Tuesday, March 11, 2008
Passive Solar Greenhouse for transplants
We built our passive solar greenhouse this past winter and as you can see we're still putting finishing touches on it. A passive solar greenhouse differs from a standard greenhouse in that you do not have to heat it with an outside source (such as a kerosene heater) during the cold months. It is heated entirely by the sun and water.
A wall facing due south and angled at 55 degrees is covered with a double layer of greenhouse plastic, held on with wiggle wire. A mounted fan between the layers inflates the plastic and keeps it rigid in high winds. The sun's path in the winter is in the Southern sky, so a South-facing wall will get most of the sun's rays during cold months, while taking in less sun during the summer when the sun is directly overhead. At a 55 degree angle at our latitude, the South-facing wall should be perpendicular with the sun's rays on the vernal equinox, March 21.
The North, East and West walls are insulated and covered with plywood. The interior will be painted all white to reflect the sunlight onto the plants. Nine 55 gallon drums filled with water are under the back transplant bench. In the day the water absorbs the heat from the sun and at night uses that stored heat to keep the greenhouse warm. Vents above both doors that we can open and close and a soffet vent along the peak help keep the heat down in the daytime.
With rising energy costs (economic/social/environmental), many are looking toward "alternative" energy sources, which in some cases may be just as if not more harmful . Others are thinking of ways to use less energy or harness solar and wind energy that is already present. Germany is building the " passivhaus " which are houses designed to require no heating or cooling systems.
We live in a small apartment above a garage, that we designed with south-facing windows. We needed something quick and cheap and with storage/workshop capacity, so we couldn't go entirely passive solar, but simply having it south-oriented means that at certain times of year (including now) we need no supplemental heat (maybe an extra blanket at night). When we have to heat it's currently with electric baseboard heating but we are going to get a wood-burning stove, hopefully by next winter, so we can be off the grid in that respect and use fuel from our woods. We get so much wind on our farm that I'm sure a windmill could at least power the refrigerator, and we'd love to be able to sell back energy from solar panels, but the infrastructure for solar and wind is so cost-prohibitive that it's impossible for people at our income level to do. In the science magazines I read there are frequent articles about less expensive solar collectors being developed so hopefully the technology can catch up to the economic realities.
In the meantime I'm wondering about the possibility of a passive solar brooder for our chicks, as we see the electric bill shoot up when we get 4-6 heat lamps going at once.