Question

I have five 4x6 sheets of old solar panel glass. What can I do with them to heat my house?

Asked by Lynn Jackson
Carson City, NV

The glass came off the side of a house that was painted black with black pipe underneath. The owner said it made his house too hot because he'd built on top of a hot spring that heated the house.

Answer

Randy Potter

Answered by Randy Potter

Santa Clara, CA

EarthBound Homes

October 10, 2010

In a cold winter climate like Carson City that still gets lots of sun during the summer, you want to use passive solar techniques to increase the amount of natural heat the sun-facing sides of the house receive (south and west).

The only thing I can think that you could use your glass panels for would be a Trombe wall.

  • In its purest form, a Trombe wall consists of a vertical wall, built of a material such as stone, concrete, or adobe (something with thermal mass), that is covered on the outside with glazing.
  • Sunlight passing through the glazing generates heat which conducts through the wall.
  • Warm air between the glazing and the Trombe wall surface can also be channeled by natural convection into the building interior or to the outside, depending on the building's heating or cooling needs.

During the day

During the day, sunlight shines through the glazing and hits the surface of the thermal mass, warming it by absorption. The air between the glazing and the thermal mass warms (via heat conduction) and rises, taking heat with it (convection). The warmer air moves through vents at the top of the wall and into the living area while cool air from the living area enters at vents near the bottom of the wall.

At night

At night, a one-way flap on the bottom vent prevents backflow, which could act to cool the living area, and heat stored in the thermal mass radiates into the living area.

  • During the day the sun heats first the air in this space, then the solid wall behind.
  • Once the air is heated, it rises and enters into the room, giving it additional heat. Also the rising air pulls in cooler air from the room below to then be heated.
  • The real trick with this, though, is that for some time after the sun goes down the now hot wall will still keep heating air and exchanging that heat into the room.

Though once the wall is cold you need to stop the cold of the outside interacting with the inside, so a one-way flap is used on the bottom vent to stop the cold coming back into the room and creating a cooling cycle with the room. A simple schematic showing this setup can be found here.

The only issue with a Trombe wall on an existing house is that it requires a thermal mass wall, so if you have a traditional stick-framed and insulated house then this might not be the best solution for you. I would recommend that you study this technology carefully before installing it, as there are lots of intricacies that can have a dramatic effect on the efficiency of the Trombe wall in varying weather conditions.

Here is a link to the Trombe wall page of the Build it Solar site where you can get full details and drawings.

Tagged In: passive solar, solar gain

Do you have a question about greening your home? GreenHomeGuide invites you to Ask A Pro. Let our network of experienced green building professionals – architects, designers, contractors, electricians, energy experts, landscapers, tile & stone specialists, and more – help you find the right solution.