The Cutting Edge

Many have heard the phrase "The Hydrogen Economy" and it stirred hopes, but reality is not so rosy.

The hydrogen molecule, just a pair of electrons and protons, misbehaves in all sorts of ways.

Its tiny size allows it to slip past tank and pipeline seals, when under pressure it embrittles metals just like the loose neutrons from a nuclear reactor, and it can explode or cause a flash fire across a wide range of conditions.

Hydrogen doesn't even qualify as an energy source as it's not found in its free form anywhere on Earth—for us it's just an energy carrier. Every bit we have we've made by either stripping it from fossil fuels or by cracking water using electricity. The only way hydrogen qualifies as “clean” is if it's made with electricity that came from a renewable source. Sometimes this is called “green hydrogen” versus “brown hydrogen.”

We need a way to make hydrogen that is clean and we need a way to transport it that is technically feasible. Ammonia is the only carbon-free hydrogen carrier we can make today. It can be feedstock for hydrogen production as it is easily created using the freed hydrogen and atmospheric nitrogen. Ocean Thermal Energy Conversion (OTEC) can provide the clean electricity needed to do this.

Those not from the corn belt might not be familiar with ammonia, a common fertilizer and potential fuel. But Iowa alone dispenses 1.5 million tons per year from its 800 filling stations. The total national pipeline network for ammonia spans 3,100 miles and petroleum pipelines can be easily converted to expand that distance. Ammonia works as a fuel in everything from converted six cylinder Ford engines designed in the 1960s to the latest fuel cell technology, but diesel engines are the easiest to convert. The farm fleet is already largely diesel, the farmers are trained to handle ammonia safely, and the coming changes in allowable diesel particulates in 2011 will be the driver that gets farm vehicles moving to ammonia fuel first.

There are several visible renewable ammonia production methods in development today involving wind, hydroelectric, and solar power. OTEC receives much less coverage, despite its many technical and political advantages.

What is OTEC? The ocean's surface in the Gulf of Mexico can be eighty degrees in the summer. Three thousand feet below the surface the temperature hovers around forty degrees all year. OTEC is the process of producing electricity from the energy generated as heat transfers from one temperature to the other. Although the temperature difference in one gallon of water would only be worth about 300 hundred BTUs, multiplying that by a functionally unlimited supply would provide a great deal of usable energy.

Steam contains enough energy to directly drive a turbine to generate electricity, but this temperature differential between tropical surface water and deep ocean water is a different type, known as low quality heat. A process called the Binary Rankine Cycle is used to capture and concentrate the heat, and then transfer it to a working fluid that is used to drive a turbine.

The sun only shines during the day, and wind energy sites are considered excellent if they produce 40 percent of the time, but this temperature differential is always there. OTEC, producing day and night, will be as solid as a Pacific Northwest hydroelectric facility once put into operation.

There have been onshore OTEC tests done in Hawaii but the natural domain for this clean energy source will be the Gulf of Mexico and an area southwest of San Diego. The Gulf of Mexico is the right place to start for a variety of reasons. That ammonia pipeline network centered in the state of Iowa has its roots in Louisiana, where ammonia brought into the U.S. from Trinidad begins its journey to the fields of the Midwest. The Gulf of Mexico has been home to oil production for the last sixty years and hosts plenty of platforms, many of which will be falling out of use as various fields are played out. There are several styles of deepwater platform, and not all of them are amenable to conversion, but there will be plenty of construction work for companies currently servicing the oil industry as the change is made to ammonia as a fuel.

Politically there are issues. Ocean floor leases for oil production are the domain the Minerals Management Service, a federal agency in the U.S. Department of the Interior. One patch of ocean produces just as well as another for this purpose, so why would one pay the MMS for a lease? Bill Kumm of Arctic Energy, Ltd. believes the best solution is to use systems that drift in a defined area, maneuvering to stay near the most productive waters, but not be beholden to the MMS. These mobile ships are said to be grazing while a fixed position platform would be described as moored.

The situation is different in Mexico where PEMEX will begin capping wells in the rapidly declining Cantarell supergiant oil field in 2009 or 2010. Some of their deepest platforms are suitable for OTEC development and the income derived would provide welcome relief from the loss of the oil field, which currently produces an estimated 20 percent of the total Mexican government revenue.

Ammonia is not the only thing that could be done with the electricity that can be made from OTEC. Researcher Robert Cohen offers many alternatives, among them this intriguing statement from a report presented in May of 2008. "There is a substantial U.S. market for OTEC-derived electricity that can be delivered via submarine electrical cable, for example, from locations about 60 to 100 miles off Tampa, New Orleans, and Brownsville." Other schemes include producing methanol with captured carbon dioxide, smelting aluminum, desalinating water, and energy storage methods more exotic than ammonia that involve the creation of various metal salts.

There's just one tiny problem in all of this. The U.S. Department of Energy shut down its OTEC research program in 1995, just short of commercial scale systems going into production at military bases in the South Pacific. Until that program is revisited, plans to capture ocean thermals are just hot steam.

Neal Rauhauser is an analyst and consultant on energy and telecommunications. He is a member of the Stranded Wind Initiative and can be found at www.strandedwind.org.