**Seasonal Energy Flexibility Through Integration of Liquid Sorption Storage in Buildings**

#### **Luca Baldini \* and Benjamin Fumey**

Empa–Swiss Federal Laboratories for Materials Science and Technology, 8600 Dubendorf, Switzerland; benjamin.fumey@empa.ch

**\*** Correspondence: luca.baldini@empa.ch

Received: 30 April 2020; Accepted: 4 June 2020; Published: 8 June 2020

**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.

**Keywords:** long-term thermal energy storage; seasonal thermal energy storage; thermochemical energy storage; liquid sorption storage; power-to-heat; seasonal energy flexibility; seasonal load shifting; virtual battery effect
