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.
Highlights
There is an increasing need for energy storage in buildings to allow for integration of intermittent on-site renewable energy sources or the provision of energy flexibility to the electric grid.Thermal storage thereby plays an important role as it allows cheaply offsetting large amounts of energy.Thermal storage capital cost is low when compared to electric batteries and allows for economical energy storage over longer time periods operation with substantially fewer cycles over its lifetime
For the assessment of the seasonal energy flexibility by using a liquid sorption storage, a sample single family home (SFH) with 140 m2 of floor area is considered as defined by the IEA SHC Task
The analysis performed captures seasonal load shifting/flexibility for a single-family home with an integrated sorption storage. It represents the electricity saved in heating operation because of seasonal thermal energy storage, called virtual battery effect
Summary
There is an increasing need for energy storage in buildings to allow for integration of intermittent on-site renewable energy sources or the provision of energy flexibility to the electric grid. Thermal storage capital cost is low when compared to electric batteries and allows for economical energy storage over longer time periods operation with substantially fewer cycles over its lifetime. Seasonal storage is of great importance for significantly increasing renewable fraction in the operation of buildings. Excess energy available in summer cannot be made available for coverage of heat demand in winter such that renewable fraction, especially for space heating remains strongly limited. Excess energy available from on-site renewable production or electricity from the grid can be absorbed in summer to be made available in winter when space heating demand is largest
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