Every year Phd students working on geothermal energy gather to have a short informal conference. This year the ETH in Zurich is the host of the 9th edition. With about 80 participants the conference attracts a stable number of researchers from countries all over Europe and beyond. With 5 people from Delft we were one of main contributing Universities. Presentations and posters cover a wide range of topics regarding geothermal energy. From the high enthalpy systems for power production all the way to the Ground source heat pumps and from technical work on simulation and field studies up to governance and management studies. Traditionally the conference is closed with a field trip; to a geothermal power plant.
Some general views on key developments that were presented:
- New drilling methods. Man kind has always used rotary drilling methods. With the trend towards more and deeper boreholes in more solid rocks the demand for contactless drilling increases. Promising developments were shown on sonic, laser and waterjet methods
- New concepts combining CO2 storage in geothermal reservoirs and recovery for power production
- New (composite) materials and monitoring methods to ensure well integrity.
World potential and salinity stratified aquifers
I had two contributions. On the first day is was co-author on the oral presentation of my colleague Marc Jaxa-Rozen, in which he presented our results on theATES potential world wide. The results show that thare is a lot of unexploited potential for energy savings with ATES in Asia and north America.
The second day I presented the results of my study with my promotor Theo Olstoorn on the effect of buoyancy flow on the efficiency of ATES systems caused by a salinity gradient in aquifers. The results show that under conditions occurring in The Netherlands such buoyancy effects do not affect efficiency significantly.
ATES systems in salinity stratified aquifers
One site specific condition for Aquifer Thermal Energy Storage (ATES) is an increasing salinity with aquifer depth. Such conditions are often present in coastal areas where also the demand for ATES application is high because urban development is concentrated in coastal areas. The seasonally alternating extraction and re-injection between ATES wells disturbs the preexisting ambient salinity gradient and causes horizontal density gradients, which trigger buoyancy flow, which in turn affect the recovery efficiency of the heat storage.
Analytical and numerical methods are used to understand and explain the processes that cause buoyancy flow to occur in such situations, as well as to quantify the effect relative to other losses. The results of this research shows that buoyancy losses may become considerable at ambient density gradients of over 0.5 kg/m3/m in combination with a vertical hydraulic conductivity of over 5 m/d. Monowell systems suffer more from buoyancy losses compared to doublet systems.