pu)
0.5
0.4
0.3
0.2
0.1
0.2
0
50
100
150
200
250
50
100
150
200
Time (min)
Time (min)
Load Power in the Winter
Load Power in the Summer
250
0.7
0.665
Power(pu)
0.66
Power(pu)
0.4
0.655
0.65
0.645
0.68
0.66
0.64
0.64
0.62
50
100
150
Time (min)
200
250
50
100
150
200
250
Time (min)
9
Frequency - Winter
Frequency Variations
60.2
~32% wind penetration
60.1
∆𝒇𝒓𝒆𝒒 (Hz)
Freq (Hz)
60
59.9
No ESS
~0.35
ESS
~0.20
No ESS
ESS
59.8
59.7
59.6
0
50
100
150
200
250
Time (min)
10
Frequency - Summer
~29% wind penetration
Frequency Variations
60.6
60.5
∆𝒇𝒓𝒆𝒒 (Hz)
No ESS
ESS
60.4
No ESS
~0.61
ESS
~0.15
Freq (Hz)
60.3
60.2
60.1
60
59.9
59.8
59.7
59.6
0
50
100
150
Time (min)
200
250
11
Power Spectrum [1]
Turbine upper limit
small magnitude
turbine acts as
low-pass filter
Short-term
Short-term
Storage Time
Scale :
≈ 10 sec – 3
hrs
Energy Storage
278
hour
s
27.8
hour
s
2.78
hour
s
16.7
min
100
sec
10
sec
2
sec
12
References
[1] J. Apt, “The spectrum of power from wind turbines”, Journal of Power Sources, v.169,
March 2007
[2] G. Lalor, A. Mullane, M. O’Malley, "Frequency Control and Wind Turbine
Technologies“, IEEE Transactions on Power Systems, v. 20, no.4, November 2005
[3] R. Doherty et al, “An Assessment of the Impact of Wind Generation on System
Frequency Control", IEEE Transactions on Power Systems, v.25, no.11, February 2010
[4] P. Kundur, Power System Stability & Control, McGraw-Hill, 1994
13
Matching Fossil Resources
to the Net Loads In Colorado
Generation
Resource
Type
Rated Capacity
[MW]
Ramp Up
[MW/hr]
Ramp Down
[MW/hr]
Coal subtotal[i]
2834
322.58
-630.27
Gas sub-total
775
37.70
-65.75
Ramp per
(MW/hr)/MW
avg.
NA
.0998
-.1926
Total
3609
360.28
-695.02
7,884 MW
786.82
-1,518.30
Extrapolated
Total
0.20%
0.15%
0.10%
0.05%
Ramp Rate MW/hr
460
343
270
217
172
99
132
69
41
-5
19
-27
-50
-77
-109
-149
-193
-256
-341
-449
0.00%
-1120
Probability Density
.
Net Load: Load - RE, Ramp Rates
Xcel PSCo Load Duration Curve and Net Load Duration Curves
Min Coal
Generation
15
Case When Wind Energy Exceeds Capacity.
 Current Law Requires use of Wind Energy
 The wind energy may exceed the amount of gas fired
energy that can be shut off and require the reduction
of heat rate to coal fired plants
 This reduces electric power generation efficiency and
increase emissions of SO2, NOx and CO2 for old plants
 It is expected to up to double the costs of maintenance.
16
Example of Wind Event and Response
17
Resulting Increase in SO2,NOx
18
Emissions for Start Up, Ramping and Partial Loads
 IEEE Power systems Nov-Dec. 2013
19
Number of Ramps per Year
20
Cost of Increasing
Wind Energy Penetration
Gas Cost Impact of wind penetration with and without storage on Xcel’s electric grid
Cost Impact of increasing wind penetration on Xcel’s electric grid
21
Lower Bound on Cycling Costs
 IEEE Power Systems Nov-DEC 2013
22
Increasing Cost with Penetration of Wind Power
1
23
Approaches to Solving the Variability
Issues.
At low penetration grid spinning reserves.
Gas fired generators
Storage
1.
2.
3.
a.
b.
4.
5.
Batteries, super capacitors, fly wheels
Pumped Hydroelectric systems, CAES
Demand Response
Biomass, geothermal
24
Energy Storage Systems
25
Comparison of efficiency of several
energy storage technologies
NREL report
26
Pumped Hydro Raccoon Mountain
1
27
Pumped Hydro In Colorado
1
28
Potential Locations and Capacity for Pumped Hydro in Colorado
1
29
Pumped Hydro
Storage in Colorado
Wind Integration Study for Public Service
of Colorado Addendum Detailed Analysis
of 20% Wind Penetration
http://www.xcelenergy.com/SiteCollectionDocuments/docs/CRPWindInteg
rationStudy.pdf
30
Snapshot of Pumped Storage Globally Rick Miller HDR/DTA
Pump Storage Units in Operation
(MW)
by Country/Continent
45,000
40,000
Pumped Storage Projects
Under Construction (MW)
35,000
CHINA
30,000
JAPAN
SWITZERLAND
25,000
SOUTH AFRICA
20,000
RUSSIA
SPAIN
15,000
KOREA SOUTH
10,000
AUSTRIA
5,000
PORTUGAL
UNITED STATES
Europe
Asia w/o China & India
China
North America
India
Middle East & Africa
Russia & CIS
Latin America
Oceania
-
0
500
1000
1500
2000
2500
Compressed Air Storage
33
Compressed Air Energy Storage
CAES
Questions of Interest
Where can we locate CAES.?
2. Some Design Considerations
3. Value of Storage
4. When is it Cost Effective?
1.
34
Current and Planned CAES Systems
1. Huntorf Germany 1978
290 MW for 2 to 3 hours per cycle
2. McIntosh, Alabama
110 MW ,19 million cubic feet and 26 hours per charge
3. Others that have been under discussion for a long time
A. Iowa Stored Energy Park
B. Norton Ohio (2700 MW)
4. Others?
35
Aerial view of Huntorf facility
36
McIntosh facility – plant room
37
CAES Characteristics
1. It is a hybrid system with energy stored in compressed
air and need heat from another source as well.
2. Require 0.7 to 0.8 kWh off peak electrical energy and
4100 to 4500 Btu (1.2 -1.3 kWh) of natural gas for
1 kWh of dispatchable electricity
3. This compares with ~ 11,000 Btu/kWh for conventional
gas fired turbine generators.
4. Efficiency of electrical energy out to electrical plus
natural gas energy in ~ 50%
38
39
CAES Characteristics
 Another way to calculate efficiency is comparing to the
normal low efficiency of natural gas turbines with heat
rate of 11000 Btu/kWh yielding 0.39 kWh of electricity
and adding 0.75 kWh off peak electricity to get 1.14
kWh’s to get 1 kWh of dispatchable electricity
 This gives an efficiency of 88%
 There are two types of CAES systems
o
Underground CAES
o Above ground CAES
40
Underground CEAS
 Potential for large scale
energy storage –
100 to 300 MW for 10 – 20
hours.
 Effective in performing
load management, peak
shaving, regulation and
ramping duty.
 Less capital cost compared
to other large scale energy
storage options.
Main components of underground CAES
41
Challenges associated with Underground
CAES
 Identification of suitable site for setting up a
underground facility.
 Optimizing the compression process to reduce the
compression work required.
 Thermal management – efficiently extracting, storing
and reusing the available heat of compression, thus
improving the efficiency of the system.
 Understanding the effect of cyclic loading and
unloading on the structural integrity of the
underground cavern.
42
Deep CAES
 Deep compressed air energy storage is an underground
CAES facility where the cavern is formed at depths of
>4000 ft. as against 1000-2000 ft. in case of conventional
facilities.
 The main advantage of going deep are,
o Maximum permissible operating pressure of a cavern increases
with depth.
- A good approximation will be 0. 75 to 1.13 psi/ft. based on the local geology.
o Hence going deep helps store air at higher pressures in much
smaller cavern volume, hence higher energy density.
The possibility of setting up a deep compressed air energy storage facility
in Eastern Colorado is being currently investigated by Energy Storage
Research group at CU, Boulder.
43
Challenges associated with Deep CAES
Deep CAES brings in additional challenges, which are
 Utilizing the high pressure compressed air effectively.
Most of the off-the-self gas turbines operate in the range of 70100 bars, hence it is necessary to design the system such that high
pressures can be utilized.
 Understanding the effect of high pressure &
temperature on the cavern structure.
 Identifying suitable equipment's / material to operate at
high pressure .
 Potential for leakage through faults.
44
Criteria for Site Selection
1. Tight Cavern
2. Adequate natural gas
3. Ability to withstand 600 to 1200psi for conventional &
2000 – 5000 psi for deep CAES.
4. Proximity to Wind or Load to minimize transmission
line losses.
5. Appropriate geology
6. A report by Cohn et al. 1991 “Applications of air
saturation to integrated coal gasification/CAES
power plants. ASME 91-JPGC-GT-2 says that this
can be found in 85% of the US.
45
Possible Geologies
1. Abandoned Natural Gas fields.
2. Old Mines
3. Dome Aquifers
4. Porous Sandstone
4. Salt Domes
5. Bedded Salt
46
Why Salt Beds / Domes?
Salt beds are more desirable for setting up new Caverns
because of the following reasons,
 Easy to be solution mined
 Salt has good Elasto-plastic properties resulting in minimal
risk of air leakage
 Salt deposits are widespread in many of the subsurface
basins of the continental US, including western states
(Colorado, West Texas, Utah, North Dakota, Kansas)
47
Salt Formations
48
Potential CAES Sites
49
Potential CAES In Colorado
50
Gas Well in The Denver Julesburg Basin
51
Neutron Porosity Log
52
Salt Beds In Pink
53
Salt Beds In Eastern Colorado
 1. Salt beds from 4100 ft to 6,800 ft.
 2.Thickness from 3 to 292 ft.
 3. Required Operating pressures in the range of 4000
to 7000 psi.
 6 At about 6,000 psi we need about 14,400 cubic
meters per gigawatt hour energy storage or a cavern of
about 30 x22 x 22 meters
54
Need for thermal management
 When air is compressed - up to 85% of the energy
supplied is lost in the from of heat.
 Even with isothermal
Polytrophic compression
compression 50% of
the energy may be lost
as heat
Figure showing the fraction of
work stored in compressed air
Vs. the pressure. Rest
dissipated as heat.
 Storing and re-using the heat of compression would
result in increasing the overall efficiency of the CAES
system and result in reduced or no fuel consumption.
55
Isothermal CAES
• Another approach to keep the temperature constant during
compression is to slow down the pumping process (As it
results in efficient heat dissipation thus constant
temperature).
• Such a system can be used for small scale applications.
Isothermal CAES developed by SustainX
The SustainX system operates at 0 to 3000 Psi and provides 1 MW for
4 hours at an expected efficiency of 70%.
56
Recent developments in AA - CAES
RWE group, Germany in collaboration
with GE are developing an AA-CAES
project. (Started 2010)
They propose no fuel operation with a
target efficiency of 70%
Findings:
Feasibility study has shown that such high
efficiencies can be achieved by system
optimization and suitable equipment
development.
Challenges:
R&D is being carried out to develop
Turbomachinary & Thermal energy
storage to achieve the above goals.
57
Storing & Re-use of compression heat
 Heat of compression can be stored in two ways
o
With the help of thermal energy storage facility
o
By storing the heat in compressed air itself
 There are two options for utilizing the stored energy
o Using the stored heat + Fuel for preheating the air
o Only utilizing the stored heat (No Fuel) also called as
Advanced Adiabatic CAES (AA-CAES).
58
Thermal Time Constants
 Thermal time constants vary with the surface to
volume ratio.
2
r
 For a Sphere S  3

V r
4K

 For a Cylinder S  2( 1  1 )
V
 For a cube
r
h
S 6

V x
 For a rectangle
S
2 1
 2(  )
V
x h
59
Physical Properties of Sensible Storage Materials
(Source: Geyer 1991)
60
Major Cavern Design parameters
 Cavern geometry & volume
 Depth of the cavern – as the overburden pressure
increases with depth
 Cavern Minimum operating pressure – as inside
pressure of the cavern acts as a static lining to the
cavern contour
 Cavern maximum operating pressure – must be fixed
to avoid gas infiltration and cracking of the
surrounding rock mass
 Cavern operation pattern
 Distance between adjoining caverns
61
Cavern operating pressures
Operating pressure of the cavern depends on the,
• Depth of the cavern
• The in-situ stresses in the surrounding rock formation.
• The maximum operating pressure of the above ground
equipment.
62
Effect of cyclic loading on cavern
 Increase in cavern inside pressure causes increase in
deviatoric stresses, this in turn results in increase in creep
rate.
 Its has been found by laboratory experiments that the
overall creep rate decreases in case of cyclic loading, thus
resulting in reduced convergence – good for CAES. But the
stresses in the rock mass increases.
 Charging & discharging of cavern is associated with rise
and fall in temperature inside the cavern as well as the rock
surrounding it. Heating of rock salt creates thermal
induced compressive stresses, cooling of rock salt creates
thermal induced tensile stresses.
*Results of experiments conducted by University of Technology, Clausthal-Zellerfeld, Germany
63
Effect of cyclic loading on cavern
Transient effect of cyclic stresses on the salt cavern (cycle period – 5 days)
The graph shows the reducing creep rate & increase in
stress with time.
*Results of experiments conducted by University of Technology, Clausthal-Zellerfeld, Germany
64
Effect of cyclic loading on Cavern
Survey of the Huntorf cavern contour
conducted in 1984 & 2001 show
negligible convergence of the cavern in
spite of continuous cyclic operation.
Visualization of thermally induced cracks in salt rock
Change in contours of the Huntorf Caverns
between 1984 & 2001
65
Effect of cyclic loading on Cavern
Further work needed:
• Understanding the thermo-mechanical effects
(convergence & creep) on surround rock at high
pressures & temperature.
• Effect of different charging and discharging periods /
operation patterns
• Effect of having a deep cavern at atmospheric pressure
for maintenance work.
66
System Integration
One of the suitable configurations to utilize the maximum available
pressure
67
Economics
1. Costs
A. A little more than conventional gas fired generators at
$4oo to $500/kW
B. CAES estimates at $600 to $700/kW (Note these
numbers could be low depending on the site etc)
C. Low Operating Costs
2. Value
A. Smooth out wind fluctuations
B. Match to transmission line limits.
C. Match to loads increasing capacity factor.
68
Economics
2. Value
D. Absorb Energy when the wind power exceeds
transmission or load. This is in contrast to gas fired
generators
E. Arbitrage , buy wind or other energy low and sell high.
F. Ancillary services , frequency control, black start etc.
G. Reduced natural gas consumption by approximately
two thirds.
69
Economics
 Factors effecting CAES capital cost
o CAES site selection
Depth of Cavern
Local geology
Proximity to transmission network
Availability of Natural gas
o
Presence of Thermal energy storage.
 Factors effecting CAES Operating cost
o Cost of off peak energy and/or Wind energy generation
cost.
o Natural gas requirement based on TES availability
70
Levelized Cost of Electricity CAES Options
71
LCOE as a function of depth
72