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My biggest worry with using hydrogen in large quantities is the way it will need to be stored.
You cannot stick the tanks in the ground and judging by the hydrogen station I have seen at Daventry on the A5, the tanks are enormous and bright white.

They would be very real targets to any idiot who wishes to make a statement. It would happen.
 

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For the Hyundai Nexo FCEV (linked earlier) we have some figures:

So the fuel cell output is 70% of the peak motor power - better than I expected but still clearly a long way below 100%.

And while they state the battery can put out 40kW I don't see the actual kWh of the battery (it can't be that big if it can only put out 40kW - maybe 12kWh ?) so it wouldn't last long at full speed.
How long would it need to last at full speed? If it's only draining the battery at 40kW that means even if it's only got 12kWh it will take 18 minutes to drain.
That's presuming full power being used - in most ev's power drops as they get to their speed limiter so in reality you could probably sit at it's speed limiter for a very long time.
 

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But they don't need to have a small battery. That's just the fluff which is being thrown out at the moment while it's in it's infancy.
For instance the i3 rex's motor can only make 34hp for it's 168hp output.
I've said a few times the rex needs more power to be a complete solution but it wouldn't need all that much more. Somewhere around the 50hp mark would do it in an i3 so it could cruise at any legal speed in any weather even if the heater is on max.
Transfer that to a crossover which is heavier and may have more drag and 75-100hp would be all that's needed with a half decent battery as a buffer.
Infact if the i3 got the fc from this thing it would have a constant 127hp available - it could still charge the battery on anything less than around 70% power.
Right but if you're going to fit a large battery so that you can have large power levels and high performance... then before long you don't need the fuel cell any more. If FCEVs need 40kWh batteries so that they can put out 200kW and have sporty performance then the fuel cell is starting to become pointless - you might as well just address the CO2/emissions/sustainability/fossil fuel issues by fitting a charging socket and replace the fuel cell with a small petrol engine, i.e. build an i3.
 

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If you want 200hp (which is roughly the level needed to haul that weight around at a reasonable speed) you need 150kW motors - assuming you need to bridge the entire power output while the fuel cell "spins up". If I understand correctly at 4C (which is about as high as you would want to draw) you therefore need 37.5kWh of battery. Or about the same as the new Leaf.

But, I assume you don't need to power the car by battery alone during acceleration, however, I don't know exactly how much bridging is needed. The Mirai, for example, has a 114kW fuel cell (and 113kW motors ...) and only has 1.6kWh of battery so if I've done the "C" calculation correctly then it only gets a brief assist of about 6kW from the battery? That would seems a tad pointless ... therefore I imagine it either draws a higher "C" rate from the battery or the Fuel Cell takes much longer to spool up to full power.

There's a chart in the Mirai brochure https://www.toyota-europe.com/download/cms/euen/Toyota Mirai FCV_Posters_LR_tcm-11-564265.pdf which appears to show the fuel cell only takes a few seconds to go from 0 to 100% output. So you are only using the battery to maybe 3 seconds before the fuel cell takes over all responsibility. Presumably you can get away with drawing maybe the entire 113kW from the battery if it's only for three seconds - in theory you have 50 seconds of full power energy draw stored in the battery.

Or I've got the wrong end of the stick.
 

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But, I assume you don't need to power the car by battery alone during acceleration, however, I don't know exactly how much bridging is needed. The Mirai, for example, has a 114kW fuel cell (and 113kW motors ...) and only has 1.6kWh of battery so if I've done the "C" calculation correctly then it only gets a brief assist of about 6kW from the battery? That would seems a tad pointless ... therefore I imagine it either draws a higher "C" rate from the battery or the Fuel Cell takes much longer to spool up to full power.
Where did you read the battery was only 1.6kWh ? I read the pdf you linked to and all it says about the battery is that it's NiMH.

Pretty disappointing if the battery is really only 1.6kWh, and the fact its old NiMH technology. Whilst it might be enough to buffer a high performance fuel cell, it doesn't give much storage for regenerative braking.

It would be enough for intermittent stopping and acceleration but not enough storage to make good use of regeneration travelling down a long decent like a hill or mountain.
 

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Discussion Starter #26
Where did you read the battery was only 1.6kWh ? I read the pdf you linked to and all it says about the battery is that it's NiMH.

Pretty disappointing if the battery is really only 1.6kWh, and the fact its old NiMH technology. Whilst it might be enough to buffer a high performance fuel cell, it doesn't give much storage for regenerative braking.

It would be enough for intermittent stopping and acceleration but not enough storage to make good use of regeneration travelling down a long decent like a hill or mountain.
The running gear is based on the Prius, just with a FC in place of an ICE.
 

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Colour me (more) disappointed then if it is indeed just a 1.6kWh NiMH battery.

One thing that doesn't quite ring true though, isn't the Prius battery 48V NiMH like most other early Hybrids ?

Surely the main electric motor in the Mirai is a 360v 3 phase AC motor like any other modern EV, not a 48v motor from a Hybrid ?

If so, how does the 48V battery fit into the picture ? What is the output voltage of the FC stack - surely not 48V at extremely high current ?

So the fuel cell stack outputs 360(ish) volts to run the drive inverter, and a DC-DC inverter is needed to step the 48V from the battery up to 360v for the main inverter ? And you also need it to be able to step 360v from the fuel cell stack down to 48V to charge the battery.

Seems like a lot of complication when you'd be better off just swapping the battery out for a small but standard 360v Lithium Ion pack! I have some doubts that they would use a 48V battery in this application, whether it is "based on" the Prius or not. Based on doesn't mean every detail is the same.
 

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Discussion Starter #29
Here’s some interesting detail on the hybrid part of the car:

Toyota didn't completely disregard its proven hybrid technology for the Mirai. A 245-volt nickel metal hydride battery pack, similar to that in the Camry Hybrid, stores surplus electricity from the fuel cell and regenerative braking, serving to smooth the energy supply needed for driving operations.

Although the Mirai felt like a production car, complete with acceptable range, there are a few compromises. Trunk space is compromised somewhat by the hydrogen storage tanks, and the rear seats don't fold down. The rear seat may look like a bench, but Toyota only rates it for two people, an effort to keep drivers from overloading the car and hurting its performance.
From here: 2016 Toyota Mirai Release Date, Price and Specs - Roadshow
 

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Discussion Starter #31
Ok 245v is a bit more reasonable, but still a bit limiting. Does that mean the fuel cell, drive inverter and motor also only operate from 245v instead of the more typical 330-400v of a BEV ?
Sorry - I’m just getting this from the Wikipedia page, but they have good citations:

The Mirai has a new compact (13-liter), high-efficiency, high-capacity converter developed to boost voltage generated in the Toyota FC Stack to 650 volts.[38]
Go figure. :)
 

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A good question would be exactly who would be storing and maintaining these cars. Will the workshops and show rooms need to be certified to store gas?
Most gas storage areas are in free air so its going to be very cold for sales staff in winter! :LOL:

Maybe local power companies and British Gas or Calor will be involved. :ROFLMAO::ROFLMAO::ROFLMAO:
 

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Discussion Starter #33
A good question would be exactly who would be storing and maintaining these cars. Will the workshops and show rooms need to be certified to store gas?
Most gas storage areas are in free air so its going to be very cold for sales staff in winter! :LOL:

Maybe local power companies and British Gas or Calor will be involved. :ROFLMAO::ROFLMAO::ROFLMAO:
They have to have a hardened workshop if they work on the H2 side.

I imagine kwikfit will probably refuse to change tyres and brakes in any case. :)
 

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They have to have a hardened workshop if they work on the H2 side.

I imagine kwikfit will probably refuse to change tyres and brakes in any case. :)
Maybe that's a good thing. Would you really want Kwikfit working on your Mirai ? ;)
 

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Ok 245v is a bit more reasonable, but still a bit limiting. Does that mean the fuel cell, drive inverter and motor also only operate from 245v instead of the more typical 330-400v of a BEV ?
If you poke around the schematic they have quite a lot of voltage transformation going on. There's a specific item for the fuel cell boost converter with 4-phase power (?) that goes up to 650V. The motor runs at 650V apparently ...
 

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My biggest worry with using hydrogen in large quantities is the way it will need to be stored.
You cannot stick the tanks in the ground and judging by the hydrogen station I have seen at Daventry on the A5, the tanks are enormous and bright white.

They would be very real targets to any idiot who wishes to make a statement. It would happen.
Just like any petrol station
 

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Having a powerful motor doesn't help if the battery is small and can't provide the power you need to drive it.
But they don't need to have a small battery. That's just the fluff which is being thrown out at the moment while it's in it's infancy.
It could be done with capacitors instead of batteries. Caps have terrible storage compared to batteries but can source a lot of current. Riversimple are using capacitors, so it can be made to work.


This is ignoring the primary issues with H2 fuel cells. Fuel Cell vehciles have very poor energy efficiency compared to BEV. They are expensive compared to BEV. Most H2 production is from steam reformed natural gas, not renewable power.

=======================


Menter Mon (Angelsey) just awarded a contract to study H2 production and storage on Anglesey. This could be interesting since our local council has blocked nearly every renewable energy project. With Wylfa Newydd in limbo the only other possible energy input is gas from the national grid. < sigh > I'm trying to keep an open mind, since this is production and storage, not a FCV.


Guto Owen (@GutoOwenH2) | Twitter
 
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