Mechanical Energy Storage

Created by Nick Stroud

Three Types of Storage

• Pumped hydroelectric storage (PHS)

• Compressed air energy storage (CAES)

• Flywheels

Pumped Hydroelectric Storage (PHS)

• Used for load balancing of energy

• Water is pumped up in elevation during time of low demand

• Water flows back down during times of high demand

• Turbines recapture the energy.

Pumped Hydroelectric Storage (PHS)

• 70-85% of electrical energy is recovered

• Energy loss due to evaporation and Pump/generator inefficiency

• Currently the most cost effective way to store large amounts of electricity

• Low energy density calls for large bodies of water

• Never used in portable technology

• 1000 kg at 100 ft = .272 kWh

Pumps: On the Grid

• The Us has 19.5 gigawatts capacity

• 2.5% of baseload• Technology is in use world

wide• Hundreds of plants around

the world• Man made reservoirs as well

as natural reservoirs

Future Of PHS

• This energy storage can be used to level the grid for renewable energy

• Wind power and solar power are not constantly on

• Using salt mines to increase energy density

Compressed air energy storage (CAES)

• Large tank is buried underground

• During times of low demand electricity compresses air

• During times of peak demand compressed air is heated and released

http://www.sandia.gov/media/NewsRel/NR2001/norton.htm

Types Of CAES

• Adiabatic storage• Heat from compression is

captured and stored in a solid or liquid

• Hot Oil 3000C• Molten Salt 6000C• Heat is reincorporated

during release• Close to 100% efficiency• No utility scale plants

• Diabatic storage• Heat is lost through

cooling• Natural gas is burned to

reheat compressed air• Very inefficient 38-68%• Uses 1/2 gas of an all

gas plant

More about CAES

• Can use sandstone layer to hold compressed air

• USA has good ground for this type of storage

• Can be used to level load from wind and solar

• 200-300 MW Plants

Compressed air in Cars

• Zero pollution Motors • Stores air at around 300atm• Under 35 mph it is zero

emissions• Over 35 mph uses

combustion engine to compress air

• Runs on many different types of fuel

• 1 air tank + 8 gal gas= 848 miles

Fueling/Refueling

• Flex engine runs off of gas, diesel, alcohol, possibly even vegetable oil

• Refueling air tank at refuel station about 3 minutes

• Home refuel unit takes 4 hours, electrical cost $2

• 3 cents per mile

FlowAir

• After 35 mph only 1/2 the CO2 emissions of Prius

• Takes advantage of light engine and light frame to be efficient

• Uses fiberglass frame filled with foam

• May lose efficiency in cold weather

Future of Air Vehicles

• Flowair- release in 2010 • First needs to pass US

safety ratings• 6 seats• 106 mpg• 800-1000 mile range• Top speed 96 mph• $17500

Flywheels

• Captures energy in a rotating Mass

• Flywheel is charged using electric motor

• Electric generator extracts energy

http://en.wikipedia.org/wiki/Image:G2_front2.jpg#filehistory

Operation Of Flywheel

• Energy held in Spinning Rotor (Steel or Carbon composite)

• Steel rotors can spin at several thousand rpm

• Carbon composite spin up to 60k rpm

• Kinetic Energy 1/2mv2

http://www.aretepower.us/images/Composite%20Flywheel%20Rotor.jpg

Bearings

• Mechanical bearings not practical• Friction is directly

proportional to speed• Magnetic bearings used

to minimize friction• Rotor is suspended-

state of levitation• Operates in a Vacuum

Superconductors

• New technology uses high temperature superconductors (HTSC)

• HTSC operate at -1960C or -3210F• Diamagnetism- creates a field of opposition to a

magnetic field • Hybrid systems use conventional magnets to levitate

and superconductors to stabilize

Flywheels Vs. Batteries

• Not effected by temperature changes

• No Memory Effect• Made more

environmentally friendly• Easy energy content

identification

Pros

• Shattering due to overload

• Safety devices add lots of mass

• Gyroscope (duel FES systems)

Cons

Energy Stats

Composite Flywheel Li-ion Battery

Cycles 100,000 to 10 million Around 1200Energy Density 130 Wh/kg 160 Wh/kgCapacity Range from 3 kWh to

Max of 133 KWhEqual to 13,825 18650 Li-ionOver 4 times what is used to power the Tesla

Charge Time 15 min Several HoursSelf discharge time “0 run down time”- Years 10-20 months

Energy Exchange Limited by generator Limited by chemical process

•Flywheels have High volumetric density

Flywheel Projects

• Gyrobuses- used in 1950s in Switzerland

• Buses run off of Flywheels

• Never gained economic foothold

• Low fuel costs compared to electricity

Flywheel Projects

• Flywheels used in electric trains to carry over gaps and regenerative breaking

• Some car models tried (Rosen Motors)

• Formula 1 competition • Used on systems that need

Uninterrupted power supply. (maintenance 1/2 cost of battery)

• Testing of fuses

Sources

• http://photo.proaktiva.eu/digest/2008_gyrobus.html• http://eco-energy.info/asp/index.asp?uc=&k=3165• http://www1.eere.energy.gov/femp/pdfs/fta_flywheel.pdf• http://www.vyconenergy.com/pages/flywheeltech.htm• http://www.isepa.com/about_isep.asp• http://finance.yahoo.com/family-home/article/106040/Air-Cars:-

A-New-Wind-for-America's-Roads• http://gas2.org/2008/07/15/an-air-car-you-could-see-in-2009-

zpms-106-mpg-compressed-air-hybrid/ • http://zeropollutionmotors.us/