SE543772C2

SE543772C2 - Thermal energy storage assembly

Info

Publication number: SE543772C2
Application number: SE1950569A
Authority: SE
Inventors: Henrik Wikström; Hy Nguyen; Jakob Jamot; Karin Kjellin; Martin Nilsson; Martin Smedstad; Mikael Fjällborg; Niklas Köppen; Torbjörn Lindquist
Original assignee: Azelio Ab
Priority date: 2019-05-14
Filing date: 2019-05-14
Publication date: 2021-07-20
Also published as: SE1950569A1

Abstract

An assembly for storing thermal energy comprising a phase change material, PCM, storage vessel and at least one heat transfer fluid, HTF, receptacle, the PCM storage vessel being defined by a thermally conductive wall, the at least one HTF receptacle being provided adjacent to and in thermal communication with at least a portion of the PCM storage vessel, thermal communication occurring via the thermally conductive wall, and wherein at least one of the HTF receptacles comprises a portion for receiving thermal energy from an external thermal energy source.

Description

THERMAL ENERGY STORAGE ASSEMBLY Field of the Invention The present disclosure relates to an assembly for the storage of therrnal energy.In particular it relates to an assembly comprising an PCM storage vessel in direct therrnalcommunication with a HTF receptacle via a therrnally conductive wall. The HTFreceptacle comprises a region for receiving therrnal energy from an extemal therrnal energy source.

Background of the invention A new aspect of electricity generation is that energy generated when energy isless costly to produce, such as incidents of during the daytime when sunlight is readilyavailable for photovoltaic systems, or high Winds available for wind power generationsystems could be stored such that energy can be generated even when energy is lessreadily available, for example, there is less sunlight or wind.

To this end therrnal energy storage systems for storing therrnal energy generatedduring periods of sunlight are known in concentrated solar power systems. A therrnalenergy storage system may comprise a two-tank system comprising for example, threeheat exchangers. The first of the two tanks is a hot tank comprising a medium capable ofstoring therrnal energy, the second of the two tanks is a cold tank comprising a mediumfor storing therrnal energy. The system further comprises a heat transfer ﬂuid which isused to indirectly transfer therrnal energy from the hot tank via a heat exchanger, to asystem or device for generating electrical energy via a heat exchanger. The energyextraction of the heat transfer ﬂuid results in the heat transfer ﬂuid having a reducedtemperature compared with the heat transfer ﬂuid entering the heat exchanger for theelectrical energy generator, the therrnal energy remaining in the lower temperature heattransfer ﬂuid is then transferred to the medium for storing therrnal energy in the cold tank.Generally this second transfer happens via a third heat exchanger. The existing systemsgenerally use two tanks and a heat transfer ﬂuid as the medium for storing heat energy inthe tanks may be unsuitable for pumping as a heat transfer ﬂuid, and furtherrnore, the respective temperatures of the hot and cold tanks, and the energy storage medium therein, may be so great that the same material may be unsuitable for both tanks. That is, twodifferent energy storage mediums may be required.

The energy storage mediums may be phase change materials (PCMs). A phasechange material is a material which is capable of storing and releasing large amounts ofenergy when the material changes from a solid to a liquid and vice versa. A PCM isgenerally a material which absorbs energy during heating as a phase change from e.g. asolid to a liquid. The PCM may release energy during the reversed cooling process.During heating of the PCM in a solid phase the solid increases temperature (sensibleenergy storage). During phase change from solid to liquid energy is stored latently. Afterphase change to a liquid, energy is again stored sensibly and the PCM in liquid phaseincreases temperature.

An issue with PCMs is that a cool, solidif1ed, PCM generally has a lower therrnalconductivity than the liquid phase PCM. Existing therrnal energy storage systems haveinvestigated complex encapsulation techniques for the PCM to reduce the effects ofsolidif1cation on performance. These may entail encapsulation in small capsules or beads,or encapsulation of the PCM in a matrix of cylinders (heat pipes) inside a storage vessel.Each of these encapsulations techniques result in complex, expensive therrnal energystorage systems and PCM vessels.

The above two-tank systems are known in concentrated solar power systems, theuse of such therrnal energy storage systems in combination with other electricalgeneration systems is not to-date performed. Furthermore, simpler, less costly and morerobust systems of therrnal energy storage are required which reduce production, installation and maintenance complexity.

Summary of the invention Accordingly, the present invention preferably seeks to mitigate, alleviate oreliminate one or more of the above-identified deﬁciencies in the art and disadvantages singly or in any combination and solves at least the above mentioned problems by providing an ï\«""~\ i _ ', f . , _. ' _; 1 V. . . l l . ' - if. t, ; .- \~.\~~~.~~.w_i> my; yli) . -ww .-\ AAA m-w »~\-_i~~\~ ~-«~-_\I~\«~ Liv a k. .oxå btwê sn.- \. voššx. X5» <1.3.:\= mmßuršmz :xxvuﬂt :i \1.3.:.$\S:\-:~ v in the appended and dependentand advantages of Which the invention isdescription of embodimentsings, in WhichieW of an assembly for the storage of therrnal iption of the draWingsidated from the followingis a cross-sectional side V' PCM storage vessel and a HTF receptacle according to an aspect. l v... .Ä n... w..Ta 4\ I. ÖvaFx. . Ä_ . Ä.cl .x _..Å _...å “s x.s ... @\ t..b I.. <1.. ....Ä .f .Ä. \..i s _. i..w e ..I :ÅÅ. t.f. t» C« . Ä._... . ..\\\ »Å \~ . .i . Ä. __. _..\ :O(_. .lr .1~. cl . Å.l.. _... .\ f.: . .Ä I. f.. š . _. _ .Å. .Å I, Äb _... .\ x.C _ _ _ >. _.\ _.~. få .t. 7 .s.. .\ . .GÅ ...s .Å _.\.~< . 4s\ .... f. .l. i .\ .w. . .Ä\\ w\a INf. “f ä. \..Û f.. . ..f Ö. Å..._ _.. _..+\ .l w... YA._~. f. l .w _u. .Ä _. w. v; _ .. .Is. w.. _.\._.\ \....W .c.m :i cl. . t .ex. M_. wl. ._\.l .t .\.ﬂ Ä. .i _...u l. .i. u. “s sm.I .år x... ._. Ä ...i flf. ._~. .f ..._. .c. Ä .~»\ ä* .l .d. f. u... f. f. w..» Å ..Ä 4.. awš \\.t. w.._ \.._... .Ä\\>s .+._. lo.a .Üwvx.Wwn. iw..xx ....\ I<2» f».w _? Ü.l ._. , __.v: u. Ää.t.. .v\.\.ÄHvK.._.\.f ﬂ..

A system for the storage of therrnal energy comprising a plurality of assemblies is also provided.A system for the generation of electrical energy from therrnal energy is also provided.

Further advantageous embodiments are disclosed patent claims.

Brief descr These and other aspects, features capable Will be apparent and eluc of the present invention, reference being made to the accompanying draW Fig. energy compr1s1ng aFig. 2 is a schematic of a Wall of a PCM storage vessel according to an aspect.

Fig. 3 is a cross-sectional view of a HTF receptacle according to an aspect.

Fig. 4 is a cross-sectional side View of a PCM storage Vessel and a HTFreceptacle according to an aspect.Fig. 5 is a scheniatic of a system for the storage of therrnal energy and production of electrical energy according to an aspect.

Detailed description Fig 1 shows an assembly for therrnal energy storage comprising a phase changematerial (PCM) storage vessel 100 and a heat transfer ﬂuid (HTF) receptacle 200, thePCM storage vessel 100 is defined by a therrnally conductive wall 108. The HTFreceptacle 200 is provided adj acent to an in therrnal communication with at least a portionof the of the PCM storage vessel 100. The HTF receptacle 200 has a portion 210 forreceiving therrnal energy from an extemal therrnal energy source 400.

Thermal energy may be provided to HTF in the HTF receptacle 200 at theportion for receiving therrnal energy 210 from the extemal therrnal energy source 400.Thermal energy is thereafter transferred to the PCM via conduction from the HTF. Thetherrnal energy may therein be stored in the PCM for extraction and use at a later time.

The assembly is an efficient therrnal energy storage means which is less complexand more efficient than existing two tank systems.

Thermal energy to be input to the therrnal energy storage assembly is ideallywaste energy, overﬂow, or curtailment energy which can be input during periods whensuch energy is available. The therrnal energy can be extracted and for example, used togenerate electrical energy, when such waste energy, overﬂow or curtailment energy is notavailable.

The PCM storage vessel comprises an inverted tapered portion 101. The invertedtapered portion 101 has a tip portion 103 and a base portion 104. The base portion 104 iswider relative the tip portion 103. The tip portion 103 is arranged beneath the base portion104. The tip portion 103 has a smaller cross-sectional area than the base portion 104.

The PCM storage vessel 100 may be rotationally symmetric as is shown inFigure 1, however, it does not need to be.

As shown in Fig. 1 the tip portion 103 may have a ﬂat base such that the bottommost part of the PCM storage vessel 100 is ﬂat. As shown in Figs. 3 and 4 the tip portion103 may be rounded such that the tip portion 103 is partially dome shaped. The lowerrnostface 107 of the PCM storage vessel 100 may form the tip portion 103.

The PCM storage vessel 100 is formed by a wall 108 enclosing a PCM storageregion thus forrning a PCM 102 receptacle. The wall may comprise tapered portion 101 and a non-tapered portion. The wall 108 may comprise a plurality of separate members Which are joined to form a single Wall 108. For example, the Wall may comprise an upperlid 112 or covering 112, at least one lateral Wall 114 at the side(s) of the PCM storagevessel 100, and a base 113 or bottom Wall 113. Traditionally PCM storage vessels havebeen designed With Walls that are therrnally insulating. At least a portion of the Wall 108of the present PCM storage vessel may be substantially therrnally conductive, that is, non-therrnally insulating, such that heat may transfer from the PCM 102 in the PCM storagevessel 100, through the Wall 108, and in to any elements in therrnal contact With the Wallof the PCM storage vessel 100. The plurality of separate Wall members may each have adifferent therrnal conductivity. The plurality of separate Wall members may have the sametherrnal conductivity. The lateral Wall 1 14 of the PCM storage vessel may be the therrnallyconductive portion of the Wall 108. The entire Wall 108 of the PCM storage vessel 100may be therrnally conductive.

The Wall 108 of the PCM storage vessel 100 may comprise a metallic layer 181.The Wall 108 may further comprise an additional layer being a ceramic 182. The materialand/or thickness of the metallic layer 181 may be selected such that the metallic layer 181is therrnally conductive. The material and/or thickness of the ceramic layer 182 may beselected such that the ceramic layer 182 is therrnally conductive. The ceramic layer 182may form the intemal layer. The metallic layer 181 may be the outer layer. The ceramiclayer 182 may be arranged on the intemal surface of the Wall 108, such that PCM 102 isin contact With the ceramic layer 182. In such an arrangement the ceramic layer 182 formsan intemal surface of the Wall 108 and the metallic layer 181 forms an extemal surface ofthe Wall 108.

The metallic layer 181 may comprise, such as be composed of, stainless steel,such as an austenitic chromium nickel stainless steel alloy comprising nitrogen and rareearth metals The metallic layer 181 may be designed to be used at temperatures greaterthan about 550 °C. The metallic layer 181 may comprise for example stainless steel oftype EN 1.4835. The metallic layer 181 may have a thickness of from about 0.5 mm toabout 10 mm, such as from about 1 mm to about 5 mm, such as about 3mm. The metalliclayer 181 is substantially non-Wetting, that is, the PCM 102 is not in contact With themetallic layer 1 8 1 .

The ceramic layer 182 may comprise, such as be composed of, boron-nitride,aluminum oxide (AlgOg), and/or another ceramic material having a suitable therrnalconductivity. The ceramic layer 182 may have a thickness of from about 0.01 mm toabout 1 mm, such as from about 0.2 mm to about 0.4 mm. A thicker ceramic layer 182 isnot advantageous as it may split or crack. The ceramic layer 182 may have a therrnalconductivity greater than the therrnal conductivity of the metallic layer 181. The ceramiclayer 182 may have a heat transfer rate of 100 - 200 times that of the metallic layer 181.The ceramic layer 182 is non-insulating. The ceramic layer 182 is in contact With thePCM 102. A therrnally conductive ceramic layer 182 increases the therrnal conductivityof the Wall of the PCM storage vessel 100. The ceramic layer 182 furtherrnore enablesthe use of a PCM Which may otherwise react With a metallic Walled vessel. The ceramiclayer 182 may comprise a plurality of sub-layers, Where each sub-layer comprises, or iscomposed of a ceramic material.

The above described PCM storage vessel 100 Wall 108 design is furtherrnorelightWeight Which reduces installation and maintenance complexity and cost.Furthermore, a therrnally conductive PCM storage vessel 100 Wall 108 enables theefficient extraction of therrnal energy compared to systems Where therrnal energy fromthe PCM 102 is extracted via separate heat exchangers and requires ﬂuid transfer Withassociated losses.

The PCM 102 may be a known phase change material. The PCM may be amolten salt, a metallic alloy, or the like. Preferably, the PCM 102 for use in the presentPCM storage vessel 100 is a composition comprising aluminum and silicon, such aseutectic Aluminum Silicon Alloy, AlSi12. The PCM 102 may be an aluminum-siliconcomposition comprising silicon at a ratio of from about 10% to about 13% by Weight,such as about 12.6%. The temperature at Which the PCM 102 melts may be from about570 °C to about 590 °C, such as about 580 °C. As is the case With a PCM the PCMundergoes phase changes from solid to liquid, and liquid to solid, during therrnal energystorage and therrnal energy extraction. The PCM 102 may be present in both solid andliquid phases throughout the PCM storage vessel 100. The PCM 102 may be initiallyprovided to the PCM storage vessel 100 in a solid phase. The PCM may undergo a solid-liquid phase change at temperature of greater than 100 °C, such as greater than 200 °C.

Due to the high temperatures at Which the PCM storage vessel operates, and the therrnalenergy storage requirements Water is not a suitable PCM.

Molten and/or solid PCM 102 may be free to circulate passively throughout thePCM storage vessel 100. The PCM 102 may be un-encapsulated, that is, it may be freefrom any form of encapsulation separating portions of PCM 102 from each other.

The PCM storage vessel 100 may comprise a Volume of PCM 102 greater thanabout 5 L, such as greater than about 50 L of PCM. The PCM storage vessel may comprisefrom about 500 L to about 2500 L of PCM, such as from about 1000 L to about 2000 L,or more specifically, from about 1600 L to about 1700 L, or about 1630 L of PCM 102.

The PCM storage vessel 100 advantageously uses the effect of gravity on thePCM 102 such that, during Warming of the PCM 102, the relatively cooler and possiblysolidif1ed portions of PCM 102 are amassed at the bottom of the vessel in the tip portion103 of the tapered portion 101. Whereupon it is heated by the HTF in the HTF receptacle200 and may rise Within the vessel 100 to the base portion 104. The PCM 102 may thusbe Warrned Within the vessel 100 passively, effectively, and efficiently. As opposed toother heat storage mediums Which are maintained in a liquid phase, such as a heat transferﬂuid (HTF), in a PCM the relatively cooler portion may be a solid and have significantlyreduced heat transfer properties compared to the liquid phase and therefore. The solidif1edPCM has less volume compared to liquid phase PCM. On solidification, in a PCM storagevessel Without a tapered portion, a gap may form between the inner Wall of the PCMstorage vessel and the solidified PCM. The gaps have very poor heat transfer properties.The tapered portion 101 of the present PCM storage vessel 100 limits the formation ofgaps as solidified PCM 102 is directed, due to gravity, doWnWard toward the bottom ofthe tip portion 103. Furthermore, in a typical non-tapered vessel, cylinders or columns,having a cross-section approximating the cross-section of the vessel, may form Within thevessel. The tapered portion 101 of the present PCM storage vessel 100 inhibits theformation of such cylinders or columns as the solidified PCM is directed towards thebottom of the tip portion 103.

The receptacle 200 for heat transfer ﬂuid (HTF) 202 is provided adjacent to andin therrnal contact With at least a portion of the PCM storage vessel 100. The receptacle for HTF 200 abuts at least a portion of the PCM storage Vessel 100. An assemblycomprising the PCM storage Vessel 100 and the receptacle for HTF 200 is thus provided.

The receptacle for HTF 200 may surround at least a portion of the PCM storageVessel 100. The receptacle 200 may forrn a sleeve around a portion of the PCM storageVessel 100. The HTF receptacle 200 may surround a portion of the tapered portion 101and/or the upper portion 110 of the PCM storage Vessel 100. The HTF receptacle 200may surround the majority of the PCM Vessel 100. The HTF receptacle 200 maycompletely surround the PCM Vessel 100.

Thermal energy stored in the PCM 102 may be transferred to the HTF 202 Viathe Wall 108 of the PCM storage Vessel 100.

The HTF receptacle 200 may be defined as a receptacle having a central aperture203 for receiVing the PCM storage Vessel 100, an inner Wall 204 arrangeable adjacent theWall of the PCM storage Vessel 100, an outer Wall 205, and a member 206 connecting theinner Wall 204 to the outer Wall 205.

The inner Wall of the HTF 204 receptacle may be therrnally conductive such thattherrnal energy is transferred from the PCM 102 to the HTF 202, Via the Wall 108 of thePCM storage Vessel 100 and the inner Wall 204 of the HTF receptacle 200. The outer Wall205 of the HTF receptacle 200 may be therrnally insulating.

The HTF receptacle has a portion for receiVing therrnal energy 210. The portionfor receiVing therrnal energy 210 receives therrnal energy from an extemal source oftherrnal energy 400. The term extemal as used herein refers to a source of therrnal energythat is not in direct communication With the PCM storage Vessel 100. It does not actdirectly on the PCM storage Vessel 100. The term extemal also refers to that the extemaltherrnal energy source is also a source of therrnal energy 400 not being the PCM 102 inthe PCM storage Vessel 100. The extemal source of therrnal energy 400 is not in directtherrnal communication With the PCM storage Vessel 100. The extemal source of therrnalenergy 400 is in indirect therrnal communication With the PCM storage Vessel 100 Via theHTF receptacle 200, and in particular Via the HTF in the receptacle 200. The extemalsource of therrnal energy 400 acts upon the HTF in the HTF receptacle 200. The extemal source of therrnal energy 400 is such that it increases the average temperature of the HTF and the PCM in the assembly during operation. That is, the average therrnal energy storedin the assembly is increased via the external source of therrnal energy 400.

Therrnal energy provided to the PCM 102 in the PCM vessel 100 may besubstantially received at a first portion 200a of the at least one HTF receptacle 200. Thefirst portion 200a is adjacent to and in therrnal communication with the PCM storagevessel 100. Receiving therrnal energy refers to that the temperature of the HTF at theportion for receiving therrnal energy 210 is greater than the average temperature of theHTF in the receptacle 200, and/or the first portion 200a of the receptacle 200. That is, thetemperature of the HTF is increased at the portion for receiving therrnal energy 210.

Therrnal energy which may be extracted from the PCM 102 in the PCM storagevessel 100 is substantially extracted at a second portion 200b of the at least one HTFreceptacle 200. The second portion 200b is adjacent to and in therrnal communicationwith the PCM vessel 100. To extract therrnal energy from the HTF receptacle 200 HTFmay be pumped to a device which uses the therrnal energy. The HTF is thereafter retumedto the HTF receptacle 200. Extracting therrnal energy refers to that the temperature of theHTF which is retumed to the HTF receptacle 200 after therrnal energy extraction is lowerthan the average temperature of the HTF in the receptacle 200, and/or the second portion200b.

In some instances the first and second portions may be separate first and secondHTF receptacles 200a, 200b. The assembly therein comprises a plurality of HTFreceptacles 200a, 200b. The HTF receptacles may be separated via an air-gap of similarsuch that they are not in direct therrnal communication with each other. They are inindirect therrnal communication via the PCM storage vessel 100.

The first portion 200a is generally proximal the tip portion 103 of the PCMstorage vessel 100. As therrnal energy is generally provided to the assembly at the firstportion 200a and the tip portion 103 is beneath, that is relatively lower, the base portion104, the PCM 102 is heated at its lower portion. The heated PCM 102, due to its reduceddensity may ﬂow upward passively within the PCM storage vessel 100.

The second portion 200b is generally distal the tip portion 103 of the PCMstorage vessel 100. The second portion 200b is therefore proximal the base portion 104 11 of the PCM storage vessel 100. Thermal energy may be extracted at the second portion200b.

The first portion 200a may have a corresponding shape to the tip portion 103 ofthe PCM storage vessel 100. For example, if the tip portion 103 of the PCM storage vessel100 is ﬂat the first portion 200a may be substantially ﬂat. If the tip portion 103 is domeshaped then the first portion 200a may be correspondingly concave such that the dome issurrounded by the first portion 200a of the HTF receptacle 200.

The PCM storage vessel 100 and HTF receptacle 200 is used for therrnal energystorage. Thermal energy may be provided to the PCM 102 Which is stored andsubsequently extracted. The therrnal energy is generally extracted via the HTF 202. Anelectrical energy generation system 500 may be provided in connection to the PCMstorage vessel 100, and/or the HTF receptacle 200. Generally, the electrical energygeneration system is provided in therrnal connection to the HTF receptacle 200. Theelectrical energy generation conversion unit may be in therrnal connection to the secondportion 200b of the HTF receptacle 200.

The extraction of therrnal energy is performed to power a electrical energygeneration system 500. The electrical energy generation system 500 converts therrnalenergy provided by the HTF 202 to electrical energy. The generated electrical energygenerated by the electrical energy generation system 500 may be fed in to an electricitygrid or electrical distribution network. The electrical energy generation system 500 maycomprise a conversion unit 501 operating on the Stirling cycle, Rankine cycle, Braytoncycle, or any other heat engine capable of eff1ciently generating electrical energy fromtherrnal energy to electrical energy.

The conversion unit 501 of the electrical energy generation system 500 is intherrnal connection With the HTF. A heat exchanger may be used to transfer therrnalenergy from the HTF to the conversion unit 501. The heat exchanger may transfer therrnalenergy from the HTF to the Working ﬂuid of the conversion unit 501.

As described above, therrnal energy may be provided to the HTF 202 via thePCM 102, and speciﬁcally via the PCM 102 through the PCM storage vessel 100.

A plurality of ﬂuid conduits may be provided to the HTF receptacle 200 for thetransfer of HTF. A heating ﬂuid conduit 211 may be provided in connection to the HTF 12 receptacle 200 at the portion for receiving therrnal energy 210. The heating ﬂuid conduit211 may have a first end 212 in connection With the portion for receiving therrnal 210.The heating ﬂuid conduit 211 may have a second end 213 in connection With the portionfor receiving therrnal energy 210. HTF may be displaced through the conduit, from thefirst end 212 to the second end 213 via the extemal therrnal energy source 400. The HTFmay be displaced by a pump.

The HTF receptacle 200 may be in the form of an annular cylinder, that is acylinder having a central aperture 203, if the HTF receptacle 200 is arranged adjacent acylindrical portion of the PCM storage vessel 100. The HTF receptacle 200 may be atoroid having a rectangular cross-section rotated around its central axis. The HTFreceptacle 200 may be in the form of an annular tapered portion, that is a tapered portionhaving a central aperture 203. The HTF receptacle 200 having an annular tapered form isespecially suitable if the HTF receptacle 200 is arranged adjacent the tapered portion 101,or if the entire PCM vessel 100 is a frusto-cone. For example, the HTF receptacle 200may have the form of an annular frusto-cone having a central aperture 203 if the taperedportion 101 of the PCM storage vessel 100 is a frusto-cone.

The HTF receptacle 200 may comprise at least one, such as a plurality ofpartitions 208 forrning a single HTF receptacle 200. Each partition 208 may be a sectionof the entire of shape of the HTF receptacle 200. For example, each partition 208 may bea section of an annular cylinder having a central aperture 203. If, for example, the HTFreceptacle 200 is formed to engage With the tapered portion 101 of the PCM vessel 100then the each partition 208 may have the form of a portion of an tapered portion having acentral aperture 203.

The extemal therrnal energy source 400 may be any device or system adaptedfor supplying therrnal energy to the HTF. The extemal therrnal energy source 400 mayfor example be a solar radiation receiver at Which sunlight is focused. The extemaltherrnal energy source 400 may be a device for converting electrical energy to therrnalenergy. The extemal therrnal energy source 400 may be an immersion heating Which heatsHTF via the conversion of electrical energy to therrnal energy. An immersion heater may be provided at the ﬂuid conduit 211 between the first and second 212, 213 ends. The 13 immersion heater is in therrnal communication with the HTF. The immersion heater maybe heat the HTF in the ﬂuid conduit 211.

The external therrnal energy source 400 may be a device which provides therrnalenergy via electromagnetic radiation, such as an infrared heater. If the external energysource supplies therrnal energy via electromagnetic radiation then the therrnal energysource 400 need not be in direct contact with the HTF, as the therrnal energy is transferredvia radiation. An external therrnal energy source 400 may be adapted such that radiationis directed towards the region for receiving therrnal energy 210. The extemal therrnalenergy source 400 may also be adapted to act upon the ﬂuid conduit 211 between the firstand second ends 212, 213.

By heating the HTF with an extemal energy source 400 adapted to convertelectrical energy to therrnal energy the HTF may be heated with electrical energy whichis otherwise not possible to input to an electricity network or grid. The electricity used topower the extemal therrnal energy source 400 may be provided by photovoltaic panels.The photovoltaic panels may be provided in the vicinity of the PCM storage vessel 100,HTF receptacle 200 assembly to reduce transmission costs.

The extemal therrnal energy source 400 may be a source of waste industrial heatsuch as an industrial gas-ﬂare system. The heat from the gas ﬂare generated may be usedto heat the HTF, and thereafter the PCM.

In both of the electrical and gas-ﬂare extemal therrnal energy sources 400therrnal energy used to heat the HTF is low-cost and environmentally friendly as wasteenergy is used to heat the HTF. The waste energy may be stored in the PCM for periodswhen electricity can be provided to the electricity network or grid.

The extemal therrnal energy source 400 may be adapted to heat HTF at a locationbeing at a height greater than the height of the PCM vessel 100 and HTF receptacle 200assembly. Height in such instances refers to the distance from ground-level. That is, theHTF may need to be displaced, vertically, to a position higher than the PCM vessel 100and HTF receptacle 200. In such instances, a pump may be used to transfer the HTFthrough the conduit 21 1.

The HTF receptacle 200 may comprise at least one opening for the provision and/or extraction of HTF 202. The opening may be in addition to the first and second 14 ends 212, 213 of the ﬂuid conduit 211. The opening may also be used for the emptyingof HTF, during maintenance. The HTF receptacle 200 may comprise a plurality ofopenings such as an aperture for a pump, an outlet for pumped HTF 202, and the first andsecond ends 212, 213 of the ﬂuid conduit 211.

The HTF receptacle 200 may be manufactured from a metal, such as stainlesssteel, such as an austenitic chromium nickel stainless steel alloy comprising nitrogen andrare earth metals. The metal may be designed to be used at temperatures greater thanabout 550 °C, the metal may for example be of type EN 1.4835. The inner 204 and/orouter 205 Walls of the HTF receptacle may comprise, such as be composed of stainlesssteel.

The HTF 202 is a ﬂuid. The HTF 202 may be a molten salt solution. Preferablythe HTF 202 is molten metal such as molten Sodium. Due to the high temperatures atWhich the HTF receptacle operates, and the therrnal energy storage requirements Water isnot a suitable HTF. In some instances the HTF may be a gas. The first portion 200a of theHTF receptacle 200 may be filled With a first HTF 202. The second portion 200b of theHTF receptacle 200 may be filled With a second HTF 202, not being the same HTF as thethat in the first portion 200a. However, they may be the same HTF 202. A different HTFin the first and second portions 200a, 200b may enable different and optimal pumps,valves and other elements to be selected depending on the operating temperature of eachof the HTFs.

The HTF receptacle 200 may be provided With a ﬂuid such as an inert gas, suchas a nitrogen (Ng). A portion of the HTF receptacle 200 may be filled With the HTF 202,the remaining portion of the HTF receptacle 200, not filled With HTF 202, may be filledWith the inert gas.

The PCM storage vessel 100 may be provided With a ﬂuid such as an inert gas,such as a nitrogen (Ng). A portion of the PCM storage vessel 100 may be filled With thePCM 102, the remaining portion of the PCM storage vessel 100, not filled With PCM 102,may be filled With the inert gas.

The inert gas above reduces oxidation of the PCM 102 and/or HTF 202 even at high temperatures.

The HTF receptacle may be substantially gas tight at its upper portion 209 suchthat any gas leakage from the HTF receptacle 200 is minimized.

A system for the storage or therrnal energy is provided wherein the systerncomprises a plurality of PCM storage vessels 100, and HTF receptacles 200 as describedherein. Each of the plurality of assemblies 100, 200 may be interconnected such that thea single external therrnal energy source 400 supplies therrnal energy to the each of theplurality of regions for receiving therrnal energy 210. Each of the assemblies may beinterconnected via their respective ﬂuidic conduit 211. A plurality of valves may beprovided between the HTF receptacles 200 in the system such that the flow of therrnalenergy via HTF can be controlled. That is, the valves enable the controlling the ﬂow oftherrnal energy to a subset of the plurality of PCM storage vessels 100 and HTF receptacle200 assemblies, being less than the total number of assemblies in the system.

Each of the assemblies comprising a PCM storage vessels 100 and the HTFreceptacle 200 in the system may be provided with a separate respective extemal sourceof therrnal energy 400. In such a manner the temperature of each of the assemblies andthe energy stored therein may be controllable separately.

Each of the assemblies comprising the PCM storage vessel 100 and the HTFreceptacle 200 in the system may be connected to a respective energy conversion unit 501for the generation of electrical energy.

A system may be housed in a housing. The housing may be a standard shippingcontainer. A standard shipping container refers to container according to ISO 66832013Series 1 standards being 12.192 m (40 ft) long, 2.438 m (8 ft) wide, and 2.591 m (6 ft 6in) high or 2.896 m (9 ft 6 in) high (high-cube). Housing the system in a standard shippingcontainer enables the system to be shipped efficiently and thus reduces the total cost ofinstallation of the therrnal energy storage system. A system may comprise four assemblieseach comprising a PCM storage vessel 100 and a HTF receptacle 200. In such a systemthe PCM storage vessels 100 and HTF receptacles 200 may be in a first portion of theshipping container. The conversion unit(s) 501 may be present in a separate, secondportion of the shipping container. A wall may be provided between the first portion andsecond portion. The wall may act as a barrier for dust, radiant therrnal energy, and safety shielding from the volume of PCM 102 and HTF 202 which may be maintained at 16 temperatures of over 500 °C as described above. A housing, such as a shipping container,may have more than one second portion. For example, two conversion units 501 may beprovided in a first second portion, and two conversion units 501 may be provided in asecond second portion in a system comprising four conversion units 501.

As described above, the PCM storage vessel 100 enables the storage of therrnalenergy which can be extracted and used to power an electrical energy generation system.A system comprising a plurality of interconnected PCM storage vessels 100 and HTFreceptacles 200 is especially useful when the amount of therrnal energy which can beprovided by the extemal therrnal energy source 400 is greater than the amount of energywhich can be stored in a single PCM storage vessel 100, and/or extracted by theconversion unit for converting therrnal energy in to electrical energy. The above systemhas numerous advantages compared to a single large PCM vessel 100 with respect toreduced installation costs, and the ability to modulate which PCM vessel 100 and HTFreceptacle 200 assemblies receive the therrnal energy if each cannot be efficientlyoperated simultaneously.

The system comprising the plurality of assemblies may be provided within ahousing.

A description of the process for therrnal energy storage and retrieval will now bedescribed with respect to the assembly comprising the PCM storage vessel 100 and HTFreceptacle 200 and an extemal therrnal energy source 400.

The HTF 202 comprised in HTF receptacle 200 receives therrnal energy at theportion for receiving therrnal energy 210 from the extemal therrnal energy source 400.The HTF 202 may be continuously pumped through the conduit 211 via the extemaltherrnal energy source 400.

The HTF 202 may be heated to greater than 500 °C, such as greater than 600 °C,such as about 650 °C.

A therrnal energy transfer occurs from the HTF 202 to the PCM 102, such thatthe PCM 102 within the PCM storage vessel 100 is warrned. The temperature of the PCM102 in the vicinity of the portion for receiving therrnal energy 210 of the HTF receptacle200 may be greater than 500 °C, such as greater than 580 °C, such as about 590 °C. 17 The warrned PCM 102 in the vicinity of the HTF receptacle 200 may be lessdense than the relatively cooler PCM 102 present in the PCM storage vessel 100. It mayhave undergone a phase change to liquid. The warrned PCM 102 may rise within the PCMstorage vessel 100, the cooler, denser, possibly solidified PCM 102 may ﬂow toward theregion tip portion 103 of the tapered portion 101 of the PCM vessel 100. This process offree het convection, or natural heat convection, continues whilst the therrnal energy isbeing supplied to the HTF receptacle 200.

In the above process the therrnal energy may be supplied to the first portion 200aof the HTF receptacle 200.

The therrnal energy present in the PCM 102 may be extracted via HTF 202 intherrnal communication with the PCM storage vessel 100. HTF 202 in the HTF receptacle200 is warrned through the wall of the PCM storage vessel 100, and through the wall ofthe HTF receptacle 200. The warrned HTF 202 may be pumped to a conversion unit 501of an electrical energy generation system 500 for converting therrnal energy in toelectrical energy. The warrned HTF 202 may then Warm the Working ﬂuid of theconversion unit 501. For example, the warrned HTF may be pumped to a Stirling engine.The Stirling engine may thereby convert the therrnal energy extracted from the PCM 102to generate electricity.

The therrnal energy extracted from the PCM 102 may be extracted via the HTF202 in the second portion 200b of the HTF receptacle 200.

In a separate arrangement the HTF receptacle 200 may comprise an intemalheater for heating the PCM 102 in the PCM storage vessel 100 directly. This is similar tothe PCM storage vessel 100 disclosed in Swedish patent application SE 1851338-2.However, instead of a region for receiving solar therrnal energy (105 in the referencedapplication), a heater is provided to heat the PCM 101 directed at the region for receivingsolar therrnal energy (105 in the referenced application) making the region therefore aregion for receiving therrnal energy. The heater may be an infrared heater powered byelectrical energy. The heater may be enclosed within an insulating wall. The HTFreceptacle 200 is still present, and the PCM 102 is used to store therrnal energy.

In a further separate arrangement the HTF receptacle 200 may comprise at least one heater adapted to directly heat the HTF 102 within the HTF receptacle 200 without 18 any pumping of the HTF to an external source of therrnal energy. Such an arrangementcomprises a PCM storage vessel 100, a HTF receptacle 200, and a heater Within the HTFreceptacle 200. The therrnally conductive Walls of the PCM vessel 100 are as describedabove. Therrnal energy may be provided to the HTF 102 in the HTF receptacle 200 Whichis thereafter transferred and stored in the PCM 102 in the PCM vessel 100. Therrnalenergy is transferred via conductive Walls of the HTF receptacle 200 and the PCM storagevessel 100.

The two arrangements presented above have the advantage that the HTF 102does not need to be pumped to an external source of therrnal energy and thereforeinstallation costs may be reduced.

Although, the present invention has been described above With reference tospeciﬁc embodiments, it is not intended to be limited to the specific forrn set forth herein.Rather, the invention is limited only by the accompanying claims.

In the claims, the terrn “comprises/comprising” does not exclude the presence ofother elements or steps. Additionally, although individual features may be included indifferent claims, these may possibly advantageously be combined, and the inclusion indifferent claims does not imply that a combination of features is not feasible and/oradvantageous. In addition, singular references do not exclude a plurality. The terms “a”,“an”, “f1rst”, “second” etc do not preclude a plurality. Reference signs in the claims areprovided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any Way.

Claims

1. An assembly for storing therrnal energy comprising a phase change material,PCM, storage vessel (100) and a separate first (200a) and second (200b) heattransfer ﬂuid, HTF, receptacles (200a, 200b), the PCM storage vessel (100)being defined by a therrnally conductive Wall (108), the HTF receptacles (200a,200b) being provided adj acent to and in therrnal communication With at least aportion of the PCM storage vessel (100), therrnal communication occurring viathe therrnally conductive Wall (108), characterized in that the first HTFreceptacles (200a) comprises a portion for receiving therrnal energy (210) froman extemal therrnal energy source (400) and in that therrnal energy to beextracted from the PCM storage vessel (100) is extracted at the second HTFreceptacle (200b) and, the first (200a) and second (200b) HTF receptacles areseparate such that they are not in direct therrnal communication, and in that they are in indirect therrnal communication via the PCM storage vessel (100). The assembly according to claim 1, Wherein the extemal therrnal energy source(400) is separate from and not in direct communication With the PCM vessel (100). The assembly according to any of claims 1 to

2. , Wherein the PCM vessel (100) is substantially enclosed. The assembly according to any of claims 1o to

3. , Wherein the HTF receptacles (200a, 200b) surrounds at least a portion of the PCM vessel (100). The assembly according to any of claims 1 to

4. , Wherein the PCM storage vessel(100) comprises a phase change material, PCM, such as a metallic alloy, and the HTF receptacles comprises a heat transfer ﬂuid, HTF, such as sodium. The assembly according to an of claims 1 to

5. , Wherein the first HTF receptacle(200a) comprises a ﬂuid conduit (211) for the transfer of HTF to the extemaltherrnal energy source (400), the ﬂuid conduit (211) having f1rst (212) and 10. 11. 12. 13. second (213) ends in connection With the portion for receiving therrnal energy (210). The assembly according to any of claims 1 to

6. , Wherein the external therrnal energy (400) is provided by an immersion heater adapted to heat the HTF. The assembly according to any of claims 1 to

7. , Wherein the energy provided tothe external therrnal energy source (400) for heating the HTF is Waste energy from an industrial process and/or electrical energy from photovoltaic panels. The assembly according to any of claims 1 to

8. , Wherein the energy provided to the extemal therrnal energy source (400) is solar therrnal energy. A system for the storage of therrnal energy comprising a plurality of assemblies according to any of claims 1 to

9. A system for the generation of electrical energy from therrnal energy comprisingat least one assembly according to any of claims 1 to 9, further comprising anelectrical energy generation system (500) for generating electrical energy fromtherrnal energy, the electrical energy generation system (500) being in therrnal communication With the HTF receptacle (200b) via a fluidic conduit. The system according to claim 11, Wherein the system for generating electricalenergy (500) comprises a conversion unit (501) operating on the Stirling cycle,Rankine cycle, Brayton cycle, or other heat engine capable of generating electrical energy from therrnal energy. The assembly according to any of claims 1 to 9, or the system according to claim10, or the system according to claim 1 1, Wherein the HTF is adapted to be heatedto a temperature of greater than 500 °C, such as greater than 600 °C.