Mapping US Tidal Power Potential

When I was young, I lived just a couple minutes from the ocean, and during the summer I went to the beach almost every day. Sometimes there was nothing more than a few yards of rocky shoreline exposed. At other times, when the tide was out, the smooth stones gave way to rippled sand that stretched over a half mile out to the horizon. Those were the best days, when my brother and I had time to collect sand dollars, dig for clams, and build sand castles. Eventually, the tide would change, and the water would start its journey back towards the rocks.

In places like Puget Sound in the Pacific Northwest, strong tidal currents could be harnessed to generate electricity. Credit: mikeyskatie/flickr.

Even though the incoming water could swallow up a sandcastle in mere minutes, I never thought of the tide as being powerful. But in some places, like Puget Sound in the Pacific Northwest, a changing tide can send water rushing through channels so narrow that it picks up incredible speed. In fact, this tidal water flow can be so powerful that its energy might someday be harnessed to generate electricity, just like water that flows through a hydroelectric dam on a river.

No power stations that use tidal power have been built in the U.S. yet (though several countries, including France, Canada, and South Korea, have operational stations), but there is growing interest in the idea of undersea turbines that capture this renewable energy source. The Department of Energy (DOE) has funded several tidal power test projects, and numerous international companies have recently been testing their turbines in places like Scotland and Cobscook Bay, Maine. More tests are scheduled off the coast of Washington during the next few years, including some that will evaluate what impact turbines might have on marine life.

Developing the right technology to harness tidal power is an important part of using it to make electricity — right now, most of the prototypes either look something like underwater windmills or submerged exhaust fans. But more than the right machinery is needed to make tidal energy a realistic renewable option for the U.S. We’re still pinpointing which parts of the coastline have tidal currents strong enough to generate useful amounts of electricity.

Thanks to a new survey, however, researchers from the Georgia Institute of Technology in Savannah, in collaboration with the DOE, have calculated how much energy is available from tidal currents along the U.S. coast (using computerized ocean models). This includes shorelines along the East, West and Alaskan coasts, as well as inlets and estuaries that experience large tidal fluctuations, like Delaware Bay and Puget Sound. In recent years, several other countries, including the U.K., China and Canada, have similarly measured the tidal energy potential along their own shorelines.

The Georgia Tech team has also put together an interactive map that illustrates average water depth, current speeds, and tidal power potential, along all U.S. coastlines. When you zoom in to get a closer look, the shoreline is color-coded to show the regions with the highest tidal power potential. 

A new interactive map from Georgia Tech illustrates the energy potential of tidal power in the U.S.. Credit: GATech.

The map also has other features for people that really want to explore some potential energy specifics, like how big a current is generated from tidal changes at specific locations. These bonus features are more useful for researchers than they are for you or me. On the other hand, the map itself shows pretty clearly where we might expect tidal power systems to be built in the future (hint: have a look near Anchorage, Alaska, and Nantucket, Massachusetts).

It’s estimated that tidal power in Alaska could generate as much as 16 TWh/yr of energy (about four times more than what Hoover Dam generates in an average year). In the Lower 48, the potential energy from tidal power is just a fraction of that (just 0.6 TWh/year from Puget Sound, for example). Considering that no tidal power plants in these areas have even been approved yet, it’s going to be several years, or even decades, before Americans can rely on tidal power for their electricity. But for some regions, DOE says the energy from tidal currents will help meet the goal of generating 80 percent of America's electricity from clean sources by 2035.