Marine renewables

Tidal energy generation and the path to commercialization

By Jonathan Colby, 2011 Young Professional

Jonathan Colby was one of the three 2011 Young Professional Leaders. Here he outlines the advances that have been made in the marine renewable energy sector and highlights the challenges that still need solutions.

Verdant Power 4th Generation KHPS - RITE tidal array deployment, Summer 2007 (Photo: Verdant Power – J Colby) Verdant Power 4th Generation KHPS - RITE tidal array deployment, Summer 2007 (Photo: Verdant Power – J Colby)

Predictability of tides is a key

Over the last decade, the marine renewable energy industry has become a growing sector of renewable energy that can contribute to renewable portfolio standards in a developing worldwide market. This sector is made up of wave energy, tidal, river and ocean current energy and OTEC (Ocean Thermal Energy Conversion). With the exception of OTEC, which utilizes temperature gradients between surface and deep-sea ocean water to do work, these marine technologies convert existing kinetic energy from water bodies to mechanical energy. This mechanical energy can be used in a variety of ways, with most developers focusing on the conversion directly to electrical energy. In particular, technology that converts tidal energy into electricity offers a significant advantage over other renewable energy sources for electricity production because the tides are highly predictable.

This predictability is an important distinction in the renewable sector over other intermittent renewable energy sources and provides for improved integration into grids (smart or otherwise). It is also more suitable as a distributed generation source for other green energy uses such as electric car/bus charging stations, LEED (Leadership in Energy and Environmental Design) buildings, desalination, etc. that can contribute to a renewable energy future.

Commercial-scale tidal energy projects underway

At present, the available energy in existing tides is captured using a wide range of evolving technologies. Projects are under development across Europe, in North America and Asia ranging in size from scale-model testing to pre-commercial scale multi-unit array deployments connected to national grid infrastructures. The U.S. Department of Energy's Marine and Hydrokinetic Technology Database provides up-to-date information on marine and hydrokinetic renewable energy, both in the U.S. and around the world. Individual technology developers have begun partnering with global engineering and marine service firms to develop commercial-scale projects and resource assessment efforts have been conducted to highlight regional-scale geographic areas with excellent tidal resources (speed, depth, etc.). [The database referenced above and the Atlas of UK Marine Renewable Energy Resources provide more information].

Additionally, a number of environmental impact studies have been published suggesting the compatibility of individual tidal energy devices (and small arrays of similar devices) with the surrounding ecosystem. Operational monitoring under an adaptive management framework will continue to assess the impact of commercial-scale energy extraction on tidal ecosystems to ensure the sustainable implementation of tidal energy technology. Coupled with these resource and environmental assessments, favorable ROCs (Renewable Obligation Certificates) and feed-in tariffs for early stage Pilot tidal array projects being promulgated by regional areas with large tidal resources (the State of Maine in the US, the Province of Nova Scotia in Canada, and the UK) make a promising climate for technology developers.

New York City's East River project

In the United States, Verdant Power is a leading developer and integrator of tidal energy technology and a pioneer in the environmental consenting process. The company’s RITE (Roosevelt Island Tidal Energy) Project in New York City’s East River (the East River is actually a tidal strait, with nearly symmetric semi-diurnal tides) has demonstrated a number of significant accomplishments and world firsts, including the successful operation of five grid-connected tidal turbines (4th generation) in a tidal array configuration in 2007, and the first US FERC (Federal Energy Regulatory Commission) Pilot 10-year license for an array of its 5th Generation (Gen5) Verdant Power KHPS (Kinetic Hydropower System) turbines. The KHPS is a horizontal-axis turbine with a downstream, 3-bladed fixed-pitch rotor. Rated at 35 kW in 2.1 m/s of flow, the Verdant KHPS turbine yaws passively to capture energy from both the ebb and flood tides at the RITE site. Electricity is produced using an induction generator with the local grid providing the excitation voltage. Three-phase, 60 Hz power is delivered at 480 V to Roosevelt Island in accordance with the local network and relevant standards. Based on the successful grid-connected demonstration at the RITE Project, the technology has now been advanced to a Gen5 commercial class system including full-scale testing of the Gen5 rotor at the RITE site.

U.S. Federal licence for commercial project

The company conducted extensive testing and environmental monitoring to quantify the KHPS turbine performance and its environmental compatibility within the project site. Working with the federal and state regulatory agencies, Verdant characterized the East River ecosystem in and around Roosevelt Island while confirming the environmental compatibility of the multi-turbine array. To do so, it deployed a wide range of underwater acoustic technology to measure a broad set of environmental parameters, from high-resolution SONAR devices capable of imaging the KHPS and fish to arrays of acoustic receivers for detecting tagged species. In addition to identifying spatial and temporal tendencies in the East River, these data validate numerical and statistical models developed to predict the KHPS-fish interaction with operating turbines at the site. 

As mentioned in January 2012 e-tech article, Verdant was granted the first FERC license [P-12611] for a commercial tidal array in the United States. This 10-year license permits the phased deployment of up to 30 turbines in the East Channel of the East River, for a rated 1.05 MW of tidal power generation, with a corresponding suite of environmental monitoring protocols. FERC, along with the other federal and state regulators, have also adopted the use of adaptive management for these monitoring protocols to ensure that best practices are used throughout the project life-cycle. [Additional information on the FERC license and associated environmental impact studies and monitoring protocols can be found at].

International Standards vital for marine renewable energy sector

As companies globally continue the development and deployment of commercial-scale licensed projects, the marine energy sector will increasingly require sustained technology development and project financing. For the sector to be successful there must be increasing certainty for regulatory approvals, device reliability and survivability, and operation and maintenance costs, among others.  Given the early stage of the marine renewable energy industry, the development of international standards plays a critical role in providing certainty and assurance as the industry grows.

Today, IEC TC 114: Marine energy – Wave, tidal and other water current converters, is developing a suite of technical specifications to support the industry at-large. These efforts focus on wave and tidal energy and cover both resource and power performance assessment.  Additional work is underway to provide guidance on OTEC, general system design, mooring design, and electrical power quality, among others.  In addition to the development of Technical Specifications, the IEC CAB (Conformity Assessment Board) is investigating the development of a conformity assessment scheme for marine energy systems. This scheme will provide guidance to certifying bodies on how to determine if the requirements contained in the aforementioned technical specifications have been met by a technology or project developer. Taken together, these international efforts are essential for the success of this emerging industry. In particular, certifying a technology and/or a project to these specifications can give developers the ability to more easily enter new markets while providing the financial community with the necessary confidence in the return on their investment.  Further, these certifications help prevent the misrepresentation of individual device performance, critical to ensuring public safety and the long-term adoption of similar technologies.

Verdant Power 4th Generation KHPS - RITE tidal array deployment, Summer 2007 (Photo: Verdant Power – J Colby) Verdant Power 4th Generation KHPS - RITE tidal array deployment, Summer 2007 (Photo: Verdant Power – J Colby)
Verdant Power Gen5 KHPS (Photo: Verdant Power – J Colby) Verdant Power Gen5 KHPS (Photo: Verdant Power – J Colby)
Verdant Power Gen5 rotor and dynamometer - RITE in-water test, September 2012 (Photo: Verdant Power – J Colby) Verdant Power Gen5 rotor and dynamometer - RITE in-water test, September 2012 (Photo: Verdant Power – J Colby)