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.*
Is a Solar
Greenhouse Appropriate for Your
Location?
- Does your location have cold temperatures that prohibit growing
during certain times of the year?
- Is it sunny where you live at least 50% of the time?
- Would you like to extend your growing season?
- Would the benefit of crops during the cold season outweigh the
costs of construction?
- 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
- Passive Solar Pit
Greenhouses
for the Developing World
- What
is a Solar Greenhouse?
- The Basics of Passive Solar Design
- Links
- Appropriate
Materials
- Cost
Estimations
- Nepal
- Bolivia
- Tibet
- Africa
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
- Solar radiation enters the greenhouse through the
glazing in
the form of light and is absorbed by the plants and other surfaces.
- 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.
- 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.
- Heat can be lost by
radiation, convection and conduction. Most
of the losses will occur by conduction through the
walls of
the
structure.
- 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.
- 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.
- 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.
- This natural exchange of heat is the beauty
of a passive system.
Here are some
links for further reading on passive
solar design:
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
Greenhouse from Sundance
Supply
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 Solar Greenhouse
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 Greenhouse in Parks,
Arizona
Typical
Profile of a Pit Greenhouse
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.
Links:
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.
Links:
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.
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
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
