The first generalization is that most electric cars have, and all benefit to some extent from, having a battery (or several) on board. Batteries store electrical energy to be used later by the electric motor whenever the demand for electric power exceeds the output of the on-board generating device. For example, in the case of a solar-powered vehicle, batteries can continue to provide power to the electric motor even when the sun is temporarily hidden behind a cloud or momentarily shaded by a building or tree.
An unintended advantage of driving an electric vehicle, especially one with quite a few batteries on board, is your ability to get safely out of the roadway (and possibly even as far as a repair shop or, better yet, to a shopping mall!) even when the on-board electrical generator quits due to mechanical problems, or lack of fuel. Think about that the next time you’re sitting in a long left hand turn lane with your gas gauge on empty. In an electric car, even if the primary power source is out cold, you can just wait for the light to turn green and drive off on battery power alone.

Efficiency
The second generalization, fundamental to all electric vehicles, relates to the fact that electric motors are able to produce their full, rated power at any speed. The speed of any motor is generally measured in how many times it turns, or revolves, during a minute’s time, and thus “revolutions per minute” or “RPM’s”. Conventional gasoline-powered engines have very little power at low RPM’s. Even a high-powered racecar engine doesn’t really start generating any serious power until it is up in the 1,500+ RPM range. The problem is, however, that a car needs the most amount of power when it is going the slowest, as when it is starting up from a dead stop. To make up for this inherent lack of high power at low RPM’s conventional gasoline-powered cars use “transmissions” which allow the engine to run at a fairly high speed even while the wheels are turning at fairly low speeds.Recall now what we said about electric motors being able to produce their full, rated power at any speed and you can appreciate the second key advantage to electric cars: They actually need no transmissions to put their full power to work even at low speeds and, if they do use one, they will do so far more efficiently than any gasoline powered engine can.
Economy
A third and final common feature among electric vehicles is called “regenerative braking” which is really just a fancy term for "you get some of your money back”. Here’s how and why it works: An electric motor and an electric generator are essentially the same device. When electrical current is feed into such a device it acts as a motor and creates mechanical power. When mechanical power is feed into the device it acts a generator and creates electrical power.
If an electric motor is connected to the wheels, sending electrical power to the motor turns the wheels. However, when the wheels are turning on their own (as when coasting to a stop or going downhill) the wheels are in effect sending mechanical power back into the motor. The motor, by receiving mechanical power, now acts as a generator; sending electrical current back up into the batteries where it can be stored for future use. This “secondary” source of electrical power is captured and stored, and supplements any power otherwise generated by the primary on-board power generation system.
By way of contrast, conventional cars use conventional brakes that merely grab the wheels and keep them from turning freely. This “drag” on the wheels produces friction, which in turn produces heat. Yes, you slow down or stop as desired, but all the energy produced in slowing the car’s forward movement is lost to the atmosphere as heat.
Thus by means of “regenerative braking” an electric car (even a battery-powered car with no “primary” on-board power generation source) can reclaim part of its “kinetic” (moving) energy when coming to a stop. Note that we said “part” and not “all”. Despite theoretical arguments to the contrary, friction prevents electrical vehicles or anything else from reclaiming all of the energy it has used. Even so, the savings are very worthwhile.