Zero Net Energy means on an annual basis, a home is designed to produce all the energy it consumes.
Although not quite zero net energy homes, responsible use can result in energy use approximately one tenth that of a home built 'to code' with the additional attributes of passive survivability, immunity to energy price 'shocks', and a general sense of security. Construction documents, plans, and other detailed information about this project are available here. Mike Duclos was responsible for Massachusetts ENERGY STAR certification for these homes. When, in the middle of the construction project, the Tier III incentive level was created, Mike consulted for RDI to modify these homes to successfully achieve Tier III certification for all units remaining to be built. Green Building Advisor recently did a story on actual energy use, which is available here.