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SDSU Combustion and Solar Energy Laboratory
Energy Storage
November 12th, 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 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
•! Pumped Hydro
•! Thermal
•! Batteries
•! Compressed Air
•! Molten Salt
•! Flywheels 9
www.storagealliance.org
Current as of April 2010
SDSU Combustion and Solar Energy Laboratory
Pumped Hydro
•! 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
http://www.tva.gov/power/pumpstorart.htm
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
•! Andasol – Trough in Granada, Spain
•! Nevada Solar One – Trough in Nevada
•! Exteresol I – Trough in Spain
•! La Florida – Trough in Spain
•! 10MW – 3hrs
•! 2x50MW – 7.5hrs
•! 64MW – 30mins
•! 50MW – 7.5hrs
•! 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
17
www.electricitystorage.org
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)
19
www.caliso.com
•! Electricity is used to
compress air into large
storage tanks or
underground caverns
•! Compressed air spins
turbines when energy
is needed
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
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