DAVIS, Calif. — As more homeowners generate their own electricity from solar panels, they still need power from a utility after the sun goes down.
Now, automakers say they may have an answer, by storing that carbon-free energy in electric car batteries for later use.
Honda on Tuesday is introducing an experimental house in this environmentally conscious community to showcase technologies that allow the dwelling to generate more electricity than it consumes.
It is one example of the way solar companies and carmakers are converging on a common goal: to create the self-sufficient home, with a car’s battery as the linchpin.
With buildings and transportation accounting for 44 percent of the United States’ greenhouse gas emissions, car companies increasingly view all-electric and hydrogen fuel-cell cars as vehicles that will meet environmental mandates and lead to development of new energy services and products beyond the garage.
Ford, Tesla Motors and Toyota are pursuing strategies similar to that.
“It’s a new world in terms of vehicles operating not as isolated artifacts but as being part of a larger energy system, and I think the greatest opportunity for automakers is figuring out how their vehicles become part of that system,” said Daniel Sperling, director of the Institute of Transportation Studies at the University of California, Davis, which provided the building site and the heating and lighting technology for the Honda Smart Home.
The heart of Honda’s 1,944-square-foot home is a room off the spotless garage that contains a 10 kilowatt-hour lithium-ion battery pack housed in a black box. The battery is a smaller version of the one that powers the all-electric Honda Fit parked nearby.
Next to the battery pack sits a bigger white box called the Home Energy Management System. It is the brains of the house, deciding when to tap renewable electricity generated by a 9.5-kilowatt solar panel array installed on the home’s roof to charge the car’s battery or store the solar energy.
The rooftop solar array is about twice the size of one typically found on a comparable suburban home. The amount of electricity generated by the solar panels and stored in the battery pack allows the home to operate independent of the power grid, if necessary.
The home sends excess electricity to the grid. And if the utilities become overloaded, say, in the summer when temperatures spike and everyone turns on their air-conditioners, the local electricity provider can send a signal directing the home to send solar electricity to the grid to help avert blackouts.
A similar size home would consume 13.3 megawatt-hours of electricity a year while the smart home would generate an estimated surplus of 2.6 megawatt-hours annually, according to Honda.
“We can get our carbon footprint below zero,” said Michael Koenig, the project leader for the Honda Smart Home, as he stood in the living room of the airy, light-filled house while a rerun of “McHale’s Navy” played on a large flat-screen television embedded in a wall.
He held an iPad that wirelessly controlled all the home’s functions, from lighting to the power systems, and that showed the house generating 4.2 kilowatts of electricity on a partly sunny morning while consuming 0.84 kilowatt.
“The system will calculate the household electricity load for the day based on the home’s history as well as the expected solar output and it’ll only buy power at the lowest price,” Mr. Koenig said.
The Honda Fit EV in the garage has been modified to accept energy directly from the solar array, too.
To minimize electricity consumption, Honda and the university have installed several energy-saving technologies. A geothermal system taps heat in the ground below the house to provide heating and cooling while an energy-efficient automated lighting adjusts the hue of LEDs to mimic natural daylight. In the early evening, for instance, the lights cease to emit blue hues, which have been found to interfere with sleep.
Making concrete is a carbon-intensive process, so Honda replaced half the concrete in the foundation with pozzolan, a volcanic ash.
Steve Center, vice president for American Honda’s Environmental Business Development Office, said the company did not expect to sell green-building innovations like that. Instead, Honda will focus on the potential to sell home energy management technology and battery systems to homeowners, builders and utilities.
“We see a lot of things converging,” Mr. Center said. “There will be new business models like home energy sharing and energy storage, using your car’s batteries.”
He said one way into the home was through alliances with solar panel installers like SolarCity. In 2013, Honda and SolarCity created a $65 million fund to finance the installation of solar arrays for Honda customers.
Ford struck a deal with SunPower to give buyers of its electric cars a discount on the company’s solar panels. A prototype of Ford’s C-Max Energi plug-in hybrid electric car uses 16 square feet of SunPower’s solar panels on its roof to charge the car’s battery. No utility needed.
“There’s clearly a business case for the home market if battery prices continue to fall,” said Mike Tinskey, Ford’s director of global vehicle electrification and infrastructure. “You could charge the battery” of the car “at night using lower-cost, potentially cleaner electrons than you could use during the day when rates are higher.”
That, of course, would threaten the revenues of utilities, which have emerged as an obstacle to such systems.
In California, SolarCity has offered some customers 10 kilowatt-hour lithium-ion battery packs made by Tesla Motors to store electricity generated by solar panels. But the state’s three big utilities have been slow to connect such systems to the grid, arguing that homeowners could use batteries to store electricity when rates are low and sell it back to them when rates are high.
Regulators have so far sided with solar companies. The California Public Utilities Commission in October ordered the utilities to obtain 1,325 megawatts of energy storage by 2020 to help balance the grid as more sources of renewable but intermittent electricity come online.
The utilities commission also issued a preliminary ruling in October that directed the utilities to plug homeowners’ battery storage systems into the grid at no extra cost. But the ruling allowed homeowners to be charged connection fees if their batteries could store more electricity than their solar panels produced.
With solar installations in the United States soaring and state subsidies paying 60 percent of the cost of home energy systems installed in California, automakers expect more homeowners to view their electric car as a backup power source in the event of disruptions in the grid.
Both electric cars and the hydrogen fuel-cell cars can be modified to return electricity to the home or grid, though that technology has yet to be deployed outside pilot projects.
The Honda Fit EV has a 20 kilowatt-hour battery while the most expensive Tesla Model S electric sports sedan has an 85 kilowatt-hour battery. And thehydrogen fuel cell cars that Hyundai, Honda and Toyota are introducing over the next year can generate at least 100 kilowatts. The average home in the United States consumes about 30 kilowatt-hours of electricity a day, the United States Energy Information Agency says.
“There’s an enormous potential for fuel-cell vehicles to serve as a power source for the home,” Mr. Center said.