The book chapter deals with both tidal rise and fall energy and hydrokinetic energy from tides, ocean currents and rivers. (River energy is included because the proposed technologies share some characteristics with those proposed for tidal currents.) Out of the many devices proposed, some have been built, but most of these have disappeared as a result of either lack of financial support, poor design or poor management. The aim of this chapter is not to catalogue every device past or present, but rather to summarize the main types of technology and the most interesting and promising.

Chapter Contents:

• 3.1 Introduction
• 3.1.1 Characteristics of tidal current energy
• 3.1.1.1 Predictability
• 3.1.1.2 Daily and two-weekly variation in tidal current energy
• 3.1.1.3 Energy production estimation
• 3.1.2 Basic physics of tidal energy
• 3.2 The resource
• 3.3 Tidal rise and fall concepts
• 3.3.1 Tidal barrages
• 3.3.2 Tidal lagoons
• 3.3.3 Dynamic tidal power barriers
• 3.3.4 Turbines for tidal rise and fall schemes
• 3.4 Tidal bridges and fences
• 3.5 Tidal, ocean current and river HKTs
• 3.6 Differences between hydrokinetic and wind energy
• 3.6.1 Limited depth suitable for turbines
• 3.6.2 Tidal and ocean current flow velocities are lower than wind
• 3.6.3 Much higher fluid density
• 3.6.4 Cavitation
• 3.6.5 Predictability
• 3.6.6 Bidirectional flow
• 3.6.7 Limited flow field
• 3.6.8 Floating debris
• 3.7 Axial flow turbines
• 3.8 Crossflow turbines
• 3.9 Ducts and diffusers
• 3.10 'Flying' turbines
• 3.11 Oscillating foils
• 3.12 Vortex shedding
• 3.13 Tidal sails
• 3.14 Arrays
• 3.14.1 Tidal farm layout
• 3.14.2 Mixing and wake recovery – streamwise and lateral spacing
• 3.15 Economics
• 3.16 Actual progress to date on large-scale grid-connected hydrokinetic power
• 3.17 Case study – development of GEM, a tidal stream energy system
• 3.17.1 GEM system configuration
• 3.17.2 Turbine and diffuser experimental tests (small-scale models)
• 3.17.2.1 General definitions
• 3.17.2.2 Model set-up
• 3.17.2.3 Tests on single turbine
• 3.17.3 Tests on full model in small scale
• 3.17.3.1 GEM tethered model set-up
• 3.17.3.2 Characterization of the submerged tethered system
• 3.17.3.3 Tether force and trim
• 3.17.4 Full-scale prototype tests
• 3.17.4.1 Test plant configuration
• References
• Symbols used

Inspec keywords: reviews; hydroelectric power; tidal power stations; rivers

Other keywords: hydrokinetic energy; river energy; tidal rise and fall energy; offshore sources; tides; current energy; ocean currents

Subjects: Energy resources; Energy extraction from the oceans; Tidal and flow energy; Reviews and tutorial papers; resource letters; Tidal power stations and plants; Rivers, runoff, and streamflow