This paper shows how much electricity generation would be needed for a passive house to achieve a zero emission balance over the year, hence to become a Zero Emission Building, ZEB. The case study is based on the passive house apartment blocks built in 2008 in Løvåshagen, near Bergen, Norway, and the analysis focuses on the consequences of adopting different heating systems. With the carbon emission factors assumed, it is shown that the sole PV installation on the roof is generally not sufficient to generate all the electricity needed to achieve the ZEB balance. Possible integrations are the use of PVT panels (to better exploit the limited roof space), adopting of a centralised cogeneration of fuel cells fuelled by biomass or biofuel, or increase of the generation capacity by adding extra PV area (e.g. on the garage roof) or a mini wind turbine.

Conceptually a Zero Emission Building (ZEB) is a building with greatly reduced energy demand and able to generate electricity (or other carriers) from renewable sources in order to achieve a carbon neutral balance. However, a rigorous and agreed definition of ZEB is yet to come. A parallel paper in this conference explains how a formal and comprehensive ZEB definition can be based on the evaluation of certain criteria. These criteria are extensively discussed in ongoing projects, both in Norway and internationally. The objective of this paper is to focus on two of these criteria: energy performance and credits used to measure the ZEB balance. For each criterion different options are considered and the implications they have on the building design are assessed. The case study is on a typical Norwegian single family house. It is shown that for certain choices on the two criteria options, a paradoxical situation could arise. When using off-site generation based on biomass/biofuels, achieving the ZEB balance may be easier for high energy consuming buildings than for efficient ones. This is the exact opposite of what ZEBs are meant to promote: design of energy efficient buildings with on-site generation options. Recommendations on how to avoid such a paradox are suggested.

A clear and agreed definition of Zero Emission Building (ZEB) is yet to be achieved, both internationally and in Norway. However, it is understood that both the definition and the surrounding energy supply system will affect significantly the way buildings are designed to achieve the ZEB goal. Since the energy system in Europe is expected to change significantly in the coming decades, especially for electricity, it is indispensable to tie the definition of ZEB to possible scenarios on such development of the energy system. A scenario is defined as a combination of options chosen within a framework of different uncertain futures. Two uncertainties are identified as most important for the development and deployment of ZEB: Technology development and Public attitude. These two uncertainties are used to span out a set of four relevant futures, also termed storylines, as a common background for scenario analysis. A formal definition of ZEB is characterized by a set of criteria that are: the system boundary, feeing-in possibilities, balance object, balancing period, credits, crediting method, energy performance and mismatch factors. For each criterion different options are available, and the choice of which options are more appropriate to define ZEBs may depend on the storyline features.