Maciej Z. Lukawski

Levelized costs of electricity and direct-use heat from Enhanced Geothermal Systems

GEOPHIRES (GEOthermal energy for the Production of Heat and Electricity (“IR”) Economically Simulated) is a software tool that combines reservoir, wellbore, and power plant models with capital and operating cost correlations and financial levelized cost models to assess the technical and economic performance of Enhanced Geothermal Systems (EGS). It is an upgrade and expansion of the “MIT-EGS” program used in the 2006 “Future of Geothermal Energy” study. GEOPHIRES includes updated cost correlations for well drilling and completion, resource exploration, and Organic Rankine Cycle (ORC) and flash power plants. It also has new power plant efficiency correlations based on AspenPlus and MATLAB simulations. The structure of GEOPHIRES enables feasibility studies of using geothermal resources not only for electricity generation but also for direct-use heating, and combined heat and power (CHP) applications. Full documentation on GEOPHIRES is provided in the supplementary material. Using GEOPHIRES, the levelized cost of electricity (LCOE) and the levelized cost of heat (LCOH) have been estimated for 3 cases of resource grade (low-, medium-, and high-grade resource corresponding to a geothermal gradient of 30, 50, and 70 °C/km) in combination with 3 levels of technological maturity (todays, mid-term, and commercially mature technology corresponding to a productivity of 30, 50, and 70 kg/s per production well and thermal drawdown rate of 2%, 1.5%, and 1%). The results for the LCOE range from 4.6 to 57 ¢/kWhe and for the LCOH from 3.5 to 14

Impact of molecular structure of working fluids on performance of organic Rankine cycles (ORCs)

/MMBTU (1.2 to 4.8 ¢/kWhth). The results for the base-case scenario (medium-grade resource and mid-term technology) are 11 ¢/kWhe and 5

Deep geothermal energy for district heating: lessons learned from the U.S. and beyond

/MMBTU (1.7 ¢/kWhth), respectively. To account for parameter uncertainty, a sensitivity analysis has been included. The results for the LCOE and LCOH have been compared with values found in literature for EGS as well as other energy technologies. The key findings suggest that given todays technology maturity, electricity and direct-use heat from EGS are not economically competitive under current market conditions with other energy technologies. However, with moderate technological improvements, electricity from EGS is predicted to become cost-effective with respect to other renewable and non-renewable energy sources for medium- and high-grade geothermal resources. Direct-use heat from EGS is calculated to become cost-effective even for low-grade resources. This emphasizes that EGS for direct-use heat may not be neglected in future EGS development.

Cost analysis of oil, gas, and geothermal well drilling

Organic Rankine cycle (ORC) power plants are the most mature and economically competitive technology used for converting low- and medium-temperature heat to electricity, especially for renewable energy sources such as geothermal and solar thermal. This paper analyzes the performance of four types of ORC plants (subcritical and supercritical cycles, both with and without heat recuperator) optimized for maximum utilization or exergetic efficiency. The analysis was performed for 13 working fluids, heat source temperatures from 100 to 230 °C, and for cycles with either a wet cooling tower or an air cooled condenser. The primary objective of this work was to investigate the effect of the molecular structure of the working fluids on the efficiency of ORC plants. Using group contribution methods, a number of thermodynamic properties of working fluids can be easily evaluated based on their molecular structures. We show that using two of such properties, namely, the reduced ideal gas heat capacity C0p/R and the critical temperature of the working fluid, one can accurately predict a number of ORC performance metrics including: (1) maximum utilization efficiency of the ORC plant and the heat source temperature at which it is achieved, (2) sensitivity of utilization efficiency to changes in the heat source temperature, and (3) increase in both thermal efficiency and heat source outlet temperature due to addition of heat recuperator.

Sustainable heat farming: Modeling extraction and recovery in discretely fractured geothermal reservoirs

In this chapter, utilization of deep geothermal energy as an economically viable source of energy for district heating (DH) systems is discussed. An overview of enhanced geothermal system (EGS) technology is presented first, focusing on the technology, economics, and challenges and advantages of using EGS for DH systems. This is followed by several case studies, of both real and modeled systems, to illustrate the current and future state of geothermal district heating (GDH).