Folded into the Roadmap is something you don’t notice until you read the fine print:
More than 10% of the electricity generated by the Roadmap (182.6 out of 1,591 GWs) will be used to isolate hydrogen gas by electrolyzing fresh water.1
As we mentioned, fuel is storage. Indeed, one tactic of the Roadmap involves using any excess renewable energy to isolate hydrogen for fuel.
Most of the hydrogen (made with 141.4 GWs) will be used to power long-haul trucking; buses; rail transportation and freight; and large-scale waterborne freight and transport. Their on-board fuel cells will use compressed hydrogento produce electricity to power these large vehicles.
The rest of the hydrogen (made with 41.2 GWs) will be used for process heat, the high temperatures used in industrial processes, by combining the hydrogen with atmospheric oxygen and burning it.
Since those long-haul and heavy-transport GWs would be 9% of our primary energy pie, this is worth exploring in detail.
The hydrogen can then be used to make heat by burning it in a combustion chamber. Alternatively, the hydrogen can be used to make some electricity (along with a lot of heat) by running it through a fuel cell.
In either case, it has to be mixed with oxygen from the atmosphere – the same amount of oxygen that was released when the hydrogen was isolated.
Burning hydrogen for process heat is a good idea – when mixed with atmospheric oxygen, it’s a high-temperature, squeaky-clean and totally green combustive fuel.
Hydrogen fuel cells, however, are far less efficient. In the process of making electricity, they squander most of the hydrogen’s potential energy as waste heat.
Even so, fuel cells play an important role in the Roadmap. And to be honest, they would probably play the same or similar role in an all-nuclear grid.
But still, when you see how these things work . . .
A hydrogen vehicle is something that would have made Mr. Goldberg proud:
Instead of using electricity to power an EV (electric vehicle), the electricity is used to power an electrolyzer at an H2 gas production plant.
The electrolyzer sheds copious amounts of waste heat in the process of destroying fresh water to isolate hydrogen, which is then used to fuel a hydrogen vehicle. Which is actually an electric vehicle (EV) with a bunch of hydrogen stuff bolted on.
To be clear: A hydrogen vehicle is an EV with an onboard fuel cell. The fuel cell grabs oxygen from the atmosphere, and combines it with hydrogen from the vehicle’s pressurized gas tank, to make heat, water vapor, and electricity to power the EV.
When the process is complete, the water vapor is released out the tailpipe. The heat is wasted as well, in the same way that an internal combustion engine sheds heat as it operates.
In fact, only 26% of the original amount of energy (that was used to split the water to isolate the hydrogen) is ultimately re-generated by the onboard fuel cell to power the vehicle’s electric motor.2
Pretty clever, huh?
We’ll grant you that it’s a pollution-free system, with an endearing Goldbergian charm, but there are several problems with the scheme, particularly if it’s done at scale. And 141.4 GWs qualifies as scale:
Hoover Dam has a peak capacity of “only” 2 GWs, so this hydrogen vehicle thing is Big Stuff.
We’re talking more than 70 Hoover Dams’ worth of power.
In spite of wasting a lot of primary energy, hydrogen power is still an attractive idea for commercial transportation, where vehicle range, cargo volume, cargo weight, and refueling times combine to affect the bottom line.
A battery-powered class 8 (big rig) tractor-trailer has a range of 60–120 miles, and takes hours to recharge. That’s fine for shuffling containers at a cargo port, or taking short hops from port to warehouse. Battery exchange could reduce downtime to a matter of minutes, by using a forklift to swap out a pallet of on-board batteries.
But maximizing cargo volume is what long-haul trucking and freight are all about. That same big rig could go 800–1,200 miles on a tank of hydrogen, and take just 15 minutes to refuel.
The batteries that would be needed to give a big rig the same range as its hydrogen-fueled twin would eat up precious cargo space, to where the numbers don’t pencil out for long-haul trucking.
So hydrogen fuel does have its advantages. However, isolating all that hydrogen would do more than just gobble up 141.4 gigawatts, and squander 105.2 of those GWs as waste heat.
It would also destroy a lot of fresh water that can’t be directly recovered: About 250 ESBs per year, or about 5 hrs of our annual national fresh water use.3
In the big picture, that may not seem like much, but those ESBs would add up as the years roll on. True, it’s all released as water vapor and will eventually come back to Earth somewhere or other as rain. But still, that’s a lot of fresh water to re-purpose in a thirsty world.
So that’s the pickle between battery vs. hydrogen rigs. Our guess is that hydrogen will win out as the fuel of choice for long-haul, and for large-scale waterborne freight as well.
Here’s why: Reducing cargo space in our freight and transport fleets, to accommodate a load of onboard batteries, would be a drag on our domestic economy. Since 70% of our commerce involves consumer goods, delivered by truck, ship, and rail, it’s cheaper to build power plants to isolate the hydrogen instead.
Imagine 105.2 GWs squandered as waste heat. Ben would have a fit.
That’s a lot of energy, especially when you’re gathering it from intermittent spurts of wind and sunlight. To put it in perspective:
Imagine 53 Hoover Dams shedding all their energy as waste heat, in the process of destroying 250 ESBs per year to isolate the hydrogen to move our freight and cargo.
If we’re going to waste that much energy, the least we could do is make sure that generating the energy is easy, cheap and reliable, with a small footprint. That’s where nuclear energy shines.
Another option for powering heavy transportation, including aircraft, is synfuel. Though it’s (almost) carbon-neutral rather than carbon-free, synfuel does have its advantages:
It can be stored, piped, and distributed by our existing fossil infrastructure, and it could power our existing trucks and ships without having to swap out the engines.
Synfuel can also be used in hybrid-electric big rigs, by powering an on-board turbine that generates electricity, giving the vehicle similar range, weight, and cargo capacities as a hydrogen rig.
Then there’d be all that water we wouldn’t have to destroy, or desalinate. But there’s a hitch:
The challenge of making synfuel is to harvest enough CO2 from the atmosphere. And thus far, carbon-capture systems haven’t been ready for prime time. But they’re working on it. And cheap,abundant nuclear power would go a long way toward making the idea feasible – yet another argument for an all-nuclear grid.
Ammonia has also been proposed as an alternative fuel, but the danger of an ammonia cloud released in a traffic accident should give everyone pause.
As you can see, there is no easy solution for carbon-free long-haul trucking, short of turning the rigs into giant slot cars (slot trucks, actually.4)
A more practical solution may be using induction to charge the vehicle on the fly, essentially a giant version of a wireless cellphone charger embedded in the roadway.5 But thus far, the transportation sector is leaning toward hydrogen for heavy transport and freight.
See Frame 5, journal page 2095
Search for Figure C. Observe Figure C call-out of 30,000 m3 water / hour.
That means 24 hours per day, forever.
30,000 m3 / hr X 8760 hr / year = 263e6 m3 /yr.
Divide by U.S. annual fresh water usage of 421e9 m3 / year:
263e6 ÷ 421e9 = 0.000 62.
Multiply 0.000 62 X 8760 hours /yr = 5.4 hours.