III ENERGY BUDGET
Figure 4 and 5 provide a comparison of the energy budget of EVs as compared to ICE vehicles. A running vehicle must develop sufficient propulsion torque in order to overcome road loads viz. (i) acceleration load, (ii) rolling resistance load, (iii) climbing or gradient load, and (iv) air drag load. A typical vehicle having a mass, along with payload of 1000 kg undergoing the city drive cycle (like in Bangalore) will have an energy efficiency of about 16%. This means that for every 100 Wh of energy delivered to the wheels, 500 Wh goes off as engine losses and another 20 Wh go off as transmission losses. The input energy requirement is 620 Wh. If petrol is used as the input fuel, it will work out to 0.065 litres of petrol.
Figure 4: ICE energy budget
On the other hand, in the case of EVs, for every 100 Wh of energy delivered to the wheels, around 40 Wh is lost in charge-discharge loss of batteries and another 20 Wh is lost as transmission loss. This mean that 160 Wh is needed as input energy. In the case of EVs and HEVs, during braking, there is energy recovery of about 4% i.e. 4 Wh. This is recovered back. Therefore, the net input energy required is 156 Wh. This works out to a system energy efficiency of 64%. The energy budget for EVs is shown in Figure 5.
Figure 5: EV energy budget