Economic Analysis and Optimal Control Strategy of Micro Gas-Turbine with Batteries and Water Tank: German Case Study

Abstract

Currently, Micro Gas Turbines (MGTs) are widely used in small buildings, such as offices, hospitals, or households, in which electricity and thermal energy are needed. Their reliability, flexibility, and compactness allow these devices to operate in different regimes to fulfill the power demand. The opportunity to operate at partial-load is deeply investigated in this paper. To cope with the fast, unpredictable demand of energy, thermal storage and batteries are most commonly installed. The potential of these two components for the operating cost is also investigated in this paper in order to provide guidelines on their sizing. Moreover, the thermal and electrical energy demands depend on different factors such as building size, weather, day of the week, and location, all modeled in this work; the possibility to buy and feed electricity into the grid adds a further variable to the economic analysis. All these factors were considered in this study and led to the creation of an optimization algorithm, which was able to determine the optimal operating profile of the system for every single scenario. The operational optimization of a micro gas turbine, the MTT Enertwin, is presented. Data from experimental measurements were implemented in the algorithm in order to characterize the system performance. Concerning the input power demands, data for Germany according to the norm VDI 4655 were considered; hence, the results are formally limited to this region. However, considerations of batteries and thermal storage were broadly valid; also, the results can be of international interest in countries with a similar climate and habits. With this study, it is shown that the optimal operational strategy is in the vast majority of cases the full-load, with savings up to 20% with respect to partial-load. Furthermore, batteries between 1.5 and 2 kWh constitute the best compromise between installation costs and savings; the investment can be generally paid off in less than 3 years. Finally, a threshold of 400 L for thermal storage was identified.