Experimental analysis of soil thermal diffusivity for optimizing surface geothermal energy systems in arid environments

Abstract In this research, the thermal behavior of shallow subsoil in Ghardaïa, Algeria, is experimentally investigated, with a focus on surface geothermal energy systems. From March 2020 to November 2023, air, surface, and subsurface temperatures (0–5 m) and other parameters such as solar radiation, humidity, wind speed, precipitation, and air pressure have been monitored. It was found that soil thermal diffusivity is a decreasing function of depth, with values of 7.31 × 10−7 m2/s and 5.64 × 10−7 m2/s in the 0–1 and 4–5 m depth ranges, respectively. At depths ≥4 m, temperatures are stable and equal to 24°C, showing a strong thermal damping effect and a notable phase lag. A predictive model of subsurface temperatures with an RMSE of 0.255°C and R2 of 0.995 is in good agreement with measured temperatures. Future research directions include a deeper subsoil investigation and the potential of integrating geothermal energy with other renewable energy resources in arid regions.