A new solar power plant is up and running in the hot and sunny Tropic of Cancer. The field site for the solar panel installation includes a farm, a lake, and the tops of local buildings. Because solar panels that track the sun’s movement can receive 10% to 40% more energy than fixed panels, the system is set up with a central controller for adjusting the panel angles.

Additionally, the facility has to record and transmit data about the current energy stability status and energy capacity, as well as check the field temperature and activate the cooling system as needed.

If, on a clear day in which the temperature is not too high, power generation is below the set parameters, the system will automatically notify attendants at the plant to clean the mirror faces.

The challenge

At that latitude, heat is a constant problem. Not just because excessive heat affects the power absorbing utility of the solar panel wafers, but also because overheating can damage or destroy the very expensive electrical and networking equipment installed on-site. Another challenge is the remote location of the plant.

It was deemed impossible to run network cabling from the local ISP, yet the facility had to be online and linked to the Cloud. For a 4G LTE solution, SIM cards with public IP addresses are prohibitively expensive. Lastly, the system had to be able to effectively connect to a Modbus controller. Modbus is a communication protocol used for transmitting data over serial cables, and many devices in the solar facility used this protocol. So the solution to be implemented had to overcome or work around these many obstacles.

System requirements include:

• Remote field monitoring and control through network connectivity
• Ability to send alarms to mobile phones
• RS-485 interface and support for Modbus protocol
• Support for MQTT cloud protocol
• Ability to operate in extremely high temperatures
• Various network failover mechanisms for redundancy
• Secure VPN tunnels

Network solution

The EW50 4G Industrial Gateway (EW50) from EtherWAN is an intelligent industrial grade gateway designed for critical infrastructure and industrial applications. It provides reliable and secure remote connectivity designed for harsh environments, giving operations and IT real-time awareness with remote monitoring.
The EW50 provides 4G LTE mobile network, Ethernet, serial RS-485, DI/DO and Modbus bridging, providing an ideal connection to the many inverters, sensors, and other devices on the site.

Importantly, MQTT is supported. MQTT is a messaging protocol based on the publish-subscribe messaging pattern. It is the most basic way of communication with SCADA systems.

Moreover, the EW50 supports comprehensive network and connectivity to secure data and network connections, maintaining best data transfer conditions.

Three major ways to secure data and connectivity are used:

1) Dual SIM cards
2) Cellular WAN and Ethernet WAN failover
3) OpenVPN failover.

Dual SIM Fail Over Function

SIM-A / SIM-B first with Failback enabled

With Failback option enabled, “SIM-A First” scenario (see diagram) is used to connect when the connection is broken. The gateway will switch to SIM-B. When the SIM-A connection is recovered, it will switch back to use the original SIM-A card.

Cellular WAN and Ethernet WAN failover backup connection:

Note:
WAN-1 / Physical interface: Ethernet operation Mode: Always On
WAN-2 / Physical interface: 3G/4G LTE Operation Mode: Failover (WAN-1)

OpenVPN Failover

To guarantee zero data loss, transmission redundancy will be necessary. Set up two server systems so if the main server goes down, the back-up server can receive the data. So, two OpenVPN tunnels are needed for the main server and backup server. In normal situations, the data is transferred to main server through VPN Tunnel 1. Once a failure occurs, the gateway can use VPN-Tunnel 2 for backup connection.

The solution is to set up two OpenVPN Tunnels in advance to connect to both servers with the EW50. Then, use the command script function to detect main server connection. If there is no response from main server for certain period, the EW50 will switch to VPN Tunnel 2 to reconnect the data with the backup server.

Conclusion

Solar power generation is becoming recognized as a renewable clean energy source and the number of distributed solar plants being built and in operation will continue to increase. These plants have critical monitoring and management needs, including real-time monitoring and messaging, control of panel tilt, power prediction, and power control systems. In many cases, traditional wired infrastructure for monitoring and management is not feasible, due to costs or environmental concerns. Equipping sites with appropriate 4G/LTE gateways is an effective approach, implementing a useful and comprehensive network backup mechanism to secure data, and keep the network always on and stable.

Technical article by EtherWAN.