Field of invention The present invention relates to apparatus to store heat energy and in particular, although not exclusively, to a heat storage unit having a construction aggregate to store the heat energy and a fluid heat transfer medium to allow energy to be both stored and extracted from the heat store. Background art

The supply of power or energy in the form of electricity typically requires an energy source, which may be subsequently converted and/or supplied as electricity. Traditionally, fossil fuels have been used as a source of energy to drive the turbines for electricity generation. As natural resources are diminished and in the face of climate change, renewable energy sources have been investigated for power and electricity generation. In particular, solar energy has received reasonable attention as an alternative energy source to conventional fossil fuels. Solar energy collection devices are well established and may be categorised according to two types. Non-concentrating collectors receive the solar radiation directly, as parallel rays of radiation. Such devices typically comprise a solar panel, or array of photovoltaic cells that may be heated and configured to transmit and store the solar radiation. A further type of solar collector is referred to as a concentrating type, which reflects or refracts the radiation using lenses or mirror assemblies so as to concentrate the rays onto a target as a more focused solar footprint.

WO 2009/147651 discloses a solar energy generator system for concentrating solar rays for use in a thermodynamic cycle that utilises a gas or steam cycle and a turbine to generate electricity. The solar-ray concentrating system comprises a plurality of concentrating mirrors that act to reflect the radiation towards a suitable absorption and an accumulation body.

US 2009/0308072 discloses a modified Brayton cycle engine that utilises a working fluid heated by solar radiation. In particular, a metal hydride material within a storage unit is heated and hydrogen driven from the hydride material is recombined with the material at a controlled rate in an exothermic reaction for heating a compressible Brayton working fluid for subsequent driving of a turbine coupled to an electric generator.

WO 2010/019990 discloses a solar energy and power generation system. The power generation system comprises a closed working fluid having a super heater, a turbine, a condenser, a subcooler, a receiver and a pump. The working fluid is separated into first and second parallel streams. A solar energy collection system is configured to heat the working fluid by a heat exchanger in both the first and second streams. The first and second fluid streams are then combined, super heated and transferred to the turbine. WO 2010/021706 discloses a steam based electric power plant operable from renewable geothermal, wind and solar energy sources. Wind or solar power is converted to hydrogen in an electrolysis unit. The generated hydrogen is then fed to a boiler for supplying heat energy to a turbine and generator. WO 2009/129166 discloses a solar thermal power plant comprising a steam generator and a turbine. Water is converted to steam using solar energy. A super heater then heats the steam from an evaporator to provide super heated steam that is supplied to the turbine. However, conventional solar energy based power generation systems have a number of disadvantages including in particular the efficiency of operation by which solar energy is captured and harnessed for power generation. Additionally, conventional systems are also limited due primarily to an insufficient capacity to store the captured solar energy. Their use is typically restricted to hot climates and there is a continual need to recharge the limited energy storage device, which may result in power or electricity being unavailable during poor or inclement weather conditions. There is therefore a need for apparatus and methods for storing energy for subsequent utilisation in the same or a different form.

Summary of the Invention Accordingly, the inventors provide the storage apparatus and methods capable of storing energy as heat for subsequent utilisation. The present heat store is capable of operation with a fluid phase heat transfer medium to both supply and extract heat energy at the heat store. Additionally, the present heat store may form an integral part of an electricity generation plant powered by any renewable energy source and in particular a solar thermal energy source. Alternatively, the present heat store may be used as a heat storage unit within any power generation plant or system.

In a preferred utilisation, the present heat store forms a component part of a renewable energy system that comprises an array of lenses or mirrors to harness a concentrate solar energy onto targets. The heat energy at the targets is transferred to the heat store via a gas phase working fluid cycle coupled to the heat store. Alternatively, the heated targets may transfer heat energy to a heat exchanger which is turn is coupled, via a separate working fluid, to the present heat store device. The present heat storage device is also suitable for coupling to a further heat exchanger and turbine arrangement such that the extracted heat energy can be used to drive the turbine and provide an on-demand supply of electricity both during and optionally between energy collection periods, for example day and night, in the case of solar energy. According to a first aspect of the present invention there is provided apparatus to receive and store heat energy from a working fluid, the apparatus comprising: an internal chamber defined by at least one side wall, a roof and a base; an inlet to allow a heated fluid to flow into the internal chamber; an outlet to allow the fluid to flow out of the internal chamber; a plurality of columns of a construction aggregate extending axially within the internal chamber in a direction between the roof and the base, the columns separated from one another by space regions to provide a plurality of fluid flow passageways extending in an axial direction between the roof and the base; a plurality of jackets arranged respectively around each of the columns to contain the construction aggregate in the form of the columns; the inlet and outlet positioned relative to the side wall, roof and/or base such that the fluid is configured to flow axially between the columns from the inlet to the outlet and in contact with the columns so as to transfer heat energy to the construction aggregate. An example system in which the present heat storage device may be utilised is disclosed in WO 2010/116162, which is incorporated by reference herein.

Within this specification, the term 'construction aggregate ' encompasses any naturally occurring aggregate, mineral or non-mineral extracted from the Earth's crust. The term includes specifically natural or synthetic materials manufactured or processed from any one or a combination of the following set of: sand, stone, rock, basalt, concrete, flyash, slag, a naturally occurring material or a synthetic construction material. Additionally, the construction aggregate may be formed as sand, gravel, stones, pebbles, boulders or other granular shaped material.

Within this specification, the term 'column ' encompasses a pillar, a wall or a block of construction aggregate that is preferably prefabricated to enable the heat storage apparatus to be assembly conveniently. Preferably the constructions aggregate is maintained in the column geometry by a jacket such as a mesh, net or a perforated structure.

Optionally, the construction aggregate comprises anyone or a combination of the following set of: sand, stone, rock, basalt, concrete, flyash, slag, a naturally occurring material or a synthetic construction material. Optionally, the construction aggregate is formed as any one or a combination of the following set of: sand, gravel, stones, pebbles, boulders or other granular shaped material. Optionally, each column comprises a uniform cross sectional size in the axial direction between roof and the base. Preferably, the columns have a substantially equal average cross sectional size. Preferably, an outer surface of the columns is provided in or near touching contact with one another in a lengthwise direction between the roof and the base. Optionally, spacers may be provided to separate the columns and maintain the

passageways. Optionally, the apparatus may comprise at least one brace configured to retain at least one or a plurality of the columns as unitary structure and to maintain the axially extending passageways. Optionally, each column comprises a plurality of braces extending in a lengthwise direction between the roof and the base. Optionally, the columns may be substantially cylindrical or comprise any cross sectional profile including block shaped segments. Optionally, the columns are modular in the axial direction between the inlet and the outlet so as to be stacked arrangements of blocks of aggregate.

Optionally, the jackets are thermally degradable so as to perish within the apparatus during initial use. Optionally, the jackets are thermally stable to persist within the apparatus. Preferably, the jackets comprise one or a combination of the following: steel, stainless steel, a metal, a metal alloy, paper, card, a cellulose based material, a polymer based material, a ceramic, a mesh, a gauze, a plurality of strips or wire or a perforated material. Optionally, each of the jackets extends axially over a part or a full length of each column in a direction between the roof and the base. Optionally, the jackets extend substantially vertically within the internal chamber. Optionally, the jackets are retained in position by at least one brace and in particular a plurality of braces that extend around a cluster of jackets to lock the jackets in position relative to one another. Optionally, the brace comprises a metal strip or a belt-type arrangement. Optionally, the jackets extend substantially vertically between the base and the roof.

Preferably, the apparatus comprises a heat exchanger having an exchanger working fluid to transfer heat energy with the fluid in contact with the construction aggregate, the heat exchanger positioned within the internal chamber. Optionally, the heat exchanger is orientated to extend substantially vertically or substantially horizontally within the internal chamber. Preferably, the apparatus comprises an insulation medium positioned at the at least one wall to thermally insulate the internal chamber. Preferably, the at least one wall comprises a generally cylindrical geometry to encapsulate the jackets within the internal chamber.

Preferably, the construction aggregate extends substantially as a continuous mass within the internal chamber and is separated by the jackets. Reference to 'a continuous mass' of construction aggregate refers to assembly of stones, boulders, pebbles, gravel and/or sand but are arranged in touching contact to form a substantially solid mass. The solid mass may be contained within each jacket or alternatively may be positioned to surround each jacket and to extend either between the at least one wall that defines the internal chamber or between the base and roof. Optionally, the stones, boulders, gravel, pebbles, sand, rocks or construction aggregate pieces contact an internal facing surface or an external facing surface of each jacket.

Optionally, the apparatus may comprise ducting to direct the fluid flow path within the internal chamber in a substantially vertical direction between the construction aggregate and the heat exchanger. Optionally, the apparatus comprises ducting or at least one fluid flow conduit in fluid communication with the inlet to direct the heated fluid to an upper region of the construction aggregate relative to a base and roof of the internal chamber, an intermediate region of the construction aggregate relative to the base and roof of the internal chamber or a lower region of the construction aggregate relative to the base and roof of the internal chamber.

Optionally, the apparatus comprises a plurality of inlets and a plurality of outlets positioned at different regions at the at least one wall so as to allow the fluid to flow into and out from the internal chamber at different regions relative to the at least one wall and the base and roof. Optionally, the base may be supported from below by a plurality of support columns configured to suspend the base above a lower substrate or support surface. Optionally, a bottom or lowermost region of construction aggregate is supported upon a plurality of support columns extending transverse or perpendicular to the length of each layer.

Optionally, a bottom or lowermost region of construction aggregate is supported upon a suitable insulating layer optionally comprising a construction aggregate of the same or a different type, a construction aggregate combined with rockwool or a similar thermally insulating medium; or a load bearing thermally insulating aggregate material, mineral or solid structure.

According to further aspects of the present invention there is provided a solar energy based power generator system that efficiently converts solar energy to heat energy that may be stored conveniently and subsequently converted to electrical energy. The system comprises an array of lenses or mirrors to harness and concentrate solar energy onto a target within a gas phase working fluid cycle that may be coupled to the heat energy storage device. A suitable heat exchanger and turbine arrangement is coupled to the fluid cycle and/or heat storage device to provide on-demand supply of electricity both during and optionally between solar energy collection periods. According to a further aspect of the present invention there is provided the solar energy collection apparatus comprising: a plurality of lenses and/or mirrors to receive and concentrate solar radiation; one or a plurality of targets to respectively receive the concentrated solar radiation from each of the lenses and/or mirrors; a conduit network to contain a gas phase working fluid and allow the fluid to flow in contact with the at least one target such that the working fluid is heated by the at least one target and a heat storage device as described herein.

According to a further aspect of the present invention there is provided apparatus for converting solar energy to electrical energy comprising: solar energy collection apparatus as described herein; a heat exchanger connected in fluid communication with the conduit network and/or heat storage device to receive the heated working fluid and to transfer the received heat energy; a turbine coupled to the heat exchanger; an electric generator coupled to the turbine to generate electricity and a heat storage device as described herein coupled in thermal communication with the heat exchanger.

Preferably, the fluid to flow through the heat storage apparatus is air. Alternatively, the fluid may comprise any gas phase medium including for example carbon dioxide.

Optionally, a high thermal conductivity gas is utilised.

Preferably, the working fluid of the heat exchanger is water and steam, including in particular supercritical water. In particular, the gaseous phase working fluid within the conduit network of the collection apparatus is capable of being heated to high temperatures above 400°C and in particular up to around 700°C, the latter being the recognised maximum operational temperature of a turbine. Preferably, the working fluid of the present collection apparatus is air, and in particular atmospheric air comprising a ground-level air composition.

According to a further aspect of the present invention there is provided solar energy collection apparatus comprising: a plurality of lenses and/or mirrors to receive and concentrate solar radiation; at least one target to respectively receive the concentrated solar radiation from each of the lenses and/or mirrors; a conduit network to contain a heat transfer fluid and allow the fluid to flow in contact with the at least one target such that the fluid is heated by the target; a heat exchanger connected in fluid communication with the conduit network to receive the heated fluid and to transfer the received heat energy to a gas phase fluid; a heat storage device connected in fluid communication via the gas phase fluid to the heat exchanger to receive the heat energy, the storage device comprising a heat storage material to store the heat energy received from the gas phase fluid.

Brief description of drawings

A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which: Figure 1 is a cross-sectional side view of a heat storage device comprising a chamber having a plurality of jackets that accommodate a construction aggregate according to a specific implementation of the present invention; Figure 2 is a plan cross-section through A-A of Figure 1 ;

Figure 3 is a further cross-sectional view of a region of the jackets and chamber of Figure l ; Figure 4 is a cross-sectional view similar to A-A of Figure 1 but with the jackets separated by discrete spacers;

Figure 5 is a cross-sectional view of a plurality of jackets similar to those of Figure 1 having a different cross-sectional profile;

Figure 6 is a cross-section through a plurality of jackets of the type of Figure 1 in which the heat storage device is configured as a counter-flow heat storage apparatus according to a specific implementation; Figure 7 illustrates a lower cross-sectional side view of the heat storage device of Figure 1 according to a further specific embodiment in which the jackets are supported on columns;

Figure 8 is a cross-sectional side view of a heat storage apparatus of the type of Figure 1 according to a further specific embodiment in which the jackets are supported upon a suspended base.

Detailed description of preferred embodiment of the invention

Referring to Figures 1 to 3, the heat storage device 100 is capable of storing heat energy for extended periods for the subsequent extraction and exploitation by, for example, supply to a conventional electricity generating turbine arrangement (not shown). The heat store 100 comprises an external wall 102 in the form of a cylindrical wall that defines an internal chamber 114. A thermal insulation material 106, such as rockwool or a similar, is positioned to extend around an external surface of wall 102 to encase and thermally insulate the internal chamber 114. Apparatus 100 comprises a roof region 110 that is also shrouded by insulation material 106. Wall 102 and chamber 114 are mounted upon a base 109 that may be a specifically constructed structure or may be level ground.

An inlet 107 extends through roof 110 to allow a fluid flow into internal chamber 114. An outlet 108 is positioned at a lower region of chamber 114 in close proximity to base 109. A plurality of jackets 105 extend within internal chamber 114. Each jacket 105 comprises a cylindrical wall (optionally formed from steel) having an external facing surface 113 and an internal facing surface 103. Internal facing surface 103 defines an internal hollow cavity 104. Each jacket 105 is elongate and extends substantially the full distance between roof region 110 and base 109. A lower region 112 of each jacket 105 is positioned in contact with base 109. Each jacket 105 at lower region 112 tapers radially inward towards a longitudinal axis 115 extending centrally through each respective jacket 105. Each lower region 111 comprises a generally frusto-conical configuration.

According to the specific implementation, the internal cavity 104 within each jacket 105 is filled with a construction aggregate. The aggregate extends continuously as a column contained within each jacket 105 between base 109 and roof region 110. According to the specific implementation, the aggregate comprises gravel. However, regions of the jacket cavity 104 may comprise gravel or small stones. As each jacket 105 comprises a generally elongate cylindrical configuration, gap regions 200 are created between the external facing surfaces 113 of each cylinder 105. The plurality of jackets 105 are retained in position as a vertically orientated assembly by at least one securing brace (not shown). The brace may comprise a strap, strip or chain type arrangement that is wrapped around to encircle the assembled jackets 105 to prevent the jackets from collapsing outwardly. The at least one brace also avoids the need to structurally reinforce chamber wall 102. The jackets 105 are positionally retained by at least one brace and/or cavity wall 102. Accordingly, main cavity wall 102 may be structurally reinforced by additionally comprising supplementary braces or support struts (not shown) to provide a radially inward constraining force as required.

As illustrated in Figures 2 and 3, the space regions 200 between the jacket outer surfaces 113 provides a plurality of flow channels for the fluid flowing into chamber 114 via inlet 107. The fluid flows in a downward direction, as illustrated in Figure 1, from inlet 107 and over the external surface 113 of each gravel filled jacket 105. The heated fluid transfers its heat energy to the jacket 105 and the gravel as it flows continuously in a downward direction through chamber 114 and out of the apparatus 100 via outlet 108. This through flow of heated fluid provides a charging of the apparatus 100. When the gravel 104 is heated to the predetermined temperature, the fluid flow through inlet 107 is terminated. Suitable valves and ducting (not shown) may be engaged to seal internal chamber 114 to extend the storage period and reduce any thermal conduction and heat loss due to fluid flow to and from chamber interior 114.

Figure 4 illustrates an optional embodiment in which the elongate jackets 105 are positionally retained adjacent each other via intermediate spacers 400. The spacers 400 increase the separation distance between the jackets' external surfaces 113 to increase the volume of the airflow channels 200 between jackets 105. The embodiment of Figure 4 may also comprise the corresponding braces to lock the spacers 400 in position between adjacent jackets 105.

Figure 5 illustrates a further embodiment in which the jackets 105 comprise a substantially square cross-sectional profile 500. Each jacket 500 comprises an integral spacer 501 extending radially outward, when viewed in cross-section as illustrated in Figure 5. A spacer 501 projects radially outward from each side face 502 and is configured to abut an adjacent spacer 501 of a neighbouring jacket 500. Spacers 501 therefore are equivalent to the non-integrally formed spacers 400 as illustrated in Figure 4. Figure 6 illustrates an alternate configuration of the apparatus of Figure 1. According to the further embodiment, the heat store apparatus 100 is configured as a counter flow device in which the fluid flow channels 200 that surround each jacket 105 are configured to allow the flow of fluid in a first direction 600 (for example in a downward direction from inlet 107 to outlet 108) and a reverse direction 601 (corresponding to an upward direction from outlet 108 to inlet 107 as illustrated in Figure 1). Suitable ducting and/or directing flanges (not shown) may be appropriately positioned within internal chamber 114 to achieve the counter flow configuration. This configuration has the effect on increasing the fluid flow contact with the heat storage medium contained within each jacket 105 at cavity 104. Additionally, any temperature gradient across the heat store is minimised with this counter flow arrangement. Figure 7 illustrates a specific further embodiment of the heat storage apparatus of Figure 1. According to the further embodiment, each gravel filled elongate column 105 is mounted and structurally supported by a respective support column 708. In particular, a lower region of each jacket 105 comprises a plate 702 extending across the otherwise lower open end of internal cavity 104 to seal cavity 104 at a bottom end. Plate 702 comprises a sufficient thickness to support the mass of aggregate accommodated within cavity 104.

According to the specific implementation, a lower region 700 of the construction aggregate comprises gravel whilst an upper region comprises gravel.

Each support column 708 comprises a cylindrical wall 704 optionally formed from steel. A diameter of cylinder 704 is less than a diameter of cylindrical jacket 105 and may be between 10 to 80% of that of jacket 105. A cylindrical neck 705 extends substantially vertically from base plate 702. Neck 705 comprises a diameter slightly less than a diameter of cylindrical column 704. Accordingly, neck 705 is configured to sit within the internal cavity 104 of column 704 to provide a tubular telescopic arrangement. The majority of the internal cavity within neck 705 and column 704 is filled with the construction aggregate and in particular gravel. A lower region 707 of each column 704 comprises gravel 706. Additionally, an upper region 703 of each neck 705 comprises gravel. According to this configuration, the combined support column 704 and neck 705 structurally support each jacket 105 and the internally encapsulated construction aggregate within each jacket 105. The lower region of each support column 707 is mounted upon a base 109 such as the ground or a specific support surface. As illustrated in Figure 1, thermal insulation material, such as rockwool 106 is positioned to surround chamber wall 102, and the same insulation material 106 also surrounds the lower support columns 708 to thermally insulate the apparatus 100 at the lower end region 702 of each jacket 105. As with the embodiment of figure 1, the embodiment of Figure 7 may comprise an outer skin or shell 712 to surround the rockwool 106.

A fluid flow outlet conduit 701 is positioned at a region immediately below plates 702 and is configured to receive the fluid flow exiting flow channels 200 in between the jackets' outer surfaces 113. Conduit 701 is therefore positioned at a lower region of chamber 114 and is in fluid communication with the passageways 200. This communication is provided by at least one aperture or valve 711 extending through wall 102. Accordingly, the fluid flows through passageways 200 and out of chamber 114 via aperture 711 and conduit 701 and subsequently outlet 108. To address any thermal expansion differential between the construction aggregate (gravel) within cavities 104 and the jacket walls 105, an internal spacer body may be provided within each jacket cavity 104. The spacer body may comprise an elongate deformable material positioned centrally within each cavity 104, for example at longitudinal axis 115. The spacer may for example comprise rockwool housed within a small diameter cylindrical cage or collapsible structure. Accordingly, as the steel wall of each jacket 105 expands at a slightly greater rate and diameter relative to the gravel, the expansion of the gravel into the radially outermost regions of each cavity 104 in close contact with the internal facing surface 103 is prevented as the gravel is capable of deforming inwardly to compress the axially orientated spacer. Such a configuration will avoid the gravel expanding into the outer regions of each jacket 105 which would otherwise prevent each jacket wall 105 from contracting back to its original position when it undergoes cooling.

A further embodiment of the heat storage apparatus 100 of Figure 1 is illustrated in Figure 8. According to this further implementation, each of the jackets 105 is supported at their lowermost region 112 by a suspended floor 801. Floor 801 comprises a plurality of apertures 802 orientated vertically and positioned to provide a fluid communication into the internal cavity 104 of each jacket 105. An airflow conduit 803 extends immediately below floor 801 with each aperture 802 providing fluid communication between cavities 104 and conduit 803. In contrast to the previous embodiments, the internal cavity 104 of each jacket 105 is devoid of construction aggregate and provides a space for fluid flow from inlet 107 to outlet 108. That is, the construction aggregate (gravel) is positioned to fill regions 200 between the jackets' external surfaces 113. Accordingly, as the heated fluid flows from inlet 107 to outlet 108 through each jacket cavity 104, the heat energy is transferred to the gravel contained within regions 200 for subsequent extraction and exploitation. The relatively cooled fluid then flows through apertures 802 and out through conduit 803 in flow direction 804 to pass out of the apparatus 100 via outlet 108. Floor 801 may be supported by columns or other support structures positioned between lower floor 109 and suspended floor 801.

According to a further embodiment of figure 8, the gravel is accommodated within each jacket 105 and the fluid flows around the outside region 200. Accordingly, the apertures 802 are shifted slightly relative to their position as shown in figure 8 to be positioned directly below internal cavity 104, so as to allow the fluid to flow through cavity 104 and into conduit 803.

According to preferred embodiments, the heat storage apparatus 100 comprises gravel as the heat storage medium. Alternatively sand, rock, pebbles, stones or other crushed aggregate such as concrete, may be accommodated within jackets 105 or at the region between jackets 200. The particle size of the gravel may be selected specifically to prevent the gravel falling into the outer region of each cavity 104 as each jacket 105 expands on heating.

According to further specific implementations, elongate jackets 105 may extend parallel to ground surface 109 so as to be aligned substantially horizontally within chamber 114. In this configuration, the air flow would then be directed substantially horizontally between inlet 107 and outlet 108, with inlet 107 positioned at a corresponding opposite side to outlet 108. The subject heat storage apparatus is advantageous and configured specifically to provide a thermal temperature gradient in the axial direction of the columns. In particular, the construction aggregate positioned axially closer to the fluid flow inlet, during use, is hotter than the corresponding construction aggregate located axially closest to the outlet. The present arrangement therefore is optimised to maximise the temperature gradient and to exhaust fluid from the storage device that is significantly cooler than the fluid flowing through the inlet. This significantly cooled fluid may then be supplied to the solar targets via suitable conduit tubing. The embodiments of figures 1 to 8 describe the flow of fluid in a downward direction from inlet 107 to outlet 108. As will be appreciated, the embodiments of figures 1 and 8 are equally implemented with the opposite fluid flow direction such that fluid flows into the storage apparatus 100 via tubing 108 and exists the apparatus 100 via tubing 107. An upward airflow direction is advantageous as the warmer air rising naturally through the storage apparatus facilitates fluid circulation.

According to the specific implementations, the heat transfer mechanism within the heat storage apparatus comprises conduction and radiation such that heat energy is transferred axially within the columns via this mechanism and any convection perpendicular to the axial direction through the columns is minimised.