Boulder Department of Electrical Computer and Energy Engineering Energy Storage Research Group Energy Storage and The Integration of Renewable Energy Into The Grid httpwwwcoloradoeduengineeringenergystorage ID: 530578
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University of Colorado at BoulderDepartment of Electrical, Computer, and Energy EngineeringEnergy Storage Research Group
Energy Storage and The Integration of Renewable Energy Into The Grid
http://www.colorado.edu/engineering/energystorage/
Frank
S
Barnes
frank.barnes@colorado.edu
303.492.8225Slide2
AcknowledgementsJonah Levine
Michelle LimMohit
ChhabraBrad Lutz
Greg Martin
Muhammad AwanTaha Harnesswala
The work leading to this talk was conducted by
2
Richard
Moutoux
Camelia
Bouf
Kimberly Newman Slide3
3 Outline of Our Work1. Potential Location of Pumped Hydroelectric Storage in Colorado2. Issues in Compressed Air Storage at 1500m in Eastern Colorado3. The use of battery storage for frequency control and voltage regulation4. Feed In Angle for Solar Power5. The Optimization of Energy Use in Water Systems. 6. Detection
of Power Theft7. Optimization of Energy Use in Water Systems Slide4
Obstacles to Integration of Wind and Solar Energy
The Variability of Wind, Solar and Hydroelectric Power and Mismatch to the Loads
The Integration and Control of a Large Number of Distributed Sources in to the Grid
Lack of low cost convenient energy storage systems
4Slide5
San Luis Valley Solar Data (09/11/2010) Good Day [1]5Slide6
San Luis Valley Solar Data (09/12/2010) Bad Day [1]
6Slide7
Intermittent Wind Generation7
7Slide8
Simplified System Model8Reference: [2]-[4]
frequency
S
base=
600 MVA
Network Electric System
Steam Generator
+
Wind Generators
+
Energy Storage System (ESS)
+
+
Load
-
Gas Generator
Load (4-hr)
Value (MWh)
Winter
~1500
Summer
~1640Slide9
Input Data9Sbase = 600 MVA11th Jan 2011: 1 pm
9
th June 2011: 1 pmSlide10
Frequency - Winter10
(Hz)No ESS
~0.35ESS
~0.20
No
ESS~0.35ESS
~0.20
~32% wind penetrationSlide11
Frequency - Summer11
(Hz)No ESS
~0.61ESS
~0.15
No
ESS~0.61ESS
~0.15
~29% wind penetrationSlide12
Power Spectrum [1]12
278 hours
27.8 hours
2.78 hours
16.7 min
100 sec
10 sec
2 sec
small magnitude:
turbine acts as
low-pass filter
Turbine upper limit
Energy Storage
Short-term
Short-term Storage Time Scale :
≈ 10 sec – 3 hrsSlide13
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
13Slide14
Matching Fossil Resources to the Net Loads In ColoradoGeneration Resource Type
Rated Capacity [MW]
Ramp Up [MW/hr]
Ramp Down [MW/hr]
Coal sub-total
[
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
Extrapolated Total
7,884 MW
786.82
-1,518.30Slide15
Xcel PSCo Load Duration Curve and Net Load Duration Curves
Min Coal Generation
15Slide16
Case When Wind Energy Exceeds Capacity. Current Law Requires use of Wind EnergyThe 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 plantsThis 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.
16Slide17
Example of Wind Event and Response17Slide18
Resulting Increase in SO2,NOx18Slide19
Emissions for Start Up, Ramping and Partial Loads IEEE Power systems Nov-Dec. 2013 19Slide20
Number of Ramps per Year20Slide21
Cost of Increasing Wind Energy Penetration21
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 gridSlide22
Lower Bound on Cycling Costs IEEE Power Systems Nov-DEC 201322Slide23
Increasing Cost with Penetration of Wind Power 123Slide24
Approaches to Solving the Variability Issues.At low penetration grid spinning reserves. Gas fired generatorsStorage Batteries, super capacitors, fly wheels
Pumped Hydroelectric systems, CAESDemand ResponseBiomass, geothermal
24Slide25
Energy Storage Systems25Slide26
Comparison of efficiency of several energy storage technologies NREL report
26Slide27
Pumped Hydro Raccoon Mountain127Slide28
Pumped Hydro In Colorado128Slide29
Potential Locations and Capacity for Pumped Hydro in Colorado129Slide30
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/CRPWindIntegrationStudy.pdf
30Slide31
Snapshot of Pumped Storage Globally Rick Miller HDR/DTA
Pump Storage Units in Operation (MW) by Country/Continent
Pumped Storage Projects
Under Construction (MW)Slide32Slide33
Compressed Air Storage33Slide34
Compressed Air Energy Storage CAESQuestions of InterestWhere can we locate CAES.?Some Design ConsiderationsValue of Storage When is it Cost Effective?
34Slide35
Current and Planned CAES Systems 1. Huntorf Germany 1978 290 MW for 2 to 3 hours per cycle2. 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?
35Slide36
36
Aerial view of Huntorf facilitySlide37
37
McIntosh facility – plant roomSlide38
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%
38Slide39
39Slide40
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 electricityThis gives an efficiency of 88%There are two types of CAES systems Underground CAES
Above ground CAES
40Slide41
Underground CEASPotential 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.
41
Main components of underground CAESSlide42
Challenges associated with Underground CAESIdentification 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.42Slide43
Deep CAESDeep 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,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.
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.
43Slide44
Challenges associated with Deep CAESDeep CAES brings in additional challenges, which areUtilizing the high pressure compressed air effectively.Most of the off-the-self gas turbines operate in the range of 70-100 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.
44Slide45
Criteria for Site Selection45 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. Slide46
Possible Geologies 1. Abandoned Natural Gas fields. 2. Old Mines 3. Dome Aquifers 4. Porous Sandstone 4. Salt Domes
5. Bedded Salt
46Slide47
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 leakageSalt deposits are widespread in many of the subsurface basins of the continental US, including western states (Colorado, West Texas, Utah, North Dakota, Kansas)
47Slide48
Salt Formations 48Slide49
Potential CAES Sites 49Slide50
Potential CAES In Colorado50Slide51
Gas Well in The Denver Julesburg Basin 51Slide52
Neutron Porosity Log52Slide53
Salt Beds In Pink53Slide54
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 54Slide55
Need for thermal managementWhen air is compressed - up to 85% of the energy supplied is lost in the from of heat.55
Even with isothermal compression 50% of the energy
may be lost
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.
Figure showing the fraction of work stored in compressed air Vs. the pressure. Rest dissipated as heat.
Polytrophic compressionSlide56
Isothermal CAES56Another 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%. Slide57
Recent developments in AA - CAES57
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.Slide58
Storing & Re-use of compression heatHeat of compression can be stored in two ways With the help of thermal energy storage facility By storing the heat in compressed air itselfThere are two options for utilizing the stored energyUsing the stored heat
+ Fuel for preheating the airOnly utilizing the stored heat (No Fuel)
also called as Advanced Adiabatic CAES (AA-CAES).
58Slide59
Thermal Time ConstantsThermal time constants vary with the surface to volume ratio. For a Sphere For a Cylinder For a cube For a rectangle59Slide60
(Source: Geyer 1991)
60
Physical Properties of Sensible Storage MaterialsSlide61
Major Cavern Design parametersCavern geometry & volumeDepth of the cavern – as the overburden pressure increases with depthCavern Minimum operating pressure – as inside pressure of the cavern acts as a static lining to the cavern contourCavern maximum operating pressure – must be fixed to avoid gas infiltration and cracking of the surrounding rock massCavern operation pattern Distance between adjoining caverns61Slide62
Cavern operating pressuresOperating pressure of the cavern depends on the,Depth of the cavernThe in-situ stresses in the surrounding rock formation.The maximum operating pressure of the above ground equipment.62Slide63
Effect of cyclic loading on cavernIncrease 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
63Slide64
Effect of cyclic loading on cavern64
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 Slide65
Effect of cyclic loading on Cavern65
Change in contours of the Huntorf Caverns between 1984 & 2001
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 rockSlide66
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 patternsEffect of having a deep cavern at atmospheric pressure for maintenance work.
66
Effect of cyclic loading on CavernSlide67
System Integration67One of the suitable configurations to utilize the maximum available pressureSlide68
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 Costs2. Value A. Smooth out wind fluctuations B. Match to transmission line limits. C. Match to loads increasing capacity factor.
68Slide69
Economics 2. ValueD. 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. 69Slide70
Economics Factors effecting CAES capital cost CAES site selection Depth of Cavern Local geology Proximity to transmission network Availability of Natural gas Presence of Thermal energy storage.Factors effecting CAES Operating cost
Cost of off peak energy and/or Wind energy generation cost.Natural gas requirement based on TES availability
70Slide71
Levelized Cost of Electricity CAES Options71Slide72
LCOE as a function of depth72