Mileage and Role of Batteries in solar vehicle

Batteries form the main source of power from the solar panels to run the BLDC motor. In the simulation a battery which can be recharged with the help of solar power is designed. So, a battery must satisfy the property of charging and discharging which is considered in the simulation. The Lithium ion batteries with the specification mentioned later in the paragraph are considered for the vehicle. When battery is in charging mode electrical energy is converted into chemical energy and while in discharging mode chemical energy is converted into electrical energy. The selection of batteries in this report is done considering the need to supply sufficient power to the motor, cost and weight of the batteries. There are two types of batteries which can be chosen to run the vehicle. They are lead acid batteries and lithium ion (cobalt) batteries. In this report, the lithium ion batteries are considered due to the long discharging time, less weight and low maintenance. The main disadvantage of lead acid batteries are heavier (weight) than the lithium ion batteries and they require regular maintenance. In this report four lithium ion batteries of 12V and 33Ah are considered which are connected in series to achieve a total of 48V and 33Ah. The calculations on charging time and discharging time are the most important in perfect analysing of the working of the solar vehicle. The calculations are based on the specifications of motor, load torque, solar panels and batteries.

Capacity of the batteries = 33Ah

Current from the solar panels (average) = 8.3A

Charging time of the batteries = capacity in Ah / Charge rate in A                                 (9)

Therefore, Charging time = 33/8.3 = 3.974 Hours.

The time mentioned above is the suitable considering only the ideal conditions. In practical the lithium ion batteries has an efficiency of 90%. Considering the practical conditions:

Charging time of the batteries = capacity in Ah / (Efficiency * Charge rate in A)        (10)

Therefore, Charging time = 33 / (0.9*8.3) = 4.417 Hours.

Discharging time = (Capacity in Ah * Battery voltage) / Applied load in watts            (11)

Considering the motor uses an average continuous current of 15.62 amps during the running of the vehicle, the applied load on the vehicle becomes 749.76 watts.

Therefore, Discharging time = (33 * 48) / 749.76= 2.11 hours.

This implies that when the vehicle runs at an average speed of 50km/h the distance travelled by the vehicle turns out to be 50 * 2.11 = 105.5 Km.

Assuming that the conditions are ideal for efficient charging of the batteries through the solar panels. By the time the batteries get totally discharged within 2.11 hours, 47.76% of the battery gets charged back according to equation (12). Due to which the battery can run for additional fifty kilometres.  

Percentage of charging = (time for charging / total time for full charge)*100               (12)

Therefore, Percentage of charging = (2.11/4.417)*100 = 47.76%

For one full charge, if the vehicle runs at a constant speed of 50kmph, the vehicle runs a distance of 105.5kms. Similarly, at 47.76% of full charge and at the same constant speed, the vehicle runs an additional distance of (0.4776*105.5=50.38) 50.38km.

In the same way according to equation (12) while the vehicle runs an additional distance of 50.38km, about 22.81% of the battery recharges which can run for 24.06kms more. Similarly, during the run of 24.06km, about 10.89% of the battery recharges and can run for extra 11.48km. The next stages can be neglected as the batteries get completely drained of charge.

Therefore the total distance covered by the vehicle at a constant speed of 50 km/h in ideal conditions for efficient charging of batteries is (105.5+50.38+24.06+11.48) 191.42km.

Day	Battery (Ah)	Current               (I)	Charging time (hr.)	Efficiency (%)	Actual time(hr)	Current drawn(A)	Load (watt)	Disc. time (hr)	Speed (km/h)	Distance (km)*
1	33	8.34	3.956	90	4.396	15.62	749.76	2.112	50	105.6
2	33	8.24	4.004	90	4.449	17.78	853.44	1.856	50	92.8
3	33	8.1	4.074	90	4.526	16.24	779.52	2.032	50	101.6
4	33	8.15	4.049	90	4.498	15.40	739.20	2.142	50	107.1
5	33	8.32	3.966	90	4.407	15.33	735.84	2.152	50	107.6

* Only for one full charge.
Tab.3.5.1. Speed, distance covered and Time taken for charging and discharging