"From 2013, Gansu province will gradually promote a “south wall plan” in village buildings to save energy.
“South wall plan” means installing a sunshine room and a warm corridor on the south façade of the building, equipped with solar energy appliances to improve occupant comfort and decrease fossil energy consumption."
Whist this all sounds commendable I wonder if there is not opportunity for utilizing more economical, low tech passive solutions such as a Trombe wall, where a sun-facing wall is separated from the outdoors by glass and an air space, which absorbs solar energy and releases it selectively towards the interior at night.
The essential idea was first explored and patented by Edward S. Morse in 1881. In the 1960s it was fully developed as an architectural element by French Engineer Félix Trombe.
Even a single-pane glass works for this process, because glass is transparent to the incoming visible light and near-visible shorter-wavelength higher-energy infra-red radiation that warms the wall mass, but less so to the longer-wavelength infra-red radiation that is the heat that is radiated back out from the wall mass.
Modern Trombe walls have vents added to the top and bottom of the interior wall, to allow heated air to flow via convection into the building interior.
The vents have one-way flaps which prevent convection at night, thereby making heat flow strongly directional. This kind of design is an indirect passive thermal collector.
By moving the heat away from the collection surface, it greatly reduces thermal losses at night and improves net heat gain. Generally, the vents to the interior are closed in summer months when heat gain is not wanted.