# Assessment of Batteries' Contribution for Optimal Self-Sufficiency in Large Building Complexes
## 1 Introduction
Batteries offer a viable solution to address the variability in renewable generation and lower energy costs [19]. They are primarily employed for energy scheduling, enabling the shifting of energy consumption over time [20]. On a grid level, batteries are utilized to stabilize renewable energy fluctuations and enhance overall reliability. Conversely, at the consumer level, efficient energy storage and load scheduling play a crucial role in managing energy consumption and minimizing costs [21; 22]. This approach, which actively involves consumers and utilities in the energy market, leads to the development of self-sufficiency designs [23; 24; 25]. As Greece is a popular tourist destination, particularly the island of Crete, which was the second most popular destination globally for the year 2023, the influx of tourists is extraordinary [26]. There is a seasonal periodicity in visitation, the peak of which is noted during the summer months, when Crete is exceptionally popular and more demanding energy-wise. There are several key energy-consuming activities and practices that need to be addressed to reduce its environmental impact and contribute to sustainability. Addressing the seasonal energy demands associated with tourism is crucial for sustainable development, while also balancing the objectives of energy sustainability and cost-effectiveness regarding tourist buildings and facilities, the prevalence of which is covering a significant portion of Crete's landscape. One of the highest energy-demanding types of tourism-based businesses is the hospitality industry [27]. Energy demands in hotels are driven by factors such as the use of energy required for heating, cooling, lighting, and other hotel operations; water heating; outdoor lighting, etc. [28; 29]. Thus, such activities require thermal and electrical energy. Over time, most of these needs are increasingly being met by electrical energy rather than thermal, due to the emergence of innovative appliances with both cost-effective and energy-efficient advantages [30]. Thus, electrical energy stands as a critical energy form for hotels, as it fuels a diverse array of crucial systems and services across an establishment [31]. As a result, hotels are particularly vulnerable to changes in energy prices, and the rise in energy costs can have a substantial effect on the operational expenditures of these establishments [32]. Increasing energy costs can have a notable impact on their operational expenses, affecting their profitability, competitive positioning, and ability to invest in sustainable practices; so, independence from the electrical grid and detachment from the fluctuating energy market prices constitute self-sufficiency, which is a pivotal goal for hotels. This paper presents an analysis of the annual consumption for the year 2022 in five hotels located in Crete. Crete's significant sun exposure throughout the year, combined with the financial feasibility of photovoltaic systems, dictates the selection of this specific technology as an optimal energy source, coupled with a storage system compensating for the lack of production on cloudy days and at nighttime. The coupling is introduced as a suggestive renewable energy technology, and an algorithm is also implemented which strives to minimize the capital expenditure of the system installation while ensuring a sufficient percentage of self-sufficiency. Finally, a correlation between the facilities' characteristics and their respective optimal solution is explored.