Category Ocean Energy

The Modest Forerunners

The term water mills has commonly designated run-of-the-river mills situated on waterways where there was/is no tidal current. The terms sea mill, and later tide mill, designated mills that took advantage of the tides with or without retaining ponds. There were thus tide mills that took advantage of the ebb and/or flood current. Some such mills were even “dual-powered”. Tidal current mills operated on one of two systems: they were equipped with a single wheel that rotated with the current between two pontoons, or the mill consisted in a single pontoon with a wheel affixed to each side, similar to the approach with paddle-wheelers.

The Dunkirk (Dunkerque, France) “Perse mill” (end of 17th century to 1714), the Bacalan mill a few kilometers north of Bordeaux on the Gironde River, the El ...

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Glance at the Past and Look into the Future

The tidal current was used by water mills on Evrepos Strait, in Cephalonia, in the floating tide mills on the Danube, Tiber, Seine and Russian rivers. A plant func­tioned briefly in northwestern Iceland and another has been mentioned for the Faroe Islands. The Danube tide mills used undershot wheels since Roman times to harness the tidal current. Some of them were still in use below the Iron Gates as late as 1970.

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Proposed Schemes

Twenty years ago, it was felt that a scheme most suitable to attain an acceptable, favorable benefit to cost ratio (“rentability”) would be one in which rotors would be anchored, but suspended in mid-water—precisely to avoid wave influence—and let drive hydraulic pumps, while conversion to electricity would occur at a central facility servicing several rotors; if these were spaced over some distance, the de­phasing due to tide variation would be compensated in partim. More turbines could be inserted in the system, an idea based on the belief that cost would be rather low.

Fifteen years ago, it was suggested to anchor in a line a series of floating tur­bine and generator units along the flow of the tidal current...

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Geographical Distribution of Promising Sites

Major tidal currents are encountered in the Arctic Ocean, the English Channel, Irish Sea, Skagerrak-Kattegat, Hebrides, the gulfs of Mexico and of St Lawrence, the Bay of Fundy, such rivers as the Amazon and Rio de la Plata, the straits of Magellan, Gibraltar, Messina, Sicily, Bosporus. The tidal range is observed as far as 800 km upstream on the Amazon River! In the Far East currents are encountered, a. o. near Taiwan and the Kurile Islands. Northwest and Western Australia have their share. There are many other locations.

Most commonly cited examples are the Pentland Firth, Irish Sea North Chan­nel, Alderney Race, Isle of Wight to Cherbourg, Orkneys to Shetlands. The Florida

Current has been mentioned repeatedly as it is assumed it could provide 25 GW, but the idea of tapping it has cau...

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Regional Potential

Подпись: Pf Подпись: 9.8 x 8760 xQxH 8760 x 360 Подпись: (8.4)

To calculate Pf(region) or linear potential for a specific region, requires to know the elevation above sea-level of the individual basins (Hi) and the mean run-off of sev­eral basins; an estimate of the theoretical linear value of the per annum potential, in millions of kWh (kWh.106), is now possible (Pf). Taking Hmed as the median of the Hi values, and V being the precipitations’ run-off, expressed in millions of m3, the potential is found through (8.5):

Pf = VxHmed/367 (8.5)

A region’s potential can thus be given in kWh/km2, but, particularly in less de­veloped countries, it often is not precised due to the lack of long-term hydrological data...

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Energy Potential

Flow-of-the-river potential is directly proportional to elevation above sea level and precipitation run-off. If a “sector” is the distance between two successive confinements—about 10 km—the linear potential of a river is given in the eq. (8.2)

Pf = 9.8xQmXH (8.2)

wherein H is the elevation difference, expressed in meters, above sea-level, between points of origin and exit of a sector, Qm the mean discharge, expressed in m3/s, at the end point of a section, and Pf the mean power expressed in kW. By summing the successive Pf values (EPf) a river’s “potential” can be calculated.

The theoretical energy (Ef) is given by (8.3):

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Tidal Current

The tide phenomenon is the periodic motion of the waters of the sea—and is ob­served upstream of several rivers—caused by celestial bodies, mainly the moon and the sun. The tide results from the gravitational pull and the earth’s rotation. Tide and tidal currents must be differentiated, for the relation between them is not simple, nor is it everywhere the same. In its rise and fall the tide is accompanied by a periodic movement of the water, the tidal current; the two movements are intimately related.

The current experienced at any time is usually a combination of tidal and non­tidal currents (cf. p. 67). Offshore, the direction of flow of the tidal current is usually not restricted by any barrier and the tidal current is rotary.

The tidal current is the rotary current that accompa...

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Current from Tidal Current

8.1 Introduction

With at least sixty major papers in print and several international conferences on the subject, over the last decade, it appears that, contrary to assertions made in some trade-and-news journals, interest in tidal power—using barrages—is far from being on the wane.1,2 This is particularly true in the Far East, viz. China, Japan, Korea.3

Tidal power can be harnessed, as did tide mills, by creating a retaining basin and using the up and down movement created by the tides, or by diverting part of a flow and using the to and fro movement of the tide induced current, pretty much like a run-of-the-river approach.4 The flow of the tidal current is diverted in part into a channel where it turns a wheel: some tide mills operated by tapping the energy of the tidal current...

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