Utility giants clashed with German government officials in court over the country's controversial decision to ditch all of its nuclear plants by 2022.
E.ON, RWE and Vattenfall are seeking €19bn (£14.9bn) compensation for the closures, which scrapped one of their main sources of profit.
Johannes Teyssen, chief executive of larger peer E.ON, said they were seeking to be fairly compensated for the shutdowns, rather than an abandonment of the policy.
The German government, which sped up the nuclear shutdown and reversed an earlier agreement to extend the lifespan of some plants following Japan's Fukushima disaster, today defended the policy.
"The decision to end the use of nuclear power as soon as possible following the drastic events of Fukushima not only meets legal requirements, it was and continues to be the right decision," Barbara Hendricks, environment minister, said.
While the case is expected to conclude for several months, the two-day hearing will be watched for insight into the thinking of the judges' panel.