Kazuichi Seki

Straight Wing Vertical Axis Wind Turbines: A Flow Analysis

This research examines the flow velocity characters around lift-based straight-wing vertical-axis wind turbines (SW-VAWT) by numerical simulation. The precision of the prediction technique was confirmed. Furthermore, we estimate the flow behaviour during the wind turbine rotation by using this numerical simulation technique, and evaluate the flow around the SW-VAWT. This paper presents an outline of the work and gives the results of the calculations.

A Feasibility Study for Floating Offshore Windfarms in Japanese Waters

This paper reports the results of technical and economic feasibility studies of floating offshore wind farms under typical environmental conditions in Japanese Waters. Outline designs are considered, with economic assessments. Both horizontal and vertical axis wind turbines are considered, although it is realised that horizontal axis machines now dominate.

Experimental Determination of Optimum Design Configuration for Micro Wind Turbines at Low Wind Speeds

This paper reports experiments and theory on some small wind turbines of rotor diameter 100 cm and less. Discrepancies in power performance have been found from predictions of blade element theory. Wind tunnel experiments showed that performance depends on the solidity of the fixed diameter rotor due to the dependence of Reynolds number on chord length. In particular, power output is lower than theory predicts on wind speed less than about 10m/s. For turbine rotors of constant diameter, output depends on solidity. In general, at low wind speeds, rotors with greater solidity give a higher output than with less solidity. This is due to the difference in Reynolds number, which itself is associated with chord length. The optimum value of Reynolds number for such small turbines is 100,000.

On-site electrolysis sodium metal production by offshore wind or solar energy for hydrogen storage and hydrogen fuel cycle

If hydrogen can be solidified at room temperature or under atmospheric pressure, its long-distance transportation and long-term storage become possible. It is, then, considered to convert hydrogen into sodium metal. This sodium metal will be produced by electrolyzing seawater salt or rock salt and stored in kerosene to transport to a consumption place; when water is added to the sodium metal, a large amount of hydrogen is generated instantaneously anywhere. Furthermore, a good thing is that the melting point of sodium hydride produced by reacting with hydrogen gas during the process of manufacturing sodium metal is 800°C, 8 times higher than 98°C of sodium metals melting point, so its handling risk becomes extremely lower. When adding water, the sodium hydride hydrolyzes vigorously to generate hydrogen in the same manner as sodium metal; the amount of the hydrogen generated is twice as large as the hydrogen produced by the reaction of sodium metal and water. Sodium hydride is a material that posses both functions of hydrogen absorption and hydrogen generation. Sodium metal, thus, is an economical, renewable, and sustainable fuel, which discharges neither CO2 nor radioactivity.

Study on the Bearing Resistance in a Wind Turbine Generator System

The vertical axis wind turbine generators are mainly used for small size wind turbine generators, and are independent on wind direction. The rotor of the vertical axis wind turbine is required to start rotating at a low wind speed and to smoothly rotate with small torque loss so that the energy loss from the energy of wind is minimized and the power generation efficiency is increased. But when the rotor is designed according to the wind conditions and the safety factors in the international safety standard for small wind turbines, IEC61400–2, commercially-available bearings are not suitable for the rotor, because both of the static and dynamic load ratings are larger than those demanded for the vertical axis wind turbine. That is, the frictional force and the rotating torque resistance of the commercially-available bearings are too large for the rotor to meet the above mentioned requirements. In this study, the bearings having the most suitable load ratings and the very low frictional force for the rotor were newly designed conforming to the wind conditions and the safety factors in the above mentioned IEC61400–2. And the low torque shaft unit for the rotor using these newly designed bearings was also designed and experimentally produced. This low torque shaft unit was equipped in the real vertical axis wind turbine and a demonstration experiment was conducted. The result of the experiment showed that the low torque shaft unit started rotating at low wind speed and the power generation efficiency was improved. It is verified that the low torque shaft unit satisfies the above mentioned requirements well.

A design strategy for the improvement of an existing 300kW WTGS rotor blade

This paper presents our design concept of a new rotor blade for an existing 300 kW WTGS with a horizontal axis rotor. This two-bladed WTGS is evaluated to have rather poor performance in terms of annual output due to the deficiencies in aerodynamic design of blade and its high noise emission level which restricts the time range of operation. The new blade must be adaptive to the existing hardware, e.g. the flange for installation and the hub and tower to assure a clearance in case of blade feathering. In order to reduce noise, and at same time, achieve high performance at the given tip speed ratio, a narrow design path was found which gives compromise among the conflicting requirements. This paper presents the outcome of this design with the airfoil, plan form and twist distribution which can attain the Betz limit on the blade from 30% to 95% radial position at the design tip speed ratio of 7.0.

A Passive System for Optimising Battery Charging using a Permanent Magnet, Variable Speed Generator

The performance of a permanent magnet, variable speed generator charging a battery via a PWM converter or rectifier is considered. It is found that in neither case can the system be configured to generate electricity at low wind speeds while maintaining optimum efficiency at rated wind speed. Accordingly, an alternative system which permits operation at close to optimum efficiency over the full range of wind speeds below rated is proposed. This uses two separate generator windings, one of which begins to charge the battery at a much lower wind speed than the other. Experimental results are presented which confirm the theoretical analysis.

On site sodium manufacturing for energy storage with offshore wind power and seawater

Sodium metal reacts with water violently and generates a huge amount of hydrogen. Sodium metal has the role as a hydrogen storage material. The fossil fuel and nuclear fuel are deposited only in a limited region in the world and reserves are limited, whereas sodium exists plentifully as a salt in seawater and exists abundantly as a rock salt on the continents. Sodium (specific gravity, 0.971) is lighter than water and is stored safely in kerosene for electric power. The solution can then be transported to a location and with the addition of water can instantaneously generate a large amount of hydrogen for power generation.

On-site sodium metal production with electrolysis by offshore wind or solar cell power generation for hydrogen generation

Sodium metal reacts with water explosively to generate hydrogen. Therefore, sodium metal can have an important role as a hydrogen storage material. Seawater contains water most and sodium second. Seawater is electrolyzed by offshore wind or solar cell power generation to produce sodium; which is transported to a thermoelectric power plant on land and then is reacted with water to produce hydrogen for electric power generation. Sodium hydroxide, a by-product, is used as a raw material for soda industries. In the sodium production process, many by-products such as fresh water, magnesium, sodium hydroxide, hydrochloric acid, and sulfuric acid are produced. Thus, sodium metal is an economical, renewable, and sustainable fuel that discharges neither CO 2 nor radioactivity.

A Study of Small Wind Turbine Generation System for Extreme Weather Conditions

This Paper Presents a study of small scall wind powered generation systems combined with solar cell generation unit as a reliable electric power source at the mountainous regions ranging from Himaraya via Tianshan to Mongolia. In these mountainous region, wind is strong in all seasons and almost constantly available. The weather conditions in these regions are extreme; e.g., air density is about 1/3 of sea level value, the lowest temperature is almost -60 degrees centigrade and the wind velocity can reach 100m/s. Since helicopters are not operatable, each part of the generation system must be carefully arranged for transportation and development. In this paper, a hybrid power system combined with the wind powered generator of 150W (max. 500W) output and the solar cell is described. Especially, the design and the wind tunnel test performance of the two-bladed propeller type wind turbine are shown in detail. This paper also presents the result of weather exposure test conducted at a site of 2800m elevation with the similar weather condition to the expected deployment points. Effects of weather especially temperature, humidity, atmospheric pressure, snow and icing on the performance of this system are investigated and we confirmed rehable and satisfactory operation of this small, independent power source.