Examples of CNLFs include: ammonia, hydrazine hydrate, carbohydrazide, and synthetic hydrocarbons that extract carbon from air or water thus meeting the carbon neutral criteria. The overarching goal is to find suitable substitutes for carbon dioxide emitting transportation fuels like gasoline and diesel while retaining their advantageous energy density, storability and compatibility with the existing distribution infrastructure.
Perhaps paradoxically, “carbon zero” liquid hydrogen is specifically excluded from consideration. No doubt, there are programmatic reasons for this exclusion based on other efforts in the DOE portfolio and investments previously made in hydrogen technologies and systems development. But there are also technical reasons to look beyond liquid hydrogen.
The Challenges with Liquid Hydrogen
Hydrogen’s low volumetric density and cryogenic normal boiling point of -253 C poses unique challenges. ARPA-E’s funding announcement document succinctly describes how this impacts storage and distribution:
“Hydrogen compression and, especially, liquefaction incur additional energy losses (up to 10 and 35%, respectively). In contrast to liquid H2, which boils-off with a rate of 1 – 4% per day depending on the tank, hydrogen storage and transportation as a compressed gas has very low losses. Therefore, the latter is a more attractive option for long-term storage (from days to seasonal).” — Source: “Renewable Energy To Fuels Through Utilization Of Energy-Dense Liquids (REFUEL)”, Funding Opportunity No. DE-FOA-0001563, April 26, 2016.
While the above may be true for currently available commercial systems, liquefaction energy and boil-off losses can be significantly reduced with proven technologies developed in the aerospace industry. In fact, zero boil-off liquid hydrogen systems have been developed by NASA and other aerospace organizations with combinations of advanced insulation, optimized structural/penetration design, Joule–Thomson cooling, para-to-ortho conversion cooling, crycoolers, and other technologies and innovative design features. An example test article is shown below.
|Source: Hastings, et al., “Large-Scale Demonstration of Liquid Hydrogen Storage With Zero Boiloff for In-Space Applications”, NASA TP-2010-216453.|
Keep It Local?
The table below shows parameters for evaluating the full costs of delivery transportation power using carbon-free energy sources from the subject ARPA-E funding announcement . Note that there’s an inherent assumption in this table that’s an artifact of our current transportation fuels paradigm that’s not in the footnotes.
By necessity, the evolution of our fossil fuel industries and infrastructure has been largely predicated on geographic separation of extraction, refining/processing and point of use. Oil or coal or natural gas doesn’t exist in every location where their derivative products are used. In addition to the far reaching geopolitical ramifications, this reality has resulted in the need for a vast distribution system to service every link in the fossil fuel supply chain.
But is this a mandatory constraint in a carbon-less energy ecosystem based on renewable energy sources and hydrogen? Renewable energy sources can be found anywhere, along with local sources for hydrogen production. It’s interesting to consider the case where transportation costs of hydrogen are not applicable due to production and point of use occurring in the same location. In that scenario, the total source-to-energy cost for hydrogen in the previous table becomes lower than the other carbon-free energy sources shown.
Many Paths Forward
Some combination of CNLFs, along with carbon-free hydrogen, will provide a transition path away from fossil fuels in transportation and stationary energy systems. Isotherm Energy is positioned for whatever that combination may turn out to be with our hydrogen energy architecture. Any of the CNLF options are compatible since they can be readily integrated into our architecture and processed into hydrogen at the point of use for the target application. The destination of a more sustainable energy future is worth the journey.
Matt Moran is the Managing Member at Moran Innovation, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems since 1982. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been involved in seven technology based start-ups; and provided R&D and engineering support to many industrial, government and research organizations. More about Matt here…