Legislative, Social and Technical Frameworks for Supporting Electricity Grid Stability and Energy Sharing in Slovakia

Abstract

The equilibrium between electricity demand and consumption is vital to ensure the stability of the transmission and distribution systems grid (TS & DS) and to ensure the stable operation of the electrical system. The aim of this review study is to highlight the current legislative and technical situation and the possibilities for managing peak loads, decentralization, sharing, storage, and sale of electricity generated from renewable sources in Slovakia. The European Union′s (EU) goal of achieving carbon neutrality by 2050 and a minimum of 42.5% renewable energy consumption by 2030 brings with it obligations for individual member states. These are transposed into national strategies. The current share of renewable sources in Slovakia is approximately 24% and the EU target by 2030 is probably unrealistic. Water resources are practically exhausted; other possibilities for increasing the share of renewable energy sources (RES) are in photovoltaics, wind, and thermal sources. Due to long-term geographical and historical development, electricity production in Slovakia is based on large-scale solutions. The move towards decentralization requires legislative and technical support. The review article examines the possibilities of increasing the share of RES and energy sharing in Slovakia, and examines the legislative, economic, and social barriers to their wider application. At the same time as the share of renewable sources in electricity generation increases, the article examines and presents solutions capable of ensuring the stability of electricity networks across Europe. The study formulates diversified strategies at the distribution network level and the consumer and building levels, and identifies physical (various types of electricity storage, electromobility, electricity liquidators) and virtual (electricity sharing, energy communities, virtual batteries) solutions. In conclusion, it defines the necessary changes in the legislative, technical, social, and economic areas for the most optimal improvement of the situation in the area of increasing the share of RES, supporting the decentralization of the electric power industry, and sharing electricity in Slovakia, also based on experience and good examples from abroad.

1. Introduction

The EU’s climate target in attaining net-zero emissions of greenhouse gases by 2050 necessitates the phase-out of fossil energy use and the transition of energy supply to renewable sources. However, the rate of RES must be in accordance with the grid stability challenges across European electricity systems. The decommissioning of operational nuclear power plants within some countries in Europe, alongside the substantial subsidization and proliferation of RES—predominantly solar and wind power plants—is engendering considerable disparities in electricity supply and consumption within the EU′s distribution systems. The performance of RES is heavily dependent on weather conditions and is considerably unpredictable. During warmer periods, marked by abundant sunlight and strong winds, RES may generate a surplus of electricity. The options for storing electricity in physical storage (see Section 3.1) are severely constrained. The imbalance between electricity production and consumption can markedly influence electricity prices in the spot market. Consequently, a sufficient number of alternative sources (fossil, nuclear, hydropower) must consistently operate to offset potential failures [1]. These sources cannot be completely deactivated because their startup processes are not immediate, particularly in the case of nuclear and fossil power plants.

Given that electrical distribution networks have been established over many decades in the previous century, a fundamental requirement for their effective operation is the stability of the system predicated on the equilibrium between electricity production and consumption [2]. This equilibrium may be augmented by a plethora of additional solutions and mechanisms [3]. These are principally categorized into physical solutions (such as energy storage systems, batteries, electricity liquidators, on-site consumption, vehicle-to-building, and vehicle-to-grid solutions…) and virtual solutions (like virtual batteries, smart metering systems, flexibility aggregation, electricity sharing & energy communities…), inclusive of electricity market design. Depending on their scope of application, solutions are delineated at the level of a single building, group of buildings, or at the urban or regional scale, and at the level of distribution and transmission grids, as well as on the transnational level [4]. It is imperative for these solutions to possess explicitly defined legislative and technical tools, alongside sanctions in cases of breaches of the prescribed regulations. The research offers an overview of the available solutions for maintaining electricity network stability in Europe, and particularly in Slovakia, at both the distribution network level and the consumer and building level. The result is the comparison of Slovak policies with EU best practices and specification of legislative, social, and technological challenges and most urgent bottlenecks that prevent the wider expansion of decentralized energy in Slovakia. The objective is to identify problems and opportunities and to formulate diversified strategies for maintaining electricity network stability and mitigating peak loads through the establishment of community prosumers engaged in electricity sharing, the aggregation of flexibility (temporal alignment of prosumer production and consumption), and the support of battery storage. Additional insights are drawn from international collaboration within EU electricity projects, such as the City Storage and Sector Coupling Lab [5], which has concentrated on cross-sectoral electricity sharing in urban contexts, and the ongoing ESINERGY project (Empowerment of the stakeholders in the implementation of the Directive on the promotion of the use of energy from renewable sources in terms of energy storages and energy networks stability), which seeks to influence policy formulation by developing a transnational strategy for peak load management. This strategy is intended to facilitate the replication of effective energy solutions in other regions, thereby furthering the European energy transition [6]. The importance of education and awareness-raising is emphasized, particularly for electricity suppliers, prosumers, energy communities, policymakers, and students across various university disciplines.

2. Materials and Methods

The methodology employed in this review article is consulted simultaneously by multiple methods.

Firstly, the research focused on EU legislation and its transposition into Slovak national legislation. Directive on the promotion of the use of energy from RES [7] establishes a standardized framework for promoting energy from renewable sources, setting a binding Union target for the aggregate share of energy from renewable sources in the Union′s final gross energy consumption by 2030. The transposition of these objectives is facilitated through the National Energy and Climate Plans (NECPs) [8] of individual member states. Nonetheless, financial support for electricity derived from renewable sources is markedly encroaching upon EU electricity market rules delineated in the Electricity Market Directive [9]. The EU-wide evaluation of the updated 10-year NECP drafts for 2021–2030 [8] offers a synopsis of national contributions and ambition gaps toward achieving the Union target of a minimum of 42.5% renewable energy consumption. According to it, 4 countries are significantly above this target, 2 above it, 1 in line, 5 slightly below or below, and 15 countries (including Slovakia) are significantly below this EU target [10]. However, decarbonization can only be achieved if decarbonization policies are well integrated into industrial, economic, and trade policies, taking into account competition principles [11].

The EU′s goal of achieving carbon neutrality by 2050 brings with it obligations for individual member states. These are transposed into national strategies. National legislations within the EU are required to transpose pertinent EU legislation, specifically the Directive on the promotion of the use of energy from renewable sources [7,12,13]. As stipulated in Article 191 of the Treaty on European Union (TEU 2025) [14], the promotion of initiatives addressing climate change is a policy objective of the EU. This objective is being actualized via an array of specific targets and legal measures adopted as components of the European Green Deal. The Slovak Republic regulates the energy sector via the amended Energy Act (Act No. 143/2024 Coll.) [15], which modifies Act No. 250/2012 Coll. [16] on Regulation in Network Industries and Act No. 251/2012 Coll. on Energy [17]. The updated Integrated National Energy and Climate Plan [8], positioned as a pivotal conceptual document in the energy domain, establishes the share of renewable energy sources in the Slovak Republic′s final energy consumption at 23% by 2030 [10]. The European Commission (EC) opposes this commitment and advocates for increasing the target to 35%. The EC recommendations have been analyzed by the relevant departments with the intention of being as close as possible to the recommended objectives. Given the constraints imposed by technical and economic factors and time-based considerations, it has become impossible to achieve them in 2030 while maintaining industrial production. Based on the results of repeated modelling, the proposed target for the share of RES in final consumption is 23% [8]. The ability to support NECP realization in Slovakia is ensured by the government′s strategic document Program Slovakia 2021–2027, approved in 2022 [18]. Key investments are in insulation and reducing the energy consumption of buildings (€722 million), in energy efficiency of enterprises (€78 million), and the use of renewable energy sources (€398 million).

Secondly, technical possibilities for reducing periodic load on the electricity grid from research and application of current EU projects are evaluated. Their generalization is given in paragraph 3. EU countries along the Danube River are searching for a transnational strategy for peak load management and the specification of strengths and weaknesses for its realization. The strategy primarily addresses three key categories of stakeholders: (1) policymakers and public authorities, (2) energy sector actors, and (3) civil society and prosumer groups.

Thirdly, we are mapping the current situation in Slovakia. The authors held 5 meetings with relevant Slovak stakeholders where technical solutions for supporting electricity grid stability and energy sharing have been presented, and prepared the questionnaires for participating stakeholders. Some results of them are mentioned in the discussion.

In addition to the data gathered through semi-structured interviews with key players in the energy sector in Slovakia (SEPS—Slovak Electricity Transmission System; SIEA—Slovak Innovation and Energy Agency; OKTE—Short-term Electricity Market Operator; DOs—Distribution operators), as well as energy specialists, representatives of municipalities, regions, professional associations, energy communities, industry stakeholders and proprietors in Slovakia, a desk review of relevant secondary sources have been conducted, included legislative and policy documents, key actors web links, energy news, project reports and empirical studies in order to formulate the recommendations for supporting RES and decentralized energy in Slovakia.

According to the Slovak Sustainable Energy Association [19], the current share of electricity production in Slovakia represents 14.1% from fossil sources, 61.6% from nuclear, and 24.2% from renewable sources. Hydropower predominates in Slovakia, accounting for up to 66% of the total installed capacity of green sources, albeit its potential is nearly exhausted. Photovoltaics follow with 29%. Bioenergy, inclusive of biogas, contributes 5% to the total installed capacity of RES. Presently, Slovakia possesses only 3 megawatts of installed wind energy, and geothermal energy is not exploited for electricity generation, primarily due to high investment costs [20]. The SAPI study [19] belongs to the most up-to-date and most accessible version of the shares of electricity generation sources in Slovakia, compared to the older version from EIA [21] and the complicated and secured data from SEPS [2]. SAPI Slovak Market Outlook for Renewables 2025 presents three distinct scenarios, delineated in Figure 1, under consideration in Slovakia for the period 2025–2050: “the business-as-usual scenario, the 2025 NECP scenario, and the Green Scenario.” While the NECP scenario mirrors current and planned policies, the Green Scenario, supported by comprehensive modelling, details a pathway to achieve carbon neutrality by 2050.

3. Results

In conceptualizing an electricity supply system in Slovakia, the focus is traditionally on large-scale solutions. This perspective is rooted in the historical development of energy networks, where centralized sources facilitate the distribution of electricity through a hierarchically structured transmission and distribution grid, progressively to both major and minor consumers. Energy transmission within the grid is unidirectional, with transmission capacity diminishing as it approaches the consumer. Nonetheless, decentralization is advantageous for the utilization of renewable resources, effectively converging the place of production and consumption. Consequently, the energy flow transitions from unidirectional to bidirectional, and the demand at the site′s consumer end strains the technical limits of the existing power lines. Current energy policy in Slovakia endorses the use of energy derived from small renewable sources directly at the site of production, incentivized by minimal to non-existent feed-in tariffs for electricity generated from small local sources. A prevailing issue is the temporal misalignment between the availability of energy from RES and its demand, necessitating energy storage solutions. Employing the electricity grid as an “accumulator” (virtual battery—see Section 3.2.1) through redistribution or linkage with central storage (large batteries, pumped storage power plants) is feasible yet limited and fails to alleviate the heightened load on the grid at production/consumption locales. Local grids (“smart grids”, energy communities, interconnection of building groups) partially address this, although their capacities frequently fall short of accommodating substantial fluctuations in production and/or consumption. This shortfall necessitates explorations of small-scale solutions for balancing production and consumption at the level of individual buildings or households. Figure 2 illustrates the systematic structural alterations within the energy sector. With respect to small-scale electricity production from RES (at building or household levels), photovoltaic technology is prioritized. Wind turbines present challenges in urban environs, with notable integrations in buildings (e.g., Bahrain WTC or Strata SE1 in London) serving more as symbolic gestures than practical applications. Small hydropower installations are particularly viable within larger energy communities, e.g., Bad Hindelang in Germany [22], as is the generation of electricity from biomass in small cogeneration (combined heat and power) units. This discourse does not extend to autonomous buildings without a public grid connection; such structures utilize alternative designs. Legislation pertaining to small photovoltaic installations is prevalent in most European nations; in Slovakia, this is governed by Act No. 309/2009 Coll. [23] on the Support of Renewable Energy Sources and High-Efficiency Cogeneration and Building Act (Act No. 25/2025 Coll.) [24]. In the realm of energy storage, the context lacks comprehensive legislative backing; consequently, distinct electricity storage solutions are enumerated herein as potential legislative catalysts. These solutions serve not only to maximize the local consumption of energy produced locally but also to mitigate peak consumption in the electricity grid. Generally, energy storage within the grid is employed for load balancing, energy shifting (from intermittent sources for application during high demand), and “peak shaving”. Implementable tools include organizational measures, batteries, chemical processes in conjunction with Common Heat and Power (CHP—cogeneration), mechanical systems, and thermal energy storage.

3.1. Physical Electricity Storages

Electricity storages are employed to retain electricity during periods of surplus and to supply it to the grid during times of shortage. The physical types of battery electricity storage encompass electrochemical energy storage, pumped-storage hydroelectric plants, underground storage facilities, or even batteries in electric vehicles that are charged during electricity surplus periods and function as batteries during electricity shortage periods, thereby offering V2B—Vehicle to Building and V2G—Vehicle to Grid solutions to a limited extent. Virtual battery storage is further discussed in Section 3.2.1. Nonetheless, these storage capacities are quite limited.

3.1.1. Electrochemical Energy Storage—Batteries

Battery storage systems are becoming an increasingly common part of the energy industry worldwide. Despite their technical versatility, economic profitability is not automatically guaranteed and depends greatly on the operating conditions set. The cumulative capacity of battery storage installed in Europe is shown in Figure 3.

Electrochemical energy storage systems are composed of electrodes connected using an electrolyte as an ion-conducting phase. Electrochemical energy storage systems can be categorized into low-temperature batteries (e.g., lead, nickel, and lithium batteries) and high-temperature batteries (sodium-sulphur batteries), as well as into external batteries (redox flow batteries) and internal storage (most batteries). Lithium-ion batteries are appropriate as buffer storage for renewable energies, for load management, grid services, and emergency power supply. Lithium-ion batteries are a common component of photovoltaic systems in buildings; their energy density is growing (Table 1). They can contribute not only to supporting local energy consumption from RES but also to peak shaving and load balancing [26]. Technological progress driven by the development of electromobility leads to enhanced efficiency and cost reduction. Nonetheless, traditional lead or nickel–cadmium batteries remain advantageous, particularly for use in buildings, where their larger dimensions and weight are not a hindrance. For larger objects or sets, red-ox batteries are also available, which should be economically viable, but in the confined spaces of buildings, their low energy density is disadvantageous.

Today, 17 MW of battery storage is certified in Slovakia. However, the Slovak Electricity Transmission System (SEPS) decided in March 2024 to temporarily suspend new certifications for the provision of automatic Frequency Restoration Reserve (aFRR) support services for devices with limited energy reserves. These are mainly battery storage systems (BESS). Limited battery application is possible up to 15% for aFRR support services from 2025, which, according to experts, is very low.

Figure 3. The cumulative capacity of battery storage installed in Europe during the previous ten years. Adapted from: Energy Portal [27] and from SolarPower Europe [28].

Figure 3. The cumulative capacity of battery storage installed in Europe during the previous ten years. Adapted from: Energy Portal [27] and from SolarPower Europe [28].

Table 1. Example of capacity and price development of Tesla batteries [28].

Model	Year	Capacity (kW)	Power (kW)	Price (USD)	Size (cm)
Powerbank 1	2015	7.0	2.0 (peak 2)	3000	130 × 86 × 18
Powerbank 2+	2020	13.5	5.8 (peak 10)	7500	115 × 75 × 14
Powerbank 3	2023	13.5	11.5 (peak 30)	7300	110 × 61 × 19

Table 1. Example of capacity and price development of Tesla batteries [28].

Model	Year	Capacity (kW)	Power (kW)	Price (USD)	Size (cm)
Powerbank 1	2015	7.0	2.0 (peak 2)	3000	130 × 86 × 18
Powerbank 2+	2020	13.5	5.8 (peak 10)	7500	115 × 75 × 14
Powerbank 3	2023	13.5	11.5 (peak 30)	7300	110 × 61 × 19

3.1.2. Energy Storage in Hydrogen

Electricity obtained from RES can also be used to run chemical processes, the products of which can be converted back into electrical energy when needed. For small scales, the most common solution is the electrolytic production of hydrogen, which can be stored efficiently and for a long time in large quantities. We can then obtain electricity from hydrogen in fuel cells or micro-CHP units. The hydrogen obtained can also be used as a heat source (for heating, water heating, or with the help of a heat pump for air conditioning) or to ensure mobility (hydrogen cars).

An interesting example of the use of hydrogen for inter-seasonal energy storage is the zero-energy house in Freiburg, built 30 years ago, at that time as an experiment, but today, small electrolyzers and fuel cells are commonly available [29].

Another option is the production of synthetic fuels; these are created by chemically combining carbon dioxide from the atmosphere and hydrogen, often using renewable energy sources or excess electricity in the public network. This fuel can be easily stored for a long time and used for mobility (including aviation), heat/cold production, or electricity production in fuel cells or CHP units.

3.1.3. Mechanical Systems

The predominant mechanical system employed for energy storage is pumped-storage hydroelectricity (PSH), primarily utilized for large-scale solutions, yet scarcely implemented for individual buildings. In the context of micro-grids, they are deemed suitable and frequently employed [22]. Gravity accumulators, flywheels, and compressed-air systems are pertinent to small-scale systems; however, they remain not widely accessible. These systems possess a relatively limited capacity but offer rapid start-up times, rendering them an appropriate solution for auxiliary electricity sources.

Pumped storage power plants can store large amounts of energy. They use water as the storage medium and consist of an upper and lower reservoir, which are often artificially constructed. Excess energy from the electrical grid is used to pump water from the lower reservoir to the upper reservoir. When electricity is needed, a turbine, through which water flows from the upper reservoir, drives a generator, and a transformer is used to supply the electricity to the grid. Gravity accumulators, flywheels, and compressed-air systems are applicable as well for small-scale systems, but they are not yet commonly available. They have a relatively small capacity but a fast start-up and are, therefore, a suitable solution for backup electricity sources. Slovakia has 4 big pumped storage hydroelectric power plants with a total capacity of around 1020 MW. Small-scale solutions were suspended mainly for environmental reasons.

3.1.4. Thermoelectric Solutions

If considering primary energy factors, it is acknowledged that the direct conversion of electricity into heat does not currently represent an efficient solution. However, in scenarios where there is a surplus of energy in the public grid or in households equipped with photovoltaic systems—energy that would otherwise be discarded inefficiently (see Section 3.1.6)—the conversion of this electricity into heat, or into cold via a heat pump, is both technically straightforward and economically viable. The challenge, however, lies in the fact that the demand for heat or cold does not always align with periods of electricity surplus, rendering a storage system advantageous in such circumstances. The most basic method of storage involves sensible heat storage, which entails adjusting the temperature of a chosen medium—typically water in smaller-scale applications. This stored energy can then be utilized directly or by means of a heat exchanger for purposes such as space heating, domestic hot water supply, or air conditioning. This method allows energy to be stored for several hours or days, and possibly up to a week. For inter-seasonal storage requirements, the volume of medium required in a well-insulated tank is considerably large. In cases where electricity serves as the heat source, selecting a medium that can withstand high temperatures, such as oil, bricks, or concrete, is beneficial. By heating the medium to elevated temperatures, the necessary storage volume can be substantially reduced. Small electric storage heating units capitalize on lower electricity rates during off-peak periods. Systems with larger capacities, such as those for inter-seasonal storage of photovoltaic surplus energy [30], are not yet widely available for small-scale applications. Latent heat storage employs phase transition processes, utilizing phase-change materials (PCMs) as the medium. A significant quantity of heat can be absorbed or released during a phase change without corresponding temperature changes. Various PCMs possess distinct properties, but the most prevalent is ice storage, which takes advantage of the high heat of fusion of water. This system employs low-cost off-peak or RES electricity to freeze water into ice, which then serves to diminish air conditioning energy demands. Ice storage may also be employed in heat pump-based heating systems, which are especially beneficial for inter-seasonal storage: excess energy accrued in summer from photovoltaics or solar thermal collectors can be utilized by a heat pump to freeze water in a storage tank, thereby providing heating in winter, again facilitated by a heat pump [31].

3.1.5. Vehicles and the Electrical Grid

The utilization of electric vehicle batteries involves storing generated energy within the battery for subsequent use in mobility, representing a straightforward yet effective solution. A more advanced system facilitates the extraction of stored energy from the vehicle to address local consumption during periods when electricity from renewable sources is unavailable. The potential for mitigating energy consumption peaks by integrating vehicles with the electrical grid is also under consideration. This solution is subject to certain constraints, such as the technological requirement for bidirectional electricity flow to and from the charger and the need for AI-driven predictions regarding energy demand for future mobility needs. Presently, this remains an area primarily explored through experimental research and pilot studies. Nonetheless, substantial benefits are anticipated in the future, particularly as electric vehicles become predominant within the automotive fleet.

3.1.6. Electricity Liquidators

Electricity liquidators are appliances currently designed to facilitate the consumption of surplus electricity generated during periods of excessive production from wind and solar facilities. Functioning as large-scale electric heaters, these devices are notably more cost-effective and straightforward to operate and maintain compared to batteries or other electricity utilization options. Constructing electricity liquidators is considered morally and ecologically unsound. Their fundamental mechanism involves the transformation of electrical energy into thermal energy. The deployment of electricity liquidators stems from a misconceived energy strategy, particularly in the subsidized expansion of renewable resources, a practice adopted in Slovakia as well [32]. In instances where large companies unexpectedly experience a reduction in production, it proves more economically viable to dispose of excess electricity than to incur substantial penalties for deviations imposed by electricity suppliers. Essentially, the focus is on financial considerations rather than environmental conservation. Consequently, another heat source is created from renewable energy, exacerbating planetary warming instead of effectively utilizing the generated electricity. Electricity liquidators represent a substantial flaw in the systemic design [33]. Despite their controversial nature, these devices are sanctioned under Slovak legislation and can even provide services to the transmission system, enabling operators to receive compensation for the immediate consumption of electricity. Furthermore, they present a more economical solution than any form of electricity storage. Thus, paradoxically, the situation arises where subsidized renewable energy sources, intended to mitigate the effects of climate change, inadvertently contribute to atmospheric heating to maintain network equilibrium.

3.2. Virtual Solutions

Virtual solutions for ensuring the stability of the electricity grid include: virtual batteries, electricity sharing and energy communities, smart metering systems, flexibility aggregation, and contract for differences.

3.2.1. Virtual Batteries

A virtual battery constitutes a service accessible to proprietors of photovoltaic (PV) systems and is facilitated by electricity suppliers. During daylight hours, a photovoltaic system generates electricity, which can be immediately utilized at the point of consumption by the system owner, stored in either a physical or virtual battery, sold to another entity within the electricity market, or introduced into the electricity distribution network without charge. The primary benefit of this service is that the PV owner can access the functionality of a battery without incurring substantial investment costs. The PV owner is relieved from considerations such as the type, capacity, and investment associated with a physical battery. An additional benefit is that the virtual battery service enables the storage of electricity generated during the summer for use in the winter months. The virtual battery can be activated promptly, without the necessity for ongoing service or maintenance, connection fees, or recycling-related expenses. A notable drawback of the virtual battery is its dependence on the operational status of the electricity distribution network; in the event of a network failure, the virtual battery service becomes non-operational. The usage of virtual battery services requires the PV system owner to adhere to the terms and conditions set forth by the supplier. The significance of virtual batteries remains minimal. Presently, electricity prices in Slovakia are substantially negative [34], thereby rendering the purchase of electricity for a virtual battery improbable.

3.2.2. Electricity Sharing and Energy Communities

Community energy can be considered a progressive element of energy decentralization. The distribution of electricity is an efficient approach to utilizing surplus energy generated, such as that from a rooftop photovoltaic power station. It is particularly advantageous when a community both generates and consumes electricity at a local level [35]. These groups may consist of residential houses, municipal, or various buildings with differing patterns of electricity consumption and production, including schools, cultural centers, swimming pools, municipal offices, and houses of mourning. Furthermore, commercial chains or industries with extensive logistics hubs implement rooftop photovoltaic systems; the energy generated from these systems can be distributed across their operations regionally or nationally. An energy community or cluster refers to a collective of prosumers collaborating on projects to address the energy demands of their participants [36]. This initiative may involve shared ownership of renewable energy facilities, such as photovoltaic power plants or biomass boilers, along with their distribution and storage, and the operation of charging stations. The development of energy communities can foster a decentralized system founded on local solutions, expedite the transition from fossil fuels to sustainable energy sources, function as a mechanism to stabilize energy price fluctuations, and enhance energy autonomy. Energy communities adhere to three fundamental principles: they are controlled and owned by consumers, municipalities, or small to medium-sized enterprises; they are inclusive and voluntary, allowing all members to engage in the governance and management of activities; and they prioritize environmental and social benefits over financial gains.

The key legal acts for anchoring community energy in the EU were mainly the Renewable Energy Directive [7,12,13] and the Electricity Market Directive [9]. They distinguish two types of communities: Renewable Energy Communities (REC) and Citizen Energy Communities (CEC). According to [37], REC is required to be located near the RES project and produce electricity only from renewable sources, and CEC is not. However, the EU leaves the implementation of energy community legislation to individual member states, including whether to allow the operation of their own distribution system [38]. Energy communities in Slovakia were defined by an amendment to the Energy Act in October 2022 (Act No. 251/2012 Coll.) [17]. The Slovak legislation supports both forms of energy communities, but they must be established as legal entities and registered with the Regulatory Authority for Network Industries (ÚRSO). They produce electricity for their own consumption, cannot make a profit, but can distribute a maximum of 50% of the profit among members. Since autumn 2023, electricity has been shared in Slovakia through the newly created data hub Energy Data Center (EDC) [39], which is operated by the state organizer of the short-term electricity market (OKTE). The condition is continuous smart metering, and within the sharing group, there must be an active consumer or energy community as a separate entity. OKTE allows the sharing of electricity regardless of who is the electricity supplier at individual consumption and delivery points. There are no fees for sharing electricity via OKTE EDC. After the new electricity sharing group starts operating and the first transactions are made, the key issue is the calculation of the sharing itself—that is, how much electricity will be delivered to individual customers, members of the sharing group. The calculation is performed daily for each quarter hour of a given day according to three methods: dynamic, static, or priority. In the dynamic method, the shared electricity is distributed among the group members in proportion to the share of measured electricity consumption of the individual consumption points of the group. The static method is implemented based on pre-agreed weighting coefficients. The priority method defines the order of consumption points with shared electricity and gradually satisfies their consumption according to the specified priority. The methodology configuration can be changed at the daily level. The specified methodology will then be applied for each quarter hour, while it is not possible to change the methodology within a single day. However, the Regulatory Authority for Network Industries (ÚRSO) directive from January 2025 ordering the energy association to have all its members belong to one supplier stopped the further expansion of communities, and even caused problems for those already established.

Energy communities are considered an important element of the decentralization of RES energy, a tool for reducing energy poverty in regions and reducing carbon footprint in line with EU strategies. However, they have varying support in specific EU countries. In some Western European countries, they have a long tradition. They have been operating for many decades on the basis of cooperatives with their own DOs (Germany, Austria, Denmark). Germany is introducing cross-border regional energy communities. Countries such as Spain, Portugal, Italy, France, and Greece have greatly supported energy communities, and their expansion in recent years is clear. The problem in this regard is in the countries of Central and Eastern Europe, where historically conditioned centralization of energy still prevails. The problem is legislative restrictions (for example, a maximum of five producers from which one customer can obtain shared electricity in the Czech Republic [40] or the condition of a single distributor for EC in Slovakia; vague legislative support in Poland or Hungary). Another current barrier in Slovak legislation is that subsidized state organizations (such as universities) cannot form energy communities [41]. Economic and financial support is another issue. SIEA in Slovakia started providing state grant aid for small and medium-sized enterprises only from June 2025 [42]. In the Czech Republic, they are still waiting for the state support program [40]. Tax incentives or reimbursement for mandatory smart meter systems in Slovakia would help in the development of energy communities. Awareness raising, management points like One-Stop Shops for Energy Communities [43] could help in the creation of energy communities not only in Central European countries, including Slovakia, but also for such a RES leader as Germany. Support for the creation of energy communities in Slovakia is provided by the non-profit association National Cluster for Energy Community Support (KEKS) [44] and SAPI with the guide for energy community founders [19]. The positive moment for the decentralized electricity market in Slovakia is the existence of the Energy Data Center (EDC) [39] provided by OKTE [45]. The EDC information system is structured to incorporate renewable sources, new activities, and actors within the Slovak electricity market.

3.2.3. Flexible Connection to the Grid—Flexibility Aggregation

The concept of flexible connection, as incorporated into the recent design of the EU electricity market, aims to enhance the efficiency of existing capacities while facilitating the integration of new sources into the system. In cases where network expansion in a particular region does not represent the most effective solution, a flexible connection may serve as a permanent strategy, inclusive of energy storage. Practically, this permits the network operator to temporarily curtail the output of sources under such a contract amid system congestion or diminished demand. Producers are granted connection rights contingent upon their agreement that the operator may disconnect them from the system when necessary. Should the operator necessitate the cessation of the production facility, it will proceed accordingly. The practice of peak cutting for photovoltaic energy constitutes an appropriate solution. Notably, the aggregation of flexibility has commenced in Slovakia. The foundational requirement for the evolution of this new market was the establishment of the Energy Data Centre (EDC), initiated by the state in 2023. Numerous smaller electricity producers have long regarded flexibility aggregation as a promising business venture and potential revenue stream. For instance, biogas plants view the provision of flexibility as an innovative business model. Informed by accrued experience, SEPS has proposed requisite amendments directly within legislative frameworks to expedite and simplify the participation of aggregators in support services provision. This initiative will facilitate the entry of aggregators into the market, extending support services derived from decentralized flexibility sources across various geographic locales in Slovakia, contributing to power input. Through flexibility aggregation, responsiveness to consumption timing is achievable. This ability is also under consideration within energy communities. Systems ought to be engineered to address both energy storage and self-consumption. At the building level, organizational solutions involve time-flexible consumption management, albeit constrained by limited balancing options, such as operating a washing machine during peak solar hours, utilizing only a few hundred Watts of photovoltaic power. The proliferation of electromobility renders the charging of electric car batteries from renewable sources particularly compelling, albeit constrained by the availability of parked vehicles during surplus energy periods. The electromobility is intrinsically linked to flexibility aggregation, particularly through the temporal regulation of consumption during electric vehicle charging.

In Slovakia, there are more and more consumers who do not have a fixed electricity price contracted for the whole year, but pay the supplier different amounts depending on the daily development of the electricity market. This means consuming less electricity when it is expensive and, conversely, increasing consumption in the opposite cases—that is, receiving de facto payment for the consumed amount of energy in the hours when the price of electricity is below zero.

3.2.4. Contract for Difference—CfD

A Contract for Difference (CfD) is an agreement between two parties, referred to as a seller and a buyer, whereby the buyer consents to remunerate the disparity in the contract′s value from the time of acquisition to the time of disposal. Should the contract′s value at the time of disposal be less than its initial acquisition value, the buyer compensates the seller. Conversely, if the contract′s value at the time of disposal exceeds its initial acquisition value, the seller compensates the buyer. The legislation governing energy within the European Union is advancing rapidly. Significant modifications are anticipated in the domain of support for the development and operation of new energy sources. Although subsidies for electricity generation are not being eradicated, they are undergoing transformation. Assured feed-in tariffs and additional charges for electricity production are set to be supplanted by contracts for difference, which are expected to impose a lesser financial burden on consumers and state financial plans. These new mechanisms aim to provide long-term stability for both energy producers and consumers. Contracts for difference are designed to facilitate new investments in renewable energy sources as well as in nuclear energy projects, which are under development by several European nations.

4. Discussion

The equilibrium between electricity demand and consumption is vital to ensure the stability of the transmission and distribution system grids and to ensure the stable operation of the electrical system. Considering the recent electricity blackouts in Spain and the Czech Republic, this is a very important issue [46]. It is necessary to diversify strategies for eliminating peak loads and maintaining the electricity network stability in every time period by creating community prosumers with electricity sharing, aggregation of flexibility (time coverage of production and consumption of prosumers), and also by supporting different battery storage. Virtual batteries are not of great importance. Currently, electricity prices in Slovakia are negative (−200 euros/MWh), so it is possible that electricity for a virtual battery will not be purchased. Electricity liquidators are a huge mistake in the system concept as well. They are permitted by Slovak legislation, and they can even participate in support services for the transmission system, thanks to which their operators receive payment for the immediate consumption of electricity. And they are cheaper than other forms of electricity storage.

A separate but fundamental structural problem, according to some experts [47,48,49], is the EU′s setting of unrealistic procedures and policies for achieving carbon neutrality by 2050 in the current global situation. This approach can be quite controversial, because the first obvious risk is that, unless other regions follow suit, the problem of climate change will never be solved, as the greenhouse gas emissions in the EU currently account for less than 7% of global emissions. These, perhaps not entirely realistic EU targets, increase production costs for industries and weaken their global competitiveness [50,51].

The Slovak Electricity Transmission System is nowadays enhancing the connection capacities for both consumption and supply at the interface of the transmission and distribution system, thereby establishing the essential conditions for the evolution of the electricity sector as outlined in the sanctioned state energy policies and pertinent action plans. Strategies must be diversified to effectively manage peak loads by fostering community prosumers through electricity sharing, flexibility aggregation (aligned production and consumption by prosumers), and supporting battery storage solutions.

There is great interest in decentralized energy in Slovakia, and it is only necessary to overcome the barriers, and then it can be implemented. The state, through its energy agency, has been providing Green grants from the structural funds to households for two years, and Green for businesses is a new feature. The interest is enormous. Subsidized electricity prices for households reduce interest in their own sources, but it is assumed that prices will be reassessed, and within 10 years, every third household will have PV. The distribution system is preparing for this.

There is no better solution than consumption at the place of production. However, currently, distribution companies in Slovakia allow connecting only 3 kW for one RES producer, because this is the optimum for one household. The argument opposed that one house may have PV, while the other does not, due to technical reasons. So they would agree that the first one produces 6 kW and shares it with the second one. This is not possible in Slovakia. In Slovakia, there is also a problem with existing apartment buildings (around 85 thousand). Electricity for common areas is about 30 kW, for elevators about 40 kW, for apartments 3 kW each, but the distribution will not allow a total capacity of about 100 kW. And it does not allow so-called secondary electricity meters even in new buildings. Legislative regulation is needed in this regard. To define the term of community source, which would produce electricity for members of the energy community, and they would consume it at the same time. PV regulation is also missing. According to the results of the questionnaires with stakeholders, the most uncertainty is caused by the knowledge of legislative conditions and support for the application of similar actions reducing peak loads in Slovakia, up to 70% of responses, as shown in Figure 4.

In general, awareness of energy sharing is low, with up to 73 percent of Slovaks unaware of energy communities [41]. One-stop shops that could support renewable and citizen energy communities in the creation phase are strongly missing. However, initiatives supported by interest groups (KEKS) [44], non-profit and professional organizations (SAPI) [19], are creating manuals for the creation of energy communities. In the near future, an online tool for simulating and evaluating PV production and consumption based on PVGIS and cloud processing will be freely available on the market [52].

The fundamental prerequisite for the evolution of this new market was the Energy Data Center [39]. The EDC information system is structured to incorporate renewable sources, new activities, and actors within the Slovak electricity market. Drawing from the experience acquired, SEPS has advocated for the requisite legislative changes to expedite and streamline the participation of aggregators in the provision of support services, thereby facilitating the entry of aggregators into the market with support services derived from decentralized sources of flexibility across various geographical locations in Slovakia, with a power contribution. Electricity sharing does not present an issue for the distribution system in Slovakia. However, the connection is currently unattainable without an intelligent measurement system (IMS). Smart meters must be paid for by each member of the community themselves.

5. Conclusions

The stability of electricity networks is an important strategic task for European countries. It is, therefore, necessary to ensure appropriate legislative, technical, economic, and social conditions to ensure this stability. European countries, including Slovakia, are currently at different levels of implementation of this task, but in general, we can define the following tasks:

In the legislative field:

• Legislative reforms must clearly establish the priority of RES.
• Remove legislative barriers—in Slovakia, electricity sharing is currently only possible within the balance group of one settlement entity; the definition of the legal form is unclear in the case of a large stock of apartment buildings built in the second half of the 20th century.
• Unify legal regulations for permitting and financing renewable energy sources (like EIA, Construction Act, and Zoning Act processes).
• Support the establishment and existence of comprehensive advisory centers for coordinated procedures between offices, the so-called one-stop shop, along with the digitalization of processes. (A good example is Denmark).

In the field of economics:

• Financial support for the introduction of RES and electricity sharing for individuals, as well as for local governments, regions, small and medium-sized businesses, and public institutions.
• Cancellation of IMS fees, tax breaks, unification of tariff fees, and overall creation of a predictable economic environment for investing in RES and electricity sharing.

In the field of technology:

• The existence of EDC, and 15 min billing of electricity consumption and production, is a positive moment in Slovakia, as well as the preparation of an online digital platform for simulating and evaluating PV production and consumption.
• It is necessary to invest in distribution networks, especially in more remote regions, and to support the possibility of cross-border electricity sharing.

In the social field:

• Increase awareness and education in the area of building renewable energy, community energy, storage solutions, and related legislative and economic conditions.
• Increase transparency and reduce bureaucratic processes to enhance the confidence and willingness of the general public to engage in energy sharing.