Current Status of Tidal Power

Abstract

Introduction It goes without saying that tidal power is an environmentally clean, renewableenergy source. Although tidal energy is available in abundance, there arerelatively few locations in the world where the tidal range makes this form ofenergy economically exploitable under existing conditions. Relatively largetidal ranges had been used on a micro-scale for driving mills and pumpsfor many hundreds of years but such small direct drive applicationsbecame obsolete with the onset of the Industrial Revolution. Technologically, this source is well within reach to exploit. It is renewable, pollution-free, relatively inflation-free, and completely predictable. It couldcontribute to energy self-sufficiency and reduce the environmental problemsassociated with the conversion of fossil fuels to electricalenergy. The obvious question is: Why has this resource not been exploited to itsfullest extent? There is no easy answer. Canadian government energy policiespreoccupied with non-renewable sources and an apparent reluctance to undertakea project which, although technically feasible, has combined with marginaleconomics and high financial risks to slow progress. There are no precedents inthe field of successful tidal megaprojects such as might be built in the Bay of Fundy. Moreover, there are only a few locations where the topography wouldproduce tidal amplitudes large enough to justify installation. Tidal Characteristics and Tides as a Power Source Tides require a unique approach to the development and utilization of theirenergy. Along the Atlantic coasts of both Europe and America the tides rise andfall twice each 24 hours and 50 minutes, phased with the apparent period ofrotation of the moon. The excess of 50 minutes over the solar day results inmaximum and minimum water levels occurring at progressively different times ondifferent days, i.e. the tidal cycle moves into and out of phase with man"sactivities. The range also varies from day-to-day, reaching a maximum every twoweeks when the sun and moon are in alignment creating spring tides. Eight dayslater, the sun and moon form a right angle with Earth and partially neutralizeone another's gravitational influence to produce "neap" tides. At the vernaland autumnal equinoxes, the range is extremely large. These latter occurrenceshave an important bearing on the design of a tidal power plant. There are, ofcourse exceptions. For example at a number of places the maximum water leveloccurs every day at the same time; at others, there is only one tidalfluctuation a day; at still others, the single maximum may be replaced by two.The cardinal feature of tides is that, regardless of their local variation, they, occur in a most orderly, predictable fashion. Large tidal ranges in the Bay Fundy and at other locations around the world aredue to a combination of two natural phenomena: the motion of the sea initiatedby forces of the sun and moon and the configuration of the coast line overwhich this motion occurs.