The solar panels — 15,000 of them — sweep down the hill from a former dairy farm here, gleaming rows of silver and blue nestled between fields of recently harvested corn. The installation, a project developed in partnership with SolarCity, the leading rooftop solar provider in the United States, and the local electric cooperative, is meant to help create more green energy options for customers, mainly a handful of utilities operating in the state.

But it is what lies toward the bottom of the array that gives the project its distinction: about 30 white refrigerator-size battery banks courtesy of Tesla, the electric carmaker

The facility, the Mountain Ash Solar Farm, is not running yet, but, along with a similar, larger project under development in Hawaii, it offers a steel-and-glass example of what Elon Musk, the chief executive of Tesla, and his cousins, Lyndon and Peter Rive, founders of SolarCity, have in mind for their merger planned for this year.

Solar energy has long been seen as an important weapon in the fight against climate change, but its usefulness is limited because the sun sets — and is temporarily blocked by passing clouds — which can create a mismatch between supply and demand or lead to complications on the grid. Adding batteries to the mix not only solves those problems, but allows solar power plant operators to sell new services to system operators.