Tidal energy measurements to come to Cook Inlet next summer
by Ben Boettger
Growing up in Homer, Levi Kilcher was accustomed to seeing small beaches grow in the course of hours into expansive mudflats, to watching for sandbars that appear and disappear, to seeing boulders far offshore rise from the water and be swallowed again – all changes brought twice a day by the extraordinary tides of Cook Inlet. The difference between Cook Inlet’s high and low tides can be up to 35 feet – the highest tidal range of any coastline in the United States, and the fourth highest in the world. Seeing this immense volume of water run its diurnal course, Kilcher wondered if the energy it carried could be tapped for human use. Next summer he may take a step closer to an answer.
Kilcher, a researcher at the National Renewable Energy Laboratory (NREL), lives in Colorado now but still spends a lot of time thinking about Cook Inlet’s tides – and not only in a nostalgic way. In 2016 he was part of a team that ranked potential sites for tidal power development, following up on a 2011 study that used a mathematical model to estimate the power available from tidal flow along entire U.S coastline. The conclusion?
"Cook Inlet is the premier site for tidal energy in the whole country,” Kilcher said. “The state of Alaska has 90 percent of the nation's tidal energy resource, and nearly 40 percent of it is right here in Cook Inlet. The lion's share of tidal resource, really in the whole country, is right off of Nikiski. That's due to the tidal harmonics, which sync up really well with the size of that basin.”
Kilcher had planned a trip back to his hometown in April to make detailed measurements of Cook Inlet’s tidal energy potential, which could be key to enticing tidal power start ups to the area. However, those measurements will have to wait. This year COVID-19 travel restrictions canceled the trip, and Kilcher is now planning to deploy the measuring instruments from April to early July 2021.
Tidal Potential
Roughly 75 miles north of Homer, Cook Inlet’s coastline tapers inward through a pinch created by the east and west Forelands. Here the Inlet and its tidal force rush through a passage about 10 miles wide, separating the upper from the lower Inlet.
“Tidal energy sites are sites where the flow is constricted between two larger bodies of water,” Kilcher said. “San Francisco is a really easy example to picture. The flow gets constricted at the Golden Gate, and you get really high velocities flowing between San Francisco Bay and the open ocean. But the actual amount of flow that goes through the Golden Gate is really small compared to the flow that goes through Cook Inlet each tidal cycle. The pinch point between the two Forelands off of Nikiski is where the flow accelerates and where we see all this tidal energy.”
Most of the “tidal hotspots” that NREL identified in its 2011 modeling of the U.S coastline are similar narrow straits. Alaska, with 55 tidal hotspots, overwhelmingly leads NREL’s list. Washington state follows with 16, and Maine is a distant third with 8. In terms of power, Alaska holds 47 gigawatts of the nation’s total 50 gigawatts of tidal potential. Within Alaska, Cook Inlet’s potential leads the list with 18 gigawatts. For comparison, the Railbelt presently has around 2 gigawatts of generation.
Potential is one thing; realizing it is another. NREL’s follow-up research in 2016 brought the needs of tidal power start-ups into the equation. In addition to power density and water depth, this study considered the size and distance of energy-consuming population centers, the cost of power at those centers, and shipping costs to the site. These commercially important factors eliminate many Alaskan locations, primarily because of their distance from existing transmission infrastructure. Electrical transmission costs roughly $1 million per mile, quickly killing a distant prospect’s economic viability.
The number of power-buyers on the other end of a transmission line is also a factor. Of Alaska's great tidal potential, "a lot of that's actually stranded out in the Aleutian chain or in south east Alaska where the population density is low," Kilcher said. "There's not as many people to use the power in those locations."
Cook Inlet, however, emerges from these considerations as an even stronger development prospect. Anchorage is about 50 miles north of the Forelands, and the closest connection to the existing power grid – Homer Electric Association’s Bernice Lake Power Plant – is just on shore in Nikiski. The Kenai Peninsula’s largest energy consumer – a refinery that produces much of the region’s automotive and aviation fuel – is also in Nikiski, as are two now-inactive industrial installations that historically also ranked among the region’s top energy consumers: a nitrogen fertilizer plant and a liquefied natural gas export terminal.
Tidal power is a developing industry, and where it may deploy in the near future will be determined in part by the cost of other power sources competing against it in a regional market. The expensive experimental technologies of tidal power can’t grab a competitive foothold where other power sources are much cheaper. But where existing power is very expensive, tidal power has the opportunity to develop into an alternative.
In Cook Inlet, the tidal power start-up Ocean Renewable Power Company (ORPC) experienced this constraint when it began pursuing a tidal project in the Forelands in May 2011. ORPC spent four years on preliminary studies before suspending the project in December 2015. In its permit surrender letter to the Federal Energy Regulatory Commission, ORPC cited the competing cost of natural gas power.
“The strength of the conventional energy market in Alaska precludes timely integration of new technology, like tidal energy systems,” wrote ORPC Environmental Affairs Director Nathan Johnson to FERC. “As a result, public and private funding sources have sought nearer-term market impact from their investments.”
ORPC has since had success with river hydrokinetic power in the small rural village of Igiugig, where the predominant power source is diesel generation. As tidal technology develops and its price falls – or if the price of Cook Inlet natural gas continues to rise – the company may find it economically viable to return to the Forelands.
The factor of competition makes Alaska overall a very favorable place for early tidal power adoption. NREL ranked Cook Inlet at the top of 36 potential U.S tidal sites, in part because of its nearness to the large, high-priced power markets of Anchorage and the Kenai Peninsula. It shares the number one spot with the Western Passage, an Atlantic coastal site near Maine and New Brunswick, also power-dense and near an expensive market.
In the longer term, NREL also considered a future scenario in which tidal power technology has matured into cost-competitiveness with other sources. With the cost of competing power excluded, Cook Inlet falls behind both the Western Passage and two straits in Washington’s Puget Sound. Though Puget Sound’s many narrow channels are rich in tidal energy, Washington’s tidal prospects are hurt by the extremely low cost of already existing hydropower from the heavily dammed Columbia River.
Measurements
The work Kilcher’s team planned this summer would check NREL’s models against reality. The group has spent the past few years taking measurements at some of the top-ranking hotspots in Maine and Puget Sound,"basically kind of training ourselves up by making these measurements at smaller, less energetic sites to prepare ourselves to go up to Cook Inlet, where the tides are so strong," Kilcher said.
The instruments the team planned to moor for two months off the coast of Nikiski include acoustic Doppler current profilers, which measure current velocity by sending high frequency sonic pulses through the water and recording the Doppler shift – how the sound wave is stretched or squished by water movement – in the echo. Pings from the current profilers would also give clues to two other lingering questions: how much equipment-clogging silt is suspended in the water column, and how often the spring currents carry damaging chunks of ice.
A less obvious but also critical measurement of Cook Inlet’s tidal flow will be its turbulence. Air turbulence was a major design obstacle for the wind energy industry, where Kilcher said early turbine builders hadn’t accounted for the roughness their equipment would experience. For the nascent technology of tidal turbines, Cook Inlet’s turbulence will be important data.
With measurements in hand, the team will mathematically extrapolate them to the whole channel.
“Once we have that model validated we'll have a much better understanding of where you’d site turbines and projects in that site,” Kilcher said.
Cook Inlet tidal test site?
NREL’s research concludes cautiously, stating in the 2016 study that early tidal power sites “will depend heavily on factors that are not considered in this analysis, including technology type, permitting barriers, local leadership, and stakeholder support.”
Neither NREL study makes any guesses about technologies for tapping tidal potential. With the industry in a very early stage, a variety of companies are developing an extraordinary variety of devices.
“The tidal energy industry is still emerging, and most of the existing cost data are for prototypes, the data for which have very little commercial-scale relevance,” states NREL’s 2016 report.
Fortunately, one tidal development path being considered by Homer Electric Association is also technology-agnostic: a testing site in the Forelands.
“The conceptual idea would be to develop some infrastructure, or at least look at the feasibility of developing some infrastructure, from our Bernice Lake substation out to this tidal resource with some sub-sea cable, and then allowing entities to bring in their tidal power equipment and test it there,” HEA Manager of Fuel Supply and Renewable Energy Development Mike Salzetti told the HEA board during a renewable energy update in June. “We would buy their test energy at basically avoided cost, just like we do in our current tariff.”
The concept isn’t a new one. In 2003, a group of public entities in the U.K created the European Marine Energy Center in Scotland’s Orkney Islands, which share with Cook Inlet not only high tidal potential but a legacy of marine oil and gas development which can also serve tidal developers. The Center currently maintains 13 grid-tied test berths that it leases to tidal companies. Established with approximately $45 million in public funding, it became financially self-sustaining in 2011, according to its website.
Closer to home, the U.S Department of Energy in 2008 funded several universities to create marine renewable research centers in Oregon, Hawaii, and Florida. The Oregon-based Pacific Marine Energy Center, which includes the University of Alaska Fairbanks among its partners, uses a river hydrokinetic test bed in the Tanana River and two wave energy test sites off the coast of Newport, Oregon. The Hawaii National Marine Renewable Energy Center also maintains wave energy test sites. For tidal energy, small U.S test sites exist in New Hampshire and Cape Cod.
Salzetti told the HEA board he’s developing a “Cook Inlet Tidal Power Working Group” to pursue the testing site concept. The group, he said, may include representatives from NREL, the University of Alaska Anchorage, and possibly the Pacific Marine Energy Center, as well as members of the local oil and gas industry familiar with working in the Inlet’s marine environment.
“It would be a win-win in that we'd get potentially some longer term test tidal power in the inlet, and they would be able to test up and see if they have commercial-ready designs,” Salzetti said.
