Nikola hydrogen generators

Discussion in 'Hydrogen fuel cell vehicles' started by bwilson4web, Jul 4, 2018.

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  1. bwilson4web

    bwilson4web Well-Known Member Subscriber


    Nel ASA has been awarded a contract for delivery of 448 electrolyzers and associated fueling equipment to Nikola Motor Company (Nikola) as part of Nikola’s development of a hydrogen station infrastructure in the US for truck and passenger vehicles.
    . . .
    A-Range Atmospheric Alkaline Electrolyzer. . . . Cell stack power consumption is down to 3.8 kWh/Nm³ H₂.
    . . .​


    1 kg = 11.126 Nm3​

    So now we can figure out how much electricity is needed to make 1 kg of hydrogen:

    42.28 kWh/kg = 3.8 kWh/Nm3 * 11.126 Nm3​

    We can now compare and contrast what happens if 42.28 kWh making 1 kg of 1 bar, hydrogen is used to charge a battery versus a hydrogen fuel cell vehicle:
    • Honda Clarity fuel-cell vehicle - 366 miles on 5.46 kg = 230.8 kWh
    • Tesla Model 3 - 26 kWh/100 mi * (366 mi / 100 mi) = 95.2 kWh
    So charging a battery instead of electrolysis will give 230.8 kWh / 95.2 kWh = 2.42 times further versus using electrolysis. Note that I did not include the energy to compress Nm3 hydrogen to 700 bar, ~13% of the hydrogen energy:
    • 230.8 kWh at 1 bar
    • 260.8 kWh at 700 bar = 230.8 kWh + (13% * 230.8 kWh)
    This changes the ratio to 260.8 kWh / 95.2 kWh = 2.74 times further charging a battery over hydrogen at 700 bar.

    Bob Wilson
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  3. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    Thanks for doing the math, Bob! :)
  4. Doodlebug

    Doodlebug New Member

    what's the total round-trip comparison, when you take into account the fuel cell efficiency on the truck?
    I've seen fuel cell makers saying they are 53% efficient but I'm unsure what they are counting, i.e. whether than includes auxiliary energy use such as the fuel cell air compressor.
    There's also battery and power electronics losses, if I'm understanding the system configuration right, i.e. battery energy needed for boost on a fuel cell system per the Mirai (or Project Portal truck)

    Would be interested in learning your take on this.
  5. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    A 53% efficiency would be the efficiency of the fuel cell stack itself, in using the energy contained in the hydrogen fuel. That would not include other efficiency losses in the vehicle, such as mechanical drivetrain losses, nor the need for auxiliary power. (But note that the need for auxiliary power will be found in all vehicles, regardless of what type of powertrain it has; diesel, BEV, or FCEV.)

    And of course it does not include the very high energy losses in the supply chain for the H2 fuel, which includes the loss from compression or re-compression of the H2 gas.

  6. bwilson4web

    bwilson4web Well-Known Member Subscriber

    This is why my analysis used the announced Nikola metrics for hydrogen generation and the new Honda Clarity fuel cell metrics. This is a systems analysis that avoids digging into the weeds that buyers have little to no ability to change.

    There is a maximum efficiency of 83% at very low power levels:

    This is an executive summary of the efficiency and comes with the chemical reaction. About 17% of the hydrogen energy becomes heat that is lost. But efficiency is also a function of internal losses (See Wiki):

    The practical efficiency of a PEM's is in the range of 50–60% .[citation needed] Main factors that create losses are:
    • Activation losses
    • Ohmic losses
    • Mass transport losses
    Here is a more technical discussion:
    • Activation losses - these occur when the hydrogen is split on one side and oxygen on the other side. These are minimized by finding more efficient catalysts. Regardless, for any catalytic combinations, it is an additional loss over the heat generated by the chemical reaction.
    • Ohmic losses - a fuel cell works by moving hydrogen protons through the electrolyte, typically a PEM film but it can be a ceramic structure. Regardless, these protons do not move without resistance so they bump against the electrolyte causing ohmic heating.
    • Mass transport losses - if you drive a car flipping between speeds with maximum acceleration and braking to change speed, you will suffer inertial losses. So at the surface where the hydrogen combines with oxygen creates a molecule that has to accelerate back into the oxygen gas stream. They bump into the atmospheric gas, heating it up. A similar mass transport loss occurs on the hydrogen side as the molecules hit the catalysts and suddenly are slowed down.
    This is why I did a 'systems analysis' based upon the advertised performance specifications. A lot of messy details including power electronics and motor losses are automatically included. Just there is a problem with an efficiency analysis that ONLY compares a fuel cell to a gasoline or diesel heat engine and ignores battery efficiency.

    Efficiency is often a function of how much power is being withdrawn:
    • Otto (gasoline) engines - low efficiency at partial power due primarily to throttle plate losses. Hybrid cars turn the engine off at low, power, inefficient levels by using the traction battery and motors. When the engine runs even when the car is crawling along, it runs at a higher power level and stores the excess energy in the traction battery.
    • Diesel engines - eliminate throttle plate losses but increase mechanical friction losses due to higher compression.
    • Fuel cells - highly efficient at low power but the dynamic losses increase with more power. Due to expense, fuel cells operate at higher power levels leading to the reports of "53%" efficiency.
    • Batteries - highly efficient at low power but similar dynamic losses increase with more power. Make the batteries larger and the relatively lower power improves system losses ... and range!
    Bob Wilson
    Last edited: Jul 4, 2018
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  8. bwilson4web

    bwilson4web Well-Known Member Subscriber

    New information:

    The complete charge took 1:48h and gave the vehicle a range of 504 kilometers (313 miles). Additionally, it juiced up the battery with 75kWh with a max charge rate of a whopping 117 kW.
    . . .
    The full charge – as reported by the owner – will set him back a total of $18.98. . . .

    Now we can compare the costs of driving 313 miles of a Honda Clarity fuel cell vehicle versus 313 miles for a Tesla Model 3:
    • 4.67 kg = 5.45 kg * (313 mi /366 mi)
    • $74.72 = 4.67 kg * $16 / kg ## Honda Clarity 313 miles
    • $18.98 ## Model 3 for 313 miles
    • 3.9 = $74.72 / $18.98
    The higher, retail price ratio, ~3.9 times versus ~2.74, comes because hydrogen is manually shipped to the retail, hydrogen fuel stations, where the local tanks are charged or exchanged (assuming the H{2} trailer remains.) In contrast, the electrical grid does not manually ship every kWh to the retail chargers. The one time, electrical installation is used over and over again without paying someone to deliver.

    One last point is charging time from the YouTube video:
    • 15 min -> 100 miles
    • 30 min -> 200 miles
    • 45 min -> 250 miles
    • 60 min -> 275 miles
    The fastest strategy is to add enough to reach the next charger + 10% safety factor. Approaching the next charger, adjust speed as necessary to reach it.

    Bob Wilson
  9. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    Yes. And to add a bit of detail:

    The fastest strategy when driving a Tesla car cross-country, using the Supercharger network to extend the range, is to run the car to as close to 0% charge as possible without actually running out of "juice", before stopping to recharge. The fastest charging at a Supercharger is achieved with the battery pack at <10% charge, so the closer the pack is to empty, the faster it charges for those first few minutes, until tapering off at a higher SOC (State Of Charge).

    This is not theoretical "armchair engineering"; this is what is reported as being the fastest way to travel by actual Tesla drivers who have tried different strategies, and found this strategy gives the fastest average speeds.

    bwilson4web likes this.

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