Nope. To efficiently tap geothermal energy, you need to boil something but not necessarily water. Isopentane, for example, boils at 28º at standard pressure, so they pressurize the secondary loop to raise the boiling point close to whatever the primary loop temperature is.

The idea that geothermal only works well at steam temperatures is outdated 20th-century thinking.

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emmelaich an hour ago | parent [-]

But the energy in boiling isopentane would be less right?

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jeffbee an hour ago | parent [-]

Yes, the efficiency is worse, but as is also the case for solar power you need to get used to not caring much about efficiency. It is nuclear energy where the primary side is provided free of charge. The Carnot efficiency is almost without relevance.

	▲	micro2588 an hour ago \| parent [-]
		In geothermal there is still a lot of interest in efficiency and exploring different working fluids because binary systems now have efficiencies of 10-20%. That is why you see companies like Sage Geosystems working on developing / deploying supercritical CO2 turbines to try and boost practical power densities.