Oscillating Water Column (OWC) – the OWC comprises a partially
submerged structure forming an air chamber, with an underwater aperture. This
encloses a volume of air, which is compressed as the incident wave makes the
free surface of the water rise inside the chamber. The compressed air can escape
through an aperture above the water column which leads to a turbine and, as the
water inside falls, the air pressure is reduced and air is drawn back through the
turbine. Both conventional (i. e. unidirectional) and self-rectifying air turbines
have been proposed. The axial-flow Wells turbine is the best known turbine
for this kind of application and has the advantage of not requiring rectifying
air valves.
Pivoting Flap – this device consists of a rectangular concrete box, which
is open to the sea at one end. A steel pendulum flap is hinged over this opening,
so that the actions of the waves cause it to swing back and forth. This motion is
then used to power a hydraulic pump, which supplies a generator. There are
currently plans for a 300 kWe scheme.
In comparison with the most other renewable energy technologies, even
these deployed devices are at a relatively early stage in their development. This
work is leading to more reliable and efficient devices, with corresponding
improvements in the economics of wave power generation. It appears that this is
a transition time for several technologies as they move from theoretical
assessment and small-scale tests to large-scale demonstration and commercial
schemes. Many energy and engineering companies are starting to show a
growing interest in these technologies. As a result, it is envisaged that within the
next five years in wave energy will start to play an increasingly important role
complementing other renewable and conventional energy technologies. In
addition, some wave energy devices will see growing use in providing potable
water through reverse osmosis.