Electric car

The most important limiting factor is storing the energy. The mostly widespread and cheap lead acid batteries can store 30Wh energy in 1kg. Even the energy density of the lythium based batteries is not more than 100÷150 Wh/kg oppose that value of 12.000 Wh/kg for the gasoline. If we should like to carry with ourselves the energy quantity stored in an avarage fuel tank during the whole way we should need about 5 tons of lythium batteries, from lead acid batteries this weight would be three times as much. In the reality the situation is not so dark. The efficiency of electric motor is much better than that of cars installed with gasoline motors. The consumption of an avarage converted vehicle is about 10÷15.000 Wh/100km which means about 1÷1.5 litres of gasoline. The effective distance of an electric car installed with lead acid batteries can be 100km with one charge for which we have to carry 300÷400 kg of batteries. A similar weight battery pack from lythium batteries can assure 350÷400 km efficient distance which can already be satisfactory.

For the first sight it could seem that there is no limiting factor regarding the output of an electric motor being to be installed. Concerning the choice of motors it is so indeed. The battery means the limitation again. We cannot get the stored energy as quickly as we want. The capacity of the lead acid batteries is generally given for 10 hours discharge period (0.1C). If we would like to take out the stored energy within 1 hour we could get only the 60% of the nominal capacity. As a general planning rule you have to choose the total capacity of the batteries for twice of the motor output. It means that in ideal case you have to install 8kW batteries to a 4kW electric motor. Typically the electric motors can give 2÷2.5 times of their output for a short period (1÷2 minutes) which is important when you want to speed up your car. The current consumption, too, grows of course. Choosing a much lower capacity for the batteries than the ideal case will restrict achieving this bigger current consumption. For this reason the total capacity of the batteries cannot be less than the output of the motor. That is you need at least 4kWh battery capacity to a 4kW electric motor. The lythium batteries have much better features. They can be discharged with 3C (3 times the capacity) continuously and with 10C (10 times the capacity) for a short period. So the minimal battery capacity can be lower. For example it is enough to install 10kWh battery capacity to a 30 kW electric motor (which is able to give 60÷70kW output for a short period).

Using the electric car for big distances is limited first of all by the need of time for charging the batteries. You need 10 hours to charge the fully discharged lead acid batteries.
To fully charge lythium batteries 3 hours and 20 minutes is enough.
Concerning the above factors you have to decide what you want to get from your electric car both in efficient distance both in upper speed limit.
The choice spreads from the moped cars installed with 3÷4kW motor, with 50÷60 km efficient distance upto the almost without compromise "asphalt breakers" installed with 50÷60kW motor which assures 150÷200km/h upper speed limit, with 300÷400 km efficient distance.

Regarding the losses of battery charger plus the losses of charging-discharging cycle about 15÷20kWh electric energy is needed from the net to take 100km distance. Counting with the tarif of normal electric energy in Europe the price is equal to the price of 2÷3 litres of gasoline. But if we count with the tarif of switched electric energy the price is equal to 1.5÷2 litres of gasoline. Does it sound well? Yes. And if we get the electric energy from our own source, for example solar cell or wind generator, the situation is much better. Today the limit of using renewable energy sources is that the big electric companies cannot do anything with the excess energy produced by wind generators and solar cells in the consumer's valley period. If there would be more consumer using switched electric energy more % of the electric energy could be produced from renewable energy sources. Using switched electric energy we could help saving our natural environment in significant rate.

The electric motor is much more simply, contains much less parts than the fluid fuel motors. Even its working temperature is much lower.
Its maintenance demands are much lower either, it's much easier to repair it. In the case of electric motor using coal brushes only the temporary (after every 50÷100 thousand km) exchange of the brushes is what to do.
Because of the limited lifetime of the batteries we need to exchange all of the batteries from time to time. This means the biggest cost during the life of our electric car. In the case of lead acid batteries the capacity decreases under 80% after 500÷600 charging cycles. This fact demands battery pack exchange every 50÷60 thousand km. The most up-to-date lythium batteries came out in 2006. These batteries can suffer more than 2000 charging cycles with the same capacity decreasing. So the exchange period for this type of batteries is above 200 thousand km.

The electric motor itself does not let out any harmful gases. It is environment-friendly. But it uses energy which have to be produced. Is it more or less than a fluid-fuel using vehicle would need? The efficiency of an electric motor is about 80% in a wide range. The efficiency of the charging-discharging cycles of the batteries is about 75%. The total efficiency is about 60% opposite 15% efficiency of the gasoline motors. Even more this needed electrical energy can be produced from renewable energy sources such as solar or wind energy. Even if we wanted to make the needed electrical energy from fossile fuel we should make less harm to our environment. The efficiency of the coal and gas power stations is about 30%. The rising heat energy can be used in the most cases. The advantage of such energy producing and using is additionally that the harmful gases leave the chimney not in the crowded towns. The air in the towns would be much more clear, living in the towns would became more pleasent.