Spain: Geothermal system to grow papayas

Felix Sanjuan is an industrial engineer who has worked in several countries throughout his career. When he was about to retire he decided to come up with some kind of occupation that was compatible with his retirement, included being creative, and that allowed him to continue having a physical and intellectual activity. Since he already had a few fields in Pedralba, he decided to devote himself to agriculture, despite not knowing much about agricultural issues. However, sometimes a lack of knowledge is what drives people to take a chance on something new.

Sanjuan decided to take a risk with a tropical crop, chose avocados, and has already obtained a production. To improve his chances he sought advice from specialized people and met Thomas Faulí, one of the top experts in tropical crops in Spain, thanks to the decades he's devoted to the production areas in Costa del Sol.

Productivity and price
Faulí spoke with Sanjuán about the possibility of trying out the papaya, given the fruit's high productivity and high prices it has had for some time in Europe, a result of the lack of supply and growing demand. Sanjuan liked the new challenge right away. Soon he realized he could apply his expertise in industrial engineering and thermodynamics on this new agricultural crop so as to avoid some initial difficulties.

The papaya's cycle can last between two and four years, and it can last one single campaign. It all depends on the weather. The plantations can last years in tropical areas, but require to be in annual cycles in places with extreme low temperatures. Thus the strategy is to grow the seedlings in greenhouses and transplant them to the field in spring, when plants are already more than half a meter tall.

Except in winter, the thermal integral prevailing in most coastal areas and the intermediate valleys of Valencia is very adequate for this plantation. The occasional frosts can be fatal to the crop, even if it is under plastic coverage, so it is necessary to have heating in the plant's growing phase, just in case there is a frost. Temperatures below six degrees will affect the plants.

That's when Felix Sanjuan thought about using geothermal energy to increase the temperature of the greenhouses and not spend money to acquire other energy sources. Geothermal energy, it turns out, is one of his specialties. It's worth recalling that geothermal energy entails using the higher temperature of the subsoil to heat a fluid (water or air) that is then circulated in a closed circuit thus transferring heat to a compartment.

In recent years, in order to harness natural energy resources, many geothermal systems have been developed to heat all types of residential, office, and educational buildings. The most common one involves drilling wells in search of warmer layers, and even capturing groundwater supplies to provide both water and heat to the building.

To ensure the papayas have an adequate temperature a pipe should be buried one and a half meters deep in a perimeter trench. At that depth, the ground maintains a stable temperature ranging between 12 and 15 degrees, said Sanjuán. Air will circulate through the pipeline and will keep the greenhouse warm when needed. If he ever needed to increase the temperature by one degree (perhaps one or two days per year) he plans to use the electric heaters fed by the solar panel battery system he already has in place.

According to Thomas Faulí, the European Union currently consumes 40,000 tons of papayas a year and, with the exception of 3,000 tons produced in the Canaries, the rest are imported. Thus, the potential market for papayas produced in Europe is more than obvious. The prices have been ranging between 2 and 5 Euro per kilo for more than ten years, which would be very profitable for the producer, as one hectare with the appropriate climate or system to manage the crop well, could yield between 40,000 and 60,000 kilos per year.


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