Jeffrey Evans's Profile

Battery
Efficiency

Energy efficiency is calculated on the amount of
power used from the
battery while discharging divided by the amount of
power delivered to the batter while charging, multiplied by 100 to
yield percent. P_out x 100 /P_in
. A lead-acid battery has an efficiency of only 75-85%. The energy lost
appears as heat and warms the battery. Keeping
the charge and discharge rate of a battery low, helps keep a battery
cool and improves the battery life.

The above losses don't include losses in the
charging circuit which may
have an efficiency of anywhere from 60% to 80%
- thus the overall- total efficiency is the product of
theseefficiencies and ends up being 45 to 68%. (To further this
example and to show why physics and not some corporate conspiracy is
the reason we don't have electric cars - suppose
the controls and motors on a car were 85% - the over all efficiency is
now only 38 - 58%. You can see that an electric
car would use about twice the energy than a conventional car - not to
mention the great cost of the regular replacement
of batteries. This is why batteries are best used where only
intermittent, or very low power use is required.)

To further explain - If the electricity is generated
from a gasoline
engine - and that energy is converted to
electricity, and then sent through power line transformers and power
lines, and then converted to DC, and then
converted to chemical energy, and then converted back to electrical
energy, and then converted to rotary mechanical
energy - it is clear that many losses have occurred. If the same
gasoline motor was providing the rotary energy
directly to the drive train it is much more efficient.