1. University of Colorado at Boulder Department of Electrical, Computer, and Energy Engineering Energy 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 303.492.8225

2. Acknowledgements Jonah Levine Michelle Lim Mohit Chhabra Brad Lutz Greg Martin Muhammad Awan Taha Harnesswala The work leading to this talk was conducted by 2 Richard Moutoux Camelia Bouf Kimberly Newman

3. 3 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 Systems

4. Obstacles to Integration of Wind and Solar Energy 1. 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 4

5. San Luis Valley Solar Data (09/11/2010) Good Day [1] 5

6. San Luis Valley Solar Data (09/12/2010) Bad Day [1] 6

7. Intermittent Wind Generation 7 7

8. Simplified System Model 8 Reference: [2]-[4] 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~1640

9. Input Data 9 S base = 600 MVA 11 th Jan 2011: 1 pm9 th June 2011: 1 pm

10. Frequency - Winter 10 No ESS ~0.35 ESS~0.20 ~32% wind penetration

11. Frequency - Summer 11 No ESS ~0.61 ESS~0.15 ~29% wind penetration

12. Power Spectrum [1] 12 278 hour s 27.8 hour s 2.78 hour s 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 hrs

13. 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

14. Matching Fossil Resources to the Net Loads In Colorado Generation Resource Type Rated Capacity [MW] Ramp Up [MW/hr] Ramp Down [MW/hr] Coal sub- total [i] [i] 2834322.58-630.27 Gas sub-total77537.70-65.75 Ramp per (MW/hr)/MW avg. NA.0998-.1926 Total3609360.28-695.02 Extrapolated Total 7,884 MW786.82-1,518.30

15. Xcel PSCo Load Duration Curve and Net Load Duration Curves Min Coal Generation 15

16. 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 SO 2, NO x and CO 2 for old plants It is expected to up to double the costs of maintenance. 16

17. Example of Wind Event and Response 17

18. Resulting Increase in SO 2, NO x 18

19. Emissions for Start Up, Ramping and Partial Loads IEEE Power systems Nov-Dec. 2013 19

20. Number of Ramps per Year 20

21. Cost of Increasing Wind Energy Penetration 21 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

22. Lower Bound on Cycling Costs IEEE Power Systems Nov-DEC 2013 22

23. Increasing Cost with Penetration of Wind Power 1 23

24. Approaches to Solving the Variability Issues. 1. At low penetration grid spinning reserves. 2. Gas fired generators 3. Storage a. Batteries, super capacitors, fly wheels b. Pumped Hydroelectric systems, CAES 4. Demand Response 5. Biomass, geothermal 24

25. Energy Storage Systems 25

26. Comparison of efficiency of several energy storage technologies NREL report 26

27. Pumped Hydro Raccoon Mountain 1 27

28. Pumped Hydro In Colorado 1 28

29. Potential Locations and Capacity for Pumped Hydro in Colorado 1 29

30. 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

31. Snapshot of Pumped Storage Globally Rick Miller HDR/DTA Pump Storage Units in Operation (MW) by Country/Continent Pumped Storage Projects Under Construction (MW)

33. ECEN 2060 Lecture 37 December 2, 2013 Compressed Air Energy Storage CAES 33

34. Compressed Air Storage 34

35. Compressed Air Energy Storage CAES Questions of Interest 1. Where can we locate CAES.? 2. Some Design Considerations 3. Value of Storage 4. When is it Cost Effective? 35

36. 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? 36

37. 37 Aerial view of Huntorf facility

38. 38 McIntosh facility – plant room

39. 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% 39

40. 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

41. 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. 41 Main components of underground CAES

42. 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

43. 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

44. 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 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. 44

45. Criteria for Site Selection 45 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.

46. Possible Geologies 1. Abandoned Natural Gas fields. 2. Old Mines 3. Dome Aquifers 4. Porous Sandstone 4. Salt Domes 5. Bedded Salt 46

47. 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

48. Salt Formations 48

49. Potential CAES Sites 49

50. Potential CAES In Colorado 50

51. Gas Well in The Denver Julesburg Basin 51

52. Neutron Porosity Log 52

53. Salt Beds In Pink 53

54. 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

55. Need for thermal management When 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 compression

56. Isothermal CAES 56 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%.

57. Recent developments in AA - CAES 57 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.

58. Lecture 38 ECEN 2060 December 4, 2013 58

59. 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). 59

60. Thermal Time Constants Thermal time constants vary with the surface to volume ratio. For a Sphere For a Cylinder For a cube For a rectangle 60

61. (Source: Geyer 1991) 61 Physical Properties of Sensible Storage Materials

62. 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 62

63. 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. 63

64. 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 64

65. Effect of cyclic loading on cavern 65 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

66. Effect of cyclic loading on Cavern 66 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 rock

67. 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. 67 Effect of cyclic loading on Cavern

68. System Integration 68 One of the suitable configurations to utilize the maximum available pressure

69. 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. 69

70. 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. 70

71. 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,TES. 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 71

72. Levelized Cost of Electricity CAES Options 72

73. LCOE as a function of depth 73

74. Batteries 1. Lead Acid 2. Metal Hydride 3. Li –Ion 4. Na S 5. Vanadium Redox –Flow 74

75. Lead-acidNaSLi-ion Vanadium redox Chemistry Anode Cathode Electrolyte Pb PbO 2 H 2 SO 4 Na S  -alumina C LiCoO 2 Organic solvent V 2+ ↔ V 3+ V 4+ ↔ V 5+ H 2 SO 4 Cell Voltage Open circuit Operating 2.1 2.0-1.8 2.1 2.0-1.8 4.1 4.0-3.0 1.2 Specific Energy & Energy density Wh/kg Wh/L 10-35 50-90 133-202 285-345 150 400 20-30 30 Discharge P rofile Flat Sloping Flat Specific Power W/kg Moderate 35-50 High 36-60 Moderate 80-130 High 110 Cycle life, cycles 200-7002500-45001000 12,000 Advantages Low cost, good high rate Potential low cost, h igh cycle life, h igh energy and good power density, h igh energy efficiency High specific energy and energy density, low self discharge, long cycle life High Energy, high efficiency, high charge rate, low replacement costs Limitations Limited energy density, Hydrogen evolution Thermal management, s afety, d urable seals, f reeze- thaw durability Lower rate (compared to aqueous system) Cross mixing of the electrolytes 75

76. NaS Battery. 76 NaS Battery Cell Diagram of electron and ion motion during discharge and charge cycles. (Courtesy of NGK)

77. NaS Batteries Twenty NaS Batteries installed in four enclosures 77

78. NaS Battery Costs Major cost components for an installed NaS-based DESS 78

79. Vanadium Redox Battery 79

80. Vanadium Redox Flow Battery

81. Vanadium Redox Battery FB10/100 Fluid, thermal, safety system. 81 1.Fluid lines 2.Positive electrolyte pumps 3.Positive electrolyte tank 4.Return lines 5.Negative electrolyte tank 6.Negative electrolyte pumps 7.Stacks (also called cell stacks or modules) 8.Rebalance valve. Source : html://www.cellstrom.com

82. 82 Capital Costs for Energy Storage

83. Life Cycle Costs of Storage

84. Mobile Battery and Supercapacitor Costs Capacity Price Energy Density 1. Lead Acid ≈ $215/KWh ≈ 25 Wh/Kg 2. NiM ≈ $3500/KWh ≈ 43 Wh/Kg 3. Li ion ≈ $1250/KWh ≈ 300 Wh/Kg 4. Supercapacitors ≈ 4 Wh/Kg 84

85. Energy Density for Batteries

86. When does Storage Pay ? 1. It depends on the details, however estimates are in the range of 15% wind energy penetration 2. Thermal Storage seems to pay almost always for large solar thermal systems. 86

87. Power Plant Transformer Substation The Regional Grid Pumped Hydro Transformer Substation Current Power Grid The Regional Grid 87

88. Transformer Substation The Regional Grid Pumped Hydro Transformer Substation Future Power Grid Wind Farm Solar Farm Communication & Control CAES Thermal Storage Power Plant The Regional Grid Batteries Solar Cells 88