FIELD OF THE INVENTION

The present invention relates to improvements in or relating to a system for generating electricity and, more specifically, to a system for optimising the energy converted by a turbine, such as a vertical axis wind turbine.

BACKGROUND TO THE INVENTION

Turbines are well known for their ability to convert kinetic energy from a fluid flow into electrical energy. Typically, in order to maximise the energy output of a turbine, its overall size is increased and/or the turbine is positioned in a location having a greater mean fluid flow speed. However, these strategies are inappropriate for turbines that are limited in overall size, fixed in location and/or subjected to inconsistent fluid flow speeds. It is therefore desirable to maximise the energy output of a turbine without having to increase its size and/or move its location. Moreover, turbines can be very costly. Therefore, it is also desirable to maximise the energy output of a turbine without significantly increasing the cost of the system.

The aforementioned principles apply to all forms of turbines, including water, steam and gas turbines, and, in particular, to specific forms of wind turbines, such as horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs).

It is against this background that the present invention has arisen.

SUMMARY OF THE INVENTION

According to the present invention there is provided a system for generating electricity, the system comprising: a turbine having at least one blade coupled to a rotatable shaft, wherein the at least one blade is configured to convert kinetic energy received from a fluid flow into rotational energy within the shaft; a variable-speed generator coupled to the rotatable shaft and configured to transform rotational energy received from the shaft into electrical energy; and a control unit configured to: continuously predict the speed of the fluid flow based on the rotational speed of the turbine and the amount of electrical energy being generated by the generator; and regulate the amount of electrical energy generated by the generator such that the rotational speed of the turbine is maintained within a predetermined range that is based on the predicted speed of the fluid flow. Conversely, in some embodiments, the control unit may regulate the rotational speed of the turbine such that the amount of electrical energy generated by the generator is maintained within a predetermined range based on the predicted speed of the fluid flow.

Of course, velocity comprises a component of speed, and thus measuring, calculating, determining and/or regulating velocity (rather than measuring, calculating, determining and/or regulating speed directly) also falls within the scope of the present invention.

The speed of the fluid flow acting upon a turbine determines the optimal rotational speed required to maximise power generation. Therefore, regulating the amount of electrical energy produced by the generator such that the rotational speed of the turbine is maintained within a predetermined range enables the system to generate the maximum amount of power at any given time.

However, directly measuring the speed of a fluid flow, such as air, requires costly equipment. Conversely, predicting the speed based on the rotational speed of the turbine and the amount of electrical energy being generated by the generator provides a more cost effective alternative. The present invention therefore provides a very efficient and low cost system that maximises the power generated from a given speed of fluid flow.

The control unit may control the rotational speed of the turbine and/or the amount of electrical energy being generated by the generator. More specifically, the control unit may control the current being produced by the variable-speed generator. The control unit may further comprise a memory. The memory may comprise a lookup table. The lookup table may comprise a plurality of data points showing the relationship between the speed of the fluid flow, rotational speed of the turbine and the amount of electrical energy being generated by the generator. These data points may be used to predict the speed of the fluid flow based on the rotational speed of the turbine and the amount of electrical energy being generated by the generator. Alternatively, or in addition, these data points may be used to determine the current to be drawn by the generator, thus the amount of power produced by the system.

The generator may comprise a sensor. The sensor may be configured to determine the rotational speed of the turbine. The sensor may be in electronic communication with the control unit. As such, the control unit may monitor the rotational speed of the turbine via the sensor. The sensor may be a hall-effect sensor. However, any suitable form of sensor may be used.

The turbine may be a wind, water, steam or gas turbine. In particular, the turbine may be a horizontal axis wind turbine (HAWT) or a vertical axis wind turbine (VAWT). However, any turbine may be used. The fluid may be a liquid or a gas. In particular, the fluid may be air, water or steam. However, the fluid may be any other form of liquid, gas or combination thereof.

As such, according to the present invention, there is provided a system for generating electricity, the system comprising: a vertical axis wind turbine having at least one blade coupled to a rotatable shaft, wherein the at least one blade is configured to convert kinetic energy received from an airflow into rotational energy within the shaft; a variable-speed generator coupled to the rotatable shaft and configured to transform rotational energy received from the shaft into electrical energy; and a control unit configured to: continuously predict the airflow speed based on the rotational speed of the vertical axis wind turbine and the amount of electrical energy being generated by the generator; and regulate the amount of electrical energy generated by the generator such that the rotational speed of the vertical axis wind turbine is maintained within a predetermined range that is based on the predicted airflow speed.

For example, for a given vertical axis wind turbine design, if the airflow speed is approximately 15 meters per second (m/s), the optimal rotational speed of the vertical axis wind turbine may be between 250 and 400 revolutions per minute (RPM), more preferably between 300 and 350 RPM, and most preferably between 315 and 330 RPM. An airflow speed of approximately 15 meters per second (m/s) and a rotational speed of between 315 and 330 RPM may generate a power output of 520 to 530 Watts (W). However, for the same airflow speed of approximately 15 meters per second (m/s), but an increased rotational speed of approximately 400 RPM, the power output may reduce to approximately 500 Watts (W). As such, the control unit may regulate the amount of electrical energy generated by the generator to 520 to 530 Watts (W) such that the rotational speed of the vertical axis wind turbine is maintained between 315 and 330 RPM.

Conversely, in some embodiments, the control unit may regulate the rotational speed of the vertical axis wind turbine to between 315 and 330 RPM such that the amount of electrical energy generated by the generator is maintained between 520 to 530 Watts (W).

The generator may be able to operate between near zero wattage output, a preferred operating window of 520 to 530 W, a higher value of 800W or even up to 2kW. The optimum operating window is selected by the control system with reference to all of the relevant parameters of the operating environment.

Similarly, for the same vertical axis wind turbine design, if the airflow speed is approximately 5 meters per second (m/s), the optimal rotational speed of the vertical axis wind turbine may be between 40 and 175 revolutions per minute (RPM), more preferably between 75 and 150 RPM, and most preferably between 100 and 125 RPM. An airflow speed of approximately 5 meters per second (m/s) and a rotational speed of between 100 and 125 RPM may generate a power output of 10 to 30 Watts (W). As such, the control unit may regulate the amount of electrical energy generated by the generator to 10 to 30 Watts (W) such that the rotational speed of the vertical axis wind turbine is maintained between 100 and 125 RPM.

Again, in some embodiments, the control unit may instead regulate the rotational speed of the vertical axis wind turbine to between 100 and 125 RPM such that the amount of electrical energy generated by the generator is maintained between 10 to 30 Watts (W).

However, the aforementioned principles apply to any form of turbine and/or any form of fluid.

The electrical energy generated by the generator may produce a current. The generated energy may be stored in a battery. Alternatively, or in addition, the electrical energy produced by the generator may be exported to an external network, such as a national, micro or island electricity grid.

The control unit may regulate the amount of electrical energy being generated by the generator by adjusting the current being draw by the generator. Alternatively, or in addition, the control unit may regulate the rotational speed of the turbine directly.

The airflow may be wind. Alternatively, or in addition, the airflow may be gusts of air movement. The gust of air movement may be generated by a body, such as a vehicle, for example. The vehicle may be a bike, car, van, lorry, bus, train, tram, boat, submarine, or aeroplane. However, any body capable of generating fluid movement would be suitable.

In some embodiments, the turbine may be a vertical axis wind turbine and the fluid may be air. The at least one blade coupled to the rotatable shaft may consist of two blades coupled to the rotatable shaft. In other words, the vertical axis wind turbine may comprise no more than two blades coupled to the rotatable shaft. Put another way, the vertical axis wind turbine may consist of two blades coupled to the rotatable shaft. It is a popular misconception that the more blades provided on a vertical axis wind turbine the better the system can harvest the kinetic energy of an airflow. However, two blades perform better than three or more blades in certain scenarios. For example, a vertical axis wind turbines having two blades generates more consistent power than a vertical axis wind turbine having three blades when the vertical axis wind turbine is located in the central reservation or a side verge of a road, for example. This is due to the additional gusts caused by passing traffic on each side of the turbine. In addition, a vertical axis wind turbine consisting of two blades (i.e. having no more than two blades) also provides the most optimal power to drag ratio. Accordingly, two blades may maximise the power output from a vertical axis wind turbine having other fixed parameters. However, any number of blades may be used. For example, the vertical axis wind turbine may comprise one, two, three, four, five, or more than five blades. As such, the vertical axis wind turbine may comprise a plurality of blades.

Each blade may be substantially half-cylindrical or half-elliptical in cross-section. Accordingly, the cross-section of each blade may be substantially C-shaped or curved. This may increase the rotational force generated in the shaft for a given airflow. Moreover, providing two blades each having a substantially half-cylindrical or half-elliptical cross-section enables a substantially S-shaped cross-section across the vertical axis wind turbine as a whole.

Each blade may be solid (i.e. not having any holes). More specifically, in some embodiments, the vertical axis wind turbine may be a Savonius vertical axis wind turbine. This enables the wind turbine to 'self-start' in the presence of an airflow. Accordingly, the wind turbine does not require a motor and/or control gear in order to begin rotation.

The cross-section of each blade may be a portion of an ellipse having a major axis that is offset from the sectional centreline of the vertical axis wind turbine. More specifically, the major axis of the elliptical cross section may be offset from the sectional centreline by between 100mm and 300mm, 200mm and 250mm, or 210mm and 230mm.

Alternatively, or in addition, the cross-section of each blade may be a portion of an ellipse having a major axis that is angled relative to the sectional centreline of the vertical axis wind turbine. The angle of the major axis of the ellipse relative to the sectional centreline may be between 30 degrees and 70 degrees, 40 degrees and 60 degrees, or 45 degrees and 55 degrees.

The elliptical cross-section of each blade may touch the outer diameter of the vertical axis wind turbine profile at a tangent before returning inboard with the trailing edge. Therefore, the tip of each blade may be angled relative to the sectional centreline of the vertical axis wind turbine. The angle may be between 30 degrees and 50 degrees, 35 degree and 45 degrees, or, more specifically, by 38 degrees to 41 degrees.

Each blade may comprise an airflow capture surface configured to receive kinetic energy from an airflow. Each blade may also comprise a non-airflow capture surface opposing the airflow capture surface. The airflow capture surface is the surface of the blade configured to receive the airflow. In a C-shaped blade profile, the airflow capture surface would be the inside surface of the 'C' shape. In other words, the airflow capture surface may be shorter in length than the non-airflow capture surface. The airflow capture surface of each blade may blend into the non-airflow capture surface of the adjoining blade across the sectional centreline of the vertical axis wind turbine. The blend radius may be between 250mm and 750, 400mm and 600mm, or approximately 500mm. The blend radius allows an airflow to be captured, using the Coanda effect, by the non-airflow capture surface with minimum drag. This captured airflow is then able to spill into the in the airflow capture surface of the adjoining blade as the vertical axis wind turbine rotates. The remainder of the airflow that contacts the non-airflow capture surface is allowed to spill off the tip of the blade and is lost. Nevertheless, the shape of the non-airflow capture surface of each blade allows this spillage to occur efficiently with minimum vortices and minimising negative pressure on the airflow capture surface of the adjoining blade.

Each blade may comprise an upper end and a lower end that are rotationally offset from each other about a longitudinal axis of the rotatable shaft such that each blade has a helical form. The lower end of the blade may be located nearer to the ground than the upper end, in use. Blades having a helical form result in a more consistent power output from a given airflow, thus increasing the total amount of electricity than can be produced from the airflow.

The upper end and lower end of each blade may be rotationally offset from each other by approximately 150-210 degrees. More preferably, the upper end and lower end of each blade may be rotationally offset from each by approximately 180 degrees. This again results in a more consistent power output for a given airflow, thus increasing the total amount of electricity that can be produced from the airflow. More specifically, a vertical axis wind turbine comprising no more than two blades each having an upper and lower end that are rotationally offset by 180 degrees results in a smooth power curve and minimises the pulsing effect of an inconsistent airflow.

The upper end and lower end of each blade may be rotationally offset from each other such that the airflow capture surface of each blade comprises a negative rake angle in the direction of rotation. A blade having a negative rake angle may result in the vertical axis wind turbine having a forward swept twist in its overall shape. In other words, each blade may lean into the airflow, in use. Accordingly, as the vertical axis wind turbine rotates, the lower end of each blade may receive a linear airflow before the upper end of the blade. It has been found that a blade having negative rake angle generates more energy from a given airflow as the vertical axis wind turbine is able to 'collect' more energy from the airflow. In additional, a negative rake angle avoids aerodynamic spillage occurring off the edge of the blade during rotation. The ratio of the height of each blade to the diameter of the vertical axis wind turbine may be between 1:1 and 7.5:1. For example, the overall height of each blade may be from 1 meter to 3 meters, 1.5 meters to 2.5 meters, or 1.9 meters to 2.3 meters. Most preferably, the overall height of each blade may be 2.1 meters. The overall diameter of the vertical axis wind turbine may be from 0.4 meters to 0.9 meters, 0.5 meters to 0.8 meters or 0.6 meters to 0.7 meters. Most preferably, the overall diameter may be 0.65 meters. Therefore, the optimal ratio of the height of each blade to the diameter of the vertical axis wind turbine may be between 2.5:1 and 4:1 or, more preferably, between 3:1 and 3.5:1.

In other words, the vertical axis wind turbine may comprise an aspects ratio between 2.5 and 4 or, more preferably, between 3 and 3.5 or, most preferably, between 3.2 and 3.25. The optimal aspect ratio may be 3.23. For a constant diameter, a higher aspect ratio represents a turbine with a smoother operation that therefore provides more efficient operation.

However, the overall size of the system is scalable. Therefore, any height of blade may be used. In some embodiments, the system further comprises a mounting pole. The mounting pole may be configured to raise the blades away from the ground. Therefore, the overall height of the system may be greater than 1 to 3 meters.

The vertical axis wind turbine may comprise a single component consisting of two blades and a central void configured to receive the rotatable shaft. The rotatable shaft may be less than 100 millimetres (mm) in diameter. More preferably, the rotatable shaft may be less than 70 mm in diameter. Incorporating the rotatable shaft into a void of a single component consisting of the two blades reduces the aerodynamic impact of the rotatable shaft and its coupling to the blades, thus maximising the power output for a given airflow. Conversely, an external rotatable shaft that disrupts the aerodynamic profile of the single component reduces the airflow efficiency into the airflow capture surface of each blade, thus reducing the power output of the system.

The rotational speed of the turbine may be selected to avoid coinciding with the harmonic frequency response of the turbine. The harmonic frequency response of the turbine has various contributing factors including, but not limited to, the length of axial centreline of the turbine and the mass in motion. The harmonic frequency response may include a number of harmonics. It may be preferable to avoid operating at or near to the fundamental frequency or the third or fifth harmonics.

The vertical axis wind turbine may be located less than 1 meter away from a roadway or railway.

More specifically, the vertical axis wind turbine may be located between, and less than 1 meter away from, two roadways, or railways having opposing directions of travel. Most specifically, the vertical axis wind turbine may be located as close to the roadway or railway as technical and safety standards of the associated authority permit. Doing so may increase the amount of kinetic energy receive by the turbine as a result of a 'push' force followed by a 'pull' force being received by the vertical axis wind turbine as traffic passes by.

According to the present invention, there is also provided a network comprising a plurality of the previously described systems. For example, the network may comprise a plurality of systems each comprising: a turbine having at least one blade coupled to a rotatable shaft, wherein the at least one blade is configured to convert kinetic energy received from a fluid flow into rotational energy within the shaft; a variable-speed generator coupled to the rotatable shaft and configured to transform rotational energy received from the shaft into electrical energy; and a control unit configured to: continuously predict the speed of the fluid flow based on the rotational speed of the turbine and the amount of electrical energy being generated by the generator; and regulate the amount of electrical energy generated by the generator such that the rotational speed of the turbine is maintained within a predetermined range that is based on the predicted speed of the fluid flow.

Again, in some embodiments, the control unit may regulate the rotational speed of the turbine such that the amount of electrical energy generated by the generator is maintained within a predetermined range that is based on the predicted speed of the fluid flow.

A network comprising a plurality of turbines increases the overall amount of energy that can be generated. In some embodiments, at least two systems may be stacked on top of each other. This increases the amount of energy that can be generated for a given area.

Each control unit may be configured to predict a future speed of the fluid flow to be received by the turbine of another system based on the predicted speed of the fluid flow at the current system. In addition, each system may further comprise a communication unit configured to send the predicted future speed of the fluid flow to the communication unit of the other system.

Alternatively, or in addition, each control unit may be configured to receive a predicted future speed of the fluid flow, and adjust the amount of electrical energy generated by the generator based on the predicted speed of the fluid flow at the current system and the predicted future speed of the fluid flow at the current system.

The turbine of the other system may be downstream and/or adjacent to the turbine of the current system. Therefore, the current system may be able to prepare for an upcoming increased speed of the fluid flow, such as a gust of wind. For example, the gust may be generated by a vehicle moving past the other system and travelling in the direction of the current system. The current system may therefore increase the rotational speed of the turbine in preparation for the gust, thus increasing the total power output over a given time period. This may be achieved by placing the turbine in an 'open-circuit mode'. For example, the control unit may reduce the current being drawn by the generator. In particular, the control unit may set the current being drawn by the generator to 0 Amps (A). As such, the turbine will rotate at an increased number of revolutions per minute (RPM), thus storing additional kinetic energy within the system. The turbine may then receive the fluid flow having an increased speed (i.e. the gust), which may further increase the kinetic energy within the system. The amount of kinetic energy received from the gust may be enhanced as a result of the pre-sped up turbine speed. As soon as the amount of kinetic energy within the system begins to reduce, the control unit may set the current being drawn by the generator to optimise the power produced by the turbine.

The kinetic energy within the system may begin to reduce as the rotational speed of the turbine begins to decrease. This may occur once the body causing the increased fluid flow speed has passed by the turbine. The rotational speed of the turbine, hence the kinetic energy within the system, may be measured by the sensor in the generator. As previously disclosed, the sensor may be a hall-effect sensor.

More specifically, each control unit may be configured to receive a predicted future speed of the fluid flow from a plurality of other systems, and adjust the amount of electrical energy generated by the generator based on the predicted speed of the fluid flow at the current system and the average predicted future speed of the fluid flow at the current system. The plurality of other systems may be at least two other systems. More preferably, the plurality of other systems may be at least 6 other systems. However, any number of other systems may send a predicted future speed of the fluid flow. For example, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more than 10 other systems may send a predicted future speed of the fluid flow. In some embodiments, more than 20, 50, 100 or more than 200 other systems may send a predicted future speed of the fluid flow.

Receiving a predicted future speed of the fluid flow at the current system from a plurality of other systems enables the current system to monitor the progression of an increased fluid flow speed, such as a gust or a wave, towards the current system. For example, the future speed of the fluid flow at the current system and the time at which the predicted future fluid flow will be received by the current system can be more accurately predicted by the control unit. In addition, the control unit may calculate the difference between the predicted speed of the fluid flow at the current system and the average predicted future speed of the fluid flow at the current system. The difference may be compared to a threshold. If the threshold is exceeded, the turbine may be placed into the 'open-circuit mode', as previously described, and the additional kinetic energy may be harvested.

In some embodiments, in addition, or alternatively, to the 'open-circuit mode', the turbine may modify the pitch of each of its blade to (further) increase the number of revolutions per minute (RPM) of the turbine, thus storing (more) additional kinetic energy within the system.

In particular, there is provided a network comprising a plurality of systems each comprising: a vertical axis wind turbine having at least one blade coupled to a rotatable shaft, wherein the at least one blade is configured to convert kinetic energy received from an airflow into rotational energy within the shaft; a variable-speed generator coupled to the rotatable shaft and configured to transform rotational energy received from the shaft into electrical energy; and a control unit configured to: continuously predict the airflow speed based on the rotational speed of the vertical axis wind turbine and the amount of electrical energy being generated by the generator; and regulate the amount of electrical energy generated by the generator such that the rotational speed of the vertical axis wind turbine is maintained within a predetermined range that is based on the predicted airflow speed.

According to the present invention, there is also provided a method for generating electricity using the network as previously described. In particular, the method may comprise receiving a fluid flow at a first system; predicting, using the control unit of the first system, the speed of the fluid flow at the first system based on the rotational speed of the turbine of the first system and the amount of electrical energy being generated by the generator of the first system; predicting, using the control unit of the first system, a future speed of the fluid flow to be received by the turbine of a second system based on the predicted speed of the fluid flow at the first system; sending, via the communication unit of the first system, the predicted future speed of the fluid flow to be received by the second system to the communication unit of the second system; receiving, via the communication unit of the second system, the predicted future speed of the fluid flow at the second system; and adjusting the amount of electrical energy generated by the generator of the second system based, at least in part, on the predicted future speed of the fluid flow at the second system. Predicting, using the control unit of the first system, a future speed of the fluid flow to be received by the turbine of a second system may also be based on the distance between the first and second system.

The method may further comprise simultaneously receiving a fluid flow at the second system; predicting, using the control unit of the second system, the speed of the fluid flow at the second system based on the rotational speed of the turbine of the second system and the amount of electrical energy being generated by the generator of the second system; and adjusting the amount of electrical energy generated by the generator of the second system based, at least in part, on the predicted speed of the fluid flow at the second system and the predicted future speed of the fluid flow at the second system.

Adjusting the amount of electrical energy generated by the generator of the second system based, at least in part, on the predicted speed of the fluid flow at the second system and the predicted future speed of the fluid flow at the second system may take precedent over regulating the amount of electrical energy generated by the generator of the second system such that the rotational speed of the turbine of the second system is maintained within a predetermined range that is based on the predicted speed of the fluid flow at the second system. In other words, the regulated amount of electrical energy generated may be further adjusted in preparation for an upcoming fluid flow.

The amount of electrical energy generated by the generator of the second system may be adjusted only if the difference between the predicted speed of the fluid flow at the second system and the predicted future speed of the fluid flow at the second system exceeds a predetermined threshold. The threshold may be at least a 5% increase in speed. Alternatively, the threshold may be at least a 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% increase in speed.

Adjusting the amount of electrical energy generated by the generator of the second system may comprise reducing the current being drawn by the generator of the second system. For example, the current being drawn may be decreased by at least 5%. Alternatively, the current being drawn may be decreased by at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100%.

The method may further comprise monitoring the rotational speed of the turbine of the second system, and increasing the amount of electrical energy being generated by the generator of the second system as soon as the rotational speed of the turbine of the second system decreases. The rotational speed of the turbine may be monitored using the sensor in the generator. The control unit may be responsible for increasing and/or decreasing the current being drawn, thus the amount of electrical energy being generated, by the generator. The current being drawn by the generator of the second system may be reduced to 0 Amps when the difference between the predicted speed of the fluid flow at the second system and the predicted future speed of the fluid flow at the second system exceeds the predetermined threshold. More specifically, the current may be reduced to 0 Amps. Subsequently, the current being drawn by the generator of the second system may be increased such that the turbine produces the most optimal power output for the predicted speed of the airflow as soon as the rotational speed of the turbine of the second system decreases. The current drawn to produce the most optimal power output may be determined using the aforementioned lookup tables.

The invention will now be further and more particularly described, by way of example only, with reference to the accompanying drawings.

FIGURES

Figure 1 shows a system for generating electricity according to the present invention;

Figure 2 shows a vertical axis wind turbine for use in the system of figure 1;

Figure 3 shows a cross section of the vertical axis wind turbine shown in figure 2;

Figure 4 shows a graph of the power (W) generate by the generator of the vertical axis wind turbine shown in figures 1-3 for different rotational speeds (RPM) and at two different airflow speeds (ms' ¹ );

Figure 4 also shows the power (W) generated by a plurality of systems having different vertical axis wind turbine blade geometries at an airflow speed of 15 ms’ ¹ ;

Figure 5 shows the turning moment (Nm) generated by a plurality of vertical axis wind turbines having different geometries when subjected to a wind speed of 5 ms' ¹ and allowed to rotate at 160 RPM.

DETAILED DESCRIPTION

Figure 1 shows a system 10 for generating electricity according to the present invention. The system 10 comprises a vertical axis wind turbine 100, a variable-speed generator 150, and a control unit 170. However, as previously mentioned, the system 10 may comprise any form of turbine. The variable-speed generator 150 is coupled to the vertical axis wind turbine 100 via a rotatable shaft 130. The variable-speed generator 150 is configured to transform rotational energy received from the shaft 130 into electrical energy.

The control unit 170 is configured to continuously predict the airflow speed based on the rotational speed of the vertical axis wind turbine 100 and the amount of electrical energy being generated by the generator 150. The control unit 170 predicts the airflow speed using a look-up table stored within a memory. The look up table comprises the relationship between rotational speed of the vertical axis wind turbine 100 and power output of the variable-speed generator 150 for a plurality of airflow speeds. The memory is firmware located within the control unit 170.

Figure 4 shows a graph plotted using data from a look-up table of the present invention. In particular, figure 4 shows a graph of power (w), rotational speed (RPM) and wind speed (m/s) for vertical axis wind turbines having different blade profiles.

The control unit 170 is also configured to regulate the amount of electrical energy generated by the generator 150 such that the rotational speed of the vertical axis wind turbine 100 is maintained within a predetermined range that is based on the predicted airflow speed.

There is also provided a network comprising a plurality of systems 10. Therefore, in some embodiments, the control unit 170 is further configured to predict a future airflow speed to be received by a vertical axis wind turbine of another system based on the predicted airflow speed at the current system. In such embodiments, the control unit 170 stored the location of and/or distance to at least one vertical axis wind turbine of another system. In addition, the system 10 further comprises a communication unit 190 configured to send the predicted future airflow speed to a communication unit of another system.

Moreover, the control unit 170 is further configured to receive a predicted future airflow speed and adjust the amount of electrical energy generated by the generator 150 based on the predicted airflow speed at the current system and the predicted future airflow speed at the current system.

Figure 2 shows a vertical axis wind turbine 100 for use in the system of figure 1. The vertical axis wind turbine 100 comprises two blades 110, 120 coupled to a rotatable shaft 130. Each blade 110, 120 is configured to convert kinetic energy received from an airflow into rotational energy within the shaft 130. More specifically, each blade 110, 120 comprises an airflow capture surface 115, 125 configured to receive kinetic energy from an airflow. Each blade also comprises a non-airflow capture 116, 126 surface opposing the corresponding airflow capture surface 115, 125. The airflow capture surface 115, 125 and non-airflow capture surface 116, 126 of each blade meet at a tip 111, 121, respectively.

Each blade 110, 120 comprises an upper end 112, 122 and a lower end 114, 124, respectively. The upper end 112, 122 of each blade 110, 120 is rotationally offset from the lower end 114, 124 of each blade about a longitudinal axis X of the rotatable shaft 130. More specifically, the upper end 112, 122 of each blade 110, 120 is rotationally offset from the lower end 114, 124 of each blade by approximately 180 degrees. Therefore, as shown in figure 2, each blade 110, 120 has a helical form.

Moreover, the upper end 112, 122 of each blade 110, 120 is rotationally offset from the lower end 114, 124 of each blade 110, 120 such that the airflow capture surface 115, 125 of each blade 110, 120 comprises a negative rake angle in the direction of rotation. In other words, the vertical axis wind turbine 100 comprises a forward swept twist in its overall shape as each blade 110, 120 leans into the airflow, in use.

The overall height, H, of each blade 110, 120 is approximately 2.1 meters and the overall diameter, D, of the vertical axis wind turbine 100 is approximately 0.65 meters. Therefore, the aspect ratio, H:D, is approximately 3.23.

Figure 3 shows a cross section of the vertical axis wind turbine 100 shown in figure 2. In particular, the vertical axis wind turbine 100 comprises a single component 105 consisting of the two blades 110, 120 and a central void 135 configured to receive the rotatable shaft 130. The central void runs along an axial centreline of the turbine 100.

Each blade 110, 120 is substantially half-elliptical in cross-section. More specifically, the crosssection of each blade 110, 120 is a portion of an ellipse having a major axis, EMA, which is offset from the sectional centreline, CR, of the vertical axis wind turbine 100. In particular, the offset is approximately 220mm. In addition, the major axis of the ellipse, EMA, is angled relative to the sectional centreline of the vertical axis wind turbine 100. In particular, the angle is approximately 51 degrees. The elliptical cross-section of each blade touches the outer diameter, OD, of the vertical axis wind turbine profile at a tangent. As such, the tip 111, 121 of each blade 110, 120 is angled relative to the sectional centreline. In particular, the angle is approximately 39 degrees.

In addition, the airflow capture surface of the each blade 115, 125 blends into the non-airflow capture surface of the adjoining blade 116, 126 across the sectional centreline, CR, of the vertical axis wind turbine. The blend radius is convex in shape. The convex blend radius is configured to capture and airflow, using the coanda effect, with minimum drag. The captured airflow is then able to spill into the airflow capture surface of the adjoining blade, 125, 115 as the vertical axis wind turbine rotates. The remainder of the airflow that contacts the non-airflow capture surfacell6, 126 is allowed to spill off the tip 111, 121 of each blade 110, 120, respectively, and is lost. Nevertheless, the shape of the non-airflow capture surface of each blade 116, 126 allows this spillage to occur efficiently with minimum vortices whilst the minimising negative pressure on the airflow capture surface of the adjoining blade 125, 115. The blend radius is between 535mm and 550mm.

Figure 4 shows a graph of the power (W) generate by the generator 150 of the vertical axis wind turbine 100 shown in figures 1-3 for different rotational speeds (RPM) and at two different airflow speeds (ms' ¹ ). In other words, the graph shown in figure 4 plots some of the data from the look up table used by the control unit 170 to predict airflow speed based on the rotational speed of the vertical axis wind turbine 100 and the amount of electrical energy being generated by the generator 150.

Figure 4 also shows the power (W) generated by a plurality of systems having different vertical axis wind turbine blade geometries at an airflow speed of 15 ms ¹ . As shown, the substantially halfelliptical blade cross-section generates the most power. Therefore, as shown by figure 4, the substantially half-elliptical blade cross-section of the present invention is advantageous over alternative blade profiles.

Figure 5 shows the turning moment (Nm) generated by a plurality of vertical axis wind turbines having different geometries when subjected to a wind speed of 5 ms' ¹ and allowed to rotate at 160 RPM. As can be seen, a vertical axis wind turbine comprising no more than two blades generated a greater turning moment over a 0.5 second period than an equivalent vertical axis turbines having three blades. In addition, a vertical axis wind turbines comprising blades having a 180 degree twist generated a greater turning moment over a 0.5 second period than the vertical axis wind turbines comprising blades having a 0 degree twist (i.e. no twist); 45 degree twist, or 67.5 forward twist. Figure 5 also shows that the vertical axis wind turbines comprising blades having a forward twist (i.e. negative rake angle) generated a greater turning moment over a 0.5 second period than the vertical axis wind turbines comprising blades having a negative twist. Finally, figure 5 shows that a vertical axis wind turbine having a larger diameter generated a greater turning moment over a 0.5 second period than a vertical axis wind turbines having a smaller diameter.

Therefore, based on the results shown in figures 4 and 5, it can be seen that a vertical axis wind turbine consisting of two blades having a substantially half-elliptical blade cross-section and a 180 degree forward twist results in the most optimal power output. It can also be seen that each of the aforementioned parameters independently improve the power output of the system.

Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure, "and/or" where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example, "A and/or B" is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein.

Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments that are described. It will further be appreciated by those skilled in the art that although the invention has been described by way of example with reference to several embodiments, it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined in the appended claims.