German Chancellor Angela Merkel hosts the third federal energy summit in Berlin on Tuesday with a huge question mark hanging over the source of Germany's future energy supplies and the environmental impact of those sources currently available.

Merkel will discuss Germany's future energy needs and how best to conserve energy with business and political leaders from around the country.

However, while the summit is likely to address such issues as reducing CO2 output by 40 percent before 2020, the upgrading of renewable source technology such as solar, wind and biomass energy and the economic impact of the new technology, the main discussion is likely to be on the highly divisive topic of nuclear power.

Current German legislation requires all 17 of Germany's existing nuclear power plants to close by 2021 but, using the argument of nuclear power's ability to help reduce carbon-dioxide emissions, plant operators and center-right politicians have been calling for a reprieve.

However, safety issues surrounding nuclear power have weakened this position, especially after two nuclear power stations went offline last week. The transformer at the Krümmel Power Station, east of the port city of Hamburg, was destroyed by fire last Thursday, two hours after a short-circuit had knocked out another nuclear site at Brunsbüttel on the far side of the city.

While the Brunsbüttel power station was back in service the next day, the Krümmel station remained closed pending an investigation.

Calls for extended lifespan

Despite the incidents, a number of politicians from Merkel's Christian Democratic Union party (CDU) called on Monday for an extension to the nuclear power grid's lifespan.

Powerful Hessen State Premier Roland Koch, Merkel's second-in-command in the CDU, told ZDF television that the ruling coalition government could still decide on lengthening the lifespan of the power stations which, he claimed, would be the most inexpensive way of protecting Germany's energy supply and reducing CO2 output.

Both CDU energy expert Katherina Reiche and the Lower Saxony Prime Minister Christian Wulff agreed with Koch's views in separate statements.

When faced with the question of plant security, Koch suggested new power stations could take the place of older plants which are more susceptible to malfunctions over time.

"The coalition has a lot of freedom to make this decision," Koch added.

Social Democrats support decommission

Environment Minister Sigmar Gabriel of the Social Democrats (SPD), the CDU's coalition partner in the federal government, doesn't agree. Gabriel is against any extension of nuclear's lifespan and warned that any attempt to get more use out of aging power plants could be catastrophic.

"The longer a power station operates, the more susceptible it is to malfunctions," he said.

The gradual shutdown of all Germany's nuclear power plants was agreed upon in 2000 by the government of former Social Democratic Chancellor Gerhard Schröder and his coalition partners at the time, the Greens.

However, in the light of rising energy prices and Germany's dependency on foreign energy, mainly from Russia, Chancellor Merkel wants a broader energy mix.

Merkel believes Germany should continue to use the edge in nuclear technology it has acquired over the years and members of the CDU are pushing for the chancellor to take advantage of clauses in the "coalition contract" on the shutdown of nuclear power to extend its lifespan to reverse the decision.

Effective, yet vilified power source

Merkel is expected to temper the unease over a potential u-turn on nuclear power at the energy summit of Tuesday by advocating a 30 percent increase in renewable energy use which would reduce CO2 output by 41 percent.

However, a reprieve for nuclear power would lead to a 45 percent reduction of carbon dioxide emissions which would make it the most attractive of the scenarios to reach the desired reduction in CO2 output by 2020.