Follow up on large svale heat storages in Denmark

Long term heat storages are important in the future energy system in Denmark. This can a.o. bee seen in two reports required by the Danish Energy Agency during 2013:

•  "Status and Recommendations for RD&D on Energy Storage Technologies in a Danish Context" and
•  ”Udredning vedrørende varmelagringsteknologier og store varmepumper til brug i fjernvarmesystemet" (analyses of heat storage technologies and large heat pumps for districtheating)

From 2011 to 2013 three large long term storages has been implemented in Brædstrup (borehole storage), Marstal (pit heat storage) and Dronninglund (pit heat storage) connected to large scale solar heat plants and heat pumps for district heating. The monitoring programs for these storages end when the projects are finalized. But long term heat storages change performance the first years because the surrounding soil is heated up. Therefore there is a need to continue the monitoring programmes. This
application has as purpose to secure a continuation of the monitoring programmes and to analyse and make the results public. Beside the application includes tests and measures that can support future storage projects.
The main activity in the project is a real time publication of monitoring results at Solvarmedatadk and yearly analysis of performance of the storages. Pit heat storages has beside that three problems, that the application shall solve for existing and future owners:

•  Corrossion in in-and outlet pipes. The problem has showed up in Marstal. Effect of actions taken and future development has to be carefully supervised.
• Life time for the liner in Dronninglund. The liner has until now not been tested for long termdurability, but the supplier has quaranteed 20 years life time by 90° C. This must be tested, because such a liner can extend the market for pit heat storages to storing heat from incineration plants, CHP and industrial processes.
• The durability of the insulation material in the floating lid constructions in Marstal and Dronninglund. Also here a test will show if the market can be extended.

Long term heat storages can make the future district heating systems flexible, so that they can integrate fluctuating power production. In Denmark the future market is estimated to 5 mio. m3 water storages. Outside Denmark similar systems are developed. For instance a resent german study has showed a marked of 15 mio. m3 water storages and China has showed beginning interest for the technology.