Peter Freere

Strength and Reliability of Wood for the Components of Low-Cost Wind Turbines: Computational and Experimental Analysis and Applications

This paper reports the latest results of the comprehensive program of experimental and computational analysis of strength and reliability of wooden parts of low cost wind turbines. The possibilities of prediction of strength and reliability of different types of wood are studied in the series of experiments and computational investigations. Low cost testing machines have been designed, and employed for the systematic analysis of different sorts of Nepali wood, to be used for the wind turbine construction. At the same time, computational micromechanical models of deformation and strength of wood are developed, which should provide the basis for microstructure-based correlating of observable and service properties of wood. Some correlations between microstructure, strength and service properties of wood have been established.

Selection of Nepalese Timber for Small Wind Turbine Blade Construction

The paper describes the selection of Nepalese timber for development of small wind turbine blades on the basis of locally based low cost timbers, along with the selection of coatings to protect the timber from weathering. The selection criterion of timber includes timber mechanical properties, weathering effect on coatings, price, growth and availability of the timber. Mechanical properties such as Youngs modulus of elasticity, breaking strength, breaking strain and Brinells hardness of selected Nepalese timbers are presented. The effects of weathering on timbers without coating, and with different coatings, are analysed on the basis of the change in weight of the timber due to the effect of humidity and rainfall over a period of nineteen months. Degradation of different coatings of timber are compared.

A Low Cost Wind Turbine and Blade Performance

A case study was performed on a commercially available low cost wind turbine. The turbine was tested in a wind tunnel with up to 13 m/s wind speed. The blade characteristics were measured as a function of wind speed, yaw angle, with and without a nose cone, and compared to theoretical models. Practical issues are noted as required for reliable operation, in particular the design of blades and their attachment to the turbine.

The shape and performance of hand-carved small wind turbine blades

This paper describes measurements of the shape of a 900 mm long, hand-carved timber blade for a 500 W three-bladed horizontal axis wind turbine. Four blades were hand-carved in Nepal by reference to a master blade cut in Australia on a numerically controlled milling machine. A high definition three-dimensional scanner was used to determine the surface of one hand-carved blade as a series of profiles at 50 mm intervals along the blades length. A surface model generated from these profiles was compared to the designed blade shape in terms of the three fundamental blade design parameters: chord, twist, and profile shape. The measured twist and chord were less that the design values, particularly in the hub region. This is consistent with the poor starting performance of the turbine when mounted with the remaining hand-carved blades. Assessment of the differences in profile shape would require a detailed computational analysis, which has not been undertaken.

An experimental investigation of the Distributed Electronic Load Controller: A new concept for voltage regulation in microhydro systems with transfer of excess power to household water heaters

Constant voltage and frequency can be generated by a stand-alone Self-Excited Induction Generator (SEIG) driven with a fixed-speed low-head hydro-turbine when the electrical load is maintained constant by an Electronic Load Controller (ELC). However for a Conventional-ELC (C-ELC) most of the generated electrical energy can be dissipated in the dump load if the village load is low. So, the objective of this research is designing a simplified ELC for each household to transfer the excess power for domestic consumption in addition to providing voltage regulation for the generator. A regular ELC, possibly of reduced rated power, should still be installed at the generator site. At the same time, a simplified and inexpensive ELC is installed at each household. The proposed controller, installed in each household, is referred to as the Distributed Electronic Load Controller (DELC). MATLAB simulation results verify the feasibility of the proposed approach. Experimental results using the MSP-430 LaunchPad microcontroller are also presented to verify the validity of the proposed DELC approach.

Kathmandu Alternative Power and Energy Group: Our Experience in Promotion of Low Cost Wind Energy Technology in Nepal

This paper describes the research and development activities carried out by Kathmandu Alternative power and Energy Group (KAPEG) in promotion of wind energy technology in Nepal. Based on the published report, a brief review of wind energy practices in Nepal is presented. The future opportunities in wind energy in Nepal are discussed. KAPEGs completed and ongoing activities in promotion of small scale wind energy are presented. KAPEG has been receiving significant technical and financial assistance from international partners to develop the expertise which is also discussed. Finally, based on the KAPEG experience some of the future works are recommended for the development of wind energy technology in Nepal.

Starting a Wind Turbine Business in Nepal — Case Study of the Kathmandu Alternative Power and Energy Group Pvt Ltd (KAPEG)

The general issues of starting and operating a wind turbine business in Nepal are presented, together with explanation of the effects of the culture, economic and political situation. Practical solutions are discussed as well as the legal and administrative arrangements required to operate the business. The effects of the geographical location on the business are illustrated, together with the impact of a low technical base. These issues will be shown to form a basis of an opportunity for business and social cohesion. Staffing issues are drawn upon to show how a business can have a beneficial effect on the development process of an area. With little government direction of the economy or higher education, considerable efforts in staff training is required. KAPEGs development of its wind energy business is explained with details about how international assistance is instrumental to this industrial development process.

Improved Stability for Wind-Diesel Generator Systems in Wind Gust Condition

Abstract With a sudden wind gust, a wind-diesel system with a large wind turbine penetration can suffer from power system instability, even though it may be stable under steady-state conditions at the same wind speeds. This suggests that the wind-diesel system should be investigated for better frequency and power stability. In this paper, a concept has been presented to improve the stability of the wind-diesel system in high wind gust condition, by placing the wind turbines in such a way that the wind turbines experience the wind gust at different times. A 1.25 MVA Caterpillar diesel generator with six NORDEX150 turbines has been modelled using MATLAB, and it has been found that when all the wind turbines experience a sufficiently large wind gust simultaneously, frequency and power control is lost. However, if the turbines are located so that they experience the wind gust at staggered times, the power system is found to remain stable for the same gust conditions. The potential stability benefits of this approach have been demonstrated for an area with a known predominant wind front movement direction.

Practical Implementation of Hysteresis Control for Maximum Power Point Tracking of a Permanent Magnet Generator Wind Turbine

A permanent magnet wind turbine is to track a dynamically changing wind from measurements of the wind speed and the rotor speed. Issues of determining the effective wind speed at the turbine rotor are investigated as well as the optimum control strategy to maintain operation at the maximum power point. This is implemented using a hysteresis control system based on the turbine tip speed ratio and then tested on a permanent magnet generator wind turbine in a dynamic wind environment. This showed a small increase in the energy output using the controller. Methods to increase the energy output further are investigated by simulation.

Effect of AC inductance on a phase shifted DC-DC bridge converter

Phase shifted DC-DC converters are a well established topology for producing an isolated DC output supply. However, the conventional topology with a DC output LC filter has some practical difficulties when issues such as diode reverse recovery effects, diode voltage ratings for wide ranging input voltages, and common mode EMI caused by the switched transformer output are considered. In many applications, these difficulties can be mitigated by moving the output filter inductor to the AC side before the bridge rectifier. However, this leads to alternative constraints of increased filter series voltage drop and higher filter capacitor current ripple. This paper presents design equations and a design process to determine which of these alternative filter arrangements better suits a particular DC-DC converter application.