Harvesting the ocean's energy

A recently completed study by CEE’s Dr. Kevin Haas is prompting many energy researchers to start looking out to sea for answers.

There, along the southeastern shores of the United States, the Gulf Stream offers an untapped source of raw kinetic power – as much as 23 gigawatts (that’s more than the output of 15 nuclear power plants).

“A lot of that energy is dissipated and cannot be converted to electricity,” said Haas, who headed up the 2 ½ year Department of Energy (DOE)-funded study with CEE’s Dr. Hermann Fritz and CoA’s Dr. Steven French.

“But if you figure that we can convert a fraction of that, we still have a very attractive energy source.”

Their findings – including a detailed national database of all identified ocean currents– revealed that from theoretical and technological standpoints, the extraction of energy from the Gulf Stream is worth pursuing. But it’s not without some competition.

“Another DOE study I completed in 2011 showed that tidal currents could produce as much as 50 gigawatts, which is a lot more. But 47 of those 50 come from Alaska, so, for the lower 48, harvesting ocean currents is at least on a par with tidal stream-generated energy. Particularly in Florida.”

His CEE colleague agrees.

“Looking at the data on tidal currents, there’s a far better chance of their generating usable energy in the northern sections of New Hampshire or Maine, near the Bay of Fundy,” said Fritz.

“What’s exciting about the ocean currents we’re seeing, particularly off the coast of Florida, is that they are close enough to make them accessible from large population centers such as Miami. It is conceivable that they could be harvested.”

Generated by a powerful combination of trade and mid-latitude winds, the Gulf Stream is a formidable energy source – able to move as many as 9 billion gallons of water per second in some areas. It is relatively shallow (extending just 800 meters below the ocean’s surface), but, it is predictable, constant, and, close enough to our shores to make it an accessible for further exploration.

So far, that exploration has been mainly theoretical. Haas’s team spent much of its time creating a database of ocean currents – using information collected from seven years of numerical modeling conducted by a multi-institutional consortium that included the United States Navy. The database was validated using thousands of existing measurements, including buoys, drifters, radar and satellites, and other real-time measures.

The team then analyzed a number of variables -- including water speed and volume flux – at more than 8,000 collection points to come up with a watts generated/square meter calculation.

“We compressed several terabytes of existing data so we could increase awareness and market penetration of ocean currents as potential energy sources,” said Haas.

The researchers have made the data available to entrepreneurs and researchers who are interested in pursuing ocean current energy. A series of layered maps contains a wealth of information on the speed, energy, and depth of various ocean currents over time.

What emerged from their analysis was an observable increase in potential energy output in the channel between Florida and the Bahamas. There, the compressed geography seemed to squeeze more energy out of the robust currents.

In the Florida Current, researchers found that there was a potential annual power of between 4 and 6 GW, with a mean around 5.1 GW. The variation in potential energy output is a result of a seasonal fluctuation that Haas’ team found. In the summer months, the potential output is 25 to 30 percent greater.

“To put that in context, we’re talking about the Florida current alone powering about a million homes for an entire year if we could harvest just 30 percent of it,” said Haas.

“This would be great for Florida, where energy usage surges in the summer. Figuring out the regulatory implications of this is going to take some time, but there are already some developers interested in testing their technologies off the coast.”

The next step in their work involved calculating the technological feasibility of extracting the energy from its source. At the present time, there are no commercial vendors extracting energy from ocean currents, but the use of turbines is a logical extension of current practices.

Researchers created mathematical models to describe the cumulative effects of turbine-extracted energy on the remaining ocean current. This work is ongoing.

“We want to document the effect that removing this energy from the Gulf Stream will have,” said Haas. “We are continuing to create models to describe its possible impact on climate, and future energy exploration.”