At first glance, the district of Niederbobritzsch, Germany is a community like thousands of others: a church, farms, businesses, a small factory, a few supermarkets and about 800 households. If you look closely, however, you will also find a gray container. This is the visible sign that the future is being written in Niederbobritzsch, near the Saxon city of Freiberg, where electricity supplier MITNETZ STROM and Reinhausen, together with two universities, are researching how to successfully implement the energy revolution.
“The energy revolution is taking place primarily in distribution grids. That is why we need research.”Jens Schwedler, Project Manager at MITNETZ STROM
To manage this, tremendous quantities of additional electrical energy will have to be transported through grids in the future. In particular, the decarbonization of the heating and transportation sectors will strain the grids in the years and decades to come (see ONLOAD 07). Grid operators are looking for new solutions to expand the grids. At Reinhausen, Stephan Rupp and Dirk Wüstenberg are working intensely on the topic. “We’re looking for new answers to the question of how grids will be able to absorb the growing amounts of energy and how, at the same time, to close the gap between generation and demand that results from the increasing volatility,” says Business Developer Rupp.
Smart distribution grids
Over the course of the energy revolution, solar electricity will have to be greatly expanded in the future. A majority of systems can be found on roofs and facades, meaning that they are in local grids. Directing this solar current through distribution grids to transportation grids is not a useful solution. The grid expansion would be extremely costly and it would be hard to find customers for the oversupply of solar current around noontime. By the same token, in the evening hours, large quantities of electricity must be drawn from the grid as the demand grows on the consumer side due to charging stations for electric vehicles and electrically powered heat pumps.
The solution might be to make the distribution grids more flexible, which means the option to store solar current near the source, i.e. in local grids. Another option for ensuring flexibility is to adjust the demand for electricity to the supply with the help of intelligent load control. And solutions that also offer autonomous operation of distribution grids in the event of a malfunction would be able to increase the supply reliability.
Jens Schwedler, who works as a project manager on the local grids of the future at distribution grid operator MITNETZ STROM in central Germany, says, “Around 55,000 systems for renewable energy are connected to our distribution grids.” Therefore, for Schwedler, it is obvious: “In addition to offshore applications, the energy revolution is taking place primarily in distribution grids. In order to maintain the power quality in the future with the increasing volatility of supply and demand, there is an urgent need for action and research today!”
Intelligent control balances the supply and demand. If more electricity is generated in the distribution grid than is needed, the surplus is stored, heat pumps are started up, and electric vehicles are charged.
GRIDCON® Power Conversion System
Reinhausen implements its energy storage solutions with this modular inverter/converter system for DC and AC supply in the low-voltage range. The system ensures the power quality and supports a broad range of field-tested applications, such as
the provision of a replacement grid. It can be configured and enhanced based on customer needs.
Decoupled local grids
For cost reasons, fully expanding the grids and laying them out with new cables and new transformers for load or generation peaks is not a viable approach. “It takes more intelligent solutions to get the volatility under control than just building up expensive overcapacity,” says Schwedler’s colleague Jan Schönfeld. In order to research exactly these solutions, MITNETZ STROM began a research project two years ago. Since then, Schwedler and Schönfeld have worked together with Mittweida University of Applied Sciences, TU Dresden and Reinhausen as technology partners. As part of the project, sponsored by the German Federal Ministry for Economic Affairs and Energy, they research the advantages of decoupling local grids.
“It takes more intelligent solutions than just building up overcapacity.” Jan Schönfeld, Project member, MITNETZ STROM
The project has the somewhat clunky name “Flexibilisierung des Netzbetriebs durch entkoppelte Ortsnetze” (English: Flexibilization of Grid Operation through Decoupled Local Grids), which is shortened to “FlexNet-EkO.” It focuses on the transition from medium-voltage to low-voltage grids. In order to test this future solution in a field test, MITNETZ STROM chose the community of Niederbobritzsch. It is like thousands of others in Germany and elsewhere in the world. There is also an increasing number of solar panels on roofs here. Particularly in the summer, the momentary production power exceeds energy consumption. “Here, we have the phenomenon of load flow reversal, and the remaining renewable energy does not appear when the residents actually need the electricity,” says Schönfeld.
Making grid operation more flexible through decoupled local grids
One of the current big questions is how to best coordinate flexible consumers and generators in a local grid, while at the same time ensuring optimal power quality, relieving the burden on existing equipment and guaranteeing or even increasing the security of supply.
It is exactly this question that MITNETZ STROM, Mittweida University of Applied Sciences, TU Dresden, and Reinhausen are tackling as part of a research project sponsored by the German Federal Ministry for Economic Affairs and Energy.
FlexNet-EkO has the following goals:
- Highly reliable supply of the local grid with a high power quality
- Testing the new grid coupling equipment in the grid
- Testing the actuation of decentralized consumers and producers using frequency modulation
- Developing the planning and operating criteria for modular grids
The four partners have now been working together on the idea for more than two years and implemented it in a field test in October 2021: How can a modular distribution grid be set up with a power-electronic grid coupling? Furthermore, can the production-side and consumer-side peaks be buffered using battery storage units in order to bring demand and supply into harmony within the distribution grid, and reduce repercussions on the upstream medium-voltage level?
“A grid-forming inverter would act like a diesel generator or a small power plant.” Stephan Rupp, Business Developer, Reinhausen
To find the answers to these questions, Reinhausen contributed its expertise in storage technology and power quality management to the project. “The decoupling of a local grid with Reinhausen technology offers us a whole range of possible advantages as a grid operator. What we discovered, first in theory and then under laboratory conditions, has now been tested in a local grid with 200 households under real-world conditions for the first time,” says project member Schönfeld.
Semiconductors stabilize load flows
In the trial grid in Niederbobritzsch, a battery storage unit from Reinhausen is now in use that stores the excess renewable energy. The project also focuses on the stabilization and harmonization of load flows within distribution grids. For this purpose, Reinhausen also placed a power-electronic grid coupling with a grid-forming inverter in the gray container, in addition to the batteries.
This Reinhausen technology is already stabilizing load flows within the distribution grid under real-world conditions. “Now, our task is to gain experience with this new equipment and see whether reality matches our simulation results,” explains grid expert Schwedler, adding, “The theory suggests that interference coming from the medium-voltage level will be filtered out, providing a clean voltage range. We’re now testing what power quality can actually be reached with an inverter and deriving planning and operating criteria from this information.”
„“Our control technology is also making the grid more intelligent.” Dirk Wüstenberg, Project Manager, Reinhausen
Another aspect is that the technology is also intended to make the grid as a whole more intelligent. MITNETZ technician Schönfeld says, “We can balance the supply and demand using intelligent control. We consume the electricity we produce locally, thus relieving the burden on the upstream medium-voltage grid. To do so, the control system of the inverter communicates directly with the control boxes installed in the customer systems with signals in the range of 10 MHz over the power grid. This means that, when a lot of electricity is generated, electric vehicles are charged, heat pumps are started up, and the battery in the container is charged. If more energy is required later than what is being produced, it is available.” It sounds like a real win-win situation for grid operators and customers.
The semiconductor technology required for this, however, introduces the next challenge: the short-circuit capacity. Schwedler says, “In order to provide sufficient short-circuit capacity with semiconductor technology, we designed the power of the system to be twice as large as would actually be needed. We played it safe and wanted to avoid negative effects for our customers during the field test at all costs.” His colleague Schönfeld adds, “This first step was about testing the technology under real-world conditions. As a result, economic considerations were not yet a high priority. We can use the findings to later dimension the power actually required. These are also needed later to be able to compare the different technological alternatives with each other.”
Reinhausen specialist Wüstenberg is optimistic, saying, “With our control technology, we are also making the grid more intelligent. If we network producers, consumers, and battery storage units within a distribution grid with each other using control technology, this alone produces compelling advantages.” Reinhausen strategist Rupp is thinking one step further, saying, “If the grid-forming battery storage units prove their worth in distribution grids, this would make it possible to relieve the burden on higher-level grids, since solar power from the local grid can be stored and consumed in the distribution grid. This also secures higher supply reliability since the grid-forming inverters can supply the grid exactly like a diesel generator or small power plant.” Currently, it seems that this is so.
Do you have questions about the project?
Dirk Wüstenberg is available for you: