Germany is taking steps to curb its booming windfarm sector in what it claims is a necessary move to stop the renewables revolution from undermining its own success.

Critics, however, say the step will deal a blow to the country’s reputation as a leader in green energy.

According to leaked plans from the German federal network agency, published on Tuesday in the Süddeutsche Zeitung, the government has had to halve its original target for expanding its windfarms in the gale-beaten northern flatlands because it cannot extend its power grid quickly enough to the energy-hungry south.

When Angela Merkel announced in May 2011 that Germany would seek to phase out its fleet of nuclear reactors by 2022, questions arose as to whether renewable sources of energy, such as wind or solar, could grow quickly enough to meet the requirements of German industry.

Yet five years later, windfarms in the northernmost states are producing so much energy that in some cases the state has to pay renewable energy companies to switch off their turbines to stop congesting the power grid.

In theory, the manufacturing sector in southern states like Bavaria or Baden-Württemberg would be supplied with green energy from the north. But plans for an ambitious north-south “energy highway” between Schleswig-Holstein and Bavaria have stalled, due in part to local protests against proposed “monster pylons”.

Revised plans for more costly underground cabling were signed off last October, but the project now runs approximately a year and a half behind its original schedule, leaving Germany’s energy infrastructure lop-sided.

In 2015, northern Germany produced 4,100 gigawatt hours in excess energy which couldn’t been transported to the south – enough, in theory, to supply 1.2 million households with energy for a year.

Protecting the national power grid from such imbalances is costly: in 2015, Germany paid €1bn, or £912m, towards system security measures, a cost which the federal network agency claims could rise to €4bn by 2022 if current trends continue.

Germany’s plans to phase out nuclear energy is creating diplomatic headaches, too. Cheap excess energy produced by German windfarms and coal power stations is often exported to neighbouring states such as Poland, the Czech Republic or Austria, where it plays havoc with local networks and impedes those countries from building up their own sustainable systems.

“Germany’s renewables revolution is making it harder to have a renewables revolution in Austria and other European countries,” Austria’s environment minister, Andrä Rupprechter, told Der Spiegel. “Germany produces too much cheap energy, which countries like Austria then have to absorb. With the current prices for energy, investing in hydro or wind energy without state support is no longer competitive.”

Some analysts argue that while Germany is right to address grid congestion, doing so by artificially slowing down the wind energy boom risks undermining the country’s credibility as a green leader. Since the start of the Energiewende, or energy transformation project, domestic demand for renewable energy has grown by about 3% per annum. Under revised proposals worked out by the government, the sector’s growth is expected slow to about 1%.

“A more forward-looking way to meet the current challenge would have been to shut down old power stations, extend the grid faster or invest more in innovative methods to use excess energy to heat homes,” said Arne Jungjohann, the author of Energy Democracy – Germany’s Energiewende to Renewables.

“On the international stage, Merkel enjoys a reputation as a green pioneer. But on the domestic stage she has been quick to give in to the lobbying of energy-greedy industry”.

While the German government admits that transforming its energy infrastructure is a more complex undertaking than originally thought, officials insist that it remains on track to meet ambitious goals, including a 50% share for renewables in gross electricity consumption by 2030.

• This article was amended on 13 October 2016 to correct a reference from gigawatts to gigawatt hours.