Using seawater thermal energy for district heating: an oceanographic point of view

Abstract:
Replacing the usage of fossil fuels by renewable energy sources is an emerging task of EU climate and energy policies, including the Green Deal. Although deep seawater has in the Baltic Sea low temperature, it is relatively stable throughout the year, and it is still warm enough that heat can be extracted from the water before cooling to the freezing temperature. However, extracting the heat in large quantities (tens of MW) needed for town district scale, requires the pumped seawater volume to be rather large, comparable to the flow rates of rivers. Therefore, with long pipelines, energy loss for pumping may become considerable. Another option, pumping the seawater through short tubes from a coastal location, is limited in time for three late autumn months, because of the seasonal cycle of sea surface temperature. Based on the Copernicus Marine Service reanalysis data 1993-2021, southern coast of the Gulf of Finland has one of the most favorable locations for seawater heat extraction in the Baltic Sea, because of the short distance to the unfreezing sub-halocline layers.

More detailed oceanographic, environmental, and engineering aspects of using seawater thermal energy are analyzed in the Tallinn Bay area with the data from different sources, including Estonian marine forecast system with a 1-km resolution, remote sensing, and dedicated observations and very-high-resolution modelling.