When Terrence Dwyer received a knock on his door and a flyer for a solar panel system small enough to fit on his deck, he was quickly sold. Solar systems that plug into regular wall outlets have been popular in Europe for years and are gaining traction in the U.S. for their affordability and simple installation.

“We thought absolutely, let’s do this right away,” said Dwyer, who lives in Oakland, California.

These small-scale solar systems could become attractive to more homeowners now that President Donald Trump’s sweeping budget-and-policy package will scrap residential rooftop solar tax credits and may shift interest to cheaper alternatives.

Even before the GOP bill passed, manufacturers of the smaller systems, known as plug-in or balcony solar, were seeing increased demand and other positive signs, such as a new Utah law streamlining regulations for homeowners to buy and install them. The systems, about the size of a door, haven’t been as widely adopted in the U.S. as in Europe because of a lack of awareness, patchwork utility rules, and limited availability.

The $2,000 plug-in solar system installed on Dwyer’s backyard deck in March consists of two 400-watt panels, an inverter, a smart meter, and a circuit breaker. It saves him around $35 per month on his power bill because he is consuming less energy from the grid, but he said reducing his carbon footprint was his primary motivation.

“We like the environmental benefits of solar and wanted to engage with solar in some fashion,” Dwyer said.

Had Dwyer opted for rooftop solar, he would have paid $20,000 for the system and $30,000 to upgrade his roof to support the panels.

Installing a plug-in solar system requires some homework. What power companies let customers do with energy-generating equipment........

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