Seasonal Energy Flexibility Through Integration of Liquid Sorption Storage in Buildings

Abstract

The article estimates energy flexibility provided to the electricity grid by integration of long-term thermal energy storage in buildings. To this end, a liquid sorption storage combined with a compression heat pump is studied for a single-family home. This combination acts as a double-stage heat pump comprised of a thermal and an electrical stage. It lowers the temperature lift to be overcome by the electrical heat pump and thus increases its coefficient of performance. A simplified model is used to quantify seasonal energy flexibility by means of electric load shifting evaluated with a monthly resolution. Results are presented for unlimited and limited storage capacity leading to a total seasonal electric load shift of 631.8 kWh/a and 181.7 kWh/a, respectively. This shift, referred to as virtual battery effect, provided through long-term thermal energy storage is large compared to typical electric battery capacities installed in buildings. This highlights the significance of building-integrated long-term thermal energy storage for provision of energy flexibility to the electricity grid and hence for the integration of renewables in our energy system.

Thermochemical storage networks for integration of renewable energy sources through seasonal load shifting

“…This is higher by a factor of 22.3 or 2 respectively, compared to the sensible water storage. In absolute terms, this storage density is still low (compared to the possible 300 kWh/m3 reported in [12]) as the maximum NaOH concentration employed was 45 wt% and the concentration difference across the sorption reactor was low. The reason for this is the relatively high return temperature from the building's space heating loop.…”

“…This maximum concentration was chosen such that for the selected soil temperature of 5 °C the solidification temperature of aqueous sodium hydroxide is not reached. The sorption reactor is modelled ideally assuming equilibrium conditions similarly as described in [12] and implemented in Modelica.…”

Static Temperature Guideline for Comparative Testing of Sorption Heat Storage Systems for Building Application

“…This includes indication of extra measures taken to circumvent restrictive temperature boundaries as proposed here. Examples could be resistive heating to reach higher material temperatures in charging or combinations of sorption storages with electric heat pumps [61] to leverage the overall available temperature lift in discharging, thus allowing as well for production of domestic hot water. Other measures such as integration of solar collectors along with ground heat exchangers to achieve higher source temperatures in discharging can be discussed with reference to the temperature guidelines proposed here.…”