A Geothermal Power Plant

A geothermal power plant uses the free heat of deeper layers of earth to generate electrical energy. While this succeeds with different methods, all are based on a similar principle: Geothermal heat converts water into steam, which then drives a turbine. In the following article, we give an overview of the different types of geothermal power plants and show when their efforts are worthwhile.

Geothermal energy is thermal energy from deep

In the geothermal it comes to the use of heat from the upper layers of the earth's crust. This is one of the renewable energies. It can be used directly as heating heat or converted into electrical energy with so-called geothermal power plants. Depending on the depth at which geothermal energy is generated, experts differentiate between deep and near-surface geothermal energy. While near-surface geothermal heat with a heat pump can be used for heating, geothermal power plants usually tap into heat storage at depths of between 400 and over 3,000 meters.

Heat reservoirs are not available everywhere

If a geothermal power plant is to work economically, it needs temperatures of over 100 degrees Celsius. With a rise of three degrees per hundred meters, very deep holes are needed. This is different in areas with so-called "high enthalpy deposits". The geological anomalies often store geothermal energy at far higher temperatures below the Earth's surface. These can be found especially in regions with volcanic activity, such as in Tuscany or in Iceland.

Dry and moist deposits for geothermal energy

When it comes to the type of deposits, experts distinguish between petro- and hydrothermal systems. While petrothermal deposits consist of dry rock, hot thermal water circulates in hydrothermal reservoirs. If geothermal power plants can use the water of damp deposits directly, an artificial heat exchanger must first be created for dry systems. The water then circulates between the power plant and the rock via two boreholes in order to transport the environmental heat upwards.

Types of geothermal power plants at a glance

Geothermal energy is a base-loadable energy source from which electricity can be continuously generated as needed. This is possible with different types of geothermal power plants. Among others, dry steam, flash steam and binary systems are used.

Dry steam systems for power generation

Simple and efficient is a dry steam geothermal power plant. It uses high-energy deposits where hot water is present under high pressure. If the drill penetrates into these areas, the steam flows up without a pump and drives a turbine. This transmits kinetic energy to a generator, which generates electricity like the dynamo on a bicycle. When the steam has given up its energy to the power plant, it flows back into the deep via an injection well in liquid form.

Geothermal power plants with flash steam system

While dry steam systems power the oldest geothermal power plants, modern plants mainly use the so-called flash steam system. This is suitable if thermal water with temperatures of 180 to 300 degrees Celsius is available. The plants reduce the pressure in different stages, whereby the water evaporates. Then it drives a generator via a turbine before the liquid flows back into the depth.

Binary power plants for cooler thermal water

If the geothermal energy is available in temperature ranges below 180 degrees Celsius, geothermal power plants with binary circuits are used. These first transfer the thermal energy from the depth to a working fluid, which evaporates and drives the turbine. Once it has given up its energy, it becomes liquid again and can once again absorb heat from the depths. As the power plants pump up the water, experts also speak of pumped systems.

The prerequisite for a geothermal power plant

So that geothermal power plants can generate a lot of electricity with little effort, they should be built on high-enthalpy deposits. These store thermal energy with temperatures of over 150 degrees Celsius, which can be used, for example, with dry steam or flash steam systems. If the temperatures in the ground are lower, experts speak of low-enthalpy deposits. These have a temperature of less than 150 degrees Celsius and are suitable for the production of heating heat. If power plants are to gain power from the cooler sources, this only works with binary or pumped systems. Researchers know that high-enthalpy deposits are usually surrounded by low-enthalpy regions.