An electric vehicle charger costs Rs 12 lakh to install. How long does it take to pay back, and how many sessions a day would halve that?

Payback is about 5.0 years, and about 12.3 sessions a day would halve it. Eight sessions of 25 kWh at Rs 6 earn Rs 4.38 lakh a year; less Rs 2 lakh of running cost leaves Rs 2.38 lakh, and Rs 12 lakh divided by that is 5.04 years. Halving payback needs Rs 4.76 lakh a year, which takes 12.3 sessions, 54% more, because the fixed cost does not grow with use.

Think of an auto-rickshaw bought for Rs 3 lakh. The driver asks how many trips a day he needs to earn the money back after fuel and the monthly permit fee. A charger is the same question. Payback is the upfront cost divided by the cash each year brings in after running costs. Work per day, then per year: 8 sessions x 25 kWh is 200 kWh a day; at Rs 6 that is Rs 1,200 a day, or Rs 4.38 lakh a year. Take off Rs 2 lakh of fixed running cost and Rs 2.38 lakh is left.

Divide: Rs 12 lakh over Rs 2.38 lakh a year is 5.04 years. Each extra daily session is worth Rs 0.5475 lakh a year, about Rs 55,000, which is the number to carry in your head for every follow-up.

Half of 5.04 years is 2.52 years, so the charger needs to bring in twice the net cash, Rs 4.76 lakh a year. Add back the Rs 2 lakh fixed cost and gross margin must be Rs 6.76 lakh. Divide by Rs 0.5475 lakh per session and the answer is 12.35 sessions a day, about 54% more than today, not double. The running cost is fixed, so each extra session goes entirely to net cash.

Both enter the same way: margin per kWh times kWh sold. The difference is how far each can move. Margin is pinned by power tariffs and nearby rivals, while sessions can swing from 4 to 16 a day depending on the site, the traffic and how many electric cars pass by. At a 60 kW charger, 200 kWh a day is about 3.3 hours of charging, only 14% of the day, so there is room above and a long way to fall.

That is why charging networks argue about site selection more than pricing. A charger at 4 sessions a day nets only Rs 0.19 lakh a year and takes 63 years to pay back, longer than it will last. Close by saying what you would test before building: traffic counts at the site, the local share of electric cars, and the session count at Urjit's comparable chargers in their second year. Then add the limit: this ignores tax, financing and the fall in charger prices, all of which a full model would include.