Tidal Energy Today - Tide Mill Institute

Today’s worldwide efforts to extract useable energy from tidal flow is a topic of primary interest to the the Tide Mill Institute. TMI’s annual conferences often include presentations about current day uses of tidal energy and the possibilities of reusing former tide mill sites for power generation.

This page offers an introduction to modern tidal generation projects and research. It is organized into several sub-topics:

Tidal Stream Power Generation
Tidal Barrage or Tidal Lagoon Power Generation
PRIMRE Marine Energy Databases
Selected Marine Energy Test Sites
Selected Technical References – Current
Repository of Tidal Energy Today Blogs

Tidal Stream Power Generation

Overview

Tidal stream power generation systems harvest energy from fast moving tidal streams or currents, much as wind turbines harness the power of moving air. These systems don’t require a dam, and for this reason they have become more prevalent than tidal barrage or tidal lagoon systems.

Turbines for tidal stream applications can be categorized as the axial flow type, as shown in Figure 1, or the cross flow type, as shown in Figure 2. Turbines can be bottom mounted as in Figure 1, or partly submerged or floating and tethered to the bottom, as in Figures 2 and 3. Turbines may be used singly, or in arrays as shown in Figure 1.

Figure 1 – Array of bottom-mounted axial flow tidal turbines. (Courtesy of Normandie Hydroliennes.)

Figure 2 – Cross flow turbine partly submerged and tethered to bottom. (Courtesy of ORPC, Inc.)

Figure 3 – Floating axial flow twin turbine generator tethered to bottom. (Courtesy of Orbital Marine Power.)

The theoretical power that can be extracted from a tidal stream is proportional to the area of the turbine or turbine array facing the flow times the cube of the water velocity (Power = Frontal Area x Velocity³). A nice rule of thumb is that a 1 meter/sec (2 knots) current provides about 0.5 kW per square meter (11 square feet) of frontal area.

One challenge is that the speed of the tidal current needs to be fast enough to drive a turbine efficiently; 0.8 m/s (1.5 knots) is a typical threshold speed, known as the “cut-in velocity” for a tidal turbine. Tidal kite generators optimized for power generation in low velocity flows are described below in “Tidal Stream Project in Development – Slow-Flow Velocities.”

Tidal Stream Projects in Development – Fast Flow Velocities

Eastport, Maine, U.S.A.
https://www.nrel.gov/news/detail/program/2024/resilience-at-the-edge-city-of-eastport-considers-harnessing-tidal-power-for-island-microgrid

Rosario Strait, Washington, U.S.A.
https://salish-current.org/2025/04/17/opalco-moving-closer-to-tidal-power/

https://openei.org/wiki/PRIMRE/Databases/Projects_Database/Projects/OPALCO_Tidal_Energy_Pilot_Project

Alderney Race, Normandy, France
https://www.tidemillinstitute.org/eu-grants-36-million-to-french-tidal-energy-project/

Anglesey, Wales
https://www.offshore-energy.biz/welsh-tidal-energy-receives-e2-3-million-boost-from-government/

Pentland Firth, Scotland
https://saerenewables.com/tidal-stream/meygen/

Tidal Stream Project in Development – Slow Flow Velocities

One tidal stream project involves a fascinating technology known as a tidal kite generator specifically designed to work in low velocity tidal currents or ocean currents. The kite (Figure 4 below) “flies” in the tidal stream just as a child’s kite flies in the wind. The kite is automatically controlled to follow a figure-eight path as it glides at high speed through the water (you can see this in the YouTube video, linked below). The high relative speed between the kite and the water (up to 10x the natural speed of the current) drives the turbine propeller on the kite to efficiently generate electricity. In other words, it’s the force of the current that causes the kite to fly, while the movement of the kite that drives the propeller – not the other way around! Electricity is fed down the kite’s tether cable to its seabed anchor and from there over to shore.

Swedish tidal energy company Minesto began testing its first 100 kW Dragon 4 tidal power kite off of the Faroe Islands between Scotland and Iceland in early summer 2022 and added a second Dragon 4 kite in 2023. Minesto plans to deploy tidal kite arrays at four sites by 2030, generating a total of 120 MW and supplying 40% of Faroe’s electricity. The kite arrays will use Minesto’s Dragon 12 kites which produce 1.2 MW each. Installation and testing of the first Dragon 12 kite began in February 2024.

https://minesto.com/faroe-islands/

https://www.youtube.com/watch?v=dkXinDn67Kw&t=131s

Figure 4 – Minesto’s Tidal Kite. (Courtesy of Minesto AB.)

Tidal Barrage or Tidal Lagoon Power Generation

Overview

Tidal barrage and tidal lagoon generation systems are generically known as tidal range systems. They are analogous to historical tide mills in that they extract power from the difference in water levels across a dam. Tidal barrage generation systems typically involve building a dam across an estuary or inlet to create a tidal reservoir. Tidal lagoon systems involve building a multi-sided seawall to create an artificial tidal reservoir in a coastal region.

Whereas most historical tide mills operated only on the ebb (outgoing) tide, some tidal range systems enhance power output by generating on both ebb and flood (incoming) tides. For tidal range systems, the average power that can be extracted is proportional to the surface area of the reservoir and the square of the tidal range (Power = Lagoon_Area*Tidal_Range²). A rule of thumb is that the average power available from a two-way scheme with a 3 meter (10 foot) tide is approximately 3 kW per 4000 square meters (1 acre). Bulb turbines are typically used in these systems as shown in Figure 5.

Figure 5 – Bulb turbine in tidal barrage. (Encyclopaedia Britannica.)

Existing Tidal Barrage Systems

Sihwa Lake Tidal Power Station, South Korea
The capacity of the Sihwa Lake plant is 254 MW, making it the largest tidal power station in the world. Power is generated on the inflow only.
https://www.hydropower.org/blog/technology-case-study-sihwa-lake-tidal-power-station

La Rance Tidal Power Station, La Richardais, France
The capacity of the La Rance plant is 240 MW. Power is generated primarily on the ebb tide (60%), enhanced by pumping from sea to reservoir (15-20%), and by a small amount of flood tide generation (2-6%).
https://en.wikipedia.org/wiki/Rance_Tidal_Power_Station

Planned Tidal Barrage Projects

River Mersey
https://lcrlistens.liverpoolcityregion-ca.gov.uk/user_uploads/70107278_a4-booklet_revd_print–1-.pdf

Planned Tidal Lagoon Projects

Swansea Blue Eden
https://www.swansealabour.org/news/blue-eden-project

PRIMRE Marine Energy Databases

The U.S. Department of Energy’s Portal and Repository for Information on Marine Renewable Energy (PRIMRE) provides broad access to information on engineering and technologies, resource characterization, device performance, and the environmental effects of marine energy projects.

PRIMRE Marine Energy Projects Database

The PRIMRE database of marine energy projects can be filtered to show only tidal energy projects by selecting Resource = Tidal, and Status = Active.
https://openei.org/wiki/PRIMRE/Databases/Projects_Database/Projects

PRIMRE Marine Energy Devices Database

The PRIMRE database of marine energy devices can be filtered for tidal devices by selecting Resource = Tidal, and Technology Type = e.g., Axial Flow Turbine, Cross Flow Turbine, etc.
https://openei.org/wiki/PRIMRE/Databases/Projects_Database/Devices

PRIMRE Marine Energy Test Sites Database

The PRIMRE database of marine energy test sites can be filtered to show only tidal energy test sites by selecting Resource = Tidal, and Status = Active.
https://openei.org/wiki/PRIMRE/Databases/Projects_Database/Test_Sites

Selected Marine Energy Test Sites

Cobscook Bay Tidal Energy Test Site, Maine
https://tethys.pnnl.gov/project-sites/cobscook-bay-tidal-energy-project

University of New Hampshire / Atlantic Marine Energy Center Tidal Test Site
https://marine.unh.edu/center-ocean-renewable-energy/projects/tidal-energy

Bourne Canal Tidal Test Site, Massachusetts
https://openei.org/wiki/PRIMRE/Databases/Projects_Database/Test_Sites/Bourne_Tidal_Test_Site
https://www.mreconewengland.org/

PacWave Wave Energy Test Facility, Oregon
While it is a wave energy test site, PacWave is worth mentioning because it is the most visible and well financed marine energy test center in the continental US.
https://openei.org/wiki/PRIMRE/Databases/Projects_Database/Test_Sites/PacWave_South_Test_Site

Fundy Ocean Research Center for Energy (FORCE) Test Site, Nova Scotia, Canada
https://openei.org/wiki/PRIMRE/Databases/Projects_Database/Test_Sites/Fundy_Ocean_Research_Center_for_Energy_(FORCE)_Test_Site

European Marine Energy Center, Orkney, Scotland
https://openei.org/wiki/PRIMRE/Databases/Projects_Database/Test_Sites/EMEC_Fall_of_Warness_Eday_Tidal_Test_Site