Renewable energy sources are becoming a more integral part of the world’s demand for energy. An increased number of countries and regions are looking to diversify their current energy mix. Oil and gas will not last forever and today, the world still depends on coal and natural gas as primary sources of electricity.
Currently, most of the renewable electricity produced around the globe comes from hydroelectric power. The power extracted from the water flow supplies electricity to around 150 countries at a relatively low cost. But lowest consumer costs are no longer the only choice criteria.
Decisions about electricity choices are now based on reliability, costs to integrate the new resources into the power grid, future prices and fluctuations, the amount of land used, environmental impact, subsidies paid by the government, security and availability of resources.
But What about Geothermal Power? Is it a Viable Energy Source?
Yes, it can. Following the energy crisis, the interest of replacing coal and shale gas has drawn attention to an unlimited source of energy: heat from the Earth. Geothermal power emerges as one of the cleanest forms of energy and it can be generated into heat and electricity. Current worldwide potential varies from 35 to 2,000 GW. Geothermal electricity is already used in countries like USA, Iceland, Italy and the Philippines, where more than 15% of the electricity production comes from geothermal power.
High Capacity Factor
Another good news is that geothermal energy is highly efficient.
Below you can see an illustration of outputs from different energy sources. Since geothermal energy does not rely on a variable source of energy (like solar or wind), its capacity factor is the highest amongst renewable sources. Also, geothermal electricity generation is as efficient as traditional sources like coal and shale gas.
Other Benefits of Geothermal Electricity
- Sustainable: the heat extracted from the earth to produce power is insignificant compared to the Earth’s total heat content. This means the Earth will not run out of resources. Besides, the Earth's crust is continuously recharging with heat captured from the sun.
- Cost of energy: the resource used (heat) is free of charge. Moreover, geothermal power doesn’t require fuel to operate, therefore is not subject to fluctuations in fuel prices. Besides, the environmental costs derived from operating a geothermal plant are very low. When operating plants that burn coal, fuels or nuclear, there are always risks of land degradation, climate change , emission of toxic chemicals and health consequences.
- Availability: unlike the wind or sun, geothermal power is available 24 hours a day, 7 days a week.
- Flexible energy: geothermal energy provides both base-load and flexible electricity due to its high capacity factor. This means it can support unforeseen changes in electricity demand. Transmission capacity and distribution infrastructure require less resources than other renewables or even natural gas.
- Low emissions: geothermal plants do not burn fuels or coal, they don't release any emissions into the air. Generally, geothermal plants have small land footprints and low air emissions. Some gasses are released into the atmosphere due to the conversion of steam into electricity. Most of these gasses are of natural origin, as the geothermal fluid contains naturally dissolved gasses. In the table below you can see the comparison between the emissions of a geothermal plant and a coal plant.
So How Is Electricity Generated from Geothermal Power?
Depending on the method used for steam-extraction, geothermal plants are built differently. Below we are going to have a brief look into the different types of power stations.
- Dry steam
In a dry-steam power plant, steam is collected directly from an underground basin and utilised to run the turbines which power the generator. This is the simplest and oldest form of a geothermal plant. Dry steam plants are very common in the US and they account for half of the total geothermal power plants. These type of plants are built in locations with high temperature in geothermal resources (above 180°C)
- Flash steam
In a flash power plant, water separates into steam and water as it rises from the ground. This is due to the high pressure and high temperature of the water when taken from the geothermal basin. The fluid’s temperature is at least 180°C. Once the steam and liquid are separated, steam is delivered to a turbine, which in turn powers the generator. The water is then injected back into the reservoir.
- Binary cycle
The most recent development in geothermal power is binary cycle plants .They can operate at lower temperatures (57°C). This means that binary cycle plants can be built in locations with cooler geothermal reservoirs. Water circulates through a closed-loop system and is fed into a heat exchanger. The heat is then absorbed by a liquid that boils at lower temperatures (e.g., isopentane). The steam resulted from isopentane will drive the turbine, which produces electricity.
175 plants are currently in development worldwide and they are expected to power 2,500 MW over the next decade. Installed capacity is expected to double by 2020. Even though the geothermal electricity generation is far from peaking, it is one of the keys for a future of clean energy consumption.