A practical motor vehicle needs about 30 KWH of deliverable energy
for a range of 100 miles.
For reasonable performance about 20 hp must be delivered to
the drive train.
Efficiency of energy delivery from batteries to drive train is
about 40%
- Delivered energy = 40% of stored energy
- So you need 30 KWH/0.4 = 75 KWH of stored energy
- Energy storage density of lead-acid batteries is .04 KWH
per kilograms
- So you need 75/.04 = 1875 = 4125 pounds of lead-acid batteries
- Power: 20 hp/0.4 = 37.3 KW
- Power density of lead-acid batteris is .07 W/kg
- So you need 37.3/.07 = 533 = 1172 pounds
So the range requirements are more severe than the power
requirements.
Improvements in battery Technology are definitely required.
Other types of batteries
- Nickel Iron ED = 55 PD = 100
- Sodium Sulfur ED = 90 PD = 100 (300-350 C operating temp)
- Lithium-Iron sulfide ED = 100 PD = > 100 (400-450 C)
- Nickel-Zinc ED = 75 PD = 120 (low cycle life)
Driving Habits and Requirements
- Long distances - Interstate --> 75 mph and 400 miles range
- Daily Commute --> 55 mph and 35 miles range
- Puttering around town --> 35 mph and 20 miles range
It is very unlikely that electric cars will ever have prodution
line performance that satisfies the Interstate requirement.
Most practical application is for in town commutting/shopping
and this would then eliminate a major source of air pollution
The Key of course is marketing --> people have to buy the product
- Performance
- Range
- Price
- Safety
An optimistic view
California Mandate:
- 1998: 2% of all vehicles offered for sale must be zero
emission vehicles (meaning electric cars)
- 2003: 10% must be zero emission
Some Prototypes:
- Ford Ecostar two-passenger electric mini-van used by
Post-Office and UPS --> sodium-sulfur batteries
- Chrysler TEVan --> nickel-iron batteries
- $500,000 given to Yosemite to replace diesel buses with
electric buses
- $500,000 given to General Motors to loan 50 vehicles to
1000 people nationwide for test drive results
Components of Government Program
Comprehensive Reference on Electric Vehicles
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