Power augmentation of cheap,sail-type,horizontal-axis wind-turbines

Popular myths concerning the origins of wind-turbines are examined and possible routes for their introduction into Western Europe are discussed. The advantages of using one primitive form—the flexible sail wind-rotor—are described. Data are presented for tests on a 0·64 m diameter, sail wind-turbine, augmented by tip-fins and centre bodies. The results show an increase in power output by a factor of at least 1·6 (compared with the non-augmented rotor) as a result of using basic flat-plate fins. Power outputs from low capital cost wind-turbines can be at least doubled by the addition of more refined tip-fins, for marginally little extra expense. Centre bodies gave a power enhancement exceeding 8 per cent.     

Controller for a small induction-generator based wind-turbine

Design of a low-cost micro-controller for a small induction-generator based grid-connected wind-turbine is presented in this paper. The controller senses the parameters of the wind-turbine generator and the grid, and makes decisions about grid connection and disconnection. Low-cost instrumentation circuitry has been developed to measure the generator and grid parameters. Based on the measurement of voltage and frequency of the wind-turbine generator and the grid side, a control decision is taken to connect the system to the grid. The controller makes decision to disconnect the system from the grid based on the power flow measurement between the wind turbine and the grid. The power flow between wind turbine and the grid depends upon the availability of the wind. The prototype controller has been developed based on a micro-controller PIC16F877 and has been tested in the laboratory.     

Design optimisation of a solar-energy harnessing system for stimulating an irrigation pump

Water from below ground level is to be raised, for the irrigation of a desert area near Cairo, Egypt, by harnessing solar power. The solar-energy collector is an array of gravity-return heat pipes, each surrounded by a cylindrical high-vacuum enclosure. The prime mover, in the form of a multi-vane expander, operates in an organic Rankine-cycle using trichlorotrifluoroethane as the working fluid. For specified conditions, the performances and optimal output temperatures of the collector (so that maximum overall efficiency of the system can be achieved) are predicted.     

Design,optimisation and conversion-efficiency determination of a line-focus parabolic-trough solar-collector (PTC)

PTCs are the preferred type of collector used for steam generation, due to their ability to work at high temperatures with high efficiencies. The results produced from a simulation program, showing the variation of collector's efficiency as a function of heat transfer fluid flux, pipe diameter, solar radiation intensity and active area of the PTC, are presented.     

Implementation of bending-torsion coupling in the design of a wind-turbine rotor-blade

An investigation is performed on the implementation of bending-torsion coupling of a composite wind turbine rotor blade to provide passive pitch-control. Limited passive torsion deformation is realised with a structural coupling between flapwise bending and elastic twist of a constant speed rotor-blade. The blade and skin laminate configuration are analysed with a FEM program, in which a complete blade with spar webs is modelled. This conventional blade configuration has some disadvantages. Therefore alternative design concepts are reviewed, where the coupling plies are restricted to a load-bearing spar, while a softer skin provides for the aerodynamic shape. From additional analysis, it is found that, while for the two alternative design concepts the stress concentrations at the leading edge joint are bypassed, the bending-torsion coupling response is lower. An experiment was performed to validate the calculation methods. The experimental results show good correlation with theoretical predictions. It is recommended to investigate further the fatigue life properties of a glass/carbon hybrid FRP with off-axis fibre orientations.     

The starting behaviour of a small horizontal-axis wind turbine

This paper presents selected results taken from an extensive investigation of the starting performance of a small horizontal-axis wind turbine. Starting was observed for blade pitch angles varying between 0 and 35° in 5° increments. At 0°, the angle for maximum power, the turbine’s 5 m diameter blades produce 5 kW at a wind speed of 10 m/s. At this pitch, starting is characterised by a long “idling period” in which the blade’s angular velocity increased only slowly because of the very high angles of attack. As the pitch angle increased, the idling period decreased. At all pitch angles, the measurements of angular velocity are compared with those obtained from a numerical integration of the equation for angular acceleration. The aerodynamic torque was obtained from a quasi-steady blade element analysis and the resistive torque of the drive train and generator was subtracted to determine the net torque accelerating the blades. The agreement between predicted and measured angular velocity was generally good and improved as the pitch angle increased.     

The near wake of a model horizontal-axis wind turbine at runaway

This paper completes a series which describes measurements within two chord lengths of the blades of a small horizontal-axis wind turbine over a wide range of operating conditions. Prior to the present experiment, the turbine was rebuilt to allow operation at its runaway point, where no power is produced. Runaway can be viewed as the upper limit on wind turbine performance at which thrust and wake expansion are maximised. The measurements, which approximate the mean and fluctuating velocity fields seen by an observer rotating with the blades, were obtained from a stationary X-probe hot-wire anemometer by the technique of phase-locked averaging. It is shown conclusively that there is negative (power-producing) angular momentum extracted from the wake, but a balancing positive angular momentum resides in the tip vortices. The mean velocity through the blades increases significantly with radius, in contrast to the near-constant velocity when the turbine is producing its maximum power. Comparisons with conventional blade calculations suggest that the circulation in the wake is related to the difference between the circumferential components of the lift and drag, rather than the magnitude of the lift as is often assumed. Within the range and accuracy of measurement, the pitch of the tip vortices is constant and proportional to the inverse of the tip speed ratio.     

Phenomenological models for post-stall airfoil characteristics of horizontal-axis wind turbines

There exist significant differences in airfoil aerodynamic characteristics between wind tunnel test data (2-Dimensional flow) and field test data (3-D dimensional flow). Through the Combined Experiment Program (CEP), efforts have been made to investigate proper approaches to analyze such differences so that it enables us to incorporate the results into wind turbine rotor performance codes to assist in optimal design of a horizontal axis wind turbine. As a step towards a more indepth, theoretical analysis of various physical effects under field conditions, we first analyze the difference in airfoil characteristics from phenomenological point of view by developing correlations from experimental data. The correlations for the difference in lift coefficient and drag coefficient between 2-dimensional and 3-dimensional flow are developed to form a basis and are suggested to be modified and included in the PROP code.     

The cost estimate for a novel cheap solar cell

The estimate for the lowest cost of SODL (silicon on defect layer) solar cell is made according to the price standard of present market. The estimate shows that the PV (photovoltaics) energy costs can be reduced from today's 25–30 cents/(kW h) to 7–8 cents/(kW h) which is comparable with the present cost of electricity generated by traditional energy sources such as fossil and petroleum fuels. The PV energy costs could be reduced to a value lower than 7–8 cents/(kW h) by developing SODL technology. The SODL solar cell manufacture featuring simple processes is suitable to large scale automated assembly lines with high yield of large area cells. Some new ideas are suggested, favoring the further reduction in the cost of commercial solar cells.     

Whirl flutter analysis of a horizontal-axis wind turbine with a two-bladed teetering rotor

An investigation to explore the possibility of whirl flutter and to find the effect of pitch-flap coupling (δ₃) on teetering motion of the DOE/NASA Mod-2 wind turbine is presented. The equations of motion are derived for an idealized five-degree-of-freedom mathematical model of a horizontal-axis wind turbine with a two-bladed teetering rotor. The model accounts for the out-of-plane bending motion of each blade, the teetering motion of the rotor, and both the pitching and yawing motions of the rotor support. Results show that the Mod-2 design is free from whirl flutter. Selected results are presented indicating the effect of variations in rotor support damping, rotor support stiffnes, and δ₃ on pitching, yawing, teetering, and blade bending motions.     

A review of resonance response in large, horizontal-axis wind turbines

Field operation of the Mod-0 and Mod-1 wind turbines has provided valuable information concerning resonance response in large, two-bladed, horizontal-axis wind turbines. Operational experience has shown that 1/rev excitation exists in the drive train, high aerodynamic damping prevents resonance response of the blade flatwise modes, and teetering the hub substantially reduces the chordwise blade response to odd harmonic excitation. These results can be used by the designer as a guide to system frequency placement. In addition, it has been found that present analytical techniques can accurately predict wind turbine natural frequencies.     

Supply of, and demand for, a resource: Fuzzy logistical optimisation technique

Fuzzy logistical analysis for exploiting a resource helps determine the relative strengths and weaknesses of various supply-demand chains linking alternative sources (in the supply sector) to their final points of use (in the demand sector). There are benefits and constraints associated with each supply and demand sector. Fuzzy theory is applied to the logistical optimisation of these sectors in order to assess the relative importance or degree of association between the supply and demand determinants, which therefore should influence the decisions made for the exploitation strategies adopted for different sectors. Each supply determinant is related to each demand determinant. From their relative values of association, the relationship corresponding to each supply-demand pathway can be calculated and compared with those for the remaining pathways. Such information is valuable, for example when devising and implementing strategies affecting waste management and the recycling of materials and/or energy.     

Modelica-AeroDyn: Development,benchmark, and application of a comprehensive object-oriented tool for dynamic analysis of non-conventional horizontal-axis floating wind turbines

The exploitation of offshore wind energy by means of floating wind turbines is gaining traction as a suitable option to produce sustainable energy. Multi-rotor floating wind turbines have been proposed as an appealing option to reduce the costs associated with manufacturing, logistics, offshore installations, and operation and maintenance of large wind turbine components. The development of such systems is forestalled by the lack of a dedicated tool for dynamics and load analysis. Standard codes, such as FAST by NREL, offer the desired fidelity level but are not able to accommodate multi-rotor configurations. A few experimental codes have been also proposed, which may accommodate multi-rotor systems, but low flexibility makes them impractical to study a vast range of innovative multi-rotor FWTs concepts. To close the gap, this work presents the development and comprehensive benchmark of a fully coupled aero-hydro-servo-elastic tool able to easily accommodate arbitrary platform and tower geometries and the number of wind turbines employed. Development is carried out in Modelica, which allows for the employment of the same code functionality in a virtually unlimited number of physical configurations. Full blade-element momentum capabilities are achieved by integrating into Modelica the well-established NREL aerodynamic module AeroDyn v15 within FAST v8. Structural dynamics of tower and blades are implemented through a lumped-element approach. Hydrodynamic loads are computed by employing the DNV software SESAM WADAM. Thorough benchmark is performed against FAST, and positive results are obtained. The dynamic performance of a two-rotor floating wind turbine is finally assessed considering different turbulence spectrums.     

Evidence for the need of a cheap simple solar radiation recorder

The recording of solar radiation data in eight tropical countries is surveyed. The author urges the development of an inexpensive solar radiation recorder with an accuracy of plus or minus five percent which would provide reliable data for engineers and agriculturalists.     

Do centre-bodies improve the performance of horizontal-axis,sail-type wind-turbines?

The power harnessing advantages of using hub-fairings—either rotating or stationary, with or without stationary after-bodies—have been measured experimentally. For the flexible sail wind-turbines tested, stationary (rather than rotating) hub-fairings produced greater power augmentations. Employing a stationary after-body is also desirable for the turbine in order to increase the rate of harnessing of wind energy.     

An analytical expression for the power coefficient of an ideal horizontal-axis wind turbine

The paper shows that an analytical evaluation of the power coefficient C_p for an ideal horizontal-axis wind turbine can be made via an expression giving the direct relationship of C_p and the axial induction factor a. The results obtained agree closely with those obtained numerically from the usual integral expression involving several variables.     

永磁直驱风力发电并网逆变器电流滞环控制

永磁直驱风力发电系统网侧逆变器采用单电流环控制时,其稳定性不足,输出电流谐波含量大、电能质量下降。文章分析了含有LCL滤波并网逆变器的数学模型,提出了瞬时功率外环、电流滞环内环的控制策略。通过仿真结果表明,在该控制策略下,并网系统输出的电流波形较好,谐波含量低,具有良好的动态跟踪响应特点,并满足了风力发电并网的控制要求,有效验证了该控制方法的可靠性和正确性     

Design of supporting devices for large diameter thin pipes

When an analysis is made in accordance with ASME Code Class 1 for piping by the stress indices method (NB 3650), the stresses induced locally in the piping by the supports are not taken into account. For piping whose thickness is small in relation to its diameter, which is subject to sudden temperature changes and to seismic shocks and which also operates at high temperature, it is undesirable to ignore these effects. This is particularly the case with piping carrying liquid sodium since the classic solutions do not provide a satisfactory answer to the thermomechanical problems and cannot resolve many uncertainties in the analysis. The design finally selected must meet the double requirement of permitting free radial expansion of the piping whilst enabling it to withstand considerable loads with minimal deformation. The design must also be justifiable by easily verified hypotheses.The design adopted consists of a rigid collar connected to the piping by blades which are flexible radially in relation to the pipe and rigid tangentially. These blades are attached to very short ring lugs welded on to the piping. In this way, the outside forces acting on the piping are reduced almost exclusively to circumferential forces which, combined with the circumferential shearing flux due to the adjacent sections, constitute a distribution of forces which is particularly favourable for limiting the circumferential bending moments in the pipe. The resulting deformation of the circular section is thus sufficiently small not to affect the longitudinal bending strength, and particularly the buckling strength.The most significant stresses prove to be those due to the moment on the lug; these are well known and are limited due to the small height of the lug. The thermal stresses due to the presence of the lug were calculated by the finite element method. The thermal and mechanical disturbance created by the lug has the effect of multiplying by about a factor of 2 the maximum total stresses occurring during thermal transients in the straight part; they thus remain limited and less than those developed in other straight discontinuities affecting the piping; for instance, the changes in thickness between straight parts and bends. To back up these calculations, a series of tests was performed to check that the technological requirements of manufacture did not question the load distribution hypotheses taken into account in the calculations.