Passive solar greenhouse

1. PASSIVE SOLAR GREENHOUSE
Dr. Ajay Singh Lodhi
Assistant Professor
College of Agriculture, Balaghat
Jawahar Lal Krishi Vishwa Vidyalaya, Jabalpur (M.P.)

2. INTRODUCTION
 A passive solar greenhouse is a
greenhouse heated entirely by sunlight,
with no additional fuel based heating.
 Passive solar greenhouse absorbs as
much as possible solar energy (sunlight
during the day) in the winter season for
the following gradual emission of
accumulated solar energy for heating
purposes.
Operation principles
 The main operation principle of a solar
greenhouse lies in accumulation and
storage of solar energy (sun radiation)
during daytime and gradual release of
the energy (heat) during the night.

3. Thus, solar greenhouse:
 Collects the maximum amount of solar radiation during the day;
 Efficiently stores the heat collected from sun radiation during the
day;
 Releases this heat to the interior of the building during the night;
 Heat losses are reduced by insulation of the whole greenhouse;
 Can be ventilated to avoid overheating.
Coverage
 Passive solar greenhouses are widely disseminated in China
since 1970s; where currently over 700 thousand ha are occupied
by solar greenhouses.
 Greenhouses of this type are suitable for use in other areas of
the Hindu Kush, Himalaya, and Pamir ranges with a similar
climate and socioeconomic situation, such as the high valleys of
India; Nepal; Bhutan; Pakistan; Afghanistan; Tadjikistan,
Kirghizstan and Uzbekistan in Central Asia.

4. Site Selection
 Site selection is key. A passive solar
greenhouse is basically a solar
collector, however it is collecting
solar energy for heat and
photosynthesis.
 Your ideal orientation is going to be
~15 degrees to the east of South in
the Northern Hemisphere. This
optimizes morning light and heat
when the greenhouse is coldest.
 Having said that, if you have limited
options you can orient it up to 45
degrees off south and still get a
decent result.
 Choose a site selection that gives
you good access to sun all year
round.

5. Design
 Passive solar greenhouse is designed along an east-west
axis, with the length of the south face increased and angled
to present the largest possible surface area to the sun.
 The size of the east and west facing walls are reduced to
minimize heat loss and shade inside the greenhouse, and
the north wall is heavily insulated.
 The design of a greenhouse for a specific location is
influenced by the site characteristics, the climate, and the
expected amount of snowfall.

6. Structure
The structure of a passive solar greenhouse consists of the
3 main elements:
 Walls on the east, west, and north sides;
 Wooden carcass with a polythene sheet on the south side,
which picks up the largest amount of solar energy. The
polythene sheet is set at an angle and supported by a
wooden frame. Depending on financial capacities,
weather conditions and the will of agricultural producers
the carcass can be made of metal and covered with glass;
 A (solid) roof on the north side to limit heat loss. The roof
is tilted to avoid shading in winter and reduce the interior
volume.

7. The walls of a solar greenhouse need to have heat insulating
properties for preventing heat loss through the walls. For this
purpose, the walls are composed of three layers:
 1. An inner wall used to store heat during the day and release it
a night, also built with mud brick, rammed earth, or stone and
painted in black for better heat absorbing;
 2. An insulating layer of materials like straw, sawdust, wood
shavings, dry leaves, dry grass, or wild bush cuttings pressed
between the two.
 3. An outer load-bearing wall built with mud brick, rammed earth,
or stone.
 Very important is also to install a good ventilation system with
doors on both western and eastern walls and windows in the
roof.
 Moveable insulation (parachute, cloth) is used as a curtain below
the polythene after sunset to reduce heat loss; it is removed
after sunrise. Alternatively, a so called thermo-blanket can be
installed above the polythene cover (or glass cover) to block the
heat inside the greenhouse and establishing a buffer layer
between the cold air and the transparent (southern) wall of the
solar greenhouse.

8. Construction steps
 The actual construction can start after the appropriate location
site is selected and all the materials are prepared. The
construction itself can be divided into the following basic steps:
 (1) Constructing the foundation. Foundations are the basis of
every structure. The orientation and outline of the wall positions
must be exactly as given in the design to ensure maximum
efficiency of the greenhouse. The outline of the walls is first
drawn on the ground and the foundations are then dug and filled.
 (2) Building the walls. The walls are built on the foundations.
The walls must be shaped in the precise way shown in the
designs so that the roof angle is correct. The back wall is a
simple vertical wall whose top is parallel to the bottom. Low
density materials (light materials like straw, sawdust, wood
shavings, dry leaves, and dry grass) are poor conductors and
storers of heat and are thus good insulators: they help retain the
heat inside the greenhouse. These materials are filled into the
cavity between the loadbearing wall and the thermal mass wall.

9.  (3) Making and installing the door. A door is
built into the wall to provide access and act as a
ventilator for cooling. It is constructed in the wall
opposite to the prevailing wind to reduce
unwanted drafts.
 (4) Making and installing the wall ventilator. In
order to cool the greenhouse by natural
ventilation, a side shutter is installed across from
the main door in the opposite wall. The ventilator
is composed of a fixed frame and an articulated
shutter.
 (5) Constructing the roof. The north and side-
walls of the greenhouse are constructed in a
shape that supports the roof.
 (6) Making and installing the roof ventilator(s).
One or two ventilators are installed in the roof of
the greenhouse, and the door and wall shutter
provide the lower openings. The roof ventilator
frames are installed at the same time as the roof
structure is constructed.

10.  (7) Finishing the walls.
 (8) Installing the polythene sheet. It is very important
point to ensure that the polythene sheet is stretched tight
and attached firmly to prevent it flapping in the wind. If this
is done properly, the sheet can last as long as seven
years. If not, damage resulting from flapping and rubbing
can destroy the sheet in one season. Polythene expands
with heat, so it should be fixed during the warmest hour of
a sunny day when it is well-expanded so that it becomes
taught as it cools. If it is fixed when cold, it will later expand
and become loose, and be more susceptible to wind
damage.
 (9) Installing night insulation. The insulation is only
effective if a space is left between the polythene and the
cloth and the air inside this space is trapped; the cloth
must be air-tight and the join between the cloth and the
polythene sealed at the top, bottom, and sides. The cloth
may be wet in the morning and should dry during the day.

11. Advantages
 Enough solar radiation is accumulated for the photosynthesis
process, needed for the plants;
 Interior climatic conditions required for growing vegetables all
year round is shaped and sustained;
 Heat losses are reduced due to thick 3-layer walls on the east,
west, and north sides;
 Design of the efficient passive solar greenhouse along an east-
west axis, with the length of the south face increased and angled
allows the largest possible surface area to the sun;
 Basic vegetables subsistence needs in remote areas can be
fulfilled;
 Rural population gets additional income generation possibility;
 Materials for constructing of solar greenhouse are locally
available wood, straw, stone), except for the transparent cover
sheet or glass for covering the southern wall;
 Can be constructed by local builders;
 The investment costs can be recouped in less than three years if
the production is well-managed and the products sold;

12.  References:
 http://www.cacilm.org/en/technologies/section/gree
nhouses/solar#:~:text=A%20passive%20solar%20g
reenhouse%20is,solar%20energy%20for%20heatin
g%20purposes.
 https://medium.com/@rob_74123/how-to-design-a-
passive-solar-greenhouse-part-1-of-3-
8c08ccbfbde8

13. Thank You