GB2473736A

GB2473736A - Provision of electricity using a wind turbine and a fuel consuming generator

Info

Publication number: GB2473736A
Application number: GB1015579A
Authority: GB
Inventors: Minoo Homi Edalji Patel; Feargal Brennan
Original assignee: Cranfield University
Current assignee: Cranfield University
Priority date: 2009-09-21
Filing date: 2010-09-17
Publication date: 2011-03-23
Also published as: GB201015579D0; GB0916566D0

Abstract

Apparatus comprises an input for electrical power from a generator 55 driven by a wind turbine, an output to provide electrical power to a load, a store 71,91,110 for electrical energy received via the input, a fuel-consuming electrical generator and a controller 130 , where the controller controls the fuel consuming generator and electrically interconnects the input, the store, the fuel-consuming generator and the output such that the power available at the output is independent of variation in the power received at the input. The equipment may all be contained in one housing and have a turbine brake. Preferably, the power from the generator has a first component varying at a frequency determined by the rotation of the wind turbine and a second component varying at a lower frequency such that the controller selectively feeds the first and second components to first and second energy stores, where the first store having time constants of energy absorption/release that are shorter than those of the second store. A method of providing electrical power is also claimed.

Description

TITLE: PROVISION OF ELECTRICAL ENERGY

DESCRI PT ION

TECHNICAL FIELD

The present invention relates to apparatus, systems and methods for provision of electrical energy utilLising power from a wind turbine.

BACKGROUND ART

Energy from the wind is nowadays being routinely harvested by large groups of wind machines based on rotors that revolve around either horizontal or vertical axes. One of the biggest drawbacks of all wind energy devices is the intermittent nature of the power that they supply -their direct dependence on the wind to produce power means that they produce no power when the air is still or there is insufficient wind. As power from the wind begins to provide an increasing proportion of mankind's energy needs, there remains scepticism about whether it can truly replace conventional power stations, which can generate a continuous power output that is not dependent on weather or wind speeds. Indeed, there are claims that if wind power were to provide a large proportion of society's energy needs, conventional power stations would still be needed to cope when wind speeds are not high enough to provide sufficient power.

Alternatively / in addition, large quantities of energy from wind turbines would need to be stored for such times as there is a shortfall between generation and demand.

Pumped storage involves the pumping by means of electrically-driven pumps of large volumes of water higher up the earth's gravitational field. The discharge of this water downhill through water turbines can then recover this electrical power. Such pumped storage is used throughout the world to match electricity demand with generation through periods of peak demand.

The raising and lowering of weights is also a means for storing and recovering energy as is done in a small way within clock mechanisms. The use of weights to store electrical energy from an intermittent source such as solar, wind or hydro is described in FR2466638.

Storage of energy by means of compressed air is disclosed in DE102005043444, which describes a vertical axis wind turbine having a central tower extending between the horizontal arms of the turbine rotor. The rotor can drive both electrical generators and air compressors, the compressors being used when the electrical generators cannot use all of the available wind energy. Specifically, when the wind is too strong, the generators and compressors work simultaneously or the compressors work alone, feeding compressed air to a reservoir. then the wind is too weak, the compressed air is fed from the reservoir to air turbines which drive the generators to generate electricity. The central tower accommodates part of the reservoir for the compressed air, although the majority of the reservoir extends below the rotor bearing.

DE37Q3269 describes a vertical axis wind turbine of the Darrieus type in which a torsionally-elastic rotational energy store for levelling out torque pulsations of the turbine is at least partially located within the hollow central shaft of the turbine.

US2008/Q273974 discloses a vertical axis wind turbine, the rotor of which is connected to a direct drive permanent magnet alternator which is in turn electrically connected to a battery for electrical storage.

DISCLOSURE OF INVENTION

According to a first aspect of the present invention, there is provided apparatus for provision of electrical energy, the apparatus comprising: an input configured to receive electrical power from a generator driven by a wind turbine; an output configured to provide electrical power to a load; a store for electrical energy received via the input; a fuel-consuming electrical generator; and a controller configured to control the fuel-consuming electrical generator and to electrically interconnect the input, the store, the fuel-consuming electrical generator and the output such that the power available at the output is independent of variation in the electrical power received at the input.

Such an apparatus provides a source of constant power that is largely generated from the wind but uses the energy store as an accumulator. In the event that persistently low wind speeds deplete the available energy storage capacity, the auxiliary fuel-consuming electricity generator can provide power, i.e. the power available at the output is independent of the wind. As a result, use of renewable sources of power is increased -thereby reducing the use of fuel, without compromising the reliability of the overall power supply. Where the fuel is a carbon-based fuel, generation of carbon-dioxide is consequently reduced. Similarly, where the fuel is derived from non-renewable sources, for example a fossil fuel, depletion of such sources is slowed. Where the fuel is manufactured remotely, fuel transport costs are reduced.

The store, the fuel-consuming electrical generator and the controller may be located within a common housing.

The fuel-consuming electrical generator may comprise a generator driven by an internal combustion engine.

The controller may be configured such that a predetermined amount of power is continually available at the power output. The controller may be configured such that said predetermined amount of power is available for minimum fuel consumption by the fuel-consuming electrical generator.

The controller may be configured to monitor the electrical power received at the input and the electrical power available from the store and, in the event that the sum of these is less than the predetermined amount of power, activate the fuel-consuming electrical generator.

The controller may be configured to monitor the electrical power received at the input and the electrical power available from the store and, in the event that the electrical power received at the input is in excess of the predetermined amount of power and that the store is saturated, divert electrical power received at the input to an electrical energy sink such as a resistor bank.

The controller may be configured to monitor the electrical power received at the input and the power available from the store and, in the event that the electrical power received at the input is in excess of the predetermined amount of power and that the store is saturated, limit the electrical power received at the input.

There is also provided a system comprising a wind turbine, a generator driven thereby and an apparatus as set out above. The wind turbine may comprise an aerodynamic brake and the controller may be configured to activate said brake, thereby limiting the power input from the generator driven by the wind turbine. The wind turbine may comprise a rotor brake and the controller may be configured to activate said brake, thereby limiting the power input from the generator driven by the wind turbine.

The wind turbine may comprise a rotor and a stationary base, with at least one -and possibly all -of said store, fuel-consuming electrical generator and controller of the aforementioned apparatus being located in the base.

The wind turbine may have a rotor configured to rotate on a bearing about a vertical axis, at least one of said store, fuel-consuming electrical generator and controller being located in said base, on the vertical axis and above the bearing.

The store for energy may comprise first and second stores, the first store having time constants of energy absorption and release that are shorter than those of said second store, the controller being configured to match a first component of electrical energy varying at frequency determined by the rotation of the wind turbine to the first store and a second component of electrical energy varying at a lower frequency that the first component to the second store. The second store may have an energy density greater than that of the first store.

A store may comprise a mass moveable in the earth's

gravitational field by a reversible electric

motor/generator, thereby storing energy as potential energy. A store may comprise a flywheel driveable by a reversible electric motor/generator, thereby storing energy as kinetic energy. A store may comprise an electrical battery. In the arrangement above, the first store may comprise a battery and the second store a flywheel.

According to the first aspect of the present invention, there is also provided a method of making available a predetermined amount of electrical power at a power output, the method comprising the steps of: providing an input for electrical power from a generator driven by a wind turbine, a store for electrical power and a fuel-consuming electrical generator; and controlling the fuel-consuming electrical generator and electrically interconnecting the input, the store, the fuel-consuming electrical generator and the power output such that a predetermined amount of power is continually available at the power output.

The method may comprise the step of controlling the fuel-consuming electrical generator and electrically interconnecting the input, the store, the fuel-consuming electrical generator and the power output such that a predetermined amount of power is continually available at the power output for minimum fuel consumption by the electrical generator.

The method may comprise the steps of monitoring the power input from the generator driven by a wind turbine and the power available from the store and, in the event that these are less than the predetermined amount of power, activating the fuel-consuming electrical generator.

The method may comprise the steps of monitoring the power input from the generator driven by a wind turbine and the power available from the store and, in the event that the power from the generator driven by a wind turbine is in excess of the predetermined amount of power and that the store is saturated, limiting the power input from the generator.

The method may comprise the steps of monitoring the power input from the generator driven by a wind turbine and the power available from the store and, in the event that the input power from the generator is in excess of the predetermined amount of power and that the store is saturated, diverting power to an electrical power sink such as a resistor bank.

The second aspect of the invention is based on the recognition that a wind driven rotor generates variable levels of power that change continuously over three inherently different time scales: The first -"short term" -variability is within the rotation cycle of the rotor. For example, a vertical axis wind turbine with rotating fins generates power with a cycle of variability that has peaks and falls to zero within each rotating cycle.

The second -"medium term" -variability in output power is induced by the variable wind speed from short term gusts as the wind fluctuates up and down in its natural state. This induces power variability over a time scale that is longer than the rotation period of the wind turbine rotor.

The third -"long term" -variability is at a much longer time scale caused by the mean wind speed slowly increasing or decreasing in response to changes in the weather related to the movements of weather fronts and so on.

The present inventors have recognised that conventional apparatus for providing electrical energy from wind powered generators fails to take account of such variability.

For example, an electrical battery may be able to absorb the energy peaks that result from the "short term" power variability discussed above and discharge the absorbed energy during the associated energy nulls, thereby smoothing the energy output. Such a system having the ability to absorb energy at the relatively high frequency of the "short term" variability can also be described as having a relatively short time constant of energy absorption, while the corresponding ability to discharge energy at this relatively high frequency can be expressed as a short time constant of energy release.

Moreover, since the amount of energy to be absorbed/discharged in each energy peak is relatively small, the physical size and weight of the electrical battery can be correspondingly small.

However, the same cannot be said of the "medium term" variability, where the amount of energy to be absorbed during the energy peaks is much greater. An electrical battery typically has a relatively low energy density (i.e. the amount of energy that can be stored in per unit volume), with the consequence that a battery capable of absorbing this amount of energy would unacceptably large and heavy, not to mention expensive.

Even more unacceptable in terms of dimensions, weight and expense would be an electrical battery capable of absorbing the energy peaks of the "third" variability.

According to a second aspect of the present invention, there is provided apparatus for provision of electrical energy, the apparatus comprising: an input configured to receive electrical power from a generator driven by a wind turbine, the electrical energy having a first component varying at a frequency determined by the rotation of the wind turbine and a second component varying at a lower frequency than the first component; an output configured to provide electrical power to a load; first and second stores for electrical energy received via the input, the first store having time constants of energy absorption and release that are shorter than those of said second store; and a controller configured to selectively feed the first component of electrical energy to the first store and the second component of electrical energy to the second store.

By virtue of the controller's algorithms being configured to take account of the different characteristics of the first and second stores and to dynamically direct energy into the most suitable store, the overall absorption of energy can be maximised. The controller may also control the release of energy to the output. So, for example, a battery based first energy store, having a relatively short time constant of energy absorption, may be suitable for absorbing and releasing energy over a short time scale to even out power fluctuations within the rotor rotation cycle and due to fast acting wind gusts. The controller ensures that such higher frequency components of the electrical energy are exclusively fed, i.e. matched, to the battery. On the other hand, a flywheel as the second energy store, having a different, longer time constant of energy absorption than the first energy store, is well suited to absorbing and releasing energy at slightly longer "medium" time scales of slower acting winds gusts and longer term weather related wind speeds. Such a flywheel is driveable by a reversible electric motor/generator, thereby storing energy as kinetic energy. The controller ensures that such lower frequency components of the electrical energy are exclusively fed, i.e. matched, to the flywheel.

In addition, the second store may have an energy density greater than that of the first store. Thus, in the case of the example given above, the higher energy density of the flywheel compared to the battery allows the apparatus as a whole to be made smaller and/or lighter. However, it is noted that certain flywheels may have a short time constant and be able to absorb quite high amounts of power in very short periods of time. In such circumstances, a flywheel may be used as the first, short-term storage and a battery used as the second, slightly longer-term storage.

A rotating fly wheel is subject to friction losses and hence over long periods is prone to losing its stored energy slowly. The time taken for a store to lose a certain amount of energy can also be described as the storage time constant of that store. To reduce such energy losses, the apparatus may further comprise a third store for electrical energy having a storage time constant longer than that of the second store. The controller may be configured to match a third component of the electrical energy varying at a lower frequency than the second component to the third store.

The third store may comprise a mass moveable in the earth's gravitational field by a reversible electric motor/generator, thereby storing energy as potential energy. Such storage does not dissipate energy through friction as does a fly wheel. The capacity of each store may be configured relative to the application of the apparatus. For example, the capacity of the flywheel should be able to accommodate the peak electrical power at high wind speed provided by the wind energy device feeding the apparatus. If the constant power level that needs to be drawn off is high, then the potential energy storage mechanism -where employed -needs to be sized to be able to provide that power in periods when there is insufficient wind. If the wind speed history in the locality where the apparatus is to be installed suggests high gust speeds, then the flywheel should be sized to be able to absorb the energy generated during such gusts.

According to the second aspect there is also provided a system comprising a wind turbine, an electrical generator driven thereby and an apparatus as set out above. The wind turbine may comprise a rotor and a stationary base, at least one -and possibly all -of said first and second stores and controller being located in said base. The wind turbine may have a rotor configured to rotate on a bearing about a vertical axis, and at least one of said first and second stores and controller being located in said base, on the vertical axis and above the bearing. The rotor may have an H configuration, as known, for example, from GB1549767.

According to a third aspect of the present invention, there is provided a system for provision of electrical energy comprising: a wind turbine having a rotor configured to rotate on a bearing about a vertical axis an electrical generator driven by the rotor; and a store for electrical energy generated by the generator, the store being located on the vertical axis and above the bearing.

An electrical energy store located on the vertical axis and above the rotor bearing utilises the otherwise wasted volume within the surface of rotation swept by the rotor. This in turn results in apparatus that is more compact.

At least 50% of the capacity of the store in terms of energy may be located above the bearing. All of the capacity of the store in terms of energy may be located above the bearing.

The topmost extremity of the store may be at least as high as the topmost extremity of the rotor.

The store for energy may comprise a mass moveable in the earth's gravitational field by a reversible electric motor/generator, thereby storing electrical energy as potential energy. The store for energy may comprise a flywheel driveable by a reversible electric motor/generator, thereby storing electrical energy as kinetic energy. The store for energy may comprise an electrical battery. The rotor may have an H configuration.

As will become evident from the description that

follows, the aforementioned first, second and third aspects may be implemented together and are not mutually exclusive.

BRIEF DESCRIPTION OF DRAWINGS

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a side view of an embodiment of a power generation apparatus; Figure 2 is a detailed cut-away view of the base of the embodiment of figure 1; Figure 3 is a diagrammatic illustration of the electrical power bus of the embodiment of figure 1.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Figure 1 is a side view of an embodiment of apparatus 10 for the provision of electrical energy according to the invention and incorporating a vertical axis wind turbine 20 having a rotor 25 of the "H" type comprising a hub 30 that rotates on at least one bearing (indicated by way of example at 50 in figure 2) about a vertical axis E As shown in more detail in the cross-sectional view of figure 2, the hub 30 drives an electrical generator 55 connected thereto. Rotor 25 and generator 55 are supported by a stationary cylinder 60 by means of bearing 50, the diameter of that portion 65 of the cylinder inside the rotor and generator being reduced to facilitate the motor and generator mechanical configuration.

Various means 71,91,110 for storing electricity from the generator are mounted together in a vertical cylindrical housing 90 located on the vertical axis E and above the bearing 50. As indicated at 71, reversible motor/generators 75 powered by electrical energy from the generator raise at least one weight 70 by means of a rack 80 and pinion 85 mechanism, thereby converting the electrical energy into potential energy. To release the stored energy, the weight is allowed to fall and drive the reversible motor/generators 75 to generate electricity.

As indicated at 91, one or more flywheels 95 are driven by a reversible motor/generator 100 powered by electricity from the generator, thereby converting that electrical energy into kinetic energy. To release the stored energy, the rotating flywheel is allowed to drive the reversible motor/generator 100 to generate electricity.

Electrical energy from the generator may also be stored in a battery pack 110.

Also present in the housing 90 is a fuel-consuming electrical generator 120 comprising an electrical generator driven by a small internal combustion (IC) engine running, for example, on petrol or diesel. This generator provides electrical power in the event that no power is being generated by the turbine (typically due to lack of wind) and the various energy stores mentioned above are empty. The management of energy flows between the turbine, the energy storage mechanisms, the IC-powered generator and a power output (indicated by arrow P) is carried out by an electric controller, shown in an arbitrary location at 130.

Figure 3 is a diagrammatic depiction of the electrical power bus 140 of the apparatus 10. At input 0 the bus receives DC electrical power from the wind turbine electrical generator 55 via a motoring drive or rectifier (not shown) of the kind known, for example, from US5083039 or tJS2003/0l55773. At output P the bus supplies DC electrical power, which may subsequently be converted to a fixed frequency AC supply by means of a regen drive or inverter, again not shown but of the kind well known from the documents cited above. The load driven by power from output P is similarly not shown in the figures. The motoring drive and regen drive may be incorporated into a turbine control panel along with the controller 130 and the various energy stores 71, 91, 110 and 120.

The bus 140 is connected to the controller 130, the weight energy storage mechanism 71, the flywheel storage mechanism 91, the battery pack 110 and the IC-powered generator 120. To ensure that the DC bus voltage -and thus power output available or emerging at P -is a constant predetermined preset value, the controller 130 also manages, i.e. monitors and interconnects, the energy flow into and out of the weight energy storage mechanism 71, the flywheel storage mechanism 91, the battery pack and the IC-powered generator 120 to keep the output at P constant.

In the event of no power entering at 0 and the energy storage being depleted, controller 130 starts the generator 120 to keep the power output at P constant. At the other extreme, if the energy storage means become saturated, controller 130 will activate means to limit the power output of the wind turbine. This may involve engaging aerodynamic brakes, rotor shaft braking and/or dissipating excess power through an electrical resistor bank.

Each of the energy storage means has specific characteristics related to its mode of operation, in particular time constants of energy absorption and of energy release, as discussed above. Thus, for example, the flywheel has an inherent inertia which influences the rate at which it can absorb or release energy, the battery has specific charge and discharge characteristics, the motor/generators driving the flywheel and the weights have particular performance characteristics. The controller's algorithms are designed to take account of these characteristics, to dynamically direct energy into the most suitable absorber and to maximise the overall absorption and release of energy.

As an illustrative example, a vertical axis wind turbine with a peak power at moderately high wind speeds of 50 kW can be fitted with energy storage means of the kind described above to deliver guaranteed output power at a lower figure, say, 20 kW. When the wind turbine is generating at a rate higher than 20 kW, the excess energy is diverted to the energy storage means. When, as a result of low or nil wind speeds, the wind turbine output is less than 20 kW or zero, the energy stored is discharged to continue to provide the 20 kW output. In the event that the wind speed is insufficient and has been so for sometime such that the energy store is depleted, an electrical generator would automatically be started up to provide the 20 kW output. In this way, the apparatus can produce reliable, guaranteed power from wind by maximising the use of storage and failing that with the capability of using a generator. Moreover, with respect to the desirability of using renewable power, the proportion of the time that the fuel-consuming generator is operating -and thus the fuel consumption of the generator -is kept to a minimum.

It goes without saying that the apparatus only provides energy output independent of variation in the input of electrical energy from said wind turbine for periods when the stores contain sufficient energy and/or the fuel-consuming generators have sufficient fuel.

Whilst the above example relates to a peak power of 20kw, a range of peak power from as low as 5 kW through to an approximate maximum of 500 kW is possible.

Whilst in the above example all the energy storage is housed above the bearing in the upper cylinder 90, it is also possible to distribute the storage between the upper cylinder 90 and the stationary cylinder 60.

However, at least 50% of the capacity of the store in terms of energy may remain above the bearing.

In one alternative embodiment, not shown, the storage, fuel-consuming electrical generator and controller are all located in said stationary base cylinder 60.

In another alternative embodiment, not shown, the storage, fuel-consuming electrical generator and controller are all located in a separate housing adjacent the base of the turbine. In a particularly preferred embodiment, not shown, the separate housing contains a flywheel and battery pack for storage and an internal-combustion engine powered generator.

It should be understood that this invention has been described by way of examples only and that a wide variety of modifications can be made without departing from the scope of the invention.

Aspects of the invention are applicable to configurations of wind turbine other than the vertical axis H-rotor described in the example, for example Savonius, Darrieus (straight and curved blades), giro-mill and cyclo-turbine vertical axis rotors, rotors with multiple arms around their vertical axis, rotors having additional blades mounted on the arms, and horizontal axis rotor designs. Such rotors could be supported on a rail-type bearing rather than a conventional annular bearing.

It is also applicable to forms of energy storage other than those explicitly mentioned above. For example, the apparatus could be -intermittently -connected to the battery of an electric vehicle via a vehicle charging station. Such a battery could serve as a reserve of last resort, once all the other energy stores had been emptied.

The vehicle battery could also absorb excess energy from a wind turbine that might otherwise simply be dissipated through a bank of resistors.

Claims

CLAIMS1. Apparatus for provision of electrical energy, the apparatus comprising: an input configured to receive electrical power from a generator driven by a wind turbine; an output configured to provide electrical power to a load; a store for electrical energy received via the input; a fuel-consuming electrical generator; and a controller configured to control the fuel-consuming electrical generator and to electrically interconnect the input, the store, the fuel-consuming electrical generator and the output such that the power available at the output is independent of variation in the electrical power received at the input.
2. Apparatus according to claim 1, wherein the store, the fuel-consuming electrical generator and the controller are located within a common housing.
3. Apparatus according to claim 1 or claim 2, wherein the fuel-consuming electrical generator comprises a generator driven by an internal combustion engine.
4. Apparatus according to any preceding claim, wherein the controller is configured such that a predetermined amount of power is continually available at the power output.
5. Apparatus according to claim 4, wherein the controller is configured such that a predetermined amount of power is continually available at the power output for minimum fuel consumption by the fuel-consuming electrical generator.
6. Apparatus according to claim 4 or claim 5, wherein the controller is configured to monitor the input of electrical power received at the input and the electrical power available from the store and, in the event that the sum of these is less than the predetermined amount of power, activate the fuel-consuming electrical generator.
7. Apparatus according to any preceding claim, wherein the controller is configured to monitor the electrical power received at the input and the electrical power available from the store and, in the event that the electrical power received at the input is in excess of the predetermined amount of power and that the store is saturated, divert input power to an electrical energy sink.
8. Apparatus according to any preceding claim, wherein the controller is configured to monitor the electrical power received at the input and the power available from the store and, in the event that the electrical power received at the input is in excess of the predetermined amount of power and that the store is saturated, limit the power input.
9. Apparatus according to any preceding claim, wherein the store for energy comprises first and second stores, the first store having time constants of energy absorption and release that are shorter than those of said second store.
10. Apparatus according to claim 9, wherein the controller is configured to selectively feed a first component of electrical energy varying at frequency determined by the rotation of the wind turbine to the first store and a second component of electrical energy varying at a lower frequency that the first component to the second store.
11. Apparatus according to any preceding claim, wherein a store for energy comprises a mass moveable in the earth'sgravitational field by a reversible electricmotor/generator, thereby storing energy as potential energy
12. Apparatus according to any preceding claim, wherein a store for energy comprises a flywheel driveable by a reversible electric motor/generator, thereby storing energy as kinetic energy.
13. Apparatus according to any preceding claim, wherein a store for energy comprises an electrical battery.
14. System comprising a wind turbine, a generator driven thereby and apparatus according to any preceding claim.
15. System according to claim 14 wherein the wind turbine comprises an aerodynamic brake and the controller is configured to activate said brake to limit the power input from the generator driven by the wind turbine.
16. System according to claim 14 or claim 15, wherein the wind turbine comprises a rotor brake and the controller is configured to activate said brake to limit the power input from the generator driven by the wind turbine.
17. System according to any one of claims 14 to 16, wherein the wind turbine comprises a rotor and a stationary base, at least one of said store, fuel-consuming electrical generator and controller being located in said base.
18. System according to claim 17, wherein said store, fuel-consuming electrical generator and controller are located in said base.
19. System according to claim 17, wherein the wind turbine has a rotor configured to rotate on a bearing about a vertical axis, at least one of said store, fuel-consuming electrical generator and controller being located in said base, on the vertical axis and above the bearing.
20. Method of providing a predetermined amount of electrical power at a power output, the method comprising the steps of: providing an input for electrical power from a generator driven by a wind turbine, a store for electrical power and a fuel-consuming electrical generator; and controlling the fuel-consuming electrical generator and electrically interconnecting the input, the store, the fuel-consuming electrical generator and the power output such that a predetermined amount of power is continually available at the power output.
21. Method according to claim 20 and comprising the step of controlling the fuel-consuming electrical generator and electrically interconnecting the input, the store, the fuel-consuming electrical generator and the power output such that a predetermined amount of power is continually available at the power output for minimum fuel consumption by the electrical generator.
22. Method according to claim 21 and comprising the steps of monitoring the power input from the generator driven by a wind turbine and the power available from the store and, in the event that these are less than the predetermined amount of power, activating the fuel-consuming electrical generator.
23. Method according to any one of claims 20 to 22 and comprising the steps of monitoring the power input from the generator driven by a wind turbine and the power available from the store and, in the event that the input power from the generator driven by a wind turbine is in excess of the predetermined amount of power and that the store is saturated, limiting the power input.
24. Method according to any one of claims 20 to 23 and comprising the steps of monitoring the power input from the generator driven by a wind turbine and the power available from the store and, in the event that the input power from the generator is in excess of the predetermined amount of power and that the store is saturated, diverting power to an electrical energy sink.
25. Apparatus for provision of electrical energy, the apparatus comprising: an input configured to receive electrical power from a generator driven by a wind turbine, the power having a first component varying at a frequency determined by the rotation of the wind turbine and a second component varying at a lower frequency than the first component; an output configured to provide power to a load; first and second stores for electrical energy received via the input, the first store having time constants of energy absorption and release that are shorter than those of said second store; and a controller configured to selectively feed the first component of electrical energy to the first store and the second component of electrical energy to the second store.
26. Apparatus according to claim 25, wherein the controller is configured to electrically interconnect the input, the stores for electrical energy and the energy output such that the power available at the energy output is independent of short and medium-term variation in the input of electrical energy from said wind turbine.
27. Apparatus according to claim 25 and further comprising a fuel-consuming electrical generator, the controller being configured to electrically connect the input, the stores, the generator and the output such that the power available at the energy output is independent of long-term variation in the input of electrical energy from the wind turbine.
28. Apparatus according to any one of claims 25 to 27, wherein the apparatus further comprises a third store for electrical energy having a storage time constant longer than that of the second store, the controller being configured to selectively feed a third component of the electrical energy varying at a lower frequency than the second component to the third store.
29. Apparatus according to claim 28, wherein the third store comprises a mass moveable in the earth'sgravitational field by a reversible electricmotor/generator, thereby storing energy as potential energy.
30. System comprising a wind turbine, an electrical generator driven thereby and apparatus according to any one of claims 25 to 29.
31. System according to claim 30, wherein the wind turbine comprises a rotor and a stationary base, at least one of said first, second and third stores and said controller being located in said base.
32. System according to claim 31, wherein the wind turbine has a rotor configured to rotate on a bearing about a vertical axis, at least one of said first, second and third stores and said controller being located in said base, on the vertical axis and above the bearing.
33. System for provision of electrical energy comprising: a wind turbine having a rotor configured to rotate on a bearing about a vertical axis, an electrical generator driven by the rotor; and a store for electrical energy generated by the generator, the store being located on the vertical axis and above the bearing.
34. System according to claim 33, wherein at least 50% of the capacity of the store in terms of energy is located above the bearing.
35. System according to claim 34, wherein all of the capacity of the store in terms of energy is located above the bearing.
36. System according to any one of claims 33 to 35, wherein the topmost extremity of the store for energy is at least as high as the topmost extremity of the rotor.
37. System according to any one of claims 33 to 36, wherein the store for energy comprises a mass moveable in the earth's gravitational field by a reversible electric motor/generator, thereby storing electrical energy as potential energy.
38. System according to any one of claims 33 to 36, wherein the store for energy comprises a flywheel driveable by a reversible electric motor/generator, thereby storing electrical energy as kinetic energy.
39. System according to any one of claims 33 to 36, wherein the store for energy comprises an electrical battery.
40. System according to any one of claims 33 to 39, wherein the rotor has an H configuration.