One of the institute's top economists Kai Carstensen told the Bild newspaper that the economy would have grown by an estimated 0.2 percent more than it did, had the government not decided to shut down seven nuclear reactors earlier in the year.
Germany's Gross Domestic Product grew by only 0.1 percent between April and June compared to the first quarter of the year.
"The mini-growth is not stagnation, but caused by turning off the nuclear power stations," he said.
The German government declared a three-month moratorium on nuclear power following the disaster in Fukushima, Japan, where a nuclear power station suffered a massive radiation leakage following an earthquake and tsunami. The decision led to a 50-percent reduction in energy output in Germany.
The government subsequently decided to close seven nuclear reactors permanently, and the rest by 2022.