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Solar Power Your Garden Dome

How to harness the power of the sun – Use the suns radiant solar energy to heat your dome

As with all greenhouses, dome greenhouses make excellent solar collectors. One reason why a dome can make more efficient use of solar energy is due to the round shape; one or more dome triangles is always on a nearly straight direct path to the sun overhead. There is a more consistent, even warming effect through out the day. Inside the dome air circulates more freely bottom to top for more ventilation and healthy plant life. For best ventilation use a cupola top with windows and exhaust fans or one or more fans attached to the dome frame. Use thermostat controlled fans, heaters and cooling system. A computer with special software can regulate the temperature and operate and monitor irrigation, humidity and other factors. Thermal actuators such as the Uni-vent can automatically operate windows.

Passive Solar Collectors

I use 55 gallon drums filled with water for my solar collectors. The are flat black plastic, previously used for detergent for car washes. The flat black absorbs more of the suns light energy, don’t use a shiny black as it reflects the light. I have 9 of them in my 15 ft. Garden Dome 2 with the Base Option, and more would do well in climates further north. The top of the drum gets the hottest. When the temperature warms up I put plants and shelves on the tops of the drums. Also the water can be easily poured or siphoned out, and the drums taken out too. I live in north Texas so the freezes aren’t that regular, and I need only a small electric heater with thermostat control to keep the dome temperature around 55-60 degrees F when it is around 32 outside. Any dark colored jugs filled with water will absorb heat during sunny days and dissipate heat at night inside the dome.

Another solar collector is rock. I’ve noticed rocks inside my dome get hot on sunny days. If they are dark colored they will get even hotter. This method of passive solar collection is a valid option to water containers. One way to do this is to make a cage of fence material to stack your rocks in, located in a position to receive maximum sunlight. A fan on the rocks will circulate the heat given off at night.

Rigid foam insulation inserted into the north triangular faces of the dome will help retain heat during winter. The silver lined type will reflect light back into the dome. Press to fit panels are easily installed and removed. For cutting them out, try making a triangle template with large cardbourd or plastic film, and marking the outline on the foam board.

I have a ceiling fan to circulate air and blow warm air down as the dome height is about 10 feet. The fan is attached on a pentagon shaped piece of 1/2″ plywood, that is screwed onto the five top struts of the dome. For greatest floor area and least height, the Garden Dome 3 is best.

Winter observations from my own Garden Dome 2 that I use as a workable demonstration dome.Inside the dome there’s no wind, circulation must be created when the windows are closed. I use the ceiling fan and an excersize bike that has a fan incorporated. I have only ornamental plants of many types, but the carbon dioxide I put out is important to them. It can be very windy outside but calm inside the dome. There’s no wind chill factor. If it is 30 and windy outside and snow on the ground, it’s 50 inside the dome on a cloudy morning and that’s without using the small electric heater. I’m not using the foam insulation, only super poly and my dome is 98% sealed from outside air flow. We had a “mild” winter.

Summer observations. The dome was getting too hot inside (110+ degrees F) so we added some misters, window, shade cloth and an extra fan. Some of the plants were baking while others (succulents) have adapted quite well to the heat. I constructed a hinged triangle frame window/vent and placed it on a top triangle. Then spray atomizer misters ( Misty Mate brand) were attached to upper dome struts, and a Y connector for a water hose in the dome (misters are plugged right into a garden hose). Next a square piece of shade cloth was stapled inside the dome to reduce afternoon heat on the herb growing area; an an extra fan to supplement the ceiling fan. We’ve had a period of unusually record breaking hot days and little to no cloud cover or rain for 3 weeks. June ’98

Some pre-engineering of you dome foundation can bring more passive solar heat by using the ground as the solar collector. Here are some ideas of how to do this:

1. Where your dome floor will be dig down about 2 feet. Here you will insulate from the ground up. Put in hard foam board insulation right on the dirt.

2. Tubes below your dome floor will bring the heat collected in the soil into the dome with a circulation fan. Array these tubes strategically spaced on top of the foam insulation. Connected pvc tubes will work well and support the weight of the dirt on them. A blower will circulate the warm air from the conducting tubes into the dome. Your insulated dirt floor makes an excellent solar collector. And you can still grow plants right in the soil without interference. Plants will do well with a warmer ground temperature. Your growing medium/soil can be replaced conveniently as necessary.

Below your dome frame base perimeter, a cinderblock retainer wall can be placed in the ground when you are excavating for placement of the foam insulation and tubes. This will also allow you to insulate the below ground block wall with foam board insulation.

3. Fill the hole back up with the excavated soil. This is your solar collector so you might plan on where no shadows are likely to be.

Some more ideas about using your Garden Dome for growing

  • Retain heat in winter with insulating techniques and solar collectors
  • Ventilate in summer with windows and fans.
  • Use thermometer to regulate temperatures Shade Thermometers, place away from direct sunlight for most accurate readings
  • Store water for heat collectors in black containers; flat black paint may be used
  • Clear jugs may be used; add black paint to the water to make it opaque.
  • Situate water heat collectors next to north side foam board insulation panels to avoid blocking light on plants
  • Use weather stripping at doors and windows and rubber sealant to minimize air infiltration
  • Grow plants/vegetables suitable for the season and temperature
  • Wind, clouds, sun, growing zone and other factors determine growing invironment-dome air and soil temperature
  • In winter heat the water in the drums (or one that is centrally located) with a submersable heater 800 – 1000 watt; or space heater near the drums
  • Use shade cloth during summer to reduce heat; it works best installed on the outside
  • Use windows with screens, for cross ventilation
  • Use an exhaust fan
  • Monitor temperatures more closely in Spring and Autumn when temperature variations may be greater
  • A thermal actuated automatic window opener works well
  • Clean the covering once a year. Use biodegradable detergent
  • Use double layers of film, and silver backed foam board for insulation.
  • Make removeable triangle panels that are covered with the horticultural film such as our Super Poly. These can be installed in winter for heat retension and removed in summer. Or attach shade cloth to reduce heat in summer. 1″ x 2″ wood will make a good frame for the removeable triangles.

 

Resources:
Books:

  1. Sunset- Garden and Patio Building Book (by Sunset Books and Magazine Copyright 1969). Old but usefull, lots of good illustrations.
  2. Growing Solar Food In Greenhouses (by Delores Wolfe, Copyright 1981, Doubleday & Company, Inc., ISBN 0-385-17603-1) “A month-by-month guide to raising vegetables, fruits, and herbs under glass” 1st Edition, 192 pages.
  3. How to Build and Use Greenhouses (by Ortho Books, Copyright 1978, ISBN 0-917102-74-6) Lots of nice color photos, charts and drawings; 95 pages.
  4. The Complete Greenhouse Book (by Peter Clegg & Derry Watkins, Copyright 1978, Garden Way Publishing, ISBN0-88266-142-6) “Building and Using Greenhouses from Coldframes to Solar Structures” More thorough and technical, 280 pages.
  5. The Big Book of Gardening Skills (Copyright 1993, by the editors of Garden Way Publishing, Storey Communications Inc. ISBN 0-8826-796-3) Good book about gardeing in general with one chapter dedicated to greenhouses. 346 pages
  6. Add-On Greenhouses and Sunspaces (by Andew M. Shapiro, Copyright 1985, Rodale Press, ISBN 0-87857-507-3) “Planning, Design, Construction” Very thorough, 355 pages. Mostly pertains to adding to an existing structure.
  7. Greenhouses, Cloches and Frames (by Peter McHoy, Copyright 1984 Blandford Press UK, ISBN 0-7137-1244-9) All aspects of flower and vegetable greenhouse gardening 128 pages w/ color photos
  8. Building a Solar Heated Pit Greenhouse (by Greg Stone, Garden Way Publishing Bulletin A-37, Copyright 1980) 28 page booklet with plans to build a partially sunken greenhouse that uses the earth and sun for heating.
  9. Building and Using a Solar Heated Geodesic Greenhouse (John Fontanella and Alvis Heller, Garden Way Publishing,  1979) Very informative but the dome building technique is difficult and primitive.

On the World Wide Web:
Solar Links from Sierra
Florida Solar Energy Center
Research in Environmental Architecture (good article on solar greenhouse by architect Raold Gunderson)
Garden Web – Greenhouses and Structures Forum