Commercialising a concept for semi-deep geothermal boreholes for Fennoscandia and beyond

Geothermal energy from semi-deep boreholes (600 – 1000 metres in depth) cannot currently compete with district heating and other commonly used heating sources in Fennoscandia on purely economic terms. As a result of this, full-scale geothermal heating systems are generally not viable in densely built city centre locations, even though the entire heating demand of a city like Helsinki could in theory be met with 1000 metre-boreholes. The relatively high cost of installations with deep boreholes derives to a large extent from the cost of drilling. Another factor is the cost of manufacturing an effective energy collector for such depths. In order to address the aforementioned challenges, Rototec Group has joined a consortium of private enterprises and research institutes in the HYBGEO (Hybrid Geothermal Technology and Data Enabling Positive Energy Buildings) project, a research and development project with the explicit goal of commercialising a geothermal concept based on 600 – 1000-metre-deep wells. Results obtained by Rototec in the HYBGEO project are presented. Factors improving the cost-efficiency of semi-deep boreholes are identified: Using a larger compressor, speeding up operation of the drilling rig and optimising borehole and collector parameters. The development of a Thermal Response Test (TRT) equipment for deep boreholes is described. A pilot building utilising semi-deep borehole technology is presented as a case example. In addition, challenges in the numerical modelling of borefields consisting of both shallow and semi-deep boreholes are discussed and results of preliminary simulations are presented.