WO2024255978A1

WO2024255978A1 - A thermal energy plant for storing thermal energy and a method of providing a thermal energy storage plant

Info

Publication number: WO2024255978A1
Application number: PCT/DK2024/050140
Authority: WO
Inventors: Jonas Ilum SØRENSEN; Svante BUNDGAARD
Original assignee: Aalborg CSP AS
Current assignee: Aalborg CSP AS
Priority date: 2023-06-13
Filing date: 2024-06-13
Publication date: 2024-12-19
Anticipated expiration: 2025-12-13
Also published as: DK202370287A1; DK182122B1

Abstract

This disclosure relates to a thermal energy storage plant for storing thermal energy from an energy source, the storage plant comprising: a liquid reservoir for being coupled to an energy source and compris- ing a reservoir volume with a top side, said top side coinciding with a liquid level of a thermal energy storage liquid in the liquid reservoir, and a surface cover comprising an insulating material, such as extruded polystyrene or mineral wool, for retaining thermal energy stored in said liquid, said surface cover at least partly covering said top side, said surface cover being divided into at least a first and a second surface cover segment positioned adjacently to each other and each comprising a circumferential periphery, wherein the first surface cover segment further comprises a first tilting device, wherein the second surface cover segment similarly further comprises a second tilting device, wherein the storage plant further comprises a solar energy system for harnessing solar energy, the solar energy system comprising at least one photovoltaic cell and/or a flowing fluid configured to be heated by solar energy, the solar energy system being mounted on a mounting system installed on and/or in and/or at an exterior surface of the first surface cover segment and/or on and/or in and/or at an exterior surface of the second surface cover segment.

Description

Title of invention

A thermal energy plant for storing thermal energy and a method of providing a thermal energy storage plant.

Technical field

The present invention relates to a thermal energy plant for storing thermal energy from an energy source, the storage plant comprising: a liquid reservoir for being coupled to an energy source and comprising a reservoir volume with a top side, said top side coinciding with a liquid level of a thermal energy storage liquid in the liquid reservoir, a surface cover comprising an insulating material, such as extruded polystyrene or mineral wool, for retaining thermal energy stored in said liquid, said surface cover at least partly covering said top side, said surface cover being divided into at least a first and a second surface cover segment positioned adjacently to each other and each comprising a circumferential periphery, wherein the first surface cover segment further comprises a first tilting device, wherein the second surface cover segment similarly further comprises a second tilting device, wherein the storage plant further comprises a solar energy system for harnessing solar energy, the solar energy system comprising at least one photovoltaic cell and/or a flowing fluid configured to be heated by solar energy, the solar energy system being installed on and/or in and/or at an exterior surface of the first surface cover segment and/or on and/or in and/or at an exterior surface of the second surface cover segment.

A method of providing a thermal energy storage plant is also provided.

Background art

Storage of thermal energy is a topic of growing importance around the world, as it may provide a significant part of the solution to meeting increasingly stringent emission regulations in the field of energy supply. With ever rising fossil fuel prices, storage of thermal energy has the potential to be a more cost- effective solution to meeting energy demands.

An energy system’s capability to store thermal energy is typically linked to the potential for a cost-efficient energy production and the possibility to decouple production and demand. Storing thermal energy often requires a large area and the storage is usually placed close to the consumer’s location. The consumer can be households in a district heating system or a manufacturing facility which requires process heat. The typical solution for large thermal storages is a pit thermal energy storage which is constructed partly below ground and leaves a levelled surface area which is currently not utilized. In areas where land is limited and expensive it is problematic to have a large flat surface unused.

An example of an improved thermal storage system is disclosed in EP 3 789 196 A1.

A thermal storage is often accompanied by electrical equipment such as pumps, sensors, etc. to be operational and therefore it is necessary to have both electricity and heat supplied.

Units or devices for production of heat and electricity require large land area and are often installed close to the consumer, similar to the thermal storage. In modem energy systems, one or more of the types of units used for production of electricity and heat rely on solar energy. These production units are characterized as solar energy systems. They may often be referred to as “panels for solar energy”, “solar (energy) panels”, and “the panels”. Panels for solar energy often require large and levelled surfaces for installation and these areas are usually difficult and expensive to obtain close to the consumer. Additionally, these large and levelled surfaces are often already being used for either agriculture, pasture, or recreational purposes.

Furthermore, solar energy systems are typically heavy-weight and consist of bulky components, which make them difficult to install and to combine with other types of energy storage systems.

On this background an object of the disclosure is to improve on and solve the afore-mentioned issues.

Summary of the invention

The present invention relates to an improved thermal storage system that can result in increased utilization of land area, cost savings and exploitation of solar energy. In a first aspect of this disclosure, this and/or other objects are met by a thermal energy storage plant for storing thermal energy from an energy source mentioned in the introduction, which is furthermore characterized in that a weight of the solar energy system and/or a weight of the first tilting device tilting a draining surface of the first surface cover segment from the circumferential periphery of the first surface cover segment downwards towards a first draining location of the first surface cover segment, whereby water from precipitate falling on the first surface cover segment will flow by gravity towards the first draining location where it can be drained off from the first surface cover segment, and that a weight of the solar energy system and/or a weight of the second tilting device tilting a draining surface of the second surface cover segment from of the second surface cover segment circumferential periphery downwards towards a second draining location of the second surface cover segment, whereby water from precipitate falling on the second surface cover segment will flow by gravity towards the second draining location where it can be drained off from the second surface cover segment.

The present thermal storage system including a solar energy system installed on, in or at an exterior surface of the surface cover enables the harnessing of solar energy, while reducing the land usage and thus increasing the overall cost savings of the system. Furthermore, a self-sufficient or autonomous energy system may be provided thus facilitating an island mode operation.

A “tilting device” according to the present disclosure, may be of any suitable material and may comprise one or more tilting device parts or objects e.g. a plurality of weights, individual particulates of a particulate tilting device which may also be denoted individual grains of a granular tilting device.

The first and the second tilting device may be substantially identical.

A tilting device may be provided above, in, or below a surface cover segment. The tilting device may be provided at and/or on portions of a surface cover surface segment. A tilting device my at least partly cover a surface cover segment. A tilting device may substantially cover an entire surface cover segment.

In an embodiment, the tilting device may further comprise a ballast material.

“Draining location” according to the present disclosure may be understood as a location that facilitates draining of a liquid.

“Drained off from the first surface cover segment” may be achieved by including a draining opening, a well, a pump, a draining system, pipes etc. at or connected to a draining location. “Drained off from the second cover segment” may be achieved in similar fashion.

The draining location may be provided substantially at a centre or midpoint of the respective surface cover segment. The draining location may be located equidistantly from a circumferential periphery thereof. The draining location of a surface cover segment may be a portion of a surface cover segment that is offset in a height direction from the circumferential periphery of the respective surface cover segment.

A draining surface may be an outer surface of the surface cover and/or a surface in the surface cover.

A draining liner may be provided above or below a tilting device. The draining liner may comprise a draining surface. “Draining liner” according to the present disclosure, may be a liner that facilitates draining of a liquid. The draining liner may be substantially fluid tight and/or substantially liquid tight.

Tilting of the respective surface cover segments towards respective draining locations thereof may have the effect that liquid e.g. water from precipitation on a surface cover segment will flow towards the respective draining location of that surface cover segment due to gravity. In this way, liquid in or on a first surface cover segment may be kept separate from liquid in or on a second surface cover segment. Thereby, the surface cover segments may be individually drained off.

The term “tilting” may be defined as a surface cover segment being slanted or inclined such that there is an offset in a height direction, between a circumferential periphery of the surface cover segment and a draining location thereof.

“Tilted” may be understood as being tilted or inclined relative to horizontal. A height direction may extend vertically. The storage plant may be in an installed position. The circumferential peripheries of one or more or all surface cover segments may extend substantially horizontally and/or may be provided at substantially the same vertical height.

The surface cover may extend in a width, length, and a height direction.

Additionally or alternatively, “tilting” may be defined as a draining surface of a surface cover segment being ramped or sloped towards a draining location thereof. The tilting of a drainage surface may be continuous e.g. linear. Additionally or alternatively, “tilting” may be defined as a draining surface of a surface cover segment having a negative gradient from a periphery thereof towards a draining location thereof.

The gradient may be in the range of -1 :200 - -1 :10, -1 :150 - -1 : 10, - 1 :100 - -1 : 10, or -1 :50 - -1 :10 vertical change: horizontal change from a circumferential periphery of a surface cover segment downwards towards a draining location thereof. The term “gradient” may alternatively be denoted “slope”.

The draining surface of the first and/or second surface cover segment may be angled downwards from the horizontal towards a draining location of the respective surface cover segment at an angle between 0<90°, 0<75°, 0<60°, 0<45°, 0<30°, 0<15° or 0.1 -10°.

One or more tilting devices may similarly be tilting downwards towards a respective draining location of a surface cover segment. The tilting device may be tilting with a gradient that is different from the gradient of the respective surface cover segment. The tilting device may be tilting with a gradient that is lower than the gradient of the respective surface cover segment. The tilting device may be tilting with a gradient that is higher than the gradient of the respective surface cover segment. The tilting device may be tilting at a gradient of between -1 :10 - -1 :500, -1 :100 - -1 :500, -1 :200 - -1 :500, -1 :300 - -1 :500-, or 1 :400 - -1 :500 vertical change:horizontal change.

One or more tilting devices may be angled downwards from the horizontal towards a draining location of the respective surface cover segment at an angle between 0<90°, 0<75°, 0<60°, 0<45°, 0<30°, 0<15° or 0.1-10°. The tilting device tilting with a different gradient than the respective surface cover segment may provide good pass-through of liquid, such as from precipitate such as rain falling on the surface cover, through the tilting device. It may also provide a good surface for walking on the surface cover e.g. during installation or a potential maintenance thereof.

The liquid reservoir may have a reservoir volume of at least 50,000 m³, 100,000 m³, 250,000 m³, 500,000 m³, 1 ,000,000 m³, 2,000,000 m³, 4,000,000 m³, or even larger.

The liquid reservoir may be embedded in a depression so as to provide the top side and to be substantially surrounded by earth material on a number of remaining sides of the liquid reservoir. The top side may have an area extent of at least 10,000 m², 50,000 m², 100,000 m², 150,000 m², or larger.

The liquid reservoir may comprise a liner substantially covering said remaining sides for substantially separating liquid in the liquid reservoir from said surrounding earth materials.

The term “thermal energy source” may be understood as solar energy, geothermal energy, incinerators, heat exchangers etc. The thermal energy source may also be thermal energy produced from power or excess power produced from wind turbines, solar collectors, waste incinerators and other power plants such as used in district heating or electricity generation. It may also be heat captured from buildings, server stations, cooling water from power stations etc. and/or power generation in general.

The thermal storage liquid may be any liquid suitable for storing thermal energy. The thermal storage liquid may be or comprise or essentially consist of water.

The surface cover may comprise at least one layer of solid insulating material. The surface cover may essentially cover said top side of the liquid reservoir.

The surface cover may comprise one or more insulating layers. The one or more insulating layers may comprise or substantially consist of or consist of insulating materials such as mineral wool, polyethylene (PE), such as expanded polyethylene (EPE) or Expanded polyethylene copolymers (EPC) and/or polystyrene (PS), such as extruded polystyrene (XPS), polyisocyanu- rate, stone wool, fiberglass, natural fibres, perlite, polymers, elastomers and/or combinations thereof.

The surface cover may comprise two or more layers of insulating material.

A layer of insulating material located closest to the top side may be of a higher density than the other layer(s) of insulating material.

This may have the advantage of stabilizing the surface cover both in use and during manufacture. This may have the further advantage of improving the ease of maintenance of the surface cover, e.g. when walking on the cover.

The division of the surface cover into individual cover segments may have the effect reducing the height difference that is created by the weight of liquid, such as precipitation falling on the surface cover, weighing the surface cover down. For surface covers comprising just a single segment, the liquid gathering on the surface cover may flow and collect at a single location on the surface cover i.e. the weight of substantially all or all of the precipitation may collect at a single location on the surface cover. This may cause the single location of the surface cover to be pushed down under the weight of the liquid forming a depression in the surface cover and thereby creating a large height difference between the depression and the rest of the surface cover. This may put stress and tension on the surface cover. The division of the surface cover into individual surface cover segments may create several locations on the surface cover for the liquid to flow to and collect. This may mean less liquid collecting, and so less weight collecting, at each location and therefore a smaller height difference between a depression and peaks of the surface cover may be created by the weight of the liquid weighing the surface cover down. This may have the effect of reducing the stress on the surface cover.

A further effect of this may be that as less liquid may collect at each location, smaller pumps may be used to pump away the liquid. This may be further advantageous in really heavy rain showers as water may be pumped away from several different locations which may be more effective than pumping away liquid weighing down the surface cover segment from a single location. By utilising several smaller pumps, it may also be possible to provide a greater pumping capacity. This may provide security as water may be effectively pumped away from the surface cover even during heavy rain showers.

The division of the surface cover into cover segments may have the effect of enabling the location of a potential leak to be narrowed down to a single segment of the surface cover. This may improve the ease with which a location of a leak may be determined, as a much smaller area has to be analysed. It may have the further effect that a leak in the surface cover may be contained within the segment where the leak occurred.

The division of the surface cover into cover segments may have the further effect that maintenance of the surface cover is improved, as individual segments may be maintained separately without impacting other cover segments e.g. when fixing a leak.

The division of the surface cover into surface cover segments may also have the effect that replacement of the surface cover is improved as a single cover segment may be replaced separately from the surface cover as opposed to replacing the entire surface cover. This may have the further effect that the efficiency of the thermal energy storage plant is improved during maintenance or replacement as only a segment of the surface cover has to be removed, leaving the remaining surface cover intact, and so the liquid reservoir will be better insulated than if the entire surface cover had to be removed.

The division of the surface cover into surface cover segments may also improve the ease of transport of the surface cover to the site, as it may be transported in separate segments. The surface cover may then be assembled on site.

The division of the surface cover into surface cover segments may have the effect that the durability and strength of the surface cover is improved as it is better able to withstand thermal expansions and contractions. A further effect may be that air under the surface cover may be transported to ventilation vents or valves.

Two, or three, or four or more, or all of the surface cover segments may be substantially of same size and shape, and/or substantially identical. Each surface cover segment may have a top surface area extent of at least 1/8, 1/10, 1/16, 1/25, 1/32, 1/40, or 1/50 of said area extent of said top surface.

The surface cover segments may be plate-shaped.

The surface cover segments may be provided as separate modules, which may be attached to each other during assembly of the storage plant.

A “thermal energy storage plant” may be a thermal energy storage plant such as a thermal storage sink pond.

The term “solid” may potentially be understood as non-fluid.

The term “drained off” may potentially be understood as “being caused to leave the surface of something”.

The term “individually” may alternatively be denoted or include “independently” and/or “separately”.

The first and/or second tilting device may comprise(s) or consist(s) or substantially consist(s) of granular matter.

This has been found to provide good distribution of the tilting device and allow liquid, such as water from precipitation falling on the surface cover, to pass through the tilting device well.

A layer thickness of one or more of the tilting devices may increase from the circumferential periphery of the respective surface cover segment towards the respective draining location thereof.

A layer thickness may substantially extend or extend in a direction perpendicular to a top surface of a surface cover segment. The layer thickness may extend in the height direction. The layer thickness may be in a range of 1- 500 mm, 1 -400 mm, 1 -300 mm, 1-200 mm, 1 -100 mm, 1 -50 mm, or 1 -30 mm. The layer thickness of the tilting device may be at least 10 mm greater at a draining location of a respective surface cover than at a circumferential periphery thereof.

In an embodiment the layer thickness may be 30 mm at the circumferential periphery of a surface cover segment and the layer thickness may be 145 mm at the draining location of a surface cover segment. The layer thickness may increase in a stepped fashion, or continuously, such as linearly, from the circumferential periphery to the draining location of a surface cover segment towards a draining location thereof.

A small layer thickness may save material and costs associated with production of the surface cover. A small layer thickness may also reduce the strength requirements of the surface cover, which in turn may reduce the amount of material required to produce the surface cover, which in turn may further reduce the cost associated with production of the surface cover.

The different segments of the system may enable a flexible and scalable system comprising solar energy units installed on one or more of the segments. The solar energy system may be installed on all surface cover segments comprised by the thermal storage system.

In an embodiment, the solar energy system comprises a mounting system installed on, in and/or at an exterior surface of the surface cover, the solar energy system being mounted on and/or in the mounting system, the mounting system and/or the solar energy system comprising a ballast material.

The provision of a mounting system installed on an exterior surface of the surface cover may allow a safe and accurate placement of the solar energy system onto the thermal system. The provision of the mounting system comprising a ballast or a ballast material, or else a ballasted mounting system or ballasted mount, may ensure a non-invasive, non-penetrated installation on the surface cover of the liquid reservoir. The ballast may comprise a ballast material. This will therefore help avoid penetration into the surface cover, which may lead to undesirable leakages through the cover or tension applied to the surface cover. The solar energy system may comprise the ballast material or be ballast mounted on the cover of the reservoir. This configuration may also allow a quick and safe installation of the solar energy system on the surface cover without it being attached to the surface cover. The ballasted mounting system may prevent any wind lift or instability occurring as a consequence of high wind loads exerted on the solar energy system.

In a preferred embodiment, the surface cover is floating freely on the thermal energy storage liquid in the liquid reservoir. The surface cover may be floating on a liquid level surface of the liquid in the liquid reservoir. The free floating of the surface cover may be understood as no fixed mounting or anchoring to the storage liquid or to the liquid reservoir is provided. The already flattened surface of the surface cover is utilized, and no additional preparation of the exterior surface is thus required. That may increase the overall cost efficiency of the system.

The mounting system and/or the solar energy system may not be anchored to the surface cover or to the liquid reservoir. This configuration may be advantageous since no severe modifications or penetration through the surface cover are required. Anchoring to the surface cover is undesired as this may introduce mechanical tension, which the surface cover is not designed for. Furthermore, anchoring to the surface cover may require drilling and introduce openings, which may interfere with the thermal insulation of the surface cover or result in undesired leakages. Avoiding anchoring to the surface cover may allow relocation of the mounting system with no adverse effect on the surface cover. Anchoring to the liquid reservoir is undesired as this may prevent the surface cover from free floating on the surface of the storage liquid.

In addition, the mounting system installed on the surface cover can be integrated with and make use of the existing ballast included in the surface cover, thus not requiring severe modifications to the existing surface cover of the thermal storage system.

The solar energy system may comprise one or more solar energy units. The solar energy units may be connected to each other.

In an embodiment, the mounting system and/or the solar energy system comprise a container installed underneath and/or adjacent to the solar energy system, the ballast material being positioned in the container. The container may be attached to the solar energy system on at least one side of the solar energy system, such that the container is adjacent to the solar energy system. A tight connection between the container and the solar energy system may be thus provided.

The weight of the solar energy system and of the mounting system may be utilized to minimize the quantity of ballast material required to be installed on the surface cover. The container may be plastic to minimize the installation and maintenance cost as well as its weight. The container may be a rectangular box. Alternatively, the container may be triangular or trapezoid, having substantially a triangular or trapezoid cross-section. The upper part of the opening of the container may be inclined such that it substantially matches the tilting angle of the solar energy unit.

The weight of the ballast material that is required per solar energy unit may vary from 5 kg to 300 kg. The weight of the ballast material per solar energy unit may thus be equal to 5 kg, 50 kg, 100 kg, 150 kg, 200 kg, 250 kg, 300 kg. The weight may also be larger than 300 kg or smaller than 5 kg, e.g. 1 kg, 2 kg, 3 kg or 4 kg. This range of the ballast weight is due to the “shadowing” effect of the wind, i.e. , a solar panel mounted behind another one does not need as much ballast to combat wind load. Additionally, the ballast weight needed may depend on the size of the solar energy unit (e.g. solar panel) and the mounting angle of it.

The mounting system may comprise sections or rails, preferably in a grid-like structure and/or containers. The mounting system may be positioned underneath the solar energy system, such that it is substantially covered by the solar energy system. The sections of the mounting system may be connected to one or both ends of each solar energy unit. The sections may be installed in parallel with each other. The mounting system may comprise one or more bases. The bases may be installed in combination with the sections. The mounting system may be rust-resistant and strong.

In another embodiment, the solar energy system comprises at least one solar panel, the solar panel area being equal to or smaller than 5m². The solar energy system may comprise solar panels, which are also known as solar cell panels, solar electric panels, or photo-voltaic (PV) modules or PV panels. Solar panels are used to capture the sunlight as a source of solar energy, which is then converted into electric energy in the form of electricity. Solar panels may comprise an assembly of photovoltaic solar cells mounted in a usually rectangular frame. The solar energy system may comprise a photovoltaic (PV) array. The solar panels may often be cumbersome and heavy-weight. The solar panel area may generally vary. Preferably, the area of each solar panel may not exceed 5m². The relatively smaller panel area may help avoid heavy weight exerted to the surface cover of the thermal storage system. Furthermore, the larger the panel area, the higher wind load that is exerted on the solar energy system. It may therefore be advantageous to limit the panel area according to the size of the liquid reservoir, structure of the surface cover and wind conditions in the surrounding area. The smaller panel area may also enhance installation of the solar energy system, practicality and operation of the system.

The solar panel area may be equal to 0.5m², 1 m², 2m², 3m², 4m² or larger. The solar panel area may alternatively be at most 5m², 6 m², 7m², 8m², 9 m², 10 m², 11 m², 12 m², 13 m², 14 m²,15 m², 16 m², 17 m², 18 m², 19 m² or 20 m².

In yet another embodiment, the solar panel is installed with a tilting angle being in the range of 0°-20° relative to a horizontal direction. The solar panel may be installed with a tilting angle being in the range of between 0-5°, 0-10°, 0-30°, 0-40°, 0-5°, 0-15° or 0.1 -2° relative to a horizontal direction.

The relative small tilting angle of the installed solar panels may minimize their projecting height and thus minimize the risk for wind lift, while ensuring collection of the solar energy.

In a preferred embodiment, the mounting system and/or the solar energy system acts as a counter-weight to a wind load exerted on the solar energy system. The ballasted mounting system and/or the ballast material may add weight to the total weight of the surface cover. The ballasted mounting system and/or the ballast material may thus counteract with forces applied by wind onto the solar energy system, thus counteracting with wind load and preventing the system from blowing off in strong winds. The solar energy system may comprise bulky and high structures, which may be prone to high wind loads and oscillations. That may be particularly damaging for the solar energy system itself and the tension applied to the surface cover. A counter-weight of the mounting system may thus contribute to the stability of the whole system and ensure that the mounting system is able to withstand any stress caused by wind in the field.

In a further embodiment, a primary tilting device comprises the solar energy system and the first or second tilting device, the weight of the primary tilting device increases from a respective circumferential periphery towards the respective draining location of the first and/or second surface cover segment.

The increase in weight may be a stepped, or continuous, such as linear, or curved, or arced, increase in weight of the tilting device towards the draining location. The stepped increase in weight of the tilting device may be provided in steps of predetermined increments at predetermined portions of a surface cover segment so as to provide a desired tilting of a draining surface.

This may provide a surface cover with the tilting desired and ensure tilting of an entire draining surface.

In an alternative or additional embodiment, the ballast material is not part of the tilting device.

In an embodiment, the ballast material comprises gravel, pebbles and/or other granular matter.

The term “granular” in the present disclosure may alternatively be denoted “particulate”.

The granular matter may comprise or substantially consist or consist of gravel, pebbles, beads and/or stones.

The granular matter may be chosen from the group consisting of coarse gravel, medium gravel, fine gravel, coarse sand, medium sand, and/or fine sand, according to ISO 14688-1 :2002, or combinations thereof.

The solar energy system may comprise a solar panel and/or a solar thermal collector and/or a photovoltaic thermal collector.

The solar energy system may comprise a solar thermal collector. Alternatively, the solar energy system may be a hybrid system, comprising a solar panel and a solar thermal collector. Solar thermal collectors collect heat by absorbing sunlight. They are used to heat air and water or generate electricity. Typically, solar thermal collectors are heavier than solar panels. That may make them harder to install and operate.

The solar energy system may comprise a hybrid panel, a photovoltaic thermal collector or a photovoltaic thermal hybrid solar collector.

In an embodiment, the solar panel is installed with an orientation facing towards east or west. While the most common orientation for installation of solar panels is south to optimize the direct sunlight received throughout the day, this may lead to increased wind load. For that reason, it may be advantageous to install the solar panels on the thermal storage system facing towards east or west, so that the risk for wind lift is minimized.

In other embodiment, the solar panels are installed facing any possible orientation, i.e. south/north, east/west. In an embodiment, a combination of different orientations for the installation of solar panels is made to optimize the collection of solar energy and the risk for wind lift.

In an embodiment, the ballast material comprises a concrete slab.

The concrete slab may act as the base of the mounting system and/or of the solar energy system, which was described above. The concrete slab may provide the weight needed to ballast the solar energy system and/or the mounting system. The concrete slab may be installed in conjunction with the sections of the mounting system or alone. The concrete slab may be installed in positions underneath the corners of the solar energy unit.

In an alternative or additional embodiment, the mounting system comprises a metal structure, preferably made of steel, the solar energy system being mounted on and/or in the metal structure. The metal structure and/or the solar energy system may comprise the ballast material. The ballast material may comprise granular matter and/or a concrete slab.

The metal structure may consist the sections of the mounting system. The sections of the mounting system may abut the exterior surface of the surface cover. The metal structure may comprise aluminium and/or stainless steel. The metal structure may further comprise legs, mounted perpendicular to the sections or rails of the mounting system. The legs may be mounted to the highest point of the installed solar energy unit.

In an embodiment, the first surface cover segment and/or the second surface cover segment comprise a plurality of solar panels installed on the surface cover segment. A plurality of solar panels may be installed on the first surface cover segment and/or on the second surface cover segment.

The solar energy units or solar panels may be installed on one cover segment or more. Depending on the desired utilization of the solar power, the area that solar panels cover may extend to a small part of the surface cover, or to substantially the entire surface cover. The segmented or sectionized surface cover may facilitate the installation and maintenance of the mounting system and the solar energy system.

In an embodiment, the tilting device may be provided on a surface cover segment according to mass per unit area. A tilting device may be provided at a circumferential periphery of a surface cover segment in the range of 1 -500 kg/m² A tilting device may be provided at a circumferential periphery of a surface cover segment in the range of 1 -100 kg/m², 1 -80 kg/m², 1 -60 kg/m², 1 -40 kg/m², 1 -20 kg/m², or 1 -10 kg/m². A tilting device may be provided at a draining location of a surface cover segment in the range of 1 -500 kg/m², 100- 500 kg/m², 200-500 kg/m², 300-500 kg/m2 or 400-500 kg/m². The tilting device may be provided at a draining location in an amount at least 10 kg/m² greater than at the circumferential periphery of the respective surface cover segment.

In an embodiment, the tilting device is provided at a periphery of a surface cover segment in the amount of 46.5 kg/m² and in the amount of 226 kg/m² at the draining location thereof.

This has been found to provide an optimum tilting of the surface cover segments and a good pass-through of liquid, such as water from precipitation falling on the surface cover, through the tilting device.

The first and/or second surface cover segment may comprise(s) at least one tilting device container for containing at least one of the first or second tilting devices respectively. The tilting device container may be part of the mounting system where the solar energy system is mounted onto.

The at least one tilting device containers may cover a predetermined portion of a respective surface cover segment. The at least one tilting device container may be of a predetermined height corresponding to a desired layer thickness of a tilting device. The at least one tilting device container may comprise a marking corresponding to a desired layer thickness of tilting device. The at least one tilting device container may be a compartment integrally formed or in one piece with a surface cover segment. The desired layer thickness may be a desired layer thickness at a predetermined portion of a surface cover segment.

The at least one tilting device container may be of different heights. The at least one tilting device container may cover a predetermined portion of a surface cover segment. Tilting device container of different heights may cover different predetermined portions of a surface cover segment. The respective height of each of the at least one tilting device container may correspond to the desired layer thickness at a given portion of a surface cover segment that the respective tilting device container covers. The at least one tilting device container may comprise markings at different heights corresponding to a desired thickness layer of the tilting device at the respective portion of the surface cover segment.

In this way, the layer thickness of the tilting device may be easily controlled. It may also be possible to quickly determine that a correct layer thickness of tilting device has been provided at a given portion of a surface cover segment by determining if a tilting device container has been filled either fully or to a desired height defined by a marking.

The tilting device may have a density that is higher than the density of the thermal energy storage liquid.

A density of at least one of the tilting devices may increase from the circumferential periphery of a surface cover segment towards a draining location thereof. The increase in density may be a stepped, or continuous, such as linear or curved or arced, increase in density of the tilting device towards the draining location. The stepped increase in density of the tilting device may be provided in steps of predetermined increments at predetermined portions of a surface cover segment so as to provide a desired tilting of a draining surface.

The first of the surface cover segments may comprise a draining system, which is isolated from a draining system of the second of the surface cover segments so that liquid on a surface of each of and/or in each of said first and second cover segments can be individually drained off at the first or second draining location respectively.

Each draining system may be located at a draining location of a surface cover segment. Each draining system may extend below the surface cover and/or a bottom of the surface cover and/or a bottom liner of the surface cover. The draining systems may extend below the top side of the liquid reservoir.

Each surface cover segment may comprise a substantially fluid tight and/or substantially liquid tight barrier at a periphery thereof. The draining systems may be isolated from each other by means of a substantially fluid tight and/or substantially liquid tight barrier.

Each surface cover segment may comprise drain channels in the surface cover. The drain channels may be provided between layers of the surface cover material. Additionally or alternatively, the drain channels may be in the form of pipes. The pipes may be made from a material chosen from the following group: polymers, ceramics, metals or combinations thereof. The drain channels may channel liquid into a well. The drain channel may comprise a one-way valve preventing water from flowing from a well into said drain channel.

Each draining system may be a draining system draining liquid upstream of an outlet of the respective segment. This may have the effect of improving the locating of a leak in the surface cover. This may be achieved by determining that a draining system is draining more liquid than another draining system.

The liquid on or in each surface cover segment that can be drained individually may be precipitate and/or condensed liquid inside a segment and/or storage liquid, which may have entered into a segment from a leak, or the like, in the segment.

Each surface cover segment may comprise a grating for preventing the tilting device or contaminants, such as plant litter etc. from entering the draining system. The grating may comprise openings of a size that is smaller than the grain size of one or more of the tilting devices.

Each surface cover segment may comprise at least one well. A first well may be for liquid drained off from an outer surface of the surface cover and the second well may be for liquid drained off from inside the surface cover. This may allow liquid from external sources such as precipitation, to be drained separately and may also allow liquid stemming from the liquid reservoir to be drained separately. This may prevent contamination of the liquid reservoir and may also the separately drained liquids to be treated separately according to the best practice.

At least the first and second surface cover segment may each comprise at least one well located at the respective draining location thereof, for collecting liquid drained off of the respective surface cover segment.

A well may extend below the top side and comprise a liquid extraction point or liquid outlet positioned below the top side. A well may be located on top of a bottom liner.

A well may be located below a top surface of a surface cover segment. The well may extend below the surface cover. Each well may comprise a pump unit for extracting the water.

At least one well may comprise at least one filter unit.

The term “well” may be understood as a shaft for collecting fluid. Additionally, or alternatively, it may be understood as a depression to hold liquid. Additionally, or alternatively, it may be understood as a depression made to hold liquid extending below a surface.

The liquid outlets and/or drainage channels may be covered by a liner and/or insulating material. The liquid outlets and/or drainage channels may be arranged at least partly inside said surface cover.

The well may comprise a tilting device or a compartment for a tilting device.

The surface cover and/or surface cover segments may comprise a bottom and/or top liner. The bottom liner may constitute the bottom of the surface cover and/or surface cover segment. The top liner may be continuous and substantially cover the entire top side of the liquid reservoir.

The surface cover and/or said bottom liner may substantially cover the entire top side of the liquid reservoir. Similarly, the top liner may substantially cover the entire top side of the liquid reservoir.

An advantage of this may be good insulation across substantially the entire top side of the liquid reservoir. The liners may be continuous or may comprise two or more elements attached together to form a continuous liner. One or more of the liners may comprise openings to accommodate a barrier. One or more of the liners may be continuous or comprise two or more elements over a segment of the surface cover. One or more of the liners may be a liner comprising two or more liner elements attached together. The liner elements of the top or bottom liner may be attached by welding, gluing, sewing, riveting, zippers, one or more overlapping flaps of material or a combination thereof. The one or more liner elements may be overlapping at a periphery of respective surface cover segments. One or more of the liners may be substantially liquid tight. Additionally or alternatively, one or more of the liners may be substantially vapour tight. One or more of the liners may be in the form of a one-way liquid and/or vapour membrane. One or more of the liners may comprise and/or be in the form of a diffusion membrane. One or more of the liners may be diffusion-open. One or more of the liners may be diffusion tight. The liners may comprise a draining surface. The liners may constitute a draining liner.

The surface cover may comprise a substantially liquid tight and substantially diffusion tight, continuous bottom liner for facing the storage liquid, the bottom liner at least partly covering said top side, and a substantially diffusion-open top liner, where one or more layers of insulating material is provided between the top and bottom liner.

This may have the advantage that liquid and/or vapour will not enter the surface cover through its bottom liner and that any liquid or vapour in the surface cover may escape out of the surface cover by diffusion through the top liner. This may further provide good insulating properties as liquid or vapour. It may further provide good durability as

“Continuous” in the present disclosure may be defined as the liner not being interrupted and/or being in on piece.

The diffusion membrane may have the effect of allowing air and/or vapour in and/or below the surface cover to vent to the atmosphere.

The term “diffusion-open” may be understood as surface or liner that allows diffusion of air and/or vapour through the surface or liner. The term “diffusion tight” may be understood as a surface or liner that does not allow diffusion of air and/or vapour through the surface.

The liners may be made from a material chosen from the following group of materials: HDPE, PE, EPDM, polymeric geomembranes, polymers, elastomers and combinations thereof.

A substantially fluid tight and/or substantially liquid tight barrier may be attached to a bottom liner and/or top liner, for isolating a draining system of the first cover segment from a draining system of the second of the surface cover segments so that liquid on a surface of each of and/or in each of said first and second cover segments can be individually drained off at the first or second draining location respectively. The barrier may be attached at least to a bottom liner of the surface cover. The barrier may be attached at a periphery of a surface cover segment.

Additionally or alternatively, one or more barriers may be attached to a bottom liner of the surface cover. A layer of insulating material may be placed and/or attached to the bottom liner and or to the barriers, above the bottom liner. A top liner may be placed and/or attached to an insulating layer and/or to the barriers, above the insulating layer. The barrier may be an integral part of the bottom liner.

The term “integral” may be understood as the barrier being integral or in one piece with the bottom liner. That is at least a part of the barrier may be part of the bottom liner.

Additionally or alternatively, the surface cover segments may comprise interconnecting portions for connecting to a barrier. The interconnecting portion may be in the form of a flap, cut-out or the like. The flap may comprise one or more strips of material. Attachment of the surface cover section to said interconnecting portion may be through welding, gluing, sewing, riveting, zippers, one or more overlapping flaps of material or a combination thereof.

In an embodiment said barrier is provided by a barrier element interposed between said insulating material of each of the first and second surface cover segments.

The barrier element may be provided potentially so as to assist in the positioning of said insulating material and/or tilting device adjacent said barrier element, and/or potentially so that at least one of said surface cover segment can be removed from said surface cover to allow individual maintenance or replacement of said at least one surface cover segment.

The phrase “assist in the positioning” may be understood as the barrier elements acting as a guide for the insulating material and/or tilting device and/or provide an attachment point for the insulating material. One or more of the barrier elements may comprise a sloped surface relative to the surface cover or a liquid level or liquid top surface, in so providing a funnel effect aiding the positioning of the insulating material and/or tilting device. Additionally or alternatively, at least one side surface of at least one barrier element facing one of said surface cover segments may be sloped relative to said liquid level of the thermal energy storage liquid in the liquid reservoir, so that at least one of said barrier elements assists in the positioning of said surface cover segments adjacently.

The barrier elements may be trapezoidal, triangular, semi-spherical, curved etc. Similarly, the barrier elements may assist in the positioning of the surface cover segments during manufacture of the surface cover or the like. The barrier elements should preferably be able to withstand the pressure from liquid collected in adjacent segments of the surface cover.

The surface cover may extend in a range of 100-600 m in a length direction and in a range of 100-600 m in a width direction.

A surface cover segment may extend in a range of 10-100 m in a length direction and in a range of 10-100 m in a width direction.

Additionally or alternatively, the surface cover segments may be 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100 m long and 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 m wide and/or any combination thereof.

The surface cover may comprise at least one vent for allowing air and/or vapour from below the surface cover to be vented to above the surface cover. Additionally or alternatively, the vent may vent vapour from inside the surface cover to above the surface cover. The vent may further comprise one or more valves. The one or more valves may be in the form of a control and/or one-way valve. The vent may also extend through the surface cover from the bottom of the surface cover to the top of the surface cover. The vent may extend from a bottom liner to a top liner. It may extend through the insulating material. This may have the effect that air and/or vapour below the surface cover or inside the surface cover may be vented to above the surface cover.

The barrier elements may comprise a vent.

According to a second aspect of the invention, a method of providing a thermal energy storage plant is also provided, the method comprising the steps of: providing a liquid reservoir for being coupled to an energy source and comprising a reservoir volume with a top side, said top side coinciding with a liquid level of a thermal energy storage liquid in the liquid reservoir, providing a surface cover comprising an insulating material, such as extruded polystyrene or mineral wool, for retaining thermal energy stored in said liquid, said surface cover at least partly covering said top side, said surface cover being divided into at least a first and a second surface cover segment positioned adjacently to each other and each comprising a circumferential periphery, providing a first tilting device by the first surface cover segment, providing a second tilting device by the second surface cover segment, and installing a solar energy system for harnessing solar energy on and/or in and/or at an exterior surface of the first and/or the second surface cover segment, the solar energy system comprising at least one photovoltaic cell and/or a flowing fluid configured to be heated by solar energy.

The above method may further comprise any or all of the additional steps of: installing a mounting system on an exterior surface of the surface cover, mounting the solar energy system on or in the mounting system, providing a ballast material on or in the mounting system and/or solar energy system, preferably by the use of a vacuum truck. The afore-mentioned steps may be performed in a different order or sequence.

A person skilled in the art will appreciate that any one or more of the above aspects of this disclosure and embodiments thereof may be combined with any one or more of the other aspects of the disclosure and embodiments thereof.

Brief description of drawings

The thermal energy storage plant will now be described in greater detail based on non-limiting exemplary embodiments and with reference to the drawings, on which:

Fig. 1 is a top view of a first embodiment of a thermal energy storage plant according to this disclosure,

Fig. 2 is a cross-sectional view of a part of the thermal storage plant according to an embodiment,

Fig. 3 is a zoomed-in view of a part of the thermal storage plant of Fig.1 ,

Fig. 4 is a side view of a part of an embodiment of a thermal storage plant according to this disclosure, and

Fig. 5 is a perspective view of the embodiment of the thermal storage plant of Fig. 4.

Detailed description

Referring first to Fig. 1 , a thermal energy storage plant 1 is shown from a top-down view. The thermal energy storage plant 1 stores thermal energy from an energy source, in this case from solar thermal collectors and surplus energy from power stations. The storage plant 1 comprises a solar energy system 4 installed on an exterior surface of a surface cover 2.

In Fig. 2, an embodiment of the thermal energy storage plant 1 is shown which comprises a mounting system 41 installed on an exterior surface of the surface cover 2. The solar energy system 4 is mounted on the mounting system 41 .The storage plant 1 comprises a liquid reservoir 11 which is coupled to the energy source, being the solar energy system 4, as well as a reservoir volume 12 with a top side 13, which coincides with a liquid level 14 of a thermal energy storage liquid 15 in the liquid reservoir 11 .

The liquid reservoir has a reservoir volume of 1 ,800,000 m³ and is embedded in a depression so as to provide the top side 13 and to be substantially surrounded by earth material on a number of remaining sides of the liquid reservoir. The top side 13 has an area extent of at least 90,000 m² and comprises a liner substantially covering the remaining sides for substantially separating liquid in the liquid reservoir from said surrounding earth materials.

The surface cover 2 substantially covers the entire top side, and comprises an insulating material 23 in the form of extruded polystyrene (XPS), for retaining thermal energy stored in said liquid 15. The surface cover 2 covers the top side 13 and is floating freely on the liquid level 14 surface of the liquid in the liquid reservoir.

The surface cover 2 comprises a substantially liquid tight and substantially diffusion tight, continuous bottom liner 24 covering the top side 13, and a continuous top liner 25, and three layers of insulating material 23, 23I, 23h provided between the top and bottom liner. The insulating layer 23h located closest to the top side 13 is of a higher density than the other layers of insulating material. Insulating 23h is of a high density expanded polyethylene, 23I is of a low density expanded polyethylene and layer 23 is of a polystyrene The continuous bottom liner constitutes the bottom of the surface cover.

The liners are made from a combination of HDPE, PE, EPDM, polymeric geomembranes polymers and elastomers.

The surface cover is divided into different cover segments. In Fig. 1 , nine cover segments are shown.

Fig. 2 shows details of a storage plant 1 in a cross-section. In Fig. 2, a first 2a and second 2b surface cover segment are positioned adjacently to each other and each comprising a circumferential periphery 29. The first surface cover segment 2a further comprises a first tilting device 21 a, a weight of which and a weight of the solar energy system 4 tilt a draining surface 22a of the first surface cover segment from its circumferential periphery downwards towards a first draining location 26a of the first surface cover segment, whereby water from precipitate falling on the first surface cover segment will flow by gravity towards the first draining location where it can be drained off from the first surface cover segment. The solar energy system 4 comprises here two solar energy units 43.

The second surface cover segment 2b similarly comprises a second tilting device 21 b, a weight of which tilts a draining surface 22b of the second surface cover segment from its circumferential periphery 28 downwards towards a second draining location 26b of the second surface cover segment, whereby water from precipitate falling on the second surface cover segment will flow by gravity towards the second draining location where it can be drained off from the second surface cover segment.

The tilting devices 21 a, 21 b are provided above the surface cover segments and substantially cover the entire surface cover segments. The draining locations 26a, 26b are provided substantially at the centre of the respective surface cover segments and equidistantly from the circumferential peripheries thereof. The draining locations are offset in the height direction from the circumferential periphery of the respective surface cover segments.

The weight of the tilting devices 21 a, 21 b which substantially consist of granular matter in the form of medium gravel according to ISO 14688-1 :2002, increases continuously, and in a linear fashion, from the respective circumferential periphery 28 towards the respective draining location of the first and second surface cover segment.

The first surface cover segment 2a further comprises a draining system 3, which is isolated from a draining system 3 of the second surface cover segment 2b so that liquid on a surface of each and in each of said first and second cover segments can be individually drained off. The draining systems 3 are located at the draining location the respective surface cover segments. The draining systems further comprise drain channels (not shown) in the surface cover 2 and a grating 32 for preventing the tilting device 21 a, 21 b, or contaminants such as plant litter etc. from entering the draining system. The grating 32 comprises openings of a size that is smaller than the grain size of the tilting devices.

The first and second surface cover segment further comprise a well 31 located at the respective draining location thereof, for collecting liquid drained off of the respective surface cover segment. The wells extend below the top side and comprise a liquid extraction point 33 positioned below the top side. Each well comprises a pump unit (not shown) for extracting the water and a filter unit (not shown) for filtering the extracted water.

The surface cover further comprises several vents 27 for allowing air and vapour from below the surface cover 2 to be vented to above the surface cover. The vents extend through the surface cover from the bottom of the surface cover to the top of the surface cover and through the insulating material 23.

As shown in Fig. 2, the mounting system 41 comprises a ballast 42. In this embodiment, the mounting system 41 comprises a container 44 installed underneath the solar energy system 4, specifically underneath each solar energy unit 43. The ballast material is positioned inside the container 44. The container 44 is substantially fully covered by the solar energy unit 43. The surface cover 2 is floating freely on the liquid level 14 of the thermal energy storage liquid 15 in the liquid reservoir 11. As shown, the mounting system 41 is not anchored or fixedly attached to the surface cover 2 or to the liquid reservoir 11 . The solar energy system 4 here comprises at least one solar panel, being the solar energy unit 43. The solar panel area is smaller than 5 m² The solar panel 43 is installed with a tilting angle of 15° relative to a horizontal direction. The horizontal direction is defined being parallel with the bottom surface of the liquid reservoir, here extending in the length direction L. The mounting system 41 acts as a counter-weight to a wind load exerted on the solar energy system 4, such that any wind lift is prevented.

In this embodiment, the tilting device comprises the ballast material 42 and the first tilting device 21 a. The weight of the tilting device increases from a respective circumferential periphery 28 towards the respective draining location of the first surface cover segment 2a.

The ballast material 42 positioned inside the container 44 comprises gravel, pebbles, stones and/or other granular matter.

Referring now to Fig. 3, a zoomed-in view of a part the thermal storage plant 1 according to this disclosure is shown, where the solar energy system 4 is clearly shown. The solar energy units 43 are here installed as an array, forming different parallel columns. No solar energy unit 43 is installed directly above the draining system 3 or on the periphery 28 of the cover segment. Alternatively, a plurality of cover segments may comprise solar energy units 43 installed on the surface cover 2.

Figs 4 and 5 show different views of the solar energy units 43, here being solar panels, installed on the surface cover 2. The solar panels 43 are installed with a small tilting angle being approx.15 degrees. The solar panels are installed consecutively one behind the other, forming a line. The distance between the two solar panels is calculated such that the solar panels do not cast shadows onto one another. This distance majorly depends on the climate and location that the storage plant in installed in. The ballast material 42 is contained inside the container 44, which is here a plastic box. The container 44 has a trapezoid cross section and is positioned such that the angle of the inclined top surface of the container 44 matches the tilting angle of the installed solar panel 43. No attachments of the mounting system 41 on the surface cover 2 are provided. The ballast 42 can thus act as a stabilizing base preventing any wind lift of the system.

Although described only in reference to part of a thermal energy storage plant, the above may equally apply to the remaining thermal energy storage plant, surface cover and surface cover segments.

List of reference numerals

The following is a list of reference numerals used throughout this specification.

I Thermal energy storage plant

I I Liquid reservoir

12 Reservoir volume

13 Top side 14 Liquid level

15 Thermal energy storage liquid

2 Surface cover

2a First surface cover segment

2b Second surface cover segment

21a First tilting device

21 b Second tilting device

22a Draining surface of the first surface cover segment

22b Draining surface of the second surface cover segment

23 Insulating material

23h High density insulating layer

23I Low density insulating layer

24 Bottom liner

25 Top liner

26a First draining location

26b Second draining location

27 Vent

28 Circumferential periphery

3 Draining system

31 Well

32 Grating

33 Liquid extraction point

4 Solar energy system

41 Mounting system

42 Ballast (material)

43 Solar energy unit I solar panel

44 Container

H Height direction

L Length direction

W Width direction

Claims

C L A I M S

1. A thermal energy storage plant (1 ) for storing thermal energy from an energy source, the storage plant comprising: a liquid reservoir (11 ) for being coupled to an energy source and comprising a reservoir volume (12) with a top side (13), said top side (13) coinciding with a liquid level (14) of a thermal energy storage liquid (15) in the liquid reservoir (11 ), a surface cover (2) comprising an insulating material (23), such as extruded polystyrene or mineral wool, for retaining thermal energy stored in said liquid, said surface cover (2) at least partly covering said top side (13), said surface cover (2) being divided into at least a first and a second surface cover segment (2a; 2b) positioned adjacently to each other and each comprising a circumferential periphery, the first surface cover segment (2a) comprising a first tilting device (21 a), the second surface cover segment (2b) comprising a second tilting device (21 b), and a solar energy system (4) for harnessing solar energy, the solar energy system (4) comprising at least one photovoltaic cell and/or a flowing fluid configured to be heated by solar energy, the solar energy system (4) being installed on and/or in and/or at an exterior surface of the first surface cover segment (2a) and/or on and/or in and/or at an exterior surface of the second surface cover segment (2b), wherein a weight of the solar energy system (4) and/or a weight of the first tilting device (21 a) tilts a draining surface of the first surface cover segment (22a) from the circumferential periphery of the first surface cover segment (2a) downwards towards a first draining location of the first surface cover segment (2a), whereby water from precipitate falling on the first surface cover segment (2a) will flow by gravity towards the first draining location where it can be drained off from the first surface cover segment (2a), and wherein a weight of the solar energy system (4) and/or a weight of the second tilting device (21 b) tilts a draining surface of the second surface cover segment (2b) from the circumferential periphery of the second surface cover segment downwards towards a second draining location of the second surface cover segment (2b), whereby water from precipitate falling on the second surface cover segment (2b) will flow by gravity towards the second draining location where it can be drained off from the second surface cover segment (2b).

2. A thermal energy storage plant (1 ) according to claim 1 , wherein the solar energy system (4) comprises a mounting system (41 ) installed on an exterior surface of the surface cover (2), the solar energy system (4) being mounted on and/or in the mounting system (41 ), the mounting system (41 ) and/or the solar energy system (4) comprising a ballast material (42).

3. A thermal energy storage plant (1 ) according to claim 1 or 2, wherein the surface cover (2) is floating freely on the thermal energy storage liquid in the liquid reservoir (11 ).

4. A thermal energy storage plant (1 ) according to any one of the previous claims, wherein the solar energy system (4) is not anchored to the surface cover (2) or to the liquid reservoir (11 ) and/or wherein the solar energy system (4) comprises a mounting system (41 ) installed on an exterior surface of the surface cover (2), the solar energy system (4) being mounted on and/or in the mounting system (41 ), the mounting system (41 ) and/or the solar energy system comprising a ballast material (42), the mounting system (41 ) is not anchored to the surface cover (2) or to the liquid reservoir (11 ).

5. A thermal energy storage plant (1 ) according to any one of the previous claims, wherein the solar energy system (4) comprises a container (44) installed underneath and/or adjacent to the solar energy system (4), a ballast material (42) being positioned in the container (44) and/or wherein the solar energy system (4) comprises a mounting system (41 ) installed on an exterior surface of the surface cover (2), the solar energy system (4) being mounted on and/or in the mounting system (41 ), the mounting system (41 ) and/or the solar energy system (4) comprising a ballast material (42), the mounting system (41 ) comprises a container (44) installed underneath and/or adjacent to the solar energy system (4), the ballast material (42) being positioned in the container.

6. A thermal energy storage plant (1 ) according to any one of the previous claims, wherein the solar energy system (4) comprises at least one solar panel (43), the solar panel area preferably being equal to or smaller than 5 m².

7. A thermal energy storage plant (1 ) according to claim 6, wherein the solar panel (43) is installed with a tilting angle in the range of 0°-20° relative to a horizontal direction.

8. A thermal energy storage plant (1 ) according to any one of the previous claims, wherein the solar energy system (4) comprises a ballast material (42), the solar energy system (4) acting as a counter-weight to a wind load exerted on the solar energy system (4) and/or wherein the solar energy system (4) comprises a mounting system (41 ) installed on an exterior surface of the surface cover (2), the solar energy system (4) being mounted on and/or in the mounting system (41 ), the mounting system (41 ) comprising a ballast material (42), the mounting system (41 ) acting as a counter-weight to a wind load exerted on the solar energy system (4).

9. A thermal energy storage plant (1 ) according to any one of the previous claims, wherein a tilting device comprises the solar energy system (4) and the first or second tilting device (21 a; 21 b), the weight of the tilting device increasing from a respective circumferential periphery towards the respective draining location of the first and/or second surface cover segment (2a; 2b).

10. A thermal energy storage plant (1 ) according to any one of the previous claims, wherein the solar energy system (4) comprises a mounting system (41 ) installed on an exterior surface of the surface cover (2), the solar energy system (4) being mounted on and/or in the mounting system (41 ), the mounting system (41 ) and/or the solar energy system (4) comprising a ballast material (42), the ballast material (42) comprising gravel, pebbles, stones and/or other granular matter.

11. A thermal energy storage plant (1 ) according to any one of the previous claims, wherein the solar energy system (4) comprises a solar panel (43) and/or a solar thermal collector and/or a photovoltaic thermal collector.

12. A thermal energy storage plant (1 ) according to any one of the previous claims, wherein the solar energy system (4) comprises a mounting system (41 ) installed on an exterior surface of the surface cover (2), the solar energy system (4) being mounted on and/or in the mounting system (41 ), the mounting system (41 ) and/or the solar energy system (4) comprising a ballast material (42), the ballast material (42) comprising a concrete slab.

13. A thermal energy storage plant (1 ) according to any one of the previous claims, wherein the solar energy system (4) comprises a mounting system (41 ) installed on an exterior surface of the surface cover (2), the solar energy system (4) being mounted on and/or in the mounting system (41 ), the mounting system (41 ) and/or the solar energy system (4) comprising a ballast material (42), wherein the mounting system (41 ) comprises a metal structure, preferably steel structure, the solar energy system (4) being mounted on the metal structure.

14. A thermal energy storage plant (1 ) according to any one of the previous claims, wherein the first surface cover segment (2a) and/or the second surface cover segment (2b) comprise(s) a plurality of solar panels (43) installed on the surface cover segment.

15. A method of providing a thermal energy storage plant (1 ) for storing thermal energy from an energy source, the method comprising the steps of: providing a liquid reservoir (11 ) for being coupled to an energy source and comprising a reservoir volume (12) with a top side (13), said top side (13) coinciding with a liquid level (14) of a thermal energy storage liquid (15) in the liquid reservoir (11 ), providing a surface cover (2) comprising an insulating material, such as extruded polystyrene or mineral wool, for retaining thermal energy stored in said liquid, said surface cover (2) at least partly covering said top side (13), said surface cover (2) being divided into at least a first and a second surface cover segment (2a; 2b) positioned adjacently to each other and each comprising a circumferential periphery, providing a first tilting device (21 a) by the first surface cover segment (2a), providing a second tilting (21 b) device by the second surface cover segment (2b), and installing a solar energy system (4) for harnessing solar energy on and/or in and/or at an exterior surface of the first and/or the second surface cover segment (2a; 2b), the solar energy system (4) comprising at least one photovoltaic cell and/or a flowing fluid configured to be heated by solar energy.