Geothermal Power: Expanding Renewable Resources to Meet Future Energy Demands

Geothermal energy is, simply put, the heat that exists under the sub-surface of the earth. Due to the constant slow-decay of radioactive particles near the earth’s core, geothermal energy is one of the few renewable energy sources on our planet. We can use the energy for heating, cooling, and electricity applications by extracting the energy from storage sources - generally, rocks and fluids. To utilize this heat, wells are constructed to reach underground geothermal reservoirs - the area of the local sub-surface optimal for heated water and steam production.

The benefits of geothermal energy production are heavily environmental, as the energy source produces just under 17% of the CO2 that a clean natural gas power plant produces. Unlike solar and wind energy, geothermal heat is constantly available, making it the most accessible resource for energy production of all the renewables. The economic benefits of geothermal energy are also substantial compared with conventional energy, with savings exceeding 80% of standard fossil fuel production methods.

There are three types of technology used to generate geothermal energy, each of which is used in different ways and has optimal applications.

1. Direct Use Geothermal
2. Ground Source Heat Pumps
3. Deep and Enhanced Geothermal Systems

Direct use geothermal systems utilize subsurface groundwater heated by geological processes. by pumping hot water or steam from a geothermal reservoir through a drilled well. Once the water reaches the surface, it is either used directly or cycled through a heat exchanger. Depending on the system’s requirements, the water may be directed back to the reservoir to avoid resource depletion. The water from geothermal reservoirs is generally hot enough for most direct use applications, as natural water temperatures often exceed 200 degrees F. The most common direct use geothermal applications include hot water supply for buildings, large-scale pool heating, and cooling.

Ground source heat pumps are a relatively simple technology that takes advantage of the difference in the above-ground air temperature and the below-ground soil temperature. Subsurface pipe installations move heat-conveying fluids through the system powered by a pump, transferring heat to structures with air temperatures lower than the ground. These systems also work in reverse, cooling air temperatures when the environment beneath is cooler. Ground source heat pumps are best for direct use applications such as space heating, space cooling, and water heating.

Installing and operating deep and enhanced geothermal systems often involve drilling a mile or more into the earth’s surface, where high-pressure environments keep water in a constant liquid state. Water and steam run to the surface through a deep well, taking advantage of the considerable pressure changes to produce a superheated steam - a requirement for high-temperature processes. Once at the surface, the system can apply the heat directly or heat a secondary fluid. After the transfer of heat, the water runs back through the system for re-use. Deep and enhanced geothermal systems are the most common technology for industrial, agricultural, and large-scale commercial applications. The energy produced drives a turbine to generate and store electricity, requiring no fuel and having considerably low operational costs.