Geothermal energy is defined as heat from the earth. In practical terms, geothermal resources are thermal energy reservoirs that can be exploited at costs competitive with other forms of energy and are classified according to their reservoir fluid temperatures into low-, medium- and high-enthalpy fields. The very shallow geothermal energy within the first 10 meters below the Earth’s surface is mainly influenced by solar energy input rather than by heat from the Earth’s core.
While in the public understanding it is mainly the energy contained in deep aquifers that comes to mind when thinking of geothermal energy resources, the fact is that even the temperatures found at very shallow depths may be used to extract and store heat. Consequently, the heat resource offered by shallow geothermal energy (SGE) can be used as an efficient source of heating and cooling (H&C) for residential, commercial and industrial buildings. SGE systems are more efficient than traditional oil & gas-fuelled H&C systems, and therefore offer significant potential for the decarbonisation of the heating sector. While there is a consistent legal definition for geothermal energy generally in various European countries, few have a detailed legal definition for SGE. In fact, agreeing specific definitions for shallow geothermal resources is one of the key recommendations arising from the ReGeoCities project, launched in 2012 with the support of the Intelligent Energy Europe programme. Nevertheless, it can be said that SGE in Europe always refers to depths of less than 500 meters, and even less in several countries.
In terms of the number of installations, installed capacity and energy produced, SGE is the largest geothermal energy sector in Europe. In some regions, such as Iceland for example, hot water or steam may be piped directly into radiators. However, the most widespread technology by means of which Europe taps into its geothermal resource is the ground source heat pump (GSHP). Ground source heat pumps convert the low-temperature shallow geothermal energy, which is available almost everywhere, into thermal energy at a higher temperature which can then be used for space and/or water heating. These systems usually involve circulating an antifreeze solution inside a closed coil to exchange heat with the heat source/sink through a ground heat exchanger. While in the United States water-to-air systems are the most popular technology, in Europe water-to-water systems are more common. The ground collector of a GSHP mainly takes the form of horizontal loops or vertical loops made of polyethylene or polypropylene tubes. A third possibility uses so-called geostructures, where the loops are installed in the foundation piles of a building. However, horizontal loops are the most common system, as these offer the lowest costs.
According to the Eurobserv’ER1. heat pump barometer, geothermal heat pump sales in 2012 amounted to about 100,000 units, down slightly from about 108,000 units in 2011. In both years brine-water systems accounted for the vast majority of sales. Largely thanks to these sales figures, and the increased efficiency of existing heat pumps, geothermal production is exceeding targets set in National Renewable Energy Action Plans (NREAPs). In 2012, shallow geothermal heat production, mainly through the use of ground source heat pumps (GSHP), exceeded the NREAP target by 40% (JRC 20152).
Recent innovations in shallow geothermal technology include the addition of underground thermal energy storage (UTES). UTES technologies include aquifer thermal energy storage (ATES) and borehole thermal energy storage (BTES). ATES systems utilise aquifers to store low-grade thermal energy such as solar heat during off-peak periods. This energy is used to heat or cool water, which is then injected into an aquifer for storage. BTES systems are designed in such a way that heat is built up in and extracted from a cylindrical volume of soil or rock. In both systems, the underground temperature is changed by injecting heat or cold which can then be retrieved for later use. Solar thermal collectors can also be added to GSHP systems. These can be added directly to the GSHP’s ground loop to increase the efficiency of the system while reducing the demand for land area (JRC 2015).
Among the recommendations made in the Geothermal Regulation Framework3, published in 2009 with the support of Intelligent Energy Europe, an emphasis was placed on the need for streamlined administrative procedures for geothermal licensing. In recognition of this requirement, the ReGeoCities project set the streamlining of administrative barriers as one of its main aims. The project, which is working to integrate SGE at a local and regional level, is focused on supporting European cities in reaching their Sustainable Energy Action Plans (SEAPS) and the 2020 climate and energy goals by examining and promoting best practices and an intelligent regulatory framework.
With a view to achieving these aims, the project consortium conducted an Analysis of the Market for Shallow Geothermal Energy, which found that after tremendous market development in some European countries until about 2009, economic factors resulted in a decrease in annual new installations over the past few years. In addition to economic factors, the report also found that overregulation in some countries resulted in increased costs and time. To evaluate the extent of this problem, the project carried out an overview of the current legislative framework in Europe. This resulting report, which was created using 11 national reports produced by the ReGeoCities partner countries, presents reliable and up to date information about the market conditions and barriers for SGE.
The ReGeoCities also conducted an analysis of best practices in the partner countries and, based on this, identified a list of key measures to provide the required basis for the development of the shallow geothermal sector at national, regional and municipal level. Many of these key measures address shortcomings in the legislative and regulatory framework, and include the development of adequate legislative and regulatory instruments for the management and deployment of SGE systems and, as already mentioned, agreeing specific definitions for shallow geothermal resources in the context of existing legislation and regulations. The project’s Best Practice Analysis Report4 also recommends the development of a simplified permitting and application system for small domestic installations, along with specific regulatory procedures for larger and more complex SGE systems.
One barrier to the development of SGE systems, mentioned by almost all the ReGeoCities partner countries, is a lack of knowledge about technologies and support incentives and a lack of information on the potential for installing GSHP systems, including the low dissemination of data from running operations. By addressing these information gaps, the ReGeoCities project is supporting European cities in their efforts to integrate geothermal into their energy mixes and promoting geothermal energy as a viable source of heating and cooling for the European market.