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Groundbreaking technology allows rocks to be melted at temperatures of 700°F, creating new opportunities for energy and industrial exploration
Geothermal energy faces challenges to expand its potential. Most of the power plants operates at temperatures between 100 and 250°C. This limits the efficiency and expansion of the technology. The solution may lie in so-called superhot rocks.
They are found at temperatures above 375°C and can significantly increase electricity production.
The difficulty lies in accessing these rocks. Drilling depths of up to 12 miles (approx. 19 km) are required. This surpasses the world's deepest borehole, the Kola Borehole, at 7,6 miles (approx. 12 km).
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An innovative solution may be on the way. The American company Quaise Energy is developing a new technology for drilling using millimeter waves. This system promises to reach greater depths by melting and vaporizing rocks.
Daniel Dichter, a senior mechanical engineer at Quaise, has published research on superheated geothermal power plants. He says conventional design principles can be applied to higher temperatures.
According to Dichter, studies analyze conventional geothermal projects and adapt them to temperatures above 300ºC.
"We have a good understanding of how to design geothermal plants in the conventional temperature domain, but we do not have much experience with geothermal source temperatures higher than this. These articles apply conventional geothermal design principles to a higher temperature range starting at 300°C (572°F)”, said Dichter.
The energy of superhot rocks
Geothermal energy relies on pumping water heated by underground rocks. Supercritical water, which is present at high temperatures, has more energy than conventional water. This phase resembles steam, but has a higher density. This makes it a more powerful energy source.
One point raised in Dichter’s research is that keeping supercritical water at the surface may not be essential. The study suggests that superheated geothermal systems can operate efficiently even at lower temperatures. This would make superhot geothermal energy more affordable.
Energy losses when transporting superheated water through pipes are a challenge. The higher the temperature, the more energy the water carries. However, the flow rate decreases. The study indicates that the temperature gain and the flow rate loss end up canceling each other out.
"As the heat content of supercritical water is higher, the mass flow rate through the tubes decreases, and they essentially cancel each other out.“, explains Dichter.
Systems that operate at surface temperatures of 350ºC may still be more efficient than current systems. However, maintaining the water in a supercritical state in the underground reservoir remains a relevant factor. This can ensure production even with losses between the superheated rock and the surface.
Affordable turbines for geothermal energy
Another relevant finding of the study is the use of conventional turbines for superheated geothermal energy. If the temperature of the surface fluids is above 300ºC, standard turbines can be used. This reduces costs and facilitates the implementation of the technology.
The research also examines turbine systems currently in use. Binary cycles, which combine two fluids, are common in geothermal generation. Hydrocarbons are used to optimize the conversion of heat into electricity.
However, Dichter suggests that water may be a better alternative. At higher temperatures, it becomes more efficient and reduces environmental impacts.
Superheated geothermal energy can benefit a variety of industries. Power plants, regional heating and heat pumps are among the possibilities.
"The applications are diverse, from power plants to regional heating to domestic ground-source heat pumps, and there are many new eyes on the field. There’s a renaissance happening in geothermal energy right now“, highlights Dichter.
The technology still faces challenges. Deep drilling requires technical advances and large investments. Heat transmission also needs to be more efficient.
Still, experts see the potential of superhot rocks as an important step forward. If made viable, this energy could become an even more competitive renewable source in the future.
With information from Interesting Engineering.
