WO2023117000A1

WO2023117000A1 - Wind turbine thermal energy storage system

Info

Publication number: WO2023117000A1
Application number: PCT/DK2022/050262
Authority: WO
Inventors: Emil Haldrup ERIKSEN
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2021-12-23
Filing date: 2022-12-06
Publication date: 2023-06-29
Anticipated expiration: 2024-06-23

Abstract

A base installation (24) for a wind turbine (2) is provided. The base installation (24) comprises a foundation (12) for supporting the wind turbine (2) and a heat storage mass (26) arranged with the foundation (12). The heat storage mass (26) is at least partially encased in a thermally insulating material (28, 40) and comprises a flow path through which heat transfer medium may flow to exchange thermal energy with the heat storage mass (26).

Description

Wind Turbine Thermal Energy Storage System

Technical Field

The present disclosure generally relates to thermal energy storage systems for wind turbine generators and wind power plants.

Background

Wind turbine generators, or ‘wind turbines’, capture wind power and convert it to electricity for distribution via a power grid. However, wind turbines are reactive to wind conditions meaning that their electric power output is highly variable and stochastic, and so rarely matches the grid load (or demand). As a result, at times wind turbines produce an energy surplus that needs to be managed.

Known power management techniques for wind turbines include approaches involving storing surplus energy for later exploitation when the grid demand is high. Examples include hydroelectric energy storage and battery storage. However, the former presents geographical limitations, while the latter is difficult to scale due to technological and economic constraints.

Thermal energy storage is another developing technique in which electrical energy is converted into thermal energy, which may be stored in a heat storage material. The stored heat may subsequently be converted back into electrical energy for distribution as required. However, known arrangements require significant new infrastructure and suffer from efficiency losses.

It is against this background that the invention has been devised.

Summary of the Invention

According to one aspect of the invention, a base installation for a wind turbine is provided. The base installation comprises a foundation for supporting the wind turbine and a heat storage mass arranged with the foundation. The heat storage mass is at least partially encased in a thermally insulating material. The heat storage mass comprises a flow path through which a heat transfer medium may flow to exchange thermal energy with the heat storage mass.

By arranging the heat storage mass with the foundation, construction infrastructure used to install the foundation can be reused to install the heat storage mass in the same construction phase. In this way, costs associated with implementing energy storage functionality are reduced and there is no need to accommodate an energy storage system separately from the foundation, thereby reducing space requirements.

Partially or wholly encasing the heat storage mass in insulating material ensures that thermal energy is retained in the heat storage mass over a useful period, for example a period measured in days or weeks, or even months in some cases. This enables the thermal energy to be extracted later for conversion to electrical energy when required. The characteristics of the thermally insulating material, including the thickness of the material and the specific material used, can be selected to provide for the required heat storage period.

The heat storage mass may be supported by the foundation for supporting the wind turbine, thus mitigating the need for a separate foundation for supporting the heat storage mass. In some embodiments, the heat storage mass and the foundation may overlap in a horizontal plane. For example, the heat storage mass may be disposed beside a portion of the foundation. Optionally, the heat storage mass may substantially surround a portion of the foundation, that portion therefore being nested within the heat storage mass.

The base installation may be at least partially embedded in the ground, thus making additional use of an excavation that has been created for the foundation. However, the heat storage mass may also extend above the ground, for example where a shallow foundation is used such that the excavation for the foundation is not of a depth that can also accommodate the heat storage mass.

The heat storage mass may extend along a curved path. For example, the curved path may be configured to follow the contours of a rotationally symmetric or circular foundation. The curved path may curve around an upright axis, which axis is optionally aligned with a central vertical axis of the tower of the wind turbine, once installed. The curved path may be substantially circular, meaning that the heat storage mass is generally annular in shape. In such embodiments, the curved path may terminate at mutually-opposed ends defining mutually-facing ends of the heat storage mass. A thermally insulating material may be disposed between the facing ends, for example the same thermally insulating material in which the mass is encased. This beneficially creates thermal separation between the facing ends of the heat storage mass, meaning that the mass can have a relatively warm end and a relatively cool end to create a heat gradient between the ends of the heat storage mass. This, in turn, may help to optimise thermal exchange between the heat storage mass and the heat transfer medium.

The base installation may also comprise a respective port at each of the opposed ends of the heat storage mass through which heat transfer medium can enter and exit the flow path.

The heat storage mass may comprise one or more bodies of solid material, and in some embodiments may comprise multiple discrete bodies such as basalt rocks or diabase stones. In such cases, the flow path may be at least partially defined by spaces between and/or around the bodies, such as interstitial spaces between individual rocks.

Alternatively, the solid material of the heat storage mass may be a single, homogeneous body, for example a body of cast concrete comprising fins or other formations with spaces between them to define the flow path, or a body having one or more embedded channels serving as a flow path.

The invention also extends to a wind turbine installation comprising a wind turbine supported by the base installation. The wind turbine installation may comprise a charging system and a discharging system. The charging system is configured to convert electrical energy produced by the wind turbine into thermal energy that is transferred to the heat storage mass through the heat transfer medium. Conversely, the discharging system is configured to convert thermal energy stored in the heat storage mass into electrical energy. The charging system and the discharging system may be separate systems, or they may form part of a single integrated system.

The wind turbine installation may be configured or operable to pump the heat transfer medium in opposed directions along the flow path. For example, the wind turbine installation may be controlled by conveying the heat transfer medium in a first direction along the flow path when transferring heat to the heat storage mass, and conveying the heat transfer medium in a second direction along the flow path when recovering heat from the heat storage mass, the second direction being opposite to the first.

The invention further extends to a wind power plant comprising multiple wind turbine installations, in which each wind turbine may comprise a respective base installation. In such power plants, the flow paths of respective heat storage masses of different wind turbine installations may be connected in series, in parallel, or a combination. The wind power plant may be controlled by operating the wind turbines to store differing quantities of thermal energy in the respective heat storage masses. In this way, heat storage mass charging and discharging can be controlled to maximise the temperature gradient of each heat storage mass across the power plant, thus enabling further optimization of the efficiency of energy transfer.

It is also possible for multiple wind turbines of a wind power plant to share a common base installation.

According to a second aspect of the invention, a method of fabricating a base installation for a wind turbine is provided. The method comprises creating a foundation for supporting the wind turbine, arranging a heat storage mass with the foundation, and at least partially encasing the heat storage mass in thermally insulating material. The heat storage mass comprises a flow path through which heat transfer medium may flow to exchange thermal energy with the heat storage mass.

Additionally, the method may comprise excavating a hole in the ground and installing the foundation and at least part of the heat storage mass into the hole.

Brief Description of the Drawings

So that it may be more fully understood, the invention will now be described, by way of example only, with reference to the following drawings, in which like features are assigned like reference numerals, and in which:

Figure 1 is a front view of a wind turbine to which embodiments of the invention may be applied; Figure 2 is an axial cross-sectional view of a base installation according to an embodiment of the invention;

Figure 3 is a transverse cross-sectional view of the base installation of Figure 2; and

Figures 4a and 4b are schematic representations of thermal and electrical flow circuits of a wind power plant comprising multiple base installations according to the invention.

Detailed Description

In general terms, embodiments of the invention provide apparatus for storing surplus energy generated by a wind turbine so that it may be recovered and exploited when required. The approach involves arranging a heat storage mass forming part of a thermal energy storage (TES) apparatus with a foundation of the wind turbine. For example, the heat storage mass and the foundation may be accommodated in a single excavation in the ground. By co-locating the heat storage mass with the wind turbine foundation, minimal additional excavation and construction is required and existing electrical infrastructure associated with the wind turbine can be adjusted to accommodate the TES apparatus.

Additionally, the TES apparatus may make use of inexpensive storage mediums as the heat storage mass, such as stone. This allows large energy storage capacities to be achieved at relatively low cost when compared to other energy storage options such as lithium-ion batteries. As a result, energy storage functionality can be implemented without excessive construction time and cost burdens.

Due to the low cost and simplicity of design, the arrangement of the heat storage mass with the foundation may be used for short term (backup) energy storage as well as longer term (seasonal) energy storage. Additionally, the energy stored in the heat storage mass may be used for powering auxiliary systems of the wind turbine, such as de-icing and hydraulic systems. Thus, local battery capacity which may be relied upon during power outages maybe reduced, since the local backup to the wind turbine can be provided from the TES apparatus instead. Furthermore, waste heat generated by various operational systems of the wind turbine (such as temperature regulation systems) may also be redirected to the heat storage mass by the TES apparatus for storage and later recovery. In this way, the energy generating capacity of the wind turbine may be improved.

To provide context for the invention, Figure 1 shows a typical horizontal axis wind turbine, also referred to below as a wind turbine 2. The wind turbine 2 includes a nacelle 4, mounted atop a tower 6, which supports a front facing rotor 8 comprising a plurality of coplanar blades 10. The base of the tower 6 is coupled to a foundation 12, which is embedded in the ground and configured to support and provide stability to the wind turbine 2.

As is common for onshore wind turbines, the foundation 12 comprises a generally cone shaped body 14, which has a short cylindrical base portion surmounted by a taller frustoconical upper portion. A frustoconical outer surface of the upper portion defines a cone surface 15 that narrows upwardly, the cone surface 15 terminating in a circular upper surface defining a central pedestal surface 16, which is positioned near or at ground level 18. A planar underside of the base portion defines a circular base surface 20, which is positioned beneath ground level 18. The pedestal surface 16 and the base surface 20 therefore extend in respective mutually-spaced horizontal planes.

In this example, the diameter of the pedestal surface 16 is slightly larger than the base of the tower 6. The base surface 20 is significantly larger, with a diameter of 21 ,6m in this example. Pedestal and base surfaces 16, 20 of other shapes are also possible.

When erect, the wind turbine 2 is coupled to the pedestal surface 16. Consequently, wind turbine loads are transferred from the tower 6 to the foundation 12 via the pedestal surface 16, and subsequently to the ground via the base and cone surfaces 20, 15.

In this example, it is contemplated that the foundation 12 is constructed as a steel reinforced concrete structure, which is cast in situ. However, other foundation arrangements, including prefabricated foundations, are possible, and in general terms embodiments of the invention may be implemented into arrangements having foundations of any construction. Figure 2 shows a cross-sectional view of a base installation 24 for a wind turbine 2. The base installation 24 includes the foundation 12 described above with reference to Figure 1, as well as a heat storage mass 26 arranged with the foundation 12.

The heat storage mass 26 comprises a material suitable for storing thermal energy. That is, a material with a specific heat capacity that is selected to provide for a desired temperature increase for a given quantity of stored thermal energy, taking into account the total mass of the material. In this example, the heat storage mass is configured to provide an energy storage capacity of between 20 to 65 MWh, whilst rising to a maximum temperature of around 700°C. It may be preferred for the heat storage mass to heat and cool within this range without exhibiting excessive thermal expansion or contraction. For example, suitable materials for the heat storage mass may comprise basalt rock or diabase stones that collectively form the heat storage mass 26. Such materials also beneficially reach the operating temperature of 700° without changing state, although in other embodiments phase-change materials may be used if the heat storage mass is suitably contained. It is also possible for the heat storage mass to be a continuous, homogeneous solid structure. In such embodiments, the flow path may be provided by a series of conduits embedded in the heat storage mass 26 through which the heat transfer medium can flow, for example. Alternatively, or in addition, the solid structure could include fins or other formations that define intervening spaces through which the heat transfer medium can flow.

The heat storage mass 26 comprises a flow path through which a heat transfer medium, such as air, may flow to exchange thermal energy with the heat storage mass 26. In the example shown, the heat storage mass 26 comprises solid material and, more specifically, comprises a plurality of discrete solid bodies 27. The solid bodies 27 may be individual basalt rocks or diabase stones, for example. The flow path is defined by the spaces 29 between the solid bodies 27. As such, the heat storage mass 26 comprises both the solid bodies 27 and the spaces 29 between them that define the flow path.

The heat storage mass 26 is arranged on top of the foundation 12 and, specifically, occupies a toroidal volume of triangular cross-section defined between the cone surface 15 of the foundation 12 and the ground level 18, the heat storage mass 26 therefore resting on the cone surface 15. However, the heat storage mass 26 does not extend over the pedestal surface 16 where the tower 6 is coupled to the foundation 12. In this way, the heat storage mass 26 is supported by the foundation 12 and embedded in the ground in such a way as to not interfere with the interface between the foundation 12 and the tower 6. There is also horizontal overlap between the foundation 12 and the heat storage mass 26 such that the upper portion of the foundation 12 is nested inside the heat storage mass 26, producing a compact arrangement. In some embodiments the heat storage mass 26 may extend above the ground level 18.

A thermally insulating material, such as expanded polystyrene (EPS), extruded polystyrene (XPS), or mineral wool such a stone wool is disposed between the cone surface 15 of the foundation 12 and the heat storage mass 26, thus forming an insulative barrier between the two. Further, the thermally insulating material substantially encases the heat storage mass 26 and so is also disposed between the heat storage mass 26 and the surrounding ground material, thus forming a continuous insulating barrier 28 which acts to retain heat in the heat storage mass 26. In the embodiment shown, the insulating barrier 28 comprises a protective shell 30 of concrete about 20cm thickness lined with insulation 32 of about 40cm thickness.

The thickness of the insulation can be varied according to the requirements of the application to provide for a desired heat storage period over which the temperature of the heat storage mass 26 is maintained within a determined range, for example to limit to a temperature reduction of 1 degree per week.

The thickness of the protective shell 30 can be varied to provide the required level of robustness to protect the insulation 32 within. In other embodiments, if the thermally insulating material is sufficiently robust the protective shell 30 may be omitted, as the soil which surrounds the heat storage mass may provide sufficient protection.

The encased heat storage mass 26 extends radially from an edge of the pedestal surface 16 to a point that is vertically aligned with the edge of the base surface 20. Accordingly, the outer diameter of the encased heat storage mass 26 is substantially similar to the diameter of the base surface 20, while the inner diameter of the encased heat storage mass 26 is substantially similar to the diameter of the pedestal surface 16. It follows that the heat storage mass 26 and the foundation 12 together form a cylindrical assembly having a central axis that is aligned with the tower 6 of the wind turbine.

As can be seen more clearly in Figure 3, the heat storage mass 26 extends along a path that curves around an upright axis 38 (shown in Figure 2) that is aligned with the tower 6 of the wind turbine 2, the curved path terminating at mutually-opposed first and second ends 34, 36 so that the heat storage mass 26 forms an incomplete loop. The first and second ends 34, 36 of the path define corresponding mutually-facing ends of the heat storage mass 26, which are spaced by a narrow gap. A thermally insulating material fills this gap to form a separating barrier 40 between the facing first and second ends 34, 36 of the heat storage mass 26, the thermally insulating material being the same as that encasing the heat storage mass 26 in this embodiment. In this way, heat transfer across the gap between the two ends of the heat storage mass 26 is resisted.

The base installation 24 further comprises first and second ports 42, 44, the first port 42 being provided at the first end 34 of the heat storage mass 26, and the second port 44 being provided at the second end 36 of the heat storage mass 26. Each port 42, 44 is configured to allow the heat transfer medium to flow through the encasing insulation barrier 28 into and out of the heat storage mass 26. In this way, for example, the heat transfer medium can flow into the heat storage mass 26 via the first port 42, along the flow path, and out of the heat storage mass 26 via the second port 44. In this case, the first port 42 acts as an inlet for the heat transfer medium and the second port 44 acts as an outlet for the heat transfer medium. Similarly, the heat transfer medium can flow in the opposite direction through the heat storage mass 26, in which case the second port 44 acts as the inlet and the first port 42 acts as the outlet.

This annular arrangement of the heat storage mass 26 with first and second ports 42, 44 separated by the insulating separating barrier 40 results in a temperature gradient developing along the curved path of the heat storage mass 26 between the first and second ends 34, 36 as the heat transfer medium flows through the heat storage mass 26. Such a temperature gradient advantageously improves the efficiency of energy transfer, as it helps to maintain a steady temperature difference between the heat transfer medium and the heat storage mass 26 at all points along the flow path.

In this respect, when transferring heat to the heat storage mass in a ‘charging mode’, the heat transfer medium enters the flow path at its hottest and cools as it flows around the flow path from one end of the heat storage mass 26 to the other. This means that the end of the heat storage mass 26 where the heat transfer medium enters when in a charging mode becomes hotter than the end from which the heat transfer medium exits. Then, when extracting heat from the heat storage mass 26 in a ‘discharging mode’, the flow direction is reversed. Accordingly, the initially cool heat transfer medium enters at the cooler end of the heat storage mass 26, and warms as it flows along the flow path. As the heat transfer medium travels along the flow path the surrounding heat storage mass also warms due to the temperature gradient, thereby maintaining a temperature difference between the heat storage mass 26 and the heat transfer medium that ensures that heat is transferred into the heat transfer medium effectively along the entire length of the flow path.

The base installation or the wind turbine may be provided with a charging unit that acts to effect the charging mode by converting electrical energy into heat that is transferred to the heat storage mass 26 by heating and pumping the heat transfer medium.

Correspondingly, a discharging unit may be provided for the discharging mode, in which the initially cool heat transfer medium is pumped through the heat storage mass 26 to extract heat, which is then converted to electrical energy.

However, it is also possible for multiple wind turbine installations to share charging and discharging units so that the storage capacities of the respective base installations 24 can effectively be combined. Such an arrangement is now described with reference to Figures 4a and 4b, which show a wind power plant or park 46 that comprises a plurality of wind turbine installations 48, each of which comprises a wind turbine 2 supported by the base installation 24 described above. Figure 4a shows schematically a fluid circuit of the wind park 46, whereas Figure 4b shows an electrical network, the fluid circuit and the electrical network together forming a system for charging and discharging the respective heat storage masses 26 of the wind turbine installations 48.

Each wind turbine installation 48 comprises a charging unit 50 and a discharging unit 52 arranged in thermal and fluid connection with the ports 42, 44 of the base installation 24 to form a heat transfer circuit around which the heat transfer medium is conveyed. As shown, the charging unit 50 and the discharging unit 52 are shared by all of the wind turbine installations 48 in this example. In the embodiment shown, the heat transfer medium is air or another suitable gas, and so the charging unit 50, discharging unit 52 and ports 42, 44 are fluidly connected by a series of pipes to create a fluid circuit. The base installations 24 are fluidly connected such that the flow paths of each respective heat storage mass 26 are connected in series; that is with the second port 44 of a first wind turbine installation 48 being thermally connected to the first port 42 of a second wind turbine installation 48. The fluid circuit, the electrical network, the charging unit 50, the discharging unit 52 and the heat storage masses 26 therefore collectively represent a TES apparatus for the wind park 46.

Bypass connections (not shown) and an associated set of valves are also provided that enable the flow rate through each heat storage mass 26, and therefore the rate at which each heat storage mass 26 is charged or discharged, to be to be controlled individually. The heat storage masses 26 may therefore be considered to be connected in parallel as well as in series.

A pump (not shown) is arranged in the fluid circuit to pump the heat transfer medium between the charging and discharging units 50, 52 and the base installations 24. The pump may, for example, be reversible so that the heat transfer medium may be pumped in either direction around the fluid circuit so as to engage either the charging or discharging functions or modes described below. Alternatively, two pumps may be provided, one for each pumping direction.

The charging unit 50 is configured to convert electrical energy produced by the wind turbines 2 into thermal energy. In more detail, the charging unit 50 is configured to use electrical power received from the wind turbines 2 to heat, or charge, the heat storage mass 26 by heating the heat transfer medium to be delivered to the heat storage mass 26 to a temperature that is higher than that of the heat storage mass 26. In this example, when the charging unit 50 is engaged (i.e. when the wind turbine installation 48 is in charging mode), the heat transfer medium is pumped in a charging flow direction along the flow path of the heat storage mass 26 from the first port to the second port 42, 44. Accordingly, the heat transfer medium transfers thermal energy to the heat storage mass 26 as it flows along the flow path and the heat storage mass 26 is thermally charged.

As the heat storage mass 26 charges, a temperature gradient develops in the heat storage mass 26, with the first end 34 of the heat storage mass 26 becoming hotter than the second end 36 of the heat storage mass 26. This continues up to an optimal point of charging where the temperature difference between the first port 42 and the second port 44 is at a maximum, which occurs when the temperature of the heat storage mass 26 at the first end 34 is similar to that of the heat transfer medium as it enters the flow path. Charging the heat storage mass 26 beyond this point will eventually result in a homogeneous temperature distribution throughout the heat storage mass 26, in which case the heat storage mass 26 is fully charged.

Correspondingly, the discharging unit 52 is configured to convert thermal energy stored in the heat storage mass 26 into electrical energy, which can be transmitted to a power grid to meet a short-term peak in demand, for example. When the wind turbine installation 48 is in discharging mode, the pump is reversed such that the heat transfer medium is pumped in a discharging flow direction along the flow path, from the second port 44 to the first port 42. Thus, the discharging flow direction is opposite to (countercurrent to) the charging flow direction. As such, as the heat transfer medium initially at ambient temperature (i.e. a lower temperature than that of the charged heat storage mass 26) flows through the heat storage mass 26, thermal energy is transferred from the heat storage mass 26 to the heat transfer medium, thereby heating the heat transfer medium and cooling the heat storage mass 26. In this way, the heat storage mass 26 is discharged. The discharging unit 52 subsequently receives the outflow of the now heated heat transfer medium from the first port 42, and converts the thermal energy therein into electrical energy for delivery to the power grid.

Turning now to Figure 4b, the electrical network connects the wind turbine installations 48 of the wind park 46 together electrically in series. The electrical network further connects the wind turbine installations 48 to the central charging and discharging units 50, 52 through a control unit 54, which is configured to mediate the charging and discharging units 50, 52 in accordance with the power output requirements of the park 46. That is to say, the control unit 54 engages the charging mode when energy needs to be stored, and engages the discharging mode when stored energy needs to be recovered and delivered to the power grid.

The control unit 54 may operate either via local control logic or based on predetermined energy values provided by an external control system, such as a power plant controller. The control unit 54 is configured to selectively engage charging or discharging mode for each individual wind turbine installation 48.

In one operating strategy, the control unit 54 is configured to maximise the temperature gradient across all of the heat storage masses 26 arranged in the heat transfer circuit. In this respect, the respective heat storage masses 26 of the wind turbine installations 48 may be charged to differing extents by making use of the bypass routes and associated valves to control the respective flow rates of heat transfer medium through each heat storage mass 26. For example, a continuous temperature gradient may be created along the entire combined flow path defined by the series of connected individual flow paths of the heat storage masses 26. Only once this gradient has been established does the control unit 54 allow any individual heat storage mass to become fully charged through further charging, typically starting with the heat storage mass 26 at the hottest end of the temperature gradient. By creating such a temperature gradient across the heat storage masses 26 collectively, when the discharging mode is subsequently activated heat transfer medium flowing along this combined path warms continuously and therefore extracts thermal energy from all portions of each heat storage mass 26. In this way, the control unit 54 may be used to improve the efficiency of thermal energy storage across the park 46.

The skilled person will appreciate that modifications may be made to the specific embodiments described above without departing from the inventive concept as defined by the claims.

Claims

1. A base installation (24) for a wind turbine (2), the base installation (24) comprising: a foundation (12) for supporting the wind turbine (2); and a heat storage mass (26) arranged with the foundation (12), the heat storage mass (26) being at least partially encased in a thermally insulating material (28, 40), and comprising a flow path through which a heat transfer medium may flow to exchange thermal energy with the heat storage mass (26).

2. The base installation (24) of claim 1 , wherein the heat storage mass (26) and the foundation (12) overlap in a horizontal plane.

3. The base installation (24) of any preceding claim, wherein the heat storage mass (26) is at least partially embedded in the ground.

4. The base installation of any preceding claim, wherein the heat storage mass extends above at least a portion of the foundation.

5. The base installation (24) of claim 4, wherein the heat storage mass (26) is supported by the foundation (12).

6. The base installation (24) of any preceding claim, wherein the heat storage mass (26) extends along a curved path.

7. The base installation (24) of claim 6, wherein the curved path terminates at mutually- opposed ends (34, 36) defining mutually-facing ends of the heat storage mass (26).

8. The base installation (24) of claim 7, comprising thermally insulating material (40) disposed between the facing ends of the heat storage mass (26).

9. The base installation (24) of claim 7 or claim 8, comprising a respective port (42, 44) at each of the opposed ends (34, 36) of the heat storage mass (26), wherein the heat transfer medium enters and exits the flow path through the ports (42, 44).

10. The base installation (24) of any of claims 6 to 9, wherein the curved path is circular.

11. The base installation (24) of any of claims 6 to 10, wherein the curved path curves around an upright axis (38).

12. The base installation (24) of claim 11 , wherein the upright axis (38) aligns with a tower (6) of the wind turbine (2).

13. The base installation (24) of any preceding claim, wherein the heat storage mass (26) comprises solid material.

14. The base installation (24) of claim 13, wherein the heat storage mass (26) comprises a plurality of discrete solid bodies (27).

15. The base installation (24) of claim 14, wherein the flow path is at least partially defined by spaces (29) between and/or around the bodies (27).

16. A wind turbine installation (48) comprising a wind turbine (2) supported by the base installation (24) of any preceding claim.

17. The wind turbine installation (48) of claim 16, comprising: a charging system (50) configured to convert electrical energy produced by the wind turbine (2) into thermal energy that is transferred to the heat storage mass (26) through the heat transfer medium; and a discharging system (52) configured to convert thermal energy stored in the heat storage mass (26) into electrical energy.

18. The wind turbine installation (48) of claim 16 or claim 17, configured to pump the heat transfer medium in opposed directions along the flow path.

19. A wind power plant (46) comprising multiple wind turbine installations (48) according to any of claims 16 to 18. 16 The wind power plant (46) of claim 19, wherein flow paths of respective heat storage masses (26) of different wind turbine installations (48) are connected in series. A method of fabricating a base installation (24) for a wind turbine (2), the method comprising: creating a foundation (12) for supporting the wind turbine (2); arranging a heat storage mass (26) with the foundation (12), the heat storage mass (26) comprising a flow path through which a heat transfer medium may flow to exchange thermal energy with the heat storage mass (26); and at least partially encasing the heat storage mass (26) in thermally insulating material (28, 40). The method of claim 21 , comprising excavating a hole in the ground and installing the foundation (12) and at least part of the heat storage mass (26) into the hole. A method of controlling a wind turbine installation (48) according to any of claims 16 to 19, the method comprising: conveying the heat transfer medium in a first direction along the flow path when transferring heat to the heat storage mass (26); and conveying the heat transfer medium in a second direction along the flow path when recovering heat from the heat storage mass (26), the second direction being opposite to the first direction. A method of controlling a wind power plant (46) according to claim 19 or claim 20, the method comprising operating the wind turbine installations (48) to store differing quantities of thermal energy in the respective heat storage masses (26).