Geothermal energy

Up to now, a lot of the focus of the blog has been on wind and solar power, the two main sources of renewable energy in the world. However, in certain locations geothermal power can be just as important. Geothermal energy relies on the heat of the Earth to generate electricity, often through the heating of water in pipes which pass through the hot rock deep underground. This is more applicable in areas of high volcanic activity, such as Iceland, where the rock only a short distance underground becomes heated. However, it is not limited as much as previously thought, and 10,715 MWe were produced in 2010. With the extra funding put into the renewable sector, and a greater need for carbon neutral energy sources, novel applications of geothermal energy have become apparent. In my research, the wealth of recent information concerning these new innovations warranted a separate blog post in the search for a solution to our energy crisis, and the opportunities that geothermal energy can offer only adds to the arsenal of energy sources available in the modern world of energy production.

The first relatively new method of geothermal energy production is its application in shallow aquifers. This involves the use of the subsurface to extract or inject heat through either groundwater pumps or pumping water underground for heating. This has been increasingly used in the last 15 years, with many more plants using these methods. However, there are a certain number of obstacles in place before these methods are deemed a sustainable energy production method. For example, the use of groundwater in energy production influences local water temperatures, either increasing or decreasing them depending on the method of geothermal use. Therefore in order to be sustainable, the production of energy must not cause damage to groundwater quality, or the ecology supported by the groundwater, which includes the water level, as well as the chemical composition. However due to the recent application of the method, the effects of shallow geothermal power are not well understood, particularly long term environmental impacts. If better understood though, the side effects of geothermal power could result in larger benefits. For example, heat extraction from groundwater can lead to a fall in temperature in the aquifer, which can combat the anthropogenic heating of aquifers in urban areas. So in cities, perhaps geothermal power would be even more beneficial for the environment beyond reduced emissions. In order to use this method effectively, there must be a safeguarding system against any negative impact on the environment, which is suggested to be possible through the use of a legal framework underpinning the use of geothermal energy and its sustainable use.

The second novel method of geothermal power use is rather more metaphorical – using abandoned oil and gas wells as a way of getting geothermal energy. In essence, this offers a way of using infrastructure from fossil fuel production in a renewable world, as a direct replacement of the old carbon-based methods. Many oil and gas wells are now abandoned, having extracted all of the fuel reserves from them, and a large number of these exist in China, having fed the massive growth of the nation. With retrofitting of these wells, it has been shown in experiments that heat can be extracted from the wells through the water flow between the bedrock, with the amount of energy determined by the flow rate of the water, and the temperature of the rocks. Even extensive use of the well for geothermal power only causes a temperature drop of 2°C over a decade. In addition, as these wells are typically far from major settlements, they can also be used for electricity generation effectively, through the use of steam turbines, which increases the utility of refitting these wells. In ideal scenarios, this form of geothermal power can bring over $36,000 each year from the electricity produced. Due to the large number of wells available in China, this could be a major method of converting energy supply to renewables for the nation, which could have huge effects on global emissions. However, it remains to be seen how massive scale use of this method effects the environment and water levels, for example.

The final use of geothermal power is more of a complementary method, which could exaggerate the renewable nature of its production. This method uses CO2 as the fluid which is injected into the subsurface, instead of water. There are a number of advantages to this approach, namely the higher mobility of CO2 in comparison to water. This allows it to exchange heat more effectively at the desired temperature and pressures that have been posed. Theoretically this could lead to up to 5x more heat energy able to be extracted, compared to engineered geothermal systems. As well as making existing power plants more efficient, this could allow geothermal electricity production in more areas, due to the greater yield. Furthermore, the CO2 injected into the bedrock slowly sequestered into the ground, leading to a net reduction in CO2 levels – making this method act as both a geoengineering and energy production method.

These technological advances show how geothermal energy could become a much larger player in the renewable sector in the future, and its flexibility if combined with CO2 use and abandoned well schemes could take it from only worthwhile in a select few localities, to a much more widespread application. It is this kind of innovation which could really change the renewable sector, and with so many different novel methods coming out of the last 5 years, the future of geothermal energy is looking pretty hot indeed.