generating power, is specified; while freedom in design
remains only with regard to the appearance of the mast and
mechanisms for securing it in storms.
Conventional techniques for securing rotors in storms, e.g. braking the rotor and bringing it to a standstill, result in the disadvantage that wind pressure still remains too high in the secured position. It is therefore proposed that the blades be able to tilt backward (seen from the wind direction) and fold against the (imaginary) extension of the rotation axis. This presupposes a leeward turbine, i.e. one that operates behind the mast as seen from the wind direction. This offers the additional advantage of always turning into the wind automatically, without any other mechanisms. The mechanism securing against storms also needs to be activated when travelling at high speeds against the wind.
Wind pressure on the wind turbine mast is minimised by selecting a streamlined design for the cross section.
|This also has the advantage that there is less disturbance of the wind flow to the turbine, running behind the mast, as would be the case with a round mast. This presupposes that the mast always turns in the wind with the wind turbine, i.e. the mast must be mounted on pivoting bearings. The radial forces on the wind turbine mast (i.e. wind pressure) are transferred to the roof of the main hull by a cylindrical roller bearing, while the axial forces (i.e. the weight of the entire wind turbine structure) as well as the remaining radial forces (i.e. wind pressure resulting in leverage) are transferred by a cone roller bearing to the bottom of the main hull. The roller bearings can be made of hardwood impregnated with paraffin, rendering them seawater-resistant. (Paraffin serves as a lubricant and repels water.) This offers the additional advantage of reduced noise as compared to steel roller bearings. While wooden bearings have more play (only in the case of the radial bearings), this is tolerable for the applications presented here.|
2. Wind energy
Assumptions about wind conditions need to be made for all of the locations where the vessel may be found in the course of a year. To this end we have based assumptions on the five wind zones depicted in the European Wind Atlas. There an average wind speed at 50 m (164 ft) above ground (or water) are given – according to the geological macro structure. The table above shows for example for wind zone 3 (yellow) a mean wind speed of 6 – 7 m/sec at the coast and of 7 – 8 m/sec above the open sea. These figures reduce with decreasing height, depending on the geological micro structure of the terrain in question – hedges and woods, towering rocks, buildings etc. This is made allowance by a so called “roughness exponent”, which, together with an appropriate formula, allows to calculate the wind speed in the height of the wind turbine hub. The hub height, which is 14 m (46 ft), is determined by taking the height of the roof above water and adding the radius of the wind turbine plus a safety margin between the roof and the lowest blade tip position. We assume that an adult is able to stand on the roof with arms stretched upward and not touch the rotating blades.
The calculations presented in the following are based on the standard
scenario, described more fully in the
using the ratio: mooring time without crew : mooring time
with crew : travel time = 50 : 273 : 42 days and a motor
operating time of 6 hours per day of travel.
Worst-case scenario: in this case the vessel lies in a wind-protected harbour, with or without crew, in zone 1, a light-wind zone. The ship also remains in zone 1, with light winds, during its voyages. Under these conditions the wind turbine would produce 1.93 MWh per year or 5.29 kWh per day.
Best-case scenario: on 50 days a year the ship lies in a harbour exposed to winds in the high-wind zone 5 and on 273 days it lies at anchor in a shallow coastal area also within the high-wind zone 5. Even during the total travel time of 42 days the ship does not leave the high-wind zone. This scenario is far from being unrealistic. A glance at the European Wind Atlas reveals that such conditions are found in the harbours and marine areas near Skagerrak, near northern England and Northern Ireland, yet also in the Mediterranean in the Gulf of Lion (between Marseille and the Costa Brava). Under these conditions the wind turbine would produce 56 MWh per year or 153 kWh per day.
Standard scenario: due to the variety of local wind conditions, a basic decision needs to be taken as to whether the Eco-Trimaran will operate mostly in bodies of water in the north (North and Baltic Sea or North Atlantic) or in the Mediterranean. For this reason a distinction is made here (just
|as for solar energy) between “northern” and “southern” versions of the standard scenario. It is assumed that the ship, including crew, will lie in a wind-protected harbour on 45 days and in a harbour exposed to the wind on 50 days (see table at right). On 20 days it will lie at anchor near a steep coastline (e.g. for scuba diving). The remaining 158 days are divided among various beaches for bathing along a low-lying coast. The assumptions regarding wind conditions in the north and south can be found in the table on the previous page (in the “Wind” column), in which the wind zones are given according to the “European Wind Atlas”. It is further assumed that the ship, without crew, will lie in a wind-protected harbour on 30 days and in a harbour exposed to wind on 20 days. The ship will travel for a total of 42 days divided up among the various wind zones as shown in lower table at right side. Under these conditions the wind turbine would produce 38 MWh per year or an average of 103 kWh per day according to the northern||
scenario. In the south, with generally poorer wind conditions, annual energy production would be 30 MWh or 82 kWh per day on the average.
The preliminary assumption for rotor diameter, reached intuitively, is 14 m (45 ft).
|to be set more precisely, requires
calculation of wind pressure (dynamic pressure) on
the wind turbine and resulting vessel heel. This
could conceivably make it possible to realise even larger
rotor dimensions. In order to estimate potential
consequences for energy production, I have also calculated
annual energy production for other rotor diameters.
From the chart below (where blue is the northern, yellow
the southern scenario) it may be seen that, when
rotor diameter is increased from 14 to 16 m (45 to 52 ft),
for example, annual capacity increases by one-third.
Considering that our mechanism for securing the rotor in
storms is very effective and responds quickly, potential
for greatly improving energy production would seem to
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