Photovoltaic emergency turn-off system and turn-off method

Abstract

The invention discloses a photovoltaic emergency turn-off system and a turn-off method, relates to the photovoltaic field, and is used for realizing global synchronous turn-off control in a multi-gateway scene. The system comprises a plurality of turn-off device terminals connected with photovoltaic panels one by one, a plurality of gateways, at least one trigger and a management platform. Each gateway is wirelessly connected with a plurality of gateway terminals, the triggers are respectively connected with the gateways, and the gateways are in Mesh networking and are respectively connected with the management platform. And the gateways control the connected breaker terminals to turn off the photovoltaic panels under the triggering of a turn-off instruction of the trigger, the management platform or the management platform, and the gateways broadcast the turn-off instruction through the Mesh network, or the management platform issues the turn-off instruction in a unified manner. According to the invention, one-key global turn-off in a multi-gateway scene can be realized, the trigger can be flexibly arranged, and the system is high in working timeliness, high in flexibility and high in reliability.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic technology, and in particular to a photovoltaic emergency shutdown system and shutdown method. Background Technology

[0002] Photovoltaic power plants, especially large-scale ones, face high-voltage risks on their DC side (i.e., the photovoltaic panel side). In emergencies, it is necessary to quickly cut off the power supply, i.e., shut down the photovoltaic panels. Traditional methods require manual shutdown at each stage, which is inefficient and dangerous.

[0003] Electrical automation technology has solved the problems associated with manual shutdown. It uses logic devices such as PLCs to connect to switches installed on the photovoltaic panel side via wired connections. The PLC sends switch signals to control the on / off state of each switch. However, wired shutdown systems suffer from drawbacks such as complex wiring, high cost, and poor scalability.

[0004] With the development of IoT and wireless communication technologies, wireless shutdown systems have emerged. These systems use wireless signals to trigger shutdown terminals within the network to turn off photovoltaic panels, overcoming the drawbacks of wired shutdown systems in terms of wiring and cost. Known wireless shutdown systems typically use a single wireless gateway, which has limited communication capacity and distance, making it impossible to cover all photovoltaic panels. To cover all photovoltaic panels, multiple wireless gateways must be deployed for individual control. However, even with multiple gateways, each gateway operates independently, failing to achieve synchronized "one-click trigger, full-area shutdown" operation. Summary of the Invention

[0005] The purpose of this invention is to provide a photovoltaic emergency shutdown system and shutdown method to address all or part of the problems mentioned above, so as to achieve synchronous shutdown control across the entire domain in a multi-gateway scenario.

[0006] The technical solution adopted in this invention is as follows: A photovoltaic emergency shutdown system, comprising: Multiple shutdown terminals are connected to photovoltaic panels one by one. In response to receiving a shutdown command, the connected photovoltaic panels are turned off. Multiple gateways, each wirelessly connected to at least one of the shutdown terminals, generate, receive, or forward shutdown commands, and send the shutdown commands to the connected shutdown terminals; the gateways are networked in a Mesh configuration. At least one trigger, which is wirelessly connected to any gateway and generates a shutdown command to be sent to the connected gateway. The management platform is connected to each of the gateways, generates or receives shutdown commands, and broadcasts the shutdown commands to each of the gateways.

[0007] Furthermore, the trigger is a rotary self-locking trigger; after being pressed and rotated to lock, it triggers a shutdown command and maintains the trigger state; after rotating in the opposite direction to unlock, it immediately releases the shutdown command trigger state.

[0008] Furthermore, the gateway is equipped with one of the following switches: Dual self-reset switches: pressing one of them triggers an off command and maintains the triggered state, while pressing the other releases the off command trigger state. A single self-locking switch, when pressed, remains locked, triggers an off command and remains in the triggered state, and when pressed again and released to reset, the off command trigger state is released; The single self-reset switch triggers an off command and remains in the triggered state after being pressed and held for a predetermined time. After being pressed and held for a predetermined time again, the off command trigger state is released.

[0009] Furthermore, the gateway has a shutdown status indicator light, the state of which is different when a shutdown command is triggered and when the shutdown command is released.

[0010] Furthermore, the trigger is a portable trigger.

[0011] This application also provides a shutdown method based on the above-mentioned photovoltaic emergency shutdown system, which includes: The system controls a trigger corresponding to the target area to generate a shutdown command and sends it to the connected gateway. Alternatively, it controls the gateway corresponding to the target area to generate a shutdown command, or it uses a management platform to generate a shutdown command and send it to the gateway corresponding to the target area. This causes the gateway to send the shutdown command to the connected shutdown terminal, thereby prompting the shutdown terminal in the target area to shut down the connected photovoltaic panels.

[0012] This application also provides another shutdown method based on the above-mentioned photovoltaic emergency shutdown system, which includes: The system controls any trigger to generate a shutdown command and send it to the connected gateway, or controls any gateway to generate a shutdown command, so that the gateway forwards the shutdown command to the management platform. After receiving the shutdown command, the management platform broadcasts the shutdown command to all gateways, so that all gateways send the shutdown command to the connected shutdown terminal, thereby causing all shutdown terminals to shut down the connected photovoltaic panels.

[0013] This application also provides another shutdown method based on the above-mentioned photovoltaic emergency shutdown system, which includes: Control any trigger to generate a shutdown command and send it to the connected gateway, or control any gateway to generate a shutdown command, so that the gateway broadcasts the shutdown command to other gateways through the Mesh network, so that all gateways send the shutdown command to the connected shutdown terminal respectively, thereby causing all shutdown terminals to shut down the connected photovoltaic panels.

[0014] This application also provides another shutdown method based on the above-mentioned photovoltaic emergency shutdown system, which includes: The management platform generates a shutdown command and broadcasts the shutdown command to all gateways, causing each gateway to send the shutdown command to its connected shutdown terminal, thereby prompting all shutdown terminals to shut down the connected photovoltaic panels.

[0015] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: The photovoltaic emergency shutdown system and method proposed in this application allow for synchronous emergency shutdown of photovoltaic panels across the entire area (all gateway-managed areas) with a single triggering action (trigger trigger, gateway trigger, or management platform trigger), offering convenient operation and high timeliness. Furthermore, achieving full-area shutdown control with a small number of triggers simplifies the system structure, reduces construction costs and complexity, and enhances layout flexibility, allowing triggers to be placed at any critical location to improve the ease of shutdown triggering. The design of multiple switches effectively prevents accidental operation and improves system reliability. In addition, this application designs two shutdown channels—one for the management platform and one for the Mesh network—sufficient to handle network failure risks and improve system robustness. Attached Figure Description

[0016] The present invention will be described by way of example and with reference to the accompanying drawings, wherein: Figure 1 This is a structural diagram of a photovoltaic emergency shutdown system in one embodiment.

[0017] Figure 2 This is a timing diagram of the photovoltaic emergency shutdown method in the first embodiment.

[0018] Figure 3 This is a timing diagram of the photovoltaic emergency shutdown method in the second implementation.

[0019] Figure 4 This is a timing diagram of the photovoltaic emergency shutdown method in the third implementation.

[0020] Figure 5 This is a timing diagram of the photovoltaic emergency shutdown method in the fourth implementation. Detailed Implementation

[0021] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0022] Any feature disclosed in this specification (including any appended claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0023] In emergency situations, photovoltaic (PV) power stations need to quickly cut off part or all of the DC power supply, i.e., shut down the PV panels. Wireless shutdown systems are among the most suitable known solutions for managing the shutdown of large-scale PV power stations. However, current wireless shutdown systems have limited capacity and coverage of individual gateways, requiring multiple independent gateways to manage regional PV panels separately. Each gateway operates independently without interfering with others. When a full shutdown is needed, each gateway must be operated individually on-site, making a one-click full shutdown impossible, resulting in insufficient timeliness and flexibility. To address this, this application proposes a PV emergency shutdown system and method, aiming to achieve one-click full shutdown in multi-gateway scenarios without limiting the location of operation.

[0024] like Figure 1 As shown, the photovoltaic emergency shutdown system provided in this application embodiment includes: (1) Multiple shutdown terminals. Each shutdown terminal is connected to a photovoltaic panel, and each shutdown terminal responds to the received shutdown command and shuts down the photovoltaic panel it is connected to.

[0025] The shut-off device can be a circuit breaker switch or a photovoltaic optimizer terminal. Its purpose is to perform a bypass or power-off operation on the photovoltaic panel after receiving a shutdown signal, thereby shutting down the photovoltaic panel.

[0026] Each shutdown terminal is equipped with an IoT communication module (such as a communication module that supports wireless communication protocols such as WIoTa, Lora, and Zigbee) to interact with the gateway, for example, to receive shutdown commands from the gateway.

[0027] (2) Multiple gateways. Each gateway wirelessly connects to at least one shutdown terminal. In practical scenarios, each gateway typically needs to connect to multiple shutdown terminals to synchronously control the operation of multiple shutdown terminals. Each gateway is used to generate, receive, or forward shutdown commands and issue shutdown commands to the connected shutdown terminals.

[0028] In other words, any of the aforementioned gateways can generate its own shutdown command, thus proactively sending a shutdown command to the shutdown terminal; alternatively, any of the aforementioned gateways can receive shutdown commands sent by other devices (such as triggers, management platforms, or other gateways in the same Mesh network), thus passively sending a shutdown command to the shutdown terminal; or, any of the aforementioned gateways can receive shutdown commands sent by other devices (such as triggers) and forward the shutdown command to other devices besides the shutdown terminal (such as management platforms or other gateways in the same Mesh network). The forwarding method can be either directly forwarding the shutdown command upon receipt, or regenerating a new shutdown command upon receipt and forwarding it.

[0029] In addition, each gateway has a built-in independent wireless communication module to enable mesh networking between them, forming a mesh network. Each gateway can broadcast data or achieve time and data synchronization through the mesh network.

[0030] The gateway can generate a shutdown signal locally, therefore, it is configured with a facility to trigger the generation of such a signal. As an optional implementation, the gateway is equipped with one of the following switches: 1) Dual self-reset switches. One of the self-reset switches triggers a shutdown command and remains in the triggered state when pressed; this can be called a self-reset shutdown switch. The other self-reset switch deactivates the trigger state when pressed; this can be called a self-reset recovery switch. The self-reset recovery switch can either directly deactivate the shutdown command trigger state when pressed, or it can continuously generate recovery commands to disable the shutdown command trigger state when pressed.

[0031] 2) Single self-locking switch. When pressed, it remains locked, triggers the shutdown command and remains in the triggered state. When pressed again, it unlocks and resets, releasing the shutdown command trigger state.

[0032] The single self-locking switch remains locked after being pressed, and is only unlocked and reset when pressed again.

[0033] 3) Single self-reset switch. Pressing and holding for a predetermined time triggers a shutdown command and maintains the triggered state. Pressing and holding again for a predetermined time releases the shutdown command trigger state.

[0034] A single self-reset switch requires a long press for a specified time (e.g., 1 second) to trigger the shutdown command. Similarly, when deactivating the trigger state, it also requires a long press for a specified time to deactivate, in order to prevent accidental triggering.

[0035] The gateway housing or other location should have a shutdown status indicator light. The state of this indicator light should differ when a shutdown command is triggered and when the shutdown command is released. For example, the light should illuminate when a shutdown command is triggered, indicating that the command has been successfully triggered, and should turn off when the command is released, indicating that the triggering state has been deactivated.

[0036] During the trigger-off state and the holding period, the gateway will continuously generate shutdown commands until the trigger state is deactivated.

[0037] (3) At least one trigger, each trigger is wirelessly connected to any gateway, and generates a shutdown command to be sent to the connected gateway.

[0038] If the existing wireless shutdown system is controlled by triggers, each gateway needs to be equipped with a trigger, and each trigger needs to be wirelessly connected to each gateway. Each gateway triggers the shutdown command through its corresponding trigger.

[0039] In this embodiment, triggers are not required to match the number of gateways; the entire shutdown system can even be equipped with only one trigger. Of course, implementations where one trigger is provided for each gateway are not excluded. Triggers can freely establish wireless connections with gateways; for example, a small number (less than the number of gateways) of triggers can connect to one of all gateways, or different triggers can connect to the same gateway. The triggers are preferably portable, being mobile and easy to carry or install, improving the flexibility of system layout. Triggers can be conveniently placed in key locations such as entrances / exits and maintenance channels, overcoming the limitations of fixed gateway locations. This facilitates personnel operation while also improving the personal safety of operators.

[0040] Since triggers are usually placed in easily accessible locations, to prevent accidental triggering, in one optional implementation, the trigger is designed as a rotary self-locking trigger. After being pressed and rotated to lock, the off command is triggered and the triggering state is maintained; after being rotated in the opposite direction to unlock, the off command triggering state is immediately released.

[0041] (4) The management platform connects to each gateway, generates or receives shutdown commands, and broadcasts shutdown commands to each gateway.

[0042] The management platform can proactively generate shutdown commands locally to automatically shut down photovoltaic panels across the entire domain or in a target area. Alternatively, it can receive shutdown commands (such as reported shutdown events) from the gateway. These commands can be generated by the gateway itself or generated by a trigger and sent to the gateway, which then forwards them to the management platform.

[0043] It should be noted that the shutdown command received by the gateway or management platform can be the same as the shutdown command sent by the gateway or management platform, for example, the payload data can be the same; or they can be different. For example, the shutdown command received by the gateway or management platform may only be a trigger signal or an enable signal, while the shutdown command sent by the gateway or management platform may involve specific destination addresses, timestamps, shutdown event payloads, etc.

[0044] The photovoltaic emergency shutdown system constructed above can flexibly trigger gateways with a small number of triggers, and can broadcast shutdown commands to all gateways through a unified management platform, or broadcast shutdown commands between gateways through a Mesh network, thereby achieving synchronous shutdown of all photovoltaic panels with only one trigger.

[0045] In this embodiment of the application, a photovoltaic emergency shutdown method is also proposed based on the photovoltaic emergency shutdown system proposed above.

[0046] In one alternative implementation targeting a specific area, such as one or more specific gateways, the shutdown method includes: The system controls the trigger corresponding to the target area to generate a shutdown command and send it to the connected gateway. Alternatively, it controls the gateway corresponding to the target area to generate a shutdown command, or it uses the management platform to generate a shutdown command and send it to the gateway corresponding to the target area. This causes the gateway to send a shutdown command to the connected shutdown terminal, thereby prompting the shutdown terminal in the target area to shut down the connected photovoltaic panels.

[0047] In other words, such as Figure 2 As shown, there are three ways to shut down the target area: (1) The user operates the trigger to generate a shutdown instruction ( Figure 2 (This is referred to as shutdown command 1 in the original text). The trigger sends the shutdown command to the connected gateway. After receiving the shutdown command, the gateway sends it to all connected shutdown terminal terminals. Figure 2 The shutdown command is broadcast by shutdown terminals 1 to n in the circuit breaker. Figure 2 The command is referred to as the shutdown command 4, which causes each shutdown terminal to shut down the photovoltaic panel it is connected to after receiving the shutdown command.

[0048] (2) The user operates the gateway to actively generate a shutdown command on the local end. Figure 2 This is referred to as shutdown command 3, which is broadcast by the gateway to all connected shutdown terminal devices. Figure 2 The command is referred to as the shutdown command 4, which causes each shutdown terminal to shut down the photovoltaic panel it is connected to after receiving the shutdown command.

[0049] (3) The user operation management platform generates a shutdown command. Figure 2The command, referred to as "shutdown command 2," is sent to the corresponding gateway. Upon receiving the shutdown command, the gateway broadcasts it to all connected shutdown terminal devices. Figure 2 This is referred to as the shutdown command 4, which causes each shutdown terminal to shut down its connected photovoltaic panels upon receiving the shutdown command. This method is typically used for planned shutdown operations, such as when maintenance personnel need to enter the photovoltaic power station for maintenance.

[0050] Regardless of the method, the gateway can report the shutdown event executed by the management platform after issuing a shutdown command (to the shutdown terminal).

[0051] In one alternative implementation targeting the entire domain, the shutdown method includes: The system controls any trigger to generate a shutdown command and send it to the connected gateway, or controls any gateway to generate a shutdown command, so that the gateway forwards the shutdown command to the management platform. Upon receiving the shutdown command, the management platform broadcasts the shutdown command to all gateways, causing all gateways to send the shutdown command to the connected shutdown terminal, thereby prompting all shutdown terminals to shut down the connected photovoltaic panels.

[0052] In this implementation, such as Figure 3 As shown, there are two ways to shut down: (1) The user operates any trigger to generate a shutdown instruction ( Figure 3 The shutdown command 1) is sent to the connected gateway, which, upon receiving the shutdown command, sends a shutdown command to the management platform. Figure 3 This is referred to as shutdown command 3, which may differ from the received shutdown command 1. Upon receiving the shutdown command, the management platform broadcasts the shutdown command to all gateways. Figure 3 After the shutdown command 4 in the middle, each gateway broadcasts the shutdown command to all connected shutdown terminal terminals. Figure 3 The shutdown command 5 in the middle enables each shutdown terminal to shut down the photovoltaic panel it is connected to after receiving the shutdown command.

[0053] (2) The user operates any gateway to generate a shutdown command ( Figure 3 The shutdown instruction 2 in the middle will shut down the instruction ( Figure 3 The shutdown command 3) is sent to the management platform, which, upon receiving the shutdown command, broadcasts the shutdown command to all gateways. Figure 3 After the shutdown command 4 in the middle, each gateway broadcasts the shutdown command to all connected shutdown terminal terminals. Figure 3 The shutdown command 5 in the middle enables each shutdown terminal to shut down the photovoltaic panel it is connected to after receiving the shutdown command.

[0054] Similarly, regardless of the method, the gateway can report the shutdown event executed by the management platform after issuing the shutdown command.

[0055] The above shutdown method is for situations where the management platform is online. If the management platform is offline or unavailable, the shutdown method can also achieve a global shutdown through another implementation method. This other implementation method includes: Control any trigger to generate a shutdown command and send it to the connected gateway, or control any gateway to generate a shutdown command, so that the gateway broadcasts the shutdown command to other gateways through the Mesh network, so that all gateways send shutdown commands to the connected shutdown terminal, thereby causing all shutdown terminals to shut down the connected photovoltaic panels.

[0056] The key difference between this implementation scheme and the previous one is that it does not require a management platform to uniformly issue shutdown commands. Instead, it uses a mesh network between gateways to broadcast shutdown commands within the mesh network, enabling each gateway to synchronously issue shutdown commands to its connected shutdown terminal, thus achieving synchronous shutdown of all photovoltaic panels.

[0057] In the above embodiments, such as Figure 4 As shown, the shutdown method also includes two approaches: (1) The user operates any trigger to generate a shutdown instruction ( Figure 4 The shutdown command 1) is sent to the connected gateway, which, upon receiving the shutdown command, broadcasts the shutdown command within the Mesh network. Figure 4 After the shutdown command 3 in the middle, each gateway broadcasts the shutdown command to all connected shutdown terminal terminals. Figure 4 The shutdown command 4 in the middle enables each shutdown terminal to shut down the photovoltaic panel it is connected to after receiving the shutdown command.

[0058] (2) The user operates any gateway to generate a shutdown command ( Figure 4 The shutdown command 2 in the middle), and broadcast the shutdown command in the Mesh network ( Figure 4 After the shutdown command 3 in the middle, each gateway broadcasts the shutdown command to all connected shutdown terminal terminals. Figure 4 The shutdown command 4 in the middle enables each shutdown terminal to shut down the photovoltaic panel it is connected to after receiving the shutdown command.

[0059] In another implementation, the shutdown method can also involve the management platform initiating a shutdown command. In this implementation, such as... Figure 5 As shown, the shutdown methods include: Use the management platform to generate shutdown commands ( Figure 5 The shutdown command 1 in the document is broadcast to all gateways. Figure 5The shutdown command 1 in the middle causes all gateways to send shutdown commands to the connected shutdown terminal. Figure 5 The shutdown instruction 2 in the middle causes all shutdown terminals to shut down the photovoltaic panels connected to them.

[0060] In this implementation, the management platform needs to be online, and the administrator needs to initiate the full shutdown operation.

[0061] The shutdown method of any of the above implementation methods can achieve "one-click triggering and synchronous shutdown across the entire domain".

[0062] In summary, the photovoltaic emergency shutdown system and method provided in this application solve the cross-domain synchronization problem of shutdown commands in multi-gateway scenarios, ensuring that a single trigger action can achieve synchronous shutdown of all photovoltaic panels. Furthermore, through global control of the management platform and Mesh networking modes of the gateways, the availability of the shutdown system can be ensured under any conditions (management platform online or offline), which is sufficient to resist network failure risks and improve the reliability of the shutdown system. The shutdown system is triggered wirelessly, resulting in low communication response time. Even in large photovoltaic power plants, it can achieve second-level (communication latency as low as 100ms) synchronous shutdown control across the entire domain, demonstrating high responsiveness.

[0063] This invention is not limited to the specific embodiments described above. The invention extends to any new feature or combination disclosed in this specification, as well as any new method or process step or combination disclosed herein.

Claims

1. A photovoltaic emergency shutdown system, characterized in that, include: Multiple shutdown terminals are connected to photovoltaic panels one by one. In response to receiving a shutdown command, the connected photovoltaic panels are turned off. Multiple gateways, each wirelessly connected to at least one of the shutdown terminals, generate, receive, or forward shutdown commands, and send the shutdown commands to the connected shutdown terminals; the gateways are networked in a Mesh configuration. At least one trigger, which is wirelessly connected to any gateway and generates a shutdown command to be sent to the connected gateway. The management platform is connected to each of the gateways, generates or receives shutdown commands, and broadcasts the shutdown commands to each of the gateways.

2. The photovoltaic emergency shutdown system as described in claim 1, characterized in that, The trigger is a rotary self-locking trigger; after being pressed and rotated to lock, it triggers a shutdown command and maintains the trigger state; after being rotated in the opposite direction to unlock, the shutdown command trigger state is immediately released.

3. The photovoltaic emergency shutdown system as described in claim 1, characterized in that, The gateway is equipped with one of the following switches: Dual self-reset switches: pressing one of them triggers an off command and maintains the triggered state, while pressing the other releases the off command trigger state. A single self-locking switch, when pressed, remains locked, triggers an off command and remains in the triggered state, and when pressed again and released to reset, the off command trigger state is released; The single self-reset switch triggers an off command and remains in the triggered state after being pressed and held for a predetermined time. After being pressed and held for a predetermined time again, the off command trigger state is released.

4. The photovoltaic emergency shutdown system as described in claim 1, characterized in that, The gateway has a shutdown status indicator light, and the state of the indicator light is different when the shutdown command is triggered and when the shutdown command is released.

5. The photovoltaic emergency shutdown system as described in claim 1 or 2, characterized in that, The trigger is a portable trigger.

6. A shutdown method based on a photovoltaic emergency shutdown system according to any one of claims 1-5, characterized in that, include: The system controls a trigger corresponding to the target area to generate a shutdown command and sends it to the connected gateway. Alternatively, it controls the gateway corresponding to the target area to generate a shutdown command, or it uses a management platform to generate a shutdown command and send it to the gateway corresponding to the target area. This causes the gateway to send the shutdown command to the connected shutdown terminal, thereby prompting the shutdown terminal in the target area to shut down the connected photovoltaic panels.

7. A shutdown method based on a photovoltaic emergency shutdown system according to any one of claims 1-5, characterized in that, include: The system controls any trigger to generate a shutdown command and send it to the connected gateway, or controls any gateway to generate a shutdown command, so that the gateway forwards the shutdown command to the management platform. After receiving the shutdown command, the management platform broadcasts the shutdown command to all gateways, so that all gateways send the shutdown command to the connected shutdown terminal, thereby causing all shutdown terminals to shut down the connected photovoltaic panels.

8. A shutdown method based on a photovoltaic emergency shutdown system according to any one of claims 1-5, characterized in that, include: Control any trigger to generate a shutdown command and send it to the connected gateway, or control any gateway to generate a shutdown command, so that the gateway broadcasts the shutdown command to other gateways through the Mesh network, so that all gateways send the shutdown command to the connected shutdown terminal respectively, thereby causing all shutdown terminals to shut down the connected photovoltaic panels.

9. A shutdown method based on a photovoltaic emergency shutdown system according to any one of claims 1-5, characterized in that, include: The management platform generates a shutdown command and broadcasts the shutdown command to all gateways, causing each gateway to send the shutdown command to its connected shutdown terminal, thereby prompting all shutdown terminals to shut down the connected photovoltaic panels.

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