Energy Storage November 12 th , 2010 SDSU Energy Discussion Group Brian Gehring, Graduate Student Prof. Fletcher Miller, Advisor San Diego State University 1 SDSU Combustion and Solar Energy Laboratory
Overview • � Benefits of Storage • � Storage Technologies • � AB 2514 • � Future Research and Projects 2 SDSU Combustion and Solar Energy Laboratory
Benefits of Storage • � Forecasting of electricity demand is difficult • � Makes the electricity grid more flexible, efficient and reliable • � Production from renewables is sporadic and unpredictable • � Store energy at night when cost and demands are low • � Smarter grid with fewer new power plants • � Lowers capital costs for utilities by reducing annual peaking requirement – fewer peaker plants available 3 SDSU Combustion and Solar Energy Laboratory
Energy Forecasting • � When forecasts are low, peaker plants are put into operation to meet demand • � Peaker plants are less efficient and smaller plants are excluded from controlling emissions 4 SDSU Combustion and Solar Energy Laboratory
Energy Storage vs Peaker Plant 5 SDSU Combustion and Solar Energy Laboratory
Energy Forecasting • � When forecasts are high, plants ramp down their utilization rate • � Adjusting output lowers efficiency • � Stresses systems and decreases the lifespan of equipment 6 SDSU Combustion and Solar Energy Laboratory
Renewable Energy Storage • � Renewables produce intermittent output • � Renewable energy production time-shift to peak demand • � Power becomes dispatchable and more predictable 7 SDSU Combustion and Solar Energy Laboratory
Off peak storage • � Time shift of energy production • � Increased efficiency and utilization rate of baseload plants 8 SDSU Combustion and Solar Energy Laboratory
Storage Technologies www.storagealliance.org Current as of April 2010 • � Pumped Hydro • � Thermal • � Batteries • � Compressed Air • � Molten Salt • � Flywheels 9 SDSU Combustion and Solar Energy Laboratory
Pumped Hydro http://www.tva.gov/power/pumpstorart.htm • � Water is pumped uphill to a reservoir when demand is low, and allowed to run down through turbines when power is needed • � Most widely utilized energy storage technology • � 98% of total worldwide energy storage capacity • � Limited by existing reservoirs • � Recovers 75% of energy consumed • � High dispatchability, can come online in as little as 15 seconds 10 SDSU Combustion and Solar Energy Laboratory
Pumped Hydro • � SDG&E has contracted with San Diego Water Authority to build a pumped hydro project • � Will take advantage of 770 ft elevation difference between Olivenhain reservoir and Lake Hodges • � Will produce 40MW for 8-10 hours 11 SDSU Combustion and Solar Energy Laboratory
Thermal Storage • � Stored primarily as cooled fluid or ice produced at night to offset air conditioning electricity demand 12 SDSU Combustion and Solar Energy Laboratory
Molten Salt • � De-couples the production of solar energy from producing power • � 60 percent sodium nitrate and 40 percent potassium-nitrate • � Can store energy for up to a week • � Insulated tanks keep salt from freezing • � Studies by Sandia show that two tank storage system could have annual efficiencies as high as 99% 13 SDSU Combustion and Solar Energy Laboratory
Molten Salt • � Andasol solar power station in Spain consists of two 50 MW solar thermal trough plants utilizing molten salt storage • � Storage almost doubles operational hours per year • � Full thermal reservoir allows 7.5 hours of full load production • � Each plant has two tanks for molten salt storage measuring 14m in height and 36m in diameter 14 SDSU Combustion and Solar Energy Laboratory
Plants with Molten Salt Storage and Capacities • � Solar II – Power tower in Barstow, CA • � 10MW – 3hrs • � Andasol – Trough in Granada, Spain • � 2x50MW – 7.5hrs • � Nevada Solar One – Trough in Nevada • � 64MW – 30mins • � Exteresol I – Trough in Spain • � 50MW – 7.5hrs • � La Florida – Trough in Spain • � 50WM – 7.5hrs 15 SDSU Combustion and Solar Energy Laboratory
Steam Accumulator • � PS 10 solar thermal power tower in Spain • � Stores heated water in four pressurized tanks at 50 bar and 285°C • � The water evaporates and flashes back to steam when the pressure is lowered • � Storage capacity is 50% load operation for 50 minutes 16 SDSU Combustion and Solar Energy Laboratory
Batteries • � Electrical energy stored in chemical form • � Several different types of large scale batteries available www.electricitystorage.org 17 SDSU Combustion and Solar Energy Laboratory
Sodium-Sulfur Batteries • � Operating temperatures of 300-350°C • � 89-92% efficient • � Liquid sodium serves as the negative electrode and liquid sulfur serves as the positive electrode • � Currently 270 MW installed capacity in Japan, 9 MW in USA • � 7.2 MW installed to support 11 MW wind power farm in Minnesota • � Rubenius will install 1GW of NaS batteries in Mexicali, Mexico from single manufacturer - NGK Insulators 18 SDSU Combustion and Solar Energy Laboratory
Compressed Air Energy Storage (CAES) • � Electricity is used to compress air into large storage tanks or underground caverns • � Compressed air spins turbines when energy is needed www.caliso.com 19 SDSU Combustion and Solar Energy Laboratory
CAES • � Diabatic Storage • � Currently only one system in US -110 MW system in McIntosh, Al • � Dissipates heat with intercoolers • � Achieves 53% thermal efficiency • � Requires fuel • � Caverns created by solution mining, available in 85% of the United States 20 SDSU Combustion and Solar Energy Laboratory
Flywheels • � Convert electrical energy into kinetic energy and back again • � Good for power conditioning and short term storage • � Efficiency can be as high as 90% • � Typical capacities run from 3 kW to 133 kW 21 SDSU Combustion and Solar Energy Laboratory
Storage Costs • � CAES and Pumped Hydro � $5/kWh – � Depends on availability of geology • � Molten Salt - $50/kWh • � Batteries - $100-200/kWh • � Flywheels - $200-500/kWh 22 SDSU Combustion and Solar Energy Laboratory
AB 2514 • � Requires investor-owned and publicly owned utilities to procure new grid connected energy storage systems or the services of such systems with a minimum capacity of: – � 2.25% of peak load by 2014 – � 5% of peak load by 2020 • � California has 1500 MW of storage or <1% of peak load 23 SDSU Combustion and Solar Energy Laboratory
Future Research and Projects • � Vehicle-to-grid • � Phase Change Materials for Energy Storage • � Concentrating Solar Brayton CAES • � Advanced Adiabatic CAES • � Iowa Stored Energy Park 24 SDSU Combustion and Solar Energy Laboratory
Vehicle-to-Grid • � Uses plug in electric vehicles as an energy storage device • � Cars are parked 95% of the time • � Electricity could flow from the car to the power lines and back 25 SDSU Combustion and Solar Energy Laboratory
Phase Change Energy Storage • � Takes advantage of heat of fusion of materials • � Less heat transfer fluid needed, smaller storage tanks • � Smaller temperature change between charges • � Capable of storing large amounts of energy 26 SDSU Combustion and Solar Energy Laboratory
Concentrating Solar Brayton CAES • � Air is compressed into a salt mine cavity during the night • � During the day, the compressed air is sent to parabolic dishes and heated • � Expanded air drives a turbo-alternator • � Each compressor storage system will serve 30 dishes 27 SDSU Combustion and Solar Energy Laboratory
Advanced Adiabatic CAES – � Retains heat produced by compression – � Heat stored in a solid such as concrete or a liquid such as molten salt – � No utility scale plans to date, efficiency expected to approach 70% 28 SDSU Combustion and Solar Energy Laboratory
Iowa Stored Energy Park • � Will use energy stored from a large wind farm to compress air into an aquifer of sandstone capped by shale • � Storage will amount to a 20 week supply • � 270 MW of generating capacity • � Anticipated completion date of 2012 29 SDSU Combustion and Solar Energy Laboratory
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