Tidal Range Energy

Tidal range mapTidal range is the vertical difference between high and low tide.

The power that can be captured from water flowing from high to low is proportional to the squared height (or head h):

Power from tidal range

with ρ = 1,023kg/m3 and acceleration g=9.81m/s2. Only sites with sufficient head can be used for commercial purposes.

The 50 sites with the highest tidal ranges in the world are in just 5 regions:
  • Bay of Fundy, Canada with up to 12m mean tide
  • Bristol Channel and Cardiff Bay, UK
  • Normandy, France
  • Magellan Strait, Argentina & Chile
  • Cook Inlet, Alaska, USA
  • Penzhinskaya Bay, Kamtchatka, Russia
Principles of Technologies
Tidal barrages have a lot in common with dams for traditional hydro power, the resource availability and patterns are the same as for tidal streams.

Illustration of Tidal Range Energy

Ebb Generation

While the tide is rising, the reservoir behind the dam is filled with water through open sluices. The gate to the turbine is closed. When high tide is reached, the sluices are shut. Once sea level has receded to sufficiently low levels, the turbine gate is opened and the water from the reservoir channeled onto the turbine.

 

Due to low head (<10m), the turbine type is similar to a Kaplan turbine

Flood Generation

While the tide is rising, water flows through the turbine into the reservoir, generating electricity during flood.

 

Less efficient than ebb generation.

 

Pumping

In combination with ebb generation, use surplus grid energy to pump additional water into the reservoir, similar to hydro pump storage.

 

 

 

Market & Outlook
To date, 260MW are installed worldwide in only a few sites:
  • La Rance estuary, France (240MW)
  • Bay of Fundy, Canada (8MW)

 

Environmental issues:

 

  • Silting: Similar to hydro power dams
  • Loss of intertidal habitat, as it alters the flow of salt water in and out of estuaries.
  • Potentially more flooding in the vicinity.

 

Economics

 

  • High capital costs > €/kWh 2,000, but long lifetime. La Rance is in operation since 1966.
  • Long payback time

 

Outlook

Only feasible in few sites, though with huge potential. Construction of tidal barrages are underway in South Korea and China. There are advanced plans for a plant in Kamtchatka (87GW). Plans for the Severn Barrage (near Bristol, UK) for 8.6GW have been scrapped in October 2010 due to cost pressure, as the expected capital outlay would have been £30bn (~£/kWh3,500).

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