FIELD OF THE INVENTION

The present invention relates to a method for generating electricity from a water tower. The invention further relates to systems for generating electricity from a water tower.

BACKGROUND

Greenhouse gases, such as CO2, in the earth’s atmosphere help to regulate global temperatures through the greenhouse effect. Greenhouse gases are therefore essential to maintaining the temperature of the earth so that it is habitable to humans, animals and plants alike. However, excess greenhouse gases in the atmosphere contribute to global warming by raising the temperature of the earth to harmful levels. A primary cause of excess greenhouse gases in the atmosphere is the burning of fossil fuels such as coal, oil, or natural gas, e.g. for the generation of electricity. The effects of global warming have already begun to be observed, e.g. in rising sea levels and in the melting of polar ice caps. According to simulation models, an increased CO2 concentration in the atmosphere is suspected to cause further and potentially more dramatic changes in the climate in the future. As a result, and also due to an ever- depleting supply of fossil fuels, scientists, environmentalists and politicians throughout the world are driving initiatives to reduce the amount of CO2 discharged into the atmosphere by combustion of fossil fuel.

One such initiative involves focussing on renewable energy resources for the generation of electricity. Renewable energy resources, such as solar power, wind power, geothermal power and biomass, are resources which are naturally replenished.

A further renewable energy resource is hydroelectric power, which involves making use of the flow of fluid, such as water, to generate electrical energy. In a hydroelectric power plant, flowing water (e.g. the overflow from a dam) is used to rotate a turbine, which is itself connected to an electric generator via a shaft. When the turbine is caused to rotate by the flowing water, the shaft also rotates and this mechanical energy is converted into electrical energy in the generator. Examples of hydroelectric systems are described in WO2016/132317 A1 , US2017/292350 A1 , WO201 1/1 14199 A1 , and US2010/259044 A1. Despite there being an awareness of the need to switch to renewable energy resources in the generation of electricity, the burning of fossil fuels for this purpose continues on a large scale worldwide. As such, there exists a need to consider further ways to manipulate hydroelectric power for the generation of electricity.

SUMMARY OF INVENTION

Viewed from a first aspect the present invention provides a method of generating electricity from a water tower, comprising:

(i) directing water from said water tower to a submersed rotodynamic pump, wherein said pump comprises an impeller on an impeller shaft and an electric motor;

(ii) operating said pump in reverse flow so that said water causes rotation of said impeller; and

(iii) generating electricity from said rotation of said impeller in said electric motor.

Viewed from a further aspect the present invention provides a system for generating electricity from a water tower, comprising:

(a) a water tower;

(b) a submersed rotodynamic pump having an impeller on an impeller shaft, wherein said pump is configured to operate in reverse flow;

(c) means for directing water from said water tower to said submersed rotodynamic pump; and

(d) an electric motor connected to the impeller shaft of said submersed rotodynamic pump to generate electricity.

DEFINITIONS

As used herein, the term“submersed” means being entirely underwater at all times, i.e. completely and constantly surrounded by water at all times.

As used herein, the phrase “submersed rotodynamic pump” describes a rotodynamic pump wherein at least the impeller of the pump is submersed, i.e. at least the impeller of the pump is entirely underwater at all times (i.e. completely and constantly surrounded by water at all times).

As used herein, the term“water tower” describes a reservoir configured to store water. Examples include an outlet structure, a weir box, and a seawater dump caisson. Preferably, the water present in the water towers described herein is cooling water.

As used herein, the phrase“RPM” means revolutions per minute.

As used herein, the term“means for directing water” includes a pipe.

As used herein, the term“substantially horizontal” means angled between 0° and 10° from the horizontal plane.

As used herein, the term“substantially vertical” means angled between 0° and 10° from the vertical plane.

DETAILED DESCRIPTION

The present invention provides a method of generating electricity from a water tower (e.g. a water tower located on a boat, an oil rig or at a power plant). This is achieved in the method of the invention by directing water from a water tower to a submersed rotodynamic pump, operating the pump in reverse flow so that the water causes rotation of the impeller of the pump, and generating electricity from the rotation of the impeller in the electric motor of the pump.

In the methods of the present invention, the submersed rotodynamic pump is operated in reverse flow. The rotodynamic pump comprises an electric motor, which functions as a generator when the pump operates in reverse flow. In this way, when water is directed to the submersed rotodynamic pump, the impeller of the pump is caused to rotate, and electricity is generated in the electric motor.

In the methods of the invention, water is preferably directed from the water tower to the submersed rotodynamic pump by at least one pipe.

In preferred methods of the invention, the at least one pipe is angled downwards from the water tower to an inlet of the submersed rotodynamic pump (i.e. the end of the pipe that is connected to the water tower is at a higher elevation than the end of the pipe that is connected to the pump). In preferred methods of the invention, the at least one pipe is connected to the water tower in the vicinity of the top of the water tower. Thus, in this embodiment, the rotodynamic pump is gravity fed water from the water tower. In other preferred methods of the invention, the at least one pipe is substantially horizontal. More preferably, the at least one pipe is connected to the water tower in the vicinity of the bottom of the water tower. Thus, in this embodiment, the weight of the water in water tower causes the water to flow into the at least one pipe, which directs the water to the submersed rotodynamic pump.

In other preferred methods of the invention, the at least one pipe is angled upwards from the water tower to an inlet of the submersed rotodynamic pump (i.e. the end of the pipe that is connected to the water tower is at a lower elevation than the end of the pipe that is connected to the pump). In preferred methods of the invention, the at least one pipe is connected to the water tower in the vicinity of the bottom of the water tower. Thus, in this embodiment, the weight of the water in water tower causes the water to flow into the at least one pipe, which directs the water to the submersed rotodynamic pump.

In preferred methods of the invention, water is directed from the water tower to the submersed rotodynamic pump via a plurality of pipes. In a preferred embodiment, water is directed from the water tower to the submersed rotodynamic pump via a first pipe and a second pipe. Preferably, the first pipe is connected to the water tower in the vicinity of the top of the water tower and the second pipe is connected to the water tower in the vicinity of the bottom of the water tower. The first pipe is preferably angled downwards from said water tower. The second pipe is preferably angled upwards from said water tower.

The preferred methods of the invention described herein, wherein the at least one pipe is angled upwards or angled downwards or is substantially horizontal, are particularly suited to onshore applications but are not limited thereto.

In other preferred methods of the invention, the at least one pipe is substantially vertical. More preferably, the water tower functions as the pipe. In this particular embodiment, the rotodynamic pump can be directly connected to the base of the water tower such that when water enters the water tower, which is substantially vertical, it falls vertically onto the pump.

The preferred methods of the invention described herein, wherein the at least one pipe is substantially vertical, are particularly suited to offshore applications but are not limited thereto.

In preferred methods of the invention, an additional pipe which bypasses the water tower feeds water into the at least one pipe, i.e. the additional pipe transfers water which has not entered the water tower to the at least one pipe. Alternatively, a plurality of additional pipes may be used to direct water into the at least one pipe.

In preferred methods of the invention, the impeller of the pump rotates at 40 to 5000 RPM, more preferably 400 to 4000RPM (e.g. 1500 RPM). In further preferred methods of the invention, a valve is present on the at least one pipe upstream of the pump to control the RPM of the pump. When a valve is present on the at least one pipe upstream of the pump, the impeller of the pump rotates at 40 to 5000 RPM, more preferably 400 to 4000 RPM (e.g. 1500 RPM). Examples of suitable valves include modulating valves, also known as control valves.

A Main Inlet Valve (MIV) is preferably employed in the methods of the present invention. A main function of the MIV is to close off the water flow during maintenance of the rotodynamic pump without needing to drain the inlet piping. The MIV also acts as a shut off valve for the rotodynamic pump in the event of pump failure. Preferably, the MIV is a concentric butterfly valve, which is typically opened by hydraulic cylinder (which itself is served by a hydraulic pressure unit (HPU)) and closed by a counterweight. The MIV is designed to close against turbine full flow for safety with respect to operating torque, material stresses, head loss and cavitation. If hydraulic pressure is lost, the MIV will close to ensure the safety of the turbine system. Commercially available MIVs may be used.

In preferred methods of the invention, the water tower further comprises an over-flow, which allows excess water to exit the water tower. The over-flow may be a pipe or an exit hole in the tower wall etc. The presence of an over-flow allows control of the volume of water sent from the water tower via the at least one pipe to the rotodynamic pump.

In preferred methods of the invention, the water tower is ventilated. Preferably, the water tower is ventilated in the vicinity of the top of the water tower. Preferred ventilation means include a gooseneck ventilation means As gas leakages may occur in a water system comprising a water tower, the presence of a ventilation means on the water tower allows combustible gases to be safely vented out.

In preferred methods of the invention, the water in the water tower has a height of at least 5 to 150 m, more preferably at least 8 to 100 m (e.g. at least 10 m) during generation of electricity.

In the methods of the present invention, water is directed from a water tower to a submersed rotodynamic pump, the pump is operated in reverse flow so that the water causes rotation of the impeller of the pump, and electricity is then generated from the rotation of the impeller in the electric motor of the pump. As at least the impeller of the pump is submersed, i.e. entirely surrounded by water, there is a larger contact area of water on the impeller blades meaning that more efficient rotation can occur compared to a situation where a flow of water comes into contact with the impeller. It is therefore thought that larger amounts of electricity can be generated using the methods of the present invention.

In preferred methods of the invention, only the impeller of the pump is submersed in water. Alternatively, the entirety of the pump, including the motor, is submersed in water.

In preferred methods of the invention, the pump is submersed in a water outlet e.g. a seawater outlet. The water outlet may be an onshore water outlet or an offshore water outlet. In preferred methods of the invention, the pump is attached to a decking or a rig. The decking or rig may be located in a water outlet, e.g. an onshore water outlet or an offshore water outlet. Alternatively, the pump is mounted in a water-filled pipe, e.g. above the water outlet. Preferably, the water-filled pipe is positioned at a maximum of 4.5 m above the water level in the water outlet.

The rotodynamic pump employed in the methods of the present invention is preferably a centrifugal pump, an axial pump or a mixed flow pump. More preferably, the rotodynamic pump is a centrifugal pump. Preferred rotodynamic pumps for use in the methods and systems of the present invention include the currently manufactured pumps by Framo, Eureka and Axflow. Representative examples of suitable rotodynamic pumps include e.g. Framo SE-series electric submersible pumps (see https://www.framo.com/globalassets/pdf-files/Sea-water-lift- pumps.pdf), Eureka

Lineshaft Pump (see http://www.eureka.no/pumps/seawater-lineshaft-pump/), Axflow VAB Vertical Mixed Flow Pumps (see http://www.axflow.com/en- gb/site/products/category/pumps/centrifugal-pumps/vab-vertic al-mixed-flow- pumps/#specification), and Axflow - Gruppo Aturia - ELV Axial Flow Pumps (see http://www.axflow.com/en-gb/site/products/category/pumps/axi al-flow-pumps/elv/).

The rotodynamic pumps employed in the methods of the present invention comprise one or more impellers on an impeller shaft and an electric motor. The electric motor is preferably located on the decking or rig and has a connection (e.g. a shaft connection) to the submersed pump, as is the case for Eureka pumps. Alternatively, the electric motor can be directly connected to the rotodynamic pump such that the electric motor is also submersed, as is the case for Framo pumps. A preferred electric motor is one that complies with the ATEX 94/9/EC (or equivalent) to prevent ignition of possible explosive atmospheres.

In preferred methods of the invention, the position of the pump is moveable (e.g. using a crane). This is advantageous during exchange and maintenance.

In preferred methods of the invention, the volume of water directed to the pump is 500 to 100000 m ³ /hour, more preferably 1000 to 50000 m ³ /hour (e.g. 45000 m ³ /hour).

In preferred methods of the invention, the speed of water directed to the pump is 1 .0 to 5.0 m/s, more preferably 1.5 to 2.5 m/s (e.g. 2.0 m/s).

In preferred methods of the invention, 0.1 to 10 MW of power is produced, more preferably 0.3 to 5 MW (e.g. 3 MW). In preferred methods of the invention, the electricity generated is sent for use elsewhere, e.g. the electricity is sent to the electrical grid and/or an electricity storage facility and/or directly to another unit (e.g. a pump in the same system). A frequency converter may be required to feed the generated electricity to the electrical grid.

The present invention also relates to a system for carrying out the method hereinbefore described. Preferred features of the method hereinbefore described are also preferred features of the system. The systems of the present invention can be used either onshore of offshore. For example, the systems of the present invention can be used on a boat, as part of an offshore oil/gas production installation, or as part of a power plant, a liquefied natural gas (LNG) plant, a gas processing plant, a petrochemical plant, or a refinery.

The systems of the present invention comprise a water tower, a submersed rotodynamic pump having an impeller on an impeller shaft, wherein the pump is configured to operate in reverse flow, means for directing water from the water tower to the submersed rotodynamic pump, and an electric motor connected to the impeller shaft of the submersed rotodynamic pump to generate electricity.

In the systems of the present invention, the submersed rotodynamic pump is operated in reverse flow. The rotodynamic pumps comprise an electric motor, which functions as a generator when the pump operates in reverse flow. In this way, when water is directed to the submersed rotodynamic pump, the impeller of the pump is caused to rotate, and electricity is generated in the electric motor as a result of the electric motor being connected to the impeller via an impeller shaft.

In preferred systems of the invention, the means comprises at least one pipe. In preferred systems of the invention, the at least one pipe is angled downwards from the water tower to an inlet of the submersed rotodynamic pump (i.e. the end of the pipe that is connected to the water tower is at a higher elevation than the end of the pipe that is connected to the pump). In preferred systems of the invention, the at least one pipe is connected to the water tower in the vicinity of the top of the water tower. Thus, in this embodiment, the rotodynamic pump is gravity fed water from the water tower.

In other preferred systems of the invention, the at least one pipe is substantially horizontal. More preferably, the at least one pipe is connected to the water tower in the vicinity of the bottom of the water tower. Thus, in this embodiment, the weight of the water in water tower causes the water to flow into the at least one pipe, which directs the water to the submersed rotodynamic pump.

In other preferred systems of the invention, the at least one pipe is angled upwards from the water tower to an inlet of the submersed rotodynamic pump (i.e. the end of the pipe that is connected to the water tower is at a lower elevation than the end of the pipe that is connected to the pump). In preferred systems of the invention, the at least one pipe is connected to the water tower in the vicinity of the bottom of the water tower. Thus, in this embodiment, the weight of the water in water tower causes the water to flow into the at least one pipe, which directs the water to the submersed rotodynamic pump.

In preferred systems of the invention, water is directed from the water tower to the submersed rotodynamic pump via a plurality of pipes. In a preferred embodiment, water is directed from the water tower to the submersed rotodynamic pump via a first pipe and a second pipe. Preferably, the first pipe is connected to the water tower in the vicinity of the top of the water tower and the second pipe is connected to the water tower in the vicinity of the bottom of the water tower. The first pipe is preferably angled downwards from said water tower. The second pipe is preferably angled upwards from said water tower.

The preferred systems of the invention described herein, wherein the at least one pipe is angled upwards or angled downwards or is substantially horizontal, are particularly suited to onshore applications but are not limited thereto.

In other preferred systems of the invention, the at least one pipe is substantially vertical. More preferably, the water tower functions as the pipe. In this particular embodiment, the rotodynamic pump can be directly connected to the base of the water tower such that when water enters the water tower, which is substantially vertical, it falls vertically onto the pump.

The preferred systems of the invention described herein, wherein the at least one pipe is substantially vertical, are particularly suited to offshore applications but are not limited thereto.

In preferred systems of the invention, an additional pipe which bypasses the water tower feeds water into the at least one pipe, i.e. the additional pipe transfers water which has not entered the water tower to the at least one pipe. Alternatively, a plurality of additional pipes may be used to direct water into the least one pipe.

In preferred systems of the invention, the impeller of the pump rotates at 40 to 5000 RPM, more preferably 400 to 4000 RPM (e.g. 1500 RPM). In further preferred systems of the invention, a valve is present on the at least one pipe upstream of the pump to control the RPM of the pump. When a valve is present on the at least one pipe upstream of the pump, the impeller of the pump rotates at 40 to 5000 RPM, more preferably 400 to 4000 RPM (e.g. 1500 RPM). Examples of suitable valves include modulating valves, also known as control valves.

A Main Inlet Valve (MIV) is preferably employed in the systems of the present invention. A main function of the MIV is to close off the water flow during maintenance of the rotodynamic pump without needing to drain the inlet piping. The MIV also acts as a shut off valve for the rotodynamic pump in the event of pump failure. Preferably, the MIV is a concentric butterfly valve, which is typically opened by hydraulic cylinder (which itself is served by a hydraulic pressure unit (HPU)) and closed by a counterweight. The MIV is designed to close against turbine full flow for safety with respect to operating torque, material stresses, head loss and cavitation. If hydraulic pressure is lost, the MIV will close to ensure the safety of the turbine system. Commercially available MIVs may be used

In preferred systems of the invention, the water tower further comprises an over-flow, which allows excess water to exit the water tower. The over-flow may be a pipe or an exit hole in the tower wall etc. The presence of an over-flow allows control of the volume of water sent from the water tower via the at least one pipe to the rotodynamic pump.

In preferred systems of the invention, the water tower is ventilated. Preferably, the water tower is ventilated in the vicinity of the top of the water tower. Preferred ventilation means include a gooseneck ventilation means. As gas leakages may occur in a water system comprising a water tower, the presence of a ventilation means on the water tower allows combustible gases to be safely vented out.

In preferred systems of the invention, the water in the water tower has a height of at least 5 to 150 m, more preferably at least 8 to 100 m (e.g. at least 10 m) during generation of electricity.

In the systems of the present invention, water is directed from a water tower to a submersed rotodynamic pump, the pump is operated in reverse flow so that the water causes rotation of the impeller of the pump, and electricity is then generated from the rotation of the impeller in the electric motor of the pump. As at least the impeller of the pump is submersed, i.e. entirely surrounded by water, there is a larger contact area of water on the impeller blades meaning that more efficient rotation can occur compared to a situation where a flow of water comes into contact with the impeller. It is therefore thought that larger amounts of electricity can be generated using the systems of the present invention.

In preferred systems of the invention, only the impeller of the pump is submersed in water. Alternatively, the entirety of the pump, including the motor, is submersed in water.

In preferred systems of the invention, the pump is submersed in a water outlet e.g. a seawater outlet. The water outlet may be an onshore water outlet or an offshore water outlet. In preferred systems of the invention, the pump is attached to a decking or a rig. The decking or rig may be located in a water outlet, e.g. an onshore water outlet or an offshore water outlet. Alternatively, the pump is mounted in a water-filled pipe, e.g. above the water outlet. Preferably, the water-filled pipe is positioned at a maximum of 4.5 m above the water level in the water outlet.

The rotodynamic pump employed in the systems of the present invention is preferably a centrifugal pump, an axial pump or a mixed flow pump. More preferably, the rotodynamic pump is a centrifugal pump. Preferred rotodynamic pumps for use in the systems of the present invention include the currently manufactured pumps by Framo, Eureka and Axflow. Representative examples of suitable rotodynamic pumps include e.g. Framo SE-series electric submersible pumps (see https://www.framo.com/globalassets/pdf-files/Sea-water-lift- pumps.pdf), Eureka

Lineshaft Pump (see http://www.eureka.no/pumps/seawater-lineshaft-pump/), Axflow VAB Vertical Mixed Flow Pumps (see http://www.axflow.com/en- gb/site/products/category/pumps/centrifugal-pumps/vab-vertic al-mixed-flow- pumps/#specification), and Axflow - Gruppo Aturia - ELV Axial Flow Pumps (see http://www.axflow.com/en-gb/site/products/category/pumps/axi al-flow-pumps/elv/).

The rotodynamic pumps employed in the systems of the present invention comprise one or more impellers on an impeller shaft and an electric motor. The electric motor is preferably located on the decking or rig and has a connection (e.g. a shaft connection) to the submersed pump, as is the case for Eureka pumps. In this embodiment, the electric motor is not submersed in water. Alternatively, the electric motor can be directly connected to the rotodynamic pump such that the electric motor is also submersed, as is the case for Framo pumps. In this embodiment, the electric motor is submersed in water. A preferred electric motor is one that complies with the ATEX 94/9/EC (or equivalent) to prevent ignition of possible explosive atmospheres.

In preferred systems of the invention, the electric motor has a protective housing. Preferably, the protective housing is made of stainless steel.

In preferred systems of the invention, the position of the pump is moveable (e.g. using a crane). This is advantageous during exchange and maintenance.

In preferred systems of the invention, 0.1 to 10 MW of power is produced, more preferably 0.3 to 5 MW (e.g. 3 MW). Preferred systems of the invention further comprise means for connecting the electric motor to the electrical grid and/or an electricity storage facility and/or another unit (e.g. a pump in the same system). A frequency converter may be required to feed the generated electricity to the electrical grid.

Preferred systems of the invention comprise a plurality of rotodynamic pumps. Preferably, the plurality of rotodynamic pumps is arranged in series. Alternatively, the plurality of rotodynamic pumps is arranged in parallel.

DESCRIPTION OF THE FIGURES

Figures 1 -5 show systems according to the present invention for use onshore.

Figure 6 shows a system according to the present invention for use offshore.

DETAILED DESCRIPTION OF THE FIGURES

Figure 1 shows a seawater outlet 1 of a water tower 2 on, for example, a decking 3. The water tower may be a part of, for example, a power plant or an industrial operation. Water is fed into the water tower 2 via line 4. When the water tower 2 fills with water, it flows into a pipe 5 connecting the water tower 2 and a rotodynamic pump 6. The impeller of the centrifugal pump 6 is submersed in water. The end of pipe 5 connected to the water tower 2 is at a higher elevation than the end of pipe 5 connected to the pump 6 (i.e. pipe 5 is angled downwards from the water tower 2 to the pump). Pipe 5 is connected to the water tower 2 in the vicinity of the top of the water tower. Thus, in this method and system of the invention, the rotodynamic pump is gravity fed water from the water tower. Optionally, water in the water tower 2 can overflow into water outlet 1 via an over-flow 7. This can be used to control the volume of water sent via pipe 5 to the rotodynamic pump 6. Optionally, the water tower 2 has ventilation means 8.

The impeller of pump 6 is submersed in the seawater outlet 1 . The pump is configured to operate in reverse flow such that it functions as a turbine. Pump 6 comprises inter alia an electric motor, which functions as a generator when pump 6 operates in reverse flow. In the embodiment shown in Figure 1 the electric motor 6a of pump 6 is not submersed in the water outlet, although this is possible. Rather, the electric motor 6a of pump 6 is mounted on decking 3.

The water in pipe 5 is directed to the submersed rotodynamic pump 6, where it causes rotation of the impeller, and therefore impeller shaft, of the pump. This rotating motion of the impeller shaft is converted into electrical energy in the electric motor. This electricity is then sent for use elsewhere, e.g. the electricity is sent to the electrical grid and/or an electricity storage facility and/or directly to another unit (e.g. a pump) in the same system (shown by dotted line 9). A frequency converter may be required to feed the generated electricity to the electrical grid. The use of a submersed rotodynamic pump operating in reverse flow also has the effect of reducing the amount of foam produced in the water outlet 1.

The embodiments shown in Figures 2 and 3 are similar to the one shown in Figure 1. Common reference numerals indicate the same feature. The main difference is that the pipe 5 is connected to the water tower 2 in the vicinity of the bottom of the water tower in the embodiments of Figures 2 and 3. As a result, pipe 5 is substantially horizontal in Figure 2 whilst in Figure 3 the end of pipe 5 connected to the water tower 2 is at a lower elevation than the end of pipe 5 connected to the pump 6 (i.e. pipe 5 is angled upwards from the water tower 2 to the pump 6). In Figure 2 and Figure 3, the weight of the water in water tower 2 causes the water to flow into pipe 5, which directs the water to the submersed rotodynamic pump 6. In these embodiments, a valve 10 is present on pipe 5 upstream of pump 6 to control the RPM of the pump. As in Figure 1 , water in the water tower 2 can optionally overflow into water outlet 1 via an over-flow 7. This can be used to control the volume of water sent to the rotodynamic pump 6.

The embodiment shown in Figure 4 is a combination of the embodiments shown in Figures 1 and 3, i.e. where a first pipe 5a (which is angled downwards from water tower 2) and a second pipe 5b (which is angled upwards from water tower 2) connect the water tower 2 to the pump 6. This arrangement increases the volume to water transferred to the pump per unit of time, and therefore the amount of electricity generated, compared to either of the embodiments shown in Figures 1 or 3.

The embodiment shown in Figure 5 is identical to the embodiment shown in Figure 1 , except that the electric motor 6a of pump 6 is also submersed in water outlet 1 .

Figure 6 shows a seawater outlet 1 1 of a water tower 12 on, for example, an offshore rig 13 or boat. The water tower 12 has ventilation means 14. A submersed rotodynamic pump 15 is connected to the base of the water tower 12. Pump 15 is submersed within the seawater outlet 1 1 and is configured to operate in reverse flow such that it functions as a turbine. Pump 15 comprises inter alia an electric motor, which functions as a generator when pump 15 operates in reverse flow. In this embodiment, the electric motor of pump 15 is also submersed in the seawater outlet 1 1 .

Water is fed into the water tower 12 via line 16 and is directed to the pump 15, where it causes rotation of the impeller, and therefore impeller shaft, of the pump. This rotating motion of the impeller shaft is converted into electrical energy in the electric motor. This electricity is then sent for use elsewhere, e.g. the electricity is sent to the electrical grid and/or an electricity storage facility and/or directly to another unit (e.g. a pump) in the same system. A frequency converter may be required to feed the generated electricity to the electrical grid.

Optionally, water in the water tower 12 can overflow into seawater outlet 1 1 via an over-flow 17. This can be used to control the volume of water sent to the rotodynamic pump 15.