Three kinds of hybrids

The next fifteen years.

Pure Electric – will be marginal

Battery energy density will probably be lousy and they will be expensive so that pure electric cars can’t fill that many needs in the next fifteen years. What kind of vehicles will we see instead?

Commuter – the frugal plugin hybrid

If most people live 20 km from their workplace, it only takes perhaps 5 kWh to move that distance in a current era car. At a conservative 100 Wh/kg, the battery only becomes 50 kg and it’s cost could be reasonable. The vehicle can and practically must still have a petrol or diesel engine for any longer trips, but this relatively small battery should cover most of the driven miles during the year. The system would be a series hybrid – the engine is only attached to a generator and all traction is through the electric motors. This mostly works at a reasonable cost for small vehicles. The engine could be a 500 cc two cylinder machine to reduce surface area vs volume and thus losses, since smooth output isn’t needed here. With opposed cylinders there would be little vibration. It would also sound funky.

Cruiser – the lean lossless one

This is for long trips on the highway, where batteries do you no good at all. Instead there’s a good diesel engine and good gearing with very little losses in the powertrain. The vehicle doesn’t need to be that light (so you can have good sound proofing for example), but good aerodynamics is important. These long trips are done often with more people and stuff onboard, so these vehicles tend to be larger because of that too.

Hybrid hybrid – a compromise between the two above

And this is where actually the largest volume of vehicles fits in, since people want to have options. Any technology could win here: hydraulic hybrids to make cruiser tech city compatible, parallel electric hybrid cruisers for mixed driving, series electric hybrid commuters with larger battery packs and / or bigger engines…

What do we have now?

The Cruiser we already have today in most European manufacturers’ Diesel cars. The Hybrid Hybrid is something that Toyota Prius and Honda Insight approach from the Cruiser end of the spectrum with the parallel hybrid system. Chevy Volt / Opel Ampera tries to approach from the Pure electric car end. The Commuter frugal hybrid, *nobody is making*. Why? That would seem like the clearly most obvious choice. One obvious reason for the lack of frugal hybrids is that there are other costs than just the battery. Even if you saved money with a smaller battery, you would still have to provide the electric motors and power electronics and charging system that all would be almost as big as in a car with a larger battery. The charger can be smaller since the smaller battery loads up quick enough even with a smaller current and/or voltage, and the vehicle would also be lighter meaning smaller electric motors and a smaller hydrocarbon engine.

Interesting tech solutions

There are a couple of ideas that I’ve gotten from reading a Finnish report on electric vehicles, made by experts for the parliament. One is using the power inverter of the car in reverse as a charger. So, simplified, the cord coming from the wall plug would be connected to the electric motor AC side of the power electronics, not the DC battery side. The power electronics has to be able to run in reverse anyway during regenerative braking. This could enable loading quite quickly, if the motor voltage was the same as the wall outlet. The European continental norm (all household outlets) 230 V AC single phase sine wave is easily changed to 350-400 V smooth sine wave with a single phase step up transformer. 16 amps is the biggest ordinary fuse so we’re only talking about the power of a 3 kilowatts with one fuse (if I got it right). This would roughly mean three hours of charging for one hour of driving. The three phase 400 V AC that every house also has, for the electric stove at least, is changed easily to 600-700 V for the battery by the car’s inverter and vice versa. Think if you could hook 400 V from the wall straight to the car with no converter whatsoever.

three phase 380 v connector

A basic European IEC 60309 32 Ampere 380 Volt three phase connector, GNU GPL Documentation licence, by Stephan Nachtsheim

16 amps would mean 6 kilowatts, or 1.5 hours of charging for 1 hour of driving. 32 amps and 45 minutes. This would also mean that it would be really easy to move energy from the battery to the network. It’s no secret that such inverters closely resemble ordinary industrial three phase 400 V inverters, which happen to be manufactured in Finland, at least by ABB and Vacon. If the battery voltage wasn’t 350-400 V or 600-700 V, more complex transformers would be needed that would yield more losses, cause harmonics to the grid and where reversing would be harder.

So all in all this would suggest strong campaigning for 350-400 V or 600-700 V battery voltages in continental Europe. I’m sure all kinds of companies have their ideas of selling their expensive proprietary charger technologies, but proper choices made early enough could remove most of the charger problem out of the equation altogether!

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6 Responses to Three kinds of hybrids

  1. Paul says:

    No mention of what may become the most common kinds of hybrids: non-electric ones.

    Hydraulic hybrids would store braking energy in a hydraulic accumulator, then accelerate from a stop using that energy. These devices can achieve instantaneous power well beyond a battery-based system. These are increasingly showing up on such things as garbage trucks, and Chrysler is looking into putting them into cars.

    Pneumatic hybrids would store energy in compressed air. The most likely scheme would be a kind of time-shifted supercharger, allowing the engine to produce compressed air that would be consumed later when a burst of power is needed. This would also enable the engine to be turned off when the car is stopped. I believe Ford has been exploring this technology.

    While the storage density of these approaches isn’t as good as batteries, the power density is better, and the cost is very low.

    • gravityloss says:

      Actually, I did briefly mention hydraulic hybrids in the cruiser portion, but yes, I agree. What makes electric interesting is the plugin capability. Perhaps hydraulic and compressed air hybrids could have that too with small electric pumps, though their reservoirs are probably small.

      Flywheels could store more energy per kg and also have less losses than compressed gas in hydraulic or compressed air hybrids but spinning flywheels could be problematic when storing energy for a long time. Perhaps a night or a workday would be fine though. Would they need standby power to maintain “full charge” if unexpectedly unused for a while?

  2. Andrew W says:

    The way I’d do it is to have electrified rails down the center line of all the highways and motorways, cars and heavy vehicles would have small batteries for getting around town and just hook directly into the highway supply for longer journeys.

    • Andrew W says:

      Just to be clear, I’m not talking about rails to drive on, more like a two rail fence with vehicles using trolley arms swinging out from the side.

      • gravityloss says:

        Might work but I think that’d be too maintenance intensive except on really dense traffic routes.

        • Andrew W says:

          What maintenance? It’s just a couple of thick rails on uprights with the top rail insulated, and this has the juice to power freight, not just cars. You also get rid of infernal combustion engines altogether, which in itself is a significant reduction in maintenance.

          The trolley poles also act as guides to keep vehicles the correct distance from the rails, electric power is cheaper than petroleum fuels, and you still have enough battery power for the 40km or so of unpowered road between the reticulated highway and your destination.

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