A net-zero energy (NZE) building is one that relies on renewable sources to produce as much energy as it uses, usually as measured over the course of a year.
Net-zero energy buildings start with energy-conscious design. Many features work without an energy source. For example, in cold climates, south-facing buildings with large expanses of windows on that side can produce well over 50% of their heat through passive solar gain. On the cold north side of the building, smaller windows can angle to wider openings, permitting more light while limiting heat loss. In warmer seasons, passive ventilation systems can pull cool air up from the lower levels and vent it through the building's highest point. Rooftop systems can collect rainwater to reduce usage of treated water. Solar panels, heat recovery systems, geothermal heating and wind turbines are among the other technologies used to achieve net-zero status.
In reality, however, the net-zero target is challenging. Homes and other structures that create almost as much energy as they use are sometimes called near-zero energy buildings. Nevertheless, it's possible for a building to produce an energy surplus, sending excess back to the electrical grid. Facilities or homes that produce more energy than they use are known as energy-plus buildings. Buildings that supply all their own energy and are not connected to an external source are described as off the grid.