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Hydrogen Won't Save Our Economy
anaesthetica writes "Physorg.com is featuring a story asserting that hydrogen is economically infeasible as a replacement for our current energy sources. The premise is that isolating and converting hydrogen into a usable energy source takes up a great deal of energy to begin with, and that subsequently converting that hydrogen fuel into usable energy results in an overall efficiency of only about 25%. Apparently, the increasing scarcity of water is going to make hydrogen too costly and just as politicized as oil." From the article: "[Fuel cell expert Ulf Bossel's] overall energy analysis of a hydrogen economy demonstrates that high energy losses inevitably resulting from the laws of physics mean that a hydrogen economy will never make sense. The advantages of hydrogen praised by journalists (non-toxic, burns to water, abundance of hydrogen in the Universe, etc.) are misleading, because the production of hydrogen depends on the availability of energy and water, both of which are increasingly rare and may become political issues, as much as oil and natural gas are today."
Transport batteries ( I think we all agree that is what we are discussing here) require a few things to be practical: low cost of materials and ease of fabrication, high energy density, ease of movement of the material from one vessel to another and finally ease of synthesis and also conversion efficiency. Non-toxicity is important as is the effect on the atmosphere. There are very few materials that can match or better liquid hydrocarbons.
There is one candidate that should at least be considered. Nitrous Oxide. N2O is a saturated fluid under about 750psia at room temperature and it has a density the same as hydrocarbons. This means that vessels to store it are efficient. It is non-toxic although it is an anesthetic gas. It is very safe to handle and compatible with nearly all materials. This means that the devices to handle it are cheap to make. It is a liquid so heat of compression losses for movement are minimized. If it leaks it has a distinct odor and will generally not pose an explosion hazard- at least compared to H2.
N2O is a monopropellant- in other words it will decompose to N2 and O2 when passed over a heated catalyst. It reacts very completely and almost no NOx species are produced- good for pollution. Better still it has a high flame temperature which makes for high thermodynamic efficiency. So a turbogenerator running N2O does not have to have a compressor- it can work at least part of the time off of the storage tank source pressure. Heat from the environment or directed waste heat from the exhaust can help keep the remaining N2O warm and vapor pressure high. N2O has a decent energy density but more importantly you can add any fuel and increase the power release enormously. So you power with N2O when you can and add fuel when you need to accelerate. The power increase is rapid and significant.
It does have problems though- synthesis is complex and not presently at large scale. What would be great is to develop a catalytic system that could take atmospheric N2 and O2 and under proper conditions directly synthesize N2O which could then be stored. Sounds hard to me but you never know. In any case there is no shortage of the precursors. It is however a nasty greenhouse gas. This could be its worst issue- lareg releases of unreacted N2O could be worse than CO2. But at least these are accidental and incidental- not part of everyday operation.
Anyway it is something to ponder. I always thought that a N2O vehicle with ethanol fuel assist sounded pretty good- and what a party car!