SOLAR GREENHOUSES
for Developing Countries


*The intention of this website is to be a starting point for those seeking to implement
solar greenhouse technology in developing countries. Since there is very little
information on this subject we will start with basic solar greenhouse principles and
then discuss ways these can be adapted for application in developing countries.
We conclude with an analysis of several case studies.*


Greenhouse Schematic

Is a Solar Greenhouse Appropriate for Your  Location? 

  1. Does your location have cold temperatures that prohibit growing during certain times of the year?
  2. Is it sunny where you live at least 50% of the time?
  3. Would you like to extend your growing season?
  4. Would the benefit of crops during the cold season outweigh the costs of construction?
  5. Are there local materials available for greenhouse construction?
If you answered 'YES' to all of the above, then you should continue exploring the option of building a solar greenhouse.


                  
                               I.                
Introduction

II.              How does it work?
III.          General Designs
IV.          Construction
V.            Examples: Links to articles
VII.        Conclusion

VIII.   References




I.    Introduction

Passive Solar Pit Greenhouses for the Developing World

    Many climates in the developing world are too harsh to grow vegetables, fruits and grains for a healthy diet.  Farmers struggle against irregular growing seasons brought on by natural disasters like droughts.  Other factors such as strong winds and disease from insects and other pests continue to be a problem for the rural farmer.  What hope is there for these farmers who seem to be at the mercy of whatever nature deals them?  Passive solar greenhouses offer a way for them to take back a little control over their given environment.  At a reasonable cost, these greenhouses offer a low-tech, easy to build solution to the farmer and his community. 

    It is our intention to orient this website toward the individual who is interested in building a simple solar greenhouse.  This would include volunteers and other workers in the developing world.  We do not presume to be experts in this field, only facilitators to what information is currently available in literature and online.

What is a Solar Greenhouse? 

    We are all familiar with the conventional greenhouse; a building or structure with glass or plastic windows used to facilitate the growing of plants.  Solar greenhouses differ from conventional greenhouses by their ability to store solar energy for times when there is little or no sunlight.  This is done in a variety of ways depending on the function of the greenhouse.  Our interest is in ‘passive’ solar greenhouses and particularly, pit greenhouses.  These buildings harvest, store and deliver energy without the use of external energy, hence their low cost.


II.    How Does It Work?

The Basics of Passive Solar Design 
    1. Solar radiation enters the greenhouse through the glazing in the form of light and is absorbed by the plants and other surfaces.  
    2. The light is then changed to thermal energy, or heat.  The light is of course essential for photosynthesis and plant growth but the real key to an effective solar greenhouse is management of the heat.
    3. Properly designed greenhouses will store enough heat to sustain the plants through colder temperatures.The task, then, is in keeping the heat in the greenhouse.
    4. Heat can be lost by radiation, convection and conduction.  Most of the losses will occur by conduction through the walls of the structure.  
    5. The plastic or glass glazing is the key to what is often called the “greenhouse effect.”  Heat that would normally be blown or radiated away is kept inside. 
    6. The basic idea of the solar greenhouse is that the radiation heat generated by the plants is absorbed by other objects in the greenhouse for storage.  These objects are usually materials such as rock, earth, and water, which are easily found and generally inexpensive.  
    7. When the greenhouse is hot, during a sunny day for example, the materials collect and store heat.  When the temperatures fall, the materials naturally release the heat to the greenhouse environment.  
    8. This natural exchange of heat is the beauty of a passive system.


Here are some links for further reading on passive solar design:

Arizona Solar Center
National Renewable Energy Laboratory
North Carolina Solar Center
US Department of Energy
Green Building Program
ATTRA - National Sustainable Agriculture Information Service
Dave MacKinnon's Greenhouse Page


III.  General Designs

The Freestanding Greenhouse

    Freestanding greenhouses are separate structures that are usually built when alarger growing area is desired than an attached design provides. Another reason is to obtain a better orientation to the sun. Plans should take into account an adequate amount of bench space, storage space and room for expansion. Large greenhouses are usually easier to manage because temperatures in small greenhouses vary more rapidly. Suggested minimum sizes are 8 to 10 feet wide by 12 feet long for a freestanding greenhouse. There are two basic designs: the shed-type and quonset hut. The shed-type design is oriented to where its long axis runs from east to west. The south-facing wall is glazed to collect the optimum amount of solar energy. The north-facing wall is insulated to prevent heat loss. Quonset hut greenhouses are rounded, symmetrical structures. Unlike the shed-type, they do not contain an insulated north wall. Instead, Quonsets you a process called Earth Thermal Storage to collect the solar energy in the soil, water, rocks or concrete. Insulating the structure is very important to prevent any loss of energy during the night.


freestanding
Freestanding Greenhouse from Sundance Supply

Links:
Photos of Freestanding Greenhouses
Sundance Supply Greenhouses
 


The Attatched Greenhouse

    Attached greenhouses are constructed as athermally efficient structure attached to the south side of another building, usually a house. It is a convenient way of adding more living space, not to mention at-hand growing area. Most people like the aesthetically pleasing look of an attached greenhouse and enjoy the benefits of the heating it helps provide to adjacent rooms. The most efficient use of space is to construct the greenhouse twice as long as it is wide. Most designs are 8 to 10 feet in width, making it 16 to 20 feet in length.

Attached Greenhouse
         
Attached Solar Greenhouse


Links:
Attached Solar Greenhouse in Virginia
Solar Greenhouse Fact Sheet
Attached Solar Greenhouses



The Pit or Subterranean Greenhouse

    A few inches below the frost line, the soil maintains a consistent year-round temperature of 50-degrees F. Thus, by constructing your greenhouse underground you can take advantage of the insulating properties of the Earth. Pit Greenhouses are popular in this regard because in a truly passive system they stay about 10-degrees warmer than a greenhouse built at the surface. Pit greenhouses can be constructed as freestanding or attached designs.

Attached Pit GreenhousePit Greenhouse Schematic
                            Attached Pit Greenhouse in Parks, Arizona                                                Typical Profile of a  Pit Greenhouse



Links:
Pit Greenhouses
Keppel Croft's Greenhouses


Solar Cold Frame

    Solar cold frame greenhouses are described as "solar-efficient hotbeds." They are constructed by people who wish to extend their growing season to include the whole year. They are considered versatile, efficient structures and applicable in situations where larger greenhouses are not appropriate. The design includes a south orientation, an opaque and insulating north-reflecting wall, and removable glazing.                                                                                                                                                                                                                                       
                                                                                                                                                                                                                                                              
Cold Frame

                 Links:                                        
Cold Frames and Hot Beds
Grow it Gold
ACF Greenhouses




                            Basic Solar Cold Frame Design
                            Image Courtesy of the Savvy Gardener



High Tunnels/Hoop Houses

    This type of solar greenhouse is big enough to stand up inside, which differentiates it from a low tunnel. Orientation for a high tunnel is not as critical as in other greenhouse designs. High Tunnels are being experimented with for tomato production in the Midwest during early Spring and late Fall periods. They cost roughly $US 0.75 - 1.50 per square foot and typically dimensions range from 10-30 feet width x 9-12 feet high and 96 feet long.

High Tunnels
                                                        Links:
Hightunnels.org
                                                        High Tunnel Fact Sheet
                                                        "Farming on the Edge - Growing Undercover"















IV.  Construction

    Construction of solar greenhouses vary immensely depending on the design and location. Since the purpose of this webpage is to give specifics on construction in developing countries, below are links to two very good websites which detail the construction of greenhouses in Nepal. We hope to include more construction guidance from other developing areas with more research.


Construction Designs for Greenhouses in High Altitude Areas

Mission Report Greenhouse applications / Nepal


V.  Examples:  Links to articles

    Although we are certain that many examples of solar greenhouse projects exist in the developing world, online documentation of these projects is scarce.  We found several articles that mentioned such projects and will continue to search for relevent examples.  If you know of any, please let us know by emailing to the address below.

Greenhouses Used to Grow Vegetables at Leh, India

Solar Greenhouses for the Trans-Himalayas: a Construction Manual

Pankar-huyu in Bolivia

Building the Pankar-huyu in Bolivia

Greenhouse Structure and Equipment for Improving  Crop Roation in Mild Winter Climates

Solar Power Village

Solar Strawbale Greenhouse in Armenia

Solar Greenhouse in Ladakh, Tibet

Food Producing Solar Greenhouses

High-Altitude Passive Solar Greenhouse in Village of Pomrang, India

Earthkeeping Technologies for Afghanistan




VII.  Conclusion

There are many benefits to constructing solar greenhouses in developing countries. Using appropriate local materials, they can be constructed to provide extended or even year-round growing seasons. The crops grown during colder months can be sold at the market during low-suppy time periods, demanding a higher price; or supplement food supplies for families and small communities. Fruits and vegetables are protected from the natural, and sometimes unpredictable environment. Plus, it will make your friends jealous and you'll likely be the talk of the town. Everyone will wonder why they didn't think of it first!


Go Solar or Go Home -
Happy Greenhousing!



VIII.  Other References

The Solar Greenhouse Book. Edited by James C. McCullagh. 1978. Rodale Press.

 Hobby Greenhouses and Other Gardening Structures

Compost Heated Greenhouses

Institute for Planetary Removal


This page was create on 3/16/2005
Last Update: 4/25/2005
Contact: Chris Fehrman, ctfehrma@mtu.edu
Luke Barrett, ljbarret@mtu.edu