Solar Heating: About Solar Greenhouses
What is a Solar Greenhouse?
All greenhouses are used in order to collect energy from the sun, however solar ones can do more than this. Solar greenhouses collect the energy during the day, store the heat and use it in cold weather, cloudy days and at night, supplying the plants with enough heat for their growth.
There are a number of types of solar heating greenhouses from which to choose:
The stand-alone type is ideal for larger scale production, and is used for vegetables and ornamental plants. There are basically two styles, the Quonset and shed types.
The Quonset type is a low cost version which looks rather like an underground pit, or tunnel, with a Quonset shaped frame, and one or two layers of plastic film. This type can save up to 40% of fuel used for heating purposes.
The shed type runs east to west along a long axis, with a south facing wall which is glazed, in order to collect as much solar energy as possible. The opposite, north facing wall, on the other hand, is insulated, to reduce heat loss. These details make it very different from a conventional greenhouse.
Active or Passive?
The Active Solar Heating Greenhouse
The active solar greenhouse collects and stores solar energy, and then moves the heated air from where it is stored to the rest of the greenhouse.
The Passive Solar Heating Greenhouse
Passive solar greenhouses are useful in areas where there is a longer cold season, and make use of supplemental electric or gas heating, in order to protect the plants from the cold.
This type still improves productivity in these areas, and is cost effective as it can increase the quantities of high value crops.
Designing a Solar Greenhouse
The solar greenhouse is not very different to use and manage than a conventional one. There are some differences, however, the main ones being:
The glazing on a solar greenhouse is oriented to make the most of the sun's warmth, even in the winter, and the materials used in its manufacture are designed for minimal heat loss; in fact rather than losing heat, the materials store it. The greenhouse is also insulated so as not to lose heat at times when the sun is not shining. During the summer it is cooled by means of natural ventilation.
Solar Heat Storage
For a solar greenhouse to stay warm even on the coldest night, its heat storage system must be able to store enough heat. One way in which this is done is to place concrete or rocks directly into the path of the sun, to absorb its heat.
Other features may include a dark colored ceramic floor, or a cinder block wall placed on the north side, both of which will store heat. Any surface, walls or floors, which are not intended for heat storage, should be light in color, so that they will reflect both light and heat and transfer it to the plants.
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