Chapter III, Section E:  An Ultimate Resource Limitation for Hydrogen?

The only byproduct of hydrogen fuel cell energy output is pure water, but with water as a source of the hydrogen, the pure water leaving a fuel-cell is derived from purified water entering an electrolyzer, a chemical electrolytic cell used for the production of hydrogen. Electrolysis can be conducted on either freshwater or saline water, however freshwater electrolysis is more efficient, putting more of the input energy (electricity) into hydrogen rather than byproducts. Freshwater electrolysis requires specific chemical solutions to be made with deionized water. Thus to avoid byproducts, the electrolysis of seawater requires initial desalination, which is also energy intensive. Desalination is increasingly being used as an option for producing fresh drinking water in arid regions, but the energy expense is only justified by the high population demand for drinking water in areas such as southern California. Alternatively the electrolysis of seawater or brine can be conducted using chlor-alkali electrolysis, but in addition to hydrogen, much of the energy is sunk into other compounds, such as chlorine gas and sodium hydroxide, requiring either market or disposal options for these byproducts.

Always the optimist and a champion for hydrogen, Rifkin extolled a 1995 project that used solar energy to produce hydrogen with an electrolyzer (Rifkin, 2002, p. 188). The hydrogen was then used to power a fleet of trucks using hydrogen combustion in vehicles, similar to vehicles converted to run on propane gas. Though the location of this project was coastal El Segundo, California, the water was de-ionized municipal water from the city’s water supply. With potable water in relatively short supply, especially in California, should it really be used for the production of hydrogen?

Reacted in a fuel-cell or in combustion, hydrogen produces pure water and becomes part of the hydrologic cycle. It is thus fitting to apply traditional concepts of source water consumption. The fuel economy of hydrogen fuel cell cars is now well known, with kilometers per kilogram hydrogen replacing the familiar miles per gallon gasoline. A value of about 110 km/kg is a good estimate for a small hydrogen fuel cell vehicle. This fuel economy can also be expressed in water consumed to make the hydrogen, clearly elucidating the water consumption implications of a hydrogen economy. The fuel efficiency is equivalent to 12 km / liter of water, or if you’d rather, 28 mpg water.

According to 1999 data from the U.S. Department of Transportation, 130 million passenger cars traveled an average 51 km (32 miles) per day. The fuel efficiency of hydrogen fuel cell cars would translate this driving into a consumption of 160 million gallons per day of highly-processed de-ionized water, and that’s just for the passenger-car-fuel fraction of the hydrogen economy. Given water scarcity, if we truly want a hydrogen economy, recycling the highly processed fuel-cell water will be essential.

Geologists are considering calling the present the close of the latest geological age, the Holocene, and the dawn of the next, the Anthropocene, a new geological age marked by the human footprint. The Anthropocene would recognize humans as the greatest agents of geomorphic and biologic change, from human modifications of the environment and human-induced extinctions reducing biodiversity. If we are truly overwhelming nature’s cycles, it is the life out of balance that requires additional energy to sustain the environment, beyond the natural energy inputs we take for granted.

How much energy is required to sustain the environment? An amount that dwarfs human consumption, though it goes mostly unnoticed. Solar energy is ultimately what removes environmental contaminants, driving the hydrologic cycle and many other biological nutrient cycles that either remove the contaminants or recycle them into the truly-renewable resources. What is that energy worth? Enough to economically consider the renewable resources–clean soil, air, and water–as equivalent solar energy resources. A complete energy economic system would assess the energy value of the order inherent in these resources. From this economic viewpoint then, solar energy is actually our most utilized energy resource already. How can these renewable resources be economically assessed in a new energy-based economy? The second law.

In the next discussion, an environmental balance sheet will be presented, a broad overview of our environmentally related energy assets and debits.

Previous
Table of Contents
Next