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Now On Keeping Heat Constant Storage Insulation
   
Heat storage is as vital for a solar greenhouses as insulation. Without it, temperatures would fluctuate in great fashion.
All the energy is in the sun-warmed air, but drafts will quickly drain off the heat, even the most tightly made building will have a fair amount of tiny cracks. However energy stored in storing materials is not lost along with escaping air. This energy is released slowly as the greenhouse cools, and the building stays warm much longer.
The counter is also true, without storage the inside temperature can soar into the 80's or 90's on cold, bright days. That is devastating for a winter greenhouse crop. But with storage absorbing some of the incoming energy, the result is a mild daytime environment.
1,000 gallons of water stacked vertically on the rear wall in direct line of the incoming light is best. Four gallons of water for each square foot of floor space is typically enough for even a relatively harsh winter environment.
Water may seem like a lot of work, but water is one of the best heat-storing material known and it is VERY cheap. Rock, sand and concrete are good alternatives, but still is outperformed by water holds by five times more heat. So water reservoirs on walls make compact heat storage that gets a good share of direct incoming sunlight.
Smaller containers are preferable over 55-gallon drums for two reasons. Drums leave empty about a third of the space they occupy, because they are big and round. They also permit warmed water to gather into a few large areas, which causes both greater heat losses and poorer collection in those areas. Smaller containers keep the energy more evenly distributed. On the other hand, the large barrels are certainly worth using if they can be had cheaply.
The amount of insulation is the same as local, energy-efficient recommendations for homes. To use less insulation is to need more heat storage, which demands more space and money.
Two other simple things are crucial to the success of a greenhouse. The earth below them must be insulated to a little below frostline with plastic foam (or Strawbale). And at night an insulating curtain is drawn over the clear south wall to reduce the high heat losses.
It pays to insulate the earth below the greenhouse because earth is a relatively poor insulator, contrary to a lot of lore.
A few inches of most common insulators match the R-value of ten to 15 feet of earth. But earth is a good heat-storing material, lying somewhere between rock and water. So insulating around the perimeter builds heat storage into the structure while stopping steady heat losses to the ground outside.
Needing a Cover for Solar Greenhouse
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