Power Generation from Renewable Energy Sources Fall 2013 Instructor: Xiaodong Chu ： Office Tel.:

1 Three Types of Storage Pumped hydroelectric storage (PHS) Compressed air energy storage (CAES) Flywheels

2 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.

3 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

4 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

5 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

6 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

Types Of CAES Adiabatic storage –Heat from compression is captured and stored in a solid or liquid –Hot Oil C –Molten Salt C –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

8 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 MW Plants

9 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

10 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

11 FlowAir After 35 mph only 1/2 the CO 2 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

12 Future of Air Vehicles Flowair- release in 2010 First needs to pass US safety ratings 6 seats 106 mpg mile range Top speed 96 mph $17500

13 Flywheels Captures energy in a rotating Mass Flywheel is charged using electric motor Electric generator extracts energy

14 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 1/2mv 2

15 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 C or F Diamagnetism- creates a field of opposition to a magnetic field Hybrid systems use conventional magnets to levitate and superconductors to stabilize

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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

19 Energy Stats Composite FlywheelLi-ion Battery Cycles100,000 to 10 millionAround 1200 Energy Density130 Wh/kg160 Wh/kg CapacityRange from 3 kWh to Max of 133 KWh Equal to 13, Li- ion Over 4 times what is used to power the Tesla Charge Time15 minSeveral Hours Self discharge time“0 run down time”- Years10-20 months Energy ExchangeLimited by generatorLimited by chemical process

Flywheels have High volumetric density

21 Flywheel Projects Gyrobuses- used in 1950s in Switzerland Buses run off of Flywheels Never gained economic foothold Low fuel costs compared to electricity

22 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