###### Abstract
Daily and seasonable meteorological conditions significantly affect energy demand profiles [5]. The energy that the end-user needs in a typical day is a highly time-dependent profile, where the amplitude and frequency depend on different factors, such as how many people live/operate in the building, the weather, and the location. Therefore, if an MGT is supposed to work in such conditions, it should operate well in partial-load [6]. An optimal strategy has to be found between reduced electrical efficiency and power at partial-load in comparison to the start/stop and standby losses during intermittent operation. We sum up the major contributions and the novelties of this work as follows:  
Major contributions:  
* The present work proves mathematically if operating an MGT-based CHP system at partial-load is economically more profitable than at full-load;
* An algorithm to determine the most economical operative profile was developed and can be extended easily to other MGTs and countries as well;
* This work provides clear guidelines for battery and water tank sizing depending on building size, occupancy, and climate zone;
* This work constitutes the foundation of any lifetime prediction of MGT components, since it clearly defines the order and number or starts, stops, and loads, hence the working cycle. Novelties:  
* Real-world energy demands (building occupancy, day of the week, season, weather, geographical area) are considered instead of constant values;
* Batteries and thermal storage are examined together in the analysis (elsewhere often treated separately);
* The possibility to feed the excess electricity back into the net is considered in the price function;
* A finite price per day can be given for any operative profile, building size, day of the week, season, weather, or geographical area. _State-of-the-Art_  
In this paper, an MGT from the dutch company MTT, the Enertwin (3.2 kWel, 15.6 kWth), is considered. Similar studies have been conducted, but either with the use of other power sources, such as solar, wind, and diesel sources [7], or with different MGTs, such as the Turbec T100 [8; 9]. The work of [10] focused on the modeling approach of the MGT, but did not include the important role of thermal storage and batteries. A recent study [11] on hybrid photovoltaic-CHP systems involved the use of a much smaller CHP system (1 kWel, 2.4 kWh) and smaller thermal storage (300 L); instead, in the present analysis, a wide range of thermal storage and battery sizes is investigated. Much larger MGTs (65 kWel, 112 kWh) have been investigated as well in similar studies [12]. The role of the battery has also been analyzed in other works, as in [13; 14] in connection with photovoltaic plants, but not with a single MGT. Although MTT intends to enter markets in many regions of the world such as China, the U.S., and Canada, the commercialization focus from MTT is, as of 2019, mainly targeted at Europe [15]. For this reason, standardized load profiles for different types of households in Germany according to the norm VDI 4655 [16] are applied in this study. As a consequence, the numerical results (costs and operative profiles) are strictly valid for this country. However, considerations made for batteries and thermal storage have a broader validity and are of general interest. Moreover, the considerations made for the MTT Enertwin can be extended to other MGT-based CHP systems with a similar power range and contribute to the international community by providing clear control strategy guidelines. It is recommended that future studies perform similar economy-based analyses by considering energy demands and environmental factors from other countries; the flexibility of the algorithm presented here allows this with relatively small effort.