CN115589011A

CN115589011A - Energy storage system

Info

Publication number: CN115589011A
Application number: CN202211245765.2A
Authority: CN
Inventors: 林晨; 王东征; 杨阳; 嵇海林; 马亚杰; 王志勇; 王双平; 陈城; 杨卿鑫
Original assignee: Shanghai MS Energy Storage Technology Co Ltd
Current assignee: Shanghai MS Energy Storage Technology Co Ltd
Priority date: 2022-10-12
Filing date: 2022-10-12
Publication date: 2023-01-10

Abstract

The present disclosure relates to an energy storage system. An energy storage system according to the present disclosure includes: a power controller; a first energy storage device connected to the power controller; a second energy storage device connected to the power controller via the first switch; and a power generation device connected to the power controller and configured to output direct current power to charge the first energy storage device and/or the second energy storage device via the power controller and/or to power a load and/or a power grid, wherein the power controller controls the first switch to be turned on and off according to the energy storage level of the first energy storage device and/or the second energy storage device and/or the direct current power output by the power generation device. The energy storage system has the advantages of high reserve capacity, high loading capacity, long service life, high energy storage benefit and the like.

Description

Energy storage system

Technical Field

The present disclosure relates generally to an energy storage system, and more particularly, to an energy storage system that improves overall energy storage yield and service life by connecting two or more different types of energy storage devices in parallel with a power generation device.

Background

With the increasing proportion of new energy resources such as photovoltaic power generation, wind power generation, tidal power generation, geothermal power generation and the like in an electric power system, the combination of new energy power generation and energy storage technology becomes important power for promoting industrial technology upgrading and mode innovation in the face of the congenital defect that new energy power generation is unstable due to fluctuation. In particular, the end-user's peak-to-valley arbitrage and self-service needs have spawned various energy storage application markets.

Taking photovoltaic power generation as an example, peak clipping, valley filling and power backup are the main operation modes of the optical storage microgrid system at present. The peak clipping and valley filling means that the energy storage system is charged in the low-ebb period of power utilization and discharged to be used by users in the peak period of power utilization, so that the utilization rate of the power grid in the low-ebb period is improved while the power supply pressure of the power grid in the peak period is relieved. In addition, the power backup means that the power grid is actively disconnected and a microgrid system is built under the condition that the power grid is in power failure or the power grid fluctuates greatly, and therefore power supply of important loads is guaranteed by means of energy storage.

However, the photovoltaic energy storage systems of the prior art have at least the following drawbacks. First, the length of standby time is limited by the capacity of the energy storage device, such as a lithium battery. Secondly, the photovoltaic energy storage yield is very unstable due to the susceptibility to external environmental factors. Moreover, the peak clipping and valley filling gains and the reserve power margin affect each other, so that it is difficult to achieve the maximum energy storage gain.

Disclosure of Invention

In order to solve the above-mentioned problems in the prior art, the present disclosure provides a novel energy storage system.

A brief summary of the disclosure is provided below in order to provide a basic understanding of some aspects of the disclosure. It should be understood that this summary is not an exhaustive overview of the disclosure, nor is it intended to identify key or critical elements of the disclosure or to delineate the scope of the disclosure. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

To achieve the object of the present disclosure, according to one aspect of the present disclosure, there is provided an energy storage system including: a power controller; a first energy storage device connected to the power controller; a second energy storage device connected to the power controller via the first switch; and a power generation device connected to the power controller and configured to output direct current power to charge the first energy storage device and/or the second energy storage device and/or power a load and/or a power grid via a direct current/direct current converter of the power controller, wherein the power controller controls the first switch to be turned on and off according to the energy storage level of the first energy storage device and/or the second energy storage device and/or the direct current output by the power generation device.

According to an embodiment of the present disclosure, the first energy storage device is a lithium ion battery or a sodium ion battery and the second energy storage device is a lead acid battery.

According to an embodiment of the present disclosure, the power generation device is at least one of a photovoltaic power generation device, a wind power generation device, a tidal power generation device, and a geothermal power generation device.

According to the embodiment of the disclosure, when the energy storage level of the first energy storage device is lower than the first predetermined threshold, the power controller controls the first switch to be conducted so as to discharge the second energy storage device.

According to the embodiment of the disclosure, when the fluctuation of the dc power output by the power generation device exceeds the second predetermined threshold, the power controller controls the first switch to be turned on to discharge the second energy storage device.

According to the embodiment of the disclosure, when the direct current output by the power generation device is higher than the third predetermined threshold, the power controller controls the first switch to be turned on so that the second energy storage device is in a floating state.

According to the embodiment of the disclosure, when the direct current power output by the power generation device is lower than a fourth predetermined threshold, the power controller controls the first switch to be conducted to discharge the second energy storage device.

According to an embodiment of the disclosure, the first energy storage device is connected to the power controller via a second switch, the power controller controls the second switch to be turned on and off, and the power controller controls the second switch to be turned off when the energy storage level of the first energy storage device is higher than a fifth predetermined threshold.

According to an embodiment of the present disclosure, a power controller includes: the first direct current/alternating current converter is connected with the direct current side of the first direct current/alternating current converter; and a second dc/ac converter, the second energy storage device and the power generation device being connected to the dc side of the second dc/ac converter.

According to an embodiment of the disclosure, the grid is connected to the ac side of the first and/or second dc/ac converter of the power controller via a third switch, and the power controller controls the switching on and off of the third switch.

According to the energy storage system disclosed by the invention, the capacity is improved by connecting different types of energy storage devices in parallel on the basis of the traditional energy storage device, so that the standby power duration and the maximum carrying capacity are improved. In addition, according to the energy storage system disclosed by the invention, the power generation devices in the energy storage system are compensated by utilizing the energy storage devices of different types which are connected in parallel, so that the external factors in a short time are not influenced, and the energy storage benefit is improved. Furthermore, the energy storage system according to the present disclosure can achieve maximum energy storage benefits by separating peak-valley arbitrage from backup power functions.

Drawings

The above and other objects, features and advantages of the present disclosure will be more readily understood by reference to the following description of the embodiments of the present disclosure taken in conjunction with the accompanying drawings.

Fig. 1 is a block diagram illustrating an energy storage system according to an embodiment of the present disclosure.

Fig. 2 is an exemplary diagram illustrating an energy storage system according to an embodiment of the present disclosure.

Fig. 3 is an exemplary diagram illustrating an operation principle of an energy storage system according to an embodiment of the present disclosure.

Detailed Description

Hereinafter, some embodiments of the present disclosure will be described in detail with reference to the accompanying illustrative drawings. When elements of the drawings are denoted by reference numerals, the same elements will be denoted by the same reference numerals although the same elements are shown in different drawings. Further, in the following description of the present disclosure, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure unclear.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms are intended to include the plural forms as well, unless the context indicates otherwise. It will be further understood that the terms "comprises," "comprising," and "having," when used in this specification, are intended to specify the presence of stated features, entities, operations, and/or components, but do not preclude the presence or addition of one or more other features, entities, operations, and/or components.

Unless otherwise defined, all terms used herein including technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which the inventive concept belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. The present disclosure may be practiced without some or all of these specific details. In other instances, to avoid obscuring the disclosure with unnecessary detail, only components that are germane to the aspects in accordance with the disclosure are shown in the drawings, while other details that are not germane to the disclosure are omitted.

Hereinafter, an energy storage system according to an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

Fig. 1 is a block diagram illustrating an energy storage system 100 according to an embodiment of the present disclosure. Fig. 2 is an example diagram illustrating an energy storage system 100 according to an embodiment of the present disclosure.

As shown in fig. 1, according to an embodiment of the present disclosure, the energy storage system 100 may include: a power controller 101; a first energy storage device 102 connected to the power controller 101; a second energy storage device 103 connected to the power controller 101 via a first switch 104; and a power generation device 105 connected to the power controller 101 and configured to output dc power to charge the first energy storage device 102 and/or the second energy storage device 103 via the power controller 101 and/or to power the load 108 and/or the grid 109, wherein the power controller 101 controls the first switch 104 to be turned on and off according to the energy storage level of the first energy storage device 102 and/or the second energy storage device 103 and/or the dc power output by the power generation device 105.

According to embodiments of the present disclosure, the power controller 101 may receive dc power from the power generation device 105 to charge the first energy storage device 102 and/or the second energy storage device 103, and may convert the dc power from the power generation device 105, the first energy storage device 102, and/or the second energy storage device 103 to ac power to power the load 108 and/or the grid 109. Further, according to the embodiment of the present disclosure, the power controller 101 may also control to cause the first energy storage device 102 and the second energy storage device 103 to charge each other. Further, according to embodiments of the present disclosure, the power controller 101 may sense the energy storage level of the first energy storage device 102 and/or the second energy storage device 103 and/or the dc power output by the power generation device 105 to control the turning on and off of the first switch 104.

According to an embodiment of the present disclosure, the Power controller 101 may be implemented to include, for example, a Power Control System (PCS), a photovoltaic inverter, and the like. Specifically, the PCS may control the charging and discharging processes of an energy storage device, such as a battery, perform ac-dc conversion, and may directly power an ac load without a grid. The PCS may include a direct current/alternating current (DC/AC) bidirectional converter, a control unit, and the like. The PCS can receive a background control instruction through communication, and control the converter to charge or discharge the energy storage device according to the symbol and the size of the power instruction, so that the active power and the reactive power of the power grid can be adjusted. In addition, the PCS may communicate with an energy storage device Management System, such as a Battery Management System (BMS), through a Controller Area Network (CAN) interface to acquire state information of the energy storage device, thereby implementing protective charging and discharging of the energy storage device to ensure operation safety. In addition, the photovoltaic inverter can convert the variable direct-current voltage generated by the photovoltaic solar panel into alternating-current inverter with commercial power frequency, and the alternating-current inverter can be fed back to a commercial power transmission system or used for an off-grid power grid. The photovoltaic inverter is one of important system balances in a photovoltaic array system and can be used together with common alternating current power supply equipment. Generally, a pv inverter may have functions that are matched to specific functions of a pv array, such as Maximum Power Point Tracking (MPPT) and islanding protection. Since the structure and function of the power controller 101, including components such as the PCS and/or photovoltaic inverter, are known to those skilled in the art, the details thereof will not be described in greater detail herein for the sake of brevity.

As shown in fig. 2, according to an embodiment of the present disclosure, the power controller 101 may include: a first dc/ac converter 1011, to the dc side of which the first energy storage device 102 may be connected; and a second dc/ac converter 1012, the second energy storage device 103 and the power generation device 105 may be connected to the dc side of the second dc/ac converter 1012. Furthermore, as shown in fig. 2, the grid 109 and/or the load 108 may be connected to the ac side of the first dc/ac converter 1011 and/or the second dc/ac converter 1012, according to embodiments of the present disclosure.

According to an embodiment of the present disclosure, the first energy storage device 102 may be an ion battery or an ion battery pack, such as a lithium ion battery or a sodium ion battery. As shown in fig. 2, a lithium battery pack as an example of the first energy storage device 102 may be connected to the power controller 101, and more particularly, may be connected to a dc side of the first dc/ac converter 1011.

Further, according to embodiments of the present disclosure, second energy storage device 103 may be a lead acid battery or a lead acid battery pack. As shown in fig. 2, a lead-acid battery pack as an example of the second energy storage device 103 may be connected to the power controller 101 via the first switch 104, and more specifically, may be connected to the dc side of the second dc/ac converter 1012.

According to an embodiment of the present disclosure, the power generation device 105 may be a new energy power generation device such as a photovoltaic power generation device, a wind power generation device, a tidal power generation device, and/or a geothermal power generation device. As shown in fig. 2, a photovoltaic power generation unit as an example of the power generation device 105 may be connected to the power controller 101, more specifically, may be connected to the dc side of the second dc/ac converter 1012. In particular, as shown in fig. 2, a photovoltaic power generation unit as an example of the power generation device 105 may be connected to the power controller 101 in parallel with a lead-acid battery pack as an example of the second energy storage device 103, and more specifically, may be connected to the dc side of the second dc/ac converter 1012.

It will be appreciated by those skilled in the art that although embodiments of the present disclosure are described herein in connection with photovoltaic power generation units as specific examples of the power generation device 105, the inventive concepts of the present disclosure are equally applicable to other new energy storage systems, such as using wind power generation devices, tidal power generation devices, geothermal power generation devices as the power generation device 105.

Further, according to embodiments of the present disclosure, the power generation device 105 may output direct current power to charge the first energy storage device 102 and/or the second energy storage device 103 via the power controller 101.

As shown in fig. 1, according to an embodiment of the present disclosure, the power controller 101 may be connected to the first switch 104 to control the on and off of the first switch 104 according to the energy storage level of the first energy storage device 102 and/or the second energy storage device 103 and/or the dc power output by the power generation device 105.

According to the embodiment of the present disclosure, when the energy storage level of the first energy storage device 102 is lower than the first predetermined threshold, the power controller 101 may control the first switch 104 to be turned on to discharge the second energy storage device 103. As shown in fig. 2, for example, when the backup power Of the lithium battery pack (e.g., indicated by a State Of Charge (SOC) Of the lithium battery pack) as an example Of the first energy storage device 102 is running out (e.g., when the SOC Of the lithium battery pack is less than a first predetermined threshold set in advance), the power controller 101 may control the first switch 104 to conduct to put the lead-acid battery pack as an example Of the second energy storage device 103 into power such that the photovoltaic inverter operates to power an important load simultaneously with the lithium battery pack. Therefore, according to the embodiments of the present disclosure, it is possible to improve the corresponding standby power period and increase the maximum load capacity according to the capacity of the lead-acid battery pack. That is to say, according to the embodiment of the present disclosure, by accessing the second energy storage device 103, the upper limit of the backup power capacity can be increased, and the continuous power supply capability to the load can be improved.

According to an embodiment of the present disclosure, when the fluctuation of the dc power output by the power generation device 105 exceeds the second predetermined threshold, the power controller 101 may control the first switch 104 to be turned on to discharge the second energy storage device 103. As shown in fig. 2, for example, by connecting the lead-acid battery pack as an example of the second energy storage device 103 and the photovoltaic power generation unit as an example of the power generation device 105 in parallel to the power controller 101, when the photovoltaic power generation unit as an example of the power generation device 105 is affected by short-time external factors to cause fluctuation of the output dc power thereof (for example, when a change per unit time of voltage, current, or the like output by the photovoltaic power generation unit is greater than a preset second predetermined threshold), the power controller 101 may control the first switch 104 to be turned on to connect the lead-acid battery pack as an example of the second energy storage device 103 to stabilize the bus voltage, assist the MPPT function of the photovoltaic inverter, and enable the photovoltaic inverter to be in the maximum power operation mode for a long time. That is to say, according to the embodiment of the present disclosure, by accessing the second energy storage device 103, the photovoltaic side efficiency can be increased, and the system operation stability can be improved. As shown in fig. 2, for example, the dc power output from the photovoltaic power generation unit as an example of the power generation device 105 can be measured by, for example, a photovoltaic meter kwh 3. Further, as shown in fig. 2, for example, the bus voltage may be measured by an element having a voltage sampling function, for example, connected in series with the first switch 104.

According to the embodiment of the present disclosure, when the dc power output by the power generation device 105 is higher than the third predetermined threshold, the power controller 101 may control the first switch 104 to be turned on to place the second energy storage device 103 in the floating state. As shown in fig. 2, for example, by connecting the lead-acid battery pack as an example of the second energy storage device 103 and the photovoltaic power generation unit as an example of the power generation device 105 in parallel to the power controller 101, when the dc power (e.g., the voltage or current output by the photovoltaic power generation unit, etc.) output by the photovoltaic power generation unit as an example of the power generation device 105 is greater than a preset third predetermined threshold (e.g., in the case of good sunlight conditions or limited photovoltaic power generation), the power controller 101 may control the first switch 104 to be turned on to charge the lead-acid battery pack by the photovoltaic power generation unit to store surplus power, while the lead-acid battery pack may be placed in a float state to improve the battery life.

According to an embodiment of the present disclosure, when the dc power output by the power generation device 105 is lower than the fourth predetermined threshold, the power controller 101 may control the first switch 104 to be turned on to discharge the second energy storage device 103. As shown in fig. 2, for example, by connecting a lead-acid battery pack as an example of the second energy storage device 103 and a photovoltaic power generation unit as an example of the power generation device 105 in parallel to the power controller 101, when the dc power (e.g., the voltage or current output by the photovoltaic power generation unit) output by the photovoltaic power generation unit as an example of the power generation device 105 is smaller than a preset fourth predetermined threshold (e.g., at night), the power controller 101 may control the first switch 104 to be turned on to perform Proportional Integral Derivative (PID) compensation on the photovoltaic power generation unit (e.g., a photovoltaic panel) by the lead-acid battery pack to improve the lifetime thereof.

For example, according to an embodiment of the present disclosure, the power controller 101 may detect the bus voltage in real time at night, and when the bus voltage is lower than, for example, 50V (i.e., a fourth predetermined threshold), the power controller 101 turns on the first switch 104.

Further alternatively, according to an embodiment of the present disclosure, the power controller 101 may further control the first switch 104 to be turned on for PID compensation by using an Energy Management System (EMS) according to a pre-counted period (e.g., night) in which the dc power output by the power generation device 105 is lower than a fourth predetermined threshold.

According to an embodiment of the present disclosure, the first energy storage device 102 may be connected to the power controller 101 via the second switch 107, and more specifically, may be connected to the dc side of the first dc/ac converter 1011 via the second switch 107, and the power controller 101 may also control the second switch 107 to be turned on and off. According to the embodiment of the present disclosure, when the energy storage level of the first energy storage device 102 is higher than the fifth predetermined threshold, the power controller 101 controls the second switch 107 to be turned off. As shown in fig. 2, for example, by incorporating a lead-acid battery pack as an example of the second energy storage device 103 into an optical storage microgrid system as an example of the energy storage system 100, peak-valley utilization may be separated from power backup functions. That is, the lithium battery pack as an example of the first energy storage device 102 only needs to reserve a small amount of power (for example, the second switch 107 is controlled by the power controller 101 so that the SOC of the lithium battery pack is lower than a preset fifth predetermined threshold), so that the peak clipping and valley filling gains are maximized. At this time, according to the embodiment of the disclosure, when the optical storage microgrid system is required to supply power to an important load, the lead-acid battery pack and the photovoltaic inverter can be used to ensure the supply and demand. Alternatively, according to the embodiment of the present disclosure, the power controller 101 may also control the second switch 107 not to be turned off, but directly control the power to be reduced to zero, where the first dc/ac converter 1011 is in a hot standby state, so as to facilitate fast microgrid configuration.

According to embodiments of the present disclosure, the power controller 101 may include a direct current/alternating current (DC/AC) converter, such as the first DC/AC converter 1011 and/or the second DC/AC converter 1012, for powering the load 108 and/or the grid 109 via at least one of the power generation device 105, the first energy storage device 102, and the second energy storage device 103. As shown in fig. 2, for example, at least one of a photovoltaic power generation unit as an example of the power generation device 105, a lithium battery pack as an example of the first energy storage device 102, and a lead-acid battery pack as an example of the second energy storage device 103 may supply power to the load 108 (including important loads and general loads) and/or the grid 109 through a DC/AC converter. As shown in fig. 2, the energy storage level of the energy storage system 100 may be measured by, for example, an energy storage meter kwh1, according to an embodiment of the present disclosure. Further, as shown in fig. 2, according to an embodiment of the present disclosure, the power supplied to the important load may be monitored using the load table kwh 2.

According to an embodiment of the present disclosure, the grid 109 may be connected to the AC side of the DC/AC converter (e.g., the first DC/AC converter 1011 and/or the second DC/AC converter 1012) of the power controller 101 via the third switch 110, and the power controller 101 may control the on and off of the third switch 110.

As shown in fig. 2, according to an embodiment of the present disclosure, the efficiency of the photovoltaic inverter may be improved by connecting lead-acid battery packs in parallel; the service life of the lead-acid battery can be prolonged by floating charging the lead-acid battery pack by utilizing the bus voltage of the photovoltaic inverter; PID compensation can be carried out on the photovoltaic power generation unit by controlling the lead-acid battery pack to be on line at night; by using different battery packs for peak-valley arbitrage and standby power respectively, the income conflict can be solved; and the maximum load carrying capacity of the standby power capacity of the microgrid can be increased by connecting the lead-acid battery packs in parallel.

An example of the operation of the energy storage system 100 according to an embodiment of the present disclosure is described in more detail below with reference to the example of fig. 2 in conjunction with fig. 3. Fig. 3 is an exemplary diagram illustrating an operation principle of the energy storage system 100 according to an embodiment of the present disclosure.

As shown in fig. 3, according to an embodiment of the disclosure, when the energy storage system 100 operates at night, that is, when the dc power output by the photovoltaic power generation unit (for example, the voltage or current output by the photovoltaic power generation unit, etc.) is less than a preset fourth predetermined threshold, the power controller 101 may control the first switch 104 to be turned on to perform PID compensation on the photovoltaic power generation unit (for example, a photovoltaic cell panel) through the lead-acid battery pack to improve the service life thereof.

Further, as shown in fig. 3, according to an embodiment of the present disclosure, when the energy storage system 100 is operated at night, the PCS, which is an example of the power controller 101, may operate in a daily policy state. At this time, the photovoltaic inverter in the PCS may determine whether or not the insolation situation is good, that is, whether or not the fluctuation of the dc power output by the photovoltaic power generation unit exceeds a second predetermined threshold, for example, whether or not the change per unit time of the voltage or current or the like output by the photovoltaic power generation unit is larger than a second predetermined threshold set in advance.

As shown in fig. 3, if the fluctuation of the dc power output by the photovoltaic power generation unit is smaller than a second predetermined threshold value set in advance, the lead-acid battery pack may absorb the surplus electric power of the photovoltaic power generation unit and enter a float charge state after the lead-acid battery pack is fully charged. By placing the lead-acid battery in a float-charged state, the battery life can be increased, the capacity loss caused by the self-discharge of the battery can be replenished and the capacity can be kept sufficient, and sulfation caused by recrystallization of the active material can be suppressed.

As shown in fig. 3, if the fluctuation of the dc power output by the photovoltaic power generation unit is smaller than the preset second predetermined threshold, the lead-acid battery pack may stabilize the bus voltage, improve the efficiency of the photovoltaic inverter, and thus improve the stability of the photovoltaic system.

While the disclosure has been disclosed by the description of the specific embodiments thereof, it will be appreciated that those skilled in the art will be able to devise various modifications, improvements, or equivalents of the disclosure within the spirit and scope of the appended claims. Such modifications, improvements and equivalents are also intended to be included within the scope of this disclosure.

Claims

1. An energy storage system, comprising:

a power controller;

a first energy storage device connected to the power controller;

a second energy storage device connected to the power controller via a first switch; and

a power generation device connected to the power controller and configured to output direct current power to charge the first and/or second energy storage devices and/or to power a load and/or a grid via the power controller,

wherein the power controller controls the first switch to be switched on and off according to the energy storage level of the first energy storage device and/or the second energy storage device and/or the direct current output by the power generation device.

2. The energy storage system of claim 1, wherein the first energy storage device is a lithium ion battery or a sodium ion battery and the second energy storage device is a lead acid battery.

3. The energy storage system of claim 2, wherein the power plant is at least one of a photovoltaic power plant, a wind power plant, a tidal power plant, and a geothermal power plant.

4. The energy storage system of claim 3, wherein the power controller controls the first switch to conduct to discharge the second energy storage device when the energy storage level of the first energy storage device is below a first predetermined threshold.

5. The energy storage system of claim 3, wherein the power controller controls the first switch to conduct to discharge the second energy storage device when fluctuations in the DC power output by the power generation device exceed a second predetermined threshold.

6. The energy storage system of claim 3, wherein the power controller controls the first switch to conduct to place the second energy storage device in a float state when the DC power output by the power generation device is higher than a third predetermined threshold.

7. The energy storage system of claim 3, wherein the power controller controls the first switch to conduct to discharge the second energy storage device when the DC power output by the power generation device is below a fourth predetermined threshold.

8. The energy storage system of claim 3, wherein the first energy storage device is connected to the power controller via a second switch,

wherein the power controller controls the second switch to be turned on and off, an

Wherein the power controller controls the second switch to be turned off when the energy storage level of the first energy storage device is higher than a fifth predetermined threshold.

9. The energy storage system of any of claims 1-8, wherein the power controller comprises:

a first DC/AC converter, the first energy storage device connected to a DC side of the first DC/AC converter; and

a second DC/AC converter, the second energy storage device and the power generation device being connected to a DC side of the second DC/AC converter.

10. The energy storage system of claim 9, wherein the grid is connected to the ac side of the first and/or second dc/ac converter of the power controller via a third switch, and

wherein the power controller controls the third switch to be turned on and off.