A Trombe (TROM-bee) wall is a passive solar device consisting of a thick sun-facing masonry wall (thermal mass) to absorb the sun's energy, combined with an air space and insulated glass. It was developed in the 1950s by Felix Trombe.
While the sun is shining, optical energy travels through and is trapped beneath the glass and absorbed by the masonry wall. The energy stored in the wall is then released slowly to the interior of the building when the sun is no longer shining. Using the sun's stored energy to heat your home reduces your conventional energy consumption.
During the summertime when heating energy isn't needed, the sun is higher in the sky and usually a Trombe wall has an overhang on it. The sun hits that overhang and bounces back rather than being collected and dispersed by the masonry wall.