Motivation and research question

The expansion of renewable energy in municipal distribution grids increasingly leads to bottlenecks
that limit further deployment. In the grid area of Stadtwerke Mürzzuschlag in Upper Styria, Austria,
the contractually defined maximum reverse power flow at the grid transfer point to the 110 kV
network of Energienetze Steiermark represents the central constraint. The proximity to the largest
wind farms in Styria (approx. 110 MW) and the growing deployment of photovoltaic systems
(currently around 15 MWp) exacerbate this situation. The project Speicher-Kaskade MZ therefore
investigates whether distributed battery storage systems, operated by different stakeholders
pursuing their own economic objectives, can be interconnected into a cascaded flexibility resource
and operated in a grid-supportive manner – without compromising the economic interests of the
storage operators.

Initial situation

Until now, compliance with the reverse power flow limit has been ensured exclusively by curtailing
generation facilities. Battery storage systems could serve as flexibility resources; however, under the applicable Austrian regulatory framework, grid operators are not permitted to operate their own
storage systems. At the same time, real-time grid monitoring at the medium and low voltage levels is largely absent, which hinders the targeted use of flexibilities.

Project contents and objectives

The project pursues four objectives: establishing the foundations for a flexibility system to enable
further PV expansion, testing a storage- and PV-based emergency power supply for critical
infrastructure using the wastewater treatment plant of Mürzverband in Langenwang as a case study,
developing and evaluating energy services for the economically viable operation of storage systems
within the cascade, and the dual use of storage systems as measurement infrastructure for grid
monitoring. The work was carried out by a consortium of five partners: 4ward Energy Research
GmbH (consortium lead), Stadtwerke Mürzzuschlag GmbH, Wasserverband Mürzverband, Venios
GmbH, and Stefan Voit (Smart 1).

Methodical procedure

For the field and pilot operation, an approach was chosen that combines real storage installations at
selected locations in Mürzzuschlag with a digital twin of the grid based on the Venios.NET platform.
The technical development comprised a multi-level communication architecture (MQTT,
Concentrator, smart1 API), a local energy management system with hierarchical control logic, a
storage simulator for reproducible scenario testing, and the overarching cascade control system.
Four energy services (PV electricity marketing, self-consumption optimisation, peak load reduction,
and emergency power supply) were tested in the field and evaluated regarding their suitability for
cascaded operation.

Results and conclusions

The trials confirm the functionality and grid-supportive value of the storage cascade. The hours of
exceedance of the maximum reverse power flow were reduced from 35 to 5 hours through cascaded
operation (approx. 86 %), and the amount of generation requiring curtailment from 117 MWh to 12
MWh (approx. 90 %). Three of the four energy services investigated are suitable for cascaded
operation. The cascade control does not significantly impair the economic objectives of storage
operators in most cases. Emergency power supply tests at the Mürzverband site demonstrated
supply durations ranging from 2 hours to over 10 days, depending on storage capacity, season, and
time of failure. The dual use of storage systems as measurement infrastructure was successfully
demonstrated; a reduction of dedicated measurement devices by up to 50 % is fundamentally
achievable. Scenario analyses show that a doubling of PV capacity in the grid area to approximately
30 MWp would be achievable without additional grid expansion measures, provided an appropriately
dimensioned cascade is deployed.

Outlook

The project results are not limited to Mürzzuschlag but are transferable to other municipal
distribution grid operators with comparable conditions. In Austria, around 50 municipal utilities and
similar entities face comparable challenges. The technology partners Venios and Smart 1 are
integrating the developed components into their commercial product portfolios, and Mürzverband is
already translating the findings into concrete investment measures. For further development, a
stepwise expansion of the pilot operation in Mürzzuschlag and a transfer to a second grid area is
recommended.

Project management

4ward Energy Research GmbH

Project or cooperation partners

• Stadtwerke Mürzzuschlag GmbH
• BlueSky Energy GmbH
• Wasserverband Mürzverband
• Venios GmbH

DI(FH) DI Martin Schloffer
Reininghausstraße 13A
A-8020 Graz
Tel.: +43 (664) 885 003 38
E-Mail: martin.schloffer@4wardenergy.at
Web: www.4wardenergy.at