FAIR-CT96-1664 Cultivo aeroponico con energias renovables

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FAIR Area 1.1 - Biomass and Bioenergy Chain

	Proposal No:	FAIR-CT96-1664
	Date Prepared:	September 1999
	Source:	Final report December 1998

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Final report December 1998

Summary

Introduction The aim of the project is the construction, in the island of Gran Canaria, of aeroponic greenhouses (for production of vegetables under continuous cycle) with a total area of 1300 M², of which 300 M² will be devoted to the Portuguese program and the rest to the Spanish (Canary Islands) program. The project will also evaluate the performance of a rock bed thermal energy storage system designed and constructed to be applied in this new cultivation method.

Objectives The overall objectives of the project are to confirm:

• the ecological benefits of the (aeroponic-renewable energy) system (no contamination of the ground, water saving, organoleptic improvements of the fruits, clean solar heating in the greenhouses, etc.)
• the reduction of the production costs achievable by this new technology
• the increase of the employment level in the local agricultural area.

Results The aeroponic greenhouse has been installed as follows.

Aeropony 1300 improved spindles (covering a total area of 1300 M² ) equipped with removable rings that have been successfully used in other plants, have been set up, resulting in a 4% reduction of the production times for some cultivation practices (transplantation). The details will be patented.

Irrigation system A set of 3 electric pumps (1.5 HP each) distributes the nutrient solution within a circuit of PVC tubes, reaching each spindle by means of adjustable micro-injectors. One computer regulates all the cultivation operations, i.e., irrigation, mixing, and tank cleaning.

Greenhouse The greenhouse has an iron structure. For the cover, different materials have been tested during the progress of the project:

• plastic film cover reinforced with polyester micro-mesh (since the area is subjected to very strong winds, the plastic film had a double protection, internal and external, with a polypropylene net, 0.2 mm threads, and 120-mm panels)
• wavy rigid sheets of methacrylate have been used in 200 m² of covering, instead of the plastic film, since they allow a better penetration of solar light (up to 97%)
• complete substitution of the plastic film by rigid transparent polycarbonate 4D plates with a cross-section that results in 30% higher luminosity.

The cross section of the greenhouse is tooth shaped, 10 m wide with an inclination of 68% in relation to the solar axis, thus allowing a better accumulation of solar energy in the months of January and February. The greenhouse is equipped with shadowed plastic meshes (75%) and manual opening to protect the cultivation in summer during the hours of peak solar intensity. It also has windows with manual opening and 20% of the area is dedicated to internal natural ventilation.

Climatization The climatization system consists of a rock bed thermal accumulator, mounted in a 3x5x30 m³ excavation. The underground parallelepiped is completely covered with insulating materials (polystyrene, plastic bubbles isolation, aluminium sheets). The whole set is 500 mm thick at the bottom on the lateral walls and 1000 mm thick in the roof. This is filled with round stones of volcanic origin. There are suctioning devices for driving the heated air from indoors to the inner part of the accumulator and outlet collectors at ground level. The first l00 M³ are used for climatic controls in a 500 m² area of the greenhouse. During the day the heated air passes between the stones, releasing part of its sensible heat, and returns to the lower part of the greenhouse.

For example the air may enter the accumulator at a temperature of 30° C and leaves the rock bed at 24° C from 11 to 15 hours. The stones, with an external temperature of 18° C at 7 o'clock reach 24° C at 17. A 1.5 HP turbine drives the air and a differential thermostat regulates its flow. When the temperature of the greenhouse roof exceeds, by 2° C, the temperature of the stones, the turbine starts working. When the two temperatures match, the turbine turns off. At night, a normal thermostat, graduated to 16° C, regulates the operation of the turbine. When the temperature is less than 16° C, the turbine starts working. By means of the collectors, the turbine collects the air, at 16° and drives it between the stones, which release a part of the heat accumulated in the day. Finally, the air returns to the greenhouse at temperatures ranging from 25 to 22° C. In December, with external temperatures of 10° C, the minimum temperature has been kept at 16° C in the 500 m² of the greenhouse where the accumulator works.

Heating of nutrient solutions The heating of solutions is by means of a series of solar collectors. Such heating is required on the basis that the temperature may drop below 10-12° C in winter in the hours of minimum peak temperature. However, so far the temperature of the tanks has never been under 18° C, so that this heating has not been necessary. The watering systems causes solution to flow within the PVC tubes arranged inside the greenhouse in the upper part of the spindles row (2.5 m above ground) with temperatures ranging from 25 to 28° C in the day hours. This is enough for the load of sensible heat to keep the minimum temperature in night hours at 18° C.

Production The 300 M² greenhouse area (Portuguese) began to produce in March 1997. The Canarian greenhouse started to produce in August 1997, with a first shipment to European markets (London) in October. The commercial aeroponic plant (tomato area) produced 92.000 kg during 1998 (i.e. 92k g/M²) . The average selling price of the aeroponic tomatoes (delivery at store, excluding transportation and packaging costs) has been 76 Pts/kg (0.46 ECU/kg). (The price has been the same as of normal hydroponic tomatoes).

Conclusion The following conclusions can be drawn at the end of the project:

• the project confirms the competitive possibilities of aeroponic products
• the water consumption to produce one kg of tomatoes has been kept below 10 liters
• employment level, two people work at the current 1000 M² greenhouse, one person is available for emergency cases or for weekly holiday shifts; the cultivation can be completely co-ordinated by one person working 8 hours a day during 5 days, corresponding to 8 persons/ha needed for an aeroponic plant rather than 4 people per ha in a normal cultivation systems
• the rock-bed thermal storage system has performed excellently during the project period, keeping the temperatures inside the greenhouse always above 16 ° C, thus allowing continuous production
• an infrastructure has been created for developing and executing acroponic projects at industrial scale