for our heatbeat Research Newsletter, we always aim to find research about district heating and cooling from which we can gain insights and inspiration for practical challenges in the green transition of the industry. In this 40th issue of our newsletter we selected two papers about large-scale pit storage and about district heating prices in Finland.

Insights into Large-Scale Pit Thermal Energy Storage

Large-scale heat storages can be an important solution to enable the use of renewable heat sources with seasonally fluctuating availability like e.g. solar thermal energy. And while at a certain scale pit storages have the potential to be the cheapest option for large-scale heat storage, their adoption so far has been limited. Thus, any insights in the actual performance of these systems can help to reduce uncertainties and help to evaluate this technology for any projects where a large-scale heat storage can be considered. Therefore, for anyone interested in the actual performance of such storage systems, we recommend the recent PhD thesis “Large pit thermal energy storage for solar district heating plant” by Yutong Xiang. We think that this work gives a great overview of several aspects of the operation of a pit storage.

The pit storage investigated in this work is the one in Dronninglund, which we already mentioned in issue 32 of our newsletter before. The storage has a volume of 60,000 m³ and openly shares a public dataset for the year 2014. In the thesis by Xiang, we also find a good overview of some other existing pit storages, the technical design and materials options, and a detailed investigation of the storage operation over several years (2014 - 2017). Furthermore, the thesis includes several papers published as the result of this PhD effort with further insights. We found it interesting to see how the storage temperatures seasonally vary from a maximum of 84 °C to a minimum of 9 °C and how around 11 GWh can be stored at a storage efficiency of around 90 %. If this can be realized in other sites, pit storages have a huge potential in the green transition of district heating.

District Heating Prices in Finland

Of course, district heating can only compete with other heating options if it’s economically feasible. And as it’s a core challenge of the green transition of district heating away from fossil fuels, we are always interested in understanding how the choice of heat sources and other factors influence the resulting heat price of district heating and its economic feasibility overall. In this context, we can recommend a recent preprint by Ranta et al. titled “The effect of fuels and other variables on the price of district heating in Finland”.

This study uses a dataset of heat prices from around 100 Finnish district heating companies which provide heat to around 170 municipalities, covering around 97 % of district heating sales in Finland. In this data, the net price of district heating for a representative apartment building customer ranges between 53 EUR/MWh and 138 EUR/MWh with an average value of 91 EUR/MWh. For us, it was interesting to see that the study found no direct effect of the fuel choice to fully explain the differences in heat prices. Other effects like plant size, regional variations, differences between municipal and private companies, and of course the demand structure also have a significant influence on the heat prices. This confirms our experience that the economic feasibility of district heating needs to be carefully investigated for each use case.

Further information

In addition to the two papers mentioned above, we can recommend that paper “Fifth generation district heating and cooling: A comprehensive survey” by Minh Dang et al. which gives an updated review of recent district heating surveys and on the ongoing 4GDH and 5GDH discussions.

The next issue of our newsletter will be published on March 6, 2024.