compressed air, flywheels and batteries

Nabil Reza

Off-peak electricity is used to power a motor/generator that drives compressors to force air into an underground storage reservoir.

When the demand for electric power peaks, The compressed air is returned to the surface, and is fed into a gas turbine, allowing the turbine to produce electricity more efficiently.

Natural Gas is burned to preheat air. Storage reservoirs can be large underground

caverns, depleted wells, or aquifers.

CAES power plant system can achieve >85% reductions in fossil fuel use.

Can achieve over 80% reduction in CO2 output

Adiabatic Compressed-Air Energy Storage recovers the heat that emerges during air compression.

The stored thermal energy replaces the need for natural gas, causing the entire system to run on renewable power alone

http://www.youtube.com/watch?v=K4yJx5yTzO4

280 MW plant in Hunthorf, Germany - been active since 1978

110 MW plant at McIntosh, Alabama - operating since 1991

Insatallation cost - Depending on hours of storage, $750/kW to $1,200/kW.

Running cost at about 10.5 cents/kWh Diabatic storage efficiency is around 55% 70% for adiabatic CAES

CAES systems can be used on very large scales. CAES is ready to be used with entire power plants.

Fast start-up time – 9 min, compared to 20 min for conventional combustion turbine

Helps solving peak load crisis

A flywheel is a flat disk or cylinder that spins at very high speeds, storing kinetic energy.

When required, the flywheel then delivers rotational energy to power an electric generator until friction dissipates it.

http://www.youtube.com/watch?v=eCtlfj4kMJs

• Ef = (1/2) x I x ω2 whereEf = flywheel kinetic energy (Nm (Joule), ft lb)

I = moment of inertia (kg m2, lb ft2)ω = angular velocity (rad/s)• I = k x m x r2 wherek = inertial constantm = mass of flywheel (kg, lb)

r = radius (m, ft)        

Tensile strength - the stronger the disc, the faster it may be spun, and the more energy the system can store.

Energy storage efficiency - 50% for mechanical bearings, 85% for magnetic bearings

Beacon Power - 20 MW plant in Pennsylvania

Installation cost - around $1,500 per kilowatt

Little affected by temperature fluctuations, Take up relatively little space Have lower maintenance requirements than

batteries Very durable.

Storage devices that convert Chemical Energy to Electrical Energy

Batteries are made up of cells, containing a chemical called an electrolyte.

Each cell has two electrically conductive electrodes immersed into its electrolyte, one releases electrons into the electrolyte, and the other absorbs them.

When an electrical device is connected to the electrodes, an electrical current flows through it and provides electric power for its operation.

Lead-Acid Lithium-ion Lithium polymer Nickel metal hydride Sodium sulfur Flow Battery

Electrolyte is stored in external containers and circulated through the battery cell stack as required.

Flow batteries use two liquid electrolytes that react when pumped through a cell stack. The battery is broken down into a cell stack and two large electrolyte tanks.

As the electrolyte flows past a porous membrane in each cell, ions and electrons flow back and forth, charging or discharging the battery.

http://www.youtube.com/watch?v=0Uk0GQNgtqg

The active materials in a NaS battery are molten sulfur as the positive electrode and molten sodium as the negative.

The electrodes are separated by a solid ceramic, sodium - alumina, which also serves as the electrolyte.

During Charge and Discharge cycle, electrons flow from Na to S and vice versa through an external circuit.

Flow Batteries◦ 250 KW installation in Castle Valley, Utah

NaS Batteries◦ 4 MW installation for Texas Power Grid◦ 270 MW installation in Japan by Tokyo-based

NGK Insulators

Parameter Zn/Br VB NaS

Rated Output (MW) 10 10 10

Efficiency 0.6 0.75 0.77

Unit cost for power electronic ($/KW)

312.5 312.5 312.5

Unit cost for storage units ($/KWH)

350 750 400

Unit cost for balance of plant ($/KWH)

7 7 7

Fixed O & M Cost ($/KW)

6.26 6.26 6.26

Electricity storage can be deployed throughout an electric power system—functioning as generation, transmission, distribution, or end-use assets.

Sometimes placing the right storage technology at a key location can alleviate a supply shortage situation, relieve congestion, defer transmission additions or substation upgrades, or postpone the need for new capacity.

http://www.rwe.com/web/cms/en/183732/rwe/innovation/projects-technologies/energy-storage/compressed-air-energy-storage/

http://thinkprogress.org/climate/2009/08/31/204578/clean-energy-storage-wind-solar/?mobile=nc

http://www.pangeaexploration.com/compressed_air_energy_storage.htm http://www.dg.history.vt.edu/ch2/storage.html http://www.ngpowereu.com/article/flywheel-power-and-energy-storage/ http://www.greentechmedia.com/articles/read/beacon-powers-bankruptcy-

autopsy http://spectrum.ieee.org/energy/the-smarter-grid/batteries-that-go-with-the-flow http://www.electricitystorage.org/technology/storage_technologies/batteries/

soidum_sulfur_batteries/ http://www.eia.gov/todayinenergy/detail.cfm?id=6910#tabs_ElecStorage-1 http://www.nrel.gov/learning/eds_batteries.html http://www.nrel.gov/learning/eds_compressed_air.html http://www.nrel.gov/learning/eds_flywheels.html