The report by the German institute for economic research, DIW, Vattenfall's Risky Business, points to economic and legal proof for the risks of the Swedish utility's vast lignite exploration in eastern Germany.

"Any potential buyer of Vattenfall's lignite unit needs to be aware of what entrepreneurial risks he would take over. Lignite exploration and power plants are ticking time bombs on any balance sheet," says Greenpeace energy expert Anike Peters.

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