The production of renewable energies in Germany is expected to grow faster than the government's forecast and account for almost half of the country's electricity within a decade, a top official said Monday.

The current boom in new installations of wind, solar and other renewable power sources will easily top the official target of 35 percent by 2022, reaching about 48 percent by then, said Stephan Kohler, who heads the government-affiliated agency overseeing Germany's electricity grid.

"I think this is a realistic dimension," Kohler said. "By then we can manage to integrate it in our electricity grid."

He cautioned, however, that his Federal Network Agency's assessment shows that more and swifter investment is needed to upgrade the electricity grid to cope with the influx of unstable and geographically dispersed renewable energies.

One of Germany's challenges in ensuring a steady supply of electricity to the world's fourth-largest economy is that it derives most of its wind power from the country's north, but demand is highest in the strongly industrialized south.

To cope with that challenge, the agency estimates that Germany needs to build another 5,000 kilometers (3,100 miles) of high voltage lines — at an estimated cost of some €20 billion ($26 billion).

Germany decided after Japan's 2011 nuclear disaster to speed up phasing out nuclear power, which then accounted for just under a quarter of the country's electricity production, about the same share as in Japan and the U.S.

Renewable energies' share has since risen from 17 percent to 25 percent, driven by subsidies and investment incentives that are mostly paid for by a tax on households' electricity bills. By 2050 Germany, Europe's biggest economy, wants to generate 80 percent of its electricity from renewable sources.

"Never has an industrialized nation tried to transform its electricity production in such a radical manner as we are currently doing it," Kohler said.

German Environment Minister Peter Altmaier recently hinted that the government could revise its target for the renewable energy expansion by 2022 from 35 to 40 percent.

Kohler, who estimated output would reach almost 50 percent by 2022, noted that figure could be even higher.

"Given the current renewable energy expansion plans by Germany's states, if all of them were implemented, we would reach a level of 63 to 64 percent by about 2025. In our opinion, that is not sustainable," Kohler said at a briefing with foreign journalists in Berlin.

Even to meet the 50 percent target, Kohler stressed that Germany needs to build more conventional power plants — for example, gas-fired plants — over the next decade to ensure backups are in place to provide a steady stream of power when the wind doesn't blow or the sun doesn't shine.

He said he was confident there would be no major problems with the grid's stability over the next three years, but added there is a risk of blackouts in southern Germany once another nuclear power plant will be shut there in 2015 because grid changes will just be under way and the region lacks the conventional power plants needed as backups.

To address that shortfall, he urged Chancellor Angela Merkel's government to do more to coordinate energy policy with other EU countries because electricity is traded freely across borders.

"Until 2015 we have the situation under control, but by then we must have a solution for the problem in southern Germany, also in cooperation with the neighboring countries Austria and Switzerland," he said.


Juergen Baetz can be reached on Twitter at http://www.twitter.com/jbaetz