Geothermal energy is a renewable energy source that can be found in abundance on our planet. Only a small fraction of it is currently converted to electrical power, though in recent years installed geothermal capacity has increased considerably all over the world. This review focuses on Enhanced Geothermal Systems (EGS), which represent a path for turning the enormous resources provided by geothermal energy into electricity for human consumption efficiently and on a large scale. The paper presents a general overview of this ever-expanding technology from its origins to the current state of the art. The Geodynamics plant in Habanero (Australia), which started up on 2 May 2013, is the first privately-run commercial EGS plant to produce electricity on a large scale. Thanks to the technological development of EGS in recent years, the future looks bright for such plants in the decades to come.

Enhanced geothermal systems (EGS): A review

Multi-objective design optimization of a multi-generation energy system based on geothermal and solar energy

Geothermal technology: Trends and potential role in a sustainable future

Analyses of fracturing and thermal performance of fractured reservoirs in engineered geothermal system (EGS) are extended from a depth of 5 km to 10 km, and models for flow and heat transfer in EGS are improved. Effects of the geofluid flow direction choice, distance between fractures, fracture width, permeability, radius, and number of fractures, on reservoir heat drawdown time are computed. The number of fractures and fracture radius for desired reservoir thermal drawdown rates are recommended. A simplified model for reservoir hydraulic fracturing energy consumption is developed, indicating it to be 51.8–99.6 MJ per m fracture for depths of 5–10 km. [DOI: 10.1115/1.4030111]

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Analysis of Hydraulic Fracturing and Reservoir Performance in Enhanced Geothermal Systems

Development of a combined flash and binary geothermal system integrated with hydrogen production for blending into natural gas in daily applications

Human population is ever-increasing and, thus, demand for energy is escalating. Consequently, seeking clean methods of producing electricity is a most crucial endeavor at this time. The shrinking reserves of oil have added urgency to the matter as well. One other recognized source of renewable energy besides wind, water, and solar (WWS) is geothermal energy, which has been proven to be useful in baseload power generation, a significant advantage over WWS. As compared to fossil fuels, geothermal energy is not subjected to the supply and cost fluctuations of which fuel is at risk. To date, there have been a number of innovative procedures explored to use geothermal energy to produce electricity. A relatively innovative yet not uncommon method has been to use hot solid rocks to heat water and pump the superheated water to use in power plants. These rocks are generally underground and at higher temperatures due to their proximity to volcanoes or natural geothermal vents. The water goes deeper down into the earth's crust to become superheated by the rocks, and then is pumped out to power turbines, and subsequently returned into the ground to repeat the process. In Krafla, Iceland, during their Icelandic Deep Drilling Project (IDDP) in 2009, a borehole was accidentally dug into the magma at 2100 m. The temperature of this magma was about 900–1000 °C. A steel casing with perforations on the flat side was cemented into the well bottom. This design was to slow the heat flow, and superheated steam was made for the following two years till July 2012. The steam reached temperatures of 450 °C and was at high pressures. Krafla was the world's first magma-enhanced geothermal system (EGS) to generate electricity. This paper will explore the feasibility of using geothermal power plant methods as a sustainable source of clean energy. Geothermal energy has tremendous potential if the right methods can be found to tap that potential, as well as if the cost may be brought down by innovation and demand. In addition, an innovative method, which already exists in some form, is proposed in the current review to harness more geothermal energy for use.

Nathanael Tan

Papers

Feasibility of Using More Geothermal Energy to Generate Electricity