In essence, hybrid electric cars have two engines: a conventional petrol or diesel engine (the same as you would find in any modern car and an electric, battery powered engine, as you might find in a milk float or a forklift truck. The magical difference is that the car’s on board computer judges which engine is necessary to provide the power needed by the driver and turns it on.
Therefore, if you are accelerating to cruising speed for motorway driving; going up hill or overtaking, the car will probably use its liquid fuel engine but then as you ease off the accelerator to, say, cruise down the motorway; go down the other side of the hill or to drive in slow traffic, the computer will turn off the liquid fuel engine and turn on the electric engine.
The electric engine can be seen as free to run, because it runs off batteries which are recharged by the car whilst it is using petrol or diesel and at some other times, such as while it is braking (and the alternators are recharging in both modes). You should never need to recharge your car’s batteries overnight as they do with forklift trucks.
There are basically two kinds of hybrid cars: the semi hybrids and the full hybrids.
The semi hybrids have the same sort of set up: two engines, one running on liquid fuel and the other running on batteries, but the electric motor is not capable of running the car on its own. It is there to ‘assist’ the petrol or diesel engine.
In this type of hybrid, the electric motor is known as an ‘assist’. These semi hybrids will save money on fuel, but whilst the car is moving, you are burning fuel all the time.
The biggest difference when it comes to the full hybrid is that both engines are capable of powering the car independently. Whilst you are running on electricity, you are running at zero cost to your wallet and at zero expense to the environment, unless you are really pushing the car and then both engines may be working in union.
This changing of power sources is done robotically without any interference from the driver. In the case of the Prius, for instance, this remarkable achievement is accomplished by what Ford calls its Hybrid Synergy Drive. Other businesses have their equivalent to the HSD.
In order to get the most out of these full hybrids, you actually need to be doing an ‘average amount’ of driving under ‘average’ or ‘mixed’ circumstances. For instance, if you are driving in traffic, the car will try to use the electric engine, but if all you do is drive in inner city traffic jams the batteries will soon become depleted and you will be driving on liquid fuel all the time, which sort of negates the main reason for spending a great deal extra on a hybrid in the first instance.
The car needs to travel on open motorways in order to recharge its batteries so that it can utilize them once it gets back into town. If you just drive in town traffic, you might be better off buying a little run around instead.