I believe the technology for home hydrogen fueling that will win out in the end will be a 1-5 cubic foot unit operating overnight, taking as inputs natural gas and electricity, and outputting hydrogen at a rate of 1-5 kg per 10 hours depending on the size (and therefore cost) of the unit. Every 36 seconds 1-5 grams of H2 at room temperature are pumped into the car at a pressure proportional to how much is already in the tank, and 3-15 grams of dry soot (broadly construed to include carbon powder, graphite, etc.) are added to a container at the bottom. Every week your waste management company collects the accumulated 25 lbs of soot per FCV separately from your garbage and recycling.
No tanks external to the car, no emissions of any gas. Assuming no subsidies, operating costs per kg should come to whatever 100 cf of gas costs, around $1.50 today, plus $0.90 for the electricity ($2.50 if you fill up during peak hours in the afternoon). $2.40 for 60 miles worth of H2 comes to 4 cents a mile. With gasoline at $2.40 a gallon you’d need a 60 mpg ICEV to match that, and you’d also miss out on the convenience of home refueling while getting frowns from your neighbors for continuing to emit 20 lbs of CO2 for every gallon you use.
Although no such unit is available today, progress towards it has been made at IASS and KIT. I see no obvious technical or economic obstacle to refining their current design to meet the above specifications, perhaps based on a different approach to methane cracking.
The 5 cf unit will fit comfortably in the Mirai’s 20 cf trunk, allowing you to take it on trips. A network of 1500 overnight filling stations at motels, hotels, and campsites every 20 miles along the major interstates would permit travel throughout the country at 300 miles a day, and further when FCVs with larger tanks come on the market. Each station would consist of one or more parking spots each with a hookup providing gas and electricity and a bin in which to deposit the night’s accumulation of 33 lbs of soot in the morning, emptied by the hotel’s waste management service. Stations could start with a single spot booked like a hotel room. With the current small FCV population, two cars are unlikely to want the same spot and when they do the second can just book a nearby spot. This very simple infrastructure could be built up gradually nationwide with only a few million dollars a year total, comparable to the cost of installing just a few $2M hydrogen stations around the country. Both will happen, but the former could easily happen faster.
Eventually FCVs will incorporate the unit the same way BEVs incorporate their charger today. Since the construction and operating costs of a regular hydrogen station will be at least a hundred times that of an overnight gas-and-electric parking spot, it is reasonable to expect the nation’s infrastructure to grow at the rate of a hundred such spots for every regular station, with the latter spaced apart ten times the spacing of the spots.
PG&E currently offers special electricity rates to BEV owners charging at home, so if they did the same for home hydrogen your cost could be as low as 2 cents a mile. This could be reduced to zero with a federal carbon tax of $0.001 on gasoline, rising to $0.002 when the milestone of a million FCVs in the US is reached. A portion of this tax would be paid to the utilities to compensate them for giving you free gas and electricity for your FCV. (Maybe this is already happening for their BEV subsidies.)