Updated 12/11/20 for clarity on fuel cells
If you follow energy transition conversations, you may have noticed that hydrogen is having a bit of a moment. From technical assessments to roadmaps, pilot projects to public-private partnerships, the topic is suddenly seemingly everywhere, rapidly assuming the mantle of deep decarbonization darling du jour.
The excitement is for good reason. Hydrogen has significant, sector-spanning potential, a carbon-free fuel that can be used in all sorts of otherwise-hard-to-decarbonize applications where fossil fuels have long been considered required. Truly, potential abounds.
But, as ever, there’s a catch. Make that a few, including these top two.
First, precisely because of the many and varied ways in which it can be deployed, hydrogen also affords easy cover to intransigent fossil fuel interests who are increasingly waving away objections to near-term natural gas investments with vague nods toward improbable—if not outright impossible—future transitions to hydrogen replacements.
Second, the entire premise of hydrogen as a decarbonization pathway hinges on the fuel itself being generated in a way that’s carbon free, and that is very much not a given. Because although the poster child is “green” hydrogen—the compelling systems-level solution of turning abundant renewable electricity (green) into a carbon-free fuel (hydrogen)—the overwhelming majority of hydrogen in use today is produced via an emissions-intensive, fossil fuel-based approach, and there are a multitude of cost hurdles, resource constraints, and pollution-heavy alternatives standing in the way of such a pivot to green. And even then, there remains a distinction between green, and truly clean.
Which all makes it critically important that conversations around hydrogen applications and hydrogen production get grounded in reality, and fast. Otherwise, we risk abetting the self-serving misdirections of flailing fossil fuel interests and the very real economic, environmental, and public health costs those misdirections bring.
So here, a brief introduction to this new frame for hydrogen, to help differentiate between the promise and potential and the distractions and misdirections.
Hydrogen applications
In today’s economy, hydrogen’s role is largely limited to that of a chemical feedstock, primarily used for oil refining and fertilizer production.
The potential for hydrogen, however, is vastly more expansive: a flexible fuel capable of shapeshifting to meet the energy needs of a wide range of energy end uses, including those that the long cord of clean-energy electrification may not readily reach—end uses like industrial applications, long-haul aviation, maritime shipping, and heavy freight, relying directly on hydrogen or a hydrogen-derived fuel.
Alongside other measures, hydrogen also has the potential to help address the small but significant balancing and gap-filling needs of a high-renewables electricity grid, displacing the role of a resource like dispatchable natural gas.
But for the hydrogen hopeful, interventions like the above are only just the start. Home heating, cooking, vehicles, trains—if it runs on fossil fuels today, a pitch exists for it to run on hydrogen, or a hydrogen-based fuel, tomorrow.
Hydrogen production
Critically, one key assumption underlies the whole of the hydrogen-as-decarbonization premise: the process by which hydrogen is generated must itself be decarbonized. Otherwise, it’s simply an exercise in shifting the point at which carbon pollution occurs.
Today, 95 percent of hydrogen in the US is produced via the emissions-intensive, fossil fuel-based approach of steam methane reforming, resulting in what’s commonly referred to as “grey” hydrogen.
But several lower-carbon production alternatives exist, primarily in the form of one of two pathways.
The first, “green” hydrogen, sidesteps emissions entirely by using renewable electricity to split water into hydrogen and oxygen through a process called electrolysis.
The second, “blue” hydrogen, lowers the carbon emissions of fossil-based approaches by applying carbon capture and sequestration to the reforming process.
Another potential source of hydrogen involves gasification of biomass, which, while immediately confronted with complex questions of where suitable biomass would come from and what that would mean for forests and competing biomass uses, is of particular decarbonization interest given that overall emissions could be carbon negative if process emissions are sequestered.
Additional research is also considering the emerging potential for iterations of these and other pathways, including pyrolysis, photolysis, autothermal reforming with capture, and high-temperature process heat from nuclear.
Minding the flags
So that’s the pitch: a paradigm-shifting fuel that enables today’s entire fuel-based paradigm to stay the same, just without the carbon this time. And for the starry-eyed, that’s where the pitch remains.
But as laid out, this vision skips past a lot of flags along the way—flags that differentiate between potential that is limited, as opposed to limitless. Here, a look at just a few.
Emissions intensity of blue hydrogen. Because the carbon case for hydrogen turns on the emissions intensity of its production, the question of whether or not blue hydrogen is actually low enough carbon leaps to the front of the line. And here’s the thing. While the capture of process emissions may improve from today’s aspirational range of 80 to 90 percent to something higher, there’s also all the methane emissions currently occurring upstream. When taken together and scaled up, these emissions are not just significant, they threaten to relegate blue hydrogen to a middling solution at best.
Cost and scalability of green hydrogen. Questions around green hydrogen have long focused on issues of cost, but cost projections are dropping as cheap renewables surge online and promising electrolyzer advances and economies of scale set in. Further, as renewable penetration increases, green hydrogen can optimize use of renewables that would be otherwise curtailed during periods of renewable abundance, yielding a system-wide benefit. However, theoretical cost projections only go so far in the face of actual scaling requirements, as the sheer capacity of renewables required for a hydrogen-based economy would present a serious challenge, especially when considered in parallel with the already-daunting procurement requirements of the transitioning electricity sector, which will itself be expanding due to widespread electrification.
NOx emissions from hydrogen combustion. What could be more elegant than using renewable power to split water into oxygen and hydrogen, and then using that fuel to generate emissions-free power with only water as a byproduct? Certainly not this: when hydrogen is combusted (as opposed to used in a fuel cell), it can generate significant NOx emissions, commensurate with that of natural gas combustion—or worse. Which means that while hydrogen can be carbon-free, an oft-overlooked fact is that unless dedicated NOx-mitigation research is advanced and combustion improvements made, hydrogen combustion may not be pollution free, unacceptably risking a further perpetuation of pollution harms.
Storage and distribution of hydrogen. The storage and distribution of hydrogen is superficially similar to natural gas but raises unique challenges requiring special materials and processes. From point of production, hydrogen can be stored in limited-capacity aboveground tanks or large-but-geographically-constrained belowground caverns, and transported as a gas via pipeline, liquified for shipment, or further converted into a more dense carrier like ammonia—each with implications for how the initial cost of production stacks up against the final price at point of consumption. Widescale distribution via pipeline is central to many visions of a high-penetration hydrogen economy, appealing in part because it can seemingly be done in a manner similar to, and even in concert with, today’s distribution and use of natural gas. However. Today, depending on the specifics of the pipeline system, hydrogen can be mixed in with natural gas at volumes ranging from about 5 to 15 percent; above that, pipelines—and compressors, and monitoring systems—can require upgrades or full replacement to prevent embrittlement of materials and leakage of product.
Conversion of end-use appliances. A key sell for hydrogen enthusiasts is that widespread use allows so much of how we currently operate to remain the same, from hydrogen in turbines to hydrogen in stoves. Except, similar to pipelines, to actually run on hydrogen, all such appliances require retrofit or replacement. And in the interim years, end uses can have very different tolerances for the amount of hydrogen that can be mixed into natural gas systems before issues arise. Development of robust safety standards specific to hydrogen will also be paramount, given its explosive nature, the near-colorless flame that occurs when it burns, and challenges associated with mitigating and identifying leaks.
Hydrogen as building block for low carbon fuels. Hydrogen can theoretically be used to synthesize zero-carbon substitutes for today’s fossil fuels, from methane to longer chain hydrocarbons including gasoline, diesel, and jet fuel. But the process of making electricity into hydrogen, pulling carbon out of the air, then building up the hydrocarbon fuels is tremendously inefficient, and vastly less efficient than using renewable power directly—it would, for example, take more than four times as much renewable energy to power a car running on synthetic liquid fuels than running it directly on renewables—and the final result would be a still-polluting fuel, meaning this approach is one of last resort, not a justification for continued broad-based reliance on hydrocarbon fuels.
Hydrogen’s role in the clean energy transition
The core components of our clean energy transition are increasingly snapping into focus: widespread investment in energy efficiency, accelerated and sustained deployment of renewables, and electrification of everything that can be switched from running on fossil fuels to running on a cleaned up power grid instead.
Those actions will get us a long way toward a clean energy future. But they can’t do it all, especially when it comes to energy end uses that don’t readily or fully lend themselves to electrification. There, interventions such as hydrogen could have a critical role to play. This includes for fueling long-haul aviation, maritime shipping, heavy freight and some on-road vehicles; supporting industries like steel production and cement making; serving as a cleaned-up chemical feedstock for things like fertilizer production; contributing to the flexible dispatch and long-duration storage needs of a high-renewables electricity grid; and supporting context-specific decarbonization requirements that cannot be otherwise met.
Hydrogen as a strategic intervention is undoubtedly a scaled back role when compared to a full-on hydrogen-centered economy; however, it’s important to recognize that even this “limited” adoption would amount to a lot of hydrogen being produced, many times greater than that already in use in the economy today.
And here’s where hope and hype collide, and the damaging reverberations of ill-considered pathways begin.
We already have our hands full building out enough renewables to clean up the electricity sector itself while electrifying a multitude of additional end uses; a commitment to widespread use of hydrogen would further grow those needs. Enter the fossil fuel industry, and its touting of blue hydrogen as a supportive bridge.
We’ve been down this road before.
And as before, once the infrastructure is built and the stakeholders are invested, path dependency is a bear to break. Meanwhile, the fossil fuel-based pathway will be perpetuating pollution in extraction and transmission, limited and largely unproven sequestration resources will be required, and there is no guarantee that the infrastructure built to support a methane-based hydrogen system will be at all aligned with the infrastructure required for a pivot to green. So what then? Will we pay to transition again, or stay stuck on a carbon-heavy ride?
We simply cannot afford the time, the cost, and the pollution of another fossil fuel folly.
Which means that hydrogen decarbonization pathways should only be pursued when better alternatives do not exist and public health and environmental impacts can be mitigated, and each pursuit must address the risks of going in with visions of green and coming out laden with the consequences of swapped commitments to grey and blue.
What’s next for hydrogen?
Hydrogen is slated to play a critical role in deeply decarbonizing our economy by extending clean energy resources to applications where clean energy resources would not otherwise reach.
But criticality of strategic interventions is different from wholesale uptake.
Hydrogen boosters push the view of one new fuel to rule them all. Yet there is a gaping distance between what hydrogen can do and what we should push for hydrogen to do—and in the chasm between lie false promises, insufficient progress, and damaging environmental and public health fallout.
To get this right, at a minimum we must fully consider and address the safety, environmental, and public health impacts of hydrogen production and use; invest in research, development, and deployment to advance green hydrogen production processes; rigorously prioritize strategic hydrogen applications, such as those where other decarbonization options do not readily exist; and continuously probe the true long-term decarbonization potential and air pollution impacts of proposed hydrogen pathways.
And most of all, for all things hydrogen we must proceed with eyes wide open, seizing opportunities to leverage this valuable resource where we can while calling out distractions and misdirections where we must.