the pressure
vessel to once again
fill
with hydraulic oil and become pressurised. The hydraulic oil coming out
of the hydraulic
motor, which is no longer under pressure, flows into a supply tank,
from
which it is once again pumped
into circulation by hydraulic cylinder HZ. Since it is virtually
impossible to
compress hydraulic oil, the smallest
movement
of the float results in oil being pumped. In the case
of
reduced wave activity, it takes a commensurately longer period of
time for one
of the two pressure vessels to be filled with hydraulic oil and thus
become
pressurised. The corresponding electricity generator will then be
driven in
longer intervals yet always with the same amount of force. In order to
further
increase the range of waves utilisable for this purpose, bearing L of
the
hydraulic cylinder is mounted to slide within a rail VS toward pivoting
point M
of the float. This acts as an infinitely
variable
gear
shifter.
One issue
still remains to be resolved in developing this mobile wave power
plant. As the
floats are able to move, vessel drag is
reduced in
rough seas, which saves energy required to power the vessel. Yet,
producing energy |
hampers
float movability to a certain degree.
This leads
to the question of the proper amount of energy to save in relation
to the
amount produced. This issue needs to be resolved by carrying out
investigations
at a research laboratory for shipbuilding. (Further details see “float
bearings”)
2.
Energy yield
It is not
yet possible to calculate the energy yield of the mobile wave power
plant
described here. The figures serving as the basis for such a
calculation, i.e.
the energy content of waves, might yet be determined. One would need to
take into
consideration the range of wave activity in the marine areas where the
vessel
could operate, i.e. empirically determined probability distributions
for wave
height and length. What is
missing in order to do further calculations is an energy efficiency
rate
reflecting the degree to which this primary energy
source is converted
by the
wave power plant into usable energy. Data from the stationary wave
power plant
“Pelamis” |
which functions
in a
similar
manner, could be referred to for this purpose. An efficiency rate
of 40 % is
given for that plant.
As long as
such calculations remain unavailable, a rough approximation based
on
the wind
turbine will need to suffice. By way of a cautious estimate we assume
that the
wave power plant achieves 50 % of wind turbine performance on the open
sea. This
seems reasonable inasmuch as wave activity correlates with wind force.
Under these
conditions, and in accordance with the other assumptions described
more fully
in the chapter on “Wind” (i.e. travel time and
mooring time within and
outside
of harbours, northern and southern scenarios), and assuming that no
wave energy
whatsoever is available in harbours, an energy yield of 7.82 MWh per
year or
21.42 kWh per day is obtained for the worst-case scenario. The best
case
results in 46 MWh per year or 125 kWh per day. Under the conditions
given for
the standard northern scenario, 28 MWh
per year or 78 kWh per day would be collected, and for the standard
southern scenario 17 MWh
per
year or 46 kWh per day. |
Illustration above:
The bow of
the front float tilts downward after passing over the crest of a wave. Illustration
below right: A
sectional view shows how the float generates utilisable energy by
moving
around its horizontal transverse axis. On the lower end of the vertical
axle A,
which connects the float with the main hull, a cylinder Z may be seen.
This
serves as a pivoting bearing, connecting the main hull
with the bottom of the float. A bearing, connected at the circumference
of the 
