3.2. Net-zero energy buildings
In current practice, the most common approach to ZEB is to use
the electricity grid both as a source and a sink of electricity, thus
avoiding the on-site electric storage systems. The term ‘net’ is used
in grid connected buildings to define the energy balance between
energy used and energy sold, the term ‘net-zero energy’ being
applied when the balance is zero. Vale and Vale [37] offer a
thorough philosophical and practical examination of the implications
of an ‘autonomous’ house versus a ‘‘net-zero energy’’ house
and with a global market perspective. Their conclusion and
approach is that connecting a domestic renewable system to the
electricity grid and achieving a ‘‘net-zero energy’’ home can have
better life cycle performance than an autonomous house as using
electric storage systems is avoided and some flexibility in the use
of appliances is gained. This argument being even more valid for
non-domestic buildings, the ‘net-zero’ concept has been adopted
widely while autonomous buildings are reserved for very specific
site conditions, education, and research.