Choosing the Next Driving-School Car: Petrol, CNG or Electric
A driving school in Coimbatore runs four petrol hatchbacks, each covering about 120 km a day, 300 days a year. Petrol costs ₹105 per litre and the cars average 16 km per litre. The school is considering three options for its next car: (a) a new petrol hatchback at ₹8.5 lakh; (b) converting a three-year-old petrol car to CNG for ₹65,000, with CNG at ₹80 per kg and 28 km per kg; or (c) a used two-year-old electric car at ₹9.5 lakh with a real-world range of 250 km, consumption of 6.5 km per kWh and home charging at ₹8 per kWh. The school has a three-phase connection and can charge overnight. All lessons stay within the city, with no more than 70 km between stops. The battery warranty runs until 2029.
1. Calculate the daily and annual energy cost for each option and rank them. Show your working.
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Petrol: 120 km ÷ 16 km/L = 7.5 L/day; 7.5 × ₹105 = ₹787.50/day; × 300 = ₹2,36,250/year.
CNG: 120 ÷ 28 = 4.286 kg/day; × ₹80 = ₹342.86/day; × 300 = ₹1,02,858/year (approximately).
EV: 120 ÷ 6.5 = 18.46 kWh/day; × ₹8 = ₹147.69/day; × 300 = ₹44,308/year.
Ranking by running cost: EV lowest, CNG second, petrol highest. Annual saving versus petrol: CNG about ₹1,33,392; EV about ₹1,91,942.
2. Recommend one option, considering both cost and non-cost factors such as training use, downtime, safety and resale.
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The recommendation depends on whether the school must buy a car or already has a sound petrol car to convert. If the three-year-old car is structurally sound and the school wants the lowest capital outlay, CNG is the strongest financial case: ₹65,000 conversion and about ₹1.33 lakh annual saving against petrol, with payback in under six months. If the school is buying a new car anyway, the used EV is attractive: it saves about ₹1.92 lakh a year against petrol and its ₹1 lakh price premium over a new petrol car is recovered in roughly six months.
Against the CNG conversion, however, the EV's extra capital of about ₹8.85 lakh (₹9.5 lakh minus ₹65,000) saves only about ₹58,500 a year, a payback of about 15 years - beyond the battery warranty. Non-cost factors matter: the EV has no clutch or gearbox for learners, is quieter and has lower routine service, but it needs assured overnight charging, a 250 km range is ample for 120 km/day but is reduced by air-conditioning and load, and battery health and resale are uncertain. CNG preserves the manual car for licence training, but adds cylinder space, refuelling time and kit certification. My conditional recommendation: CNG for the existing car if it is in good condition; EV only if a new car is being purchased and charging is guaranteed.
3. What data would you verify before committing, and what is the biggest risk in your recommendation?
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Verify the actual city range and consumption of the used EV with air-conditioning on, a battery state-of-health report from the dealer, warranty transferability and terms, charger installation cost and whether the three-phase supply has capacity, electricity tariff and time-of-day charges, CNG kit approval and insurance endorsement, cylinder test date and boot space, resale values, and insurance premiums for each option. Also confirm whether the driving-school licence class requires a manual-transmission vehicle.
The biggest risk is that the EV's battery degrades faster than expected, or that the charger and tariff assumptions fail; that would wipe out the running-cost advantage and strand a 120 km/day vehicle. For CNG, the risk is refuelling queue time and reduced boot space, not fuel cost.