Geothermal energy: Power plant technology and direct heat applications

The transition from current fossil-fuel energy system towards a sustainable one-based requires renewable energy technology. Although geothermal energy presents its own particular challenges in comparison with other renewable energy technologies, geothermal energy has showed significant potential to reduce environmental impact and greenhouse gas emissions from electricity production. Advantages of geothermal energy are not only the generation of electricity in different plant configurations but also the direct application of heat in industry and household uses regardless of meteorological conditions. In this study, a research review is carried out on the aspect of geothermal energy development, assessing power plant technology and direct heat applications. Five power plant configurations are studied: single-flash, double-flash, dry-steam, binary and advanced. The thermodynamic aspects are addressed in order to consider them for future geothermal power plant analysis. Furthermore, the most common direct uses of geothermal heat are discussed. Results illustrate that Binary Organic Ranking Cycle Power Plants might play a vital role in the exploitation of low temperature geothermal resources. Furthermore, it is identified a need for research in hybrid geothermal-solar-biomass configurations for poly-generation purposes. These configurations increase the energy output, increasing the thermal efficiency and increasing the life of the geothermal reservoir. Similarly, direct applications of geothermal heat present good opportunities for increasing the revenue of a geothermal project. Depending of the geographic zone, cascade configurations contributes to maximise the use of geothermal resources. Future research reviews should consider the financial, economic and policy aspects of geothermal developments along with the geology, geophysics, geochemistry, drilling, reservoir engineering and environmental aspects. The main goal of addressing these topics is to provide the state-of-the-art of geothermal development for developers, policy makers, researchers and communities interested in geothermal energy.