Danish solar energy storage system design

Since the 80ties large scale thermal storages have been developed and tested in the Danish energy system. From 2011 five full scale pit heat water storages and one pilot borehole storage have been built.

The SUNSTORE® concept consists of a large heat storage (pit heat storage, borehole storage or tank storage), solar collectors to heat up the storage, a heat pump to use the storage as heat source (and at the same time extend solar production, reduce heat loss from the storage and extend the storage capacity) combined with a CHP plant.

At the opening in May 2014, the solar collector field was the largest in the world. The Dronninglund storage is a pit thermal energy storage (PTES) of 60,000 m3. The design is similar to the storage in Marstal, but the in- and outlet enters through the bottom of the storage where the pipes in Marstal enters through the side.

Over the years the distribution network has been rolled out to a large per-centage of the population. With solar thermal plants providing the energy, production at the district heating plant is fossil free. In Den-mark the need for electricity is bigger in the winter where the hours of sunshine are limited.

A residential project complying with the Danish building standard 2015 is considered as a case study to assess the feasibility of using the proposed heat and power supply system with the seasonal thermal energy storage unit to bridge the gap between the energy demand and supply in Denmark residential and housing sector.

But many heat sources as solar thermal, heat from waste-to-energy plants, geothermal energy and excess heat are available only during summer or constantly during the year. Large scale thermal storages make it possible to utilize these sources, replace peak fossil based production and integrate fluctuating electricity from PV and wind.