Smart Grid - energy distribution and network control

Supply network security through isolated network operation and intelligent network management

Local isolated networks - feasibility study
In regions with a particularly high amount of renewable energy, some distribution grids are already approaching their capacity limits. Without intelligent management of the distribution grids, the supply from a variety of decentralised photovoltaic systems alone can already lead to severe grid overloads and partial shutdowns. On the other hand, a variety of decentralised generation can also open up the possibility to operate isolated off-grids. Intelligent automation and control technologies in conjunction with grid control, protection and telecontrol technology can solve these two points – increasing the supply grid security through isolated off-grid operation and intelligent network management determined through a decentralised feed – together in a practical manner.

An example of these challenges is the power grid region of Ritten near Bolzano in South Tyrol. It has about 2,500 inhabitants and a considerable number of commercial and industrial companies. Commissioned by Sprecher Automation Deutschland GmbH, Fraunhofer AST prepared a feasibility study of the isolated off-grid-system in Ritten for Etschwerke Netz AG, the largest regional provider in South Tyrol. The purpose of this feasibility study was to test the possibility of operating the existing medium- and low-voltage grid in the Ritten grid along with 20 local grid stations as an autonomous island in the event of a blackout. In the grid for the Ritten isolated off-grid project, there are basically two relevant production units: a district heating plant with electricity that is produced through an ORC process, and two combined heat and power units that are powered with rapeseed oil. Furthermore, there is an emergency generator available at the site of the district heating plant.

In addition to these larger production units, there are many photovoltaic systems connected to the grid. The performance of the photovoltaic systems ranges from a few kWp to several hundred kWp. With approximately 2 MWp, the power output of all of the installed photovoltaic systems reaches far beyond 50% of the maximum grid load in the investigated grid area; it is continuing a strong upward trend. In addition to modelling and simulating the isolated off-grid structure, extensive investigations into the protection, control and automation concepts were developed. The control concept involves both the uninterrupted transfer of operative powers to the isolated off-grid from the parallel grid operation as well as the black start construction of the isolated off-grid after a power failure.

The results show that during the summer months and the transition period, an isolated off-grid operation throughout the entire Ritten region is technically feasible. The foundations for the stability and frequency of the isolated off-grid are biomass power plants as well as a stationary emergency generator. Combined with energy storage, photovoltaics can also contribute to grid stability.

contact details/company:
Fraunhofer Application Center System Technology AST
Am Vogelherd 50
98693 Ilmenau

contact person:
Martin Käßler
R&D Marketing
+49 3677 461-128