Introduction

Currently, geothermal power plants generate electricity in 24 countries and is heavily utilized in some developing countries, such as Kenya and Costa Rica (Gupta and Roy, 2006). Geothermal power plants generate 10,715MW of electricity worldwide as of 2010, and if utilized worldwide could produce up to 8.3% of the world’s total electricity (Fridleifsson et al 2008). Because BC is close to subduction zones and the “Ring of Fire”, there is sufficient tectonic activity for geothermal resources to be present (BC Ministry of Energy, Mines and Petroleum Resources, 2009).

BC has utilized geothermal resources for direct use, such as in the Harrison Hot Springs and in ground exchange heat pumps to heat buildings for decades, but there is currently only one geothermal power plant in development in BC. Exploration is vital to encouraging more development of BC’s geothermal resources, which is why I have chosen this topic.

Geothermal power plants use generate electricity using heat from the subsurface of the earth. Because no fuel is burned, there are very little to no carbon dioxide or other harmful chemicals emitted. Geothermal power plants also have a consistent base load and constantly run at capacities of around 90% and require little maintenance, making them very reliable (BC Ministry of Energy, Mines and Petroleum Resources, 2009). The Earth’s temperature at the core is believed to be 4982 degrees Celsius as a result of radioactive decay, and this is the source of geothermal energy of the Earth (BC Ministry of Energy, Mines and Petroleum Resources, 2009). Typically, the temperature gradient of the earth’s crust is 30 degrees Celsius per kilometer, but if stronger gradients and gradient anomalies, such as magma directly beneath or in the crust, are found in a site, the heat at a geothermal reservoir can be utilized directly in hot springs, for direct industrial uses such as heating, or to generate electricity (Gupta and Roy, 2006). To generate electricity, these geothermal reservoirs are accessed by drilling into the earth to depths of 2-5 kilometers (Kimball, 2010).

Currently, hydrothermal systems, or geothermal reservoirs with permeability in the geothermal resource, are most commonly used.The two types of hydrothermal systems are dry steam dominated and hot water dominated. Dry steam dominated reservoirs use steam directly from the high temperature and pressure reservoir to run turbines. In hot water dominated systems, hot water from the geothermal reservoir is held in a low pressure tank, where some of the water flashes into steam and is used to run turbines. In both cases, condensed water is then re-injected into the reservoir so the water can be reused and so that contaminant chemicals are kept in the subsurface. Temperatures of at least 150 degrees Celsius are required for vapour dominated reservoirs and temperatures of at least 180 degrees Celsius are required for hot water dominated resources to generate electricity economically (U.S. Department of Energy, 2010).

In resources with sufficient permeability but not temperature (120-180 degrees Celsius), binary cycle turbines can be used to generate electricity (BC Ministry of Energy, Mines and Petroleum Resources, 2009). Binary cycle turbines use hot water from the geothermal reservoir to heat another fluid with a lower boiling point, which is used to power turbines (BC Ministry of Energy, Mines and Petroleum Resources, 2009).

In geothermal reservoirs with high temperatures but low permeability and low water content, fracking (the high pressure injection of water to create fractures) is used to make the rock more permeable, and water is injected to make use of the heat (Gupta and Roy, 2006).