The term "net-zero" energy (or NZE) describes the concept of buildings generating their power needs by renewable on-site power generation. This is typically done by photovoltaic (PV) panels, sometimes by wind mills or a combination. There are several definitions of what "zero" means, the most common ones being net-zero "cost" or net-zero "site energy". The cost definition just means that your annual energy bill would be zero, which can be easily accomplished by over-producing electricity in the summer, running your meter backwards, and then using the "credit" you accumulate in the winter. Due to metering tariffs such as "time of use metering", net-zero cost can be accomplished even if you don't quite break even on power consumption. The higher goal is to actually offset all the kilowatts you use on an annual basis, completely eliminating the operating carbon footprint. Ideally, a building would produce even more power than it consumes, a net-positive balance that over time would compensate for the embodied energy that had been used to build it.
In the competition design below, we designed 240 dwelling units to exceed net-zero site energy standards: In addition to offsetting all the electrical building loads, the excess capacity of the roof integrated PV systems would also give each household some 10,000 miles in electrical vehicle charge.