Photovoltaic solar panels on roof of Honda Smart Home at UC-Davis, California
Electric-car owners can cut their ownership costs significantly by avoiding the gas pump and charging up at home.
But they can also save money by making the homes where they park their cars at the end of the day more efficient.
Continuing decreases in the price of solar cells and related technologies mean it's getting easier and easier for modern homes to rely less on grid electricity.
Some new homes are now being built with the goal of "zero net energy"—to generate as much energy as they use.
Yet that ambitious target is largely reliant on electric utilities' willingness to allow decentralized renewable energy generation into their midst.
A cluster of 20 homes in a subdivision near San Bernardino, California, is serving as an experiment in this concept, as detailed in a recent article in The New York Times.
Photovoltaic solar power field at Volkswagen plant in Chattanooga, Tennessee
The houses were designed and built from the foundations up for zero net energy, and are being monitored by the Electric Power Research Institute, a utility-funded nonprofit.
Because the homes are clustered together on a single transformer, they can be directly compared to homes that receive their electricity only from the grid.
They all have SunPower rooftop solar systems, which were planned for and integrated during design work to ensure maximum effectiveness.
Half of the 20 test homes also have energy-storage systems, with LG battery packs and Eguana inverters.
Storing energy allows any excess electricity harvested by the solar panels to be collected for later use, prolonging the amount of time homes can operate independent of the grid.
To cut energy use, the homes also have spray-foam insulation, dual-pane glass, LED lighting, more-efficient water heaters, and smart thermostats.
Photovoltaic solar panels on house [photo: Marc Lausier]
All of this equipment raises their cost compared to more traditional homes, but energy savings can offset much of the premium.
This has put net-zero homes on the radar not just for high-end suburban developers, but also for low-income developers like Habitat for Humanity.
Since 2013, the Department of Energy (DOE) has certified 700 homes as "zero-energy ready," meaning a renewable-energy system would offset most or all of a house's annual energy consumption.
The DOE expects to certify roughly 1,000 homes this year, and 3,000 more in 2017.
Those homes won't provide much benefit if they can't actually be equipped with their rooftop renewable-energy systems though.
Some utilities increasingly view home solar arrays as a threat to their traditional business model—and are fighting more widespread adoption.
NRG eVgo Freedom Station at Whole Foods Market, Fremont, California
The renewable energy isn't necessarily the problem; the concern is consumers generating their own electricity.
Under new CEO Mauricio Gutierrez, NRG Energy is shifting its focus away from "empowering customers" via residential solar, according to a New York Times report that appeared in the same issue as the net-zero housing profile.
NRG is still interested in solar power, it says, along with natural gas, carbon sequestration, and other technologies that could reduce carbon emissions from its power plants.
Yet it recently folded its home-solar division into its retail sales division, making it more difficult for consumers to get solar power without signing on for a larger service agreement.
The company also sold its majority stake in the EVgo electric-car charging network, which operates public charging stations in 50 U.S. metropolitan markets.
These moves, analysts say, are to ensure NRG continues to earn a profit in the rapidly evolving world of decentralized and renewable energy.