What is geothermal energy and how does heating with geothermal heat work?

Geothermal energy, the use of heat stored in the Earth's crust, has great potential in Austria but is currently hardly utilized. Geothermal energy can provide climate-friendly heating and reduce energy costs in the long term. This means geothermal energy provides renewable energy and is independent of weather and season.

What is geothermal energy and how does it work?

Geothermal energy uses the Heat inside the EarthWater is directed deep down, heats up there, and brings the heat back up. Like wind, water, and solar energy, it is a renewable energy source. However, unlike wind and sun, geothermal energy provides constant heat. It is completely independent of the weather and season.

The heat inside the Earth originates from two primary sources: residual heat from the planet's formation and the decay of radioactive isotopes.

The heat in the Earth's interior is generated by multiple processes. A portion comes from the residual heat from the Earth's formation around 4.6 billion years originated. In addition, there is heat from the decay of radioactive elements such as uranium. This process occurs constantly and continuously generates new heat. However, it should not be confused with Nuclear fusion, as it occurs in the sun and other stars.

Unlike nuclear fusion, where light nuclei fuse into heavier ones, the atomic nuclei of radioactive elements spontaneously decay, generating heat in the process. Around 99 percent the Earth's crust is hotter than 1000 degrees Celsius. Even the outermost ten kilometers of the Earth's crust contain so much heat that it could cover the Earth's entire energy demand could cover 100,000 times. The comparatively cool temperatures that we know on the surface, on the other hand, only prevail in a very small part of the Earth's mass – namely 0,1 %.

Near-surface and deep geothermal energy

The heat from the Earth's interior can be utilized in various ways. Fundamentally, there are two types of geothermal energy: near-surface and the deep geothermal. In both cases, holes are drilled into the earth and the heat from the earth's interior is transported upwards using pipes. The difference lies in the depth of the boreholes.

Near-surface geothermal energy

Shallow geothermal energy comes in Heat pumps for use. The boreholes mostly only go a few one hundred meters deep. There the temperatures are around 10 to 25 degrees Celsius.

U-shaped pipes run through the boreholes, through which a heat transfer fluid flows. It usually consists of water with antifreeze and transports the heat upwards. A heat pump compresses the low heat from 10–25 °C to 40–60 °C operating temperature, so that buildings can be heated with it.

The U-shaped pipes are also called geothermal probes. One or two such probes are sufficient to heat a single-family home. However, electricity cannot be generated this way.

Deep geothermal

Deep geothermal drilling reaches several kilometers into the Earth. At this depth, temperatures are significantly higher. Geothermal power plants These utilize this heat to supply entire city districts. These power plants can generate both heat and electricity.

However, not all locations have the necessary geological conditions. While shallow geothermal energy is almost everywhere For deep geothermal energy, either underground thermal water or hot underground rock layers are needed, which is possible on Earth.

Hydrothermal Geothermal: Turning Water into Heat and Electricity

Hydrothermal geothermal energy utilizes naturally occurring hot water underground. This water circulates in deep rock layers. A borehole brings the hot water to the surface. There, it releases its heat or drives a turbine for electricity generation. Afterward, it flows back into the depths via a second borehole. There, it heats up again, and a closed loop.

This technique is proven and has been used since used for decades. Among the most important countries are the USA, China, and Turkey. However, geothermal power plants for electricity generation are only in volcanically active regions economically. Iceland, Indonesia, and the Philippines are particularly leading in this regard.

There are also geothermal plants in Austria. And some of them have been around since the 1970s. Many are located in Upper Austria and Styria. Another significant region is the Vienna Basin. There, Wien Energie, Austria's largest regional energy provider, is planning several new facilities.

Petrothermal Geothermal

Petrothermal geothermal energy extracts heat from underground rock and does not require natural thermal water. Instead, water artificial pumped into underground rock. To do this, companies drill two holes several kilometers deep into the earth. They pump water into one of them under high pressure. The pressure creates fine cracks in the rock. This allows the water to distribute and heat up. It returns to the surface through the second boreholes.

The procedure resembles frackingIn both cases, water is pumped into the solid rock under extreme pressure until fine cracks form. In fracking, however, sand is also added to the water. environmentally harmful chemicals mixed in. And of course, the procedures have different goals: With fracking, Oil promoted, with geothermal energy only heat.

Theoretically, this technique can almost everywhere use. Experts estimate the potential of petrothermal geothermal energy accordingly at a Multiple times higher than that of hydrothermal geothermal energy. In practice, however, there are problems. The technology is Elaborate and expensive. By altering pressure conditions in the rock, perceptible earthquakes can be triggered. A well-known example is a project in Basel in 2006.

There a geothermal project solved 3.4 magnitude earthquake. The drilling had to be stopped. Due to these risks, there are hardly any economically operated plants to this day. Therefore, when talking about geothermal energy in general, it primarily refers to hydrothermal geothermal energy, meaning the use of naturally occurring hot water and steam reservoirs underground.

Geothermal energy in Austria

The potential for geothermal energy in Austria is greater than many suspect. Three regions exhibit favorable geological conditions: the molasses basin in the Upper Austrian Innviertel and Hausruckviertel, which Styrian Basin in southeastern Styria and the Vienna Basin. Hydrothermal systems exist there, in which thermal water circulates at greater depths.

In Upper Austria and Styria has had geothermal projects for decades. In the city of Ried im Innkreis, there are already 60 % for all households heated with geothermal energy. Additionally, the local energy provider Ried Energie also supplies 300 households in surrounding communities with heat from deep within the earth. Ried is therefore often referred to as the Austria's Geothermal Hotspot designates.

In Southeast Styria, in addition to existing facilities, since 2026 seismic measurements instead of exploring the subsurface for new geothermal plants. The third region with high potential – the Vienna Basin – has been less utilized so far. Meanwhile, Wien Energie is now strongly focused on expanding geothermal energy and plans, with the „deeep“ project, to 7 Appendixto build. From 2028 should 20,000 households to be supplied with green energy from deep within.

Anyone who wants to know where geothermal energy could potentially be used in Austria will find information on the website Geothermal Atlas found. Currently, only data for Vienna is available, but work is underway to expand it nationwide.

Costs: Is geothermal heating worth it?

For a single-family home, the costs usually range between 15,000 and 30,000 Euros. However, those who want to have a heat pump installed usually don't have to bear the entire cost themselves. This is because the state subsidizes the „heating boiler replacement,“ meaning the conversion to climate-friendly heating in private households, with up to 30 %.

In contrast, the investment costs for deep geothermal plants are typically in the Millions. Because of the high initial investments, many energy providers have shied away from expansion in the past. However, a geothermal power plant is worthwhile in the long term: once built, it supplies almost Unlimited energy.