||This article needs additional citations for verification. (December 2009)|
A Trombe wall is a sun-facing wall 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 by Edward S. Morse and patented by him in 1881. In the 1960s it was fully developed as an architectural element by French engineer Félix Trombe and architect Jacques Michel.
Even single-pane glass works for this process, because glass is transparent to the incoming visible light and near-visible shorter-wavelength higher-energy ultraviolet 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.
Current basic design 
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, preventing convection in the opposite direction at night when the wall has cooled, 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.
Because temperature variations tend to propagate through dense masonry materials (thermal diffusion) at a rate of approximately 1 inch per hour, daytime heat gain will be available at the interior surface of the thermal mass in the early evening when it's needed. This time lag property of thermal mass, combined with its thermal decrement (dampening of temperature variations), allows the use of fluctuating daytime solar energy as a more uniform night-time heat source.
Since 1980, passive solar expert Douglas Balcomb has recommended that Trombe walls should not be vented to the interior.
Common variations 
Common modifications to the Trombe wall include:
- Exhaust vent near the top that is opened to vent to the outside during the summer. Such venting makes the Trombe wall act as a solar chimney pumping fresh air through the house during the day, even if there is no breeze.
- Windows in the trombe wall. This lowers the efficiency but may be done for natural lighting or aesthetic reasons. If the outer glazing has high ultraviolet transmittance, and the window in the trombe wall is normal glass, this allows efficient use of the ultraviolet light for heating. At the same time, it protects people and furnishings from ultraviolet radiation more than do windows with high ultraviolet transmittance.
- Electric blowers controlled by thermostats, to improve air and heat flow.
- Fixed or movable shades, which can reduce night-time heat losses.
- Trellises to shade the solar collector during summer months.
- Insulating covering used at night on the glazing surface.
- Tubes or water tanks as part of a solar hot water system.
- Fish tanks as thermal mass.
- Using a selective surface to increase the absorption of solar radiation by the thermal mass.
Application in developing regions 
In Ladakh, India, the Ladakh Project is designing Trombe walls that complement Ladakh's traditional architecture and has promoted building them in Ladakhi homes. This has shown Ladhakis a clean, reliable alternative to fire as a source of heat. The traditional fuel, dung, burns poorly and offers poor relief from the bitter winter temperatures. The smoldering dung produces significant amounts of smoke that fouls the air and causes many health problems. Trombe walls offer relief from both the cold and the smoke. Ladakh receives about 320 days of sun annually, and the traditional building materials — stone and mud brick — provide the thermal mass needed for heat collection in a Trombe wall.
See also 
- Old Solar: 1881
- Mazria, Edward (1979). The Passive Solar Energy Book. Emmaus, PA: Rodale Press. ISBN 0-87857-237-6.
- Denzer, Anthony (2013). The Solar House: Pioneering Sustainable Design. Rizzoli. ISBN 978-0847840052.
- Infrared#Different_regions_in_the_infrared- Near-infrared exhibits low losses in SiO2 glass
- Passive Solar Design Guidelines for Northern New Mexico Gain (Trombe Wall) Guidelines
- Hales, Carolyn (1986). The Ladakh Project. Cultural Survival, 10.3 (Fall 1986) Mountain Peoples. Retrieved from http://www.culturalsurvival.org/publications/cultural-survival-quarterly/hales/ladakh-project.
- Drukpa Trust (2008). Sustainable Design Examples page. Retrieved from http://www.dwls.org/Sustainable-Design-Examples.html.
- Drukpa Trust (2008). Overview of Awards page. Retrieved from http://www.dwls.org/Overview-Of-Awards.html.