Checking The Claim: A House That Produces More Energy Than It Consumes

Forget carbon-neutral—Honda and the University of California have built a house that claims to give energy back

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The Honda smart home's energy efficient interior features a passive heating and cooling design and an LED lighting system that adapts to the body's natural circadian rhythm. Honda

Building residential units that use less energy has, over the past half decade, become a goal shared by many architects, designers and consumers alike. But is it possible to build a home that actually produces more energy than it uses? 

A recently-launched experiment out of the University of California-Davis hopes to answer just that. 

The goal of the Honda Smart Home US, a collaboration between the automaker and scientists at the university, is to see whether it's possible to not only eliminate the combined carbon footprint of both car and home, which account for a 44 percent of greenhouse gases emitted in the U.S., but to toss power back to the grid, too. 

The experimental 1,944 square foot, two-bedroom unit, located in the west village of the University of California, Davis, was unveiled late last month. For three years, a group of up to four faculty and staff members will live in the home while researchers monitor how it performs under the day-to-day demands of human occupants. Researchers hope to have the group move in by September.

Whereas a conventional house of similar size consumes about 13.3 megawatt-hours of electricity a year, the smart home, through a series of energy-saving modifications, would actually generate an estimated annual surplus of 2.6 megawatt-hours, according to computer simulations.

Like with other "net-zero" concept homes, the smart unit's power supply comes from an array of roof-mounted solar panels. Electricity is converted from sunlight through a 9.5-kilowatt solar photovoltaic system and then funneled through Honda's custom-built home energy management system (HEMS), a wall-mounted white box mounted in a room next to the garage. The device is programmed to distribute the influx of renewable energy throughout the home as efficiently as possible. Researchers say power for all of the home's heating, cooling, water, lighting and appliances is supplied by the panels; the home also generates enough energy to recharge a Honda Fit, an electric plug-in vehicle that occupants will use for daily commutes.

"We all know that cars contribute to global carbon emissions, but it's not the lion share," says project head Michael Koenig. "We're looking at both vehicles and the built environment as well as how to coordinate them as a way to completely mitigate their impact on the natural environment."

Excess energy is distributed to a 10 kWh lithium-ion battery, which helps power the house during a blackout or when there's peak demand. When demand is exceptionally high, such as in the summer months,  the home can even offload the stored energy into the grid; presumably, the energy would be sold back to utility companies for money, or, in the form of credits on electricity bills. 

Honda Smart Home US Overview

The Honda smart home isn't the first aiming to produce more energy than it uses. You can find similar energy efficient principles in the passive design styling of the "Active House" in Denmark and the energy management system used by the "Zero Home" in Utah. It does, however, showcase a major automaker's vision for what the eco-friendly home of the future—with electric car in tow—will look like. 

The home includes a geothermal radiant heating and air conditioning system that harnesses natural heat from the ground and pumps it up to the home, where it's then used to boil water and regulate indoor temperatures. An advanced LED lighting system also helps cut energy use by mimicking the shift in natural light conditions throughout the day. Bulbs radiate bright, blue-rich light during the daylight hours, gradually transitioning in the evenings to an amber hue that not only requires less energy, but also works in tandem with the body's cyclical sleep patterns, researchers say.

Several passive energy-saving ideas have also been incorporated into the house's design. Five large windows with blinders are positioned on the south side of the house, which receives the most sunlight during the winter months and the least during the summer, reducing the power demands for indoor heating and cooling. The six smaller north-facing windows, meanwhile, generally collect very little heat, making them ideal for ventilation. The use of double stud walls, which allow for better insulation, along with cooling roofing material and an insulated concrete slab all help to further reduce the amount of energy the house consumes.

None of these concepts are entirely new; it's the way they're used together (and the inclusion of car charging capability) that sets the project apart. While there are enhancements that could have yielded even larger energy efficency gains, Koenig says the research team wanted to stick with well-established, mainstream techniques instead of some of the more experimental concepts being piloted elsewhere, like this water-recycling shower.

During the trial phase, researchers will test different battery sizes, upgrade HEMS' learning and self-correcting capabilities and address any inefficiencies. And just because the house, in theory, produces more energy than it needs doesn't mean residents are off the hook: power usage will be monitored, and residents will also sit down for interviews on their habits and living conditions. 

All of the data will eventually be available online. But for now, it's too soon to tell when, if ever, any of these features will be available for home renovation or new construction.

"Ultimately, it will be up to the research and development people ... to decide whether it's prudent to take what we learned and develop a product for consumers,” he says. "What we want to show with this is that we're affecting change and can build something that contributes to the solutions directly."

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