As chancellor mulls Germany's nuclear future, energy firms say solar and wind power may not make up shortfall in winter

Germany could face widespread winter blackouts following Angela Merkel's "knee-jerk" decision to decommission the country's nuclear power stations, according to German power grid operators.

The warning from four energy providers came after the German chancellor suggested she agreed with a proposal to shut down all of Germany's 17 nuclear power plants by 2022.

Seven nuclear power stations have been off-grid ever since Merkel announced in the immediate aftermath of the Fukushima disaster a "three-month moratorium" on her controversial decision last year to extend the lives of the plants.

Merkel ordered safety checks on all reactors and set up two commissions – one on safety and another on ethics – to look at whether Germany had a nuclear future.

The resultant safety report will be evaluated by the German government, along with a separate report by an ethics commission due on May 28, before it makes a final decision on nuclear power.

But over the weekend, Merkel said the year 2022 was "the right space of time" to set as a goal for Germany's total withdrawal from nuclear power. She was speaking after the CSU – the Bavarian sister party of her Christian Democratic CDU – voted for all German nuclear power plants to come off-grid by 2022. Merkel did not herself commit to a firm date for nuclear decommissioning.

The timetable is too slow for many of Merkel's opponents. Claudia Roth, co-head of the national Green party, which beat the chancellor's CDU in elections in Bremen on Sunday, insists it would be feasible to close down all plants by 2017.

According to a report in Monday's Süddeutsche Zeitung, four firms which operate Germany's network of high-voltage power cables and pylons - 50Hertz, Tennet, EnBW Transportnetze and Amprion – believe Germany cannot currently cope without nuclear power. The companies say that the grid is already "largely exhausted" during winter months when solar power is at a minimum and when wind cannot be relied on to keep turbines in motion.

The firms warned in a statement that calm winter days with no wind could result in "large-scale supply disruptions", particularly in Germany's affluent and industry-heavy south, which guzzles much of the country's electricity. "A safe supply to customers in these cases could be severely compromised," they said.

There are no current problems because good weather in Germany has meant that solar panels have been able to compensate for the shortfall left by the decommissioned nuclear plants.

The industry group German Atomic Forum cautioned against abandoning nuclear power without careful consideration.

"A quick and rash exit from German nuclear power would raise costs for the whole economy, make us miss climate goals, raise our reliance on fossil fuels and make our power supply less secure, meaning more power imports and problems with network stability," said president Ralf Gueldner. "It would also spark intense debate in the European Union," he added.

Nuclear power has long been unpopular in Germany and Merkel's decision last year to extend the life of nuclear plants was a major factor in her party's loss of power after 60 years in Baden-Württemberg – a prosperous conservative state – in March. Her about-turn on nuclear policy was derided as "knee-jerk" by many of her critics.

Currently, nuclear energy supplies 22.3% of Germany's electricity while coal provides 42%, natural gas 13.6% and renewable energies 16.5%, according to the environment ministry.