Why is geothermal power generation slow to spread?

In order to prevent global warming and environmental pollution, it is important to utilize renewable energy to reduce greenhouse gas emissions, so solar power generation and wind power generation are becoming popular. On the other hand,

regarding geothermal power generation , even in Japan, which is one of the world's leading volcanic powers, (PDF file) Geothermal power generation accounts for 0.2% of the total as of 2018, which is not as advanced as other renewable energies. It is the current situation. Blogger Austin Vernon pondered the question, 'Why isn't fuel-free, semi-permanently available renewable energy geothermal power generation so popular?'

Is Geothermal Really Going to be a Thing? --Austin Vernon's Blog

According to Mr. Vernon, there are three factors that make geothermal power generation difficult.

◆ 1: Slow heat conduction of rock
In the case of geothermal power generation, it is common to repeat a cycle in which cold liquid is sent to hot rocks underground to extract heat, and the cold rocks are re-supplied with heat from the surroundings. However, the thermal conductivity of rock is about 1/100 that of copper, which is very slow. Therefore, a large amount of hot rock is needed to obtain enough heat to generate electricity.

◆ 2: Low efficiency
The average geothermal power plant converts 12% of its thermal energy into electricity, and few have this conversion efficiency above 20%. On the other hand,

the thermal efficiency of the latest natural gas combined cycle power plant will reach 65%.

The efficiency of a heat engine is determined by the difference between the temperature of the heat source and the temperature of the outside. Therefore, it is possible to extract energy with much higher efficiency from the thermal power of natural gas, which reaches several thousand degrees, than the hot water of several hundred degrees generated from geothermal heat. Power plants with low heat conversion efficiency require large equipment to obtain the same power, which increases construction costs and running costs, which is holding back geothermal power generation, Vernon said. I pointed out.

◆ 3: Drilling cost
Basically, the deeper you excavate, the hotter the rocks, so the more efficient geothermal power is, the deeper the rocks are. However, the excavation cost, which is a problem when excavating deep underground, does not increase in proportion to the depth, but increases exponentially as the excavation goes deeper.

For example, in general excavation technology, a method is used in which the well is stabilized and excavation is performed while injecting excavation liquid with high pressure so that water does not enter the well from the surrounding bedrock. As the drill reaches deeper underground, the pressure of the drilling fluid also needs to be increased, but if the pressure is too high, the shallow rock mass will be destroyed and the well will collapse. To prevent this, when excavating deeply, the well is protected by an iron pipe called caging, but if caging is used a lot, the well becomes huge and the cost increases. These technical issues are increasing the drilling costs required to start geothermal power generation.

The geothermal power generation technology that has been put into practical use in the article creation time, geothermal reservoirs and the conventional method using the hot water, injected obtaining heat from the water enhanced geothermal system , such as 'open loop system' and a sealed underground There are 'closed loop systems' that bury the pipes and circulate the refrigerant, but all of them have problems such as the risk of earthquake occurrence, efficiency, and cost. Similarly, from the viewpoint of cost, it seems that it is more practical to use a relatively simple and long-used technology that uses air or water than a complicated technology that uses plasma or laser for excavation. ..

From this point, Mr. Vernon said, 'In order for geothermal power generation to produce more than a niche value, it needs to be able to generate electricity at a very low cost. To do so, geothermal wells must be dug deep, and Drilling must also be low cost, while geothermal power has little room to scale up without government assistance, as solar and wind power and batteries that store those energies are becoming cheaper and cheaper. The reality is that there is no such thing. '

in Note, Posted by log1l_ks