# Assessment of Batteries' Contribution for Optimal Self-Sufficiency in Large Building Complexes
## 1 Introduction  
Achieving sustainability is the way to achieve the energy transition. Climate change objectively requires the attainment of sustainability. Thus, reducing too many negative impacts such as CO\({}_{2}\) emissions and greenhouse gas (GHG) emissions from the atmosphere by 2050 is paramount [1]. The EU has set a central goal to limit global warming below two (2) degrees Celisius above pre-industrial levels in response to the Paris Agreement (Paris Agreement Goal). The European Green Deal's implementation set an aim of reducing CO\({}_{2}\) by 55% [2; 3; 4]. Furthermore, the EU has developed a broad range of policies to advance its goal of transforming its economy to achieve climate neutrality by 2050 [5; 6]. In the context of these specific goals, the EU is promoting, through various policies, the development and implementation of various types of clean energy sources, such as solar power, wind power, hydropower, biomass energy, geothermal energy, etc. A crucial step toward this goal is the decarbonization of the building sector [7]. The International Energy Agency (IEA) stressed the importance of clean energy technologies for achieving net-zero emissions, and one key aspect of this effort involves decarbonizing buildings by supplying them withrenewable energy [8; 9]. The primary goal of the Energy Performance of Buildings Directive (EPBD) is to improve the energy efficiency of buildings and reduce their carbon emissions by transforming them into highly energy-efficient and decarbonized structures, with a particular focus on achieving nearly zero-energy buildings (NZEBs) [10; 11]. Greece, like all EU country members, must conform to the Union's goals and guidelines. These goals are achieved by pursuing the production of clean energy, a catalyst for energy security and lower energy costs. Clean energy technologies should also try to maintain environmental protection and social well-being and preserve the alignment of the principles of sustainable development for a stronger, more resilient economy [12]. These goals are difficult to accomplish under the specified conditions, due to certain difficulties regarding economic feasibility, technological prowess, and logistical issues. Currently, various efforts are underway to address these issues [13]. Both the public and private sector are currently facing these issues. In the private sector, where economic growth is a key decision-making factor, the measures to be taken should meet the highest clean energy standards while also satisfying logistical constraints and ensuring economic prosperity to the maximum extent. In Greece, tourism stands out as the primary driver of the national economy and energy consumption among all the sectors within the private service provision industry [14]. A requirement for sustainable tourism is the utilization of renewable energy technologies applied to building infrastructure, since the highest energy consumption is noted in buildings [15]. Such patterns of consumption call for a holistic approach to sustainable building operation. It is particularly essential to emphasize the integration of renewable energy technologies into buildings to minimize their energy (thermal and electrical energy) consumption. Photovoltaic (PV) technology is considered one of the most promising technologies to developize buildings [9]. The significant growth of photovoltaic (PV) installations in recent years can be attributed to several key factors, including increased electricity costs and the decreasing price of PV modules [16]. The widespread installation of rooftop photovoltaic (PV) systems on buildings can potentially create challenges and stress on distribution networks, particularly if not managed effectively [17]. Coupling photovoltaic (PV) systems with battery energy storage systems (BESSs) can effectively address many of the technical challenges [18]. While renewable energy holds promise, its intermittent and unpredictable nature makes it unreliable for both power grids and consumers.