Solar Greenhouses for Back
Yards and Neighborhoods
L. David Roper
Professor Emeritus of Physics
Virginia Polytechnic Inst. & St. Univ.
roperld@vt.edu
http://arts.bev.net/RoperLDavid/
This slide show is available on the Internet:
http://www.roperld.com/science/SolarGreenhouse.ppt
Eat Local
Average food is transported
~1500 miles.
 Peak Oil: This must stop!
 How to eat local food in the
winter months?
 Preserve by canning or drying.
 Grow in solar greenhouses.
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World Crude Oil Extraction
30
Peak Oil
Oil discoveries will not
allow higher average
extraction.
10^9 barrels/year
25
20
15
10
5
0
1900
1920
1940
1960
1980
2000
2020
2040
year
Extraction Fit
Extraction Rate
2060
2080
2100
You can’t extract it if you have not
discovered it!
World Crude Oil Discoveries
60
Areas under both curves are the same.
That is, the amount discovered equals the
amount extracted. Mass is conserved.
10^9 barrels/year
50
40
30
20
10
0
1900
1920
1940
1960
1980
2000
2020
2040
2060
2080
2100
year
Discoveries Rate
Discoveries Fit
Extraction Rate
Extraction Fit
The areas under the two curves are the same: ~2x1012 barrels.
Solar Greenhouse Principles
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Double-glazed long side roof facing south.
North, east and west walls well insulated.
North roof well insulated.
Foundation well insulated.
Sealed to prevent air infiltration.
North wall and north roof reflective on inside.
Heat storage to gather heat when Sun is
shining to be released to greenhouse air when
Sun is not shining.
Standard SGH Heat Storage
Water is the best medium.
 Rocks are second best.
 Soil is the third best.
 The big question is:
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How does one get heat supplied by
the Sun transferred to the storage
medium?
Heat Transfer from Sun To Storage
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Standard methods:
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Direct radiation.
Air flow, passive or active.
Subterranean Heating and Cooling System
(SHCS):
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Use phase change of water vapor to liquid to get
large amount of energy stored under planting beds.
An Integrated system with plant transpiration of water.
Use small fan to blow hot moist air, or cold dry air,
under the planting beds for energy exchange.
Subterranean Heating and Cooling
System (SHCS)

When the Sun is shining, 90% of
water taken up by plant roots is
transpired (evaporated) into the
air, which makes the greenhouse
air hot and humid. Much of the
photosynthesis energy provided by
the Sun is used for this purpose.
Subterranean Heating and Cooling
System (SHCS)

SHCS pushes that hot and humid
greenhouse air into the rocks/soil
under the planting beds where the
water vapor condenses into liquid,
releasing a huge amount of energy to
be stored as heat energy in the water
and rocks/soil there. The air emerges
into the greenhouse cool and dry.
Subterranean Heating and Cooling
System (SHCS)

When the Sun is not shining,
SHCS pushes the cold and dry air
of the greenhouse under the
planting beds where it is heated
and made humid. The air emerges
warm and humid.
Subterranean Heating and Cooling
System (SHCS)

Thus, an artificially
moderate “weather system”
that is beneficial for plant
growth is created in the
SGH, in cooperation with
the plants’ transpiration.
First SHCS (China 1990)
Bricks made from local clay were used for the
ducts under the planting beds and the main duct.
 Fan has two thermostats: one turns fan on at 20°
C (68° F) and off at slightly above 15° C (59° F);
the other thermostat turns fan on at 10° C (50° F)
and off at slightly below 15° C (59° F).
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USA Version of SHCS (Colorado)
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Use three layers of 4” perforated corrugated
drain pipes 2’ apart horizontally and 1’ apart
vertically below planting beds, surrounded by
rocks and dirt that will hold maximum amount
of water.
Push the greenhouse air through the perforated
pipes, entering from the east side and exiting
on the west side.
Using petroleum products to create the
infrastructure to reduce the amount of
petroleum burned, which is its best use.
SHCS Design Criteria
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Flow greenhouse air volume underground 5
times per hour when fan is operating.
Restrict flow in underground drain pipes to
less than 4 ft/sec.
Adjust thermostat #1 to turn fan on at 70° F
and off at slightly above 60° F.
Adjust thermostat #2 to turn fan on at 50° F
and off at slightly below 60° F.
Keeps greenhouse temperature between 50°
F and 70° F and air humidity in a middle
range.
Neighborhood Solar Greenhouse
• Area = 576 ft^2
• Volume = 4750 ft^3
• Glazing: double-walled
polycarbonate at 45° slope
• North insulated 6”-thick
roof at 60° slope
• 6” insulated north wall
with berm
• 2” termite-protected
extruded polystyrene
around foundation and
heat storage
Neighborhood Solar Greenhouse
Neighborhood Solar Greenhouse
Dave Nickerson Model of a
Neighborhood SGH
Back-Yard Solar Greenhouse
• Area = 200 ft^2
• Volume = 1340 ft^3
• Glazing: double-walled
polycarbonate at 50° slope
• North insulated 6”-thick
roof at 60° slope
• 6” insulated north wall
with berm
• 2” termite-protected
extruded polystyrene
around foundation and
heat storage
Back-Yard Solar Greenhouse
Back-Yard Solar Greenhouse
Cistern for Rain Water for Plants
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A 1500-gallon cistern for the SGHN and a 500gallon cistern for the SGHBY to collect rainfall
on the roof, placed underground for gravity
flow from roof and to keep water at proper
temperature for plants.
A hand pump or electric pump to lift the water.
A drip irrigation system to conserve water and
to minimize overwatering.
An overflow directed far away from the SGH.
Easy Composting
Fill one while the other is composting.
 Low sled makes it easy to empty and transport.
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Carbon Dioxide and Composting from
Worms in the SGH
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Red-worm beds over the 24” pipes at the ends of the
SGH sufficient to supply carbon dioxide and compost
for the plants.
Fed by partially-composted organic matter brought
into the SGH.
The worm-castings finished compost is regularly
deposited on the growing beds for plants.
Provides a closed cycle between the oxygen expelled
by the plants and the carbon dioxide expelled by the
worms. The fuel is the partially-composted organic
matter regularly brought into the SGH.
Natural Pest Control
Garlic, onions, mints, chives & herbs
scattered plantings
 Lizards (also supply carbon dioxide)
 Toads (also supply carbon dioxide)
 Lady Bugs
 Praying Mantises
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Proposed Network of Solar
Greenhouses for the NRV
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Build a test neighborhood SGH using
SHCS somewhere in NRV.
Build a test back-yard SGH using SHCS
somewhere in NRV.
Collect data for a year.
Build more SGHN and SGHBY in the
NRV.
VT YMCA Community Gardens
First location of a
neighborhood solar
greenhouse in NRV.
Construction
completion scheduled
for 1 October 2008.
First plantings
scheduled for
1 November 2008.
Maywood
Street
SGH at YMCA Community Gardens
Maywood Street
Thanks so far!
Gail Billingsly (YMCA)
Pat Bixler (Steering Committee Chair)
Tim Colley (Architect)
Dave Nickerson (Model Builder)
Travis Rookstool (Architecture Student)
Volunteers Needed!
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Excavator
(Insulated Concrete Forms)-experienced person
Carpenters
Plumber for cistern installation and watering system
Electrician
Solar greenhouse manager
Horticultural researcher
Want More Information about the
SGH Project for the NRV?
Give your e-mail to
Dave Roper (roperld@vt.edu)
to be put on a SGH interest-group list.
Send ideas about the SGH project to
Dave Roper.
This slide show is available on the Internet:
http://www.roperld.com/science/SolarGreenhouse.ppt