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.