As vehicles get electrified, the conventionally followed fuelling option is to charge the batteries. Vehicle batteries are best slow-charged overnight in six to seven hours. Lower temperature and lower charging rates make the battery last longer. However, if a vehicle is driven in a day longer than the range provided by the battery (say 100 kms), the batteries are fast-charged.
This can be done in 45 minutes to an hour as long as battery is cooled during charging to keep battery temperature as close to 25-degree C, as possible. Waiting for 45 minutes to an hour for charging can be very often problematic. There are batteries which can be fully charged faster than this, but they are expensive. Of course, one can use larger batteries, which would give longer range (say for example, 300 kms), so that vehicle rarely requires more than one charge on a day. This, however, also significantly increases the cost of the batteries and therefore that of the vehicles. Also, higher weight of the battery implies lower energy-efficiency of the vehicles and therefore lower range.
An alternative, not considered in nations where affordability is not a serious issue, is to use smaller battery providing limited range. The vehicle weight is also reduced, enhancing the overall vehicle energy-efficiency. When the battery runs out, one does not go to a charging station; instead, one goes to a Swapping Outlet, which keeps an inventory of charged batteries and swaps the discharged battery with a charged one. This can be done in less than five minutes, time that a petrol/diesel vehicle takes to fill the tank. Further, the batteries may be no longer purchased with the electric vehicle, reducing the capital costs of the vehicle.
Instead, the battery is purchased by an “Energy Operator (EO),” which carries out charging and swapping and leases out the battery to the user. Once a discharged battery is swapped at Swapping Outlet, the discharged battery is taken to a conditioned environment, where the battery is cooled and charged in about two hours, ensuring that the life of the battery is maximised. The battery-lease charges depend upon the energy actually consumed and the battery-leasing rates are based on the depreciation and the interest-cost of the battery plus the charging-cum-swapping costs.
With Battery Swapping emerging as an option, a taxi-fleet may have two options:
EV with RE-battery
This option may be more meaningful for a private vehicle rather than a taxi. The vehicle is sold with a small fixed battery (say with a 100 km range). But the vehicle has a slot for a second battery, called Range-extension battery (RE-battery), which may be added or swapped at a swapping station, as and when needed. The fixed battery is slow-charged overnight and the vehicle can have 100 kms range in a day. Most private vehicles travel less than this range for 90 per cent to 95 per cent of days. On the days the vehicle needs to travel longer distance, it just drives to a Swapping Outlet and gets RE-battery mounted, doubling the range. This is just like getting petrol filled, as it happens only once in 10 to 15 days. If one needs even longer-range, the RE battery is swapped. The RE-battery is returned to any swapping outlet, once used. So, the vehicle does not require any fast charging; slow-charging of fixed battery during night-time is adequate, maximizing the life of the battery.
EV purchased without a battery
In this case, the taxi is purchased without a battery. The capital cost of the vehicle is even lower as compared to the vehicle with RE battery. Battery is just leased in, when required. Only a single battery would normally be used, but a taxi-driver, going on a long-route, where the Swapping Outlet is unlikely to be available, may choose to get both the batteries mounted. Only disadvantage is that a person may have to go to a swapping outlet every day, but for a taxi it may be a better option.
Comparisons between different approaches
Table 1 compares the two approaches discussed here and the conventional approach of charging a vehicle for a taxi. It is assumed that swappable battery has 100 kms range and costs about Rs 250,000 and has a cycle-life of 2,000. The vehicle without battery is assumed to cost about Rs 650,000 and that with RE-battery of 100 km range may cost about Rs 900,000. The conventional EV is assumed to have a large battery with 300 km range.
From the table 1, one may conclude that EV with RE-battery may be the best for personal vehicles, EV without battery may be best for taxi-fleet.
In case of conventional EV, the battery is purchased by customer and the operating costs are electricity costs and overall maintenance of vehicle. When charged at home, the costs will be close to Rs 1.25 per km. This compares well with the operation costs of the petrol vehicle, which is closer to Rs 7 per km. When the EV is charged with a fast charger, the operator of charger will charge a premium over the electricity costs. The costs may be closer to Rs 2.25 per km.
When vehicle is purchased without battery, the leasing costs of battery plus vehicle maintenance may amount to Rs 4 per km. This is still much less than the operational cost for petrol vehicles.
For an EV with RE-battery, the costs per km is different based on whether fixed battery or RE-battery is used. Along with maintenance costs, the operation costs with fixed battery is Rs 1.25 per km, and with RE-battery is Rs 4 per km. Since RE-battery is used only in about once in 10 days, this will be highly acceptable.
Four-wheeler EVs in India need to be different from what is used in other countries, to match the affordability in India. Vehicles with large battery and fast-charging does not make economic sense. An option, as discussed here is to purchase EV without battery and lease battery as required, swapping batteries when needed. This approach implies that the capital costs of the vehicle is similar to that of petrol vehicle and operational costs are much lower than the petrol-vehicles. This is an excellent approach for taxi-fleets. For personal vehicle, one may use EV with RE batteries. Capital costs will be slightly higher as compared to petrol-vehicles as well as EVs without batteries, but the operational costs will be much lower. RE battery swapping ensures no range limitation. This may be ideal for personal vehicles. The capital as well as operation costs for petrol vehicles, EV without batteries and EV with RE-batteries is carried out here.
Comparing Capital and Operational costs in petrol vehicles, EV with only swappable batteries and in EVs with RE-battery
Assumptions for 5-seater, semi luxury vehicles
- a) Petrol vehicles: Capital cost = Rs 700,000; Operation cost per km = Rs 7
- b) EV with swappable battery: Capital cost = Rs 650,000; Operation cost per km = Rs 4
- c) EV with range extension battery (100 km fixed with 100 km swappable): Capital cost = Rs 900,000; Operational cost per km = Rs 1.30 (operation cost per km 90 per cent of time at Rs 1 and 10 per cent time at Rs 4).
Comparing total cost of operation for 10000km, 20000km, 40000km per year
Here a total depreciation and interest cost to be 30 per cent of capital cost is assumed. Though depreciation of petrol vehicle should be higher than that of EV with fixed battery which should still be higher than EV with only swappable battery, however here we assume everything as same.
The total cost of operation for different km usage per year are illustrated in Table 2 and 3.
This article is based on a whitepaper titled ‘Electrifying Growth – Adoption of Electric Vehicles in Corporate Fleets’ that has been co-authored by Move-in-Sync Technology Solutions (MIS) and Prof. Ashok Jhunjhunwala. The paper was unveiled at the MIS hosted tech conclave ‘TransporTech 2019.