Sea-land cooperative seawater pumped storage-ocean temperature difference heat energy composite power generation system and method

Abstract

The invention provides a sea-land cooperative seawater pumped storage-ocean temperature difference heat energy composite power generation system and method, and aims to solve the problems of low energy utilization rate, poor stability and high cost caused by independent operation of seawater pumped storage and OTEC. The system comprises a seawater pumped storage subsystem, an OTEC subsystem, a cooperative control subsystem and a heat energy recovery module, and three-way reversible conversion of electricity, potential energy and heat energy is achieved through a three-in-one framework. According to the method, energy conversion paths are dynamically switched based on power grid loads (a low ebb period, a peak period and a flat period), surplus power is stored in double paths in the low ebb period, power is supplied cooperatively in the peak period, and energy consumption is optimized in the flat period. The ocean energy utilization efficiency and the power grid stability are improved, the construction and operation cost is reduced, and remarkable economic and environmental benefits are achieved.

Description

Technical Field

[0001] This invention belongs to the field of new energy utilization and electrical energy storage technology, specifically relating to a combined seawater pumped hydro storage (SPHS) and ocean thermal energy conversion (OTEC) power generation system and method. Background Technology

[0002] With the rapid development of renewable energy, grid peak shaving and energy storage have become key challenges. In existing technologies, pumped-storage hydroelectric power utilizes seawater as the working medium. During periods of low grid load, water is pumped to high-altitude reservoirs or deep-sea energy storage units, and released to generate electricity during peak load periods, achieving a conversion of electrical energy into potential energy. However, this technology is limited by terrain, and its efficiency is significantly affected by water level differences. On the other hand, ocean thermal energy conversion (OTEC) technology utilizes the temperature difference between surface warm water (approximately 26-28°C) and deep cold water (approximately 4-6°C) to generate electricity through an evaporation-condensation cycle using a low-boiling-point working medium (such as chlorofluorocarbons). However, its power generation efficiency is low, and it is affected by fluctuations in the marine environment, making it difficult to meet grid demands independently.

[0003] Currently, there is no mature technology that can organically combine seawater pumped storage and OTEC to overcome their respective shortcomings. Existing systems mostly operate independently, resulting in low energy utilization and infrastructure redundancy. Therefore, there is an urgent need for an integrated solution to achieve the coordinated conversion and storage of multiple energy forms, thereby improving overall efficiency and grid adaptability. Summary of the Invention

[0004] The first objective of this invention is to provide a combined land-sea pumped storage and ocean thermal energy conversion power generation system, addressing the aforementioned problems.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A sea-land coordinated seawater pumped storage-ocean thermal energy conversion hybrid power generation system includes a seawater pumped storage subsystem, an OTEC subsystem, a coordinated control subsystem, and a heat recovery module.

[0007] The seawater pumped storage subsystem includes a coastal high-level reservoir, a pumping unit, a turbine generator unit, a water conveyance pipeline, and a water level monitoring module. The water conveyance pipeline includes a pumping pipeline and a discharge pipeline. One end of the pumping pipeline is connected to the near-shore water intake, and the other end extends to the bottom of the coastal high-level reservoir. One end of the discharge pipeline is connected to the bottom of the coastal high-level reservoir, and the other end extends to the near-shore drainage outlet.

[0008] The OTEC subsystem includes a surface warm water intake device, a deep cold water intake device, an evaporator, a condenser, a low-boiling-point working fluid circulation loop, a heat engine generator set, and a temperature monitoring module. The input end of the evaporator is connected to the surface warm water intake device via a pipe, and the output end is connected to the condenser via a pipe. The input end of the condenser is connected to the deep cold water intake device via a pipe, and the output end is connected to the low-boiling-point working fluid circulation loop via a pipe. The heat engine generator set is connected in series with the low-boiling-point working fluid circulation loop.

[0009] The collaborative control subsystem includes a power grid load sensor, a seawater temperature sensor, a reservoir water level sensor, a working fluid pressure sensor, a central controller, and a power distribution module. The central controller receives signals from each sensor and outputs control commands to the pumping unit, the turbine generator unit, and the auxiliary equipment of the OTEC subsystem through a preset algorithm. The power distribution module realizes the power flow control between the power grid, the seawater pumped storage subsystem, and the OTEC subsystem through electrical control components.

[0010] The heat recovery module is located between the water discharge pipe of the seawater pumped storage subsystem and the evaporator of the OTEC subsystem. It adopts a shell-and-tube heat exchanger, with the inner tube being the water discharge pipe and the outer tube being the working fluid flow channel.

[0011] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions:

[0012] As a preferred technical solution of the present invention: the surface warm water intake device is located in shallow waters below sea level and is equipped with a filter screen to prevent marine organisms from clogging it.

[0013] As a preferred technical solution of the present invention: the deep cold water intake device is located in the deep waters below sea level and uses corrosion-resistant alloy pipes.

[0014] As a preferred embodiment of the present invention, the low-boiling-point working fluid circulation loop is filled with a chlorofluorocarbon working fluid.

[0015] As a preferred technical solution of the present invention: the central controller adopts a PLC control system, which has a fast response capability.

[0016] The second objective of this invention is to provide a combined land-sea pumped storage and ocean thermal energy conversion method for power generation.

[0017] Therefore, the above-mentioned objective of the present invention is achieved through the following technical solution:

[0018] A method for combined land-sea pumped storage and ocean thermal energy conversion power generation, the method being based on the system described above, specifically as follows:

[0019] During periods of low grid load: Utilize surplus power from the grid to pump nearshore seawater to the coastal high-level reservoir to store potential energy, or increase the evaporation temperature of the low-boiling-point working fluid through auxiliary equipment of the OTEC subsystem to store thermal energy in the low-boiling-point working fluid circulation loop, or use the electrical energy generated by the OTEC subsystem to assist in seawater extraction.

[0020] During peak grid load periods: Water is released from the coastal high-level reservoir to drive the hydro-turbine generator unit to generate electricity. At the same time, the OTEC subsystem utilizes the temperature difference between the surface warm water and the deep cold water to generate electricity. If the surface water temperature drops, the heat recovery module uses the waste heat from the released water to heat the working fluid, thereby increasing the power generation of the OTEC subsystem.

[0021] During periods of flat grid load: the OTEC subsystem maintains partial power operation, while the seawater pumped storage subsystem uses intermittent pumping mode to maintain the reservoir water level. At the same time, the warm water discharged from the OTEC subsystem is transported to the near-shore intake to preheat the seawater to be pumped.

[0022] This invention provides a combined land-sea pumped storage and ocean thermal energy conversion power generation system, which has the following beneficial effects:

[0023] 1) During off-peak periods, surplus power from the power grid is utilized through a dual-path system of "potential energy storage in high-level reservoirs + thermal energy storage in OTEC working fluid," avoiding energy waste and significantly improving the system's utilization rate of surplus power from the conventional level of pumped storage alone. During peak periods, the combined power supply of potential energy and thermal energy significantly improves the overall utilization efficiency of ocean energy compared to operating either of them separately.

[0024] 2) Significantly optimized power generation stability: Through the heat recovery module and power auxiliary regulation, the power generation fluctuation of the OTEC subsystem is significantly reduced; based on the rapid response characteristics of the pumped storage subsystem of the high-level reservoir, the slow start-up of the OTEC subsystem is effectively compensated, and the power supply demand of both short-term peak load and long-term continuous load of the power grid can be met at the same time.

[0025] 3) Enhanced peak-shaving flexibility: It realizes a hierarchical peak-shaving mode of "short-term peak - high-level reservoir potential energy power supply" and "long-term peak - OTEC thermal energy + reservoir potential energy power supply", which can cope with short-term peak loads of the power grid (only high-level reservoir water release for power generation) and long-term peak loads (both of which supply power in coordination), and the peak-shaving coverage is significantly expanded compared with a single system;

[0026] 4) Reduced construction and operation costs: The surface warm water intake device of the OTEC subsystem and the near-shore water intake of the pumped storage subsystem share marine engineering facilities, reducing the amount of marine pipelines and infrastructure construction, and the overall construction cost is lower than that of building them separately; at the same time, the design of preheating the seawater to be pumped by the flat section warm water discharge further reduces the annual operating energy consumption of the pumped storage subsystem, and the operating cost is reduced accordingly.

[0027] 5) Enhanced system resilience: It has multiple energy conversion paths such as "electricity-potential-electricity", "electricity-heat-working fluid-electricity", and "potential-heat-electricity". When a single subsystem fails, another subsystem can maintain the basic power supply of the power grid or make up for the power supply gap, thus significantly improving the overall resilience of the system. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall structure of the land-sea cooperative seawater pumped storage-ocean thermal energy composite power generation system provided by the present invention.

[0029] Figure 2 Schematic diagram of energy flow path 1 during grid off-peak periods (electrical energy - potential energy);

[0030] Figure 3 Schematic diagram of energy flow path 2 during grid off-peak periods (electrical energy - thermal energy - working fluid energy storage);

[0031] Figure 4 Schematic diagram of energy flow path (electrical energy-thermal energy-electrical energy-potential energy) during grid off-peak periods;

[0032] Figure 5 This is a schematic diagram of the energy flow path (potential energy to electrical energy) during peak power grid periods.

[0033] Figure 6 This is a schematic diagram of the energy flow path (heat energy - electrical energy) during peak power grid periods.

[0034] Figure 7 Schematic diagram of the energy flow path (potential energy - thermal energy - electrical energy) during peak power grid periods;

[0035] Figure 8 This is a block diagram of the collaborative control logic.

[0036] In the diagram: 1-Coastal high-level reservoir; 2-Pumping unit; 3-Hydrogen turbine generator set; 4-Pumping pipeline; 5-Water discharge pipeline; 6-Nearshore water intake; 7-Nearshore drainage outlet; 8-Surface warm water intake device; 9-Deep cold water intake device; 10-Evaporator; 11-Condenser; 12-Heat recovery module; 13-Heat engine generator set; 14-Cooperative control subsystem; 15-Power grid; 16-Low-boiling-point working fluid circulation loop; 17-Seawater. Detailed Implementation

[0037] The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

[0038] like Figure 1 As shown, a sea-land coordinated seawater pumped storage-ocean thermal energy conversion hybrid power generation system includes a seawater pumped storage subsystem, an OTEC subsystem, a coordinated control subsystem, and a heat recovery module.

[0039] The seawater pumped storage subsystem includes a coastal high-level reservoir (built on a coastal highland with a certain altitude and an anti-seepage coating on the inner wall), pump sets, turbine generator sets, water conveyance pipelines, and a water level monitoring module. The water conveyance pipeline is divided into a pumping pipeline (one end connected to the near-shore water intake 6, and the other end extending to the bottom of the high-level reservoir) and a discharge pipeline (one end connected to the bottom of the high-level reservoir, and the other end extending to the near-shore drainage outlet 7). The pump sets are connected in series in the pumping pipeline (for pumping near-shore seawater to the high-level reservoir), and the turbine generator sets are connected in series in the discharge pipeline (for using the potential energy of the water discharged from the high-level reservoir to drive power generation).

[0040] The seawater pumped storage subsystem uses the coastal high-level reservoir 1 as the core energy storage carrier. It realizes "seawater pumping and energy storage" through the pumping pipeline 4 and the pumping pump set 2, and realizes "seawater release and power generation" through the water release pipeline 5 and the turbine generator set 3. The water level monitoring module (integrated in 14) monitors the reservoir water level in real time to ensure the safety of potential energy storage and release.

[0041] The OTEC subsystem includes a surface warm water intake device (located in shallow waters below sea level, equipped with a filter to prevent clogging by marine organisms), a deep cold water intake device (located in deep waters below sea level, using corrosion-resistant alloy pipes), an evaporator, a condenser, a low-boiling-point working fluid circulation loop (filled with chlorofluorocarbons), a heat engine generator set, and a temperature monitoring module. The evaporator's input end is connected to the surface warm water intake device via a pipe, and its output end is connected to the condenser via a pipe. The condenser's input end is connected to the deep cold water intake device via a pipe, and its output end is connected to the low-boiling-point working fluid circulation loop via a pipe. The heat engine generator set is connected in series with the low-boiling-point working fluid circulation loop to convert the mechanical energy generated by the phase change of the working fluid into electrical energy.

[0042] The low-boiling-point working fluid circulation loop 16 is a closed-loop pipeline, and its loop is: condenser 11 outlet → heat recovery module 12 outer pipe → evaporator 10 → heat engine generator set 13 → condenser 11 inlet.

[0043] The OTEC subsystem uses surface warm water intake device 8 and deep cold water intake device 9 as energy input terminals. Surface warm water is transported to evaporator 10 through pipelines to heat the working fluid in low boiling point working fluid circulation loop 9 to generate high-pressure steam, which drives heat engine generator set 13 to generate electricity. Then, it exchanges heat with deep cold water through condenser 11 to condense and return the working fluid. Temperature monitoring module (integrated in 14) monitors the temperature of seawater 17 in real time to ensure the efficiency of temperature difference utilization.

[0044] The collaborative control subsystem 14 includes a power grid load sensor (which collects power grid data in real time), a seawater temperature sensor (which monitors surface warm water and deep cold water temperature respectively), a reservoir water level sensor (installed on the inner wall of the high-level reservoir to monitor water level changes), a working fluid pressure sensor (installed in the low-boiling-point working fluid circulation loop to monitor working fluid pressure), a central controller (which adopts a PLC control system and has fast response capability), and a power distribution module. The central controller receives signals from each sensor and outputs control commands to the pumping unit, the turbine generator unit, and auxiliary equipment of the OTEC subsystem (such as warm water circulation pumps and evaporator electric heaters) through a preset algorithm. The power distribution module realizes the power flow control between the power grid 15, the pumped storage subsystem, and the OTEC subsystem through electrical control components.

[0045] The collaborative control subsystem is centered on a PLC central controller. It collects data on grid load (connected to the grid), seawater temperature, reservoir water level, and working fluid pressure through sensors (integrated in 14). After algorithm analysis, it outputs instructions to the pumping unit 2, the turbine generator unit 3, and the OTEC auxiliary equipment. The power distribution module (integrated in 14) realizes the flow of power between the grid and each subsystem through cables, forming a control closed loop of "data-instruction-execution".

[0046] The heat recovery module is located between the drain pipe of the pumped storage subsystem and the evaporator of the OTEC subsystem. It adopts a shell-and-tube heat exchanger (the inner tube is the drain pipe and the outer tube is the working fluid flow channel). The water flow in the drain pipe (carrying the waste heat generated during the potential energy conversion process, and the water temperature is higher than that of the near-shore seawater) exchanges heat with the low-boiling-point working fluid in the evaporator, thereby increasing the working fluid evaporation temperature and reducing the dependence of the OTEC subsystem on the surface water temperature.

[0047] The heat recovery module acts as an "energy bridge" between the two subsystems. Its inner pipe, which is connected to the blue water discharge pipe 5 (to obtain waste heat from the discharged water), and its outer pipe, which is connected to the low-boiling-point working fluid circulation loop (to heat the working fluid), not only solves the problem of waste heat from the discharged water, but also compensates for the impact of surface water temperature fluctuations on OTEC.

[0048] like Figure 2-8 As shown, the system dynamically switches operating modes based on grid load conditions. The energy flow and control logic of each mode are as follows:

[0049] During off-peak hours of the power grid, such as Figure 2-4 As shown in Figure 8:

[0050] The power grid load sensor (14 branches) collects the "surplus power" signal and feeds it back to the central controller 14. The controller then outputs a command:

[0051] Command 1: Start pumping unit 2 and pump seawater to coastal high-level reservoir 1 via path 1. After the water level sensor (14 branches) monitors the water level and it reaches the highest design level, the feedback controller stops pumping.

[0052] Instruction 2: If there is still surplus power, start the OTEC auxiliary equipment (speed up the warm water circulation pump and power on the electric heater) to increase the working fluid evaporation temperature through path 2. If the power grid does not require power, instruct the heat engine generator set 13 to stop and store the working fluid in the pressure tank. If the power grid allows power generation, transmit the OTEC power to the water pump set 2 through path 3 to assist in water pumping. The power distribution module 14 adjusts the power flow in real time.

[0053] During peak power grid periods, such as Figure 5-8 As shown:

[0054] The power grid load sensor (14 branches) collects the "power shortage" signal and feeds it back to the central controller 14. The controller then outputs a command:

[0055] Command 1: Open the water release valve of Binhai High-Level Reservoir 1, drive the water turbine generator set 3 to generate electricity through path 1, quickly replenish energy, response time < 5 minutes;

[0056] Command 2: Start the OTEC subsystem to operate at full load, and use the thermoelectric generator via path 2 to generate electricity as the base power;

[0057] Command 3: If the seawater temperature sensor (branch 14) detects a drop in surface water temperature, the feedback controller activates the heat recovery module 12, which uses the waste heat from the discharged water to heat the working fluid through path 3, thereby increasing the output of OTEC. The working fluid pressure sensor (branch 14) monitors the working fluid status in real time to ensure stable circulation.

[0058] Power grid level section:

[0059] The power grid load sensor (branch 14) collects the "load stability" signal and feeds it back to the central controller 14. The controller then outputs a command:

[0060] Instruction 1: The OTEC subsystem maintains partial power operation, and the electrical energy is fed into the grid;

[0061] Command 2: Pumping unit 2 operates intermittently, water level sensor (14 branches) monitors water level and maintains it at the middle position, power distribution module 14 allocates a small amount of grid power to drive pumping;

[0062] Instruction 3: The warm water discharged from condenser 11 is transported to the near-shore water intake through a pipeline to preheat the seawater to be pumped, reduce the energy consumption of pumping unit 2, and the temperature sensor (branch 14) monitors the preheating effect and dynamically adjusts the flow rate of warm water discharge.

[0063] like Figure 8As shown, the system features "closed-loop control" and the "brain" function of the collaborative control subsystem 11—by collecting key parameters in real time, it dynamically adjusts the operating status of the equipment, avoiding the shortcomings of existing technologies that rely on "no collaboration and manual adjustment," and providing control assurance for the stable operation of the system.

[0064] The following example, using my country's tropical coastal areas (with suitable coastal highlands and surface and deep seawater temperatures meeting the OTEC operation requirements), illustrates the specific implementation of this invention in detail:

[0065] System parameter selection:

[0066] 1) Seawater pumped storage subsystem based on high-level reservoir: The volume and dam height of the coastal high-level reservoir are determined according to the power grid load demand of the sea area where the project is located and the topographic conditions of the coastal highlands; the number and rated power of the pumping units and turbine generator units are matched according to the potential energy storage capacity and power generation demand of the high-level reservoir; the material and diameter of the water transmission pipeline are selected according to the seawater transmission flow and pressure requirements; the water level monitoring module uses equipment with high-precision measurement capabilities to ensure real-time monitoring of reservoir water level changes.

[0067] 2) OTEC Subsystem: The installation depth and structure of the surface warm water intake device are determined based on the distribution characteristics of surface warm water, and the filter specifications meet the requirements for preventing marine organism blockage; the installation depth and pipe material of the deep cold water intake device are selected based on the distribution of deep cold water and the corrosiveness requirements of seawater; the type and heat exchange area of ​​the evaporator and condenser are matched with the temperature difference utilization requirements and the working fluid circulation rate; the type of low-boiling-point working fluid is determined based on the temperature difference range and environmental protection requirements; the type and power of the heat engine generator set are selected based on the phase change energy output characteristics of the working fluid; the temperature monitoring module uses equipment with stable measurement performance to ensure real-time monitoring of seawater temperature changes.

[0068] 3) Cooperative control subsystem: The measurement range and accuracy of the power grid load sensor are determined according to the power grid capacity; the measurement range and accuracy of the working fluid pressure sensor are selected according to the circulating pressure characteristics of the low-boiling-point working fluid; the central controller uses a PLC device with high computing speed and reliability to ensure rapid output of control commands; the electrical component specifications of the power distribution module are matched according to the power requirements of each subsystem and have safety protection functions.

[0069] 4) Heat recovery module: The material and heat exchange area of ​​the shell-and-tube heat exchanger are determined according to the water flow characteristics of the drain pipe and the heat exchange requirements of the working fluid, to ensure high heat exchange efficiency and meet the working fluid heating requirements of the OTEC subsystem.

[0070] Based on grid load conditions (off-peak, peak, and flat periods), dynamic switching of multiple energy conversion paths is achieved:

[0071] 1. Off-peak periods of power grid load (times when the power grid has surplus power):

[0072] (1) Path 1 (electrical energy → potential energy): The central controller commands the pumping unit to start at full load according to the power grid load sensor signal, and uses the surplus power of the power grid to pump the nearshore seawater to the high-level reservoir through the pumping pipeline until the reservoir water level reaches the highest design water level (reserve safe storage capacity) to complete the potential energy storage.

[0073] (2) Path 2 (electrical energy → thermal energy → working fluid energy storage): If the surplus power of the grid is not completely consumed, the central controller instructs the auxiliary equipment of the OTEC subsystem to start up - the warm water circulation pump speeds up and the evaporator electric heater is powered on, which improves the heat exchange efficiency of the surface warm water to the evaporator, and raises the evaporation temperature of the low boiling point working fluid; if the grid does not require additional electrical energy input, the heat engine generator set of the OTEC subsystem stops running and stores the low boiling point working fluid in the high temperature and high pressure state in the pressure-resistant working fluid storage tank to realize indirect thermal energy storage.

[0074] (3) Path 3 (electrical energy → thermal energy → electrical energy → potential energy): If the power grid allows OTEC to generate electricity, the central controller instructs the OTEC subsystem to operate at full load. The electrical energy generated by the heat engine generator set is transmitted to the water pump set through the power distribution module to assist in seawater extraction, reduce the power consumption of the water pump set on the power grid, and improve the utilization rate of surplus power.

[0075] 2. Peak load periods (times of power shortage in the power grid):

[0076] (1) Path 1 (potential energy → electrical energy): The central controller commands the high-level reservoir to open the water release valve according to the power grid load gap signal. Seawater drives the water turbine generator to generate electricity through the water release pipeline. The generated electricity is directly connected to the power grid to quickly fill the short-term power gap.

[0077] (2) Path 2 (thermal energy → electrical energy): The central controller instructs the OTEC subsystem to operate at full load. The surface warm water enters the evaporator to heat the low boiling point working fluid and cause it to evaporate. The high pressure steam drives the heat engine generator set to generate electricity. The generated electricity is connected to the power grid to provide a continuous and stable basic power supply.

[0078] (3) Path 3 (potential energy → thermal energy → electrical energy): If the surface water temperature drops due to weather or seasonal factors, resulting in a decrease in the power generation of the OTEC subsystem, the central controller will automatically start the heat recovery module. The residual hot water in the drain pipe will flow through the shell-and-tube heat exchanger to heat the low-boiling-point working fluid in the evaporator, thereby increasing the working fluid evaporation temperature and thus allowing the power generation of the OTEC subsystem to recover to near the rated level.

[0079] 3. Peak load periods (times when power supply and demand are balanced):

[0080] The central controller regulates the output ratio of the two subsystems: the OTEC subsystem maintains partial power operation, and the generated electricity is fed into the grid as basic power; the pumped storage subsystem adopts intermittent pumping mode, and the pumping pump group consumes a small amount of grid power each time it runs, maintaining the water level of the high-level reservoir at the middle design water level (ensuring that potential energy can be quickly stored during the off-peak period and can be stably released during the peak period).

[0081] Meanwhile, the central controller instructs the warm water discharged from the OTEC subsystem condenser to be transported through pipelines to the near-shore water intake of the pumped storage subsystem to preheat the seawater to be pumped and reduce the pumping energy consumption of the pumping pump unit.

[0082] In this embodiment, the annual surplus power utilization rate of the system is significantly improved, and the total annual power generation is higher than the sum of the seawater pumped storage based on high-level reservoirs and the OTEC technology operating alone; the power generation fluctuation of the OTEC subsystem is controlled at a low level, the grid peak-shaving response speed is fast, and the power supply demand can be met during different load periods; the overall construction cost and annual operating cost of the system are reduced compared with the construction of either one alone, and it has significant economic and environmental benefits while improving the comprehensive utilization efficiency of ocean energy.

[0083] The above specific embodiments are used to explain and illustrate the present invention, and are only preferred embodiments of the present invention, not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A combined land-sea pumped storage and ocean thermal energy conversion power generation system, characterized in that, It includes a seawater pumped storage subsystem, an OTEC subsystem, a collaborative control subsystem, and a heat recovery module. The seawater pumped storage subsystem includes a coastal high-level reservoir, a pumping unit, a turbine generator unit, a water conveyance pipeline, and a water level monitoring module. The water conveyance pipeline includes a pumping pipeline and a discharge pipeline. One end of the pumping pipeline is connected to the near-shore water intake, and the other end extends to the bottom of the coastal high-level reservoir. One end of the discharge pipeline is connected to the bottom of the coastal high-level reservoir, and the other end extends to the near-shore drainage outlet. The OTEC subsystem includes a surface warm water intake device, a deep cold water intake device, an evaporator, a condenser, a low-boiling-point working fluid circulation loop, a heat engine generator set, and a temperature monitoring module. The input end of the evaporator is connected to the surface warm water intake device via a pipe, and the output end is connected to the condenser via a pipe. The input end of the condenser is connected to the deep cold water intake device via a pipe, and the output end is connected to the low-boiling-point working fluid circulation loop via a pipe. The heat engine generator set is connected in series with the low-boiling-point working fluid circulation loop. The collaborative control subsystem includes a power grid load sensor, a seawater temperature sensor, a reservoir water level sensor, a working fluid pressure sensor, a central controller, and a power distribution module. The central controller receives signals from each sensor and outputs control commands to the pumping unit, the turbine generator unit, and the auxiliary equipment of the OTEC subsystem through a preset algorithm. The power distribution module realizes the power flow control between the power grid, the seawater pumped storage subsystem, and the OTEC subsystem through electrical control components. The heat recovery module is located between the water discharge pipe of the seawater pumped storage subsystem and the evaporator of the OTEC subsystem. It adopts a shell-and-tube heat exchanger, with the inner tube being the water discharge pipe and the outer tube being the working fluid flow channel.

2. The land-sea coordinated seawater pumped storage-ocean thermal energy composite power generation system according to claim 1, characterized in that: The surface warm water intake device is located in shallow waters below sea level and is equipped with a filter to prevent marine organisms from clogging it.

3. The land-sea coordinated seawater pumped storage-ocean thermal energy composite power generation system according to claim 1, characterized in that: The deep cold water intake device is located in deep waters below sea level and uses corrosion-resistant alloy pipes.

4. The land-sea coordinated seawater pumped storage-ocean thermal energy composite power generation system according to claim 1, characterized in that: The low-boiling-point working fluid circulation loop is filled with a chlorofluorocarbon-based working fluid.

5. The land-sea coordinated seawater pumped storage-ocean thermal energy composite power generation system according to claim 1, characterized in that: The central controller uses a PLC control system and has a fast response capability.

6. A method for combined land-sea pumped storage and ocean thermal energy conversion power generation, characterized in that: The method is based on the system as described in any one of claims 1-5, and includes: During periods of low grid load: Utilize surplus power from the grid to pump nearshore seawater to the coastal high-level reservoir to store potential energy, or increase the evaporation temperature of the low-boiling-point working fluid through auxiliary equipment of the OTEC subsystem to store thermal energy in the low-boiling-point working fluid circulation loop, or use the electrical energy generated by the OTEC subsystem to assist in seawater extraction. During peak grid load periods: Water is released from the coastal high-level reservoir to drive the hydro-turbine generator unit to generate electricity. At the same time, the OTEC subsystem utilizes the temperature difference between the surface warm water and the deep cold water to generate electricity. If the surface water temperature drops, the heat recovery module uses the waste heat from the released water to heat the working fluid, thereby increasing the power generation of the OTEC subsystem. During periods of flat grid load: the OTEC subsystem maintains partial power operation, while the seawater pumped storage subsystem uses intermittent pumping mode to maintain the reservoir water level. At the same time, the warm water discharged from the OTEC subsystem is transported to the near-shore intake to preheat the seawater to be pumped.

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