Generating electricity from geothermal power plants is usually a good alternative. It is usually said that temperatures should be raised around 150 ℃ in order to obtain good profitability, but the conditions vary greatly between different places so that you can make a lot of money in investigating the conditions before making a decision.
Although the geothermal water never reaches the boiling point of water, electricity can be generated by using a secondary "binary" liquid that has a lower boiling point instead of using a traditional steam-powered turbine. In Chena Hot Springs, Alaska, the geothermal power plant in the world uses the lowest bedrock temperature for commercial power generation.
Although they only use a water temperature of around 70 ℃, they have radically lowered the costs of generating electricity by reducing the distribution costs of the diesel that was previously used to generate electricity.
In this case, as in all situations where one is producing, or intending to produce electricity, careful investigations and comparing the various methods available should be performed. Both the financial result and the consequences for the environment should be compared in the short and long term.
A simple rule when generating electricity from geothermal energy is that the higher the efficiency, the higher the temperature you get from the bedrock.
There are many examples of power plants where they have a borehole temperature of around 150 ℃ and have an efficiency above 10 % when generated in ORC machines. This may seem low, but given the low costs of running the plant to extract energy from the bedrock, it is usually significantly more profitable than it seems. An ORC machine or "Organic Rankine Cycle".
The letter O in the ORC stands for using a high molecular weight organic liquid with a liquid vapor phase change, or boiling point, which occurs at a lower temperature compared to water vapor. The properties of the liquid enable the use of sources with lower temperatures.
More recently, manufacturers of ORC machines have marketed themselves by saying that the efficiency of their machines has increased by lots of percent. This may be true, but these, seemingly large improvements can be meaningless given the large constraint that lies in the total heat energy one can use to perform the work required to generate electricity.
A Carnot motor or heating motor operates according to the Carnot cycle. The theory behind the engine was originally developed by the Frenchman Sadi Carnot in 1824 and the model was later developed by Benoît Paul Émile Clapeyron and mathematically studied by Rudolf Clausius. This work led to the basic thermodynamic concept of entropy.
Although ORC machines have relatively low efficiency, they are often an excellent alternative for generating electricity. Given the large amount of energy that can be extracted from the bedrock by building larger geothermal plants, you get low operating costs for the long time that the plant can produce electricity. Large parts of the world have excellent geological and thermal conditions for generating electricity and this has also been done since the beginning of the 20th century. Because the production is emission-free, geothermal power plants can be built close to consumers and placed where they are needed.