A few weeks ago, Brian Valle was at work in the mechanical room of a new house in Yarmouth, Maine, hooking up the last few parts of its solar energy system. Valle and a co-worker wrestled two gleaming Tesla Powerwall batteries, each of them weighting 276 pounds, up on their waiting wall brackets while another two-person team from ReVision Energy installed 34 solar modules on the roof.
It was all going like clockwork, and in an era when rooftop solar arrays are becoming more common than ever, none of it seemed all that remarkable—even to someone who doesn’t know much about solar. That was until Valle, a self described “electrical geek,” began explaining in detail how the panels, the Powerwall batteries, and the other components that make up the $60,000 system actually work. Then it seemed anything but ordinary.
On its face, the system could be described simply as a grid-tied, 10.8 kW solar array with battery storage. Each of the rooftop panels has a rated capacity of 320 watts, so the system could theoretically deliver 10,880 watts of electricity on a sunny day. The system is connected to the Central Maine Power grid, and like any grid-tied system, it will export excess electricity to the grid during times of plenty, and import energy on the long, dark days of winter. The two 13.5 kWh Powerwalls can store enough electricity to keep the house running—at least on paper—for about two days.
Off-grid solar-and-battery systems have been around for decades, but the no-maintenance Tesla batteries are nothing like the banks of lead-acid batteries that solar enthusiasts have tended in the past. In itself, they represent a big step forward. But the controllers and software that knit the system together make this system flexible, intuitive, and capable of near autonomous operation.
The system is complex,…