|Image credit: Raphael.concorde - Photo taken at NASA KSC chemical processing facility, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=81758142|
Colorless by Any Other Name
Take a look at the above photo of liquid hydrogen being poured. What color is it? If you see anything other than colorless, it's time to make an appointment with your eye doctor.
Well into my fourth decade of developing and testing hydrogen systems, I can confirm that hydrogen is colorless in all it's forms: liquid, gas, solid, and supercritical. (Liquid oxygen, however, has a faint bluish tint; and it has an elemental issue with us arbitrarily assigning it's natural color to hydrogen even though it loves meeting up with a couple of them and hanging out at the pool).
So why the rainbow of colors being assigned to hydrogen based on how it's produced and whether carbon is involved (among other aspects)? We could create similar color labels for batteries based on similar criteria but we don't. So why are we doing it with hydrogen?
Choosing the Right Metrics
“For the simplicity on this side of complexity, I wouldn’t give you a fig. But for the simplicity on the other side of complexity, for that I would give you anything I have.” ― Oliver Wendell Holmes Sr.
I would argue that the various color schemes being concocted for hydrogen fall on 'this side of complexity'. They are an attempt to characterize the environmental impact of various methods for producing hydrogen. Unfortunately, however, they obscure a more accurate and circumspect accounting of the benefits and drawbacks of these methods.
A better set of metrics that would get us to 'the simplicity on the other side of complexity' should include a lifecycle assessment of: environmental impacts, effects on public health, and depletion of resources.
And since we humans like to assign a monetary value to everything, it would be most useful to distill these metrics into a single Cost (with a capital 'C') value per joule of energy provided. Then we can make a much more comprehensive comparison of options based on this all-inclusive aggregate metric.
A Definition of Terms
Lifecycle - sometimes called 'cradle to grave' - takes account of everything associated with a particular system or process. Exploration for natural resources; mining; refining; sourcing; distribution; manufacturing; assembly; commissioning; operation; maintenance; replacement; recycling; and other aspects all fall within a lifecycle assessment.
Environmental impacts include contamination of soil, air, and water; the multitude of greenhouse gas effects; destruction of biodiversity; and other damage caused to the global shared commons. This damage caused by a particular energy source can be assigned a monetary value per joule that is the present value of a series of 'payments' in perpetuity.
Effects on public health include diseases, injuries, and deaths attributable to an energy source. These can be cumulative over a long period of exposure time, or result from associated accidents or catastrophic events. Similar to environmental impacts, a monetary value can be calculated based on the causal statistical occurrences projected into the future.
Depletion of resources extracted from the ground or oceans that do not naturally replenish are the most obvious examples here. But wealth is also a limited resource; whether individual, organizational, or governmental. Capital invested in new energy production or storage assets does not reappear in the bank account the next day. All of these depleted resources can be assigned a monetary value per joule projected into the future similar to the other metrics.
Let's Put the Color Wheel Away
Is putting together such a set of metrics and distilling it down to an all inclusive Cost per joule for comparison of energy options doable? Or should we keep using incomplete simplifications like color coded hydrogen to inform our decision making?
I think we should go beyond the color coding and typical business case metrics, especially when it comes to public policy. The associated lifecycle environment, health, and resource depletion costs for a particular energy process or system are rarely levied on the producer or user. Yet they are significant real costs paid by all of us to varying degrees, and every generation after us.
It's much more work to quantify these costs, but not impossible. And when large amounts of taxpayer money are being diverted to incentivize one energy option over another, the extra effort should be made to assess these externality costs.
The math is relatively simple. It's finding, processing, and inputting the right data that's a challenge. But there are mountains of relevant historical data that can be brought to bear. Perhaps this is a worthy focus for some of the machine learning and AI capability developing so rapidly now.
Or we can keep adding new colors and hope for the best. I'm with Oliver Wendell Holmes on that approach... wouldn't give you a fig for it.
Postscript (Aug 20, 2023):
Have had some very good discussions on this topic after publishing the above post. One colleague mentioned the relative benefits of 'blue' vs 'green' hydrogen with regards to emissions and cost. He stated that approximately 95% of all hydrogen is currently produced from natural gas and coal (so called 'grey' and 'black' or 'brown'). And if these processes are converted to 'blue', between 9 and 12 tons of carbon dioxide would be stored instead of emitted for every ton of hydrogen produced.
He then compared this with 'green' hydrogen produced through electrolysis which he said requires precious and rare metals such as platinum along with water distillation, and then stated that this makes the green hydrogen up to 15 times more expensive than the polluting ‘grey’ one. An interesting perspective that I appreciated him sharing, and a good example of why color coding of hydrogen is inadequate to compare options.
PEM electrolyzers currently use platinum, but alkaline and other water splitting options use little or none. And direct solar hydrogen production methods using iron based catalysis are under development. So 'green' can mean a lot of things with very different cost drivers.
It is true that most of the current and legacy hydrogen production has been via steam methane reforming (SMR) of natural gas. So doing carbon capture, utilization, and storage (CCUS) of the resulting carbon dioxide eliminates that greenhouse gas (GHG) source.
But what about fugitive natural gas leaks that recent satellite monitoring shows are significantly higher than previously documented, and are a much more powerful GHG source? And coal has it's own issues regarding public and worker safety and health (e.g., respiratory and other diseases, mining injuries and deaths, etc.)
Should public policy support new hydrogen production capability using natural gas and/or coal feedstocks with CCUS, or only retrofits of existing SMR assets? Should we focus on less use of platinum, or recycle and utilize it better? 'Green vs blue' won't answer these questions, we need the monochrome tools of engineering and economics.