Optimization of integrated energy storage for implicit demand-side flexibility : The case study of Singapore office buildings

Abstract: Demand-Side Flexibility (DSF) is a very attractive option to solve challenges that are emerging from the evolution of modern power systems all around the world. The greater integration of intermittent renewable energy sources into the energy mix creates the need for flexible end-user behavior and demand management. In Singapore, distributed power production grows steadily in the form of rooftop solar PV panels installed on both households and commercial buildings, where the main load demand is cooling and air conditioning. Challenges arise also from the projected rapid increase in the penetration of Electric Vehicles (EVs). The charging routines of EVs could represent a high and potentially dangerous power peak that the current electrical grid is not able to withstand. Providing the ability to shift the demand profile of a large building or a neighborhood with minimum modifications of the electrical grid, DSF is poised to play a central role in solving these challenges during the next 10-20 years. This study proposes linear mathematical modeling for the optimum utilization of sensible-heat thermal and electrochemical battery energy storage, implemented in the already existing building modelling framework developed by TUM-CREATE, the CoBMo. An optimization problem is defined aiming to minimize the total cost as the sum of operational costs from the electricity consumption of the HVAC system and the investment costs for the energy storage. Financial payback analysis is performed using the CoBMo version improved with the mathematical model to estimate the achievable annual savings. The discounted payback time is considered as an economic indicator to whether the storage would be a valid investment or not depending on the electricity price signal – wholesale and retailer – as well as on the storage operation setup and installation costs, lifetime, efficiency, etc. The economic analysis shows that both the thermal energy and battery storage options are feasible for office buildings in Singapore considering the investment conditions from year 2020 onwards. While chilled-water thermal energy storage is well established and relatively simple technology, the battery storage displays better economic return when selecting Li-Ion Nickel Manganese Cobalt (NMC) technology. The optimal daily schedule of both storage solutions is presented in this study, showing how the optimization tool leverages the price signals, relying on trade-offs between operational expenditures and investment costs for the energy storage systems.