HEMS balances the energy needs of the car, home, and grid.
HEMS balances the energy needs of the car, home, and grid.

The Honda Smart Home in Davis, Calif., effectively uses renewable energy to embody the company’s vision of a zero carbon footprint for living and transportation.

“The home is a net-zero energy design that’s sustainable and that is possible in the near future,” says Adele Chang, principal at Lim Chang Rohling & Associates in Pasadena, Calif. To generate the considerable energy required to efficiently fuel the home’s Honda Fit, the southern roof was maximized to fit a 9.54 kW photovoltaic system, she explains. 

To make its vision truly achievable, Honda had to move beyond the home in isolation and consider how these fluctuating energy inputs and outputs impact the larger balance of power supply and demand.

“If every house has solar and is feeding to the grid, that causes disruption because the voltage is too high, but if everybody has an electric car and is charging it at the same time, it can overload the transformers,” says Ryan Harty, manager of environmental business development at Honda. “Ubiquitous cars charging at home with ubiquitous solar energy breaks down into practical trouble. We needed to develop the technical systems and solutions to prevent that vision from being stopped on a technical feasibility level.”

Enter Honda’s experimental Home Energy Management System (HEMS), which can store up to 10 kW hours of energy in an on-site battery for use when solar is not available and provide excess power back to the electrical grid. The system uses a DC/DC converter—as opposed to converting to AC—to minimize energy loss during both storage and transfer.

HEMS constantly communicates with the grid to sense the frequency and voltage, and it uses that to manage the home’s energy consumption. If the frequency drops below the standard 60 hertz, HEMS will use the battery instead of drawing from the grid and feed power back to the grid if possible. If it rises above, the system will use energy from the grid for in-home applications.

“Sensing what the grid is doing and managing what you do with that is part of a future where energy devices have those features built into them and can neutralize the impact of renewable energy on the grid,” Harty says.  

Going forward, both energy management and sustainable design are essential, he adds. “First, reduce your need for energy generation. Then, figure out what you need to do to manage the need that you do have.”