Mention solar technology and most people automatically assume that solar panels are involved in one way or another. While this is generally true, the concept of passive solar energy has been used from thousands of years to heat structures. The trombe wall is one form of low tech used in passive solar for heating a home at night.
The trombe wall is named after Felix Trombe, a French inventor who created the modern version in the 1950s. The basic idea behind the wall is the manipulation of thermal storage and heat release. Put in simpler terms, the wall is used to capture and hold heat during the day and release it in the evening. In doing so, the wall becomes a repository for heat much like the pavement on a parking lot during the day.
To understand how the trombe wall functions, it helps to first contemplate how passive solar energy works as a heating process. A simple example suffices. Imagine you drive to the grocery store. You park in the parking lot and head inside. You are there for no more than 30 minutes. When you come out to the car, what has happened? It has turned into an oven! This is passive solar at its finest. The sunlifht has heated up every dark surface in the interior of the car, which then radiates heat. During the summer, sitting down on the seats can be a delicate maneuver, particularly if you are in shorts!
What if you could capture this heat during the hottest periods of the day and slowly release it at night when temperatures drop? This is exactly what the trombe wall is designed to do. The average trombe wall is between 8 and 16 inches thick. It is typically made of concrete. On the exterior face, the wall is covered with a heat absorbing material. This can be a painted on dark color or absorbent material. A double layer of glass is then placed about an inch outside of this and forms the exterior of the structure. It looks a little odd to have a wall inside of glass, but the heating impact is significant.
As sunlight penetrates the glass, it heats up the surface of the concrete wall. The wall then absorbs the heat at a rate of about an inch an hour. By the end of a sunny day, you have a concrete wall that is heated up much like the rocks in a sauna, although obviously not as hot. The double glass serves to insulate one side of the wall. Once the temperature in the area starts to cool below the heat level of the trombe wall, it will start to emit heat. The heat rises. Vents and small fans can be put in to circulate the warm air into the interior of the home where it can be funneled to rooms in use. This can be done day-after-day so long as the sun hits the wall.
Solar power is a complex energy platform and involves much broader techniques then just solar panels or water heaters. Passive solar can be a powerful way to deal with heating issues and the trombe wall is one example of this.