Editorial comment

	Vol. 230 No.6
PERRY A. FISCHER, EDITOR

Ocean thermal energy, ammonia and other dreams

The recent OTC conference drew over 66,000 attendees—the biggest oilfield event in North America, perhaps the world. Those who stick it out through Thursday are often treated to something a little different; this year it was Ocean Thermal Energy Conversion, or OTEC. I last wrote about OTEC in this column (June 2008), so this is in part an update, as well as a report on the special OTC session. I used the word “dreams” in the title, in part to acknowledge those who think that an abundant energy source is unachievable, at least in practical or economic terms. That is regrettable because it is not true, certainly not with OTEC.

Ocean thermal energy conversion is not new. The first functional plant was built in 1930. Nine plants have been built, three of them designed to produce net power; the rest tested heat exchangers or other subsystems. All were successful.

OTEC exploits a nearly inexhaustible energy source: the heat stored in the Earth’s oceans. Specifically, it employs a heat engine that uses the difference between temperatures at the surface and in deep water, say, 40−80°F.  The efficiencies are terrible, less than 7%, but that is not too important. The fact that the fuel is free overcomes the low efficiency, so only the capital cost of the project matters, i.e., the Capex. And the Capex makes this a very doable technology considering that the cost of the resulting electricity is about 20−25 cents per kWh, at least for the first couple of projects, after which costs would almost certainly come down. Also, since the process generates copious amounts of freshwater, if it can be sold into a water-needing market, the cost could be much less.

One consideration is the heat distribution in the oceans. While deepwater temperatures are about 39°F at nearly all latitudes, warm surface waters are oddly distributed. Still, they occur farther away from the equator than you would think, reaching 30° latitude in places, depending on currents. One study showed that, in the Gulf of Mexico, some 2,000 power plants of 100-MW size—about the equivalent of 200 large nuclear power plants—could be sustained without initiating any depletion of the heat source.

Estimates for a 100-MW plant are in the $1−2 billion range. The way that economy-of-scale works in a deepwater project like this is that if you try to build a plant smaller than about 75−100 MW, the cost per kWh soars. That’s because the costs do not scale down. Mooring systems, cable installations, construction vessels and other things do not cost less just because the plant only produces 1 MW. Even though there now exists enough know-how with the technology and with previous pilots to forge ahead and build the 100-MW plant, funding constraints and technical risk will still probably favor a much smaller plant, say 10 MW, which, if built, will no doubt be criticized for producing power at sky-high prices.

This is not to say that all of the parts for such a project are waiting on the shelf. But most of them can be adapted from existing industries. Our deepwater oil industry can contribute all of the structural components, such as deep-draft submersibles, poly-rope mooring systems, and cable/pipeline trenching and installation. Another key component, high-capacity heat exchangers, already exists across several industries. But the turbines, pumps and deepwater delivery pipe all have to be scaled up, since they don’t exist in the sizes needed for OTEC.

 The deepwater delivery pipe is a critical piece of equipment that will account for about 20% of the project cost. It needs to be at least 30 ft in diameter. Lockheed Martin, under a cooperative agreement with the US Department of Energy, is planning a pipe-making experiment off a floating barge. The pipe comprises longitudinal vinyl planks. Carbon fiber is wrapped around the planks, which are then “plastered” inside and out in epoxy. The resulting seamless pipe is lowered into the water as it is being constructed. The company has also completed a preliminary design of a semisubmersible-based OTEC plant and sees “no technology barriers to our project.”

Platform placement is a prime consideration. The closer to shore, the shorter the distance to transmit power, but the longer the distance to cold deep water, depending on the slope of the seafloor. Puerto Rico was cited as an ideal location due to deep water just offshore.

There is an old idea that is being increasingly contemplated as an energy carrier, and it’s not a hydrocarbon liquid, nor is it hydrogen. It’s ammonia. A new Solid State Ammonia Synthesis (SSAS) approach appears to be a game-changing technology for energy storage and transport, particularly for wind farms and OTEC. It is a 75% efficient process using electricity. Ammonia can be (and already is) transported much like oil, in barges, pipelines, trains and trucks. Less known is that ammonia can directly fuel an internal combustion engine. It did so in some countries during World War II, including bus lines, and could do so again. (Google The Ammonia Fuel Network.)

So, why hasn’t OTEC technology soared over the decades? Unfortunately, there isn’t a good answer to that. Status quo-ism is as good as any. Other technologies suffer from the same problem. Yes, it costs more, but given the tremendous benefits, plus the fact that this is reliable baseload power (unlike solar, wind and waves), you would think that it was a no-brainer to get funding and move forward. But you would be wrong.

Like nuclear power, private money doesn’t have the stomach for long-term research and billions of investment; in fact, if only private monies were used, there would be no nuclear power plants in the world. But unlike nuclear power, governments only want to throw token amounts to the OTEC community, since it traditionally has no GE, Bechtel, Brown & Root or other big corporate interest to be an activist (i.e., lobbyist) for it.

The ocean thermal community, long-frustrated for lack of a deep pocket, needs a couple billion or so to bring this technology into commercial use. Researchers are hopeful that it will get a modicum of money—probably in the tens-of-millions range—from President Obama’s increased spending on renewables.

Cheap? No, but not too expensive for a clean, (seemingly) environmentally sound, nearly inexhaustible energy source. All of the six presenters at the session kept repeating the same refrain that I did in my earlier column: There are no showstoppers here.