On 6 November 2026, the consortium RegioNet WasserBoden in Groitzsch presented findings from twelve studies on the management of Saxony’s former open-cast mining lakes . The key finding is that former lignite mines could be not only restored to nature but also used as sites for renewable energy technology and as seasonal heat storage facilities The researchers also stressed that the ecological impacts and integration into existing networks need to be examined systematically in further work.
The studies identify three priority options. First, floating photovoltaicmodules on large bodies of water, which benefit from relatively stable temperatures and the availability of open space. Second, using lake water and shoreline infrastructure for large-scale heat pumps, for example to feed into district heating systems. Third, pit thermal energy storage (PTES), which could store surplus heat for months and make it available in winter. Combining these approaches is described as technically feasible in principle; economic viability, permits and local acceptance are considered the main hurdles.
In parallel, the GFZ Helmholtz Centre for Geosciences Potsdam is working on the EU project TRIDENT to scale up PTES technology in former mining areas. In a statement dated 5 November 2026, GFZ announced that it would test the storage technology with partners from Germany, Poland and France. The aim is to demonstrate seasonal heat storage in flooded open-cast mining pits and connect it to local networks. The projects are considered pilot schemes; reliable data on performance and costs are expected to follow from field tests.
Practical and legal frameworks remain unresolved. State mining remediation bodies and operators such as the Lusatian and Central German Mining Administration Company (LMBV) point to questions concerning water quality, shoreline stability and connections to existing energy and heating networks. Examples such as the Rhine water transfer pipeline show that water management and the filling of large lakes require long-term planning and permitting processes.
Ecological risks are the subject of ongoing research. Potential effects on water quality and nutrient dynamics are being discussed, as are long-term processes such as renewed acidification caused by pyrite weathering. Funding programmes, including projects run by the German Federal Environmental Foundation, are investigating pH stabilisation and phosphorus retention. The findings presented in Groitzsch therefore provide a conceptual basis, while also setting out specific tasks for planning, permitting and monitoring. Whether, and to what extent, former mining lakes will make a significant contribution to regional heat and electricity supplies in the coming years depends on further pilot projects, robust environmental assessments and coordination between researchers, operators and authorities.
Editor: Mira Cadena (Article created with AI assistance).