'Passive Solar / Passive House' design is not to be confused with 'Passivhaus'.
Originating during the 1970s, the Passive Solar concept is to minimise the energy needs of a building through making best use of solar gain.
Typically, passive buildings will collect solar energy through south-facing glazing and direct it into the building to be either used immediately or stored for future use.
The advantage of passive solar design is that it reduces the need for mechanical and electrical intervention, but the disadvantages are that buildings require high levels of thermal mass and can easily suffer from overheating problems in the summer.
Perhaps the most distinctive problem is how increasing levels of insulation work against the solar gain principle. In winter, solar gain is minimal and in summer it is likely to perform in excess. As insulation is added, the heating periods become smaller until passive solar heating becomes useful only for short periods in spring and autumn - at which point it is worth examining the system cost benefits.
Pure passive solar design has gradually faded out. Perhaps its last iconic manifestation was with the 'Millenium House' built at the BRE in 1997. The design retains all the key features associated with passive solar design, including the familiar 'wedge' shape generated by the large south-facing 'sunspace'.
Though passive solar houses are no longer thought of as a solution in their entirety, building evolutionists will observe that aspects of the solar gain concept are still 'in play'. The truncated 'sunspace' can be see on many low-energy solutions (eg BASF house, Nottingham, above) as the spaces is combined with other functions such as weather-buffering or conservatory space.