Techno-economic coupling model of U-shaped closed-loop geothermal system

Recently, geothermal energy has gained attention from researchers and enterprises as a form of clean energy with zero carbon emissions. U-shaped closed-loop geothermal system (UCLGS) shows great application potential because of its unique well structure. However, there is a big debate on whether they can be economic because no economic evaluation model is available. The method of net present value (NPV) is used in this study to establish a techno-economic coupling model of UCLGS. The proposed model was applied and analyzed in a UCLGS in Xi'an, China. The results indicate the following. (a) The fully implicit transient wellbore heat transfer model established in this study is in good agreement with the field test data, and the relative error is <6%. (b) The outlet temperature and heat extraction power increase with the increase in the horizontal section length, but the rate of increase slows down; the longer the horizontal section length, the higher the drilling cost. The proposed techno-economic model can be used to design an optimal horizontal section length of UCLGS. (c) The service life, government financial subsidies, and drilling costs have a great impact on the profitability of UCLGS projects.