The Dutch capital's tall, thin historic houses dating from the 16th to the 18th centuries are poorly insulated and energy hungry.

Solar panels are already allowed on roofs of protected buildings, so long as they cannot be seen from the street. But now the local council wants to relax the rules further in a bid to make the mansions more sustainable.

Starting in 2025, the Amsterdam council is allowing panels to be "visibly installed on all roofs of monuments and buildings located in protected areas".

But heritage activist Karel Loeff is up in arms at the change.

"Of course sustainability is very important," he told AFP in the Grachtengordel canal district, a UNESCO World Heritage site.

"But these solar panels are really ugly and they should not be allowed on roofs visible from the canal," the 55-year-old said.

"It would clearly blight the view of what you can see now, a beautiful original 18th-century gable."

- 'Chaos' -

With around one-third of its land below sea level, the Netherlands is particularly vulnerable to global warming, but is also one of Europe's biggest per capita emitters of CO2 emissions.

The country's goal of reducing CO2 emissions by 55 percent by 2030 compared to 1990 levels seems out of reach, according to official estimates.

The new coalition government, led by the far right, is expected to unveil its proposals early next year.

"We must contribute to sustainability in all areas," said Alexander Scholtes, Amsterdam's Green Party deputy mayor. This also applies to the city's 10,000 listed buildings, he told AFP.

It won't be the Wild West, he insisted, with rules about the colour of the panels and how they are placed.

High energy bills means many homeowners want to make their homes more sustainable, Scholtes added.

"We can achieve responsible sustainability with fewer rules and faster procedures, and still take into account this cultural heritage," he argued.

But Loeff is not convinced, predicting "chaos".

He said he was not against solar panels on homes, but only outside the historic centre.

- 'Without spoiling the view' -

Another heritage group, the Friends of Amsterdam City Center, said "installing solar panels in plain sight seriously damages the protected urban landscape."

The capital is not the only Dutch city relaxing solar panel rules. Rotterdam, Utrecht and others are following suit.

The changes come as the Netherlands Cultural Heritage Agency is pushing to make monuments more sustainable.

Authorities want protected buildings to reduce CO2 emissions by 40 percent by 2030 and 60 percent by 2040.

"There are approximately 120,000 monuments in the Netherlands, including some 60,000 national monuments, 30,000 homes, 10,000 farms and 5,500 castles, manors and parks," said climate change scientist Jan Rotmans.

"These monuments account for one percent of gas and 1.5 percent of electricity consumption in the Netherlands," he told AFP.

"So we're talking about significant quantities. Making these monuments more sustainable can lead to significant energy savings and CO2 reductions," he said.

Deputy mayor Scholtes, 42, believes all this can be done "without spoiling the view".

"Even with solar panels on our roofs, the canal belt will always be beautiful."