GB2404700A

GB2404700A - Roof mounted wind turbine

Info

Publication number: GB2404700A
Application number: GB0318064A
Authority: GB
Inventors: Robin Matthew Hilder
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-08-01
Filing date: 2003-08-01
Publication date: 2005-02-09
Also published as: GB0318064D0

Abstract

A horizontal axis turbine 1 is mounted for rotation about a vertical axis (B in fig. 2) on a roof. The turbine may comprise means for rotating the turbine and holding it at any orientation to the instantaneous wind direction. The turbine may be of a Savonius type or of a bladed type.

Description

Field of the Invention Title of the Invention Wind Turbine with Low Visual Impact This invention relates to the production of heat or electricity using a wind turbine so constructed as to minimise its visual impact making it more suitable for use in the urban environment than conventional machines.

Background of the Invention Use of wind turbines to generate electricity is widespread, but has generally concentrated on large installations in remote locations. Although a wide variety of turbine designs exist, even ignoring the mounting tower, they are characterised by having their largest extent in the vertical direction, be it due to the length of blades on horizontal axis vane machines or the height of the axle assembly and guide wires in vertical axis ones. This means that wind turbines are easily visible and difficult to camouflage or otherwise blend into the background. In the urban environment there is significant potential for small scale local sources of heat or power to supplement room and water heating and electricity requirements and the use of both thermal and photovoltaic room panels is widespread and practical. However since most of the demand for energy falls either in winter or at night scope to make a major contribution to the household energy demands is limited. Wind on the other hand is particularly abundant in the cold winter months and is available under suitable weather conditions 24 hours per day rather than the maximum of 12 or so hours for meaningful sunlight collection even in summer. As is the case with solar panels, house roofs represent a good potential mounting point being high up and away from most obstructions; however in many countries planning regulations and aesthetic considerations preclude the mounting of highly visible structures on roofs. Furthermore many wind turbines designed to generate electricity have fast moving parts such as the blade tips and drive train which contribute significantly to noise pollution. When looking at heat generation however it is possible significantly to reduce the speed of moving components and in the urban environment with co-location of use and production transmission losses need not be prohibitive. Broadly speaking wind turbines can be divided into two types. The first and most common use aerodynamic lift giving relatively high efficiency at rotor speeds suitable for generating electricity without very high gearing ratios. An example of this type of wind turbine is given by Darrieus in US 1,835,018. The second rely predominantly on differential wind resistance on either side of the rotor axis to produce a net turning force. The efficiency of drag based rotors falls extremely rapidly with rotor tip speed although they do potentially offer high starting torques. Perhaps the most well-known of this type of wind turbine is the Savonius rotor, US 1,766,765, which consists of a pair of oppositely arranged hollow shaped vanes overlapping to such an extent that an air gap is provided between them. Since the wind resistance to the incident wind of the closed side is less than that of the open one, the rotor turns. Using very simple materials, for instance a split oil drum, it is possible to create a Savonius wind pump which is self-starting and requires no steering gear or other control equipment. Both of the examples cited are classed as vertical axis wind turbines as opposed to the more conventional horizontal wind mill types familiar for many hundreds of years. Thus horizontal axis machines have their blades arranged in a radial pattern, whilst vertical axis machines have them in an annular one. However the invention breaks this convention by having the blades in an annular pattern around a horizontal axis and the optimum orientation of this axis is across the wind direction rather than in line with it. Object of the Invention The object of the invention is to provide a wind turbine with reduced visual impact to improve its acceptability in urban environments.

Summary of the Invention A wind turbine is provided comprising: i) A rotor with a horizontal axis of rotation whose maximum extent is along the direction of said axis. The rotor is further equipped with vanes in an annular disposition about this axis of rotation such that wind, blowing in a direction that is not parallel to that axis, incident upon the rotor generates a turning force about it. ii) A means of steering the rotor so that the horizontal axis of rotation can be set and held at any angle to the incident wind. iii) A means of converting the mechanical forces derived from the movement of the wind to electricity or heat. iv) A mounting system that allows it to be attached to building roof structures. Advantages of the Invention The principle advantage of the invention is that it minimises the height of the wind turbine system and maximises its co-location with the mounting feature. This means that the height of an object at any given distance required to obscure the wind turbine is reduced and it makes it easier to disguise the turbine when mounted on an existing feature such as a house. The distance from the point of attachment to the point of action of the wind induced forces is also reduced meaning that the induced torque is less than it would be for a conventional wind turbine. Preferred or Optional Features of the Invention In its preferred form the wind turbine is mounted on a domestic dwelling and is used to provide heat via transfer fluid since this is the most efficient use of the extracted energy from the wind and the single largest energy use for this type of building. Whilst it would be impractical to raise the temperature of the heat transfer fluid to such a level that it could be used for cooking the main use of thermal energy is room and water heating which can utilise relative low temperature gradients. Using a heat transfer fluid system would also allow the system to be used in combination with solar thermal heating panels, which would complement the energy production by the wind turbine since the period of maximum solar insulation coincides with the minimum availability of suitable wind conditions. The heat generating unit should, in the preferred form, have a means of varying the resistance to rotation in such a way that it is very low when starting to turn and can be raised in proportion to the level of wind derived forces available when running so as to limit the maximum rotor tip speed for a given level of heat extraction. This has two main benefits, firstly it reduces the minimum wind speed required to start the turbine and secondly it enables the maximum rotor speed to be controlled, which can improve aerodynamic efficiency and reduce noise pollution. Heat generation may also be further improved by using a heat pump arrangement to extract heat from the surrounding air and transfer it to the heat transfer fluid. Looking at the choice of materials it is clear in terms of reducing visual impact that it is advantageous for them to be transparent, however colours that mimic the surrounding features may also help to disguise the invention to the casual observer. There are many designs of blades available from vertical axis wind turbines which would also rotate if turned through 90[deg] to lie horizontally and directed into the wind. However the effects of gravity on the rotor structure need to be considered when doing this and in particular ones utilising thin vane blades need significant additional bracing from the axle in order to maintain their correct form. Lightweight and stiff rotors based on the aerodynamic principles given by Savonius in US 1,766,765 can however be made from transparent plastic sheet and so offer a good combination of mechanical and visual impact properties. One disadvantage of vertical axis wind turbines in comparison to conventional horizontal axis machines is that the orientation and hence aerodynamic properties of the rotor blades changes as the rotor structure turns. This leads to a cyclic variation in the torque available, which in some rotor designs is so severe that they are unable to self-start. The basic geometry of the invention means that it is also subject to this effect and so in the preferred form a series of symmetrically rotationally displaced rotor assemblies is provided on the primary axis and these are further arranged in symmetric pairs on either side of the secondary rotor axis about which the rotor is turned in order to correctly align it with the wind direction. In this way the turning forces induced by the wind resistance of the individual sections of the rotor balance each other out reducing the net force on the alignment system. A principle advantage of conventional vertically mounted Savonius wind turbine is its simplicity since it does not require any steering gear; however, as has previously been indicated, because it relies on the differential wind resistance of the rotor blades on either side of the axis to turn its aerodynamic efficiency is relatively low and falls rapidly with increasing rotor speed. One reason for this is that the side of the rotor moving up wind is retarded not only by the resistance to its own motion, but also by the pressure from the incident wind. Numerous modifications to the Savonius system have been proposed to address this; but since they add to the complexity and costs commercial uptake of these has been limited. Since the invention however already calls for a system that orientates the rotor with respect to the incident wind the up wind and down wind sides of the rotor are fixed in respect of said wind. This means that a static wind deflector can be mounted ahead of the upwind side of the rotor, which in the preferred form is the bottom half, reducing the drag due to the incident wind. Suitable forming of this air deflector can also increase the air flow into the down wind side of the rotor increasing the available torque. The simplest way of directing a wind turbine into the wind is to make use of a tail fin, or other such feature, for example a suitably formed static air deflector system, that generates significant turning forces when the turbine is at non-optimal alignment. Whilst this could also be applied to the invention it is not the preferred solution since the alignment feature would increase the visual impact of the device and also because in the turbulent air flow expected at mounting point due to air flow and deflection over the roof structure this type of system would tend to lead to oscillation about the optimal alignment direction reducing average efficiency. In the preferred form therefore the wind turbine is equipped with a wind direction sensor and a means of translating this into a control signal for a motorised system capable of turning and holding the complete assembly into the incident wind. Brief Description of the Drawings Figure 1 is a perspective view of a wind turbine in accordance with the invention mounted on a pitched roof. Figure 2 is a close up perspective view of this wind turbine. Figure 3 is a side view of the rotor showing the arrangement of the blades in one of the rotor sections. Figure 4 is a perspective view showing the wind turbine with a static air deflector fitted. Figure 5 is a side view showing a rotor section and the air deflector. Detailed Description of the Drawings Referring to figure 1 a wind turbine 1 in accordance with the invention is shown mounted on the pitched roof 2 of a house. The turbine is able to rotate freely on its mounting to align the primary axis of the rotor at right angles to the incident wind which in this case would be blowing directly towards the pitched face of the roof. Looking at the turbine in more detail in figure 2 it can be seen that it is equipped with a symmetrical pair of rotors 3 and 4 each comprising a pair of Savonius vane sections 3a & 3b and 4a & 4b which are set at 90[deg] to each other on the horizontal rotor axis AA. These two rotors 3 and 4 are attached to the heat generator 8, via drive shafts projecting along the horizontal rotor axis AA, such that they can rotate under the influence of the incident wind driving said heat generator which heats water provided to the assembly via a pipe attached to the inlet manifold 4 and discharges this to a pipe attached to outlet manifold 5. The rotor assembly comprising the rotors 3 and 4 and the heat generator 8 are mounted on a spigot 10 which can be driven by a motor 9 so as to rotate the whole assembly through 360[deg] around the vertical axis BB. The drive assembly is suitably equipped to supply a positional feedback signal to a control system, located either on the wind turbine or elsewhere, which adjusts the direction of the rotor assembly to take account of the incident wind direction as determined by the wind direction sensor 5. Referring to figure 3 which shows a side view of rotor section 4a mounted on the heat generator 8 the shape and overlapping arrangement of vanes 4c and 4d can clearly be seen. The incident wind blowing left to right as shown generates the maximum torque on the drive shaft in this configuration. Referring to figure 4 a static wind deflector 11 has been added to the turbine which shelters the lower vane from the incident wind as it moves in the opposite direction to said wind thereby reducing the retarding forces due to drag of the rotor as a whole. This can be seen more clearly in figure 5 where the incident wind is represented by the three arrows running from left to right on the left side of the diagram.

Claims

1. A wind turbine mounted on a building roof structure equipped with an energy conversion device capable of producing either heat or electrical energy from the mechanical energy extracted from wind incident on the structure.

2. A wind turbine as described in claim 1 with a central assembly that can be rotated about a vertical axis through 360[deg] equipped with two input spigots to the energy conversion device drive train arranged at 180[deg] to each other, but with coincident horizontal axes of rotation so that two aerodynamically equivalent rotors can be attached.

3. A wind turbine as described in claim 2 whose rotors are equipped with vanes in an annular disposition about the horizontal axis of rotation suitably formed and arranged so that wind, blowing in a direction that is not parallel to the axis of rotation, incident upon the rotors generates a turning force about said horizontal axis of rotation.

4. A wind turbine as described in claim 3 equipped with a means of rotating the rotor assembly about a vertical axis and holding it at an orientation such that the horizontal axis of rotation lies at any angle to the instantaneous wind direction.

5. A wind turbine as described in claim 4 where the means of orientating the rotor is driven by a motor, controlled by an electronic control device equipped with sensors capable of determining the angular position of the rotor assembly, angular rotor speed and wind direction, such that the rotor assembly can be positioned and held so that the horizontal axis lies at an angle between 60[deg] and

120. to the instantaneous wind direction when in operation and at any angle when not.

6. A wind turbine as described in any of the previous claims where the rotors contain one or more aerodynamic sections that induce rotation primarily by differential aerodynamic drag between elements on opposite sides of the axis of rotation.

7. A wind turbine as described in any of the previous claims where the rotors contain one or more aerodynamic sections containing blades that induce rotation due to the net sum aerodynamic lift generated by the flow of air over the blades.

8. A wind turbine as described in claim 6 where features capable of deflecting the incident wind away from areas within the structure where aerodynamic features move towards the incident wind, without hindering the flow of air to those areas where aerodynamic features move away from the incident wind, are provided in a fixed spatial relationship to the rotor and maintain this relationship regardless of the orientation of the rotor assembly on the vertical axis.

9. A wind turbine as described in any of the previous claims where the rotors are made partially or completely from a transparent material.

10. A wind turbine as described in any of the previous claims where the colours of components of said turbine are so selected as to make it difficult to differentiate the turbine from the structures surrounding it.