Channeling an untapped renewable energy

Featured research: Marine and hydrokinetic energy

A call for clean energy resources
In his 2011 State of the Union address, President Obama set an aggressive goal for America: produce 80% of the nation’s electricity with clean energy sources by 2035. Locally, there is a similar objective: the state of Minnesota and the Xcel Energy Renewable Development Fund want to see 25% of Minnesota’s electricity produced by environmentally sustainable and renewable resources by 2025.

Where will this clean energy come from? How will it be harnessed? One significant resource is in the nation’s tides, river currents and waves, collectively known as marine and hydrokinetic (MHK) energy resources.  The field of MHK energy, however, is presently in its infancy and lags approximately 20 years behind the technology and development progress made in wind energy engineering. A broad range of MHK technologies and device concepts have been proposed but a clear technology leader has yet to emerge. A major challenge stems from the lack of a comprehensive scientific framework for improving the design and assessing the potential and technological readiness of various devices especially with regard to environmental impacts.  St. Anthony Falls Laboratory (SAFL) is uniquely positioned to lead the way for clean energy, especially MHK energy, thanks to a long history of hydropower and environmental research.

MHK research: A new opportunity
In the United States, development of traditional hydropower systems has essentially stopped due to major environmental challenges associated with dams that impound water for energy generation. MHK installations could also impact the aquatic environment, so there is need and opportunity to study environmental impacts and device hydrodynamic performance simultaneously.

With the water level lowered, this image shows a 1:10 scale model of an axial flow tidal turbine. An acoustic Doppler profiler (white cylindrical device) and 3 acoustic velocimeters measure flow turbulence and turbine wake characteristics while internal model turbine instrumentation monitors the turbine power output.  These instruments and others allow SAFL researchers to take simultaneous measurements of turbine performance and the surrounding hydrodynamic environment.

SAFL’s scientific and technical approach
Funded by grants from the industry (Verdant Power), government laboratories (Oak Ridge National Laboratory, Sandia National Laboratories, and the National Renewable Energy Laboratory), and a recent special opportunity grant from the University of Minnesota Initiative for Renewable Energy and the Environment (IREE), current MHK research at SAFL focuses in three key areas:

1. Hydrodynamics of turbines and turbine arrays – By modeling turbulent flows around MHK devices computationally and experimentally, research will help to determine optimal device designs and multi-device array layouts that maximize energy generation; reduce structural loads and enhance reliability; perform optimally on a site-specific basis; minimize the levelized cost of energy; and improve environmental compatibility.
2. Geomorphology and turbine interactions – Novel experiments in SAFL’s flumes will address issues of bed topography and turbine interactions and effects on the surrounding environment. Innovative computational fluid dynamics tools are being developed and validated with laboratory experiments that can predict streambed erosion patterns induced by a single turbine or multi-turbine arrays.
3. Aquatic ecosystem and turbine interactions – A laboratory-scale fish tracking system is being developed to address turbine-fish interactions, turbulence-induced physiological stressors, and MHK-altered ecosystem conditions. Computational models for simulating the motion of fish bodies through turbine arrays will provide new knowledge in this area. Both will lead to guidelines and protocols for assessing environmental impacts in field installations of turbines and other MHK devices.

The work is led by Fotis Sotiropoulos, Professor of Civil Engineering and Director of SAFL; Civil Engineering professors Michele Guala and Miki Hondzo; research associates Leonardo Chamorro, Ali Khosronejad and Seokkoo Kang; senior research associate Chris Ellis; engineer Craig Hill; and several graduate and undergraduate students.

Project spotlight: RITE research
Ongoing work focuses on the Roosevelt Island Tidal Energy (RITE) project.  SAFL is working together with Verdant Power to develop the next generation of hydrokinetic turbines for the RITE site in New York City. The research group is gathering data from numerical simulations and experiments in the SAFL main channel.

Welcoming the future of MHK
Expanding the focus on MHK energy is a natural transition for SAFL thanks to its long history of collaborative, interdisciplinary research. Since 2002, the laboratory has been home to the headquarters of the National Center for Earth-surface Dynamics (NCED), a National Science Foundation-funded Science and Technology Center that excels in research on environmental restoration, with a particular focus on streams and rivers. In addition, SAFL recently received Academic Research Infrastructure (ARI) program funding to renovate the laboratory to become a major research facility focusing on the energy/environment nexus. Part of the ARI project covers a major upgrade to the main channel, improving the wave maker and other capabilities to fuel MHK research. And of course, SAFL is situated on the nation’s largest and most prominent river. Being on the Mississippi River means the laboratory can play a major role in local, regional and international MHK research and development projects.

MHK research activities at SAFL will only intensify in the near future as a result of a new special opportunity grant from the Initiative for Renewable Energy and the Environment. The IREE funds will be used to develop the research infrastructure and partnerships required for engaging the emerging MHK industry and government laboratories in a comprehensive effort to advance MHK technologies in the U.S. through cutting edge scientific research.