Download Energy Storage

Energy Storage
(batteries)
Today we will discuss the most common form of
portable energy source: batteries. One of the most recent
and important applications of portable electrical energy
is in electric vehicles. In this lesson we will look at the
specifications for GM's IMPACT 3, also knows as EV1.
This started as GM's attempt to develop a future electric
Figure 1:
Equipment for Energy Storage
vehicle. Information on the EV1 was obtained from
GM's website for the vehicle. In 1997, GM attempted to
AA batteries (2)
market this as a commercial product in California. The
battery
holder
(with slots for 2 AA batteries)
price was in the $30,000 range, and the attempt to
copper wire
market it failed. The vehicle was discontinued after the
multimeter
1999 model.
resistors
stopwatch
Objectives [At the end of this lesson students will be able to...]
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describe the use of batteries as a portable source of electricity.
explain the practical limitations to the use of portable electricity.
Start-up questions
1.
2.
3.
4.
5.
What are the attractive features of using electric cars?
What are the problems with their usage?
How would you describe electric power? What unit would you use?
How would you describe electric energy? What unit would you use?
What is the relationship between power and energy?
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Energy Storage -- Page 1 of 5
Batteries: Portable Electricity Sources
Following are the relevant specifications for
the EV1. Although the EV1 is discontinued, both
Toyota (Prius) and Honda (Insight) are now
marketing hybrid gas-electric vehicles that can get
over 50 mpg of gasoline and do not require
external recharging.
EV1 Propulsion/Electronics
Power Rating: 102 kilowatts (137 horsepower) @ 7,000 rpm
Battery Packs:
Standard: 26 valve-regulated high-capacity lead-acid modules
Optional: 26 valve-regulated nickel-metal hydride modules
1 underhood accessory module
Rated Maximum Battery Pack Storage Capacity:
Standard: High-capacity lead-acid battery pack - 18.7 kW·hours/60 amp hours (312 volts)
Optional: Nickel-metal hydride battery pack - 26.4 kW·hours/77 amp hours (343 volts)
Battery Pack Weight:
Standard: High-capacity lead-acid battery pack - 1310 pounds
Optional: Nickel-metal hydride battery pack - 1147 pounds
Performance
0-60 mph acceleration in less than 9 seconds
Electronically regulated top speed of 80 mph (129 km/h)
0.19 aerodynamic drag coefficient (25% lower than any other production car)
Estimated Range*:
Standard: High-capacity lead-acid battery pack - 55 to 95 miles per charge*
Optional: Nickel-metal hydride battery pack - 75 to 130 miles per charge*
Estimated Energy Consumption Information (kW/hr per 100 miles):
Standard: High-capacity lead-acid battery pack - 26 city/26 highway
Optional: Nickel-metal hydride battery pack - 34 city/30 highway
Estimated Time from Zero to Complete State of Charge at 70 degrees with normal humidity:
Standard: High-capacity lead-acid battery pack - 5.5 to 6 hours using the 220-volt (6.6kW)
charger; 22 to 24 hours using the 110-volt (1.2kW) convenience charger
Optional: Nickel-metal hydride battery pack - 6 to 8 hours using the 220-volt (6.6kW) charger
*Actual mileage and range will vary as a result of driving style, terrain, temperature and accessory usage,
particularly as affected by ambient temperature and the use of heating and air conditioning.
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Energy Storage -- Page 2 of 5
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Batteries are normally rated by their voltages. In normal batteries you purchase from
stores, what are their voltages?
How do I measure power given off by a battery? Remember Ohm's law. Power is related
to voltage, current and resistance.
How is this related to the energy stored in a battery (energy, not power)?
Demonstration of storage capacity of battery:
1. Use one AA alkaline battery and connect it to a resistor of known value.
2. Monitor the voltage output of the battery as a function of time.
3. Plot the power output of the battery (=V²/R) as a function of time.
4. Determine the current output of the battery as a function of time.
5. Replot the power output of the battery (=VI) as a function of time.
6. Do this until the voltage drops to a low value (how low?? Come to class and find
out!)
7. How do you determine the energy stored in the battery?
What is the difference between a D-cell and an AA cell, both being 1.5 V?
What are the possible ways (units) you can express the energy stored in a battery?
They are: V·A·h, W·h, J and other related units.
Measure the weight of the battery.
What is the energy storage density of the battery?
How does my battery energy density compare with lead acid car batteries?
I have determined the weight of a full size lead acid car battery today, it is 35 lbs or about
15 kg. It is of course 12 V and it has an ampere·hour rating of about 50 A·h. So what is
its energy density? Energy in the battery is Volt × Amp × Time = 12 V × 50 A·h = 600
W·h.
The energy density of a lead acid car battery is then 600 W·h/15 kg = 0.04 W·h/g.
Assessment questions
1. Compare the various parameters in the EV1 specifications to see if they make sense (are
the specifications self-consistent?).
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Energy Storage -- Page 3 of 5
Example problems
1. I just purchased an electric vehicle (cost me $200,000). It has a 30. HP motor and has a
battery pack with an energy storage capacity of 20.0 kW·h. My maximum speed is 70.
mph and I can maintain that speed when I operate the motor at full power.
a. Under this maximum power condition, what is my range?
Solution: To determine the range, we first need to calculate the time my car can
run at max power:
Energy = Power × Time
20 kW·h = 30 HP × Time
or 20,000 W·h = (30 × 746 W) × Time
Time = 0.89 hour
So the range is: Time × Speed = 0.89 h × 70 mph = 62 miles.
b. If my motor is operating at 200. V, what is the ampere·hour rating of my battery
pack?
Solution: 20 kW·h = 200 V × (Ampere·hour Rating)
20,000 W·h = 200 V × (Ampere·hour Rating)
Ampere·hour Rating = 100. A·h
2. I am an engineer working for Toyota to develop electric cars driven solely by batteries. I
have twenty 12.0 V batteries in the car and each battery has a 100. A·h rating. In my
experiments on the test track, I found that my range is 120. miles on the highway if the
car is driven at a constant speed of 60.0 mph.
a. How much energy is stored in my twenty batteries?
Solution: 20 batteries × 12.0 V × 100. A·h = 24,000 V·A·h or 24.0 kW·h.
b. At 60.0 mph, how long will the batteries last?
Solution: 120. miles / 60.0 mph = 2.00 hours.
c. What is the power (in unit of kW) drawn by my motor when I run my car at 60.0
mph?
Solution: From (a) and (b): 24.0 kW·h / 2.00 h = 12.0 kW.
d. However, the range dropped to 100. miles if the speed is at 70.0 mph. What is the
power (in unit of kW) drawn by my motor when I run my car at 70.0 mph?
Solution: Time at 70 mph = 100 miles/70 mph = 1.43 hours
Total energy available is still 24 kW·h. Therefore power at 70 mph is
24kW·h/1.43h = 16.8 kW.
e. If my motor runs at 20.0 kW at 80.0 mph, what is the range at 80.0 mph?
Solution: Available energy = 24 kW·h. At 20.0 kW, it will last 24 kW·h/20.0 kW
= 1.20 hours
In 1.2 hours at 80.0 mph, the range is 96.0 miles.
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Energy Storage -- Page 4 of 5
Homework
I am an engineering working for Chrysler to develop electric cars driven solely by batteries. In
my experiments on the test track, I found that my range is 100. miles on the highway if the car is
driven at a constant speed of 60. mph whereas the range dropped to 80. miles if the speed is at
70. mph. I further found that at 60. mph, my electric motor was operating at a power level of 15.
kW.
a.
b.
c.
d.
How much time can my car run at 60. mph?
How much time can my car run at 70. mph?
What is the power level that my electric motor operates at 70. mph?
What is the energy storage capacity that my battery has (I want the unit in Joules)?
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Energy Storage -- Page 5 of 5