Agricultural geothermal utilization in Kébili region, Tunisia

Abstract

Direct utilization of geothermal energy in the Kébili region is mainly in agriculture. It is used for irrigation of oases and heating and irrigation of greenhouses. Geothermal resources are rare and non-renewable due to the absence of recharge in aquifers which are over-exploited. The main reason is that the irrigation practised is by submersion and all the area is irrigated resulting in significant water wastage. Date palms, trees, grass and vegetables compose the oasis system. Generally, when the geothermal water temperature is less than 40°C, it is used directly for irrigation but when it exceeds 45°C, it is cooled by means of atmospheric towers. Although the date palms and trees can tolerate relatively hot water, the vegetation is sensitive and, for some farmers it is of low interest. Geothermal energy is also used in greenhouse farming which is considered a promising and feasible sector, but the reality of operation is totally different. In addition to bad conceptualization of some projects, farmers are confronted by several constraints such as lack of organization and of techniques. Therefore, obtained yields are very low and under expectations. A big variability between sites and inside the same site is observed and farmers show a real heterogeneity. The economical evaluation of the greenhouse sector shows bad results for one third of the growers. These bad results concern 50% of them when the risk is considered (increasing of prices inputs).