Utilisation on geothermal in food production – a study for North Iceland

Fridheimar greenhouse, Iceland (source: flickr/ Christophe PINARD, creative commons)
Alexander Richter 10 Oct 2018

Geothermal energy could be used for dehydrating tomatoes grown in greenhouses heated by geothermal expanding the direct use opportunities in the Northeast of Iceland, so a recent paper by a student in Iceland.

In a short study shared with ThinkGeoEnergy this week, a student of the University of Reykjavik looked at how geothermal energy could be utilised in food production, specifically for the dehydration of tomatoes.

The document looks at how sustainable use of resources could be promoted in the north eastern part of Iceland. Traditionally, tomatoes grow naturally in higher temperatures than what can be experienced in the climate of Iceland.

That is the reason why farmers in Iceland, mostly in southern Iceland have used geothermal energy as heating source for tomato and cucumber cultivation in greenhouses. The idea now is to actually expand that operation with dehydration of the tomatoes in dryers. So utilising geothermal energy not only for heating but also food processing could be an opportunity for farmers in the Northeast of Iceland.

Drying agricultural products, such as fruits and vegetables of various kinds, actually is a suitable way to reduce food waste and ensure durability of an otherwise perishable food product. Traditionally, dried food is then packed with vacuum packaging for transportation between parts of the country and or export.

So how does one use geothermal energy for drying?

A low-temperature area below 150?C is most commonly used in the drying of food because at that temperature you can get the most out of the drying process. The heat can be either used in the form of water or steam, but also the waste water that is too cold for use in geothermal plants could be used for the purpose. The big advantage of using geothermal energy in tomato farming rather than fossil fuels or electricity is that it cuts down cost.

Geothermal heat has been used to dry a wide variety of agricultural products all over the world, including rice, flour, tomatoes, onions, cotton, chilli and garlic.

Tomato drying in Nea Kessani Greece began in 2001. Tomatoes are dried with geothermal water at 59?C in 14 m long rectangular dryers (1 m wide and 2 m high). Tomatoes are sorted and washed to remove dust, dirt, the plant, etc. They are then cut in half and placed on stainless steel trays. Each pallet of 25 bake is dried for 45 minutes, with about 7 kg of tomatoes on each tray. The dried tomatoes are then immersed in olive oil and are made ready for transportation and sales. In the first year of their work there were 4 tons of high quality tomato products manufactured.

So the “sundried” tomatoes from Greece are actually “geothermally” dried.

Equipment used for drying

In Iceland, geothermal energy has been used for fish drying and the same equipment could be used to dry tomatoes.  Air is blown with fans through a hot water pipe system, through which hot water flows.  Tomatoes would be placed on trays on stacks on top of boards into space through which hot air passes. Below in Figure 3a you can look at the method in the drawing.

At the same time, one could buy ready-made units that can deliver higher output. They work in a similar fashion then the one mentioned above, while the unit is denser and air flow is better controlled.

Figure 3b, shows such a new unit.


Use of geothermal energy in greenhouses

Geothermal heat has been used to heat up greenhouses in Iceland since 1924 and is one of the largest types of direct use of geothermal energy in Iceland today. Hot water is simply run through pipes in the mold and alongside plants to keep warmth close to the plant being cultivated.

Source: Aron Heidar Steinsson, “Skýrsla um nýtingu jardvarma í matvæli, tómataraekt til thurrkunar”