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Monday 16 March 2009

Blue Sky Engineering

Koenigsegg, those mad Swedes beloved of Top Gear make supercars that arguably demonstrate some of the most incredible real world engineering skills on the planet, seem to have lost the plot somewhat and started drinking some serious hallucinogens.

They’ve just announced an electrically powered “eco” supercar with the rather oddball name of “The Quant”. Possibly they’re making some in joke swipe at their usual customer base and this is just an early release of an April Fool’s joke but the numbers linked to this magical beastie are pure fantasy - “Blue Sky Engineering” as its called in the space business.

Some key "performance” claims and characteristics of the components they claim they have developed or that are near completion:

Top Speed 171mph, 0-62mph: 5.2 seconds , Range 312 miles, Power 381kW/512bhp / torque 715nm / 527 lb ft. Mass 1780kg.

So far so good. Those are probably doable in something shaped like a supercar although it’s definitely not getting 312miles doing 171mph speeds but they don’t specifically claim that so we’ll let them off.

The battery\energy storage system they claim they will use is called the Flow Accumulator Energy Storage (FAES) from some crowd called NLV. This amazing widget will provide the energy storage to facilitate the aforementioned 312mile range. Interestingly it also claims that it has a volumetric energy density of 600 Wh/l and can store a full charge in 15-20 minutes. The amount of energy it would take to hit ~300miles is going to be as near as makes no difference to the amount of productive energy produced by a petrol engine in a similar standard car with the same range. Let’s say that would be about 40 litres of petrol which has a volumetric energy density of about 9600Wh/l. Petrol engines are pretty inefficient so only about 25% of that potential actually gets converted to useful energy so that sort of range requires something like 90,000 Wh. To put 90,000Wh into a storage system in 20 minutes you have to push in 3 times that amount of Watts ie 270kW. That’s a lot of juice – even with industrial grade 380v 3-phase power you need to push almost 240 amps of current into it. Frankly I can’t see how you would be able build a power handling system into a car sized system that could handle that without using something like 5kV input voltage and that brings its own serious safety issues (not that 380V 3phase is exactly safe either but 5kV is distinctly dangerous especially when it would still be delivering 15-20A of current).  On the plus side if they actually have that miracle power system then they should be able to store that amount of energy in something like 200litres of battery which is nice – most current electrical cars currently need 5 times that volume.

Impossible? Probably not impossible but quite unlikely and certainly totally impractical today.

The part that sets my alarm bells going though are the “invisible..high efficiency Pyradian thin film solar cells” that (according to el Reg) has a conversion efficiency between 38 and 50%. I don’t think so folks. The very best hand made multi-junction monocrystaline PV cells barely hit the bottom end of that range and they cost a fortune by any measure. Thin film tech is currently languishing around with conversion efficiencies in the mid to high teens and I’ve never seen any evidence of serious work on multilayer (presumably multi-junction actually) thin film PV. Assuming they have this other wonder material though what good would it be? They say the whole car is covered with it, so at 4.8*2*1.3m that’s about 25m^2 of PV cells that could (in theory) yield about 1kW of power on a reasonably clear day in summer time at these latitudes. Even under ideal conditions (Sun directly overhead in California in Mid Summer) that would be worth about 3kW. That would make some sense – give it 8 hours in the California sun and you’d have enough juice to drive 100miles or so. Unfortunately, as I said, the PV conversion capabilities of thin film PV is less than half the claimed number and even in California you don’t get 8 hours of peak sun per day so the actual amount of power such a system would give you would probably only give a Quant owner a useful range of around 30-40 miles under ideal conditions and more like 5-10 miles per day in most places (on a good sunny day too).

I’m hopeful that I’ve got some of the numbers wrong here because I’d love it if this was all real but I suspect that it’s basically a better version of the Tesla, possibly with some technical improvements but without any of the tectonic technical advancements that are being claimed for them.

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