Estimation of Potential Low-temperature Geothermal Energy Extraction from the Closed-loop Systems Based on Analysis, Interpretation and Reclassification of Geological Borehole Data in Poland

Abstract

Recent growth of renewables share in the total mix of energy production in Poland aims at complying with the binding EU regulations on energy and adaptation to climate change. The ground source heat pumps (GSHP) extracting low-temperature geothermal energy through the closed-loop system are the efficient, safe and stable source of renewable energy for space heating and cooling. Application of GSHP contributes to reduction of low emissions which in effect positively influences state of the natural environment and human health. Effectiveness of the GSHP is, to a large degree, determined by local geological and hydrogeological settings. Therefore, detailed studies of the subsurface and identification of natural conditions is crucial for an appropriate design and exploitation of the GSHP installations. For example, the thermal conductivity of soils and rocks, one of the key geothermal parameters which needs to be calculated for optimal GSHP design, depends on mineral composition of surrounding rocks, their texture as well as presence of groundwater. For the sake of the research geological and hydrogeological data originating from the thematic databases, atlases and serial maps have been gathered in a unified database showing a uniform structure enabling spatial analysis with use of the GIS techniques. According to an algorithm adopted for calculations under the terms of research presented in this paper, reclassification of lithological parameters into the geothermal parameters have been performed and values of thermal conductivity λ [W/m∙K] of analysed rock and soil types have been calculated. Based on the results of calculations 2 spatial layers of average geothermal conductivity coefficient λ have been computed, each for the depth interval up to 40 and 100 metres.