Section VII Energy Storage

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Section VIIEnergy Storage
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Wind is Intermittent

• Because wind energy production is not stable over
  time and is not accurately predictable, some wind
  farms utilize energy storage systems to help
  regulate power flow.
• These are generally expensive and only used when
  necessary for the application.

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Energy Density by Volume of Some Materials
(Wh/cm3)

• Hydrogen
• Liquid or 800 bar 2.6
• Compressed 150 bar 0.405
• STP 0.003
• Diesel 10.7
• Gasoline 9.7
• Ethanol 6.8
• Methanol 4.6
• Natural Gas (Methane)
• LNG 7.22
• Compressed 250 bar 3.10
• STP 0.011
• Li-Ion Batteries 0.20
• NiMH Batteries 0.28
• Lead/Acid Batteries 0.04

1 bar 100 kPa 0.98692 atm
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Energy Density by Mass of Some Materials (kWh/kg)

• Hydrogen 38
• Diesel 12.7
• Gasoline 12.2
• Natural Gas (Methane) 12.1
• Ethanol 7.89
• Methanol 6.4
• Compressed Air 2 (per m3)
• Pumped hydro storage 0.3 (per m3)
• Flywheel, Carbon Fiber 0.2
• Flywheel, Fused Silica 0.9
• Li-Ion Batteries 0.15
• NiMH Batteries 0.10
• Lead Acid Batteries 0.025

This has little relevance for gaseous materials
because of storage volume issues!
1 kWh 3.6 J 0.8598 cal
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Energy Storage Technologies

• Pumped Hydro (water)
• Compressed Air
• Batteries
• Alternatives in the future may include
• Hydrogen production operating electrolyzers to
  split water

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Pumped Hydro
This is the most economical way to store massive
amounts of energy for production of electricity.
The USA has 19.5 GW capacity of pumped storage.
Lake holds 27 billion gallons of water

• The worlds largest hydro-storage facility at
  Ludington, Michigan, uses Lake Michigan as the
  lower reservoir and an artificial lake 100m
  higher as the upper reservoir. The plant can
  deliver 2,000 MW at full power and can store
  15,000 MWh (54 TJ) of energy.

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Wind Energy Storage

• Smooth wind speed variations into a constant
  power output system.

165.6 MW Nysted, Denmark Offshore Wind Farm using
72 turbines.
Source In store for the future? Interconnection
and energy storage for offshore wind farms, J.
Enslin and P. Bauer, Renewable Energy World,
Jan-Feb, 2004.
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Power Grid Storage

• Flow Battery Systems
• Vanadium flow battery in lieu of upgrades to a
  190-kilometer transmission line in Castle Valley,
  Utah
• Sodium bromide and sodium polysulfide to provide
  backup electricity in Little Barford, England.

3 Times the energy density of Lead-Acid Batteries
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Storage No Good Solution

• Pumped hydro and underground compressed air are
  limited by the specific geography and geology of
  an area (e.g. whether there is a large body of
  water available to pump or the rock formation
  allows air to be pumped and compressed)
• Batteries are relatively expensive to maintain
  and have limited life.

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Exercise 13

• 1). High quality batteries are approximately
• never used in conjunction with power systems.
• inexpensive and have a long life
• 100 times less energy dense by mass (weight) than
  liquid fuels like gasoline.
• 50 times less energy dense by volume than liquid
  fuels like gasoline.
• C. and D.
• A. and C.
• B. and D.

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Exercise 13

• 2). The two best options for large-scale energy
  storage are
• batteries and flywheels
• compressed air and pumped hydro
• pumped hydro and batteries
• compressed air and batteries