Germany is debating granting its 17 nuclear power plants an extra 10 to 15 years of production time as it prepares to unveil a comprehensive energy strategy next month.

The decision is likely to become a hot issue for Chancellor Angela Merkel's government, which is already troubled by dwindling popular support and infighting. Nuclear energy has been unpopular for decades, and polls suggest most Germans want to stay with the current timeline of shutting down all nuclear power plants by 2021.

The government on Monday presented the results of a study on what would happen if it extended that timeframe, which was put into place by a previous government back in 2000.

Three think tanks used various scenarios to calculate what it would mean for the German economy — Europe's largest — if the plants were kept online for an additional 4 to 28 years beyond 2021.

The study suggests that "a low two-digit extension would have very positive effects in three fields — energy prices, security of supply and reducing carbon dioxide," Merkel spokesman Steffen Seibert told journalists.

"Judging purely from those facts, the study suggests an extension by 10 to 15 years," Seibert said.

However, the government will also take safety and legal issues into consideration before it decides how much longer to keep the nuclear plants online, he said. A decision is expected by Sept. 28, when the government is to present a national energy strategy for the next 40 years.

Merkel has said that the 2021 timeline needs to be extended so that Germany can have more leeway as it switches to renewable energies. But even within the government there still is a rift as to how many extra years the nuclear plants should be granted.

Economy Minister Rainer Bruederle said an extension of 12 to 20 years would be best, because it could save energy users several billion euros (dollars) and would help cut greenhouse gas emissions considerably.

In contrast, Environment Minister Norbert Roettgen said the new information showed that "longer production times have marginal effects at best."

For example, in the most optimistic scenario consumers would save only 1.8 euro-cents (2.3 US cents) per kilowatt hour over the next 40 years, Roettgen said, calling that effect negligible.

Still, Roettgen said longer use of nuclear energy is necessary to have enough time to fortify the power grid for more wind, solar, and biomass power and to develop ways to store those renewable energies.

Both ministers, who are to draft the long-term energy strategy jointly, did agree that the decision on nuclear energy is just one point of many.

They both said the key to a safe, environment-friendly, and affordable energy supply is efficiency.

According to the new expertise, Germany is to cut its total energy consumption in half by 2050. Electricity consumption is to go down by 25 to 28 percent.

The new energy strategy is to make sure that Germany can stick with its ambitious climate goals to cut greenhouse gas emissions to 40 percent below 1990 levels 2020 and to 80 percent by 2050.