IN recent months, there had been a quiet yet nonetheless discernible increase in the volume of interest and discussion about the use of hydrogen as an alternative energy source or to use a broadly encompassing term for it, the “hydrogen economy.”
The topic has piqued my interest for a couple of reasons. First and more generally, as a tree-hugging radical greenie, I consider any non-carbon energy concept worth careful study; second and more specifically, hydrogen power was a major area of research and development in my last couple of years with BMW at the beginning of this century. So, I have, perhaps, a slightly better than average understanding of the basic idea and applicable technology.
For the sake of not keeping my valued readers in suspense, let me cut to the chase: hydrogen is not a promising idea for large-scale alternative energy, at least not until there are some major advances in technology. Even then, it will likely not resemble the essentially painless substitute for fossil fuel energy that its most ardent advocates portray it to be, although it would be unfair to say that it would not have some worthwhile smaller applications.
Hydrogen as an energy source can be used in two basic ways: First, it can be used directly as fuel, more or less as a substitute for some form of petroleum. Second, it can be used for energy storage; when mixed with oxygen in a fuel cell, the reaction produces water, electricity and a small amount of heat. Also, when used as a vehicle fuel, hydrogen is considered “clean,” as the by-product of its combustion is mostly water vapor.
First, harvesting hydrogen is an inefficient and energy-intensive process. Hydrogen is the most abundant element in the universe, but because it is highly reactive, it does not exist in pure form anywhere on Earth in anything other than minute quantities. It can be separated by electrolysis of water (basically the opposite process of a fuel cell) or by refining it out of petroleum compounds (usually natural gas), but it requires a great deal of electricity. The subsequent energy that can be obtained from the hydrogen either as a fuel or as energy storage is less than that required to create it, which makes it an economic dead end.
While it is true that using renewable energy sources to provide the power needed to create hydrogen could render that inefficiency irrelevant, there are other technical problems that make hydrogen difficult and expensive to use. For one thing, a fuel cell requires pure oxygen, which is as expensive and energy-intensive to produce as pure hydrogen, if not more so. Atmospheric air, containing large amounts of nitrogen and carbon dioxide, will quickly “poison” a fuel cell and render it inoperative. An alternative – used mainly for vehicle applications – is to use a catalyst such as platinum or a conducting polymer, but these exotic and expensive materials drive up the cost of the system by several orders of magnitude.
Finally, the most promising use of hydrogen – as a vehicle fuel – has so far turned out to be nearly unworkable because hydrogen, being the least dense element in existence, has very low energy by volume. A hydrogen engine with performance that is acceptably comparable to a petroleum-fueled engine requires insanely high compression, which in turn requires more complicated metallurgy and construction of major engine components. BMW built several versions of hydrogen engines that worked as well as any of their tried-and-true gasoline-powered engines, but they were several times more expensive and required construction techniques that could not easily be repeated on a large, assembly-line scale; at least not without enormous expense.
If anything has doused hopes for a “hydrogen economy” more than other factors, it is probably the rapid development of efficient batteries. At the time hydrogen fuel cells were more seriously being considered as an energy storage system, battery technology had yet to evolve to the lighter weight, higher capacity forms we take for granted today. At the moment, there simply is neither a need nor a good business case that can be made for developing an alternative that is more expensive and less efficient.
Be that as it may, the evolution of batteries, while having essentially killed off hydrogen as a viable option for the foreseeable future, somewhat paradoxically also suggests that hydrogen technology may indeed still have a future, if one that may be much more distant than hydrogen proponents wish. Unlike nuclear power, hydrogen power has the fundamental advantages of being potentially limitless and completely clean, if its many technical challenges can be overcome. As long as someone still believes in it, there is the possibility those challenges can be hurdled, eventually.
Source: Manilla Times – Ben Kritz.