Storage Systems Balance out Solar Power

As part of the Smart Grid Solar project, the Bavarian Center for Applied Energy Research is testing how storage devices can help equip local networks for the increased supply of solar electricity. Controllers from WAGO ensure secure communication between individual systems and the control center.

The integration of current from fluctuating sources into the low-voltage networks is one of the greatest challenges of the energy transition. The Bavarian Centre for Applied Energy Research (ZAE Bayern), together with partners from science and industry, has initiated a field test in the small city of Arzberg in Upper Franconia that should provide some solutions. “How is it possible to link a large number of PV arrays into the local network without costly expansion of the latter? How will it be possible to operate the local networks securely and efficiently in the future, when even more renewable energy systems are supplying the power?” These are two of the questions behind the project, according to Project Leader Philipp Luchscheider from ZAE Bayern.

To get answers, the researchers established a smart grid test center in the Schlottenhof district of Arzberg. In addition to PV modules with a total peak output of approximately 50 kilowatts, the facility includes three redox-flow batteries as short-term buffers, as well as an electrolysis system with a hydrogen tank and fuel cell for long-term storage. A drop cable connects the test field to the local network in Schlottenhof. The location offers the best conditions for the project, because many households operate solar arrays, and some are equipped with residential storage units. The test will conclude at the end of the year.

“To balance fluctuating generation and smooth out supply peaks, short- and long-term storage devices must cooperate intelligently. This includes taking weather predictions and expected consumption into account,” explains Luchscheider. These tasks are performed at the control level using a powerful server; the control center itself is located in a prefabricated office at the edge of the test center. The computer generates instructions, with the aid of simulations and mathematical models, which it then transmits to storage devices as signals.

What does such control actually look like? For example, on a sunny day, the residential battery storage units begin charging somewhat later in the day instead of the early morning. This ensures that they still have free capacity when the solar arrays reach maximum production. The owners of the storage devices don’t see any change – the batteries are still charged when they need electricity in the evening. The server calculates the optimum time for energy intake based on the network and system data, as well as the weather and load predictions.

“The quality and availability of the data are of enormous importance for the success of our field test,” emphasizes Luchscheider. This was the reason why ZAE organized communication between the individual components and the control center using a WAGO PFC200 Controller. “The WAGO product is extremely reliable. We have never had a problem,” explains Luchscheider. In addition, the controller guarantees that the researchers have a maximum level of flexibility for configuring their field tests. “Due to the many different inputs, WAGO’s solution allows us to connect the individual systems and aggregates without limitations,” explains the project leader. WAGO’s 3-Phase Power Measurement Modules are used to measure voltage, current and phase angle. Data is exchanged via the Internet using GSM and DSL. “There are very few manufacturers that offer all of this,” says Luchscheider.

The researchers also benefited from the PFC200’s flexibility when it came to programming. “WAGO’s controllers are able to process data using our preferred programming language: R. This is important to us, because we can use the same code to develop our models and for the controllers. This saves time and prevents errors during porting.” Data transfer between controllers and servers uses the MQTT protocol, “which is very efficient and offers additional advantages during configuration,” says Luchscheider.

The openness guaranteed by WAGO’s components and the control platform gives researchers the opportunity to develop additional scenarios and to test new algorithms. “For this, we are going to need new hardware that we can test in industrial situations or projects and integrate into the system,” explains Luchscheider. The test center, which ZAE will continue to operate into the future, will also have space for additional new technologies that need to be prepared for the smart grid.

Some of the controllers are mounted directly on the solar arrays, so that the scientists can test the supply behavior of different modules and devices in different weather conditions. With only scant protection from the modules, these controllers are exposed to wind, rain, snow, frost and heat. The technology experienced no problems. “We have not lost a single measured value since the project began. The controllers are definitely suited for outdoor use,” says Luchscheider with satisfaction.

As is the case in many other rural towns, communities and villages, Schlottenhof also produces a large portion of the power it consumes – thus, the ability to provide PV current in a targeted way has enormous potential for the future. ZAE Bayern and its partners in the research project are contributing to a vision of a climate-friendly, decentralized energy supply in Schlottenhof and elsewhere, without the need for an expensive expansion of the local network.

Text: Heiko Tautor, WAGO

Photo: Kurt Fuchs, ZAE Bayern; Ralph Diermann