The group said adjusted core earnings (EBITDA) at its renewables unit would develop in a range of -10 to +5 per cent, down from previously expected profit growth of 10-20 per cent.
"A cause of concern for us this year in particular ... is something we cannot influence: the weather," finance chief Thomas Kusterer said.
"Currently, low river levels and weak wind conditions are having a negative impact on our business."