Week 4 : EV Challenge
EV Battery Capacity
The EV battery capacity is estimated in KWH for a passenger car. An EV with more kwh is better to use.
The electrical energy in kilowatt-hours is equal to the charge in amp-hours times the voltage, then divided by 1,000.
Example:
- Tata nexon has 30.2 kwh battery capacity for 312 km range
- BMW i3 has 42 kwh battery capacity with 270 kg battery weight for 245 km range.
How is the no. of cycles & battery life correlated?
The number of discharge-charge cycles the battery can experience before it fails to meet specific performance criteria. Cycle life is estimated for specific charge and discharge conditions.
The time when battery is unable to meet 80% of rated capacity after certain number of charge and discharge cycles.
The actual operating life of the battery is affected by the rate and depth of cycles and by other conditions such as temperature and humidity. The higher the DOD, the lower the cycle life.
The C rate also affects the battery life.
The above graph indicates that when the DOD(Depth of discharge) increases then the cycle life reduces along with it. This also gives us the strong relation between the no. of cycle and battery life.
Battery pack of Li-ion vs lead acid for 10 years operating life.
Most lithium-ion batteries are 95 percent efficient or more, meaning that 95 percent or more of the energy stored in a lithium-ion battery is actually able to be used.
Conversely, lead acid batteries see efficiencies closer to 80 to 85 percent. Higher efficiency batteries charge faster, and similarly to the depth of discharge, improved efficiency means a higher effective battery capacity.
The numbers vary from study to study, but lithium-ion batteries generally last for several times the number of cycles as lead acid batteries, leading to a longer effective lifespan for lithium-ion products.
For a 10 years operating life lead acid battery will be replaced more times than the li-ion battery.