Influence of electricity prices on energy flexibility of integrated hybrid heat pump and thermal storage systems in a residential building

The aim of the present paper is to investigate the influence of electricity tariffs on energy flexibility in buildings and associated energy costs. A residential building located in Stuttgart, Germany, equipped with a hybrid heat pump which is coupled with a thermal energy storage unit and a gas boiler is used as a case study. A model predictive control algorithm is used to minimise the daily operational cost over a full heating season. Several demand response programs based on controlling the heat pump power consumption were tested and analysed by adopting different metrics capable of describing the flexibility potential and cost of demand response programs. Several tariff structures, including: real-time pricing, two-level day-night tariffs and critical-peak pricing with both fixed and variable feed-in price components, were investigated. The results show that the building can provide up to 1370 kWhe of energy flexibility over the heating season with an average specific (marginal) costs of between €0.024–0.035 per kWhe of flexibility provided. The demand response programs lead to higher utilisation of thermal energy storage along with increased boiler consumption, by up to 17.1% and 12.1%, respectively in case of maximum demand response intensity. This in turn leads to a higher overall primary energy consumption of between 1.6% and 9.1% depending on demand response intensity. Typically, real-time pricing is the most favourable tariff structure, capable of offering the greatest energy flexibility with lowest associated electricity costs.