Integrating Controls for Hydrogen Production

Hydrogen has long been discussed as a high potential alternative energy source, but most discussions of it focus on its use in automobiles. As such, the discussion quickly gets bogged down in two areas: infrastructure issues (replacing the current gasoline delivery pipeline) and the energy inputs required to produce hydrogen for fuel.



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Hydrogen has long been discussed as a high potential alternative energy source, but most discussions of it focus on its use in automobiles. As such, the discussion quickly gets bogged down in two areas: infrastructure issues (replacing the current gasoline delivery pipeline) and the energy inputs required to produce hydrogen for fuel.

But there are multiple other uses for hydrogen as a fuel source, from powering buildings to electronics and equipment, and it can be created using the energy from alternative energy sources, not just fossil fuels. Hydrogen’s important environmental advantage—when burned, hydrogen produces no contaminating emissions—has led to a growing interest in designing processes that use stored hydrogen as an energy source. Moreover, in cases where the hydrogen is produced by wind power or other renewable energy sources, the environmental impact is almost zero.


A description of the equipment used to produce and store hydrogen and deliver power at the Sotavento virtual power plant in Spain.
A description of the equipment used to produce and store hydrogen and deliver power at the Sotavento virtual power plant in Spain.

These considerations are behind an ongoing venture by the Sotavento Virtual Power Plant in Galicia, Spain, which was designed by Gas Natural SDG, Spain’s largest energy company, in conjunction with the Galician Regional Government (Xunta) and the Sotavento Foundation. In essence, a virtual power plant is a group of distributed power generation installations operated collectively by a central control unit.

The project goals for Sotavento are to assess the suitability of hydrogen as a storable form of energy in its gas state. The company’s objectives include:

  • Commercial green energy production;

  • Demonstration of the various wind technologies present in Galicia;

  • Establishment of an education and training center;

  • Establishment of a conference center for related events; and

  • General promotion of renewable energy.

To do this effectively, however, integration of the control systems used to operate the various power generation units at Sotavento has to take place.

The system integration hurdle

For large enterprises like power plants and water treatment facilities, it is common for myriad disparate control systems to be in operation. In most cases, the control equipment—sourced from different vendors, each with its own area of expertise—is often composed of a programmable logic controller capable of operating a particular piece of equipment, but with little additional functionality. The operator interface to these controllers is typically some form of a local display panel with some or no connectivity to the rest of the enterprise.

To address Sotavento’s multiple control system issues, Gas Natural contracted systems integrator Optomation Systems to design an integrated supervisory system for the Sotavento site. The system is based on the Opto 22 Snap PAC System platform (see sidebar box).

In consultation with Gas Natural, Optomation concluded that Sotavento’s system would need to:

  • Serve as a common manageable platform for process monitoring, data acquisition, and auxiliary control;

  • Provide complete supervision of electrolyzers, compressors, and hydrogen motor-generator units via a common operator interface;

  • Access and integrate data from the wind generator’s existing SCADA system;

  • Provide level and temperature monitoring in the hydrogen storage area (which is classified as explosive);

  • Enable remote monitoring of the installation, along with remote stop/start/shutdown capability over a secure Internet connection;

  • Provide data storage in a commercial relational database; and

  • Export production data via the Internet.

Employing a mix of analog and digital I/O connections, Optomation used Snap PAC stand-alone and rack-mounted PACs to connect the electrolyzers, motor generator units, and other plant equipment and, as required, communicate with this equipment directly or via interface with other SCADA systems (see graphic).

Across the Sotavento sites, disparate machinery, systems, and instrumentation from vendors such as Hydrogenics, Emerson, and Bauer Compressors are all linked to the Opto 22 controllers, which communicate to each subsystem or machine using the same protocol originally specified by the manufacturer. Specifically, these protocols include Profibus, for control and acquisition of production data from the electrolyzer units, and Modbus for control and acquisition of production data from the compressors. There is also an RS-232 serial link to the motor-generator units for taking analog measurements and digital readings. The Snap PAC controllers aggregate all data and serve it to a Sotavento database that’s accessible to select personnel via a secure Internet connection.

An outline of the various controllers, protocols, analog measurements, and digital I/O connected using Snap PAC across the Sotavento units.
An outline of the various controllers, protocols, analog measurements, and digital I/O connected using Snap PAC across the Sotavento units.

Protocols and integrator expertise

“The secret to successful implementation of projects like this rests in defining the protocols at the hardware purchase stage, well before writing the first line of code,” said Fabio Alberini, one of Optomation Systems’ project managers on the Sotavento project. “If the customer fully understands and insists on the importance of data integration, suppliers will be obliged to include the necessary hardware interfaces and software support as part of their deliverables. Conversely, trying to design the communication links after the equipment is chosen and installed is more difficult, costly, and beyond the core competencies of the supplier.”

Alberini advises control system purchasers to “understand what communications options are possible and always try to standardize on protocols.” He maintains that there is still no better standard than Modbus for moving data between industrial devices. “It requires no special hardware or software interfaces,” he says, “and it’s royalty free and easy to implement. At the Ethernet level, Modbus/TCP is an even better alternative.”

When hiring a system integrator, Alberini recommends ensuring that they have experience writing software for the hardware platform being used, as well as expertise integrating data.

Author Information
David Crump of Opto 22 can be reached at .

How the Sotavento virtual plant works

Electrolyzer units produce gaseous hydrogen and oxygen from water for two sets of compressors that pressurize the hydrogen before storage in an onsite tank farm. All electrical power for this particular process is supplied by wind-powered aero generators. The hydrogen is used to drive a motor generator that provides stability by “topping-up” (i.e., supplementing) the wind power production, which naturally varies with the weather. Combined, the hydrogen and wind provide a constant power level to the national electricity network.


Sotavento’s annual production of 38,500 MWh meets the domestic consumption of approximately 11,000 Spanish households and its use of clean wind and hydrogen, in place of fossil fuels, eliminates about 36,000 tons of carbon dioxide emissions into the atmosphere per year.



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Snap PAC explained

The Snap PAC (programmable automation controller) System from Opto 22 can be used not only for automation and control, but also data acquisition, enterprise connectivity, and communication to databases. The system family PACs come with a mix of two Ethernet interfaces and up to four serial ports for RS-232, RS-422, RS-485 serial communication, plus PPP modem connections.


As highlighted in this case study at Sotavento, the Snap PAC System provides connectivity via open, standard protocols and technologies, such as TCP/IP over Ethernet, SMTP (Simple Mail Transfer Protocol), SNMP (Simple Network Management Protocol), and FTP (File Transfer Protocol.)


The system is designed for interoperability and data integration through its support for numerous other communication protocols, such as Modbus and Modbus/TCP, which allow communication with serial and Ethernet devices from Schneider Electric; DF1 and Data Highway, which enables serial interfaces to Allen-Bradley hardware; Profibus, which supports communication to Siemens-brand equipment; and EtherNet/IP, which allows communication to Ethernet-based control systems from Rockwell/Allen-Bradley.


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