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Session: System Design and Optimization I
Session starts: Monday 07 October, 11:10
Presentation starts: 11:50
Room: Ruys & Rijckenvorsel Zaal

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Stefan Lecheler (Bundeswehr University Munich)

Abstract:
A program was developed to estimate the payback period for geothermal heat and power plants including district heating grid with only a few input parameters, which are usually available for a desired location. With this program, investors and communities can easily estimate, if a new geothermal heat and power plant will be profitable at the intended place. In a first step all thermodynamic quantities are calculated. Volume flow and temperature of the thermal water give the available heat. From the number of inhabitants and the length and shape of the waste water grid, the needed power for district heating of a nearby village is estimated. The remaining heat is then used for an ORC- or Kalina-power plant. The thermodynamic cycle is automatically adapted to the actual temperature levels. Different working fluid can be chosen, where the thermodynamic properties are automatically calculated from fluid databases. Also the coupling between heat and power station can be changed from serial to parallel or combined. Finally the power output and the thermal efficiencies are calculated. In a second step all costs of the geothermal project are estimated via cost functions. This includes drilling, components like heat exchangers, turbine, pumps, piping and measurement equipment, the build-up of the geothermal heat and power plant and of the district heating grid and finally management. The inflation rate is also taken into account. The cost functions are a function of power and calibrated by values from literature and existing plants and district heating grids. In the third step the profit is estimated. With known prices for thermal and electrical power and typical operating hours, the yearly earnings can be estimated for the next years. Taking also interest rates for credits and inflation rates into account, typical amortization maps show, after how many years the investment is profitable. By varying input parameters, their influence can be easily investigated. The program is available in MS-EXCEL and uses currently fluid property libraries for iso-butane, n-butane, propane and ammoniac-water-mixture from FluidEXLGraphics [1]. It could be easily extended to other fluids, if libraries are available. It is already used for several geothermal projects around Munich, where a large aquifer is available in a depth between 3000 and 5000 meters. The validation of the program with existing data is still ongoing, because not many financial data are available. [1] FluidEXL Graphics, H.-J. Kretzschmar, Hochschule Zittau/Görlitz, Germany, http://thermodynamik.hs-zigr.de