A dearth of public information, complicated marine environments, and even the corrosive effects of bubbles are some challenges facing companies that seek to produce energy from river currents, tides, and waves, so Sandia is helping companies on the frontier of the coming marine hydrokinetics (MHK) industry navigate these and other concerns.

Through DOE support for Sandia’s MHK research, the Labs plans to release its first report this fall analyzing the computer-simulated performance of a tidal turbine, a river turbine, and a wave-point absorber, which bobs on the surface to capture energy from waves, says engineer Rich Jepsen (6122). Eventually, Sandia will analyze up to 10 devices.

MHK is the study of harnessing the kinetic energy that results from the motion of water.

“The current MHK industry looks a lot like wind did 30 years ago,” says Daniel Laird, manager of Water Power Technologies Dept. 6122. “We want to take what we’ve learned to compress the MHK development from the 30 years it took wind energy down to 10 years.”

Sandia’s analysis aims to accelerate the MHK industry in the US by showing companies and DOE where investments can be made to bring down the costs of using America’s waterways and the oceans to produce energy — whether from an engineering, environmental permitting, or administrative standpoint. Companies will be able to use these reference models to make their own decisions about which design or system components are worth their investment, Rich says.

Real-world experience

“As a nation, we don’t have a handle on what the performance is and the actual cost of the energy that is generated,” Rich says.

Sandia also is getting real-world experience through its partnership with New York City-based Verdant Power, which is at the forefront of the MHK industry.

Verdant has operated the world’s first grid-connected array of multiple tidal turbines in the East River and will operate the first tidal power plant in the country, says Dean Corren, the company’s director of marine current technology.

After Sandia began working with Verdant in 2008, DOE awarded an Advanced Water Power Project grant that expanded the partnership to include the National Renewable Energy Laboratory in Golden, Colo.

Verdant’s turbines are mounted on towers on the river bottom, turning with the changing currents to always point downstream so they catch the currents and produce energy as they rotate.

“The goal of the project was for Sandia to design a stronger, more efficient blade made of composite materials, similar to what’s used in wind,” says Sandia engineer Josh Paquette (6121).

Sandia surveyed and studied prospective blade foil shapes, performed essential, computational fluid-dynamics analyses of the rotor, and then of the turbine as a whole, Corren says.

The result is a blade that is stronger and thicker, more resistant to corrosion and cavitation, and one that can be mass-manufactured, Josh and Corren say. Cavitation is the creation of tiny water vapor bubbles at low pressure that can collapse and damage the surface of the blade.

“When these bubbles collapse, they put out a lot of energy and it can be very erosive, so it can literally chew up an underwater propeller,” Josh says. “We tackled this issue using the same methods we used in wind, where we did computational fluid-dynamics analysis of the blade.”

This Fifth Generation Free Flow System is being built by Verdant and will be tested this fall. Should all go as planned, Corren says, Verdant plans in 2012 to begin installing, in phases, 30 turbines in the East River, which at peak production could supply enough energy for the equivalent of about 700 homes.

Operate for three years unattended

Earlier generations of turbines were tested for two months; this commercial-type turbine is designed to operate for three years unattended, Corren says.

Sandia also is learning from Verdant’s experience in the water by studying the debris, mud, and biological contaminants that grow on the underwater turbines, Josh says.

Other companies and government agencies have had a difficult time obtaining research and performance data because nearly all of it is proprietary.

When Sandia started its research, DOE noticed this and asked Sandia to create reference models that established benchmarks companies could use to test their own custom models to determine whether they should enter the market, Rich says.

Sandia is analyzing basic designs, environmental factors, and costs, Rich says.

Sandia hydrologist Jesse Roberts (6122) says an array optimization tool developed by Sandia specifically for MHK devices analyzes both the effects of the environment on the devices and, conversely, the devices’ effects on the environment.

“You can use this tool to place turbines in whatever fashion you think is appropriate throughout your water column to see how they interact with each other,” he says. “It will tell you how much energy you converted with that layout and how the water flow changes throughout the system, near and far field.”

While the water flow is faster near the surface, potentially creating more energy, turbines sometimes can’t be placed too close or they would interfere with shipping, recreation, or wildlife, such as birds that dive deeply for their food, Jesse says.

Tide power is ‘weather-proof’

Sandia provides information about how underwater turbines and wave devices change the physical

environment to aquatic ecologists at partner labs, who study the effects on marine life. Jesse says that while each aquatic environment is different, the more questions that can be answered up front, the better companies can predict environmental permitting costs or research requirements.

Early estimates show that a significant amount of the current US national electricity demand may eventually be met through tidal and wave energy generation, and, moreover, these power sources will be located near population centers on the East and West coasts where demand for energy is high.

Tidal power in estuaries and straits is predictable and steady, as opposed to wind and solar power, Corren says. “We look up at the moon and can know what’s going on, and we don’t have worry about the weather,” he says.

Rich also is looking at another potential resource for the MHK industry at Sandia, a 50-foot-deep pool with a nearby large electrical power source that could be converted into a large-scale facility to generate waves under controlled conditions needed for accurate large-scale testing of devices.

With some additional investment, “our lake is big enough that companies could put in a prototype and do full-system tests all the way to generating electricity,” Rich says.

There are signs that Sandia’s efforts to help the MHK industry are paying off. Rich says a growing number of companies are becoming interested in Sandia’s work on the array optimization tool and materials and coating research for the turbine blades.

“Being in this industry at the early stage, being able to define the future of an entire industry is interesting. It’s like being a researcher in wind energy 20 to 30 years ago,” Jesse says. “Hopefully, we’ll be able to follow this for quite some time and help influence the direction it goes.”