Research of the geological and geothermal conditions for the assessment of the shallow geothermal potential in the area of Ljubljana, Slovenia

Shallow geothermal energy is a renewable source of energy. Using it provides benefits for climate, health and economy. A prerequisite for its efficient and sustainable use is the knowledge of its potential as well as the barriers that limit its use. The paper presents the preliminary results of research carried out within the GeoPLASMA-CE project for the assessment of the shallow geothermal potential in the area of the City of Ljubljana. By compiling existing geological data and field work, a detailed geological map of the study area was elaborated. The spatial distribution of thermal conductivity was estimated with measurements of thermal conductivity on 47 representative samples of 18 lithostratigraphic units and field measurements in unconsolidated Sediments at 12 localities. The measured values range between 0.63 and 5.18 Wm-1K-1. Continuous groundwater temperature measurements in 17 Observation wells with depth to 118 m show relatively small temperature changes over time of 5 months. The measured values on the Ljubljansko polje range between 10.6 °C and 14.6 °C, while in the Ljubljansko barje the temperature increases up to 15.6 °C. Multi-level groundwater temperature measurements in 9 Observation wells indicate three different conditions: both negative and positive temperature gradients and a constant temperature in different depths of the aquifer, which reflects the deeper geothermal or hydrogeological conditions and the anthropogenic impact.