There are currently three types of plants: Dry steam plant, Flash power plant and a Binary power plant. Dry steam plant operates the dry steam reservoirs, which produce very little water. The electricity is produced by directly piping the steam to push the turbines of the power plant. F;ash power plant is used to collect energy from natural reservoirs, where the temperature range is much lower 300-700 degrees F. The water is brought to the surface from the deep reservoir through the production well, while being released from the pressure, so some water is flashes into steam and transferred into a separator, which then spins the turbine and generates the electricity. The third type of plant, the binary plant can be used in even lower temperatures, as it is able to collect energy from a source where the temperatures range from 250 to 360 degrees F. This plant uses a heat exchanger and a liquid, that has a lower boiling temperature than water, e.g. opentane, which then vaporizes and forces the turbines to spin generating electricity. The vapor, like water is then re-condensed and returned into a heat exchanger, like the water returns to the natural reservoir. No waste is produced, because it is, as well as in the other systems above, a closed cycle with no emissions into the air.
That is why type of energy production is considered one of the cleanest.
The three types of plants we talked about above use underground water and steam from natural reservoirs and while they are only present in places with specific geological environment, underground hot dry rock is available everywhere. A new way of harnessing geothermal energy is currently being improved. The new type of power plant uses hot rocks buried very deep under the ground to heat up water via heat exchangers and piping, the cycle is basically the same, but more complex due to the more complicated heat transfer. With improving drilling technology geothermal energy from hot dry rock could be available virtually anywhere and in the near future we will be able to find out the true capacity of earth’s heat resources without harming the environment.
Although geothermal power plants are not common everywhere in the world due to their costs, they are used in most of the developed countries. The biggest producers and utilizes of geothermal energy are United States, New Zealand, Italy, Iceland, Mexico, the Philippines, Indonesia and Japan.