Electric Car where the technology stands challenges examples
Lecture prepared with the able assistance of Eric Klem, TA in 2009
History
• 1834: First electric vehicle • 1859: Rechargeable lead‐acid batteries invented • 1890’s: Electric vehicles outnumbered other vehicles 10 to 1 • 1912: 38,842 EVs on road
Karen Endicott
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The Demise of the EV • 1910: First mass production of gasoline engines while EV’ss were still hand‐made while EV were still hand made
• 1913: First electric starter on a gasoline engine Until this point, many people could not hand‐start gasoline engines
• 1990’s: Renewed interest drops after a few years – Range issue Range issue
Energy Flow in an Electric Vehicle Coal Plants
Nuclear
Renewable Sources
Power Grid At fixed installations
Battery Charger
Onboard Vehicle
Batteries
Motor Controller Motor Controller
Electric Motor
Vehicle Driveline
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Power Source – The Electric Grid • Electric vehicles typically charge off the grid. • P Power plant and transmission efficiency need to be l t dt i i ffi i dt b considered.
or
Is the electric car: a Zero-Emission Vehicle or an Elsewhere-Emission Vehicle???
Solar Panels on an EV? • Typical power required to drive vehicle – 18kW
• Required area of solar panels – 1450ft2 (using Evergreen panels)
• This assumes ideal conditions – Sunny weather – Correct panel angle – No shading
• Panels are much more efficient at fixed sites.
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Chargers • There exists a wide variety of battery chargers on the market. th k t • Chargers are typically 90% efficient. • Most chargers are flexible and can take many different inputs (AC, DC, varied voltages).
www.manzanitamicro.com
Charging Limitations
• Battery bank holding 260 Ah at 120 V – 260 Ah x 120 V = 31.2 kWh capacity • Average household plug 120V, 15A – 120 V x 15 A = 1.8 kW • Charge Time – 31.2 kWh/1.8 kW = 17.33 hours – > 17 hours to recharge a totally depleted pack.
(Ah = amp x hour; 1 amp x 1 V = 1 W; 1000 Ah x 1 V = 1 kWh)
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Best‐Case Scenario • Use an outlet plug with 220V, 30A – 220 V x 30 A = 6.6 kW
• Time to charge – 31.2 kWh/6.6 kW = 4.73 hours • Note: Note: Charging at this rate is significantly less Charging at this rate is significantly less efficient and is not possible with all batteries.
Comparison with Internal Combustion Engine
Electric Vehicle Internal Combustion Engine
Charge Time
Driving Time
5 hours
2 hours
0.08 hours
7 hours
Conclusion: The electric vehicle (EV) has a major handicap.
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Energy Storage • Batteries • Ultra‐Capacitors
• Other – Hydrogen tank – Metal hydride
Controllers • Purpose = to provide to the electric motor an amount of power corresponding to the t f di t th driver’s input. • Many AC and DC controllers are available. • Efficiencies are high (~90%).
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Why an electric motor? Because the internal‐combustion engine is so bad…
(http p://www.fueleconomy.gov/feg/atv.shtml)
No idling 1.04% body skin 1 04% underfloor 1.04% & wheel wells 0.52% throughflow
Direct drive – No driveline losses If more efficient, this number smaller
A Comparison of Two Engines Internal‐combustion engine Only 33% efficient at best (needs a radiator) Air emissions Peaky torque‐rpm curve (needs a transmission) Power loss in idle Irreversible energy conversion Big and heavy (250 hp in 600 lbs = 0.7 kW/kg) Noisy
Electric motor 90‐95% efficient (no need for a radiator) Zero direct emissions Broad torque‐rpm curve (does not need a transmission) No idle Regenerative braking Small and light (75 kW in 13 kg = 5.8 kW/kg) Quiet
So, why don’t we have electric motors in our automobiles today? Because we do not have good enough batteries to store the electricity on board of the vehicle !
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Batteries: Important Considerations • Cost – Different technologies have different costs • NiMH (Nickel NiMH (Nickel – Metal Hydrides) cost an estimated $450/kWhr Metal Hydrides) cost an estimated $450/kWhr (= $14,040 for previous example)
• Weight – Lead acid batteries ~0.035 kWh/kg (31.2 kWh/0.035 kWh/kg = 891kg = 1,964 lbs for previous example)
• Discharge/Charge rate – Limits maximum power Limits maximum power – Limits minimum charging time
Li-polymer Nickel-Cadmium Nickel-metal hydride Sodium-Sulfur Zinc-Bromine Military
100
Super Capacitor Internal Combustion Engine
10
1 1
10
100 Energy Density (Wh/kg)
1000
10000
Compilation by Ryan Rosston ‘04
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Batteries: cont’d • Most common technology is Lead‐Acid – Cheap to purchase – Reliable and long lasting
• Most promising technology is Lithium‐Ion M t ii t h l i Lithi I – Considerably more expensive – Better power delivery
Lithium‐Ion Batteries • Developed by materials engineers • Development started in 1970’s‐80’s • 1991: Sony started commercial production. • Use a lithium anode • Use porous carbon at the cathode
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Li‐ion Battery Reactions At positive electrode (cathode): LiCoO2 ↔ Li1-xCoO2 + xLi+ + xe– At negative electrode (anode): 6C + xLi+ + xe– ↔ C6Lix Overall reaction: LiCoO2 + 6C ↔ Li1-xCoO2 + C6Lix → reaction is charging g g ← reaction is discharging • Danger of overcharging – Synthesis of cobalt oxide • Danger of overdischarging ‐ Creates lithium oxide
A123 Battery
• Most advanced commercial Li‐ion battery • Standard battery found in DeWalt cordless tools – Production just meets the DeWalt demand, making it hard to get these batteries • Uses nanophosphate electrode
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Ultra‐Capacitors Battery Comparison 100000
10000
•
Pros – Extremely quick energy delivery – Quick recharging Cons – Low energy density gy y – Takes up a lot of volume
Lead-acid
Specific Power (W/kg)
•
1000
Li-ion Li-polymer
100
Nickel-Cadmium
10
1 1
10
100 1000 Energy Density (Wh/kg)
10000
Example of a capacitor‐based vehicle
Doug Fraser
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Fuel Cells • Could replace batteries in electric vehicle – Hydrogen produces electricity onboard.
• Quick “recharge” possible – Hydrogen can be transferred relatively quickly.
• Technological/cost hurdles to be overcome
Example – Goals Assume: • Normal N l4 4-seatt car – Note: If an efficient car design is used, the vehicle will have a much improved range.
• Typical driving style • Ability to travel 400 miles per charge • Li-ion Li ion batteries Question: What is the required battery weight?
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400‐mile range EV Assume an energy density of 180 Wh per kg of batteries Non-battery weight of vehicle
1100
kg
B tt Battery weight i ht
1000
k kg
Total vehicle weight
2100
kg
Average power consumption
0.018
kW/kg
37.8
kW
40
mph
400
miles
10
hours
Energy needed on board
378
kWh
Energy available onboard
180
kWh
Power needed on board Average driving speed Desired range Driving time
Conclusion: Not possible with a 2200 lbs battery pack !
Try more batteries to see if that can do it… Assume an energy density of 180 Wh per kg of batteries Non-battery weight of vehicle
1100
kg
Battery weight
10000
kg
Total vehicle weight
11100
kg
Average power consumption
0.018
kW/kg
Power needed on board
199.8
kW
40
mph
400
miles
10
hours
Energy needed on board
1998
kWh
Energy available onboard
1800
kWh
Average driving speed Desired range Driving time
Even with 22,000lbs of batteries, it isn’t possible
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Now try a 200‐mile range EV Assume an energy density of 180 Wh per kg of batteries Non-battery weight of vehicle
1100
kg
Battery weight
1100
kg
Total vehicle weight
2200
kg
Average power consumption
0.018
KW/kg
Power needed onboard
39.6
kW
Average driving speed
40
mph
200
miles
5
hours
Energy needed onboard
198
kWh
Energy available onboard
198
kWh
Desired range Driving time
It’s now possible! However, it is quite expensive and heavy. To make this feasible, a more efficient car should be designed.
Tesla Roadster • Up to 244‐mile range 1000 lbs of Li‐ion ion batteries batteries • 1000 lbs of Li (energy equivalent of 8 liters gasoline) • Minimum recharge time = 4 hours • Aerodynamic body • Low rolling resistance tires • Composite body work • > $100,000
GM Volt • 161 horsepower Only 40‐mile mile range range • Only 40 (ok for 78% of trips) • Recharge time: 8 hours at 110V or 4 hrs at 220V y y • Aerodynamic body • Low rolling resistance tires
• $32,780
Areas for Future Improvement in EV’s • Batteries: Making lighter batteries that have hi h higher power outputs t t • Charging: Reducing recharge times • Vehicle efficiency: Other vehicle systems can be improved upon (true for all vehicles) • Aerodynamics, rolling resistance, weight Aerodynamics rolling resistance weight
