Imagine not only never paying another dime for electricity, but making money from the energy you produce. It’s already a reality for many homeowners living off the grid, and it may become far more widespread in the future as builders set ambitious goals for ‘zero net energy homes’, which operate without monthly utility bills.

Such homes are hyper-efficient, using a combination of passive solar, added insulation, high-efficiency windows, natural ventilation, LED lighting and other techniques and equipment to consume the least amount of energy possible. They’re often designed to make use of energy gained from other sources – for example, drawing heat from refrigerator exhaust or even the body heat of occupants.

Also known as zero energy buildings (ZEB), these structures produce their own energy on-site through solar cells, wind turbines, geothermal energy and biofuels. The goal of zero energy buildings is not only to produce more energy than is used, but to produce zero carbon emissions as well.

General Electric says it will deliver zero net energy homes by 2015, and the California Public Utilities Commission set a goal to have all new homes using zero net energy by 2020. That may seem unlikely, especially given the state’s budget crisis, but sustainable design expert Scott Shell of EHDD Architecture in San Francisco says zero net energy homes are not only coming in the near future, they’re already being built around the country.

“Very few people see it coming, but the world is going to change in a profound way in the next few years.”

Shell’s firm has built a number of zero energy buildings, including a school, an office facility and his own home. Another example of a legitimate and documented zero net energy home is located in Vermont. Designed by Pill-Maharam Architects, the 2,800-square-foot farmhouse is the first LEED Platinum home in the state and exported 16 kWh of electricity to the grid between January 2008 and January 2009.