In current times, sustainability is paramount, and businesses are increasingly adopting renewable energy sources (RESs) and electric vehicle (EV) charging infrastructure to minimise their environmental impact and operational costs. Such a transition can prove challenging to multi-location businesses since each chain store functions under different constraints; therefore, the implementation of a corporate policy requires adaptations. The increased electricity demand associated with EV charging stations and their installation cost could prove to be a significant financial burden. Therefore, this study aims to investigate and develop strategies for effectively incorporating RES and EV charging stations into the operations of a supermarket chain in Crete. Monthly electricity consumption data, parking availability, and premise dimensions were collected for 20 supermarkets under the same brand. To achieve a more tailored approach to custom energy system sizing, the integration of energy storage coupled with a photovoltaic (PV) system was investigated, using the Moth–Flame Optimiser (MFO) to maximise the Net Present Value (NPV) of 20 years. The algorithm managed to locate optimal solutions that yield profitable installations for all supermarkets by installing the necessary number of PV units. Manual exploration around the solutions led to the optimal integration of energy storage systems with a total upfront cost of EUR 856,477.00 and a total profit for the entire brand equal to EUR 6,426,355.14.

Energy usage in large-scale premises exhibits a distinctive pattern, encompassing both thermal energy and electricity. As a result of the recent energy crisis, the operational expenditures associated with these demands have markedly risen. In line with EU Energy Policies, one of the future goals is the transition towards energy-wise self-sufficient buildings powered by renewable energy sources (RES). Nowadays, a combination of contemporary energy management systems, electricity storage and RES are proposed to achieve nearly zero emission-producing energy consumption in buildings. This paper examines the energy consumption patterns of a hotel situated on the Mediterranean, in order to investigate the potential of RES-induced independence and forecast future expansion prospects. An algorithm has been introduced to both optimize and enhance the self-sufficiency of the hotel under consideration. The proposed algorithm successfully enhances the hotel's energy self-sufficiency, achieving a remarkable 99% rate through the dimensions of PV power and corresponding battery capacity for all years under examination, yielding the corresponding financial and environmental conclusions.

European islands have been leading the charge in renewable energy innovation. Yet, the intermittent nature of sources like solar and wind poses challenges such as grid saturation and frequency variations. Limited interconnection with mainland grids exacerbates these issues, necessitating backup from conventional power sources during low-production periods. Until 2021, Crete operated independently, but new infrastructure now integrates it with the Greek mainland grid, facilitating swift energy transfers. This integration enables surplus power from Crete’s solar and wind systems to be transmitted to the mainland and vice versa. However, reliance on remote power production exposes the island to market fluctuations and distant disruptions, impacting electricity production. Storage technologies offer a solution, enhancing renewable energy penetration while reducing carbon emissions. Green hydrogen, a rising storage method, shows promise in offsetting carbon emissions. Its clean-burning nature minimizes environmental impact and reduces reliance on costly and harmful conventional sources. This study aims to evaluate the feasibility of achieving carbon-neutral electricity production in Crete, Greece, using hydrogen storage to offset annual carbon emissions in a financially viable and sustainable manner. Hydrogen’s clean-burning properties reduce environmental impact and lessen dependence on expensive and environmentally harmful conventional sources. The methodology prioritizes the independence of the Cretan electricity system, utilizing electrolysis to produce green hydrogen and proton-exchange membrane (PEM) fuel cells for energy generation. It investigates the optimal expansion of renewable energy systems, including photovoltaic (PV) and wind turbine (WT) parks, alongside the installation of hydrogen storage, under specific assumptions. This proposed installation aims to achieve both island independence and profitability, requiring an additional expansion in PV capacity of 2.13 GW, WT capacity of 3.55 GW, and a hydrogen system with electrolyzer and fuel cell capacities totaling 278.83 MW each, along with a hydrogen tank capacity of 69.20 MWh. The investment entails a capital expenditure (CAPEX) of 6,516,043,003.31 EUR for a nearly zero net present value (NPV) over 20 years. However, carbon neutrality cannot be attained through this optimal solution alone, as relying solely on carbon sequestration from olive groves, the primary crop cultivated on the island, is insufficient as a carbon sink method. The annual net carbon emissions from electricity production, island transport, residential heating, and carbon sequestration are estimated at 94,772.22 tCO₂.

The EU has set ambitious targets to combat climate change. Incorporating renewable energy technologies to reduce greenhouse gas emissions is a critical aspect of achieving the European Union’s (EU) 2030 climate goals. Similarly to all member countries of the EU, Greece shares the same climate goals. In order to achieve these goals, ensuring a consistent supply and the effective use of clean energy is pursued, as it has a significant impact on the sustainable development and growth of the country. As the Greek tourism sector is one of the most energy-consuming of the national economy and a major contributor to the country’s GDP, opportunities are presented for innovation and investment in sustainable practices. Such investments must focus on buildings and facilities, where the energy consumption is concentrated. One of the most popular holiday destinations in Greece is the island of Crete. Visitation patterns are seasonal, which means during the summer months, Crete is exceptionally popular and more demanding energy-wise. One of the highest energy-demanding types of tourism-based businesses is the hospitality industry. Energy demands in hotels are driven by factors such as heating, cooling, lighting, and hot water. Thus, such activities require thermal and electrical energy to function. Electrical energy is one of the most essential forms of energy for hotels, as it powers a wide range of critical systems and services throughout the establishment. Therefore, the hotels are highly susceptible to fluctuations in energy prices which can significantly impact the operational costs of hotels. This paper presents an analysis of the annual consumption for the year of 2022 of five hotels located in Crete. An algorithm is also implemented which strives to minimize the capital expenditure (CAPEX), while ensuring a sufficient percentage of self-sufficiency.

The main difficulty that microgrids face is an economically feasible state of self-sustainability. The unpredictable behavior of dispersed Renewable Energy Sources (RES) and their stochasticity along with the usually high variability of electricity demand is a challenge for the stability of a microgrid. Therefore, innovative models for the development of energy systems that integrate new technologies in optimal and sustainable ways are required. Green hydrogen production is an emerging technology aiming to solve such problems through its use as a storage system within a viable business scheme. Integrating hydrogen production with RES and storage systems can enhance energy independence and economic opportunities. The focus of this paper is the proposal of a profitable financial scheme that leads to sufficient levels of the system’s independence from a main grid. Such an approach is implemented by a cost-effective pathway for a microgrid located in Crete through the simulation and investigation of its system that achieves high levels of selfsufficiency by incorporating RES backed by hydrogen-based energy storage. The proposed methodology relies on assessing the system’s sizing through the calculation of values that replicate its operation, with Net Present Value (NPV) serving as an indicator of the scheme’s profitability. The financial evaluation of the investment predicts, under specific assumptions, a total initial cost equal to 12,037,150.00 EUR, and an NPV of 20 years equal to 2,489,862,897.40 EUR.

Since 2021, Crete has been connected to the mainland’s power system grid providing security regarding load peak demand and intra-day fluctuations. The grid provides, also, the opportunity to take full advantage of it in order to alter the island’s energy mix, making the island’s power system more climate neutral and reduce the emissions produced by conventional power production means. In the current paper, the utilization of mathematical models and a few numerical solution algorithms lead to the optimization of the power production of RES, under certain constraints regarding the system’s rejections. The approximation of each optimal solution for all three cases is satisfactory, which is, for the first two cases, an immediate result of the linear properties of the objective function that expresses the annual production of RES in each case. Those linear properties prevent each approximated solution from deviating from the problem’s feasible region, while, also, permitting the use of optimization techniques which can be easily implemented and require very little computational time. For the third case, a search algorithm has been designed and implemented, yielding accurate, yet low-precision solutions, which approximate sufficiently the optimal ones.