Green-Ship Technology

Introduction

The first wind turbines in the 90s produced a maximum of 400kW; however the current turbines produce over 4mW of power. Wind turbines generate electricity at wind speeds of 4-5 meters per second. Wind passes over the blades producing a rotating force. The blades then turn the shaft in the nacelle connected to the gearbox. The gearbox increases the speed for the generator. The generator converts the mechanical energy to electrical energy. The power generated is then fed into the transformer which steps down the voltage before usage. The turbines have a wind vane and anemometer which measure the direction and speed of the wind.  The motor constantly changes the direction of the blades to face into the wind to optimize power generation.

Literature review

A few private cargo companies have embraced green ship technology. In the North Sea the Estraden –a Finnish- ship uses wind turbines and solar panels in addition to oil. The Swedish Energy Organisation has done intense research on wind powered ships. ‘Development and Demonstration of  New Technology’ research paper explores on the designs of the turbine blades, calculation of thrust and power generation on a ship. This research was done in 2015. The Avontuur is a Timbercoast cargo ship that uses solar and wind turbine power.  The ship was built in 1920 but was refurbished to use renewable energy in 2016. The ship sails successfully between Europe and America.

Design and calculation of wind blades and power generation

Let’s take for instance a 200m long tanker with a 20m diameter of folding turbine.

The ship is sailing at an angle of α and the wind direction in relation to the destination of the ship is β.

Let’s take the speed of the wind to be V.

We can thus calculate the force of the wind turbine symmetrical to the ships destination using Axial momentum theory

A is the rotor disk area of the turbine y is the density of air and a is the induction factor of the axial.

However the water propeller will be producing the following force. The power losses are accounted by the propulsive efficiency

The net force propelling the ship forward is thus

Fnet = F – Fe

This means that sailing upwind at half speed gives α = 0.33 and a = 0.22

To optimize power generation, one should know wind direction, the yaw offset angle the pitch angle and the rotor speed. Two bladed turbines are preferred offshore so that it will be easy to house and unfold the blades on the deck. The low efficiency of the two blades turbine will be compensated by increasing their diameter.

The analysis in Table 1 was carried out by the  Swedish Energy Organization to check the impact of  changing the parameters of the wind turbine and the power generated  ; in particular was chord length ,rotor speed and blade angles.

From the table, it is seen that a decrease in chord length causes a decrease in power and thrust. However an increase in chord length increases the thrust but has no effect on power generation. 

The table shows that increasing the thrust increase the propulsion of the ship. These calculations can be used to create a turbine controller unit to calculate the average yield. The calculations can also be used in determining the best route to use to a destination according to the weather patterns. 

The following results are from a prototype of a Panamax oil tanker that used wind turbines. The ship has two 1Mw wind turbines. This research was done by Carlson & Nilsson in 2015. Another research done by Lloyd’s Register Marine had the same findings.  The study is based on a 7200kw ship being propelled at 14.5knots.

Discussion

Table 3 shows that an increase in wind sped leads to an increase in power generated. Furthermore, it is seen that an increase in speed causes a reduction in the fuel consumption. From the results it is seen that wind turbines save nearly 16% of fuel consumption. Another advantage of using wind turbines is that the Clean Shipping Index (CSI) and environmental shipping index (ESI) gives discounts to such companies for reducing green house effects. The route and average weather conditions should be put into consideration when sailing.  Super capacitors and batteries should be used to store excess energy.

Conclusions

The wind turbine lowers natural gas fuel consumption. The wind turbines are both producing electrical power and again providing the thrust for the ship. An extensive study and testing of ship wind turbines should be done by Kenya Maritime. The testing can be done on long distance cargo ships on routes with calm weather conditions. The Swedish government, German and a few private companies in the USA have implemented this green ship technology and have found it robust and economical.  The Kenyan government should embrace this technology to reduce fuel cost and green house effect.

Table 1 yield contribution from power and thrust on the Rotter-dem New York route for rotor concepts

Table 2. The different parameters for the engine model

Table 3. Variation of speeds of wind turbine and the power consumption and net fuel saved