Have we lost you already in the eternal alternative fuels discussion? From gas to electric to hydrogen to natural gas – there are no shortages of powertrain options these days for those looking past diesel. But what we haven’t talked a lot about is hydrogen. While everyone has been focused on electrification, hydrogen has been steadily making inroads.
Hydrogen offers an effective alternative to batteries. You can “fuel up” faster and the storage medium and supporting infrastructure is lighter and more compact. Hydrogen can also be stored indefinitely with zero energy loss. And while hydrogen is a volatile gas, it is actually much safer than people think. And when compared to lithium-ion, which can burn for days in the event of a breach, hydrogen doesn’t react that way.
Hydrogen can also be renewably harvested from wind and solar power generation and can be created and used on site. It can also be made to scale and stored at commercial-scale production facilities and then transported safely to where it is needed. And it doesn’t need a heavy amount of infrastructure.
How Does it Work
But the question is, how are hydrogen trucks powered? Put simply, once on the truck, the hydrogen – which is in a gaseous state, enters the fuel cell and recombines with oxygen pulled from ambient air. This air itself has flowed over a catalyst-lined membrane. In industry parlance, this is called an electrochemical transaction. The reaction itself produces an electron and the capturing of that electron produced power.
Of course, this is a huge oversimplification of what is otherwise a very complex process taking place within the fuel cell. Yet, in the end, the byproduct is quite simple: water vapor. While most people would ask what is not to like about a power source emitting nothing but water vapor, hydrogen is not without its critics.
Critics say that the energy loss problems start at the production side. Consider the primary ways hydrogen is produced, through steam reforming of natural gas and electrolysis. Currently, 95% of all hydrogen used in commercial vehicles and other forms of production comes from steam reforming of natural gas, or methane. Electrolysis only accounts for about 4% of the total, according to the Department of Energy.
Problems with the Process
The problem is with steam reforming. This process creates a high-temperature steam which produces hydrogen when combined with natural gas. While this is the least expensive way to produce hydrogen, it creates a wealth of greenhouse gas components, such as carbon monoxide and carbon dioxide. And depending on the feedstock used in production, a ton of hydrogen could yield ten tons of CO2. In the end, net energy yield from steam reforming is negative.
Conversely, electrolysis uses electricity to split water molecules into two atoms of hydrogen and one oxygen atom. This form of capture can be compressed and stored for future use. Yet, this method is not without its downsides. The process itself consumed 30% more energy than it produces. Fortunately, there have been advances in materials engineering to increase overall efficiency.
Engineers and researchers have come up with something called a Proton Exchange Membrane (PEM) electrolyzers. These devices use the same type of process utilized in a hydrogen fuel cell, but they do it backwards. As this process is further refined, many believe it could reach up to 80% efficiency before 2030.
Another issue lies in losses that occur when the hydrogen is compressed. To put hydrogen into a state that makes transport and storage economical, it must be compressed to between 5,000 and 10,000 psi, or it must be cooled to around minus 425 degrees in liquid cryogenic tanker trucks. Not only is this a huge process, but energy losses occur during these transitions.
Looking Past Efficiency and Batteries
Still, it is important to note that efficiency is not the entire story. While some may think net energy loss may be a good reason to forget about hydrogen power, it is important to remember that efficiency isn’t everything. Energy harvested from solar, wind, and other renewable sources cannot always be used at the moment they are produced. This all depends on local electric grid loads, of course.
Fortunately, excess renewable energy can be stored and used later, even if the efficiency of the collection and consumption of the energy is not entire optimum. There is an argument to be said for charging batteries from the grid, however, as this method is much more energy efficient.
Batteries come with their own drawbacks. There are environmental and worker considerations related to mining the materials needed to make batteries. There are also decommissioning concerns. What is the most environmentally conscious way to dispose of batteries? We all have heard and read about mountains of electronic waste in third-world countries. Are battery technologies destined for the same fate?
There are also significant downstream problems that come from battery power. The size and weight of batteries when compared to hydrogen storage tanks is far, far heavier. Hydrogen tanks can also be refueled faster than batteries.
Truckers waiting at an electric charging station may find themselves spending an excessive amount of time waiting for their truck to charge. Even fast-charge stations cannot match the time it takes to refuel with hydrogen or diesel. Compare 10 to 20 minutes to fill a hydrogen tank compared to a battery, which can take several hours, and there really is no comparison on that front.
Fuel Cell Stack Optimization
Hydrogen fuel cells are powered by fuel cell stacks, which is comprised of dozens of proton-exchange membrane fuel cells. You recall we referred to PEM technologies earlier. PEM forms the basis of a fuel cell stack. Since a single hydrogen fuel cell produces a small amount of energy, the fuel cell is set up with stacks of these cells. When combined the output can be quite high.
Put together, around 400 fuel cells put together produces around 120 kilowatts. And while this may differ depending on the producer and methodology, the eventual energy output is usually similar. Producers may use different membranes or catalyst formations, or they may use a different reaction method, but in the end, it is still hydrogen power.
In the end, the more stacks you add, the higher your overall kilowatts will go. So, you must increase the stack output proportionally with the number of fuel cells. Once fully assembled, the fuel cell can be further optimized by careful calibrating the amount of air that runs through the stacks. The cooling process also provides another opportunity to refine energy density.
Hydrogen power shares some similarities with diesel powerplants. Diesel engines require additional water pumps if you want to add more cylinders or increase displacement. For hydrogen-powered variants, you would simply increase the size of the water pump. Fuel cells do face the same types of problems battery makers do, such as available real estate on the vehicles.
Since OEMs want to fit fuel cells into the engine bay, fuel cell manufacturers have had to adjust the shape of their cells. Many have opted for easily interoperable cube shapes. Modular fuel cells allow them to be stacked next to other vehicle components. Compact spaces allow for more real estate for other truck components.
The Future of Fuel Cells
Even as we talk about the pros and cons of fuel cells and other energy generation methods, we have to acknowledge we are a long way off from seeing full-scale commercialization in big rigs and other commercial motor vehicles. Many OEMs are looking at 2021 as a year that the hydrogen industry breaks out, but then again, many have been saying it was ready for a breakout for a long time.
Still, full-scale hydrogen power for commercial motor vehicles is a tantalizing idea. Hydrogen is, after all, the most abundant element in the universe. We would certainly never want for a fuel source. It also occurs naturally in a compound form. And since water and hydrocarbons are among the world’s most abundant sources of hydrogen, the key is to figure out an environmentally friendly and cost-effective method for extracting it and utilizing it as a fuel source.
Whatever happens, the carbon-free transportation supply chain is upon us. As the world emerges from the shadow of COVID-19 and looks towards a renewable future – with states like California pressing the mandate – alternative fuels like hydrogen will only become more and more commonplace.