Increased density of geothermal energy systems for greater CO2 reduction

Aquifer thermal energy storage systems (ATES) accumulate in cities because they are installed near the buildings they supply with geothermal energy. In areas with high building density these systems can influence each other in the subsurface, but such mutual interaction is not possible or permitted under current regulations. The result is that the geothermal sources are kept far apart from each other, creating an artificial shortage of sources. This problem has also been signalled by the Geothermal Energy Knowledge Platform and included as a priority issue in their research agenda. This research project will explore the frameworks and conditions to make more intensive and efficient use of the subsurface for geothermal energy systems.

 Activities

1: Gain insight into the performance of geothermal energy systems
This involves getting a clear picture of the relation between thermal losses in the subsurface and the total energy savings and costs of geothermal energy systems. This will take into account, in contrast to the situation in practice, the dependence of the efficiency of heat pumps on the temperature of the extracted groundwater, as well as the conditions of a building for the proper functioning of the system: for example, the delivery capacity of cooling within a building. After all, if the cold water lens in the subsurface becomes too warm, the building can no longer be cooled to the required level of comfort.

2: Determine the impact of an increase in the number of systems on total energy savings
This involves determining the overall energy savings in an area resulting from the increase in the density of geothermal energy systems, while taking into account the minimum operational requirements for an individual system. We will study whether collective geothermal energy systems can reduce spatial use. We will also consider the financial implications with regard to the operational costs.

3: Determine the optimal/maximum density of systems in the subsurface
Currently a licensing authority disposes of no general criteria to clearly assess the thermal influence of an additional geothermal energy system. This is why in cases of thermal influence, following the precautionary principle, no license is issued for the new system. We would like to break this logjam by:

• Conducting simulations of energy losses resulting from the interaction of several systems in the subsurface.
• Establishing a uniformly applicable assessment framework for the mutual interaction of geothermal energy systems.

We will take seasonal variations into account and compare a situation in which many individual systems are used with the use of a single collective system.

The theoretical studies for activities 1,2 and 3 will produce uniform assessment criteria and management instruments for geothermal energy systems in congested areas.

4: Examine high density in practice
We will apply the criteria and management instruments we develop to the case of the Utrecht Oost station area. Together with our partners, we will determine whether the criteria and management instruments are satisfactory or need to be adjusted. In this phase, we will work with the authorities concerned (provinces and municipalities) to establish where the opportunities exist in the current regulatory framework. If the regulations appear to be constraining we will make recommendations to modify them. This will also involve doing simulations to test whether the generic instruments and criteria meet the expectations.

The established and validated assessment criteria and management instruments will then be evaluated and further elaborated into a concrete proposition for the design and planning of geothermal energy systems in congested areas. To build support for the implementation, it will be necessary to organise a workshop to discuss and reflect on the proposition with the remaining stakeholders: other provinces, municipalities and market players.

Results

This research will produce the following substantive results:

• Insight into the extent to which heat/cold loss in the subsurface is acceptable before it has a significant impact on the energy savings of a geothermal energy system.
• Insight into how much extra energy savings can be made in areas with geothermal energy systems.
• Insight into which soil and system properties have the most impact on mutual interaction and how ‘busyness’ can be uniformly quantified; and insight into what levels of busyness require supplementary regulatory measures and when they are not required.
• Insight into the impact of the extension of geothermal energy systems on groundwater quality.
• A uniform framework with assessment criteria and management instruments for geothermal energy systems in congested areas. The framework will be directly applicable in all areas of the Netherlands where many geothermal energy systems are installed.