Although a variety of engineering guidelines, planning software, and modelling techniques are available for shallow geothermal system planning and design, only a few studies have investigated their long-term operational effects in the field. The present study deals with an in-situ experiment on a borehole thermal energy storage (BTES) from combined heat and power production (CHP), which has been in operation on the site of Green Gas DPB in Paskov (the Czech Republic) for more than three years. This experimental BTES was monitored through six monitoring boreholes, and the temperatures were measured at various depths up to 80 m under the ground. The maximum temperatures measured at the centre of the BTES at the depths of 2-60 m under the ground ranged from 69.0 degrees C to 78.5 degrees C. The data acquired from the BTES operation was then used to set up and calibrate a heat transport model in the rock environment by means of the FEFLOW code. The calibrated numerical model contributed to optimisation of the BTES operation by simulation of various cycles of injection and exploitation of heat with an objective to minimise the loss of heat due to dissipation to the ground. The long-term feasibility of 65-percent recovery of heat stored underground in the BTES in Paskov was predicted, and recommendations concerning efficient operation of this BTES were provided. (C) 2016 Elsevier Ltd. All rights reserved.