NL2020743B1

NL2020743B1 - Process to generate and store energy

Info

Publication number: NL2020743B1
Application number: NL2020743A
Authority: NL
Inventors: Franciscus Alphonsus Verhaaren Alfred
Original assignee: Helena Sustainable Innovations B V
Priority date: 2017-04-13
Filing date: 2018-04-11
Publication date: 2021-10-13
Also published as: NL2020743A; NL2028471A

Abstract

The invention is directed to a process to generate and store energy comprising the following steps: (a) heating a starting working liquid by indirect heat exchange with waste heat, ambient air and/or by solar irradiation to obtain a heated working fluid, (b) increasing the temperature of a liquid storage medium to obtain heated liquid storage medium using a heat pump and using the heated working fluid obtained in step (a) as heat source of the heat pump, and (c) storing the heated liquid storage medium in a stratified thermal storage facility.

Description

PROCESS TO GENERATE AND STORE ENERGY The invention is directed to a process to generate energy and store energy in a stratified thermal storage. The invention is also directed to a stratified thermal storage.

Stratified thermal storage systems are known and for example described in CH594795, DE2729215, US2016370016, FR2465946 and FR2504099. In such systems, usually water is stored in a vertically extending zone of water and wherein the temperature of the water is relatively high in the upper end of the zone of water and decreases when the vertical distance to the upper end increases. DE2657244 describes a stratified thermal storage in a lake. A vertically extending zone of water is formed by a flexible plastic wall extending from a platform floating on the lake. Cold water from a lower region in the lake is pumped up and distributed on the surface of the platform where it is heated by the sun. The heated water is stored in the upper region of the stratified storage. In the winter relatively hot water is withdrawn from the upper region of the stratified storage and used to heat buildings. The present invention is directed to a process for generating and storing energy in a stratified thermal storage in a more efficient manner as compared to the known processes. This is achieved by the following process. Process to generate and store energy comprising the following steps: (a) heating a starting working liquid by indirect heat exchange with waste heat, ambient air and/or by solar irradiation to obtain a heated working fluid, {b) increasing the temperature of a liquid storage medium to obtain heated liquid storage medium using a heat pump and using the heated working fluid obtained in step (a) as heat source of the heat pump, and {c) storing the heated liquid storage medium in a stratified thermal storage facility.

Applicants have found that the process can very efficiently increase the temperature of the liquid storage medium by using a combination of a heat pump and indirect heat exchange with waste heat, ambient air and/or by solar irradiation. Further advantages will be discussed when describing the preferred embodiments below. In step {a} a starting working liquid is heated by indirect heat exchange with waste heat, ambient air and/or by solar irradiation to obtain a heated working fluid. Applicants found that even in the absence of direct solar irradiation a substantial heat exchange can take place against ambient air to obtain a heated working fluid which can be used in step {b). An even more heated working fluid may be obtained when the working fluid is heated by solar irradiation. Therefore, it is preferred to heat the working liquid by indirect heat exchange with ambient air and by solar irradiation. The working fluid may also be heated against waste heat. By waste heat is here meant any liquid or gaseous stream of an industrial process which has an elevated temperature. Examples are used cooling water of chemical process plants, refineries, power plants, waste incineration plants and datacentres. The working fluid flows in a closed system and is not in direct contact with the liquid storage medium of steps ({b} and {c). The skilled person will have no difficulty choosing a suitable working fluid depending on the temperature range at which the heat pump operates. Examples of suitable working fluids are water, aqueous mixtures, for example glycol/water mixtures. Suitable glycols are propylene glycol, ethylene glycol, bio-glycol and so-called solar glycol.

The heat exchange with ambient air and solar irradiation in step (a) is preferably performed in solar collectors. More preferably the process comprises a step {d) of generating electrical power in a photovoltaic cell. Preferably the starting working fluid of in step (a) is first used to cool the photovoltaic cell. These steps {a} and (d) are preferably performed in a so-called Photovoltaic thermal hybrid solar collectors, sometimes known as hybrid PV/T systems or PVT collectors. The PVT collectors may be of the insulated or non- insulated type. The collectors may be panels or have other designs. The electrical power generated in step (d) is at least in part used to drive the heat pump in step (b). This is advantageous because part of the electricity will then be converted to energy contained in the heated liquid storage medium. in this manner more of the total solar energy can be stored in step (c). The collectors may for example be directed in an east-west configuration directed to any direction or directed to the sun in a south configuration.

In a preferred embodiment the stratified storage facility is a floating platform having walls extending vertically into a body of water as will be described in more detail below. In case the above collectors are directed to the sun on such a floating platform it may be desirable to rotate the platform such that the collectors are continuously directed to the sun to achieve an optimal energy transfer. In case a group of stratified storage facilities are used it is preferred to rotate the entire group.

The starting working liquid may have a temperature ranging from -10 to 70 °C. In moderate climates such as in The Netherlands the starting working liquid may have a temperature of between -5 and 60 °C and the heated working fluid may have a temperature of between 10 and 90 °C, preferably between 20 and 70 °C and more preferably between 30 and 70 °C wherein the temperature of the heated working fluid is higher than the temperature of the starting working fluid. The temperatures here mentioned will be valid for the average local conditions and will depend on the type of heat source, namely the waste heat, ambient air and/or solar irradiation used in step (a). It is not excluded that for example in more extreme weather conditions these temperatures may temporally be outside these ranges.

The heat pump may be any known type of industrial heat pump suited to transfer energy from one fluid medium to another fluid medium. Examples are mechanical heat pumps, gas engine heat pumps, absorption heat pump, adsorption heat pump, transcritical CO) heat pump and the hybrid heat pump. Preferably a mechanical heat pump is used.

The liquid storage medium used in steps {b} and (c) may be every liquid suited for heat transfer processes. In view of the large volumes it is preferred to use water. To the water other liquids or additives may be added to improve its properties such as anti-algae antimicrobial additives, boiling point increasing additives and /or freeze point lowering additives. The liquid storage medium may be obtained from any source. Preferably the liquid storage medium used in step (b) is obtained from a vertically lower region of the stratified thermal storage facility of step (c). Alternatively, the liquid storage medium used in step (b) may also be obtained from outside the stratified thermal storage facility of step (c). For example, the liquid storage medium used in step {b) may be obtained from a different stratified thermal storage facility than the stratified storage facility of step {c) or from the body of water outside the stratified storage as will be described in more detail further below. The temperature of the heated liquid storage medium as obtained in step (b) may be between 30 and 90 °C. The stratified storage facility described for this invention may comprise of a vertically extending zone of water. Suitably the temperature of the liquid storage medium as present at the lower end of the stratified storage facility at the end of the loading cycle is more than 50 °C lower than the temperature of the liquid storage medium as present at the upper end of the stratified storage facility. This temperature difference will decrease at the stratified storage facility is unloaded by extracting thermal energy from the stratified storage facility.

Preferably the temperature difference in a single stratified storage facility between the upper end and its lower end is increased. This is advantageous because a more elevated temperature storage medium at the upper end is advantageous because energy can be extracted from it more efficiently for heating purposes. But also a colder storage medium at the lower end of the storage facility is advantageous because this cold can be efficiently used for directly or indirectly cooling uses. Such cooling uses may be for example district cooling systems to cool data centres, office buildings and/or houses. The temperature difference is preferably increased in the following manner, wherein the stratified storage facility of step (c) consist of three vertically neighbouring zones, an upper zone, an intermediate zone and a lower zone and wherein in a step (e) the temperature of liquid storage medium as extracted from the intermediate zone is increased in temperature to obtain a second heated storage medium. The increase in temperature is performed in a heat pump using liquid storage medium as extracted from the intermediate zone as heat source thereby producing a colder liquid storage medium leaving the heat pump. The second heated storage medium is supplied to the upper zone and the colder liquid storage medium is supplied to the lower zone. The size of the different zones can vary depending on the average temperature and temperature differences between the zones. In this manner energy is vertically moved from the lower half of the stratified thermal storage to the upper half of the stratified thermal storage. The heat pump used for this purpose may be a heat pump as described above. it is possible to combine these two heat pumps in a combined heat pump configuration.

5 In case a group of stratified storage facilities are interconnected it may be envisaged that the average temperature of the storage medium in one storage facility will be different from the average temperature of the storage medium in another interconnected storage facility. For example, when a group of storage facilities is provided as one or more concentric rings of storage facilities around one or more centrally positioned storage facilities the average temperature may be higher in the centrally positioned storage facilities as compared to the more outwardly positioned storage facilities. This will especially be the case when this group is positioned in a larger body of water having an even lower average temperature than the liquid storage medium in the respective storage facilities. In such a situation it may be advantageous to move energy from the outwardly positioned storage facilities to the more centrally positioned storage facilities in a comparable manner as the above described vertical movement of energy within one single storage facility. in such an embodiment, it may be advantageous to further increase the temperature difference between the outer positioned storage facilities and the central storage facility. Preferably this process is performed wherein the stratified storage facility of step {c} is part of a group of at least two storage facilities having a different average temperature of the storage medium contained in respective storage facility and wherein in a step (f) the temperature of liquid storage medium as extracted from the storage facility having the higher average temperature is increased in temperature to obtain a heated storage medium. The increase in temperature is performed in a heat pump using liquid storage medium as extracted from the storage facility having the lower average temperature as heat source thereby producing a second colder liquid storage medium leaving the heat pump. The heated storage medium is supplied to the storage facility having the higher temperature and the second colder liquid storage medium is supplied to the storage facility having the lower temperature. The liquid storage medium as extracted from the storage facility having the higher average temperature is extracted from a lower position in the storage facility and the obtained heated storage medium is supplied to the same storage facility at a position higher than the lower position in the storage facility having the higher temperature. The liquid storage medium as extracted from the storage facility having the lower average temperature is suitably extracted at a higher position and the second colder liquid storage medium is supplied to this storage facility at a position lower than this higher position. If there are more than one storage facilities having substantially the same lower or higher average temperature as described above one should understand that the above reference to one single storage facility may also include a reference to one of the other storage facilities having substantially the same average temperature of the liquid storage medium. For example if the group has concentric rings of storage facilities wherein each ring has about the same average lower temperature it may be envisaged that liquid storage medium is extracted from one storage facility in the ring and wherein the second colder liquid storage medium is supplied to another storage facility in the ring. A further source of heated liquid storage medium may be produced in an electrical boiler and may be stored in the stratified thermal storage facility of step (c). This may be advantageous in a situation wherein excess electrical power is available as generated by one or more wind turbines and/or by one or more photovoltaic cells. The energy stored in the stratified storage facility may be extracted at any convenient time and may be extracted in any conceivable manner. One manner to extract energy from the energy storage is to exchange this energy to a district heating medium, suitably water. In such a system hot water is distributed to a large number of households, office buildings, green houses and/or company buildings for heating uses. Preferably the energy of the heated liquid storage medium is converted to the district heating medium by means of a heat pump. The process therefore suitably further comprises a step {g} in which energy is extracted from the stratified thermal storage facility by using part of the heated liquid storage medium as heat source of a heat pump to increase the temperature of a district heating medium. The temperature of the heated liquid storage medium as extracted from the stratified thermal storage is suitably between 30 and 70 °C and the temperature of the heated district heating medium is suitably between 70 and 115 °C.

The electrical power as generated in the photovoltaic cell or cells may be added to the electrical grid. Preferably at least a part of the electrical power is used to drive the heat pump in step {e), {f) and/or (g). This is advantageous because part of the electricity will then be converted to thermal energy contained in the heated liquid storage medium or of a district heating medium, The energy contained in the stratified thermal storage facility may also be extracted to generate electricity. A suitable method of extracting thermal energy to generate electricity is by making use of the so-called Rankine Cycle. This may be a Rankine Cycle or an organic Rankine Cycle. In a Rankine Cycle a working fluid is pumped to a boiler where it is evaporated against a heat source, passed through a turbine to generate electricity and then through a condenser where the working fluid re-condensed such that it can be pumped. In the present process energy is suitably extracted as thermal energy to generate electricity from the stratified thermal storage facility by extracting heated liquid storage medium from the stratified storage facility and using this heated storage medium as heat source of a Rankine Cycle. The Rankine Cycle subsequently generates electricity. The heated storage medium is preferably extracted from the upper end of a stratified storage facility. When more than one interconnected storage facilities are present it is preferred to use the warmest storage medium available. This heated storage medium may be extracted from upper end of the most centrally positioned storage facility having the higher temperature storage medium.

Suitably storage medium having a temperature below the heated storage medium is extracted from a stratified storage facility and used as cooling medium in the condenser of the Rankine Cycle. This may be extracted from the same stratified storage facility or a different stratified storage facility or even from the body of water exterior of the one or more storage facilities. Preferably the temperature difference between the heated storage medium and the storage medium used in the condenser of the Rankine Cycle is as large as possible.

In a preferred embodiment the heated storage medium used as heat source in the Rankine Cycle is a high boiling fluid having a normal boiling point of more than 100 °C. Such a fluid may for example be glycerol or aqueous mixtures containing glycerol. The use of such a fluid allows storage of the fluid to a temperature between 50 and 175 C. The use of such a fluid is advantageous because the efficiency of the Rankine Cycle will be higher as compared to when the heated storage medium is water.

Such a process is preferably performed using at least two stratified storage facilities comprising different storage mediums.

For example one storage facility may comprise the above described high boiling fluid while the one or more other storage facilities comprise water as the storage medium.

In an even more preferred embodiment the stratified thermal storage facility comprising the above referred to high boiling point fluid is comprised within another stratified storage facility which comprises another storage medium, suitably a lower boiling point fluid, and preferably water as illustrated in Figures 4 and 5. In this embodiment it is preferred that a storage medium having a temperature below the heated storage medium is extracted from a different stratified storage facility than the storage facility comprising the high boiling fluid and used as cooling medium in the condenser of the Rankine Cycle.

Preferably the storage medium as used as cooling medium is water.

In a situation wherein the water comprising storage facility comprises the storage facility comprised with the high boiling fluid it is preferred that the storage medium is extracted from a lower position in the water comprising storage facility and the heated storage medium extracted from a higher position from the storage facility comprising the high boiling fluid.

At periods of surplus wind and solar power the second heat pump and electric boiler may be used to increase the temperature of the high boiling fluid to a temperature between 90 and 175 °C.

The second heat pump take the upper zone of the stratified storage as its heat source.

At periods of low wind and solar power and high demand for electricity a turbine generator of the Rankine Cycle generates electricity taking the high boiling fluid as it heat source and the lower part of the stratified water storage as its cooling medium.

The heat pump and Rankine Cycle can be combined by adding a four way valve to reverse the flow through a combined turbine-compressor and a liquid pump to increase pressure in the electricity generating mode as described in the International Journal of Refrigeration 54 (2015) 190-203. Also the cold liquid storage medium may be advantageously used.

As described above preferred embodiments of the invention are directed to further cool down the lower zones of the stratified thermal storage facility. it is especially this cold, for example having a temperature of between 5 and 15 °C which may be used. Suitably a district cooling system medium is lowered in temperature by indirect heat exchange against liquid storage medium as extracted from the stratified storage facility. This colder district cooling system may be connected to numerous household and/or office buildings. Alternatively, a cooling medium of a data centre may be reduced in temperature by indirect heat exchange against liquid storage medium as extracted from the stratified storage facility. After cooling of the data centre, for example by direct CPU cooling, the warmer cooling medium may be used in a similar manner as the working fluid in step (b) to increase the temperature of liquid storage medium, which can subsequently be stored in the stratified thermal storage facility as in step {c).

The process is suitably controlled by a control system that maximises the revenue of the generated and stored energy. For this purpose the control system is coupled directly to the energy exchange market such to receive up to date monetary values of the different types of energy. The control system calculates for the coming period based on actual and forecasted weather data the value of the generated and stored energy and compares this with the actual and forecasted value of energy produced by external sources such as wind and solar power and industrial waste heat. Based on these calculations the control system decides automatically on the operating mode. At actual and/or forecasted surplus power from external sources the heat pumps and electrical boiler will be set to maximise generation of energy for storing in the high temperatures stratified storage and stratified storage. At actual and/or forecasted low power during periods of little wind or solar energy and/or high demand from external sources, energy storage is supplying energy and/or thermal energy for generating electricity through the Rankine cycle as described. internal electric consumption may be minimised by increasing the COP of the heat pumps by setting the PVT collectors at a higher temperature.

The invention is also directed to a stratified thermal storage comprising of a roof positioned above or in a body of water wherein a wall extends downwards from the periphery of the roof such that a downwardly extending zone of water is defined, and means for extracting water at a first variable vertical position in the zone of water and a means for adding water at a more elevated second variable vertical position than the first vertical position and wherein both means are fluidly connected to a first heat pump. Such a stratified thermal storage is advantageous because it can increase the temperature of water extracted at a lower vertical position in the heat pump and add the obtained heated water to a higher position in the stratified storage facility.

The first heat pump is suitably further fluidly connected to one or more indirect heat exchangers which in use can heat a fluid to obtain a heat source using waste heat, ambient air and/or by solar irradiation. The heat source is used as heat source for the first heat pump to increase the temperature of the water as extracted by the means for extracting water at the first vertical position. Preferably the one or more heat exchangers are combined with photovoltaic cells. Even more preferably the earlier referred to Photovoltaic thermal hybrid solar collectors are used.

Preferably the stratified storage facility further comprises means for adding water at a third variable vertical position in the zone of water and a means for extracting water at a more elevated fourth variable vertical position than the third vertical position and wherein both means are fluidly connected to a second heat pump. This is advantageous because energy can now be extracted from the stratified storage facility by using relatively hot water as extracted from the storage at an elevated position as heat source in a heat pump. The second heat pump itself can for example be used to increase the temperature of a domestic heating medium or be combined with a Rankine Cycle to generate electricity. The second heat pump is thus suitably fluidly connected to a district heating system such that in use energy can be extracted from the stratified thermal storage to the district heating system.

In case the second heat pump is combined with a Rankine Cycle it may be preferred to use relatively cold water extracted from a lower region of the zone of water of the stratified thermal storage or from a different stratified thermal storage as cooling medium in the condenser of the Rankine Cycle.

Suitably the means for extracting water at a first variable vertical position in the zone of water are also fluidly connected to a heat exchanger of a cooling system for district cooling or datacentre cooling.

The means for adding water at the second variable position and at the optional third variable position is preferably one or more stratified lances. Stratified lances are vertically extending conduits in the zone of water having openings in its conduit wall at more than one openings at different elevations. In the stratified lance water having a certain temperature will flow upwards and exit the stratified lance at the position where the density and temperature of the water surrounding the stratified lance at that elevation and the density and temperature of the water in the lance are about the same. This enables one to add water to the stratified storage facility at the elevation in the zone of water having about the temperature of the water added to the storage. This is advantageous because it avoids that volumes of water having different densities move within the stratified storage and disturb the stratified temperature distribution. The stratified lance is connected to an inlet conduit which transports the water to the lower end of the stratified lance. The conduit may be a U shaped conduit having a downward directed inlet part, a U-bend at the lower end and an upward directed stratified lance part, Preferably this inlet conduit is a conduit within the stratified lance having an opening at its lower end and space away from the closed lower end of the stratified lance such that the water can change flow directions and flow upwards in the resulting annular space between stratified lance and inlet tube. The openings in the wall of the stratified lance are preferably provided with one way valves to prevent water from the zone of water to enter the stratified lance.

The means for extracting water are preferably vertically extending conduits in the zone of water which are provided with numerous inlet openings at different elevations. The openings can be opened and closed depending on where in the stratified storage water is to be extracted. The conduit may be provided with valves which can be opened and closed. The conduit can also be composed of an inner conduit with openings and an outer conduit with openings. The dimensions of the inner and outer conduit are such that no or substantially no water can flow in the space between the outer wall of the inner conduit and the inner wall of the outer conduit. The openings in both conduits are so positioned that when the inner and outer conduit are rotated or axially moved relative to each other coinciding openings at different elevations result. In this manner water can be extracted at different elevations from the zone of water.

The stratified thermal storage may further comprise an electrical boiler fluidly which is connected with the thermal storage such that in use heated water as produced in the boiler can be added to the upper end of the stratified thermal storage.

The lower end of the zone of water of the stratified thermal storage may be open to the remaining part of the body of water. To avoid the inflow of larger particles, like leaves and marine waste, a water permeable screen may be provided at the lower end of the zone of water. Preferably the lower end is closed to avoid for example seeds of mussels to enter the zone of water and to avoid possible bacteria and algae growing in the warmer water to enter the body of water.

The roof of the storage may be submerged. This is advantageous in a situation wherein the storage is placed in a recreational body of water. In this manner the water surface above the storage remains available for water sports and the like.

Preferably the roof is a platform positioned above the body of water. This allows that the one or more indirect heat exchangers may be positioned on the platform. The first and/or second heat pump may be positioned on the platform or elsewhere, for example on shore. The first and second heat pump may be integrated. Preferably the platform floats on the body of water. This is advantageous because it enables that the stratified thermal storage can be built at one location and transported over water to its final destination. Furthermore the platform can be easily rotated such that the collectors can follow the sun during its daily cycle.

The wall extending from the roof may be made of one or more layers of a flexible material such as neoprene. The wall suitably will have some insulating properties. To achieve such insulating properties more than one flexible wall may extend from the roof. Preferably the outer wall extends towards the lower end of the stratified storage system and the one or more inner walls are shorter. In this manner the warmer layers of water at the upper region of the zone of water are better insulated as compared to the lower positioned colder layers.

The wall may also be comprised of one or more structural parts. Such parts may be metal constructions or more preferably concrete structural parts. For example applicant found that floor plates of the hollow core concrete slabs type are very suited to be used as wall for the stratified thermal storage system. These floor plates have good insulating properties because of the hollow core. Preferably the hollow core is filled with a closed cell foam as insulating material. To lower the buoyancy of the resulting system the lower end of the hollow core may be filled with a heavier material than the insulating material. Examples of such heavier material is concrete, sand and/or metals. To create a substantially water impermeable wall the floor plates may be connected at their longitudinal end by means of locking means and rubber seals. Optionally at the upper end of the wall may be provided with one or more inner walls of such floor plates to provide a better insulation for the warmer layers of water.

Preferably the platform has a design which enables a continuous surface when seen from above when the stratified storage system is combined with one or more of such neighbouring stratified storage system. By continuous surface is here meant that no substantial openings result between the stratified storage systems showing the body of water as seen from above. In this manner the exterior of the walls of the neighbouring stratified storage systems will align. Examples of suitable shapes for the platform are the triangular shape, a rectangular shape, a pentagonal shape or a hexagonal shape when seen from above. Preferably the platform has a rectangular or hexagonal shape.

The invention is also directed to a group of more than 6 interconnected stratified storage systems as described above. The advantage of such a group is that the total storage capacity increases. Furthermore such a group provides the possibility to extract thermal energy from the inner and outer positioned storage systems and heat and cool water further using a heat pump, wherein the heated water can be supplied to a more central positioned storage system and the cooled water can be supplied to the more outward positioned storage systems as also described above. Examples of such a group may be 19 hexagonal shaped stratified storage systems composed of one central storage system, an inner ring of 6 storage systems and a second ring of 12 storage systems. A group with a next ring of 18 storage systems is also conceivable totalling the number of storage systems in such a group to 37. Preferably the group further includes one or more stratified storage facilities as described below. Such facilities are preferably positioned in the centre of the group such that the highest average temperatures can be achieved in such a storage facility.

The invention is also directed to a stratified thermal storage comprising of a roof positioned above or in a body of water wherein a wall extends downwards from the periphery of the roof such that a downwardly extending zone of water is defined. The zone of water comprises a second separate zone comprising a high boiling fluid having a higher boiling point than water. The facility further comprises means for extracting water at a first variable vertical position in the zone of water and a means for adding water at a lower variable vertical position than the first vertical position. The means for extracting water at a first variable vertical position and the means for adding water are fluidly connected to the inlet and outlet of the evaporator of a heat pump. The storage facility further comprises means for extracting high boiling fluid at a second variable vertical position in the second zone and a means for adding high boiling fluid at a higher variable vertical position than the second vertical position in the second zone. The means of extracting high boiling fluid and the means for adding high boiling fluid are fluidly connected to the inlet and outlet of the condenser of the heat pump. Preferably an electrical boiler is present in the second zone. This boiler may further heat the high boiling liquid in a situation wherein excess electrical power is available as generated by one or more wind turbines and/or by one or more photovoltaic cells. The stratified storage facility comprising water may be a facility as described before in this description. The high boiling fluid may be as described before. The presence of the second zone with the high boiling fluid as described above enables one to more effectively extract thermal energy to generate electricity from the combined storage facility. The above described heat pump moves energy from the water zone to the second zone. The energy can be effectively extracted as thermal energy to generate electrical energy by combining this storage facility with a Rankine Cycle as described below. The stratified thermal storage further comprising means for extracting water at a third variable vertical position in the zone of water and a means for adding water at a higher variable vertical position than the first vertical position. The means for extracting water at a third variable vertical position and the means for adding water are fluidly connected to the inlet and outlet of the condenser of a Rankine Cycle. The storage further has means for extracting high boiling fluid at a fourth variable vertical position in the second zone and a means for adding high boiling fluid at a lower variable vertical position than the fourth vertical position in the second zone. The means of extracting high boiling fluid and the means for adding high boiling fluid are fluidly connected to the inlet and outlet of the evaporator of the Rankine Cycle. This configuration allows an efficient extraction of the stored energy to generate electricity. The invention shall be illustrated by the following non-limiting Figures.

Figure 1 shows a stratified thermal storage 1 containing water as the liquid storage medium, a heat pump 2 and a photovoltaic thermal hybrid solar collector (PVT) panel 3. The stratified thermal storage is not drawn to scale. The storage 1 can have a height of 5-30 meters, while the PVT panel 3 can have a height of 1.6 — 4 meters. The temperatures here listed are for illustration purposes only. In PVT panel 3 a working liquid having a temperature of 10 °C as supplied via stream 4 is heated by indirect heat exchange with ambient air 5 and by solar irradiation 6 to obtain a heated working fluid having a temperature of 20 °C as discharged via stream 7. In the PVT panel 3 also electricity is generated which is discharged as current 8 to the power grid and heat pump 2. The heated working fluid in stream 7 is used as heat source to run heat pump 2. In heat pump 2 a stream 10 of water is increased in temperature from 20 °C to 50 °C in stream 11. The heated water in stream 11 is stored in the upper part 12 of the stratified thermal storage 1. The water in stream 10 is extracted from the lower part 13 of the stratified storage 1. The heat pump 2 comprises a compressor 9, an expansion valve 14, a condenser 15 and an evaporator 16. The circulating working fluid of the heat pump 2 may be 1,1,1,2- tetrafluorethaan {also known as R134a).

In Figure 2 the stratified thermal storage facility 1 is shown wherein three neighbouring zones are defined, an upper zone 20, an intermediate zone 21 and a lower zone 22. The zones together form one continuous body of water. The temperature of water as extracted via stream 23 from the intermediate zone 21 is increased in temperature in a heat pump 24 to obtain heated water in stream 25. In heat pump 24 water as extracted via stream 26 from the intermediate zone 21 is used as heat source. The used heat source is discharged from the heat pump as colder water in stream 27. The heated water in stream 25 is supplied to the upper zone 20 and the water in stream 27 is supplied to the lower zone

22. Figure 2 also shows how electrical power may be stored as thermal energy in the stratified thermal storage facility 1. Electrical power may be excess electrical power from a wind turbine park 28 as supplied to an electrical boiler 29 via lines 30. Electrical boiler 29 may be positioned in the upper zone 20 of the stratified thermal storage facility 1 as shown or positioned outside said storage facility. In Figure 3 shows the stratified thermal storage facility 1. Energy is extracted from the stratified thermal storage facility 1 by using part of the heated water having a temperature of between 40 and 70 °C as extracted via stream 31 as heat source of a heat pump 30 to increase the temperature of water of a district heating in stream 32 having a temperature of about 60 C to water having a temperature of about 70 to 115 °C in stream 33. The used heat source is added via stream 34 to the stratified thermal storage 1 at a lower elevation where the temperature of the water in the thermal storage 1 is about the same as the temperature of the water in stream 34. The working fluid of heat pump 30 may be for example CO; or NH3. Figure 4 shows a stratified thermal storage facility 1a having a downwardly extending zone 36 of water. Storage facility 1a may be positioned in a larger body of water and may also be part of a group of storage facilities including storage facilities as shown in Figures 1-

3. The zone 36 of water comprises a second separate zone 35 comprising a high boiling fluid having a higher boiling point than water. The facility 1a further comprises an outlet 26a for extracting water at a first variable vertical position in the zone 36 of water connected to the inlet of the evaporator 37 of heat pump 24a. The outlet of evaporator 37 is connected to an inlet 27a for adding water at a lower variable vertical position than the first vertical position. The storage facility 1a further has an outlet 23a for extracting high boiling fluid at a second variable vertical position in the second zone 35 connected to the inlet of a condenser 39 of heat pump 24a. The outlet of condenser 39 is connected to an inlet 25a for adding high boiling fluid at a higher variable vertical position than the second vertical position in the second zone 35. The scheme of Figure 4 enables one to move energy from the lower temperature zone 36 to the second zone 35 using heat pump 24a. An electrical boiler 29a is present in the second zone 35. This boiler 29a may further heat the high boiling liquid in a situation wherein excess electrical power is available as generated by one or more wind turbines 28 and/or by one or more photovoltaic cells.

Figure 5 shows the stratified storage facility 1a of Figure 4 in combination with a Rankine Cycle 400. In the Rankine Cycle a working fluid is pumped in stream 401 to a evaporator 402 where it is evaporated against heated high boiling fluid as extracting via stream 403 at a fourth variable vertical position in the second zone 35. The evaporated working fluid is passed through a turbine 404 to generate electricity 405 and then through a condenser 406 where the working fluid re-condensed such that it can be pumped in pump

407. The high boiling fluid leaving the evaporator 402 is added to the zone 35 via stream

408. Cooling in the condenser is achieved by extracting cold water from zone 36 via stream 409 and adding the used water leaving condenser 406 via stream 410 back to zone 36 at a higher position.

The heat pump and Rankine Cycle which may be used in combination with the stratified storage facility of Figures 1-3 and especially Figures 4 and 5 may also be combined as shown in Figure 6. Such a reversible heat pump/Rankine cycle 500 is provided with a evaporator 501, condenser 502, pump 503, expansion valve 504 and a compressor- expander 505 connected by conduits 506 through which a working fluid may flow. Depending on the position of the four-way valve 507 working fluid is expanded in compressor-expander 505 or compressed in compressor-expander 505. In this manner configuration 500 can alternatingly act as heat pump and as Rankine cycle.

Figure 7 shows a stratified thermal storage 40 according to the invention provided with a platform 41 as roof. The storage 40 is not drawn to scale. The platform is positioned above a body of water 42. A wall 43 extends downwards from the periphery of the platform

41 such that a downwardly extending zone of water 44 is defined. On top of the platform 41 numerous PVT panels 49 are positioned in an east-west configuration. Vertically extending conduits 45, 46 in the zone of water 44 are present which conduits are provided with numerous inlet openings at different elevations. Conduit 45 is the means for extracting water at a first variable vertical position 50 in the zone of water 44. Further shown are two stratified lances 47, 48 for adding water to the zone of water 44. Stratified lance 47 is the means for adding water at a more elevated second variable vertical position 51. PVT panels 49, conduit 45 and stratified lance 47 are connected to a first heat pump (not shown) as illustrated in Figure 1. Inlet conduit 46, stratified lance 48 may be connected to the second heat pump (not shown) as shown in Figure 3. Stratified lance 48 is the means for adding water at a third variable vertical position 52 in the zone of water 44 and inlet conduit 46 is the means for extracting water at a more elevated fourth variable vertical position 53 than the third vertical position 52 and wherein both means are fluidly connected to a second heat pump (not shown). A enclosed compartment (35a) may act as a second zone wherein a high boiling point fluid is comprised as also shown in Figures 4 and 5. The figure does not show the means to extract and add medium to this compartment.

Figure 8 shows the stratified thermal storage 40 of figure 7 wherein the stratified lance 48 is described in more detail. The stratified lance 48 is connected to an inlet tube 55 which transports the water to the lower end 56 of the stratified lance 48. This inlet tube 55 is a conduit within the stratified lance 48 having an opening 58 at its lower end and space away from the closed lower end 56 of the stratified lance 48 such that the water can change flow directions and flow upwards in the resulting annular space 49 between stratified lance 48 and inlet tube 55. The wall of the stratified lance 48 is provided with openings 57 which are vertically spaced away from each other. Water flowing upwards through annular space 49 will exit this space at an elevation at which the temperature and/or static pressure of the zone of water 44 is substantially the same as the water flowing through the annular space

49.

In Figure 8a an alternative stratified lance 59 is shown in which the openings 60 in the wall of the stratified lance 59 are provided with one way valves 61 to prevent water from the zone of water 44 to enter the stratified lance and only to leave at the position 62 where temperature of the water in the annular space 63 is substantially the same as the temperature of the zone of water 44. The lance is also provided with an inner tube 64. Figure 9 shows, as seen from above, how a group 70 of floating and interconnected stratified storage systems 71 according to the invention can be linked. A separate floating stratified storage system 72 is shown having a platform 73 (not shown) which has a hexagonal shape. The system 72 has periphery sections with vertically downward extending walls 74 which are connected at the 6 respective corner sections 75. Two periphery sections 76 and 77 are temporally periphery sections with no vertically downward extending wall sections because they will be removed when the storage system 72 is linked with group 70. The structural integrity of the system 72 is provided by three tension cables 78. Group 70 has one storage facility provided with a platform 79. Figure 10a-c shows a possible wall for the stratified storage facility. Figure 10a shows a group of three hollow core concrete slabs type floor plates 80 as seen from above. Each floor plate 80 is provided with a series of parallel orientated hollow cores 81. The separate floor plates are connected by means of locking means 82 and rubber strips 83 to form for example a rectangle or hexagonal shape when seen from above. A single floor plate 84 of an inner wall is shown. Floor plate 84 will be connected to other floor plates to align with the outer wall. Figure 10b shows how three floor plates 80 are connected in a corner section 85 when two stratified storage facilities are combined. Figure 10c shows part of the wall as seen from aside. The hollow cores 81 in the upper part 86 are filled with a closed cell foam as insulating material. The hollow core 81 at the lower end 87 is filled with concrete to lower the buoyancy of the resulting system.

Figure 11 shows the upper end of a group 90 of stratified storage facilities 91 each having a hexagonal shape. The group 90 is centred around a central storage facility 92. Three concentric rings 93, 94 and 95 of stratified storage facilities 91 are positioned around central storage facility 92. Only the upper surface 96 of a body of water is shown. The average temperature of the central storage facility 92 and in the concentric rings 93, 94 and 95 and of the body of water is listed in the Figure. Such a group 90 may be advantageously used to increase the temperature of the central storage facility 92 and decrease the temperature of the water in the storage facilities of ring 95. This may be achieved by extracting water ring 94 or 95 in a heat pump using water as extracted from ring 93 or 94 as heat source thereby producing colder water which is supplied to the lower layers of ring 94 or 95 and heated water which is extracted from lower layers of ring 92 or 93 and supplied to higher layers of central storage facility 92. The invention will be further illustrated by the following example.

A lake near a city of about 125.000 inhabitants and 55.000 houses in the Netherlands climate is provided with a hexagonal shape stratified storage facility according to the present invention having a diameter of 60 m and a depth or vertical wall length of 20 m has an area of 2338 m2 and a volume of 46765 m3. One m3 of water can store 4.2 MJ per °K assuming an average DeltaT of 30 °K (55 °C - 25 °C) varying between 20 °K and 70 °K This amount of energy is equivalent to 0.126 GJ/m3. The energy consumption of an average house in the Netherlands is approximately 1500 m3 natural gas (36 GJ) per year and 3500 KWh electricity.

It is expected that about 300 m3 gas (10.8 GJ) per house needs to be stored seasonally to overcome periods of low renewable energy supply from solar and wind energy in the winter period.

So one house requires approximately 86 m3 storage.

This would result in that this storage facility could provide the energy of 546 houses.

PVT collectors on top of the floating storage facility produce approximately 700 KWh (2.5 GJ) per m2 per annum of thermal energy from sun irradiation and from convection with air.

To elevate the temperature of a 20 meter water column an average of 30 degree C requires also 2.5 GJ (= 20 * 0.126 GJ). By combining the PVT solar energy facility with a heat pump according to this invention it is possible to generate the required energy for storage in this storage facility.

However, for maintenance and inspection reasons the area available for PVT collectors is 15 % less than the total gross the top surface area.

The energy loss in the storage facility (60 m diameter, 20 m depth) is further approximately 5 % and the he energy loss in the district heating system is approx. 15 %. So in total 35% energy loss has to be compensated from other energy sources.

This energy could be provided by the heat pumps using the water of the body of water surrounding the storage facility. In this manner the energy collected by this body in the summer period can be used as an additional energy source. These heat pumps could be operated at peak availability of renewable energy during sunny and/or windy periods using the surplus energy or alternatively at night when the PVT collectors require less heat pump capacity. These heat pumps and in particular an optional electrical boiler could help to stabilise the grid at sunny and windy days. With an optional Rankine cycle electricity could be generated from thermal energy stored in the storage facility at times of low supply of energy from wind turbines and photovoltaic cells and/or high demand for electricity.

The application and capacity of the heat pumps to boost the temperature for injection in the city district heating system depends on the required temperature. The temperature setting for a local district heating could be set at a lower temperature for well insulated houses with low temperature heating facilities. The storage facility can be flexible arranged to cover relative low as well as high supply temperatures required for district heating depending on the climatic conditions at the time.

The PVT collectors generate also electrical energy. The energy produced by the PVT collectors is approx. 170 KWh per m2 per annum. The storage facility (60m diameter, 20 m depth, 2238 m2 gross surface area, 46765 m3 volume) will produce approximately 340.000 KWh. Based on a net PVT area of ca. 2000 m2. This energy is equivalent to 600 KWh per house for the 556 houses serviced by this module. This energy produced by the PVT collectors is however used for a large part to drive the heat pumps.

For the 55.000 houses of this city 101 modules { 60m diameter, 20 m depth) would be required covering an area of 22 ha.

Claims

CONCLUSIONS

A method of generating and storing energy, comprising the steps of: a. heating an initial working fluid by means of an indirect heat exchange with waste heat, ambient air, and/or by means of solar radiation, to form a heated working fluid to obtain, b. raising the temperature of a liquid storage medium to obtain a heated liquid storage medium by using a heat pump and by using the heated operating fluid obtained in step (a) as a heat source for the heat pump , and c. storing the heated liquid storage medium in a stratified thermal storage facility.

The method of claim 1, further comprising a step (d) of generating electrical power using a photovoltaic cell, and wherein the initial operating fluid from step (a) is first used to cool the photovoltaic cell,

A method according to claim 2, wherein the electrical power generated in step (d) is used at least in part to drive the heat pump in step (b).

A method according to any one of claims 1 to 3, wherein in step (a) the operating fluid is heated by indirect heat exchange with ambient air and by using solar radiation.

A method according to any one of claims 1 to 4, wherein the initial operating fluid has a temperature comprised between -5°C and 60°C, and wherein the heated operating fluid has a temperature ranging is between 20°C and 70°C, and wherein the temperature of the heated working fluid is higher than the temperature of the initial working fluid.

A method according to any one of claims 1 to 5, wherein the temperature of the heated liquid storage medium obtained in step (b) is between 30°C and 90°C.

A method according to any one of claims 1 to 6, wherein the liquid storage medium used in step (b) is obtained from a vertically lower zone of the stratified thermal from step (c).

The method of any one of claims 1 to 6, wherein the liquid storage medium used in step (b) comes from outside the stratified thermal storage facility of step (c).

The method of claim 8, wherein the liquid storage medium used in step (b) is obtained from a stratified thermal storage facility which is not the same as the stratified storage facility of step (c).

10. A method according to any one of claims | through 9, wherein the temperature of the liquid storage medium contained in the lower end of the stratified storage facility of step (c) is more than 50°C lower than the temperature of the liquid storage medium contained in the upper end of the stratified storage facility.

The method of any one of claims 1 to 10, wherein the stratified storage facility of step (c) consists of three vertically adjacent zones, namely an upper zone, an intermediate zone, and a lower zone, and wherein in a step (e) increasing the temperature of liquid storage medium as extracted from the intermediate zone so as to obtain a second heated storage medium, the increase in temperature being realized by means of a heat pump using liquid storage medium such as that as a heat source is extracted from the intermediate zone, producing a colder liquid storage medium exiting the heat pump, and the second heated storage medium is supplied to the upper zone, while the cold liquid storage medium is supplied to the lower zone.

A method according to any one of claims 1 to 11, wherein the stratified storage facility in step (c) is part of a group of at least two storage facilities that have a different average temperature of the storage medium as present in the respective storage facilities, and wherein in a step (f) the temperature of liquid storage medium as extracted from the storage facility having the higher average temperature is increased to arrive at a heated storage medium, the increase in temperature is realized by means of a heat pump that uses as heat source liquid storage medium as extracted from the storage facility possessing the lower average temperature, so as to arrive at a second colder liquid storage medium exiting the heat pump, and where the heated storage medium is delivered to the storage facility holding the higher temperature while the second colder liquid storage medium is delivered to the storage facility possessing the lower temperature.

A method according to any one of claims 1 to 12, further comprising a step (g) of extracting energy from the stratified thermal storage facility by using a portion of the heated liquid storage medium as a heat source for a heat pump to adjust the temperature. of a district heating heating medium.

The method of claim 13, wherein the temperature of the heated liquid storage medium as extracted from the stratified thermal storage is between 30°C and 70°C, and wherein the temperature of the heated district heating medium is between 70°C. and 115°C.

15. A method according to any one of claims | through 14, wherein energy is extracted from the stratified thermal storage facility in the form of electricity by extracting heated liquid storage medium from the stratified storage facility, and using this heated storage medium as a heat source for a Rankine cycle, and wherein the Rankine cycle generates electricity.

The method of claim 15, wherein the storage medium having a temperature lower than that of the heated storage medium is extracted from a stratified storage facility, and used as a cooling medium in the condenser of the Rankine cycle.

The method of claim 15 or claim 16, wherein the heated storage medium is a fluid having a normal boiling point greater than 100°C.

The method of claim 17, wherein a storage medium having a temperature lower than that of the heated storage medium is extracted from a different stratified storage facility, and used as a cooling medium in the condenser of the Rankine cycle.

The method of claim 18, wherein the storage medium used as the cooling medium is water.

The method of any one of claims 1 to 19, wherein the temperature of a district heating cooling system medium is reduced by indirect heat exchange with liquid storage medium as extracted from the stratified storage facility.

A method according to any one of claims 11 to 20, wherein the method further comprises a step of generating electrical power in a photovoltaic cell, and wherein the generated electrical power is used at least in part to operate the heat pump in step (e) , (f), and/or (g).

The method of any one of claims 1 to 21, wherein an additional source of heated liquid storage medium is produced in an electric boiler, and wherein this heated liquid storage medium as produced is stored in the stratified thermal storage facility of step (c). ).

A method according to claim 22, wherein the electric boiler consumes electrical power generated by one or more wind turbines and/or by one or more photovoltaic cells.

A method according to any one of claims 1 to 23, wherein the stratified thermal storage facility or stratified thermal storage facilities comprises a roof positioned over or in a body of water, a wall extending downwardly from the perimeter of the roof in such a manner defining a downwardly extending zone of water, means for extracting water in a first variable vertical position in the zone of water, and means for adding water in an upper second variable vertical position which is above the first vertical position and wherein both means are in fluid communication with the heat pump, hereinafter referred to as the first heat pump.

The method of claim 24, wherein the stratified thermal storage facility further comprises means for adding water in a third variable vertical position in the zone of water, and means for extracting water in an upper fourth variable vertical position above the third vertical position, and wherein both means are in fluid communication with a second heat pump.

A method according to claim 24 or claim 25, wherein the means for adding water in the second variable position and in the optional third variable position are one or more stratified lances.

A method according to any one of claims 24 to 26, wherein the lower end of the zone of water of the stratified thermal storage facility or stratified thermal storage facilities is closed.

The method of any one of claims 24 to 27, wherein the roof of the stratified thermal storage facility or stratified thermal storage facilities is submerged.

The method of any one of claims 24 to 27, wherein the roof of the stratified thermal storage facility or stratified thermal storage facilities is a platform positioned above the body of water, and wherein one or more indirect heat exchangers are positioned on the platform for performing of the indirect heat exchange in step (a).

The method of claim 29, wherein the platform of the stratified thermal storage facility or stratified thermal storage facilities floats on the body of water.

The method of any one of claims 24-30, wherein the platform of the stratified storage facility has a design that allows for a continuous surface when viewed from above when the stratified storage facility is combined with one or more such in the said stratified storage facility. nearby stratified storage facilities.

The method of claim 31, wherein the platform of the stratified storage facility has a triangular shape, a rectangular shape, a pentagonal shape, or a hexagonal shape when viewed from above.

The method of claim 32, wherein the platform of the stratified storage facility has a rectangular or hexagonal shape.

The method of claim 9 and any one of claims 31-33, wherein the different stratified thermal storage facilities are part of a group of multiple stratified thermal storage facilities each comprising a platform having a triangular shape, a rectangular shape, a pentagonal shape, and/ or have a hexagonal shape when viewed from above and wherein the various stratified thermal storage facilities of the group are combined to result in a common continuous surface of platforms.

A method according to claim 12 and any one of claims 31-33, wherein the different stratified thermal storage facilities are part of a group of multiple stratified thermal storage facilities each comprising a platform having a triangular shape, a rectangular shape, a pentagonal shape, or a hexagonal shape, viewed from above, and combining the group's various stratified thermal storage facilities to result in a common continuous surface of platforms.

The method of any of claims 34 or 35, wherein the group of multiple stratified thermal storage facilities consists of stratified thermal storage facilities with a hexagonal platform positioned in one or more rings around a centrally located stratified thermal storage facility with a hexagonal platform wherein the average temperature of the storage medium as it is present in the middle storage facility is higher than the average temperature of the storage facilities in the ring positioned around it.

A method according to any one of claims 1 to 36, controlled by a control system that maximizes the yield of the generated and stored energy by using updated monetary values of the different types of energy, such as those obtained by direct coupling from of the control system with the energy market.

38. Stratified thermal store (1,40), comprising a roof (41) positioned over or in a body of water (42), a wall (43) extending downwardly from the perimeter of the roof (41), on such that a downwardly extending zone of water (44) is defined, means (45) for extracting water in a first variable vertical position (50) in the zone of water (44), and means (47) for extracting water in a higher located second variable vertical position (51) located above the first vertical position (50), and wherein both means (45,47) are in fluid communication with a first heat pump (2,24).

The static thermal storage of claim 38, further comprising means (48) for adding water in a third variable vertical position (52) in the zone of water (44), and means (46) for extracting water in a upper fourth variable vertical position (53) located above the third vertical position (52), and wherein both means are in fluid communication with a second heat pump (30).

A stratified thermal store according to claim 38 or claim 39, wherein the means (47,48) for adding water in the second variable position and in the optional third variable position are one or more stratified lances.

Stratified thermal storage according to any one of claims 38 to 40, wherein the lower end of the zone of water (44) is closed.

The filtered thermal storage according to any one of claims 38 to 41, wherein the first heat pump (2,24) is additionally in fluid communication with one or more indirect heat exchangers (3,49) which, in use, can heat a fluid to to obtain a heat source, by using ambient air and/or using solar radiation, the heat source being used as the heat source for the first heat pump (2,24) to raise the temperature of the water as extracted by the means (45) for extracting water in the first vertical position (50).

The stratified thermal storage of claim 42, wherein the one or more heat exchangers (3,49) are combined with photovoltaic cells.

A stratified thermal store according to any one of claims 39 to 43, wherein the second heat pump (30) is in fluid communication with a district heating system (32,33) so that, during its use, energy can be extracted from the stratified thermal store. (40) and can be sent to the district heating system (33).

Stratified thermal storage according to any one of claims 38 to 44, wherein the means (45) for extracting water in a first variable vertical position (50) in the zone of water (44) is also in fluid communication with a heat exchanger of a cooling system for district heating or for cooling data centers.

The stratified thermal storage of any one of claims 38 to 41, wherein means (46) for extracting relatively warmer storage medium from the upper end of the zone of water (44) is in fluid communication (403) with the inlet of the said water. evaporator (402) of a Rankine cycle (400).

Stratified thermal store according to any one of claims 38 to 46, further comprising an electric boiler (29) in floidum communication with the thermal store (1) so that, during its use, heated water such as that generated by the boiler (29 ) is produced can be added to the upper end (20) of the stratified thermal store (1).

A drained thermal store according to any one of claims 38 to 47, wherein the roof (41) of the thermal store (40) is submerged.

A stratified thermal store according to any one of claims 42 to 47, wherein the roof (41) is a platform positioned above the body of water (42), and wherein the one or more indirect heat exchangers (49) are positioned on the platform .

The stratified thermal storage of claim 49, wherein the platform floats on the body of water (42).

A stratified thermal storage as claimed in claim 49 or claim 50, wherein the platform has a design that allows for a continuous surface when viewed from above when the stratified thermal storage is combined with one or more such adjacent ones. stratified thermal stores.

The stratified thermal storage of claim 51, wherein the platform has a triangular shape, a rectangular shape, a pentagonal shape, or a hexagonal shape when viewed from above.

The stratified thermal storage of claim 52, wherein the platform (72) has a rectangular or hexagonal shape.

54. Static thermal storage according to any one of claims 38-53, wherein the downwardly extending wall (43) consists of hollow-core slab floor parts (80) connected to each other.

Stratified thermal storage according to claim 54, wherein the upper portion (86) of the hollow channels (81) of the hollow-core slabs (80) are filled with closed cell foam and the lower portion of the hollow channels (81) of the hollow-core slabs floor parts (80) are filled with closed cell foam. (80) be filled with a high density material to decrease the buoyancy of the wall (43).

56. Stratified thermal store (1a), comprising a roof (41) positioned above or in a body of water (42), a wall (43) extending downwardly from the perimeter of the roof (41), in such a manner defining a downwardly extending zone of water (36,44), said zone of water (36,44) comprising a second discrete zone (35,35a) comprising a high-boiling fluid having a boiling point higher than that of water, means (264) for extracting water in a first variable vertical position in the zone of water (36,44), and means (27a) for adding water to the zone of water (36,44) in a variable vertical position which is lower than the first vertical position, wherein the means (26a) for extracting water in a first variable vertical position and the means (27a) for adding water are in fluid communication with the inlet and with the outlet of the evaporator (37) of a heat pump (24a), m means (23a) for extracting high boiling fluid in a second variable vertical position in the second zone (35,35a), and means (25a) for adding high boiling fluid in a variable vertical position higher than the second vertical position in the second zone (35,35a), and wherein the means (23a) for extracting high boiling fluid and the means for adding high boiling fluid (26a) are in fluid communication with the inlet and outlet of the condenser (39) of the heat pump (24a).

The stratified thermal storage of claim 56, further comprising means (409) for extracting water in a third variable vertical position in the zone of water (36,44), and means (403) for adding water in a higher located variable vertical position than the first vertical position in the zone of water (36,44), the means (409) for extracting water in a third variable vertical position, and the means (403) for adding water in fluid communication with the inlet and outlet of the condenser (406) of a Rankine cycle (400), means (403) for extracting high boiling fluid in a fourth variable vertical position in the second zone (35,35a), and means (408) for adding high-boiling fluid in a variable vertical position lower than the fourth vertical position in the second zone (35,35a), and wherein the means (403) for extracting high-boiling tluidum and the means (408) for the addition of high boiling fluid are in fluid communication with the inlet and outlet of the evaporator (402) of the Rankine cycle (400).

A stratified thermal store according to claim 56 or claim 57, wherein the means (27a) for adding water comprises stratified lances.

A drained thermal store according to any one of claims 56 to 57, wherein the roof (41) of the thermal store (40) is submerged.

A stratified thermal store according to any one of claims 56 to 57, wherein the roof (41) is a platform positioned above the body of water (42}, and wherein the one or more indirect heat exchangers (49) are positioned on the platform .

The stratified thermal storage of claim 60, wherein the platform floats on the body of water (42).

A stratified thermal store according to claim 56 or claim 61, wherein the platform has a design that allows for a continuous surface when viewed from above when the stratified thermal store is combined with one or more such adjacent ones. stratified thermal stores.

The stratified thermal storage of claim 62, wherein the platform has a triangular shape, a rectangular shape, a pentagonal shape, or a hexagonal shape when viewed from above.

The stratified thermal storage of claim 63, wherein the platform (72) has a rectangular or hexagonal shape.

Stratified thermal storage according to any one of claims 56-64, wherein the downwardly extending wall (43) consists of hollow-core slab floor parts (80) connected to each other.

The stratified thermal storage of claim 65, wherein the upper portion (86) of the hollow channels (81) of the hollow-core slabs (80) are filled with a closed cell foam and the lower portion of the hollow channels (81) of the hollow-core slabs floor parts (80) are filled with closed cell foam. (80) be filled with a high density material to decrease the buoyancy of the wall (43).

A group (70) of more than 6 interconnected stratified thermal stores (71) according to any one of claims 51 to 66.

The array of claim 67, wherein the array (70) further comprises one or more stratified thermal stores of claims 56 to 66.

The pool of claim 56, wherein the pool (70) comprises a stratified thermal store (71) according to claim 56 to claim 66, wherein the mean temperature of the zone of water (36,44) of said stratified thermal store is higher. than the mean temperature of the zone of water (36.44) of the other stratified thermal stores of the group.

The array of any one of claims 67-69, wherein the adjacent stratified thermal store (72) share a wall (74).

71. Stratified lance comprising a vertical channel (48) provided with orifices (57) along its vertical outer wall, provided with an inner tube (55) connected at its top to a supply for a liquid and provided with an opening at its bottom (58) which is in fluid communication with an annular space (49) formed by the vertical channel (48) and the inner tube and wherein the opening (58) is lower than the orifices (57).

The stratified lance of claim 71 wherein the orifices (57) include a one-way valve (61).

Use of a stratified lance according to any one of claims 71 or 72 in a method according to any one of claims 1-37.

A stratified lance according to any one of claims 71 or 72 as part of a stratified storage according to any one of claims 48-66.