U.S. energy officials are reassessing the risk posed by Chinese-made devices that play a critical role in renewable energy infrastructure after unexplained communication equipment was found inside some of them, two people familiar with the matter said.

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.

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