May 2015, François Lempérière
– Traditional hydropower supplies 3 500 TWh/year.
– Tidal power has the same potential and supplies 1 TWh/year.
Tidal power, if used in “Tidal Gardens”, may supply 2 000 TWh/year with same cost as hydropower and better impacts.
A new solution
The cost per MW for manufacturing of in-stream turbines may be low but there are few natural places at sea with an efficient water speed and the cost for placing and maintaining turbines of low capacity (1 MW) is generally too high.
A new solution, the “Tidal Gardens” creates conditions for the best utilization of more powerfull in-stream turbines. Large basins along shore are open to sea by wide channels about some hundred meters long in which are placed five to ten rows of turbines operating in a permanent speed about 4 m/s (fig. 1 and 2).
The overall cost per MWh is much lower than with turbines as in La Rance or Shiwah and remains low for tidal ranges of 3 to 5 m, i.e. for most of the world potential.
Four choices favour the environment :
– The « Tidal Gardens » are operated both ways and the tides along shore are thus quite the same as natural ones, shifted by two hours (as per fig.3).
– The dykes closing the basins, 10 or 20 km offshore, avoid high waves along shore.
– The channels are spread along the dyke as well as streams in the basin.
– The offshore methods used for construction, i.e. prefabricated caissons and dredging will keep natural tidal conditions during construction.
The enclosure dykes
They may associate an usual prefabricated breakwater with a sand and gravel dyke built in calm water by large marine dredges (fig.4)
The dyke, about 10 m over sea level will be hardly seen from shore except at both ends where a fishing or yachting harbour may be placed (fig.5)
Placing large wind farms along the dyke and in calm water of the basin may be the most cost effective utilization of wind energy. The production per km² may be as high as tidal energy.
It is possible to devote few per cent of the basin area to P.S.P. (Pumping Storage Plants) built in calm water. They may be used as well for tidal or for wind energy. They may be more efficient and less expensive than traditional onshore P.S.P.
Civil engineering per MW is a small part of civil engineering with bulb units and yearly supply is 4 000 hours of the rated power instead of 2 000. The cost per MWh for channels and plants may be 50$; the cost for dykes may be 20 to 50$ according to sites.
Tidal energy may be cost effective in twenty countries
Most past tidal studies were made where tidal range is exceptionally high. The new solution of Tidal Gardens applies as well in places with tidal range as low as 3 m, i.e. to much more countries. Large basins of hundreds km² are possible because the sea depth is usually under 20 or 30 m within over 20 km from shore. The total potential of tidal energy may be close to 2 000 TWh/year directly and increased by 1 000 TWh of wind energy.
About 10 countries may produce each between 50 and 200 TWh/year of tidal energy: Russia in Europe (Mezen and White Sea) and in Siberia (Tugursk), France, United-Kingdom, China, India, Australia, Canada, Brazil, Argentina, South Korea and about 10 countries also may supply each about 20 TWh/year : United-States, Netherlands, Germany, Ireland, Panama, North Korea, Vietnam, Pakistan, Myanmar, Bangladesh, Mozambic.
For many countries and especially in populated areas, the possibility of reducing high water levels may be essential for mitigating the increase of oceans levels, especially in deltas areas.
Some possibilities are suggested below
North of Liverpool (U.K.)
With five meters tides, 10 GW may be cost effective .North of Liverpool and 1 or 2 GW one hundred km North of London.
Chausey Island (France)
The scheme may produce 10 GW at low cost.
The 2 sites may produce over 10 GW.
It may also be possible to use the White Sea itself.
Along 2 000 km, tidal range in China is over 3 m and sea depth is under 20 m.
To implement 20 or 30 GW appears cost effective.
West India and Pakistan
Gulfs of Kutch and Kambay may supply 20 GW.
Pakistan shore may supply 5 GW.
Tidal range is about 5 m and sea depth under 25 m upon 10 000 km².
To implement 20 GW appears realistic.
It may be possible to implement 5 GW and to optimize water level at the Mekong Mouth, improving living conditions for 10 millions people.
This solution is presented in detail in “Hydropower & Dams” 2014 – Issues 1 – 2 – 4 – 5.