Power inverters, which are predominantly produced in China, are used throughout the world to connect solar panels and wind turbines to electricity grids. They are also found in batteries, heat pumps and electric vehicle chargers.

While inverters are built to allow remote access for updates and maintenance, the utility companies that use them typically install firewalls to prevent direct communication back to China.

However, rogue communication devices not listed in product documents have been found in some Chinese solar power inverters by U.S experts who strip down equipment hooked up to grids to check for security issues, the two people said.

Over the past nine months, undocumented communication devices, including cellular radios, have also been found in some batteries from multiple Chinese suppliers, one of them said.

Reuters was unable to determine how many solar power inverters and batteries they have looked at.

The rogue components provide additional, undocumented communication channels that could allow firewalls to be circumvented remotely, with potentially catastrophic consequences, the two people said.

Both declined to be named because they did not have permission to speak to the media.

"We know that China believes there is value in placing at least some elements of our core infrastructure at risk of destruction or disruption," said Mike Rogers, a former director of the U.S. National Security Agency. "I think that the Chinese are, in part, hoping that the widespread use of inverters limits the options that the West has to deal with the security issue."

A spokesperson for the Chinese embassy in Washington said: "We oppose the generalisation of the concept of national security, distorting and smearing China's infrastructure achievements."

Using the rogue communication devices to skirt firewalls and switch off inverters remotely, or change their settings, could destabilise power grids, damage energy infrastructure, and trigger widespread blackouts, experts said.

"That effectively means there is a built-in way to physically destroy the grid," one of the people said,

The two people declined to name the Chinese manufacturers of the inverters and batteries with extra communication devices, nor say how many they had found in total.

The existence of the rogue devices has not previously been reported. The U.S. government has not publicly acknowledged the discoveries.

Asked for comment, the U.S. Department of Energy (DOE) said it continually assesses risk associated with emerging technologies and that there were significant challenges with manufacturers disclosing and documenting functionalities.