To achieve the PV expansion targets, huge quantities of valuable resources such as aluminum, copper, and steel are required. The resulting demand will lead to shortages and thus increase costs, which will especially impact the relative cost share of material-intensive components. While the prices for PV modules have fallen by about 80 percent over the past 10 years, balance of system costs (e.g., inverters, cabling, AC and DC distribution boxes, grid connection) are playing an increasingly important role in the overall costs and profitability of PV power plants. In order to achieve further cost reductions and resource savings in PV power plants, the focus must be placed on balance-of-system components. "This is exactly where the project comes in. Our objective is to develop a holistic and sustainable concept for large PV power plants that optimizes electricity production costs and increases resource efficiency. We consider the entire system, from the PV module string to the grid connection, including all key components," explains Andreas Hensel, group manager Power Electronics and System Technology at Fraunhofer ISE.

Savings in large PV power plants

The “SeVen” project is evaluating a holistic concept for PV power plants larger than five megawatts in the multi-megawatt laboratory at Fraunhofer ISE. Combiner boxes and other system components are being tested in the medium voltage range.

Current large-scale PV power plants use AC system voltages between 400 V and 880 V. By increasing the system voltage to medium voltage (> 1000 V), the currents can be reduced, which has two positive effects: On the one hand, the cable cross-sections can be greatly reduced, resulting in considerable savings in both material and installation costs for the cabling. On the other hand, the performance of the subsystems can be increased. For the same power plant size, this results in a smaller number of transformers and switchgear.

The project will develop and compare different system topologies and voltage levels in the power plant. Based on the most suitable concept, the researchers will then develop a demonstrator inverter and a string combiner, which will subsequently be evaluated in the laboratory. The specific project goals consist of material savings of 20 percent in heat sinks, 75 percent in cables, and 30 percent in copper and ferrite in winding materials.

In addition, potential savings in protective elements in the power plant are being considered. Together these measures should lead to a reduction in electricity production costs. Cost-efficient DC-side integration options in PV hybrid power plants and the integration of additional analysis functions in the string combiner are also being researched in the project.

KACO New Energy GmbH and SUMIDA Components & Modules GmbH are partners in the project, which will run until 2028, along with associated partners Streamergy GmbH and BayWa r.e. Solar Projects GmbH.