EV Fueling Time

FCEV fueling time. The driver of a fuel cell EV refuels his or her car much the same as a conventional car.  A hose is connected to the car, and hydrogen gas flows into the car tank(s).  This is the same procedure used by hundreds of thousands of natural gas vehicle owners since World War II.

The National Renewable Energy Laboratory has been monitoring the operation and fueling of 155 FCEVs (See their slide #7.).  These vehicles have operated on the road by ordinary citizens for 131,000 hours and have logged more than 3 million miles as of the end of March 2011 and drivers have refuled their vehicles with with high pressure hydrogen over 28,00 times wuthout incident.  The average time to fill the hydrogen tanks was 4.4 minutes, and 74% of the fillings took less than five minutes.

BEV fueling time. Estimating the fueling time for battery EVs is  much more complex, depending on the capacity of the external charging circuit, the state of charge of the battery bank, the current acceptance rate of the battery system, the range of the BEV (which determines the energy required to charge the battery), etc. If a BEV was designed and built to achieve ranges above 200 miles, then the battery banks would require many hours of charging time even with special high current charging circuits. One way to compare fueling times is to consider the power flowing through a gasoline hose when you fill up your current car tank: pumping 13 gallons of gasoline in 3 minutes is equivalent to a power transfer of 10 million watts (10 million watts or 10 MW) of electrical power. A typical home 120 Volt/20Amp outlet can deliver 1.9 kilowatts (1.9 kW) power, so the home outlet is over 5,200 times slower than pumping gasoline into your car. Similarly, the average hydrogen filling rate monitored by the National Renewable Energy Laboratory for over 28,000 fueling events was 0.77 kg/minute which is equivalent to 1.82 MW of power, or 958 times faster than a residential 120 Volt/ 20AMP circuit, and 237 times faster than a TYpe II 240 V /40A circuit.  Fortunately, the BEV is approximately 3.5 times more efficient than a conventional gasoline car (tank-to-wheels efficiency only), so the 5,200 times disadvantage compared to pumping gasoline falls to “only” 2,100 times slower for a given range and the 958 times disadvantage compared to pumping hydrogen decreases to 358 times slower energy transfer. So if it takes 3 minutes to pump 14 gallons of gasoline to go 350 miles in your current car, it would take 4.4 days to charge batteries to go 350 miles from a Type I home outlet (assuming car makers could cram enough batteries into a BEV to achieve 350 miles range) and 7.7 minutes [10] to fill a hydrogen tank for a FCEV to go 350 miles assuming that the FCEV has 2.4 times [11] greater tank-to-wheels fuel economy than an ICV

Note also that the power cord connecting the 10 MW power source (such as a GE or Pratt & Whitney aero-derivative natural gas generator...essentially a jet engine connected to a generator) would have to be solid copper, at least 2 inches in diameter to avoid excessive losses; lesser conductors such as the terminals of batteries would be destroyed by the I2R power losses and the resulting charging efficiency would be very low.

Conclusion: it is much easier, faster, and more efficient to move molecules of gasoline or molecules of hydrogen to fill car tanks than to move electrons to charge a battery

This chart shows how the fueling time varies with EV range from 150 to 300 miles, depending on the power of the charging circuit:

For a Level 1 120-volt, 20-amp residential charging circuit, the time to charge an EV would vary between 29 hours for 150 miles range up to 77 hours for 300 miles range. For a higher power 240-volt, 40-amp circuit such as those used for dryers, charging times would vary between 7 and 19 hours.  Shorter times would be feasible for smaller vehicles traveling shorter distances; these estimates are all based on a full-size Mercury Sable class vehicle with a lightweight aluminum body. For comparison, the Nissan Leaf requires 16 hours of charging to go 100 miles (or 73 miles as measured by the EPA), while the Chevy Volt requires 10 hours of charging to go 40 miles in battery-only mode.

For a commercial charging station, these fueling times could be reduced to between 1 to 2.5 hours for a 60-kW charger, and as low as 0.4 hours (24 minutes) and one hour for a 150-kW charger  These higher power chargers would be expensive,[These high power charges would cost between $25,000 to $50,000; for example, Nissan offers a high power charger for $45,000 that could charge their Leaf battery pack to 80% charge in 30 minutes.] and advanced Li-Ion batteries might not be able to accept such a high charging rate without severe damage to the battery and/or much limited life-time.  So these lower charging times are speculative at this point, depending on future battery improvements in terms of charge rate acceptance.

[10] The internal combustion engine vehicle (ICV) would have a fuel economy of 350/14 = 25 mpg if 14 gallons of gasoline was enough to travel 350 miles. The FCEV would then have a fuel economy of 25 X 2.4 = 60 mpgge (miles per gallon of gasoline equivalent, or 59.27 miles/kg of hydrogen. The FCEV would then require 350/59.27 = 5.9 kg of hydrogen to go 350 miles, and it would take 5.9 / 0.77 kg/min = 7.7 minutes to fill the hydrogen tank.

[11] We have used a fuel economy advantage of 2.4 in this model based on a review of prior estimates from the literature. However, the only direct comparison of an ICV with a FCEV in real-world driving showed a larger advantage. The Toyota Highlander SUV was converted to a FCEV. Two National Laboratories certified the Highlander FCEV at 58.3 miles/kg fuel economy, which is equivalent to 69.1 mpgge.  Since the conventional (non-hybrid) gasoline Highlander gets between 20 and 22 mpg fuel economy, this translates into a FCEV efficiency advantage between 3.14 (69.1/22) and 3.45 (69.1/20)  With these advantages, the fueling time for the FCEV to go 350 miles range would decrease to between 5.4 minutes and 5.9 minutes .

A fuel cell vehicle is refueled with hydrogen much like a conventional gasoline car (except there are no obnoxious fumes!)

Hydrogen Fueling Nozzle:

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