Battery, ICE, Hybrid: What About Temporary Mixes?

The history of the wave of electrification in cars had given us several classes of cars, all of which were created for the different driving habits and economic constraints of the time. I want to review all these classes, and ponder if there isn’t a new potential class which may become the most popular in time.

The pure gasoline/diesel car

While electric cars dawned over a century ago, “ICE” cars have dominated for a century for good reason. Gasoline is super power dense and flexible, and we’ve built a huge infrastructure to distribute it. Today, it’s on the wane because it’s expensive and pollutes too much, and ICE power trains are complex and expensive to maintain.

Hybrid

Hybrid cars like the Toyota Prius were an immediate success. They had small batteries (because batteries were very expensive, among other reasons) and get fantastic mileage. All hybrids, however, face the problems of having the cost and maintenance of two different power systems, and indeed for many cars in the history of hybrids, the added cost of the hybrid version cost as much as the money saved on gasoline – but other electric advantages like less pollution, less noise and more peak power, kept them attractive.

Short range BEV

The earliest electric cars (of which the Leaf was the first success) could only go less than 100 miles. This created a lot of real and imagined “range anxiety” and kept sales low. Batteries were just too expensive. People loved the wins of the pure electric – zippy acceleration, low maintenance, low sound and low energy cost, but the range and slow charging kept sales pretty meager.

Very short range PHEV

The next step were hybrids which could plug in, and had batteries good for fairly short ranges, like 40 miles. Because the average car only drives about 40 miles/day, such cars can do a large fraction of their yearly miles on electric, effectively offering the best of both worlds. Of course, it’s also the worst of both worlds, in that you pay for two full power trains, and in the early days batteries were quite costly, keeping that electric range small. These vehicles took on the “Electric First” strategy where you used up the electric charge and then turned on the ICE motor when done. Since you would do all long trips on the gasoline motor, it had to be fully capable of that, but could never match the zip of a BEV.

Most hybrids and PHEVs are “parallel” hybrids which have the ICE engine directly power the wheels, assisted by the electric motor. This is more efficient but gives driving in that mode many of the characteristics of ICE driving.

It is worth noting that while most EV charging stations are not very useful, they are of value to these cars, not because they can’t get home without a charge, but because it assures their whole day will be all-electric.

Long range BEV

Tesla showed the world how to do it with all-battery cars with more than 200 miles of range. Cars with superb performance, low noise and no visits to gas stations. Due to battery costs, they started off quite expensive. The long range got rid of range anxiety for all local travel. Tesla partly solved the problem on long trips with their supercharger network, but while nice, that’s far from perfect and doesn’t duplicate the “go everywhere in the world with little concern for energy” style of ICE cars and PHEVs. Even so, the advantages of going all electric all the time made many choose such cars over PHEVs, and most new generation BEVs are of this class.

Medium range PHEV

One unique car that teaches worthwhile lessons, both good and bad, is the BMW i3 REX. This is a BEV with an 80 mile range, with a cheap and small (38hp and 0.7l displacement) gasoline motorcycle engine for use when the electricity runs out. This is meant to be driven as a BEV with “range extender” – electrical almost all the time, but the ability to go on longer trips. Unfortunately, due to this philosophy and the small engine, the car’s performance once the battery is used up is quite poor (especially for a BMW) while the electric mode is zippy. For legal reasons, the gas tank is very small (good for under 100 miles) and in the USA it is required to follow the electric first strategy.

This car is a “serial” hybrid where the ICE engine only generates electricity, it doesn’t drive the wheels. That’s less efficient but more flexible.

The electric-first strategy is the greener strategy, and the right one for urban driving, but it’s the wrong one for longer driving days. A more reasonable (though sometimes less green) approach is to know in advance that it’s a heavy driving day, and to run the gasoline engine from the start, with a target of just barely depleting the battery at arrival at a charging station – meaning usually by the end of the day. Then plug in, recharge and repeat. This approach gives the car its electric advantages all day. Importantly, though, it still allows the use of a smaller, cheaper gasoline engine. The i3 uses a motorcycle design, which runs at a fixed speed, which has many advantages.

Two potential designs exist, which may hold interest in the future, both relying on the ability to make use of a simple, inexpensive gasoline powered generator like the BMW i3 REX.

Long range PHEV

A car with a 200 mile range and a range-extender generator would be able to go anywhere in the world, without concern for finding high speed charging. The reason this might never exist is the generator would only be needed for those long trips and voyages off the beaten path. On long trips, those trying to reduce emissions might still rely on fast electric charging if it comes at low inconvenience, namely if one can always time it to suitable meals. This would leave the generator to use only on trips of unusual schedule, or voyages off the network, or hotels without charging. That might have particular appeal for pickup trucks and RV travel, where having a generator is already very popular.

If you knew you had the range, the generator would never engage. It would find minimal use in flat areas, but on hills the combined power of the battery and generator (with recharging when not on an upslope) would provide good results. While the low usage generator would be low cost and be designed to need low maintenance, the question would remain whether the cost, space and emissions of the generator are truly worth it for such limited use.

Temporary power slot

The most interesting approach might be an vehicle designed to receive a temporary rental generator. This would involve a large door on the side of the vehicle, leading into the trunk, into which a generator module could be inserted. The module would contain fuel tank, generator and exhaust piping, venting out the door or other planned vent. A cooling hookup may also be needed. Of course there would need to be a high current electrical connection. They might be available for rent at gas stations, who of course fill them with gasoline as part of the service and have the gear to make them easy to insert and remove. Any BEV could have a slot for one. The receiver area would be designed to securely hold the weight and tolerate the heat, though the module would be expected to be well insulated as it would become an item in the trunk or frunk of the BEV.

The idea of temporary power has been around for a while, including companies that dreamed of trailers with generators or extra batteries you could hook on a car.

These rental generators would not normally be used for urban driving, only for longer road trips. They would allow driving everywhere. They would also offer a solution for times when superchargers are overloaded due to high traffic, like Thanksgiving.

Of course, one could build a module that just contained batteries as well. This would add range to the car, perhaps converting a 200 mile range car to a 300 mile range car for the duration of a road trip, which may would find quite satisfactory. Modules could be swapped, though all the arguments against battery swap continue to be true about that approach. Nonetheless, this also could be a partial solution to charging station overload. This would put considerable weight in the location of the module dock, which must be planned for.

Factors suggest the generator module might cost around $3,000, and thus rent for under $100/week profitably. The module receiver would add some cost to the car. Trunk or frunk space would be lost when it was in use. Standardizing the modules may present a challenge, though it can be done within a brand, but stations would not want to stock too many different sizes. It could end up offering the best of both worlds. It is as close to a zero-compromise car as you can get:

1. Driving around town (most driving) it is entirely electric, and does not carry the weight of the generator module.
2. It drives like a sporty, quiet electric car all day, even on road trips
3. It can go anywhere in the world there is gasoline
4. Where there is convenient supercharging or overnight charging, it remains fully electric in operation. However, finding this, or enduring its delays is no longer a must.
5. It only needs about 200 miles of battery, costing much less than a 300 mile battery vehicle, even including costs of generator rental and gasoline.
6. The generator is small and light and efficient, matching the best hybrid cars when using gasoline. Costs of the generator are low and maintenance is simple and done by the rental companies and included in the price.

The utility of such generators would be less with batteries which can recharge very quickly, but they would still retain value even then, because the network of such chargers will take a long time to cover the backcountry.

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