Sustainable Fig Farm Using Renewable Solar and Geothermal Energy

Final Report for FNC05-559

Project Type: Farmer/Rancher
Funds awarded in 2005: $6,000.00
Projected End Date: 12/31/2007
Region: North Central
State: Missouri
Project Coordinator:
Ivan’s Fig Farm
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Project Information


The major efforts are focused on growing Figs but a variety of heirloom vegetables are successfully grown on the farm. Currently one whole High Tunnel equipped with a solar panel for automatic opening and closing of side curtains and a Clean Burn furnace for heating with waste cooking oil is dedicated to growing several varieties of Figs. A second High Tunnel with an underground geothermal and solar heating and cooling systems is under experimental testing of new alternative energy sources for growing in High Tunnels.

I developed a method for sustainable growing of figs both outside, and in a High Tunnel, by using leaf mulch for protection from the winter freezing conditions. I also practiced organic gardening for tomatoes, papers, herbs and other vegetables for over 20 years.

The goal of this project was to establish a sustainable Fig Farm in Missouri, to grow and sell fresh ripe figs locally, instead of shipping them from far away places like California.
Another goal of the project was to research and develop a better utilization of Solar and Geothermal Renewable Energy in a High Tunnel, by converging them into a complete and efficient GEO-SOLAR renewable energy system.

By carefully analyzing the results and data from growing figs in a High Tunnel I came to the conclusion that the current High Tunnel use has big limitations for temperature control during nighttime or on cloudy days and inefficient utilization of the solar energy in the cold but sunny winter days. For example in the middle of the winter on a sunny day the High Tunnel can quickly build up temperatures in excess of the normally required and the curtains of my High Tunnel would open automatically, releasing all this enormous amount of energy outside through the open curtains. This waste of energy seemed even more absurd, after knowing how hard it was fighting the single digit temperatures over night, burning 1.2 gallons/hour waste cooking oil in the Clean Burn furnace, to barely keep it from freezing inside the Tunnel. It was not difficult to come to the idea of finding a better way of utilizing this wasted energy, when seeing the heat going out through the curtains, soon after the sun comes out early in the morning. The solution was to trap this extra heat during the day and then use it during the cold night, when the temperature inside the Tunnel is almost the same as outside. That is how I came with the idea of trapping the heat into the heat sink of an underground system. In addition the underground system could tap into the practically unlimited geothermal heat source with a constant 55-60 F temperature. Thus such a system uses both alternative energy sources for heating at night and cooling during the day, converging them into a complete and efficient GEO-SOLAR renewable energy system.

The design and technical completion of the project was very challenging. Earlier attempts to build a system with 100‘ long 4” pipe at a depth of 10’ have failed (see University of Missouri Demonstration Award Grants ). The authors had reported very high backpressure and less than 10% flow through the underground system.

The design of our system consists of two separate systems for each half of the High Tunnel. Each system uses three layers of 45’ long, 4” corrugated pipes, parallel to each other at 22” off center and 18” off center above each other. The pipes are joined by perpendicular 12”culverts – two in the middle and two at each end of the High Tunnel at one half the dept of the excavation (see picture). The whole system is installed into a 3-4” deep excavation within 1” of the perimeter of the Tunnel. The bottom layer of pipes of the system was laid over a 6”thick layer of 1” clean gravel for drainage of the condensing water, then covered with another 6” of gravel, thus entirely buried in a water permeable drainage bed with a drainage pipe installed, opening outside way from the Tunnel. A layer of soil separating cloth was put on top of the gravel layer before laying the second layer of pipes. Then the other two layers of pipe and two layers of soil were installed. The whole process was done with a wide track bobcat to avoid smashing of the pipes under the 6000 LB equipment. A top layer of 2”soil was placed for the roots of the plants. The 1”culverts opened into four 30gallon drums installed on each end with two1500cfm fans mounted one on each system. The fans are coupled with two stage thermostats so that thy can operate only when the temperatures go above or under the normal growing temperature range. Thus the system is fully automated and can be adjusted for wide range of temperature choices.

The following people and businesses were involved in the process of putting together the High Tunnel with the subterranean geothermal system:

• George Saltz Excavation did the excavation of the 4’deep trench and back filled stepwise the gravel and soil over each layer of pipes installed.
• My neighbor Willibald Pfeiffer and Henry Rentz, Missouri Valley Renewable Energy, helped with the installation of the pipes, culverts and fans of the system as well as the High Tunnel installation.
• Fifteen friends and neighbors came to help with the covering of the High Tunnel with the double layer of polyethylene.
• Dean Wilson, Agriculture and Rural Development Specialist has strongly supported the research and development activity of the project and his recommendations were very important for the grant application.

The key result achieved was the sustainable way of heating a High Tunnel during the cold season, using more efficiently on one hand geothermal energy and on the other hand storing the excess solar energy in the heat sink under the High Tunnel and using it back at night for heating. This results in a better control of the big fluctuation of temperature inside a Tunnel without the use of fuel, wood or other carbon dioxide emitting sources. The new system will enable farmers to further extend growing in a High Tunnel off-season when it was not possible before without the use of additional CO2 emitting heating source.

The High Tunnel equipped with the SGSHCS was tested simultaneously side by side with the first High Tunnel equipped with furnace at the coldest temperatures outside of ~0OF. The results were amazingly good. The temperature difference was only 3-5 degrees between the heated with oil Tunnel and the no oil Tunnel with SGSHCS system while the temperature outside was ~0OF. This means that the SGSHCS system can provide the equivalent energy of at least 150,000 BTU/h furnace, without using any oil. The lowest temperature of the air coming from the ground below was 48F after a prolonged week of no sun and single digits night temperatures. The system regenerates quickly the lost heat as soon as the sun is out even on a very cold day. Since it takes ~ 1500 gallons of waste oil for a winter season to keep the High Tunnel warm and above freezing at night and on cold winter days, the use of a furnace coupled with the SGSHCS will save a lot of oil and allow to achieve higher temperatures at much lower cost.

Another result as part of the project was the planting of more than 500 fig cuttings outside and 500 inside the new Tunnel with the SGSHCS system for comparison of the success of transplanting under these extremely different conditions.

Thanks to this grant it was possible to design and build up an alternative energy system for better utilization of the solar and geothermal energy in a High Tunnel. It is now possible to grow figs in the Tunnel providing protection from freezing even in the coldest subzero temperatures in the winter, when the fig branches freeze to the ground even in a High Tunnel without additional protection. The figs don’t have to be pruned all the way down and covered with leaf mulch or any other protective cover. In early spring and late fall it uses all of the excess solar energy that is lost through opening of the High Tunnels curtains to protect the plants from overheating. This energy is used at night to increase the soil and inside temperature. The results from this project open the doors for further applications of growing in a High Tunnel and research in optimization of the use of GEO-SOLAR systems. For example it would be useful to find out how much deeper or wider the underground system could be installed to provide a even better utilization of the geothermal and solar energy. The surface area is critical for the heat exchange processes taking place under the ground. The 4320 sq ft surface of the underground system is approximately equal to the above ground surface. A higher surface will allow for a faster and more efficient energy transfer to and from the underground heat sink.

Evaluate the economic, environmental and social impacts of this sustainable practice by completing the enclosed forms. Also, if possible, provide hard economic data.

The energy provided by the new system was found to be almost equivalent to a 175,000 BTU/hour furnace. Since it takes ~ 1500 gallons of waste oil for a winter season to keep the High Tunnel warm and above freezing at night and on cold winter days, the use of a furnace coupled with the SGSHCS will save the equivalent of 1500 gal of heating oil per 2880 sq. ft of High Tunnel or 22,708 gal/acre. At current prices of ~$2.70/gal of heating oil, it equals $61,312/acre.

The ever rising price for heating and cooling will make the use of the alternative energy sources now and in the long term a sustainable and environmentally friendly solution. The system is completely automated and does not require farmers to spend time and efforts on opening or closing curtains or vents at the right but not always predictable time. The fans do not consume much energy and could be powered entirely by solar photovoltaic or wind energy and there will be no CO2 emission.

I had the wonderful opportunity to be invited by Dr Ted Kerry, University of Missouri Kansas as a plenary speaker at the Great Planes Vegetable Growers Meeting in 2007 in St. Joseph, Mo. The presentation allowed me to present my ideas about using alternative energies for growing in High Tunnels and for growing Figs in particular. The presentation covered the use of automatic curtain control powered by a solar panel, the Subterranean Solar and Geothermal Heating and Cooling System and the Clean Burn's automated waste cooking oil-heating system.

The successful growing of figs in the High Tunnels has excited many growers and several have already started growing them in High Tunnels on their farms. I have provided them with detailed instructions on the aspects of growing the figs and the technical knowledge for operating the systems. I even supplied them with rooted fig plants ready for planting in their High Tunnels. Several groups of interested farmers have visited the operation during the summer of 2007. Among them was a group of 5 from the University of Missouri Fruit Experimentation Station with Patrick Byers and Marilyn Odneel, the extension specialist from the University of Missouri, Columbia Dr Lewis Jet, 12 people from the St. Louis Botanical garden Club, many individual local farmers, neighbors and friends. Another group of 20-30 grower, members of the University Growers association from Columbia, Missouri with Dr James Quin, the Extension Specialist for the University of MO, Columbia is scheduled to visit on a Field trip on April 19, 2008.

Another way to provide information on the project was the participation in the High Tunnel on-line communication and discussion. A website will be posted for wide access availability for all members.

Last but not least important was the opportunity to provide fresh figs to local restaurants, two green markets twice a week from early summer to late fall. It was the most rewarding experience I have had to be able to bring this delicious fruits to the people in St. Louis months before and after they were available from California or other wormer but distant places. People simply could not believe, that this ripe delicious figs, were locally grown for them and many were trying this fruit for the first time in their life.

I find the SARE Program as one of the most valuable way to help Farmers use their creativity, based on their invaluable knowledge from personal experience, to come up with new solutions of problems and introduce new beneficial applications of sustainable methods and practices. I strongly support the growth of this Program in the future and I believe the rewards from it for future generations will follow. I participated in the newly formed Green markets, selling my products side by side with other farmers that had received SARE grants for their innovative ideas. Many farmers have their dreams come true thanks to this program.
Sustainable Agriculture on the planet is the SUM of every individual piece of land with sustainable agriculture practices. That is where SARE matters


Participation Summary
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.