A “net-zero” building is designed to produce sufficient energy from renewable sources as its occupants consume, average (or summed) over an average one-year period. Generally, electricity is produced using some combination of microgeneration technologies (such as solar photovoltaic (PV) panels, wind turbine, small-scale hydro power) in sufficient quantity to meet all the occupants’ needs. Some systems are “off-grid” meaning that all power generation must meet demands year round; more generally “grid-tied” systems allow excess power to be exported to the grid when production exceeds immediate needs, to be “repaid” later when demand exceeds generating capacity.
Off-grid systems rely on some form of power storage, typically batteries, which require maintenance and which limit how much power can be stored and used. Grid-tied systems allow customers of the utility company to supply power from a “distributed” system.