In short: A good balcony solar kit is certified for U.S. use, sized to your space and electricity use, fitted with a standard 120-volt plug, and backed by a real warranty. Beyond the hardware, the thing that varies most between sellers is total cost, your energy savings and how transparent they are about it. Here is how to compare your options without the marketing noise. Balcony solar, also called plug-in solar, is finally arriving in the United States, and the number of kit