A passive house is a building that can be heated (or cooled in hot climates) merely by using the air flow, which is necessary for a healthy indoor air quality (hygienic air change). It must be understood that this approach is substantially different from the standard air heating systems, as common e.g. in North America, where the (large) air heating system is designed to meet the heating load (much larger than the hygienic air supply). This approach of the double use of air for "breathing and heating" is only feasible with a drastic reduction of the building heating demand, which in turn requires a high level of insulation for the abatement of heat losses (or heat gains in hot climates).
A separate, conventional heating system is then in most cases superfluous, with an obvious economic advantage.
The choice about architecture and construction type, use of renewables or other energy sources is completely left to the building owner.
Passive houses are equipped with a mechanical ventilation with heat recovery to ensure fresh air with minimized heat losses; nevertheless windows can be opened at any time!
The Passive House Institute has developed and published a large documentation about principles and structural-physical background.