Electric vehicles (EVs) differ fundamentally from IC engine (ICE) vehicles in the source of motive power.
The latter harnesses the energy produced by burning fuel, which drives a set of mechanical linkages: the pistons, the crankshaft, the clutch, the gearbox and the wheels (in that order). EVs achieve the same propulsive force through motors that are mated to the wheels and are driven by electricity stored in on-board battery packs. Thus, it has much fewer moving parts — on average 20 for an average electric car vs 2,000 for an equivalent ICE vehicle.
Yet the simplicity has so far come at the cost of limited driving range per charge, and relatively long charging periods for the batteries. Access to charging points, whether in public spaces, along highways or even at home, has also been a deterrent for customers, as recently shown in a University of California (Davis) study. It found that one in five Americans was switching back to ICE cars, since without access to a level 2 charger — that charges an EV about 10 times faster than a regular power outlet at home — recharging an EV on the go took too long (an average of 8 hours) for them to be practical.
EV manufacturers had anticipated this, and we thus see several variations to the class leading, 100% electric vehicle. The following are the key categories and their defining characteristics:
Battery electric vehicle (BEV)
These are fully-electric vehicles that run purely on the power in their battery packs, and are charged by plugging into charging points via an assortment of connecters. The latest models support fast charging of up to 150kW/hr, which can charge their battery packs from 0 to 80% in about 20 minutes. The batteries are also charged to an extent by regenerative braking — which converts the braking force at the wheel to electricity through magnetic induction.
BEVs do not generate any tailpipe emissions and their current driving range varies from around 120km to 500km per charge. The most popular EVs in this segment have been the Tesla Model 3 and the Nissan Leaf, both of which have sold in excess of 500,000 units. Future improvements to battery energy density (the amount of charge carried per unit weight) and their falling are likely to help BEVs dominate global electric mobility.
Plug-in hybrid (PHEV)
These are vehicles that have both an IC engine and an electric motor with an on-board battery pack. PHEVs are so called since they can be plugged into a power outlet just like BEVs, but the IC engine can also power the vehicle on its own, or function as a “range extender” to charge the battery packs as and when needed. Thus, at low speeds (~60 kmph) the vehicles can run for about 15 – 70km on batteries alone, or use the IC engine in conjunction to drive much further than an equivalent ICE car.
Similar to BEVs, these cars also use regenerative braking to charge their battery packs, but they do have some tailpipe emissions. The most popular PHEVs have been the Chevrolet Volt, the BMW i3 and the Toyota Rav4 Prime. The Volt, for instance, can drive 53 miles on batteries alone and has a combined range of 420 miles.
Hybrid electric vehicle (HEV)
HEVs follow a similar setup to PHEVs, except that their on-board battery packs are smaller and cannot be plugged in. HEVs therefore use the IC engine and regenerative braking to recharge the batteries. This has its advantages, in that the car may use a smaller IC engine than its equivalent ICE counterpart, and the additional range from the battery pack results in better overall fuel economy without sacrificing performance.
The most popular HEVs so far have been the Toyota Prius C, Toyota Camry Hybrid and the Chevrolet Bolt.
- Fuel cell vehicles (FCVs)
FCEVs use the chemical reaction between two very common elements, Hydrogen and Oxygen, to generate motive power. They do this by using compressed hydrogen stored on-board in a tank, which is passed over specially formulated cells that react the hydrogen with atmospheric oxygen to produce energy and droplets of water (the byproduct). The energy produced is then captured by the fuel cells to power the Vehicle, and the US Dept. of Energy does a good explainer here.
The most popular FCEV to date has been the Toyota Mirai, and a key advantage of FCEVs is that they can be “recharged” very quickly (as little as 4 minutes), since the process only requires a top up of the on-board hydrogen tank. Current FCEVs also have a driving range of over 300 miles. However, a particularly challenging disadvantage is that storing and transporting hydrogen to filling stations requires extensive investments in Infrastructure, since the gas is very light and needs to be stored in liquid form.
This raises the lifecycle costs of FCEV powertrains to $7,360 – $22,580, vs. $6,460 – $11,420 for BEVs $4,310 – $12,540 for FCHEVs (fuel cell hybrid EVS).However, given their greater energy density (~280-400 Wh/litre vs. 200 Wh/litre for li-ion batteries), FCEVs can be excellent power sources for heavy duty vehicles like trucks and buses, where li-ion batteries would add considerable weight to the vehicle to achieve the same power output.
EVs with swappable batteries
This is a developing segment that may be useful for EVs that are on the road quite often, such as ride hailing cabs and delivery vehicles that benefit from minimal down time. The concept relies on taking depleted battery packs out of the EV and replacing them with fully charged packs within a matter of minutes.
The merit with battery swapping is that it slashes the time needed to “charge” an EV and also makes it more affordable, since batteries account for 40-50% of the total cost. However, the system needs an extensive network of battery swapping outlets, especially on inter-city routes, and swapping batteries at automated docks requires significant investment.
However, the system has so far been popular in China, where carmaker Nio has had battery swapping available since 2014 and has completed 500,000 swaps till date. It is able to swap the packs out in a mere 3 – 5 minutes, and battery swapping stations have also been proposed for India.
Changes are also being explored in li-ion battery chemistries — some are stepping away from lithium entirely to opt for sustainable, readily available raw materials — but at the moment the competition rests between the technologies listed above.