Energy Market Transition and Climate Change: A Review of TSOs-DSOs C+++ Framework from 1800 to Present

Abstract

In response to the pressing global challenges around climate change and the imperative of transitioning the energy market towards sustainability, this paper presents a comprehensive review starting from the late 18th century. The study examines the pivotal role of Transmission System Operators (TSOs) and Distribution System Operators (DSOs) in shaping the evolving energy landscape, with a specific emphasis on the C+++ Framework. This framework emphasizes coordination, cooperation, and collaboration between TSOs and DSOs to achieve sustainable energy systems through the integration of renewable energy technologies, storage systems, and efficient energy demand management. In addition, the review provides a historical overview of global warming from 1800 to the present, highlighting key events and developments related to greenhouse gas emissions. Furthermore, the paper delves into the significance of international agreements such as the Paris Agreement and the importance of reducing greenhouse gas emissions for a sustainable future. Recognizing the vital role of the C+++ Framework, the paper concludes with a discussion of future hybrid sustainable technologies incorporating various storage and efficient lighting technologies that can optimize energy management and reduce carbon emissions. This research aims to contribute valuable insights to inform energy policy and decision-making processes for a reliable, efficient, and sustainable energy delivery system.

1. Introduction

The urgency of building a sustainable future and establishing a global sustainable energy system highlights the critical importance of fostering strong collaboration between transmission system operators (TSOs) and distribution system operators (DSOs) [1,2,3,4,5,6]. TSOs and DSOs working together are vital for effectively managing and integrating renewable energy sources and storage systems, ensuring grid stability, and meeting the energy demands of a rapidly evolving world. Recent studies [7] have demonstrated the potential of incorporating storage systems such as battery storage systems (BSSs) [8] and considering their role in conjunction with TSO-DSO coordination models [9]. This can lead to effective leveraging of distributed energy resources, enhanced grid stability, and optimal utilization of sustainable resources.

To address these challenges, this paper introduces the C+++ Framework, which emphasizes the key elements of coordination, cooperation, and collaboration between TSOs and DSOs within the energy sector. Each “C+” symbolizes one of these essential elements, serving as a guiding principle for optimizing energy management in sustainable energy systems. The framework facilitates the seamless integration of renewable energy technologies such as wind stations (WSs) [10], solar photovoltaic (PV) sources [11,12], and efficient storage systems [13]. Section 3 intricately delves into the inception of the C+++ framework, which facilitates collaborative agreements between TSOs and DSOs. This is preceded by a concise overview of the historical evolution of the global sustainable energy system.

In this context, a sustainable energy system is defined as a comprehensive approach that meets current dynamic energy needs while simultaneously minimizing detrimental environmental effects and safeguarding resources for future generations. A crucial goal of such a system is to minimize global greenhouse gas emissions [14], measured in Gigatons (Gt) of carbon dioxide (CO₂) equivalent (CO₂e) [15,16]. Lowering CO₂e is essential for addressing climate change and reducing the impact of human activities on the environment [17]. Note that greenhouse gases are essential for maintaining a habitable planet by trapping heat and supporting life as part of the natural greenhouse effect. However, human activities have led to an enhanced greenhouse effect, causing anthropogenic global warming [18] and climate change, making it crucial to reduce greenhouse gas emissions for a sustainable future.

Because global warming is a complex and ongoing process that is shaped by various natural and human-induced (or anthropogenic) factors, a brief overview of significant events and developments related to global warming from 1800 to the present is provided below:

• Industrial Revolution (Late 18th to 19th Century). Between 1739 and 1792, numerous experiments on inflammable air were purely for philosophical curiosity, yielding no practical results [19]. These were used in the past to describe gases such as hydrogen [20], which can readily ignite and burn in the presence of oxygen. In the late 18th century, Murdoch pioneered gas illumination, starting with his house and office in Redruth, Cornwall in 1792, and continued his significant contributions to gas lighting technology by erecting a gas production apparatus at the Boulton and Watt manufactory at Soho in 1798 [19,21]. The industrial revolution marked a significant turning point in human history, with the widespread use of coal and later oil as primary sources of energy. This led to a substantial increase in greenhouse gas emissions, particularly CO₂, as factories, transportation, and other industries burned fossil fuels at an unprecedented rate.
• 19th Century. During the 19th century, global average temperatures began to rise gradually as a result of increasing greenhouse gas emissions. The widespread adoption of fossil fuels for electricity, transportation, and other industrial processes continued to drive the trend. Over the past two centuries, the United States (US) economy evolved from a rural nation into an industrial powerhouse, surpassing the United Kingdom (UK) as the global technology leader and becoming the world’s wealthiest nation by the early 20th century, while the “Second Industrial Revolution” witnessed a substantial influx of European immigrants, driving the country’s economic growth [22].
• 20th Century. Early 20th century: the warming trend persisted, driven by rapid industrialization and urbanization, leading to increased greenhouse gas emissions. Mid-20th century: a slight cooling trend was attributed to industrial aerosols and pollution blocking sunlight, though not enough to counteract long-term warming. Late 20th century: a significant acceleration in global warming has been fuelled by the continued rise in greenhouse gas emissions from human activities such as fossil fuel burning and deforestation.
• Intergovernmental Panel on Climate Change (IPCC) [23]. In 1988, the United Nations (UN) established the IPCC to assess scientific research on climate change. The IPCC plays a crucial role in providing regular reports and scientific assessments of climate change, including the impacts of global warming.
• UN Framework Convention on Climate Change (UNFCCC) (1992) [24]. The UNFCCC is an international treaty adopted in 1992. It came into force on 21 March 1994. Its main objective is to address climate change and its global impacts.
• Kyoto Protocol (1997) [24]. The Kyoto Protocol was adopted in 1997, aiming to curb greenhouse gas emissions and mitigate global warming. The treaty established binding emission reduction targets for developed countries. However, some major emitters, such as the US, did not ratify the protocol, limiting its global impact.
• Paris Agreement (2015) [25]. In 2015, the Paris Agreement was adopted, aiming to limit global warming to well below 2 degrees Celsius (°C) above pre-industrial levels, with efforts to limit it to 1.5 °C. This landmark agreement brought together nearly all countries in the world to commit to reducing greenhouse gas emissions and enhance climate resilience.
• Ongoing Trends. Global temperatures have continued to rise in the 21st century, with some years being the hottest on record (23 July 2023), as shown in Figure 1a [26]. The global mean surface air temperature for this period is approximately 14 °C. In addition, Figure 1b [27] shows temperature anomalies for the period of 1980–2015 in °C based on GISTEMP dataset from the NASA Goddard Institute for Space Studies (GISS). There have been more frequent and severe extreme weather events, such as heatwaves, hurricanes, floods, and droughts, linked to the impacts of global warming [28].

Temperature anomalies refer to the difference between the observed temperature and a reference temperature. In the context of climate science and global warming analysis, they are typically used to measure how much the Earth’s surface temperature deviates from a specific baseline or average temperature. The baseline is often chosen as a reference period, such as pre-industrial times or a recent historical period with stable climate conditions. For example, the pre-industrial baseline could be the average temperature during the 19th century, around 1850–1900. Any temperature data collected after this period can be compared to this baseline to calculate temperature anomalies. A positive temperature anomaly indicates that the observed temperature is higher than the reference baseline, while a negative temperature anomaly means the observed temperature is lower. Temperature anomalies are typically measured in degrees °C or Kelvin (K).

Figure 2 shows share of global cumulative CO₂ emissions in 2021 as a percentage, while Figure 3 shows the development from 1750 to 2021 [29]. Two maximum values can be observed in 1900 for the European Union (27) and 1950 for the US.

Figure 4 shows the global carbon emissions from energy combustion and industrial processes, and their annual change from 1900 to approximately 2020 [14] and the projected figures towards 2050 [30]. Here, three main scenarios, which are crucial in understanding and predicting global carbon emissions, are expected: (I) New Momentum, (II) Accelerated, and (III) Net Zero. These scenarios offer different routes to tackle global carbon emissions. New Momentum envisions the energy system’s current path, driven by heightened decarbonization goals. Accelerated shows moderate advancement in clean technology and policies. Net Zero is ambitious, targeting emissions reduction through strategies such as carbon capture and behavioral changes. New Momentum follows trends, Accelerated seeks moderate change, and Net Zero aims for transformative emission reduction.

Here, the unit of CO₂e is used to measure greenhouse gas emissions, providing a standardized measurement for comparing and tracking emissions across different gases and sources. This approach allows scientists and researchers to estimate historical greenhouse gas emissions [31] and understand the evolution of emissions since 1750. However, these estimations may have uncertainties and limitations due to the lack of direct monitoring data from that period.

In the dynamic landscape of energy systems, the effective interplay between TSOs and DSOs is vital for reliable, efficient, and sustainable energy delivery. The three key elements (coordination, cooperation, and collaboration) are inspired by principles from supply chain management (SCM) [32] and supply chain partnership (SCP) [33]. SCM involves strategic coordination and optimization of activities in the production, procurement, conversion, and distribution of goods or services to ensure efficient flow and customer satisfaction. On the other hand, an SCP is a strategic alliance between two independent entities in the supply chain aiming to achieve specific objectives, such as enhancing financial and operational performance by reducing costs and inventory or sharing information. Comparing terms used for collaborative arrangements in the literature promotes uniformity in their usage within different contexts, preventing confusion and misuse [34].

To provide a context for the developments in 2012, this paper briefly presents a historical overview of optimal power flow (OPF), active–reactive optimal power flow (A-R-OPF), and voltage regulation solutions in interconnected power networks. This overview aims to familiarize readers with the foundational concepts underlying the framework inception, and can be read with the recent companion review in [7].

2. Brief History

In 1780, Galvani’s discovery laid the foundation for electrophysiology, and unexpectedly opened the path to Volta’s invention of the electric battery in 1800 [35]. This breakthrough, along with subsequent milestones, led to the development of direct current (DC) and alternating current (AC), as well as the understanding and management of power flow in electrical power systems. The following compilation provides an overview of the historical development of DC and AC technologies and the mathematical formulation of power flow and A-R-OPF, presenting key dates while acknowledging the significant contributions of numerous researchers in the field, even if not listed here. In cases where no reference is provided or for more detailed information, readers are encouraged to refer to [36,37].

2.1. DC/AC Power Flow (1800–1930)

The history of DC/AC power flow spanning the years from 1800 to 1930 was marked by significant milestones and breakthroughs in the field of electricity, including the invention of the battery, the discovery of electromagnetism, and the development of generators for DC and AC electricity, leading to advancements in power distribution and control.

1800	Volta announced the invention of the battery, which converts chemical energy into electric energy and vice versa [36].
1820	Oersted discovered the magnetic field [38].
1820s	Ampère’s research showed that using a 20 m long wire carrying an electric current and moving a compass closer to the wire resulted in concentric circular loops forming in the plane perpendicular to the wire [39].
1823	The initial devices and setups used for conducting experiments aimed at understanding the properties of electricity were developed [40].
1827	Ohm conducted his work on resistance and published his results [41].
1831	Faraday discovered the principle of electromagnetism [42].
1842	Grove produced a gas voltaic battery, a device that combined hydrogen and oxygen to produce electricity [43,44].
1845	Kirchhoff described what are known as Kirchhoff’s circuit laws [45].
1860s– 1870s	Many inventors explored ways to use Faraday’s induction principle to generate electricity mechanically, leading to the development of generators for DC and AC electricity.
1880	Edison invented the electric lamp, followed by the electric meter in 1881, and developed underground and overhead conductors for DC electrical distribution systems in 1883 and 1888, respectively.
1886	Benz applied for a patent for his vehicle with a gas-powered internal combustion engine operation [46].
1886	Stanley and, in 1887, Westinghouse invented different electrical transformers (TRs) for practical usage.
1888	Tesla invented the induction motor and made improvements in the transmission of AC power.
1890	The earliest application of electric storage batteries in Germantown, Pennsylvania coincided with the predominance of isolated DC power systems [47].
1891	Brown Boveri was co-founded by Charles E. L. Brown. In his paper titled “High voltages, their generation, transmission, and distribution” he pointed out that voltages of 30 or 40 kV are quite feasible compared to 2−4 kV [48].
1895	Dobrowolsky invented an apparatus for indicating phase differences between an electric AC current and the electromotive force.
1896	Arrhenius advanced the understanding of ice ages by using physical chemistry principles to calculate the impact of increased atmospheric CO2 on Earth’s surface temperature through the greenhouse effect [49].
1897	Peukert, in presenting Peukert’s law, explained how the capacity of rechargeable lead–acid batteries decreases as the discharge rate increases [8,50].
1900	Ångström’s research on the spectral analysis of sunlight and absorption of radiation by gases in the Earth’s atmosphere contributed to the understanding of atmospheric physics and the role of water vapor and carbon dioxide in the natural greenhouse effect [51].
1901	Browne introduced the concept of the power factor in AC systems, which represents the cosine of the phase angle between the voltage and current.
1902	The first mercury vapor lamp was invented in the early 1900s by Hewitt and introduced for commercial use in the early 1910s [52].
1909	Walker emphasized the need to improve the power factor in AC systems to reduce losses and increase generator capacity.
1913	The International Commission on Illumination (CIE), known by its French title, the Commission Internationale de l’Eclairage, was established [53]. The CIE is dedicated to global collaboration and the exchange of knowledge about light, lighting, etc.
1915	Philip described the flow of energy in an electric distribution system and introduced terms such as lagging/leading power factor, transmission losses, and power flow directions.
1923	Kapp introduced an apparatus for power factor improvement and voltage control, and proposals were made to include the power factor in electricity tariffs.
1926	Jansen invented the on-load tap changer (OLTC) to control the voltage of electrical TRs [54].
1926	In 1926, Germer and other scientists published a description of how preheating the electrodes facilitates ignition at lower voltage values; they filed a US Patent on 19 December 1927, which was granted in December 1939 [55].
1930	The first AC network analyzer was installed at the Massachusetts Institute of Technology, using equivalent-π circuits [56] to model AC networks.

2.2. Mathematical Formulation of OPF (1943–1990)

The period from 1943 to 1990 saw significant developments in the mathematical formulation of OPF, with pioneering contributions in power network loss modeling, power flow problem solving methods, and the optimization of active and reactive power flows to improve system efficiency and performance.

1943	George proposed the first loss model for power networks, considering both active power (P) and reactive power (Q) flows in a transmission network (TN) [57].
1946	The concept and sign of reactive power and its flow were extensively discussed.
1947	Dunstan introduced a machine for studying and analyzing the performance of power networks, aiming to facilitate power flow problem handling.
1956	Ward et al. presented a method for solving the power flow problem using digital computers, based on a loop approach.
1957	Glimn et al. proposed an iterative method based on the Gauss–Seidel algorithm to determine system voltage distribution using a nodal approach.
1961	Van Ness and Griffin described an elimination method for load flow studies, later known as Newton’s method.
1962	Carpentier formulated the general problem of OPF subject to equality and inequality constraints.
1963	Smith et al. presented a method for minimizing power transmission losses through reactive volt–ampere control.
1967	Tinney et al. introduced Newton’s method to solve AC power flow, describing its characteristics and advantages.
1968	Dommel et al. presented a method for solving the power flow problem with control variables adjusted to minimize costs or losses.
1968	Peschon et al. formulated the problem of minimizing the operating cost of a power system through proper selection of active and reactive productions.
1968	Dura proposed dynamic programming for optimal sizing and allocation of shunt capacitors in radial distribution feeders.
1969	Sasson presented a unified approach to solve the OPF problem based on Carpentier’s formulation.
1971	Fletcher presented an effective algorithm for quadratic programming with general applicability [58].
1972	Power flow optimization methods were classified into exact and approximate categories considering active and reactive power flows.
1974	Borkowska introduced a method for solving the power flow problem, accounting for uncertainties with linear approximations and neglected losses.
1979	Felix et al. developed a two-stage approach for solving large-scale OPF problems, excluding transmission line flows.
1982	Shoults et al. decomposed the OPF problem into subproblems (P-Problem and Q-Problem) to overcome system constraints.
1982	Tripathy conducted a study to deal with load-flow solutions for ill-conditioned power systems using a Newton-like method, addressing challenges faced by Newton’s method in solving OPF problems.
1988	Bacher et al. presented a two-stage approach for a real-time OPF in an energy management system, using a constrained economic dispatch with a parametric quadratic programming algorithm to address network flow violations and meet performance requirements [59].
1990	The German Electricity Feed-In Act (Stromeinspeisungsgesetz) came into effect on 1 January 1991 [60]. In the US, Phase I of the Clean Air Act Amendments of 1990 (CAAA), specified in Title IV, commenced on 1 January 1995 [61].

2.3. OPF with Renewable Energies and Storage Systems (1980–2011)

During the period of OPF development with renewable energies and storage systems from 1980 to 2011, electrical lighting systems remained a substantial load in power networks, particularly in buildings and urban areas. Researchers explored innovative methods to optimize the integration of energy storage systems, addressing the challenges of demand fluctuations (as lighting is a major source of energy demand [62]) and improving overall energy efficiency in numerous applications. Efforts were made to balance demand through load management and storage strategies, contributing to the sustainable and intelligent utilization of electricity in modern installations.

1980	Davidson et al. emphasized the value of integrating storage with renewable energy sources, particularly batteries in small customer-centric units, within different types of large-scale electrical energy storage systems.
1990	Walker described a bidirectional 18-pulse voltage source converter utilizing gate turn-off thyristors for connecting a BSS to a utility grid.
1994	Ter-Gazarian emphasized that BSSs located close to consumers can help to provide a smoother load on the distribution network (DN).
1994	Rau et al. proposed an initial step towards optimum allocation of distributed generation (DG) units, introducing different objective functions such as network losses and line loads.
1996	Miller et al. presented the design and commissioning of a 5 MVA, 2.5 MWh BSS at the GNB Battery Recycling Plant in California. This BSS served critical loads during external disturbances and provided energy during peak load periods.
1996	Common rules for the internal market in electricity were established through Directive 96/92/EC [63]. The overall objective was to create a well-functioning, competitive, and integrated internal or single market in electricity within the European Union.
1998	Tregenza et al. authored a book focusing on lighting in buildings specifically aimed at architects, interior designers, and building services engineers [64]. At this time, it was shown that a 400 W high-pressure sodium lamp has an efficiency of 120 lm/W.
2001	Ribeiro et al. provided a detailed review of BSS capabilities, including dynamic stability, voltage support, frequency regulation, transmission capability, and power quality improvement.
2002	Liew et al. proposed alternative control strategies to increase the penetration of wind-based DG units, including generation curtailment, reactive power absorption, and coordinated OLTC.
2003	Abido introduced a multi-objective evolutionary algorithm for the Environmental/Economic Power Dispatch problem [65]. This proposed approach, which combines fuzzy theory [66] and genetic algorithms [67], was evaluated using the standard IEEE 30-Bus/6-Generator test system.
2003	Various energy storage technologies were examined for bulk energy storage, DG units, and power quality applications with variations in discharge time and storage capacity.
2005	Chacra et al. evaluated the impact of energy storage costs on the economic performance of a distribution substation, comparing Vanadium Redox Batteries and Polysulfide–Bromine batteries.
2005	Harrison et al. proposed a mathematical model for maximizing DG capacity in distribution networks (DNs) using a single deterministic optimization approach.
2006	The International Energy Agency (IEA) raised concerns about a projection showing that without prompt action, global energy used for lighting would surge by 80% in 2030 [68]. However, the IEA emphasized that by harnessing available and cost-effective energy-efficient lighting technologies and strategies this increase could be averted, resulting in substantial energy savings, reduced CO2 emissions, and significant cost reductions.
2006	Gabash authored a book on electrical illumination engineering, exploring the efficiency of various electrical lamps [69]. At this time, lamp efficiency ranged from 35 to 49 lm/W for fluorescent lamps, whereas incandescent lamps exhibited an efficiency of around 12 lm/W. The efficiency of high-pressure sodium lamps had improved to 130 lm/W for a 1 kW lamp as compared to 1998 [64].
2007	Al-Hassan et al. developed an electronic monitoring system using the AT Mega 16 Microcontroller to monitor distribution TRs (20 kV/0.4 kV), accurately indicating future demand [70]. Visual Studio 2005 software was used to interface and communicate with the hardware design, as shown in Appendix A.
2008	Poonpun et al. conducted a cost analysis considering the life cycle of grid-connected electric energy storage.
2008	Viawan et al. addressed the impact of DG units on voltage stability of DNs, highlighting the possibility of power flowing in reverse.
2009– 2011	Teleke et al. developed an optimal control method integrating a BSS with a large wind farm [71,72]. Ochoa et al. proposed models and optimization techniques to maximize energy penetration from DG units in DNs, aiming to reduce curtailment of renewable energy [73]. Atwa et al. suggested a technique for sizing and optimal allocation of BSSs in DNs with high penetration of wind-based DG turbines, indicating that BSSs could help reduce renewable energy curtailments [74]. Burke et al. investigated factors influencing wind energy curtailment in transmission networks (TNs) [75,76]. Oh proposed modeling storage devices in the OPF framework to consider the impact on a TN [77].

2.4. Bidirectional A-R-OPF

By 2012 [76], the demand for diverse voltage regulation solutions had emerged in power systems due to the necessity of effectively managing bidirectional active–reactive power flows, as illustrated in Figure 5. Such dynamic management facilitates seamless transfer between power sources and loads, enabling energy to flow bidirectionally [7].

However, this gave rise to energy curtailment and power rejection issues at that time. Here, power rejection refers to a situation where TSOs are unable to accommodate or accept the full amount of electricity generated by power producers (such as power plants, renewable energy sources, or storage systems) into their high-voltage TNs. As a consequence, the excess electricity that cannot be transmitted through the TSO’s network may be rejected or curtailed. Recently, wind and solar energy curtailment has become a significant challenge in several countries, including Europe, North America, and Asia [78,79], demanding immediate attention and innovative solutions to optimize the integration of renewable energy sources into the power grid, particularly in light of new plans [7].

The concept of upstream and downstream networks in power systems involving energy storage, renewable energy integration, and electric vehicle charging is commonly observed [80,81]. The upstream network pertains to the part of the power system closer to power generation sources, comprising high-voltage transmission lines and substations responsible for transmitting electricity over long distances. In contrast, the downstream network represents the distribution system delivering electricity from the TN to end-users, involving lower voltage distribution lines, TRs, and local substations. The upstream and downstream networks should collaborate to efficiently transmit and distribute electrical power, with the upstream network supplying electricity to the downstream network for distribution to end-users. In addition, terms such as Slack/Infinite Bus are used in power systems with specific meanings. A slack bus serves as the reference point for the voltage and phase angle in the system, and is typically linked to a large power source or generation unit (GU), while an infinite bus is a theoretical concept used for power system modelling that represents an idealized system with constant voltage and unlimited power supply. Note that a transmission system can have numerous conventional generation units (GUs) [82] and a complex network of transmission lines [7].

Furthermore, an OLTC is a crucial device installed on a transformer (TR), allowing adjustment of the TR’s voltage ratio while it is energized and under load. This differs from traditional off-load tap changers, which require de-energization before adjusting the tap position. OLTCs enable TRs to adapt to changing voltage conditions while maintaining a stable output voltage within desired limits. TRs with OLTCs find application in voltage regulation in electrical DNs, TNs, and industrial setups, offering flexibility and efficiency. The first isolated DC TRs were designed to meet the safety demands of DC charging stations, particularly for electric vehicles [81], by employing galvanic isolation to separate electrical circuits while enabling the transfer of signals or power between them. The high efficiency and bidirectional energy transfer capability of such TRs make them versatile for various applications, including beyond DC charging stations for electric vehicles. Throughout the years, Maschinenfabrik Reinhausen has been a key driver of advancements in TRs and DC/DC converters [42,83], as shown in Figure 6 for comparison.

3. C+++ Framework

The initial C+++ framework for collaborative agreements was introduced with the aim of exploring the effects of bidirectional A-R-OPF between an upstream TN and downstream passive/active distribution networks (PDNs/ADNs), as shown in Figure 7. Since its inception in January 2012 [76], the author is unaware of any published work on this framework that demonstrates the exchange of active and reactive power between ADNs, incorporating renewable generation and energy storage systems, as later exemplified in November 2012 [84] and August 2013 [67]. This framework can be understood in the advanced control of industrial processes, the theory of hierarchical multi-level systems, and optimization [85,86]. Here, PDNs–demand/ADNs–demand profiles are obtained based on internal optimal operation strategies; see the detailed mathematical formulations in [67,84]. Note that transmission line ampacity remains a critical challenge, as highlighted in a study from 2016 [87].

Because TSOs and DSOs are typically independent organizations (companies or entities) responsible for managing and operating distinct parts of the power grid, this paper aims to highlight the importance of the three crucial terms (coordination, cooperation, and collaboration) derived from the principles of SCM [32] and SCP [33]. The distinctions among these terms are of significant relevance, and this study seeks to elucidate them as follows:

• Coordination: this refers to the process of organizing and harmonizing activities or efforts to ensure efficient and effective outcomes. It involves aligning tasks, resources, and schedules to achieve a common goal. As shown in Figure 8, coordination represents the basic level of interaction between individuals or groups, where they exchange information and adjust their actions to work together smoothly. It minimizes conflicts, optimizes system performance, and ensures smooth energy transmission and distribution. Examples include data exchange protocols, coordinated maintenance schedules, and joint contingency planning, all contributing to a harmonious and efficient energy network.
• Cooperation: this goes beyond coordination by emphasizing a more active and collaborative approach. It involves willingly working together, sharing knowledge, and contributing to a collective effort. Cooperation often involves a higher level of interaction, communication, and mutual support among individuals or groups. As shown in Figure 8, cooperation represents a deeper level of engagement and joint effort between entities in which they actively collaborate to achieve shared objectives. Examples include joint efforts to enhance grid stability, integrate demand–response measures, and incorporate renewable energy sources and storage systems.
• Collaboration: this represents the highest level of interaction and synergy among individuals or groups. It involves actively working together, pooling resources, and combining expertise to achieve a shared vision or outcome. Collaboration typically entails open communication, trust, and a strong sense of collective responsibility. Collaboration represents a deep and integrated level of cooperation in which entities engage in intensive collaboration to achieve common goals, as shown in Figure 8. Through collaboration, TSOs and DSOs leverage their combined knowledge and expertise, amplifying their impact and accelerating the transition to a sustainable energy future.

The synergy between coordination, cooperation, and collaboration is pivotal in achieving the seamless functioning of sustainable energy systems. TSOs and DSOs must recognize the importance of these three elements and actively cultivate them to optimize system performance, enhance grid resilience, and enable the integration of renewable energy sources and storage systems. By embracing coordination, cooperation, and collaboration, TSOs and DSOs can navigate the complexities of the evolving energy landscape and pave the way for a sustainable and efficient energy future.

Table 1. Terms in the C+++ Framework.

C	Term	Meaning
+	Coordination	The process of organizing separate things so that they work together. It operates at a low-level framework.
+	Cooperation	The process of working with another company/organization in order to achieve something. It operates at a medium-level framework.
+	Collaboration	The situation of two or more companies/organizations working together to achieve the same thing. It operates at a high-level framework.

summarizes the three terms.

In this context, advancing the energy transition relies on effective coordination, cooperation, and collaboration between TSOs and DSOs in power systems. TSOs, represented by four operators in Germany, transmit electricity at high voltages over long distances, ensuring reliable transmission from generation sources to distribution systems or major industrial consumers. DSOs, comprising over 800 operators in Germany, manage the DN and handle customer connections, distributing electricity at low and medium voltages to the end consumers [7]. Establishing a clear C+++ framework between TSOs and DSOs is crucial, as it enhances power flow management, system stability [88], voltage quality [89], and operational planning [90,91], all of which contribute to the successful implementation of optimal initiatives for the energy market transition.

In brief, countries worldwide are transitioning from traditional power systems centered on synchronous generators to low-carbon resources involving a significant presence of converter-interfaced generators [92]. As adoption of these generators, along with storage systems, increases, numerous fast power electronic devices can be integrated into the grid, leading to more agile and intricate dynamic response in the system [7].

3.1. Offline and Online A-R-OPF Frameworks

In power engineering [48,93,94,95], two main frameworks are employed for effective A-R-OPF management:

• Offline Framework. The offline framework (deterministic/stochastic) involves planning [93,94], simulation, optimization, and pre-operational analysis of power systems [36]. It focuses on tasks such as load flow analysis, contingency analysis, parameter optimization, and other comprehensive analyses to make informed decisions before actual power system operation takes place.
• Online Framework. The online framework can be further classified into two sub-frameworks:
  • Computer-based A-R-OPF frameworks [96]. These frameworks utilize computer algorithms and real-time data to continuously optimize and control power system operations. They involve monitoring real-time parameters such as power demand, generation output, and network conditions to adjust control settings dynamically.
  • Web-based A-R-OPF frameworks [97]. Web-based frameworks leverage the power of the internet to access and exchange real-time data and perform optimization remotely. They provide a flexible and accessible approach, allowing users to interact with power system management tools and decision-making processes from remote locations.

The utilization of these frameworks in power engineering is crucial for ensuring efficient and reliable operation of power systems. The offline framework enables strategic planning and thorough analysis of different scenarios, while the online frameworks offer dynamic control and decision-making capabilities to respond promptly to real-time changes and optimize power system performance. Together, these frameworks play a pivotal role in enhancing the stability, efficiency, and sustainability of modern power systems, contributing to the successful integration of renewable energy sources and the effective management of complex power grids.

It is important to note that in a web-based framework, a read–execute–write procedure (REW-Procedure) is usually necessary, as shown in Figure 9 [97].

This is important for synchronizing the computational flow, especially if wireless hardware sensors are used to capture wind speed measurements from specific locations and send them to web-based software where an optimization algorithm is running in real time. The reserved time periods that taken equally, and the summation of all periods is equal to a cyclic time T_cyc, as follows:

T_cyc = T_A + T_B + T_C

(1)

T_A = T_B = T_C

(2)

where T_A is the reserved time period for reading data, T_B is the time period reserved for executing the computational optimization, and T_C is the time period reserved for managing the data and online monitoring the results. Here, k ∈ ${\mathbb{N}}_0$ is a running variable and {A, B, C} is the set of three time slots; details can be found in [97]. Considering the computational capabilities of the web-based A-R-OPF framework, it has been determined that dividing the process into three equal time slots, each lasting 1 s, can facilitate efficient data transmission and visualization. This data transmission method and data management scheme are required to measure and monitor weather-dependent variables such as wind speeds using sensors such as wireless-based sensors. In general, there are two types of data transmission methods, namely, synchronous and asynchronous, each of which has its own advantages and disadvantages [98,99].

Based on the initial C+++ framework, several collaborative agreements and mathematical formulations have been developed taking into account clear market strategies for active and reactive energies. The fundamental idea behind the mathematical formulation of the combined A-R-OPF approach is to simultaneously optimize the management of both active power and reactive power. For example, Figure 10a shows a fixed A-R-OPF without BSSs in a low-voltage network, while Figure 10b shows fixed a A-R-OPF with BSSs in a medium-voltage network. It is worth mentioning that a BSS was not needed in low-voltage networks in 2012 [100] due to full use of the reactive power capability of all installed PV systems and differences in energy prices.

In contrast, in medium-voltage networks, in order to avoid any power rejection from the TSO, the following assumptions were made in the initial C+++ Framework [67,84]:

• Integration of a BSS in the DN with a significant presence of DG units is economically viable [74].
• DG units and BSSs incorporated within the DN contribute active energy back to the TN, and the associated active energy losses are accounted for through a consistent pricing model such as the two-tariff model [84].
• Both active and reactive power flow from the DN to the TN are permitted without any rejection. Such an assumption is important when planning, for example, DG capacity [10,56] and storage systems in ADNs [101].

Here, the total yield maximization in DN operation refers to the optimization of power generation and utilization within a DN to achieve the highest overall energy yield or efficiency. The goal is to ensure that the available energy resources, including renewable energy sources, conventional generators, and storage systems, are utilized in the most effective and optimal manner.

To ensure clarity and simplicity, the loads in a medium-voltage DN are assumed to behave as PDNs. This assumption implies that there is no reverse active/reactive power/energy flow from low-voltage networks back to the medium-voltage DN. This simplification has been considered for a flexible A-R-OPF with BSSs as well [67], as shown in Figure 11, and in a flexible A-R-OPF with BSSs and an OLTC control system [54].

3.2. Environmental and Grid Protection

Within the realm of safeguarding the environment and ensuring the reliability of energy systems [102], two pivotal domains come to the forefront, namely, environmental protection [65] and grid protection. While environmental protection focuses on mitigating air pollution and enhancing air quality through legislative measures, such as the CAAA in the US [61], grid protection, especially in Net-Zero AC Microgrids [103], addresses the intricate challenges posed by the transformation of power grids into DNs with the integration of renewable energy sources and storage systems. Therefore, it is imperative to comprehensively investigate their collective contributions toward a sustainable and resilient future while taking into account information security frameworks [104] and advancements in hybrid sustainable technologies.

4. Future Hybrid Sustainable Technologies

Future hybrid sustainable technologies, known as clean or green technologies, encompass forward-thinking or strategic approaches in the context of the C+++ Framework for TSOs and DSOs. It refers to the extent to which these operators actively contemplate the future, anticipate its consequences, and proactively plan ahead before implementing innovative solutions. Such strategic thinking plays a crucial role in advancing the development and adoption of these technologies to ensure their effectiveness and long-term impact on the environment and society in the power grid management domain.

In general, a hybrid refers to a mixture of two different things. In the context of sustainable technologies, the term “hybrid” refers to the combination or integration of two or more different types of sustainable technologies. These technologies are designed to work together synergistically, leveraging the strengths of each component to create a more efficient and effective solution. For example, in the field of renewable energy, a hybrid sustainable technology could involve combining solar power and wind power systems, as shown in Figure 5, to harness energy from both sources. By integrating these technologies, the system can take advantage of sunlight during the day and wind energy during periods of high wind, resulting in a more stable and reliable power generation system. Similarly, in transportation, hybrid sustainable technologies could involve combining EVs with other alternative fuels or energy sources to extend their range and reduce emissions further [81]. The overarching goal of future hybrid sustainable technologies is to maximize the benefits of various sustainable solutions, overcome individual limitations, and promote a more comprehensive and sustainable approach to addressing environmental and societal challenges.

Strategically, in addition to wind-based and solar-based energy systems and technologies, the literature review above summarizes several other options for hybridization and improved energy efficiency [105,106].

• Microgrids and Smart Energy Systems: smaller-scale localized power systems that can operate independently or in connection with the main grid, often incorporating advanced monitoring and control technologies [107].
• Water-Based Energy Systems: hydroelectric power systems use dams and reservoirs to convert the potential energy of flowing or falling water into electricity through turbines, hydrokinetic energy systems capture the kinetic energy of water currents or waves using underwater turbines or wave energy converters, tidal energy systems harness the energy from the rising and falling tides to generate electricity, wave energy systems convert the kinetic energy from ocean waves into electricity, and ocean thermal energy conversion uses temperature differences between warm surface waters and cold deep waters to produce electricity. Global hydropower expansion is expected to slow this decade due to project slowdowns in China, Latin America, and Europe, although growth in Asia Pacific, Africa, and the Middle East should partially offset these declines; furthermore, erratic rainfall due to climate change may further disrupt hydro power production worldwide [108].
• Heat-Based Energy Systems: these consist of are various technologies, including thermal power plants that use fossil fuels or renewable sources to generate electricity through steam, geothermal power plants that harness heat from the Earth’s subsurface, concentrated solar power plants that use sunlight to produce high-temperature heat for electricity, waste-to-energy plants that convert municipal solid waste into energy, and combined heat and power systems that simultaneously produce electricity and usable heat from a single fuel source. In the Net Zero Scenario, efficiency improvements and decarbonization would cut buildings’ heating-related emissions in half by the end of the decade, reducing the global energy intensity of heating by 4% annually through 2030 [109].
• Organic-Based Energy Systems: including bioenergy using biomass and biogas, these rely on organic material derived from plants or living organisms as the primary source of energy. While combustion releases carbon, the process is considered near zero-emission due to carbon absorption during photosynthesis, making it both sustainable and the largest source of renewable energy, accounting for over 6% of the global energy supply. To achieve UN Sustainable Development Goal 7 on Affordable and Clean Energy, the Net Zero Scenario aims to eliminate the traditional use of biomass by 2030 [110].
• Other Sustainable Approaches: the goal of many other sustainable approaches is to optimize waste management, for example, in the oil and gas industry [111], thereby minimizing its environmental impact and maximizing its potential for reuse, recycling, or conversion into valuable resources or energy. In addition, sustainable water treatments must prioritize energy efficiency as a crucial requirement and identify methods with minimal or no adverse impact on the environment in order to ensure a sustainable future [112]. Energy-efficient appliances, energy-efficient LED lighting [113], smart frameworks [114], smart building design, and smart lighting systems are examples of technologies that reduce energy consumption and lower greenhouse gas emissions. It is expected, for example, that due to advances in technology the efficiency of LEDs in the Net Zero Scenario will be 141 lm/W in 2030 [115].

Similarly, future hybrid storage refers to the potential evolution of energy storage technologies beyond conventional BSSs. Storage solutions can combine different storage technologies to leverage their individual strengths and overcome limitations. This approach aims to enhance the overall performance, efficiency, and flexibility of energy storage systems. Such storage systems could involve combinations of BSSs (or flow BSSs [13,116]) with other storage technologies, such as:

• Flywheel energy storage
• Thermal energy storage
• Pumped hydro energy storage
• Superconducting magnetic energy storage
• Compressed air energy storage
• Capacitor and supercapacitor bank energy storage
• Hydrogen or other synthetic fuels

For example, in Germany [117] the National Hydrogen Strategy (NHS) of the German government creates a coherent framework for hydrogen-related activities, encouraging innovation and investment while contributing to climate goals. The NHS aims to establish new value chains and foster international energy policy collaboration [118].

• Accelerated market ramp-up of hydrogen: increase ambition along the entire value chain for hydrogen and its derivatives.
• Ensuring sufficient availability: increase domestic electrolysis capacity to at least ten gigawatts by 2030, with the remaining demand to be covered by imports.
• Development of efficient hydrogen infrastructure: create a hydrogen core network with over 1800 km of converted and new hydrogen lines in Germany by 2027/2028, add around 4500 km across Europe (European Hydrogen Backbone), and connect major generation, import, and storage centres to relevant customers by 2030.
• Establishment of hydrogen applications: use hydrogen and its derivatives in industry, heavy commercial vehicles, aviation, shipping, and the electricity sector for energy security. Promote the use of hydrogen in the central and decentralized heat supply.
• Expand technology leadership and offer the entire value chain of hydrogen technologies, from production, such as electrolysers, to various applications, for example fuel cell technology.
• Creation of suitable framework conditions: establish coherent legal requirements at the national, European, and international levels to support market ramp-up. Streamline planning and approval procedures, implement uniform standards and certification systems, and ensure well-coordinated administration at all levels.

In addition [119], a new approach called Carbon Contracts for Difference (CCfD) has been introduced in Germany to address climate protection concerns in energy-intensive industries. Under these contracts, the government aims to offset the additional costs of climate-friendly production methods compared to conventional methods; an illustrative example is provided in Appendix B [120].

Future research could focus on the following areas:

• Strategic Thinking in the C+++ Framework for TSOs and DSOs: investigating operators’ proactive planning for innovative solutions in power grid management, especially concerning hybrid sustainable technologies.
• Advancing Hybrid Sustainable Technologies: further exploration and development of combinations of renewable energy, energy efficiency, sustainable transportation, and other technologies for maximum environmental and societal impact.
• Enhancing Hybrid Energy Storage Systems: investigating the evolution and combinations of various energy storage technologies to improve overall performance, efficiency, and flexibility.
• Assessing the effectiveness and scalability of energy-efficient technologies, such as LED lighting and smart building designs, in reducing energy consumption and greenhouse gas emissions.
• Assessing National Hydrogen Strategies: analyzing the impact of hydrogen strategies such as Germany’s NHS on coherent frameworks, innovation, investments, and climate goals; studying the effectiveness of CCfD in addressing climate concerns and incentivizing climate-friendly production in energy-intensive industries.

5. Conclusions

In conclusion, the C+++ Framework is emerging as a pivotal approach to address the pressing need for collaboration between transmission and distribution system operators in forging a sustainable energy future. Emphasizing coordination, cooperation, and collaboration, this framework unlocks the potential for seamless integration of renewable energy sources and storage systems, ensuring grid stability and a significant reduction in greenhouse gas emissions. The historical overview of global warming presented in this review paper underlines the urgency of transitioning towards low-carbon resources and embracing cutting-edge technologies such as hybrid storage solutions and hydrogen-based storage as a means to optimize energy management.

The amalgamation of offline and online optimal power flow frameworks plays a crucial role in driving efficient power system operations, while the Carbon Contracts for Difference mechanism offers an incentive for climate-friendly practices in energy-intensive industries. By leveraging the principles of the C+++ Framework, energy operators can lead the successful energy market transition, fostering a sustainable and resilient energy ecosystem for a more promising future. As we progress, future research and advancements in storage and power system technologies promise to unlock even greater potential, paving the way for a cleaner and more sustainable energy landscape. Together, through relentless innovation and collaboration, we can create a world powered by renewable energy and a steadfast commitment to preserving our planet for generations to come.