Hybrid Power Plants

Medium Voltage – Hybrid Power Plants
© Fraunhofer ISE

Higher system voltages enable completely new system architectures for renewable hybrid power plants, whose individual components are linked together in a resource-efficient manner via the medium voltage. This allows system approaches for hybrid power plants and the integration of decentralized energy provision to be rethought and enables more resilient power supplies for districts, charging infrastructure or industrial operations with reduced dependence on the traditional power grid. 

PV Battery

The expansion of large stationary battery storage systems has an enormous potential, particularly in combination with photovoltaic power plants. In a PV-battery plant, electricity can be fed into the interconnected grids when in demand and thus in a yield-optimized manner. Also, large-scale storage facilities can be set up at former fossil-fuel or other conventional power plant sites so as to make use of the existing grid connections. Such large-scale storage facilities will play an important role in the resilience of the electricity supply of the future.

In the short study "Battery storage at former power plant sites", Fraunhofer ISE examined the systemic and grid-related benefits of large-scale storage systems. One of the results: Installing battery storage systems at former fossil fuel or nuclear power plant sites makes sense, as the connected load already available there can be used. This could cover up to 65 percent of the storage requirements needed in Germany by 2030.

PV Mobility (Rail)

The current rail traction network extends over 8,000 kilometers with its own power lines. These cover almost all of Germany and are operated at a specific frequency of 16.7 Hertz. The areas next to the tracks offer enormous potential for PV installations. However, a cost-efficient system technology to technically exploit this potential away from the usual 50 Hz feed-in points is currently lacking, although it is principally possible.

PV Battery Charging Infrastructure (Charging Hubs)

With the CO2 reduction target and the planned end to new registrations of combustion engines in public transport as of 2035, the transition to electric vehicles will be accelerated. While intensive research is being carried out on vehicles and charging systems, little attention is paid to the connection between the charging station and the public grid and to the required provision of power. This presents both challenges and opportunities for high-power electronic systems. Currently, cars are able to be fast charged with up to 850 VDC / 350 kW. In future, however, trucks will be able to be charged with up to 1250 VDC / 3 kADC in accordance with the MCS standard.

The study "Einfach Laden an Rastanlagen" (Easy Charging at Service Areas) by the German National Center for Charging Infrastructure deals with the power requirements of electric charging stations. The study takes into account different vehicle classes, traffic junctions, simultaneity factors and power prioritization and also assumes 50% electrified truck traffic by 2035. The study found that fast-charging systems with capacities ranging from 8 MVA (previously unmanaged, simple parking lots along the highway with seating) to 26 MVA (large rest and car stations at international junctions and highway sections with high traffic volumes) will be required in the future.  The requirement for a charging facility for trucks and cars at least every 50 km along Germany's freeways, which cover a total of around 13,200 kilometers, translates to a total installed charging capacity in the high double-digit gigawatt range. This estimate does not include large electric charging stations in urban areas and charging stations at trucking companies. For large truck stops with up to 150 parking spaces, the charging capacities at night can add up to 5-7 MVA, depending on the assumed simultaneity factor.

To relieve the load on the grids, a combination of storage and renewable generation directly on site is a promising solution. Parking lot roofs offer a large PV potential here. However, the connected load must also be distributed on site and routed to the individual charging points. To achieve a high level of efficiency and limit the use of materials, the move to medium voltage offers a sensible approach. As PV, storage and charging technology are DC-based, an MV-DC bus system would probably be the most efficient solution in the future.

R&D Services

Our R&D services for component, plant and system manufacturers, energy suppliers, transmission system operators, power plant operators, project developers, plant planners, power plant designers and system integrators cover the entire value chain of medium-voltage applications: from research and development, characterization and testing of components and systems to the design of an entire hybrid power plant:

Energy Provision

  • Development of highly efficient PV modules and associated tests for type approval
  • Module analysis, damage assessment and reliability tests
  • Potential analyses and feasibility studies for PV power plants
  • Development and expert consultations on efficient medium-voltage power converters

Energy Storage

  • Development of high-power converters and reliable battery systems
  • Concept studies and operating strategies for technical integration and grid stability
  • Development and evaluation of hydrogen infrastructures
  • Error analysis and troubleshooting in the lab and on the field

Energy Distribution

  • Development and studies on high-power converters
  • Network simulation and system modeling according to guidelines
  • Analysis and optimization of protection systems
  • Error analyses and tests in the laboratory and field

Energy Utilization

  • Development of high-power converters and heat pump systems
  • Consulting and concept studies for power electronic systems
  • Development of climate-friendly refrigerants for heat pumps
  • System analysis and optimization of heat pump systems

Our R&D Infrastructure on this Topic


R&D Infrastructure

Center for Power Electronics and Sustainable Grids

  • Independent connection to the high-voltage grid
  • Power electronics in the multi-megawatt range in low and medium voltage
  • Highly dynamic 1 MVA grid simulator 
  • The Power Converters Lab, Digital Grid Lab, Multi-Megawatt Lab and Medium Voltage Lab provide unique opportunities for research and development in the field of power electronics and dynamic grid control.

Accredited Lab

TestLab Power Electronics

Testing and characterization of power converters up to the multi-megawatt range.


Medium Voltage Lab


Center for Electrical Energy Storage

Novel materials and innovative production processes for battery systems technology


Center for Fuel Cells, Electrolysis and Synthetic Fuel

Characterization of components for hydrogen technology


Digital Grid Lab

with intelligent, fully integrated charging infrastructure for electric vehicles.


Center for Heating and Cooling Technologies

Examination and characterization of equipment and components for use in building services engineering


TestLab Heat Pumps and Chillers

State of the art technology for developing, measuring and characterizing heat pumps and chillers, as well as their components



TestLab PV Modules

Measurements and tests for the design qualification and type approval of PV modules


Outdoor Performance Lab

Precise Evaluation of PV Modules

Selected Research Projects



Medium-voltage Converter with High-voltage SiC Power Modules for Large-scale Storages and System-serving Distribution Grids



Bidirectional Medium-voltage Converter with High-voltage SiC Devices for Increased Integration of Renewable Energies and Inner-city Storage in Innovative Grid Structures



Components and Systems for HVDC Transmission from Generators and Storages to Suppliers in the European-North African Electrical Network



Hydrogen production at sea by PEM water electrolysis

Further Information on this Research Topic


Materials, Cells and Modules


Solar Power Plants and Integrated Photovoltaics


Power Electronics and Grids


Electrical Energy​ Storage


Climate-Neutral​ Heat and Buildings


Hydrogen​ Technologies​