Sustainable Fig Farm Using Renewable Solar and Geothermal Energy
During 2006 the transplanting of over 500 fig trees was completed using cuttings from the fig trees that were successfully grown thanks to a 2005 Missouri Sustainable Agriculture Demonstration Award grant from the Missouri Department of Agriculture and University of Missouri. Cuttings from three different varieties were used and another two varieties have also been adapted for use in the future.
The installation of the Solar System was completed and turned out to be an exceptionally valuable attribute of the High Tunnel allowing very accurate and consistent control of temperature inside the High Tunnel. The Solar System uses only one single 110 W Photovoltaic panel, which charges two 12V batteries. The power stored in the batteries is sufficient for automatic opening and closing of the two 96-foot curtains along each side of the High Tunnel via the Curtain controller and an adjustable thermostat. The System opens automatically in the morning when the temperature inside gets above the preset temperature and closes in the evening when the temperature drops below it. The system kept working during the big summer storm that left more than half a million residents in the St Louis area, including our home, without power for almost a week. This alone paid off by saving my crop inside the High Tunnel. It also saved the High Tunnel from lifting up by closing the curtains in time before an 80-mile-per-hour storm hit our area and broke big cedar trees like toothpicks.
The design of the subterranean geothermal and solar heating and cooling system was completed and consists of a total of 4,200 feet of 4-inch corrugated polyethylene slotted pipe in two equivalent system units. The pipes in each system are buried in 15 parallel trenches, 3 inches deep. Every trench has sets of three pipes, 1 foot of center above each other and 2 foot of center between the trenches. The pipes collect perpendicular in 30’x12” culverts on each end side of the Tunnel and in two parallel 30’x12” culverts in the middle of the Tunnel. The culverts open into 55 gallon drums. Two 1000 cfm fans are mounted on two of the drums and the other two are used as plenums for the exiting air.
The fans are turned on automatically when the temperature reaches above the desired 85 to 95F and the hot air is circulated under the ground. The hot moist air reaches dewpoint and the water vapor condenses, releasing the solar generated heat into the ground and comes out as a colder air with lower humidity. This allows the system to store the solar generated energy in the huge thermal mass of the soil and use it later in the season or at night when needed. The thermal mass can store over 20 million BTUs that can be released for 3 months later through the cold winter season. The constant geothermal energy input from the depths of the earth maintains a constant 55 F temperature of the ground during winter. The big surface of 44,000 square feet of the underground pipes allow for a very efficient heat exchange with the enormous thermal mass of the soil. At the same time it allows me to control the temperature and the humidity without opening the high tunnel.
Thus the Subterranean geothermal and solar heating and cooling systems converge to provide a better utilization of the solar and geothermal energy. While the single panel solar system is sufficient to run the automatic opening and closing of the curtains, as well as the small air blower used to inflate the double polyethylene roof, it is not sufficient to run the fans for the subterranean system or the fan of a backup heater.
For this purpose it was necessary to install an electric hook up to the nearest electric post on the property. The hookup was completed successfully with the adequate permits. In the future if an entirely solar photovoltaic system is installed to power the subterranean system, it will be possible to sell back electricity to the utility company during the periods when excess electricity is produced.
The first major result in 2006 was the transplanting of over 500 fig trees, which establishes the beginning of a Sustainable Fig Farm and the supplier of fig trees for many other Sustainable Fig Farms in areas where it was not possible to grow them before. There are already three orders for fig trees for three High Tunnels in Missouri and one already sold in Kansas and more are expected next year. It turned out that there is a significant interest in growing figs in High Tunnels and additional profits will be made from selling fig trees.
The second result was the installation of the photovoltaic solar system, which opens and closes automatically the side curtains for temperature control inside the High Tunnel. Using the thermostat, various temperature settings were used for the growing of the different crops in accordance with their requirements. Thus it was possible to grow simultaneously several crops in the same Tunnel starting with early crops of lettuce, green unions, radishes at lower temperatures, followed by strawberries, later at 85F with tomatoes, peppers and eggplants and finally at the highest thermostat settings of 100 F for the period of figs ripening.
The third important result was the completion of the thermodynamic calculations and design of the Subterranean Geothermal and Solar Heating and Cooling System, which will allow a better utilization of the geothermal and solar energy for further extension of the growing season in the High Tunnel. The energy from the summer and the daily excess of heat beyond that will be used for heating in the colder seasons. The necessary electric hookup to power the fans of the subterranean system, as well as the blower of the backup heat furnace, was completed successfully.
For a comparison reference I called a restaurant in San Diego, California during the first week of October and I was told that they had just discontinued from the menu their salads with figs due to closing of the season for fig supply. I was still picking figs from the High Tunnel in December.
WORK PLAN FOR 2007
The major work will be associated with the completion, testing and data generation for the performance of the Subterranean Geothermal and Solar Heating and Cooling System, and its effect on the growing of figs and other fruits and vegetables with emphasis on extension of growing season, quality and quantities of products and their marketing.
Caring for the Sustainable Fig Farm will continue and more transplants will be produced from the next year’s cuttings for sale to other farmers.
Preliminary data will be generated in regard to using the Subterranean Geothermal and Solar Heating and Cooling System in conjunction with a waste vegetable oil furnace. The coupling of the subterranean system with the waste vegetable oil furnace has a mutually beneficial effect. The furnace is an important component for a backup for the subterranean system during extremely low temperature periods as well as late in the cold season when the capacity of the system is exhausted. On the other hand the subterranean system can significantly reduce the quantity of oil required if the furnace was used alone for heating the tunnel. The goal will be to obtain year round temperature control in the High Tunnel for year round production of warm loving plants, the dream of every grower. Currently High Tunnels are either not used in cold periods due to the high heating cost or only limited low temperature resistant crops, like lettuce, are being grown.
There are millions of gallons of waste vegetable oil produced that could be efficiently utilized for that purpose. In the long term with the depletion of fossil fuels on the background of constantly growing prices, the vegetable oils will become an important alternative renewable energy source for heating. Farmers are already setting aside a portion of their land to produce oil for bio-diesel. They could do the same for oil for heating purposes if they had an efficient system using cheap and renewable energy source.
During 2006,I organized several field trips for people interested in the project. I had over 50 visitors. Among them was Lewis Jett – Horticulture Specialist, University of Missouri Extension; Steve Sparks – Manager Whole Foods St. Louis – accompanied by 6 associates; Niel Zimmerman – manufacturer of High Tunnels (now incorporated under Morgan County Seed Supplies); Mari and Jacob Zimmerman from Versailles, MO; Curtis Langwish from Kansas. As a result of the visit, Curtis is now in the process of building his new High Tunnel that will be dedicated to growing figs, which he already purchased from my farm.
I participate with presentations at the Great Plains Vegetable Growers meetings and will give presentations in St. Joseph MO on January 11, 2007 and in Columbia, MO in the fall of 2007. As a member of the online High Tunnel group, I participate by providing information on successful achievements of the project that may be useful to other growers. There are several requests for interviews by news media, magazines and newspapers.