Some of the methods to eliminate venting losses due to boil-off gas (BOG) in liquid hydrogen systems are briefly mentioned here: https://blog.matthewemoran.com/search?q=myth+busting. This is also an example of the last option for me... needing to vent about the persistent myths regarding hydrogen.
Everyone agreed on the last option not being part of systems engineering. Unfortunately some version of that argument is often made when a new project starts. The cost and time impact of the decision often comes back to haunt the project for the remainder of its life. For an example approach to avoid this trap, see: https://blog.matthewemoran.com/2020/08/on-august-24th-i-was-on-forum-360-panel.html
This topic is discussed in detail here: https://blog.matthewemoran.com/2023/04/hydrogen-myth-busting-episode-3.html
When hydrogen gas is liquefied by bubbling it up through a container of liquid hydrogen, there is no system energy input associated with liquefaction for that isolated process. A lifecycle analysis is required to find the total liquefaction energy for the system based on its lifecycle operations. This would include the liquefaction input energy for the initial LH2 quantity plus any make-up LH2 added over the system lifetime.
The lifecycle analysis should also take into account any cold sink functions that the LH2 enables such as: cooling of various process streams; reduction of environmental heat leak; temperature difference driven power cycles; refrigeration cycles; etc. The resulting lifetime effective energy cost of liquefaction will be higher than zero but less than 20% for many systems.
This is why quoting "energy loss" due to liquefaction as a single value is a misleading figure of merit. In properly designed LH2 operational systems, a significant amount of this "lost" energy is utilized for other functions.
Everyone got this answer right! Unfortunately, most reports and studies still bake in the assumptions of distributed production, storage, and distribution when it comes to hydrogen. This is a remnant of the fossil fuel paradigm that doesn't apply to hydrogen systems that do all of those functions in one place. More on this topic here: https://blog.matthewemoran.com/2023/04/hydrogen-myth-busting-episode-3.html
The ability to produce prodigious quantities of potable water from hydrogen usage is also a significant and unique benefit that is often ignored. Same with the ability to have an isolated renewables microgrid operating anywhere on the globe using hydrogen storage. Additional comments about these aspects can be found here: https://blog.matthewemoran.com/2022/05/energy-shapeshifting-with-hydrogen.html
The answer to this question is 1 W/m^2. More details can be found in Section 3.2 of the Cryogenic Fluid Management report available online here: https://sites.google.com/view/matthewemoran/training#h.ir8xm9d8wn6h
This is a handy value to remember for doing quick assessments of heat load into an LH2 vacuum jacketed dewar (or an LH2 tank in space) with an inch of MLI applied. Equations for the surface area of common tank shapes can be found in Section 3.3 of the same report cited above.
There has been a great deal of inaccurate media coverage about hydrogen being a potential so-called "indirect" greenhouse gas (GHG). This reporting has grossly misrepresented the contents of some recent studies that are based on a series of unproven hypotheses that would require a good deal of research (and funding) to address.
Whether or not scientific investigation of this topic is a good use of research funds is debatable. The one known fact on this topic is that hydrogen is not a GHG. And there are no evidence-based facts to support that it will become an "indirect" GHG of any consequence. More of my thoughts on this can be found here: https://blog.matthewemoran.com/2022/05/hydrogen-myth-busting-episode-2.html
Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and break-through liquid, slush, and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a co-founder in seven technology startups; and provided R&D and engineering support to many organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management series. He also leads the monthly LH2 Era™ Webinar.