Plug-in solar systems are drawing U.S. interest because they can cost a few hundred dollars to about $2,000, far below rooftop installations that can run up to $36,000.
No products now sold in the U.S. have UL 3700 certification, and safety experts say buyers should wait for that approval because it tests the full system against shock and circuit-overload risks.
10 states already allow the systems, which are lightweight and aimed at renters and homeowners who can often install them without professional help, though some states require electricians or special outlets.
Germany's wider adoption has helped spotlight the model, while U.S. users still need suitable outdoor sun exposure and may have to notify landlords or comply with lease rules before installing panels.