To do that, Mr. Narayanamurthy said, it was important to conduct the study, in partnership with the California Public Utilities Commission and its program manager, Itron, in real homes with people using them the way they normally would.

But they also needed to have groups of homes clustered on individual transformers to allow them to compare the results with the traditional method of providing power. With that information, they can determine the value for homeowners and grid system operators of adding features like solar panels, heat pumps and, in some cases, battery storage.

They found a willing collaborator in Meritage, a leading builder of energy-efficient homes, and are expanding the test program to additional subdivisions in Southern California, the Central Valley and the Bay Area.

For buyers, part of the appeal of a home built to be zero-energy is that they do not have to change their behavior to save energy.

At Meritage, the company insulates every house with spray foam, sharply reducing the amount of heating and cooling needed, and allowing smaller or fewer units to be installed. Making the homes even more efficient are dual-pane windows that help retain or keep out heat (depending on the need), LED lighting and advanced water heaters that work by funneling heat from the ambient air into the water.

All of the test homes have SunPower rooftop solar systems, which are among the most efficient on the market. And because they were designed along with the houses, the arrays can be oriented for maximum production.

Half of the test homes also have energy storage systems with LG batteries and Eguana inverters, which help manage the flow of electricity between the solar installation, home and grid, to allow researchers to test and compare how much value they add. The houses come equipped with A. O. Smith water heaters that can be remotely controlled and Trane smart thermostats that can manage all the equipment and can connect to cameras and security systems.