Increasing Resource Efficiency in PV Power Plants

In the “SeVen” research project, we are developing a sustainable concept for large PV power plants that aims to optimize electricity production costs and resource efficiency in the power plant by raising the system voltages to low medium voltage. The focus is on inverters and the corresponding components, integration options for additional renewable energy generators, and other components in the power plant such as cables and transformers.

Initial Situation

For the energy transition to be successful, significant renewable energy capacity must be added in Germany alone by 2045. In the field of photovoltaic systems alone, the planned expansion figures will require enormous resources, not only in Germany. Achieving these goals will require very large quantities of valuable resources such as aluminum, copper, and steel. The resulting demand will lead to shortages and thus to cost increases, so that the relative cost share of material-intensive components will increase significantly, leading to a change in the cost structure of PV power plants and the associated inverters. The “SeVen” project of the Fraunhofer Institute for Solar Energy Systems aims to make these components more efficient and cheaper through innovative medium-voltage technology.

Objective

In this project, active combiners and string inverters for large PV power plants (>5 MW) will be used to develop a comprehensive concept in detail and verify it on a laboratory scale, which will result in significant resource and cost savings compared to the current state of the art. The focus is on inverters and other balance-of-system (BOS) components. To this end, a wide variety of system topologies and voltage levels in the power plant are varied and compared. After selecting the most suitable concept, a demonstrator of an inverter and an active combiner will be developed and built in accordance with the specifications, which will then be evaluated on a laboratory scale.

The conceptual approach includes the following project goals for reducing resource consumption in PV power plants:

• 20% savings in heat sinks
• 75% savings in cables
• Cost-efficient integration option in PV+X power plants
• Reduction in electricity generation costs (LCOE)
• Savings of 30% in copper and ferrite in winding materials
• Integration of additional analysis functions in combiners
• Savings in protective elements in the power plant

Approach

Current large-scale PV power plants use AC system voltages between 400 VAC and 880 VAC. However, the upper end of this range can only be achieved by devices with DC-DC converters, as without converters the AC output voltage is highly dependent on the current MPP voltage of the PV strings. By increasing the system voltage, the currents can be reduced. This can be utilised in two ways. Firstly, the cable cross-sections can be greatly reduced. This results in considerable savings in both material and installation costs for the cabling. At the same time, the performance of the subsystems can be increased. For the same power plant size, this results in a lower number of transformers and switchgear.

This is precisely where the planned project comes in. The aim is to optimise the entire system from solar strings to the grid connection, including consideration of all important components. This holistic approach requires a very good detailed knowledge of all components.

The “SeVen” project is funded by the Federal Ministry of Economic Affairs and Energy (BMWE).