The Hype about Hydrogen? A Life Cycle Perspective
By Davis Bookhart
Depending on who you talk to, hydrogen is either the savior of the world and fuel of the future, or a scam and pipe dream that is leading us down a road to ruin. One thing is certain, hydrogen is a versatile gas with great potential to benefit our decarbonization efforts. However, it is also vitally important that we understand precisely what this gas is and what it's not.
First, let's recognize that hydrogen is not a fuel. More precisely, it is an energy carrier, meaning that it can store energy, but only if you use energy to produce it in the first place. In this respect hydrogen is much more like electricity or a battery than a fuel like oil or natural gas. No one would ever mistake a battery for a fuel because it’s obvious that energy needs to go in before energy can come out. This is the same for hydrogen. Hydrogen doesn't exist naturally in a pure form. To get to the pure form, energy is needed. According to the laws of thermodynamics, more energy must go in than the amount of energy that will come out in the form of hydrogen.
Secondly, we recognize that every time hydrogen is converted into a usable form (like electricity or heat for a turbine) it loses energy in the conversion process. From a life cycle perspective we can count all of the energy consumed upstream and deduct all of the energy losses that come out through each conversion process. Figure 1 shows an evaluation done by Volkswagen when they were trying to determine whether they should invest in hydrogen fuel cells or electric batteries. When the life cycle of energy from beginning to the end of the process is laid out graphically, it becomes clear that hydrogen (even from green energy) is not ideal for passenger vehicles when compared to a high capacity electric battery.
Figure 1: Hydrogen and the Electric Drive
There's an argument that hydrogen may be a good option for heavy duty vehicles that run continuously throughout the day and night, like a public bus or transport shipping. There's also a strong argument that hydrogen, because of its high energy density, may be the only real green alternative for high heat processes like steel making. In each of these cases the life cycle of energy conversion can be graphed out in the same way. The conclusions might be different because the situations and alternatives require different life cycle analyses.
Of course, there are many different ways of looking at the life cycle of hydrogen, and this is a very simple exercise looking only at the energy conversion from production to end use. To really understand the benefits of hydrogen within a decarbonization strategy, we'll have to look at many other inputs including the original energy source that produces the hydrogen in the first place, conversion factors, infrastructure, and many other items. These are topics for future issues of the newsletter. However, this brief overview demonstrates the power of life cycle thinking.
Agree or disagree? Leave us your thoughts and let's start a conversation!
The opinions expressed within the writeup are solely the author's and do not reflect the opinions of the HKUST Life Cycle Lab.