WO2016187659A1

WO2016187659A1 - A hydroelectric generation system and a method for hydroelectric generation

Info

Publication number: WO2016187659A1
Application number: PCT/AU2016/050397
Authority: WO
Inventors: Christopher Leslie Waring
Original assignee: Mc2 Energy Pty Ltd
Priority date: 2015-05-25
Filing date: 2016-05-25
Publication date: 2016-12-01
Also published as: AU2016234957B2; AU2016234957A1

Abstract

A hydroelectric generation system (1) including a formation, in the form a manmade dam (2) having a dam wall (3), for containing a body of water (4). A first outlet (5) is disposed in the base of wall (3) at an effective elevation (E₁) for receiving a first flow (6) of water from the body of water (4). A hydroelectric generation unit (8) is disposed at a second elevation (E₂) that is lower than elevation (E₁) and is driven by flow (6) for supplying first electrical energy (9) to transmission lines (10). A PV electrical power generation unit, in the form of a plurality of floating PV arrays (13, 14 and 15), supplies second electrical energy (16) via transmission lines (17). Distribution infrastructure, in the form of a transformer and switching yard (20), transmits energy (9 and 16) via transmission lines (21) to an electrical distribution network in the form of a public electricity distribution grid (22). A controller (23) regulates the transmission of energy (9 and 16) by controlling the switching within yard (20).

Description

A HYDROELECTRIC GENERATION SYSTEM AND A METHOD FOR

HYDROELECTRIC GENERATION

FIELD OF THE INVENTION

[0001 ] The present invention relates to a hydroelectric generation system and a method for hydroelectric generation.

[0002] The invention has been developed primarily for water supply dams with potential or existing hydroelectric generation facilities and will be described hereinafter with reference to that application. However, it will be appreciated that the invention is not limited to that particular field of use and is also applicable to future hydroelectric generation facilities, and modifications and modes of hydroelectric generation operation that were not originally designed to incorporate respective embodiments of the invention.

BACKGROUND

[0003] Any discussion of the background art throughout the specification should in no way be considered as an admission that such art is widely known or forms part of common general knowledge in the field.

[0004] Global construction of many large-scale hydroelectric power generation schemes in the 20^th century formed the bulk of the world's renewable energy generation capacity. In Australia construction of the Tasmanian hydroelectric generators and the Snowy Hydroelectric Scheme, completed in 1974, provided an important contribution to Australia's industrial development. The shortage of suitable new dam sites and the environmental impact of flooding forested catchments has since limited the construction of new large hydroelectric schemes in most countries except China. As a consequence, the proportion of renewable energy supplied by hydroelectric and bagasse fuelled generation in Australia diminished from 1974 until about ten years ago. In Australia's mainland states approximately 85% of electric power provided by the networked distributors is generated by burning fossil fuel resources such as coal, and natural gas in very large power stations. This hub-and-spoke model of centralised electricity generation with transmission and distribution networks is also dominant internationally. However, with increasing public and international concerns about the environmental sustainability and cost escalations of maintaining the hub and spoke electricity supply model there has been considerable appetite at both the individual and government levels to seek out alternative electricity supply solutions. This has accelerated the adoption of renewable energy generators such as small scale PV arrays and commercial solar farms, solar thermal, and wind turbines which, in turn, has led to significant reductions in the unit costs associated with such solutions as the benefits of mass manufacturing are able to be gained. For example, in broad terms, PV panel costs have fallen by about 80% since 2008 and are predicted to fall further. These decentralised renewable electricity generators are also advantageous as they can be implemented at any scale from 1 kW to 1 GW, may be matched to local demand, and are able to contribute to a reduction or an elimination of transmission and distribution networks. The levelised cost of electricity from rooftop PV delivered to households in most parts of Australia is less than half the cost of the retail price of electricity delivered by centralised power generators and networks.

[0005] As a result of this global trend it is usual for an electrical power distribution network to be supplied by a wide variety of electrical power sources with considerable time dependent variability of supply due to local weather conditions. This variability is particularly problematic for the large coal fired generators due to their poor transient response capabilities and is becoming more problematic as the popularity of renewable energy generation systems increases and the proportion of total energy supplied to the networks from renewable energy generation grows.

[0006] The benefit generally attributed to non-renewable sources for generators is that those generators are able to provide a consistent base load to the network. However, the demand of electrical energy from the network by all the connected loads varies significantly over any given day, or day of the week. The typical demand profile includes a morning and evening peak, with a fall from the morning peak that rises relatively steeply into the evening peak, and a moderate plateau over night between the peaks. When such networks are supplied by generators making use of non-renewable energy there is considerable inefficiency and overcapacity required if there is a desire to prevent blackouts or brownouts. For such generators, particularly those fuelled by coal or nuclear fuel, take considerable time to change their outputs. Due to this poor transient response from such generators, and the considerable capital cost of having available but not used capacity, considerable effort has gone into developing predictive modelling of future demand in an attempt to better manage the generators and to avoid having to consume more fuel than is required to meet the actual demand and maintain the safety margin for generating the possible peak load. These models can provide some benefit but only typically provide a second order impact.

[0007] An example of the consequences arising from the poor transient response of typical coal-fired generators is provided by looking at the more extreme conditions in the demand profile. Due at least in part to the modern phenomenon of widespread use of air conditioners in households, commercial and office buildings and government buildings, there has arisen extreme demands for electricity during heat-waves. For example, in the summer of 2013-2014 in Australia, the National Electricity Market (NEM) (which covers the states of Queensland, New South Wales, Victoria, South Australia and Tasmania) encountered about twenty days in which heatwave conditions were experienced. On these days the wholesale electricity prices rose at peak demand to near the extreme market cap of AU$13,100 / MWh. This cap is set by the NEM regulator - the Australian Energy Market Operator (AEMO) - and was far in excess of a normal daily average of approximately AU$30 / MWh. On 15 January 2014, the state of Victoria was warned by AEMO to expect forced electricity supply shortages - that is, regional blackouts - despite estimates from AEMO that the NEM enjoyed overall an excess generation capacity of 9 GW. Another impact is that, as it is known such extreme demands will likely be experienced, regulators and governments wish to ensure the generation capacity is sufficient to supply those peaks. The conventional solution for non-renewable generators to be able to quickly supply such peaks is to have large "spinning reserve" that is ready to come on-line to ensure that the elevated supply can be guaranteed as and when it is demanded. However, that spinning reserve must be powered almost continuously, typically by burning coal, which comes at a financial and an environmental cost. A further consequence of the existing generation capability in this network is that between consecutive hot days - that is, those days in which the non-renewable generators are required to anticipate the need to supply the elevated peaks - the overnight wholesale electricity prices are often negative.

[0008] Renewable energy powered generators are mostly intermittent, with the exception of hydroelectric generation which is typically more controllable. As increasing use is made of renewable energy powered generators - for economic, social and environmental reasons - increasing strain will be put on the non-renewable powered generators. That is, while the earlier generators had to cope with load variations due to demand for energy from the network, they increasingly have to cope also with additional variations due to alternative supplies of energy to the network that can change quickly.

[0009] Due to the irresistible drivers for increased renewable energy generation of electricity - by individuals, corporations and governments - and the supply of that electricity to electrical distribution networks, the supply and demand imbalances in those networks will continue to build. Accordingly, over time, the fuel, health and environmental costs of persisting with non-renewable generators to provide base load will become prohibitive, just as to obtain 100% of the required on-demand supply from renewable generators will, at least in the short-term, remain prohibitive. [0010] The above factors make it more and more difficult for coal-fired generators to cost-effectively operate as the demand they experience from the network is subject to more and more transient factors all of which come with a high degree of unpredictability and which change at a fast rate. The rate of change being experienced by traditional energy generators has also become more pronounced in recent years due to the changing nature of the demand for energy, customers reducing energy consumption largely in response to high electrical distribution network charges, and the increasing supply of energy to the network from distributed sources such as PV arrays. In particular, due to the widespread use of PV arrays, the demand profile for energy from traditional forms of generators in a number of networks has been progressively changing over the years to include a more pronounced dip during day-time, and a more pronounced ramp during the evening. Accordingly, the "base load" - that is, the minimum load at any given time - is falling precipitously. This factor alone is problematic, and is exacerbated by the following more rapid increase in the required supply as the ramp up into the evening peak occurs just as the contribution from the PV arrays is tapering. Both these factors are problematic for traditional non-renewable energy generators which operate best in a steady state environment, or where any change is gradual as well as highly and accurately predictable.

[001 1 ] The increasing availability and use of renewable energy generators, particularly wind turbines and PV arrays, has made it more feasible for individual consumers, or groups of consumers, to omit connecting to the broader electrical distribution network and "go off-grid". This involves installing some form of energy storage device, such as a battery bank. While this can be superficially attractive, it does require each of the individual systems to be overdesigned to accommodate the anticipated peak loads or, alternatively, for the users to accept that there will be energy shortages from time to time. This invariably leads to times of excess electricity generation and times of insufficient electricity generation, requiring a very large storage capacity. While the cost of this storage is falling, it remains substantially uneconomic in all but isolated instances. These compromises would be greatly ameliorated by eliminating the need for the storage device or allowing the use of a much smaller storage device. This could occur by connecting the generation capacity to the broader network to theoretically allow any excess energy to be supplied to the network, and for the network to supply any shortfall that may occur at other times. However, as mentioned above, this can be incompatible with the overall network settings that have historically been developed to primarily accommodate a supply from non-renewable sources. [0012] The increasing variability and volatility of supply and demand has not been matched by any reduction in the public or commercial expectation about all electricity demands being met. The need for the NEM to provide this certainty of electricity supply to meet any electricity demand from the network, in an environment where increasing proportions of the supply are volatile and sourced from a greater number of smaller distributed generators, has resulted in greater electrical distribution network costs and higher running costs for the larger and established coal fired generators. This in turn has resulted in higher electricity cost to consumers that provides a greater financial incentive for those consumers to use less electrical energy, or to install localised renewable energy generation systems (such as household PV systems). This has led to a concern amongst some commentators and industry luminaries about a potential self-perpetuating migration toward intermittent sources (and away from the NEM) which has been colloquially referred to as "a death spiral" for the networks and traditional generators. This so-called "death spiral" is also exacerbated by the high cost imposed by the electricity distribution network in Australia having been historically designed and optimised around a hub-and-spoke arrangement with the coal fired power generators defining the hubs. The resultant cost faced by those using distributed generation in connecting to the network only provides further impetus to those generators to remain off grid.

[0013] The more stable form of renewable electricity generation is, as mentioned above, provided by hydroelectric generators. These systems require custom built facilities including dams and pipes between dams. In Australia many of the best sites for building dams were identified and exploited during the first half of 20^th century. These dams were constructed often with the objective of providing secure water supply to Australia's cities and for agricultural irrigation. Renewable hydroelectric power generation was an additional benefit that has been undervalued in an era of low cost coal fired base-load power generation and was not a decisive factor in the selection and design of most dams.

[0014] During the latter part of the 20^th century there has also emerged growing concern for the environmental impact from dam construction, exemplified by disputes in the state of Tasmania, where action was taken to block the construction of the Franklin Dam. As a result, there is likely to be no new major dams constructed in Australia. In response to climate change in the 21 ^st century, and an era of increasing renewable energy generation, the value of the flexible supply from hydroelectric generation assets is appreciating. However, the dual use of these dams for water supply and power generation places constraints upon the ability to supply the full power capacity when it is needed in the electricity market. For example, when drought conditions exist the hydroelectric power supply is curtailed. [0015] Many large dams built in the state of New South Wales primarily for water supply purposes have MW scale hydroelectric generators that are used infrequently as they are not designed or operated to meet rapidly fluctuating electricity power loads.

[0016] In partial response to the above problems there has been limited use made of pumped hydroelectric systems to consume energy from the network during low demand periods to pump water to a higher elevation, and to allow that water to flow back to the original location during a second period when demand from the network is high, so as to generate electricity and supply it to the network at that time. This partial solution of offering an energy storage facility, whilst beneficial, is not suited to many geographic locations and is often of marginal benefit in existing installations which were not originally designed with such an operation in mind.

[0017] The abovementioned problems typically apply in many other jurisdictions and geographic areas, although local conditions may vary the degree of any one or more aspect of the problems.

[0018] Accordingly, there is a need in the art for an improved hydroelectric system and a method for operating such a system.

SUMMARY OF THE INVENTION

[0019] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

[0020] According to a first aspect of the invention there is provided a hydroelectric generation system including:

a formation for containing a body of water having a first layer that is substantially fresh water and a second layer below the first layer that is substantially sea-water; a first outlet in the formation at a first elevation for receiving a first flow of sea- water from the second layer;

a generation unit disposed at a second elevation that is lower than the first elevation for being driven by the first flow to supply electrical energy;

a first inlet in the formation for receiving a second flow of sea-water into the second layer; and

a pumping unit for selectively pumping sea-water to define the second flow.

[0021 ] In an embodiment the inlet and the outlet are defined by a common structure.

[0022] In an embodiment the inlet and the outlet are defined by respective separate structures.

[0023] In an embodiment the first inlet defines a plurality of inlet paths and the first outlet defines a plurality of outlet paths. [0024] In an embodiment the electrical energy is supplied to an electrical distribution network and the pumping unit includes one or more electrically powered pumps that draw electrical energy from the network.

[0025] In an embodiment the generator unit and the pump unit are collectively defined by a reversible hydroelectric generator.

[0026] In an embodiment the reversible hydroelectric generator is disposed adjacent to a sea and expels and draws the first flow and the second flow respectively into and from the sea.

[0027] In an embodiment the formation includes at least one second inlet for receiving a third flow of freshwater to be added to the first layer.

[0028] In an embodiment the formation includes at least one second outlet for receiving a fourth flow of freshwater to be removed from the first layer.

[0029] In an embodiment the second inlet receives the third flow from at least one first watercourse and the second outlet directs the fourth flow to at least one second watercourse.

[0030] In an embodiment the system includes a controller for regulating the operation of the generator unit and the pump unit to allow the first flow and the second flow.

[0031 ] In an embodiment the electrical energy supplied to the electrical distribution network occurs at a first price and the energy drawn from the electrical distribution network occurs at a second price, the controller being responsive to the first and second prices for regulating the operation of the generator unit and the pump unit.

[0032] In an embodiment the prices are time dependent.

[0033] In an embodiment the time dependency of the prices is relative to the time of day that the energy is drawn from or supplied to the network respectively.

[0034] In an embodiment one or more of the prices are unit prices.

[0035] In an embodiment, during a first period and a second period in a day, there are respective first and second pricing structures for energy drawn from the network, and wherein the first pricing structure is generally higher than the second pricing structure and the controller is responsive to the periods for primarily drawing energy from the network during the second period.

[0036] In an embodiment, during a third period and a fourth period in a day, there are respective third and fourth pricing structures for energy supplied to the network, and wherein the third pricing structure is generally lower than the fourth pricing structure and the controller is responsive to the third and the fourth periods for primarily supplying energy to the network during the fourth period.

[0037] In an embodiment one or more of the periods are continuous. [0038] In an embodiment all the periods are continuous.

[0039] In an embodiment at least one of the periods is discontinuous.

[0040] In an embodiment more than one of the periods are continuous.

[0041 ] In an embodiment the pricing structures allow for varying prices within the respective period.

[0042] In an embodiment the controller is responsive to any one or more of the periods such that the electrical energy supplied to the network occurs at least primarily during the first period.

[0043] In an embodiment the controller is responsive to any one or more of the periods such that the electrical energy drawn from the network occurs at least primarily during the third period.

[0044] In an embodiment the formation has a capacity and the controller is responsive to the capacity for ensuring, during use, the second layer occupies up to 80% of the capacity.

[0045] In an embodiment the controller is responsive to the capacity for ensuring, during use, the second layer occupies up to 20% of the capacity.

[0046] In an embodiment the controller selectively operates in one of a plurality of modes including:

a first mode in which the second layer occupies up to 20% of the capacity; and a second mode in which the second layer occupies more than 20% of the capacity.

[0047] In an embodiment the first mode is either a normal mode or a flood mode.

[0048] In an embodiment the second mode is a drought mode.

[0049] In an embodiment the formation is substantially a geographic formation.

[0050] In an embodiment the formation includes a dam wall and the first outlet is disposed in the wall.

[0051 ] In an embodiment the first and second flows do not substantially agitate the second layer.

[0052] In an embodiment the first inlet directs the second flow into the second layer along one or more diffuse flow paths.

[0053] In an embodiment the first outlet receives the first flow along one or more diffuse flow paths.

[0054] In an embodiment the layers maintain substantially stratified due to a halocline.

[0055] In an embodiment the system includes a desalination plant for converting sea- water into desalinated fresh water, wherein the plant:

draws electrical energy from the distribution network and/or the generator unit; and adds at least some of the desalinated fresh water to the first layer. [0056] In an embodiment the system includes at least one PV generation device that is disposed on the first layer and which produces electrical energy.

[0057] In an embodiment the electrical energy produced by the PV generation device is supplied to the distribution network.

[0058] In an embodiment the PV generation device includes one or more structures for floating on the first layer, wherein each structure supports an array of PV panels for generating the electrical energy.

[0059] In an embodiment the electrical distribution network is associated with an industrial production facility.

[0060] According to a second aspect of the invention there is provided a method for operating a hydroelectric generation system, the method including the steps of:

containing a body of water in a formation, the body of water having a first layer that is substantially fresh water and a second layer below the first layer that is substantially sea-water;

providing a first outlet in the formation at a first elevation for receiving a first flow of sea-water from the second layer;

disposing a generation unit at a second elevation that is lower than the first elevation for being driven by the first flow to supply electrical energy;

providing a first inlet in the formation for receiving a second flow of sea-water into the second layer; and

selectively pumping sea-water with a pumping unit to define the second flow.

[0061 ] According to a third aspect of the invention there is provided a hydroelectric generation system including:

a formation for containing a body of water;

a first outlet in the formation at a first elevation for receiving a first flow of water from the body of water;

a hydroelectric generation unit disposed at a second elevation that is lower than the first elevation which is driven by the first flow for supplying first electrical energy;

a PV electrical power generation unit for supplying second electrical energy;

distribution infrastructure for transmitting the first and second energy to an electrical distribution network; and

a controller for regulating the transmission of the first and second energy by the distribution infrastructure. [0062] In an embodiment the body of water includes a surface and the PV electrical power generation unit includes at least one floating PV array that is disposed on the surface.

[0063] In an embodiment the PV electrical power generation unit includes a plurality of floating PV arrays each of which is disposed on the surface.

[0064] In an embodiment the controller regulates the transmission of the first and second energies to provide a predetermined total energy output to the electrical distribution network.

[0065] In an embodiment the predetermined total energy output varies with time.

[0066] In an embodiment the controller regulates the operation of the hydroelectric generation unit to regulate the transmission of the first energy to the distribution by the distribution infrastructure.

[0067] In an embodiment the controller is responsive to one or more characteristic of the second energy for regulating the operation of the hydroelectric generation unit.

[0068] In an embodiment the one or more characteristics of the second energy include: the present instantaneous value of the second energy; the anticipated instantaneous value of the second energy at a given future time; the instantaneous value of the second energy at a past time; the total second energy supplied during a given past period; the anticipated total second energy to be supplied in a future period; the average second energy supplied during a given past period; and the anticipated average second energy to be supplied in a future period.

[0069] In an embodiment the predetermined total energy output defines a target output for the system for a given time interval, and the controller is responsive to the target output for the given time interval for regulating the transmission of the first and second energies to the electrical distribution network.

[0070] In an embodiment the controller is responsive to the target output in the given time interval for allowing up to all of the second energy to be transmitted to the electrical distribution network.

[0071 ] In an embodiment the controller is responsive to the second energy during the given period being less than the target output for allowing the first energy to be transmitted to the electrical distribution network.

[0072] According to a fourth aspect of the invention there is provided a method for hydroelectric generation including the steps of:

containing a body of water in a formation;

providing a first outlet in the formation at a first elevation for receiving a first flow of water from the body of water; disposing a hydroelectric generation unit at a second elevation that is lower than the first elevation which is driven by the first flow for supplying first electrical energy;

supplying second electrical energy with a PV electrical power generation unit; providing distribution infrastructure for transmitting the first and second energy to an electrical distribution network; and

regulating the transmission of the first and second energy by the distribution infrastructure with a controller.

[0073] According to a fifth aspect of the invention there is provided a hydroelectric generation system including:

a barrier layer for defining an interface between the two layers.

[0074] In an embodiment the barrier layer is pliant.

[0075] In an embodiment the barrier layer is substantially rigid.

[0076] In an embodiment the barrier layer is substantially water impermeable.

[0077] In an embodiment the barrier layer is a plastics sheet.

[0078] In an embodiment the barrier layer is woven.

[0079] In an embodiment of the barrier layer is loosely woven.

[0080] In an embodiment the first layer includes a first density, the second layer includes a second density that is greater than the first density and the barrier layer includes a third density.

[0081 ] In an embodiment the third density is intermediate the first density and the second density.

[0082] In an embodiment the barrier layer includes a barrier member having a fourth density that is greater than the second density and one or more buoyancy devices.

[0083] In an embodiment the barrier layer includes a barrier member having a fourth density that is less than the first density and one or more weight devices.

[0084] In an embodiment the barrier layer defines an interface between the two layers above one or both of the first outlet and the first inlet. [0085] In an embodiment the barrier layer includes a first edge and a second edge that is spaced apart from the first edge, wherein the first edge is disposed at or adjacent to a peripheral edge of the formation.

[0086] In an embodiment the first edge extends along substantially all of the peripheral edge of the formation.

[0087] In an embodiment the first edge is fixed to the peripheral edge.

[0088] In an embodiment the first edge moves vertically in response to the first and second flows.

[0089] In an embodiment the barrier layer extends between substantially all of the first layer and the second layer.

[0090] In an embodiment, the barrier layer is spaced apart from a peripheral edge of the formation.

[0091 ] In an embodiment the system includes a pumping unit for selectively pumping sea-water to define the second flow.

[0092] In an embodiment the first inlet and the first outlet are defined at least in part by a common opening in the formation.

[0093] According to a sixth aspect of the invention there is provided a method for hydroelectric generation including the steps of:

defining an interface between the two layers with a barrier layer.

[0094] According to a seventh aspect of the invention there is provided a dam for a hydroelectric generation system, the dam including:

a formation for containing a body of water having a first layer that is substantially fresh water and a second layer below the first layer that is substantially sea-water; a first outlet in the formation for receiving a first flow of sea-water from the second layer;

a first inlet in the formation for receiving a second flow of sea-water into the second layer; and a barrier layer for defining an interface between the two layers.

[0095] In an embodiment, the first outlet is disposed at a first elevation for receiving the first flow of sea-water, and the hydroelectric generation system includes a generation unit that is disposed at a second elevation that is lower than the first elevation for being driven by the first flow to supply electrical energy.

[0096] In an embodiment the hydroelectric system includes a pumping unit for selectively pumping sea-water to define the second flow.

[0097] In an embodiment the first inlet and the first outlet are defined at least in part by a common opening in the formation.

[0098] In an embodiment the barrier layer is pliant.

[0099] In an embodiment the barrier layer is substantially rigid.

[00100] In an embodiment the barrier layer is substantially water impermeable.

[00101 ] In an embodiment the barrier layer is a plastics sheet.

[00102] In an embodiment the barrier layer is woven.

[00103] In an embodiment of the barrier layer is loosely woven.

[00104] In an embodiment the first layer includes a first density, the second layer includes a second density that is greater than the first density and the barrier layer includes a third density.

[00105] In an embodiment the third density is intermediate the first density and the second density.

[00106] In an embodiment the barrier layer includes a barrier member having a fourth density that is greater than the second density and one or more buoyancy devices.

[00107] In an embodiment the barrier layer includes a barrier member having a fourth density that is less than the first density and one or more weight devices.

[00108] In an embodiment the barrier layer defines an interface between the two layers above one or both of the first outlet and the first inlet.

[00109] In an embodiment the barrier layer includes a first edge and a second edge that is spaced apart from the first edge, wherein the first edge is disposed at or adjacent to a peripheral edge of the formation.

[001 10] In an embodiment the first edge extends along substantially all of the peripheral edge of the formation.

[001 1 1 ] In an embodiment the first edge is fixed to the peripheral edge.

[001 12] In an embodiment the first edge moves vertically in response to the first and second flows.

[001 13] In an embodiment the barrier layer extends between substantially all of the first layer and the second layer. [001 14] In an embodiment, the barrier layer is spaced apart from a peripheral edge of the formation.

[001 15] According to an eighth aspect of the invention there is provided a method for damming a body of water for a hydroelectric generation system, the method including the steps of:

containing the body of water in a formation, the body of water having a first layer that is substantially fresh water and a second layer below the first layer that is substantially sea-water;

providing a first outlet in the formation for receiving a first flow of sea-water from the second layer;

defining an interface between the two layers with a barrier layer.

[001 16] In the claims below and the description herein, any one of the terms "comprising", "comprised of" or "which comprises" is an open term that means including at least the elements/features that follow, but not excluding others. Thus, the term "comprising", when used in the claims, should not be interpreted as being limitative to the means or elements or steps listed thereafter. For example, the scope of the expression "a device comprising A and B" should not be limited to devices consisting only of elements A and B. Any one of the terms "including" or "which includes" or "that includes" as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, "including" is synonymous with and means "comprising".

[001 17] As used herein, the term "exemplary" is used in the sense of providing examples, as opposed to indicating quality. That is, an "exemplary embodiment" is an embodiment provided as an example, as opposed to necessarily being an embodiment of exemplary quality.

BRIEF DESCRIPTION OF THE DRAWINGS

[001 18] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic view of a hydroelectric power generation system according to one embodiment of the invention;

Figure 2 is a schematic view of a hydroelectric power generation system according to another embodiment of the invention; Figure 3 is a schematic side view of the dam in Figure 2 including a barrier layer; and

Figure 4 is a schematic top view of the dam of Figure 3. DETAILED DESCRIPTION

[001 19] Described herein are a hydroelectric power generation system and a method for operating such a system.

[001 20] Referring to Figure 1 there is illustrated a hydroelectric generation system 1 including a formation, in the form a manmade dam 2 having a dam wall 3, for containing a body 4 of water. A first outlet 5 is disposed in the base of wall 3 at an effective elevation Ei (due to the hydraulic pressure provided by body 4 of water) for receiving a first flow 6 of water from the body 4. A hydroelectric generation unit 8 is disposed at an effective elevation E₂, which is less than elevation E_{1 5} and is driven by flow 6 (that falls a vertical distance of {E-i - E₂)) for supplying first electrical energy 9 to transmission lines 10. Note that unit 8 itself is disposed at an elevation lower than both elevation and E₂. A PV electrical power generation unit, in the form of a plurality of floating PV arrays (only three arrays 1 3, 14 and 15 are exemplarily illustrated), supplies second electrical energy 1 6 via transmission lines 1 7. Distribution infrastructure, in the form of a transformer and switching yard 20, transmits energy 9 and 16 via transmission lines 21 to an electrical distribution network in the form of a public electricity distribution grid 22. A controller 23 regulates the transmission of energy 9 and 16 by controlling the switching within yard 20.

[001 21 ] It will be appreciated that outlet 5 is the outlet in dam 3 for flow 6 to be directed into pipes 24a that further direct that flow to unit 8 to enable the subsequent generation of electricity. After exiting unit 8, flow 6 is directed through pipes 24b to a second outlet 24c where it is released back into the environment. In this embodiment flow 6 is released into a holding pond 24d. However, in other embodiments different or additional environmental formations are used. For example, in the Figure 2 embodiment use is made of a sea 24e. Outlet 24c is able to be considerably geographically spaced from outlet 5, even by many kilometres. In this embodiment the geographic spacing between outlet 5 and 24c is 1 1 km.

[001 22] Unit 8 includes eight like hydroelectric pump/generators that are within a single facility and arranged physically side-by-side in a linear array and electrically in parallel. Each of the pump/generators are able to be run independently of the other. Accordingly, flow 6 drives at least one, and up to all, of the pump/generators in response to control signals from controller 23. In other embodiments a different number of pump/generators are used. [00123] In this embodiment the vertical difference between E^ and E₂ is about 300 metres. That is, {E-i - E₂) = 300 metres. In other embodiments {E-i - E₂) is other than 300 metres, and preferably more. The greater the vertical separation the greater the potential energy that is stored in body 4 and which is able to be converted into electrical energy by unit 8.

[00124] The body 4 of water has a top surface 25, and each of arrays 13, 14 and 15 have a generally circular buoyant base having a diameter of about 12 metres that rest upon surface 25. Supported on each base is sufficient PV panels to generate about 30 kW of electric power. In the present embodiment there are five thousand such arrays, providing a combined instantaneous electricity generation capacity of about 150 MW. In other embodiments a different number of arrays are used, or different arrays of other capacities, to provide a correspondingly different power generation capacity. Preferentially the bases cover substantially all of surface 25 to reduce evaporation. Disposing the arrays on or close to a large body of water also has the advantage of keeping the PV cells at a lower and more stable temperature, enhancing the power generated by and longevity of the PV. Covering a portion of a water supply dam with floating PV substantially reduces light penetrating into the water. This aspect of covering the dam's surface with floating PV is also advantageous in reducing photo-synthetic activity of algae. Some blue-green algae produce toxins harmful to human health when consumed from drinking water. Outbreaks of blue-green algae have caused closure of the water supply dams until the algae have cleared.

[00125] Surface 25 includes a large surface area and is able to support a large number of floating PV arrays. The number of arrays indicated above is indicative only, and many more are able to be included, either initially, or added over time, to increase the electricity generation capacity available from the arrays.

[00126] In further embodiments different forms of arrays are used, such as rectangular arrays. For example, in some embodiments the arrays are constructed from laminar flexible thin film sheets incorporating PV cells. These sheets are mounted on a low density plastic substrate that floats directly on the surface and which does not require a separate base (such as frames, pontoons etc.). This allows deployment costs to be minimised further due to the orientation issues for the PV arrays be resolved (in that the arrays are substantially horizontal) and they need not be fixed. Additionally, the stiffness of the thin film is able to be selected to match the most desirable "surface tension" for surface 25. That greatly reduces the risk of wind damage to the arrays by creating suction with the water underneath. The reduction of lifting by the wind, combined with the flexibility to conform with the contour of surface 25, greatly simplifies the required fixing infrastructure. These PV arrays are typically manufactured in large rolls having a width of about 5 to 10 m and a length of about 20 m. Other sizes are also available.

[00127] In still further embodiments system 1 includes one or more PV arrays that are land based.

[00128] All the energy 16 generated by arrays 13, 14 and 15 (and any other arrays used in system 1 ) is transmitted by lines 17 to an inverter station 27 where the DC signal is converted to an AC signal, and the resultant electrical energy (that is, energy 16 less losses) is transmitted along a transmission line 28 to yard 20. In other embodiments use is made of distributed micro-inverters such as those supplied by Enphase Energy, Inc. Each micro-inverter takes the output from one or two PV panels and creates an AC signal. The output from the individual inverters are then connected in parallel to provide the AC signal at the desired voltage (typically 240 Volts AC in Australia) and frequency (typically 50 Hz in Australia). These micro-inverters are designed to typically output less than 500 W. It will be appreciated that micro-inverters of different size provided by other manufacturers and suppliers are also applicable.

[00129] In another embodiment each of the pump/generators in unit 8 include a drive shaft about which are disposed respective DC electric motors. The DC power provided by arrays 13, 14 and 15 is supplied to and drives the DC electric motors. As the output electricity from the pump/generators is AC this arrangement of DC electric sharing a common drive shaft reduces or eliminates the need for power inversion of the DC power. In this embodiment the operation of the electric motors is also by controller 23. More particularly, controller 23 selectively engages or disengages the pump or the DC electric motors and the AC pump/generator based upon a variety of inputs. These inputs include, but are not limited to, the DC power being supplied by arrays 13, 14 and 15 at any given time, the 5 minute (or other) NEM market price, whether flow 6 is to be used to drive unit 8, or whether unit 8 operated in a pump mode to provide for a reverse of flow 6. That is, the following combinations are available:

• DC power alone is used to drive unit 8 to act as a spinning generator. That is, the DC power is used to maintain one or more of the pump/generators of unit 8 spinning at an operable speed without any of flow 6 being used. Should additional power be quickly required for supply to grid 22, flow 6 is commenced to the spinning generator and the required power is able to be supplied rapidly.

• DC power alone is used to drive unit 8 to pump water into body 4. That is, a reverse flow 6 is provided. • DC power and AC power from the grid is used to drive unit 8 to pump water into body 4

[00130] In some embodiments the DC voltage provided by arrays 13, 14 and 15 is increased to reduce any electrical transmission losses between the arrays and unit 8.

[00131 ] The above embodiment, which makes use of DC electric motors, is particularly intended to reduce the cost of integrating the floating PV arrays with hydroelectric power generation.

[00132] It will also be appreciated that as the relative amount of electricity generated in a given network by renewable power sources increases that there arise issues with voltage and frequency control to provide network stability. Accordingly, for a network such as the NEM, as the penetration of renewables continues to grow so too will the value of having a large spinning generator, such as that outlined above. The provision of these frequency and voltage control services to the NEM by system 1 will earn direct revenue from the ancillary services market. In this further way the embodiment allows for this asset to be provided in a cost and energy effective way.

[00133] In a number of jurisdictions there are electric rail networks that make use of DC power. For example, in the state of New South Wales, Australia, the electric rail network makes use of 1 ,500 Volts DC. The embodiment above, which is able to supply DC power, is able to directly supply that power to the rail network. In further embodiments, controller 23 allows flow 6 to drive the DC electric motors to generate a DC voltage. This voltage is able to be converted into a high voltage DC signal for low loss transmission. This form of transmission is particularly attractive for long transmission lengths where system 1 is significantly spaced apart from the grid 2.

[00134] Controller 23 regulates the transmission of energy 9 and 16 to provide a predetermined total energy output 30 to grid 22 via transmission lines 21 . Controller 23 is responsive to a variety of inputs for regulating the predetermined total energy output 30 to vary with time. This includes controller 23 regulating the operation of the hydroelectric generation unit 8 to regulate the generation of energy 9 and the distribution of that energy by yard 20. Controller 23 also controls the operation of yard 20 (as described above) and of station 27. In this embodiment, where system 1 is retrofitted into an existing hydroelectric generation facility, controller 23 is located within an existing control centre (not shown) and control lines 35 and 36 are provided for linking controller 23 to the various pieces of existing infrastructure being controlled. Also provided is a further control line 37 for allowing communication between controller 23 and station 27. While lines 35, 36 and 37 are typically communication lines - in that they enable two-way communication between the connected infrastructure (accommodating both command signals and sensor signals) - there are in other embodiments dedicated sensor lines for gathering specific local data to which controller 23 is responsive in regulating the operation of system 1 . It will be appreciated that any one or more of lines 35, 36 and 37, or any one or more of the sensor lines, are able to be implemented using wireless technology, or are able to make use of public telephone networks, other public or private communications networks, or a combination of these.

[00135] System 1 makes use of a second body 40 of water into which flow 6 is directed after having driven unit 8. In this embodiment body 40 is a pre-existing manmade dam that was specifically constructed for use with unit 8. However, in other embodiments, body 40 is a river or other watercourse, or a lake or other natural water body. In further embodiments, body 40 is a sea or other body of sea-water.

[00136] Dam 2 is based upon a natural geographic formation into which a watercourse flows from an upstream water capture area. In this embodiment the water capture area provides an intermittent flow 41 of water into dam 2 by way of an inlet 42. In other embodiments flow 41 is from a further dam and is regulated by controller 23. In further embodiments, flow 41 is regulated by other than controller 23.

[00137] Wall 3 of dam 2 includes a second outlet 43 for allowing a third flow 44 of water from dam 2. This flow 44 is typically provided to ensure sufficient environmental flows in the watercourse downstream of dam 2, as well as to satisfy other demands such as downstream irrigation usage, anticipated inflow into dam 2 (that is, the anticipated volume and timing of flow 41 ), the risk of overflow of dam 2, and other such factors.

[00138] Grid 22 allows for the transmission of the electricity from all the electricity generated, including system 1 , to the electrical loads such as central business district users 47, commercial users 48 and residential users 49. Additionally, there is also an industrial user 50 that draws the electricity from grid 22 via higher voltage transmission lines 51 into a dedicated transformer and switching yard 52. The transformed and switched lower voltage electricity is transmitted by transmission lines 53 to the relevant industrial load.

[00139] System 1 defines a hybrid power generation system that is capable of supplying grid level amounts of electricity in an improved and effective manner. As will be described below, the user of controller 23 allows the two forms of power generation to be complementarily combined whilst using little additional infrastructure, and certainly less infrastructure than would be required if the two forms of generation were separately built and operated. That is, system 1 allows capital savings to be achieved and offers grid supply benefits that would not be practically available to two independently operated generators.

[00140] The operator of system 1 is typically a corporation or a government or semi- government authority. This operator is participating in an electricity market where bids are placed for the supply of electricity (in predetermined amounts) by the various generators for given time periods. For the NEM these bids are placed just ahead of time and typically for periods of about half an hour. If a bid is successful, and taken up, the energy is supplied during the relevant period. If the bid is not successful a further bid is made, should there be time. The following explanation of the operation of the NEM is provided by the AEMO:

"Electricity production is matched to electricity consumption, and spare generating capacity is always kept in reserve in case it's needed. The current energy price then can be calculated. Electricity production is also subject to transmission limitations so that the network is not overloaded.

In delivering electricity, a dispatch price is determined every five minutes, and six dispatch prices are averaged every half-hour to determine the "spot price" for each NEM region. AEMO uses the spot price as its basis for settling the financial transactions for all electricity traded in the NEM."

[00141 ] Given the above, the hybrid embodiments of the invention are particularly advantageous, not only due to being able to quickly accommodate changes (by providing additional supply, or consuming any excess supply from other generators), but also by allowing other generators to operate more effectively to supply at the times and prices best suited to those individual generators.

[00142] It will be appreciated that the amount of electricity generated collectively by PV arrays 13, 14 and 15 varies significantly with time depending upon such factors as the array orientation, the available sunlight/the prevailing cloud cover, the number of PV panels operating, and temperature. Typically, the amount of electricity produced by these arrays will ramp up quickly by mid-morning before peaking in the early afternoon, before ramping down toward the end of the day. For unit 8, on the other hand, the amount of electricity generated is finely controllable so long as there is available water in body 4 to form flow 6.

[00143] In determining how to regulate flow 6 to unit 8 controller 23 is responsive to the amount of electrical energy that the operator has successfully bid to supply to grid 22, the time in which that supply is to occur, the current time, and the anticipated capacity of arrays 13, 14 and 15 to supply electrical energy 16. Accordingly, the operator is able, through appropriate software controls executed by controller 23, very precisely match the generation of electricity with the demand required to be filled by system 1 .

[00144] It will also be appreciated that unit 8 able to be run by controller 23 as an electric motor to pump water from dam 40 to form a reverse of flow 6 which exits back through inlet 5 and into body 4. Accordingly, if the operator of system 1 is unsuccessful in selling all the electrical energy 16 in a given time period, that energy is available to drive unit 8 to increase the volume of body 4 (assuming dam 2 is not full). It will also be appreciated that for a given period controller 23 is able to have some of energy 16 supplied to grid 22 via yard 20 and lines 21 , and other of energy 16 transferred via yard 20 and lines 10 to drive unit 8 as a pump. In all cases, system 1 allows for greater use of the available generation capacity by enabling time shifting of the supply of energy from the generators. That is, system 1 at least partially de-couples the timing of the generation of the electricity with the supply of the electricity to allow for better use of the infrastructure, lower capital costs, increased capital returns, and a more dependable supply of energy for grid 22.

[00145] In another embodiment one or more of arrays 13, 14 and 15 are land based.

[00146] In further embodiments one or more of arrays 13, 14 and 15 are located distal from dam 2. Even so, controller 23 ensures that the PV arrays and unit 8 are coordinated and co-regulated to provide the same functionalities and advantages of system 1 . For example, in one such embodiment the floating PV arrays are located at another dam that is spaced apart from dam 2.

[00147] These embodiments provide a hybrid generation system making use of at least two forms of renewable energy generation that are coordinated to take advantage of electricity supply and demand variations in grid 22. This allows the operator of system 1 to store electricity at times of elevated supply (when that electricity is able to be purchased a first price) and to generate electricity at times of elevated demand (when that electricity is able to be sold at a second price that is higher than the first price). This purchase and sale of electricity by the operator of system 1 is able to occur over a daily cycle.

[00148] It will be appreciated that other forms of renewal energy generation, such a wind generation, are also suitable for use in the hybrid generation system described above.

[00149] Reference is made to Figure 2 where there is illustrated a second embodiment of the invention, where corresponding features are denoted by corresponding reference numerals. In particular, a hydroelectric generation system 201 includes dam 2 for containing a body 202 of water having a first layer 203 that is substantially fresh water and a second layer 204 below layer 203 that is substantially sea-water (or saltwater). An outlet 205 is disposed at a low point of body 202 for receiving a flow 206 of sea-water from layer 204. A third elevation E₃ is the same as the elevation of surface 25 and a fourth elevation E₄ is the same as the level of surface 40. These elevations define the effective available vertical fall (or rise) of the water through which flow 206 (or the reverse flow 206) progresses. Generation unit 8 - which is a pumped hydroelectric generation unit for being driven by flow 206 to supply electrical energy 9 - is disposed below elevation E₄ for allowing gravity filling of unit 8 from sea 24e. A first inlet, defined also by outlet 205, receives a second flow of sea-water into the second layer in the form of a reverse flow of flow 206. A pumping unit, in the form of generation unit 8 when driven, selectively pumps sea-water to define the reverse flow of flow 206.

[00150] It will be appreciated that outlet 205 need not be at the lowest point in body 202. For engineering and other reasons, outlet 205 is more often not directly disposed at the lowest point of dam 2. Even so, outlet 205 is maintained relatively low within dam 2, and below layer 203 during normal operating conditions.

[00151 ] In this embodiment the inlet and the outlet are defined by a common structure, being outlet 205 and the water pipes extending between that outlet and unit 8. In other embodiments, the inlet and outlet are separate.

[00152] The difference in density between sea-water and freshwater allows layers 203 and 204 to remain stratified due to a halocline effect. To best maintain this stratification outlet 205 a plurality of outlet paths and, hence the inlet defines a plurality of inlet paths. This ensures that water is drawn from and placed into layer 204 from a diffuse source. This reduces the risk of turbulence of the water in layer 204 and the intermixing between the layers. In other embodiments different or additional means are used to reduce the risk of turbulence, as will be described in further detail below.

[00153] In this embodiment body 40 is a saltwater sea in a coastal region. Unit 8 is a reversible hydroelectric generator (as mentioned above) and is disposed adjacent to the sea to expel and draw flow 206 and the reverse flow respectively into and from the sea. In other embodiments, body 40 is able to be another saltwater or sea-water body. It will be appreciated that, in the context of the invention, sea-water and saltwater are used interchangeably to refer to water containing dissolved salt or other matter and, as a result, having a density greater than freshwater such that the stratification of the layers 203 and 204 is possible.

[00154] It will be noted that the runoff water flow 41 of freshwater that enters body 4 via opening 42 is added directly to layer 203.

[00155] System 201 includes arrays 13, 14 and 15, similarly to system 1 . In other embodiments those arrays are omitted from system 201 . [00156] Controller 23 regulates the operation of unit 8 to allow flow 206 and the reverse flow. That is, controller 23 varies the volume of sea-water within body 204. This is done in response to the amount of energy needed to be supplied to grid 22 by system 201 , or indeed whether it is possible to purchase electrical energy from grid 22 - when prices are low or negative - such that unit 8 produces the reverse flow and increases the amount of sea-water in layer 204. This allows system 201 to act as an extremely large energy storage device and to store in the order of gigawatt hours, or tens of gigawatt hours, of electric power. If dam 202 has a capacity of 95,000 Mega-litres, layer 204 occupies up to 80% of the volume of body 4, and (E₃ - E₄) is about 300 metres, then the maximum energy storage for system 1 is about 45 Gigawatt-hours.

[00157] Under normal operation controller 23 operates unit 8 such that layer 203 fluctuates between 20% and 30% of the capacity of dam 2. That is, when there is excess electricity supply in grid 22 that is purchased by the operator of system 201 and used to drive unit 8 to return water to dam 2. Conversely, when there is a need for additional supply of electricity to grid 22 the operator of system 201 generates electricity with unit 8 through the use of flow 206. Over a given day there is typically two cycles of up to a 10% fluctuation in the amount of water in dam 2. During the two peak electricity demand periods the amount of water in layer 204 will fall, whereas between those two peaks the amount of water in level 204 will increase. If the full 10% fluctuation in the capacity is used over a six-hour period (with unit 8 having a 1 GW generation capacity) this will result in a storage and release of 6 GWh of electricity from the movement of about 8,400 Mega litres of water to and from layer 204. More fresh water could be produced by allowing this interface to move up such that it now operates between 70-80% of capacity. This may take a decade of double the fresh water production whilst maintaining environmental flows.

[00158] With the level of energy storage available, controller 23 is able to be programmed to selectively draw and supply energy from and to grid 22 to take advantage of pricing differentials. However, due to the available capacity of system 201 it will have a non-negligible impact upon the pricing of electricity from the grid, as it will create meaningful demand for low price electricity (which will increase the lowest available price) while also having meaningful impact upon the amount of generation capacity that can be brought online to supply peak electricity needs (which will reduce the highest prices). This additional stability to the overall grid - that is, reducing the extremes in supply and corresponding reducing the pricing extremes - is highly advantageous not only to other participants, but also to governments, businesses and individuals. [00159] The above example deals with normal operating conditions for dam 202. For other operating conditions, for example during drought conditions, controller 23 is responsive to the capacity of dam 202 for ensuring, during use, layer 204 occupies up to 80% of the capacity. In short, controller 23 includes a plurality of modes and is responsive to a variety of environmental and other inputs for selectively operating in one of those modes. In this embodiment, the modes include:

• a first mode in which the second layer occupies up to 30% of the capacity; and

• a second mode in which the second layer occupies more than 30% of the capacity.

[00160] The first mode is either a normal mode or a flood mode, while the second mode is a drought mode.

[00161 ] System 201 includes, in other embodiments, one or more PV arrays such as arrays 13, 14 and 15.

[00162] The embodiments of the invention are also able to be combined with desalination plants. More particularly, the electricity generated by unit 8 is able to be supplied directly to the desalination plant. Moreover, the freshwater produced by the plant is able to be pumped to dam 2 by unit 8, and seawater required by the plant is able to delivered by unit 8. These multiple uses of existing or the same infrastructure allows for reduced initial capital costs and more productive utilisation of the infrastructure once it is operating.

[00163] Reference is now made to Figure 3, where corresponding features are denoted with corresponding reference numerals. More particularly, dam 2 defines a formation for containing body 202 of water. In this embodiment, dam 2 additionally includes a pliant and continuous thin barrier layer 301 for defining an interface between the layers 203 and 204. Layer 301 extends between the two layers 203 and 204 primarily to reduce turbulence and intermixing between those layers.

[00164] In this embodiment, layer 301 is made from a plurality of adjacent sealingly engaged translucent plastic sheets. In other embodiments, layer 301 is made from a substantially opaque plastic sheet. In further embodiments, layer 301 is made from a plurality of connected natural fibre sheets. It will be appreciated by those skilled in the art, given the benefit of the teaching herein, that other materials and combinations of materials are also suitable for use in layer 301 . For example, in further embodiments, layer 301 is a laminate, while in other embodiments the layer is one or more woven layers.

[00165] Preferentially layer 301 is substantially water impermeable and continuous to provide a strong barrier to intermixing between layers 203 and 204. However, in other embodiments layer 301 is manufactured from one or a combination of porous materials and is still able to reduce intermixing between layers 203 and 204.

[00166] In other embodiments, layer 301 is composed of a substantially unbroken layer that extends continuously between layers 203 and 204. In further embodiments, layer 301 includes a plurality of separate layers that are not joined to each other.

[00167] As mentioned above, body 202 is stratified due to the difference in the densities of layers 203 and 204. Preferentially, layer 301 is selected to have a density that is intermediate the first density and the second density. However, in some embodiments, layer 301 includes a barrier member, such as a porous fabric, that in use has a density greater than the density of layer 204. In these embodiments, use is made of one or more buoyancy devices to reduce the overall density of layer 301 such that it is better retained between layers 203 and 204. The buoyancy devices are either secured to the barrier member, or placed under the barrier member.

[00168] In further embodiments layer 301 includes a barrier member, such as a thin plastics sheet, having a density that is less than the density of layer 203. In these embodiments, use is made of one or more weight devices to increase the overall density of layer 301 such that it is better retained between layers 203 and 204. The weight devices are either secured to the barrier member, or placed on top of the barrier member.

[00169] Reference is now made to Figure 4 where there is illustrated a schematic top view of dam 202 and where corresponding features are denoted by corresponding reference numerals. Dam 202 includes manmade wall 3 that spans between naturally formed dam walls 303 and 304. Where surface 25 engages with walls 3, 303 and 304 it defines a continuous dam upper peripheral edge 305. It will be appreciated that this peripheral edge extends about dam 202 although in Figure 4 it is only exemplarily illustrated in the region of wall 3. The intersection of layers 203 and 204 also engages with walls 3, 303 and 304, and defines an intermediate peripheral edge 306 that is lower than edge 305. Due to the contours in walls 303 and 304, edge 306 typically lies inwardly of edge 305. In this embodiment, edge 305 directly overlies edge 306 at wall 3 as the water facing surface of wall 3 is substantially vertical. It will also be appreciated that edges 305 and 306 are typically irregular as they follow closely the contours of walls 303 and 304.

[00170] Layer 301 includes a first outer edge 307 and a second inner edge 308 that meet at two corners 309 and 310. Edge 307 directly overlies edge 306, whereas edge 308 is disposed inwardly of edge 306.

[00171 ] It will be noted that layer 301 overlies outlet 205, and underlies outlet 43. For it is adjacent to these outlets that there is the greatest risk of turbulence and, hence, the greater risk of intermixing between the layers. Accordingly, in the embodiments, layer 301 is preferentially adjacent to one or more of such inlets or outlets.

[00172] In other embodiments, layer 301 extends further across dam 202 to define an interface for a greater proportion of layers 203 and 204. For example, in one such embodiment, layer 301 extends directly between corners 309 and 310. In other embodiments, layer 301 extends about a majority of the peripheral edge 306. In still further embodiments, layer 301 is segmented and disposed at those locations in dam 202 susceptible to turbulence, for example, at or adjacent to inlet 42.

[00173] In still further embodiments, layer 301 defines an interface between substantially all of layers 203 and 204.

[00174] In this embodiment layer 301 is loosely tethered to walls 3, 303 and 304 to allow for some vertical movement - in response to layer 204 being depleted or added to - while restraining large horizontal movements. In other embodiments, layer 301 is more tightly tethered and constrained to permit predominantly only horizontal movement. In further embodiments, edge 307 is fixed to one or more of walls 3, 303 and 304, and the inward extend of edge 308 varies as sea-water is added to or removed from layer 204. In still further embodiments, layer 301 is not fixed or tethered to any of the walls. Further embodiments have layer 301 tethered to poles or other objects. This includes having layer 301 spaced apart from the walls.

[00175] In another embodiment, use is made of a barrier layer that is substantially rigid, or which includes a plurality of connected substantially rigid segments.

[00176] According to a preferred embodiment of the invention there is provided a method for damming a body 202 of water for a hydroelectric generation system 1 . The method including the steps of:

containing the body 202 of water in a dam 2, the body 202 of water having a first layer 203 that is substantially fresh water and a second layer 204 below the first layer 203 that is substantially sea-water;

providing a first outlet 205 in dam 2 for receiving a first flow 206 of sea-water from layer 204;

providing a first inlet (also performed by outlet 205) in dam 2 receives a second flow of sea-water (which is the reverse of flow 206) into layer 204; and

defining an interface between layers 203 and 204 with a barrier layer 301 .

[00177] According to another preferred embodiment there is provided a hydroelectric generation system 1 including: a formation in the form of a dam 2 for containing a body 202 of water having a first layer 203 that is substantially fresh water and a second layer 204 below layer 203 that is substantially sea-water;

a first outlet 205 in dam 2 at a first elevation for receiving a first flow 206 of sea- water from layer 204;

a generation unit 8 disposed at a second elevation that is lower than the first elevation for being driven by flow 206 to supply electrical energy;

a first inlet (also performed by outlet 205) in dam 2 for receiving a second flow (the reverse of flow 206) of sea-water into layer 204; and

a barrier layer 301 for defining an interface between layers 203 and 204.

] The main advantages provided by the different embodiments include:

• The ability to effectively coordinate different renewable energy generation types to provide a single hybrid generator to meet fluctuating electricity demand.

• Leveraging existing infrastructure more effectively to provide increased flexibility in localised and grid-wide energy generation.

• More easily maintaining a high water level in a dam to maximise the available surface water area for a floating solar PV. This also has the advantage of maximising the height difference (and the potential energy available to be stored or released) by the water stored/released from the dam via the pump generator.

• Leveraging from complementary and/or synergistic relationships between the different energy generation types.

• The ability to more readily offer substantial amounts of energy storage capacity for an electrical distribution network.

• The ability to balance a network to gain the best benefits from both the so- called base load generators and the typically more distributed renewable generators.

• Reduces the network reliance on any one form of generation, and allows a varying supply from all. This additional supply flexibility offers opportunities for existing providers to optimise the operation of their generators and to consider alternative generation technologies, and lowers the barriers to entry into the market for potential new forms of generation. • Allows renewable energy generators to be seamlessly used in combination with non-renewable sources. For example, it allows gas turbine generators to be used more or less frequently in response to gas prices, and coal-fired generators to be used when necessary to meet peak demand but otherwise being curtailed to minimise C02 emissions, without any disruption to the network.

• Accommodates the public desire for increased use of renewable and distributed energy generation while taking advantage of the existing network infrastructure.

• Making use of the most mature and proven energy storage technology - that being hydroelectric pumping - in a unique combination with the pumping of sea-water into a freshwater dam.

• The scale to quickly store and release enough energy to have a significant impact upon a large electrical distribution network.

• Relatively simple, and offering a long operation lifetime of many decades or more.

• Providing governments with a more flexible and stable electrical distribution network that is able to harness conventional non-renewable generation techniques, newer renewable generation techniques, and future techniques.

• Offering more choice about the generation sources that are used to supply the network.

• Increases energy security notwithstanding the ongoing transition from nonrenewable sources to renewable sources.

• Providing a bridge between the current centralised power generation and supply model and the anticipated future decentralised models with lowest cost network back-up.

• The ability to create an "energy hub" near existing cities and industries that can benefit from the nearby generation of large quantities of inexpensive electricity.

• A rapid response to changing demand, whether that demand is rising of falling. • The maintenance of freshwater in the dam to sustain existing environmental values.

• The maintenance of a high water level in the dam, even during drought times.

• The ability to maintain a stratified body of water due to the halocline between the freshwater and the sea-water.

• The ability to rapidly expel sea-water from the dam during flood conditions. This then allows for a buffer to full dam capacity to prevent flooding in the downstream watercourse.

• The recognition of the positive pressure exerted on certain dams floors by groundwater discharge to the dams and how this maintains the sea-water in the dam. In dams where the water table is lower than the dam floor, use is made of a lining to reduce drainage of the sea-water to groundwater.

• The storage of the energy is easily converted from one form to another, and is reversible. Using more recent hydroelectric pumping technology incurs relatively small pumping and generation losses (in the order of 13% for a cycle).

• The ability to use inexpensive energy from the network during off peak periods, and to supply energy back to the network when the price is higher during peak periods. This will change the pricing conditions to raise the price during the off peak period (by creating more demand for off peak energy), and reduce the price in the peak period (by supplying more energy during that period).

• The ability to flexibly adapt to the changing definition of peak and off-peak demand due to new loads such as electric vehicles.

• Allowing use of existing infrastructure, be that electrical distribution infrastructure, dams, electric train electrical distribution infrastructure, water pipelines and the flat surface area on dams.

• Reduces the risk of energy consumers going "off grid" by smoothing prices within the network and providing better network backup. In turn, this reduces the risk of a so-called "death spiral" developing as network costs are able to be shared amongst a higher number of consumers.

• Increasing the number of available sites for hydroelectric pumping systems. • Allowing more effective coordination of non-renewable energy generation and renewable energy generation within a single electrical distribution network.

• The ability to supplement the hydroelectric pumping with other generation sources such as floating PV arrays, wind turbines and others.

• The synergistic relationship that arises when used in combination with floating PV arrays.

• The additional flexibility that arises when used in combination with a desalination plant. That is, one or more of the following can apply: the hydroelectric pumping system is able to be located near the desalination plant; and the electricity generated by the hydroelectric pumping is able to be used to pump sea-water to the desalination plant and/or power the desalination plant and/or pump the water produced by the desalination plant to the freshwater layer in the dam or to another water body.

• The additional flexibility that arises when used in combination with hydrogen and ammonia synthesis plant. Hydrogen and ammonia are chemical energy storage substances and feedstock for fertiliser manufacture or used as transport fuel.

• Retrofit-able into existing dams.

• Being able to dynamically accommodate a wide range of climatic and environmental variations while providing the required storage and generation capability, and while maintaining the required environmental flows in the associated watercourses.

• Reducing the risk of disturbing the stratification of the freshwater and sea- water.

• Allowing a barrier layer to be selectively extended across areas of greater potential for turbulence.

[00179] It will be appreciated that the disclosure above provides various significant hydroelectric and pumped hydroelectric systems and methods for operating such systems.

[00180] It should be appreciated that in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, Figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention.

[00181 ] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[00182] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[00183] Similarly, it is to be noticed that the term "coupled" or "connected", when used in the description and claims, should not be interpreted as being limited to direct connections only. The terms "coupled" and "connected," along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression "a device A coupled to a device B" should not be limited to devices or systems wherein an output or other element of device A is directly connected to an input or other element of device B. Rather, it means that there exists a connective path between an output of A and an input of B which may be a path including other devices, structures or means. "Coupled" may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.

[00184] Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as falling within the scope of the invention. For example, any formulas or flowcharts provided are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.

Claims

1 . A hydroelectric generation system including:

a pumping unit for selectively pumping sea-water to define the second flow.

2. A system according to claim 1 wherein the electrical energy is supplied to an electrical distribution network and the pumping unit includes one or more electrically powered pumps that draw electrical energy from the network.

3. A system according to claim 1 or claim 2 wherein the generator unit and the pumping unit are collectively defined by a reversible hydroelectric generator.

4. A system according to claim 3 wherein the reversible hydroelectric generator is disposed adjacent to a sea and expels and draws the first flow and the second flow respectively into and from the sea.

5. A system according to claim 2 including a controller for regulating the operation of the generator unit and the pumping unit to allow the first flow and the second flow.

6. A system according to claim 5 wherein the formation has a capacity and the controller is responsive to the capacity for ensuring, during use, the second layer occupies up to 80% of the capacity.

7. A system according to claim 6 wherein the controller is responsive to the capacity for ensuring, during use, the second layer occupies up to 20% of the capacity.

8. A system according to any one of claims 5 to 7 wherein the controller selectively operates in one of a plurality of modes including:

9. A system according to claim 5 including at least one PV generation device that is disposed on the first layer and which produces electrical energy.

10. A system according to claim 9 wherein the electrical energy produced by the PV generation device is supplied to the distribution network.

1 1 . A system according to claim 9 or 10 wherein the PV generation device includes one or more structures for floating on the first layer, wherein each structure supports an array of PV panels for generating the electrical energy.

12. A hydroelectric generation system including:

a formation for containing a body of water;

a PV electrical power generation unit for supplying second electrical energy;

a controller for regulating the transmission of the first and second energy by the distribution infrastructure.

13. A system according to claim 12 wherein the body of water includes a surface and the PV electrical power generation unit includes at least one floating PV array that is disposed on the surface.

14. A system according to claim 13 wherein the PV electrical power generation unit includes a plurality of floating PV arrays each of which is disposed on the surface.

15. A system according to any one of claims 12 to 14 wherein the controller regulates the transmission of the first and second energies to provide a predetermined total energy output to the electrical distribution network.

16. A system according to any one of claims 12 to 15 wherein the controller regulates the operation of the hydroelectric generation unit to regulate the transmission of the first energy to the distribution infrastructure.

17. A system according to claim 16 wherein the controller is responsive to one or more characteristic of the second energy for regulating the operation of the hydroelectric generation unit.

18. A system according to claim 17 wherein the one or more characteristics of the second energy include: the present instantaneous value of the second energy; the anticipated instantaneous value of the second energy at a given future time; the instantaneous value of the second energy at a past time; the total second energy supplied during a given past period; the anticipated total second energy to be supplied in a future period; the average second energy supplied during a given past period; and the anticipated average second energy to be supplied in a future period.