Wave energy — Tidal study to map where power may be harnessed

By Naomi Klouda

This map shows the tide sampling stations in Cook Inlet.

Homer Tribune

Imagine a time ahead when tidal power will be as easy to tap as hanging up a solar panel. A time when turning on the lights involves depending on the power of storms rather than crude oil hauled from the depths of the earth.

That possibility might not be too far into the future.

Three partners launched 10 tidal monitoring stations last week from Turnagain Arm in Upper Cook Inlet to Kachemak Bay in Lower Cook Inlet for a viable start to the process. The National Oceanic and Atmospheric Administration Center for Operational Oceanographic Products and Services measures the currents and the Coast Survey Development Laboratory built a hydrodynamic model. The Alaska Energy Authority has the funding.

The project involves collecting readings from the meters over a two-month period, said Kris Holderied, manager of the NOAA Kasitsna Bay Laboratory.

“The current meters will be in place for two months and will be recovered in August,” Holderied said. “The current meter deployments are part of a partnership project between NOAA and the Alaska Energy Authority to quantify the tidal energy potential in Cook Inlet.”

Pursuing tidal energy was started in 2008 when Homer applied for a grant from the AEA. Work was done to establish partnerships between Homer, CO-OPS, Kasitsna Bay Lab, Kachemak Bay Research Reserve and private industry. The proposal twice was left out of the state’s energy funding proposals. Then in 2011, AEA and NOAA took the lead role with funding granted through the Renewable Energy Fund.

Now the task ahead is to create a “numerical model of water movement” within Kachemak Bay

Photo courtesy of Homer Tribune. Kenai Peninsula Borough Assemblyman, Bill Smith; Ann Marie Holen, who helped originate the tidal project while working for the city of Homer; Terry Thompson, director of the Kachemak Bay Research Reserve; Kris Holderied, manager of the Kasistna Bay Research Lab; Homer Mayor Jim Hornaday; and Rep. Paul Seaton aboard the MV Susitna.

and Cook Inlet, Holderied explains. The model will be used to produce estimates on a tidal energy potential for the entire inlet. In addition to this summer’s measurements, scientists also will look at currents and tidal reports from 2004-05, and measurements taken on elevation at tide stations. They will incorporate mapping details of the ocean’s hills and valleys from the recent NOAA Hydropalooza mapping project.

The CO-OPS team spent four days in Cook Inlet last week to drop off the meters, in what turned out to be unusually great weather. Chris Paternostro, a NOAA oceanographer, said they were fortunate to have calm sunny days on the water. “I’ve never seen Cook Inlet so placid as it was the four days we were at sea,” he said.

At each station a current meter is mounted looking upward in mooring buoys near the sea floor that are anchored by one or more railroad wheels — purchased for the project from the Alaska Railroad. During deployment of the equipment, the boat is positioned on the station. The crew then lays the buoys in the water and hoists the anchor over the side of the boat. When all is clear, the anchor is released into the water and the equipment free-falls to the bottom.

The buoys are attached by a mechanism that can be released with a pulse of sound when the crew comes back to retrieve the equipment and get the data. The meters were placed in some of the highest current regions in Cook Inlet.

It is precisely the strong, ripping currents that could have the potential to produce a lot of energy. One of the first to comment on Cook Inlet in the historical record was Capt. James Cook during his 1778 voyage. The tidal movement caused the ships to drift south on the current, the captain complained, so an anchor was set with each tide to prevent losing ground. They crept forward, sailing with the flood and anchoring with the ebb.

Just because a waterbody has tremendous storms and muscular tidal currents doesn’t mean

Deploying tidal measurement equipment in Cook Inlet.

it’s a good candidate for tidal or river-driven energy, however. Remote places in the Bering Sea, the Chukchi and even rivers like the Yukon possess great energy potential. But the tides need to be hooked into population densities and infrastructure to make it less costly to produce, Holderied said.

“So exactly here in Kachemak Bay, we are on the leading edge of it. We are close to power transmission lines,” Holderied said.

Other places in Alaska could be off the beaten path and still produce tidal energy to fuel small operations, like ice plants for canneries, she added.

“Cook Inlet and Kachemak Bay provide places most likely to have tidal energy development, close to the population grid. The model will produce a tidal energy potential map for the entire area,” Holderied said.

Tidal power remains expensive. Examples are on the increase, however, as a small number of projects prove the feasibility of tidal power each year. The Bay of Fundy project in eastern Maine provides a successful model in the U.S. France has vowed that by this summer, it will build the world’s largest tidal energy project near Paimpol-Bréhat in Brittany. That one is expected to bring power to 4,000 homes.

In the meantime, private industries are at work on producing the technology that will be necessary to harness and convert tidal energy into power. The technology used in the Cook Inlet study — that fit snugly in the bright yellow buoys shaped like little submarines — were developed by private enterprise. These are called Acoustic Doppler Current Profilers or ADCP, developed by Teledyne RD Instruments of Poway, Calif.

The ADCP bounces sound off little particles in the moving water and uses the change in frequency of the return sound to tell how fast they are moving. It’s similar to the way the sound of an ambulance changes as it moves towards or away from you.

“The ADCP is ingenious technology, because every five meters you get a measurement of velocity. So in 100 meters there are 20 separate measurements of water speed and direction from the bottom to the top. Like this one, in the near future we may get to see how smart folks in private industry, maybe including the local marine trades, will figure out new technology to produce tidal energy,” Holderied said.

The NOAA Office of Coast Survey in Silver Spring, Md., is developing the ocean circulation model. Data collected includes currents (this project), temperature and salinity (includes Kasitsna Bay Lab and KBRR oceanographic surveys) and water levels (NOAA tide gauges).

The prized product at the end of the study is this ocean circulation and tidal energy potential map that will go to the AEA. It will highlight the energy potential of the entire Inlet and Kachemak Bay.

“The second benefit is we will have an operational model to look at to plan for oil spill response, help with our ocean acidification studies, and understand movements of larval clams and shellfish between different bays. And we’ll see how water flow in Kachemak Bay is connected to the ocean,” Holderied said.

The information can then be used by scientists at Kasitsna Bay Lab, Kachemak Bay Research Reserve, Alaska Fish and Game resource managers and for planning at the Homer Port and Harbor.


1 Comment

Filed under Cook Inlet, science

One response to “Wave energy — Tidal study to map where power may be harnessed

  1. There is nothing “wave-like” about tidal currents. Wave water particles move in a circular path. Tidal water particles move in and out. Devices which produce electricity from waves are much different than those which generate from tides. Just to clarify the issue!

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