Energy flexibility quantification of grid-responsive buildings: Energy flexibility index and assessment of their effectiveness for applications

The demand side is increasingly expected to provide energy flexibility for power grid economy and reliability. Buildings have various flexibility sources that can be effectively utilized for such purposes. According to different requirements of demand responses to power grid on response duration, response direction and response speed (within seconds, minutes, or even longer timescales), building energy flexibility is categorized as fast regulation, moderate regulation, load shedding, load shifting and load covering. In this paper, a comprehensive method is proposed to quantify building energy flexibility based on these categories. Two sets of flexibility indexes (flexibility capacities and flexibility ratios) for the above five energy flexibilities are proposed. An implementation case study is conducted to illustrate the use of these indexes and to validate the effectiveness of using them in flexibility performance assessment of buildings in particular. The impacts of different system design and control parameters on flexibility performance are also investigated quantitatively. The potential economic benefits of utilizing those energy flexibilities are analyzed in a real electricity market with an optimized use of different flexibility sources. Results show that electricity costs can be reduced by up to 21% if the market is available for such grid-responsive buildings.