Page 86 - Fundamentals of Ocean Renewable Energy Generating Electricity From The Sea

78 Fundamentals of Ocean Renewable Energy

FIG. 3.29 La Rance tidal barrage in Brittany—generating electricity since 1966. (From S. Neill.)

FIG. 3.30 Schematic of a tidal lagoon; ebb generation case.

no electricity would be generated. The turbine gates will open at Point 2 and
energy conversion would continue as long as there is sufficient head on the
turbines. During this period (generation), the water elevation inside the lagoon
decreases. At Point 3, which usually happens after low tide, the difference of
water elevation inside and outside the lagoon is no longer sufficient for turbine
operation. At this point, the turbine gates will be closed. There will be another
standing period (all gates closed), until the tide returns and sluice gates are
opened for filling. This process would be repeated for each tidal cycle. Here, we
will show that the amount of energy converted is approximately proportional to
the area between water elevation curves—inside and outside the lagoon—when
the turbines operate.