The evolution of interstate power grid formation

0 Introduction

The development of interstate electric ties (ISETs),interstate power grids (ISPGs), and power markets is a global integration process that is ongoing in various regions worldwide for almost a century.Numerous ISETs and powerful ISPGs have been developed in the United States and Europe.They are also rapidly developing in southeast Asia and some regions of Africa; moreover, prospects for developing ISETs and creating ISPGs in south and northeast Asia are being investigated [1].Similarly, prospects for developing a global power grid have been discussed, mainly from a conceptual point of view [2].

The driving forces behind the electric power integration process are represented by the effects induced by such an integration, including 1) reduction in the demand for the interconnection between the installed generating capacities owing to the time difference of load maxima occurrence(both in the daily and annual load curves) in different countries, which correspondingly causes a reduction in investment cost (saving); 2) reduction in fuel consumption and related fuel costs owing to the optimization of power equipment load within power system interconnection;3) higher reliability of interconnected electric power systems (EPSs) owing to their mutual backup; 4) more significant opportunities for involving renewable energy sources (hydraulic, tidal, wind, and solar energy) into the joint power balances of different countries introduced into extensive interstate power interconnections due to higher flexibility of the interconnection; 5) expansion of electric power markets and intensification of power trade between countries for obtaining profits; 6) opportunities for constructing more powerful power plants with larger units,which is still relevant despite the widely observed tendency of distributed-generation development; 7) environmental,social, and other effects.

Electric power integration contributes to the achievement of the Sustainable Development Goals (SDGs) proclaimed by the United Nations (UN) [3], as well as to the attainment of net zero target [4] in terms of carbon neutrality by facilitating the large scale renewables penetration in power interconnections.

Despite these notable advantages, the development of ISETs with the formation of ISPGs faces specific challenges: 1) interconnection of different energy and power legislations, technical parameters, and standards in the electric power industries of countries; 2) high cost of ISETs; 3) mutual interdependence of interconnected EPSs, likely compromising the energy and power security of countries importing large volumes of electric power;4) lack of concerted strategies for the expansion of interstate electric power interconnections; and 5) likely political tension between countries.However, these challenges can be overcome by concerted efforts of the concerned countries and parties by building confident relationships and bilateral and multilateral agreements regulating the technical,economic, market, and organizational aspects of interstate power system interconnection and cooperation.

In this study, the European, American, African,and Asian experiences in the field of interstate electric power integration, including system, spatial, technical,organizational, and market aspects, are analyzed and generalized.We aim to help mold the foreign energy and power policies for various countries.

1 Europe

1.1 History of grid development

The first ISET in Europe emerged as early as the beginning of the 20th century.Thus, electric ties among Switzerland, France, and Italy were implemented in 1906[5].ISETs were further developed in these regions, and in 1951, the Union for the Coordination of Production and Transport of Electricity (UCPTE), the largest ISPG in Europe at that time, was formed by interconnecting the EPSs of Austria, Belgium, Italy, Luxemburg, the Netherlands,France, the Federal Republic of Germany, and Switzerland.In 1961, the Union Franco-Ibérique pour la Coordination de la Production et du Transport d’Électricité (UFIPTE), i.e.,French-Iberian Union for Coordination of Power Production and Transmission, which included the EPSs of France,Spain, and Portugal, was formed.Nordel ISPG was formed in 1963, and included the EPSs of Scandinavian countries(Norway, Denmark, Finland, and Sweden).The South East European Interconnected System (SUDEL) ISPG included the EPSs of Austria, Greece, Italy, and Yugoslavia.MIR, an energy interconnection of socialist countries that embraced the territory of Eurasia, was not exclusively European.Therefore, it has been discussed separately.

The creation of the above-mentioned power interconnections ensured a reliable and effective electric power supply for consumers as a result of the aforementioned system integration effects.

Owing to further integration processes by the end of the 1990s, only two ISPGs remained in Europe, namely UCPTE, later united with UFIPTE and SUDEL, and Nordel, which remained as it was.In 1999, UCPTE was transformed into the Union for the Coordination of Transmission of Electricity (UCTE).However, the UCTE lost the function of electric power production.Because,during that period, the market transformations in the electric power industry continued in Europe.Market mechanisms invaded the power generation sector.These mechanisms were expected to determine the supply and demand balance,and consequently, the required volumes of electric power produced by generating companies.Additionally, the electric networks remained a natural monopoly; therefore,the UCTE maintained the functions of power transmission coordination and control.

CENTREL, a new energy interconnection, emerged in Europe in 1992; it included the EPSs of East European countries (Poland, Hungary, Czech, Slovakia, and East Germany), which after the disintegration of the USSR and the Council for Mutual Economic Assistance (CMEA), left the MIR power interconnected system and formed their own ISPG.In 1995, it commenced parallel operation with UCPTE.And in 1999, it was included in the UCTE.

In 2009, all the above-mentioned ISPGs were united into a single interconnection, the European Network of Transmission System Operators for Electricity (ENTSO-E),which included more than 40 networks and system operators from 35 European countries.Thus, the European ISPG does not have a single system operator.Moreover, this interconnection is not synchronized.It has five synchronous zones interconnected by DC back-to-back links and transmissions for joint operation.The zones include continental Europe, Scandinavia, Great Britain, Ireland,Northern Ireland, and Baltic countries.

Bulk power electric networks, including interstate networks, are mainly designed for 380-400 kV AC [6-7].DC ±450-500 kV lines are mainly designed for the connection of asynchronous zones of continental Europe on the one hand, and Scandinavia and Great Britain on the other hand (Fig.1).The main indicators of this interconnection are listed in Table 1 and Fig.2 [7,8].

According to Table 1 and Fig.2, the European interconnection is extremely large, exceeding 1 TW of installed generation capacity.Germany has the largest national generation capacity, followed by France, Italy,and Spain.Thus, the European power interconnection has extensively developed electricity grids, enabling an annual exchange of approximately 450 TWh of electric power.

Fossil-fuel thermal power plants (TPPs) are commonly used in Europe, with approximately more than 40% of the installed capacity and power generation in the regional electric power sector (Fig.2).Nearly half of the TPPs are coal-fired plants, whereas over 40% are gas-fired plants [9].Renewable sources are still not prevailing power sources in Europe, with a 28% share in installed capacity and 16%in power generation.Traditional renewable - hydropower,takes about 20% in installed capacity and nearly 17% - in power generation.

1.2 Subregional interconnections

Subregional electric power integration goes in parallel with the general European integration.For example, the Baltic Sea Ring (BSR) project aims to connect 11 countries in that region (the Netherlands, Germany, Poland, Russia,Belarus, Estonia, Lithuania, Latvia, Sweden, Finland, and Denmark) [10].This project began in 1998 when power companies of the named countries founded the Baltic Ring Electricity Cooperation Committee (BALTREL).Thus far,the BSR has been practically formed.

A memorandum of understanding signed in 2004 by system operators from Russia, Ukraine, Georgia, Moldova,Armenia, Bulgaria, Romania, and Turkey marked the beginning of the Black Sea Regional Transmission Planning Project (BSRTP) [11], also known as the Black Sea Ring.USEA, an energy association in the USA,actively participated in developing the project.This project extends beyond Europe and covers the territory of Asia Minor, which makes the project intercontinental.However,despite the long duration since the commencement of the project, the implementation stage has not been completed yet.Political differences between countries in this region are expected to be the leading cause.The Mediterranean Electricity Ring (MEDRING) also extends beyond Europe and covers the EPSs of North African countries, Asia Minor,and Middle East [12,13], thus constituting an interregional and intercontinental project.MEDRING includes 22 countries from three continents.This project aims to enhance the region’s energy security through intensification of low-cost power flow exchange between countries, largescale involvement in electric power balances of renewable energy sources (RES), etc.The creation of MEDRING is expected to enable the formation of the Mediterranean Power Pool (MPP) [14].However, the political situation hampers project implementation in the Middle East.

1.3 Further development

National electric power markets are being developed in European countries.Moreover, there is a tendency to open them to participants from neighboring countries to integrate and create the European electric energy market.

Electric power integration in Europe is expected to eventually reach a new level.The so-called European Super Grid based on RES would include windmills located in the North, Baltic, and Norwegian Seas, hydro resources in Iceland and Scandinavia, and solar energy resources in North Africa [15].The construction of powerful HVDC transmissions aims at closer integration of the mentioned sources and Europe’s ISPG.

Europe’s electric power integration, in all its aspects(technological, economic, ecological, and market), is a process guided and controlled by appropriate European authorities and developed for the benefit of the entire European Union.

2 America

2.1 North America

The first ISET in North America (NA) appeared between the USA and Canada in 1901 and was used for electric power transmission from the power plant on the Canadian side of Niagara Falls to consumers in the New York state [1,16].Interestingly, the construction of hydropower plants (HPPs) in Canada promoted the creation of interstate electric ties and interconnections in NA.Owing to the substantial water resources in Canada, HPPs were intensively constructed both to meet the internal power demand and to import power to the USA.

Seasonal difference in the annual maxima of electric load in those countries (in wintertime in Canada and predominantly in summertime in the USA) was another factor stimulating the electric power integration of the USA and Canada.It is conditioned by natural climatic (high summer temperatures in the USA) and socio-economic (air conditioning, which shifted the annual load maximum in the USA to the summer period) factors.Calculations [1] show that the interconnection of EPSs with winter and summer peak loads produces a significant system effect (reduction in the need for installed capacities and, hence, costs for their commissioning and operation), and its implementation requires reverse seasonal power exchange via ISETs between the USA and Canada.

In 1905, an interstate electric tie connecting the USA and Mexico was constructed in the south of NA [1].To date,this is the largest ISPG worldwide.It primarily encompasses the Eastern Interconnection, which embraces the eastern states of the USA and Canadian provinces, and the Western Interconnection, which includes western states of the USA,Canada, and Mexico provinces.

The main indicators of these ISPGs are listed in Table 2 and Fig.3 [9,17-19].In terms of capacity and power generation indicators, the Eastern NA ISPG is practically identical to the European interconnection.However, the interstate power exchange in North American interconnections is an order of magnitude below that in European interconnections.This can be attributed to the fact that the number of countries in NA is substantially smaller than that in Europe.

Fossil-fuel TPPs are the dominant sources in North American ISPGs.As depicted in Fig.3, the Western Power Grid has over half of its capacities installed on fossil-fuel power plants, generating nearly 60% of the total power production of the grid.Gas-fired power plants are dominant,accounting for approximately three-quarters of the TPP generation [9,17-19].Fossil-fuel power plants constitute a more significant fraction in the Eastern Power Grid, with the share of coal reaching approximately 45% of the TPP generation [9,17,19].Although the new renewable solar and wind facilities are insignificant in both NA ISPGs, they are continuing to grow.

A multi-branch powerful electric high voltage alternating current(HVAC) network infrastructure(up to 765 kV, inclusive) was constructed in the North American ISPG, along with DC lines and back-to-back links that ensure reliable non-synchronous operation of large synchronous zones.This enhances the controllability and reliability of the interconnection as a whole (Fig.4) [20].

The formation of the electric power market in the countries of this region has also influenced and intensified the interstate power exchange [21].Therefore, different levels of deregulation of the electric power industry in NA(despite the emergence of competitive markets of power and capacities and the controlled vertically integrated companies that remain) did not hamper the electric power integration in the region.

Interstate trade in NA, including electric power trade,is subject to the North American Free Trade Agreement(NAFTA) [21].

2.2 South America

ISET development and creation of ISPGs are rapidly progressing in South America (SA), and is mostly motivated by the creation of large interstate hydropower facilities, such as the HPP in Itaipu and others.Other RES have also been developed (solar, wind, and geothermal energy) for their use within ISPGs.

The power system in Brazil is the largest in SA.This country, together with neighboring countries, demonstrates a rather high hydro potential.Therefore, the development of Brazilian national EPSs and hydro resources, in particular,is expected to influence the prospects of ISPG development in SA as a whole.

AC 750 kV (inclusive) electric networks, ±600 kV DC lines, and back-to-back links are used in the ISPG of SA(Fig.5) [22].The frequency of EPS in Argentina, Chile,Uruguay, Paraguay, and Bolivia is 50 Hz.The remaining national EPSs of SA operate at a frequency of 60 Hz.This requires the use of DC transmissions and back-to-back links to connect the national EPSs at different current frequencies.

The ISPG of South American countries has not yet been sufficiently integrated.However, its main outlines are evident, and one can refer to an interstate power interconnection in this region as it is.The main indicators of the ISPG in SA are listed in Table 3 and Fig.6 [23].Although the South American interconnection is extensive,it is still considerably smaller than the NA ISPG.By contrast, power exchange within the South American interconnection is almost equal to that within the North American interconnection.

As can be seen from Fig.6, the South American ISPG is hydro-dominated, with the hydropower plants accounting for over 50% in installed capacity and 60% in power generation.Gas-fired TPPs dominate the generation of TPPs, accounting for 80% of the total thermal power plants generation [9].

Along with the creation and strengthening of electric ties among South American countries, a system of interstate pipelines for natural-gas transportation was developed.Thistendency is expected to continue [24], and demonstrates complex interstate cooperation in the field of energy.This cooperation of countries in SA is coordinated by Organizaciόn Latinoamericana de Energía - Latin America Energy Organization (OLADE), which also covers Central America (CA) [25].

2.3 Central America

Although countries in CA are among the poorest worldwide, the process of electric energy integration in CA is rapid.CA includes the neck of land connecting the southern areas of Mexico with Columbia.The region includes seven countries with a population of approximately 40 million people (Guatemala, Salvador, Honduras, Costa Rica, Nicaragua, Panama, and Belize1.which is not a member of the ISPG in CA and, therefore, is not discussed here.).Hydropower prevails in the generation mix of these countries.This energy subsector is planned to be developed in the future.Costa Rica, in particular, is assumed to demonstrate good potential for the construction of new HPPs to meet the regional electric energy demand, necessitating the development of ISETs in CA [26].

Another factor stimulating electric energy integration in the region is the varying electricity consumption modes in different countries.Thus, the daily peak loads in different countries occur at different times.Moreover, even seasons with different annual maxima are different.For example,the annual load maximum in Nicaragua occurs in spring,whereas that in Guatemala occurs in summer [27].

Sistema de Interconexiόn Eléctrica de los Países de América Central - Power Interconnection of Central America Countries (SIEPAC), a power grid of CA countries,is being formed in this region.The objective of SIEPAC is to overcome the constraints originating from insufficient volume and low effectiveness of regional trade, which is conditioned by the small size and limited interrelations of national EPSs, which cause their fragmentation at the regional level.The main power indicators of this ISPG are listed in Table 4 and Fig.7 [28,29].Note that there is a small interconnection.

As depicted in Fig.7, hydropower plants play a significant role (accounting for nearly 40%) in the electricity generation of the CA ISPG.

Discussions on the concept of regional ISPG by governments of Central American countries under the support of Spain’s government and the Spanish energy company Endesa started as early as 1987.An interstate master agreement was developed to form the basis for the integration project.The Council on Central America Electrification (Consejo de Electrificaciόn de América Central - CEAC) was officially founded in 1989 as a platform for discussion and coordination of activities between energy companies in the region.As a body of regional planning, CEAC plays a key role in supervising the development and coordination of the activities of SIEPAC institutions [27,30].

An interstate dispatching center whose activity is iteratively consistent with that of national dispatching centers was formed for coordinated online control of EPSs in the region.

The AC electric network infrastructure of SIEPAC (Fig.8) favors a higher effectiveness by using the hydro resources of the region and constructing more efficient large TPPs [31].Apart from trade within the region, the main transmission line (TL) would enable power trade with Mexico, thus resulting in new export opportunities for developing the hydro energy potential in CA.The sale of electric power to Columbia is also expected to be possible once a TL to this country is constructed.

Reforms and development of the electricity market in CA countries advance at different rates.Thus, the region is characterized by the diversity of market structures and the irregular development of the electric energy market.Moreover, a regional market is formed as a superstructure over national markets.

Therefore, the diversity and irregular development of national electric energy markets do not act as obstacles for CA countries in their path toward electric energy integration.

2.4 Further development

Eastern ISPG in North America is to be further developed, especially in the field of RES.E.g., large-scale development of the off-shore wind generation is planned along the eastern coast of the USA from New Jersey to Virginia (Atlantic Wind Project) with the adequate development of DC electric ties for collecting of power generated by windmills and its transmission to the shore to consumers [32].In the future this project may become an essential component of North American interconnection and Pan-American Super Grid in the long term.

The ISPG of Central America, with further development of its internal and external electric ties, is considered as a kind of a link between power interconnections of Northern and Southern America.Hence, we can speak about the formation of outlines of the future Pan-American Super Grid.

3 Africa

3.1 Launch of electric power integration

Africa also undergoes the integration of national EPSs.First, an ISPG emerged in the northwestern part of Africa in the 1950s; Algeria and Tunis were connected by a 220 kV TL for electric power exchange during emergencies [1].This laid the foundation for the formation of the North African ISPG Comité Maghrébin de L'Électricité - Magrib Electric Energy Committee (COMELEC), which was later included in the integration project of the MED mentioned above.

At present, there are several interstate grids on the African continent.However, they are relatively small ISPGs owing to the weak electric power sector in most African countries due to the general low levels of social and economic development in these countries.Southern and eastern interconnections represent the largest ISPGs across the continent.Their main characteristics are listed in Table 5 and Fig.9 [29, 33-35].

The African ISPGs considered are insignificant.They feature the domination of fossil-fuel power plants (70%-80%) with a share of hydro generation (18%-20%) and a minuscule participation of wind and solar energy.Coalfired power plants constitute more than 90% of the TPP generation in the South African ISPG [9,29].In contrast,gas-fired power plants prevail in the East African ISPG,accounting for over 80% of the TPP generation [9].

3.2 South African ISPG

The southern interstate power interconnection is the largest across the African continent.However, it is small in comparison with the European and American power interconnections.This interconnection was formed in 1995 upon the South African Development Community initiative to connect the countries’ power systems in the region and improve the reliability, effectiveness, flexibility of power production and supply, and formation of the regional power market [36].In 2009, a spot (day-ahead) market was formed within the ISPG.Work on planning and development of generating capacities and electric networks is ongoing within this interconnection.

The national EPS of the Republic of South Africa(RSA), whose generating capacity is equal to three-quarters of the total capacity of the ISPG, plays a leading role in South African ISPG.The 2 GW nuclear power plant in the continent operates in this country as well.RSA is an absolute leader in capacity and power flow exchange with other countries included in the interconnection; thus, it serves as the driving force of the integration process in the region.From this perspective, the dominant position of RSA in power generation, power consumption, and power exchange with neighboring countries is expected to be maintained.

Democratic Republic of the Congo (DROC) has considerable hydro resources that can be involved in the power balances of ISPGs of Southern Africa and other regions of Africa, thus favoring the creation of new interconnections and expanding the available ISPG across the continent.

AC TLs are mainly used as ISETs in the South African ISPG, although DC TLs are also available.A schematic of the electricity network of the ISPG is illustrated in Fig.10 [37].

3.3 East African ISPG

The East African ISPG was formed in 2005 to optimize the use of energy resources available in the region, intensify the capacity and power exchanges between countries in the region, reduce power production costs, and ensure effective coordination of the activity of power production and transmission entities [35,36].In 2009, a spot (day-ahead)market was formed within the ISPG.The development of generating capacities and electric networks within this ISPG is stimulated by the considerable growth in power consumption, which is expected to reach 100% within the coming decade.Note that this development optimally continues at minimum cost within the entire ISPG.

The East African ISPG was mainly formed and developed under the aegis of the regional economic organization referred to as the East African Community(EAC).This community is smaller than the South African community, and Egypt plays a dominant role in it.The installed capacity available in this country accounts for more than 60%, and electricity consumption accounts for approximately two-thirds of the entire ISPG.

DROC participates in the Southern ISPG and partially participates in the Eastern ISPG, having ISETs with each of them.Moreover, as a member of COMELEC, Libya joined the ISPG of East Africa.This implies that interregional power integration when electric ties between separate interconnections are formed continues across the continent,thus outlining the contours of a continental grid.

A schematic of the electricity network of the ISPG is illustrated in Fig.11 [38].

3.4 Further development

Overall, the African ISPG has not yet reached the level of European and American ISPGs, which can be attributed to the development of the economy, industry, and services of the country as a whole rather than the development of the power industry; moreover, social and economic indicators in most African countries are at a low level.Nevertheless,the continuous development and integration of the ISPG,and formation of a continental African super grid are expected in the future.Projects of RES development in Africa, including hydro resources (e.g., the Grand Inga HPP project in DROC) and solar resources in Sahara for power transmission to Western European countries, play an essential role in this process.

4 Asia

As for the Asian region, the ISPGs of Central, South,South East, and North East Asia are at different stages of development.

4.1 West Asia ISPG

Gulf Cooperation Council Interconnection (GCCI)operates in West Asia [39-40].The construction of a regional power grid interconnecting the Gulf states, and shaping GCCI was completed in 2011.Its main purpose was to provide backup in case of power emergencies.Moreover,trading power via the grid is expected to save the Gulf states about US$5 billion in electricity sector investments and US$1.8billion in fuel costs between 2014 and 2038 [41].

The main indicators of GCCI are presented in Table 6 and Fig.12 [9].

As can be seen from the table, Kingdom of Saudi Arabia and United Arab Emirates dominate in the ISPG,having two thirds of the total installed capacity of GCCI interconnection, while KSA alone has nearly half of the total capacity.

Generating capacities are almost all fossil fueled,complemented by minuscule amount of renewables (Fig.12) [9].Fossil fuel is gas, used practically in all Gulf countries.In Saudi Arabia gas is complemented by oil.Coal is not used for electricity generation in Gulf countries.

The concept of electrical interconnection was raised by the Gulf Cooperation Council in early 80s.GCCI Authority was established in 2001 with aim to link up the power grids of the six Gulf countries; to operate and maintain the interconnection; to become a leading player in the regional electricity market.Establishing GCCI was in 2005-2011,and initiating GCCI market was in 2010-2015 [39].

The design of the grid is such that in the event of an emergency, each GCCI country could import up to the transfer capability of the interstate electric tie (see Fig.13)[42-43].Since the beginning of the operation of GCCI,the security and reliably of the overall interconnected network is highly enhanced.GCCI helped to avoid partial or total blackout during some of the critical incidents [39].However, the utilization of the interconnection for energy trading is low, one-off, irregular trades are dominant [40].

Development of regional power markets, increasing the share of renewable energy in power generation to free up hydrocarbons for export are considered to contribute to sustainable future of the region.

4.2 South East Asian ISPG

This ISPG is the most advanced, and covers the Association of Southeast Asian Nations (ASEAN) countries[38].It is relatively large, with a size greater than that of African ISPGs, and close to that of the South American ISPG.The main performance metrics of the ISPG in South East Asia are given in Table 7 and Fig.14 [9,29].

As depicted in Fig.14, fossil-fuel power plants prevail in terms of installed capacity and power generation of the South Eastern ISPG, with a share more than 70%.Hydropower plants account for nearly 15% of the total capacity and generation, while renewable sources are marginal.Coal-fired power plants account for more than half of the total TPP generation in the ISPG, whereas gasfired plants account more than 40% [9].

The ASEAN association supported the concept of creating an ISPG in the region.In 1999, an energy center was created to generate innovative solutions to ASEAN’s energy problems regarding policy, law, and technology.It also acts as a catalyst for interconnecting and strengthening ASEAN’s energy cooperation and integration by realizing related programs and projects.Finally, it serves as an energy database for ASEAN and favors the exchange of energy information, knowledge, and technologies.

The center focuses on other fuel and energy industries,particularly the gas industry.For example, there are gas reserves in South East Asia, and the center favors its production and use for the interests of all the countries in the region, thus supporting regional integration in this sphere.

In 2007, the ASEAN countries signed a memorandum of understanding to form an ISPG in this region.The objective was to officially support the general policy of ASEAN countries regarding ISPG formation in South East Asia and the development of power trade to enhance the energy security of the region, energy supply reliability, and effectiveness of their mutual benefit.The interconnection was implemented stage-wise.Bilateral power trade was planned to be started at the initial stages, and multilateral trade was planned at the final stage [44].

The electric network infrastructure consists of 16 ISETs with a total transmission capacity of 23.3 GW (Fig.15) [44-46].These are predominantly DC electric ties.A naturalgas pipeline network is being developed in the region along with the formation of ISETs.

Given that many countries in the region are located on islands, their national EPSs are connected by DC submarine cables.Despite the high cost of this method of interconnection, it is recognized as the most effective one.This indicates that the system effects due to EPS integration exceed the costs of interconnecting cables.

4.3 Other Asian ISPGs

The process of electric power integration is underway in other Asian sub-regions.For example, the South Asian ISPG is rapidly formed under the auspices of the South Asian Association for Regional Cooperation (SAARC).The main characteristics of this interconnection are given in Table 8 and Fig.16, 17 [47-49].

The installed capacity and power generation of the ISPG is large, significantly exceeding those of South American and South East Asian interconnections, primarily at the expense of India.Fossil-fuel TPPs account for the major share of the installed capacity (nearly 70%) and power generation (about 75%) of the ISPG.Coal-fired power plants are dominant, accounting for nearly 85% of the total power generation of TPPs [9].

The development of the Central Asian ISPG, i.e., the Central Asian Power System (CAPS), is ongoing, together with the Central Asia-South Asia Regional Electricity Market (CASAREM) project [50-52].The CAPS ISPG is part of the interstate electric power interconnection that emerged in the post-Soviet territory, and is analyzed in the next section.

Studies on the Northeast Asian ISPG, i.e., the North East Asia Regional Electric System Ties and the Gobitek project are underway [1,51-58].

Interregional electric power integration occurs in parallel with integration processes occurring in different sub-regions of Asia.For example, a Caspian energy ring has been suggested to interconnect the countries of Central and South Asia, the Middle East, Caucasus, and Russia by interstate TLs [54].This project is a link between the ISPGs of Asia and Europe, forming the basis for creating the Eurasian ISPG.

4.4 Further development

Asian Super Grid [54] that includes West, Central,South, South-East, and North-East Asian sub-regional ISPGs is expected to be formed in the future.This process was supported by an authoritative international organization,namely, by UN Commission on the Economic and Social Commission for Asia and the Pacific (UN ESCAP).UN ESCAP considers formation of Asian Super Grid as a tool to attain Sustainable Development Goals (the UN’s blueprint for a more sustainable future for all), in particular SDG 7,which is to ensure access to affordable, reliable, sustainable and modern energy for all.

West along with Central (further presented) Asian ISPGs developing their external electric ties can be expected to connect Asian Super Grid with the emerging African and European Super Grids in the long term.

5 Post-Soviet Space

5.1 MIR ISPG development

The integration of the USSR EPSs and the power systems of the East European countries began in 1959 when the Commission on Energy Exchange and Complex Use of Hydro Resources of the Danube River, which was operating within the Council for Mutual Economic Assistance,developed and approved a report on interconnecting the EPSs of CMEA countries for mutual electric power exchange [58].This report presented specific proposals on interconnecting the national power systems whose implementations began subsequently.The first 220 kV TLs for interconnecting the EPSs of East Germany, Poland, Czechoslovakia, and Hungary were built in 1960.A 220 kV TL for electric power export from the USSR to Hungary and Poland was put into operation in 1962.This was also the year in which an agreement on creating the Central Dispatching Board for the power interconnection of the East European Countries and the USSR, named MIR, was signed.

The interstate electric network infrastructure of this interconnection was continuously enhanced.In 1963, it was connected to the power interconnection of Romania by a 220 kV line.Then, 220 kV TLs between Romania-Bulgaria(1967) and USSR-Mongolian Republic (1974) were built.A 750 kV TL for USSR-Hungary was commissioned in 1978,and in the early 1980s, a line of the same voltage was built to connect the USSR with Poland and Bulgaria.

Initially, the Lviv power system of the USSR was the only system operating in parallel with the EPSs of East European countries.In 1979, the entire Unified Power System of the USSR was connected to them, and was operated in parallel with the Central EPS of Mongolia [59].Consequently, the MIR ISPG covered the area from Ulan-Bator (Mongolia) in the east to Erfurt (East Germany) in the west, becoming the largest ISPG worldwide, with the installed capacity of power plants exceeding 400 GW.The MIR ISPG was created under the supervision of the CMEA,a supranational organization.

However, the MIR ISPG ceased to exist after the disintegration of the USSR and CMEA.As noted before,the East European countries joined the West European ISPG.The Unified Power System of the USSR was converted into an interstate energy interconnection that included former Soviet republics and was named as the Interconnected Power System/Unified Power System (IPS/UPS).Its main characteristics are listed in Table 9 and Fig.18 [60-63].

This ISPG stands out in terms of installed capacity and power generation, following the European, Eastern North American, and South Asian power grids.Fossil-fuel power plants account for approximately 65%-70% of the total ISPG generation and capacity.Two-thirds of the TPP generation is provided at the expense of gas-fired power plants [9].Hydropower plants rank second, accounting for 17%-19% of the ISPG generation and capacity, respectively.

5.2 Post-Soviet ISPG

A schematic of the ISPG IPS/UPS is illustrated in Fig.19.Currently, this interconnection is poorly integrated.Power exchange characterizing the degree of integration and implementation of system effects owing to the EPS interconnection between former USSR republics reduced by almost four-fold since the 1990s [64].Nevertheless, the potential for growth still exists.

Some system effects are currently implemented in IPS/UPS [56].For example, Belarus reduces the cost of fuel required for power generation by increasing the imports from Russia and other neighboring countries.This minimizes the power tariffs for Belarus consumers, thus implementing an operating cost-saving effect.Furthermore,owing to the electric power imports, Belarus can reduce its maintenance reserve, resulting in the implementation of the capacity saving effect.Russia, in turn, has an economic(trade) effect on power exports to Belarus.

The operating cost-saving effect due to the joint optimization of operating modes of the European section of Russia’s UPS and Siberian’s EPS is implemented using electric networks at North Kazakhstan for the power flow exchange between two Russian regions.Kazakhstan demonstrates an economic effect by allowing power transit in Russia.Another example is the increase in the reliability owing to the use of electric networks in North Kazakhstan for power transmission from the European part of Russia to Siberian’s EPS to cover the power deficit caused by a large emergency at the Sayano-Shushenskaya HPP in 2009.

In countries of Central Asia, the hydro resources of Tajikistan and Kyrgyzstan are jointly used, thus minimizing the power tariffs for consumers.Thus, a cost-saving effect is achieved; however, owing to specific political differences between countries of Central Asia, its implementation is far from complete.This effect is also enabled by the load flow exchange between national EPSs of Caucasian countries and Russia.

Regarding the creation of a common electricity market in the post-Soviet space under the influence of customs and Eurasian economic unions, a tendency of electric power disintegration is expected to be substituted by integration,representing a global trend.

5.3 Further development

The common electricity market on the post-soviet space under the influence of the Customs and Eurasian Economic Unions is being formed.The market aims at ensuring the sustainable development of the economies and the energy security of the Union countries, improving the economic efficiency and reliability of the functioning of their electric power systems, forming the common electric power space, etc.All this is expected to reverse electric power disintegration tendency dominant in powst-soviet area to an integration tendency, which corresponds to the global trend.

6 Global Grid

Issues related to the creation of a global grid covering all continents have been discussed for decades.As early as 1971, the UN Department of Natural Resources offered the creation of electric ties from north to south to reduce the consumption of fossil fuels in developed countries through the use of hydro resources in Africa and Latin America.

Famous inventor Dr.Buckminster Fuller wrote in 1973,“This now feasible, intercontinental network would integrate America, Asia, and Europe, and integrate the night-andday, spherically shadow-and-light zones of Planet Earth”[65].He claimed later “I have summarized my discovery of the option of humanity to become omnieconomically and sustainably successful on our planet while phasing out forever all use of fossil fuels and atomic energy generation other than the Sun.I have presented my plan for using our increasing technical ability to construct high-voltage,superconductive TLs and implement an around-the-world electrical energy grid integrating the daytime and nighttime hemispheres, thus swiftly increasing the operating capacity of the world's electrical energy system and, concomitantly,living standard in an unprecedented feat of international cooperation” [65], thus anticipating the concept of a global super grid.

In 1986, the Global Energy Network Institute was founded to promote Dr.Buckminster Fuller’s idea to create a global electric network involving RES in the energy balances of countries worldwide [66].

In the early 1990s, Russian scientists published papers in which the formation of the so-called World Grid was discussed as a priority issue [67-69].They suggested creating the following electric ties: USSR-Eastern Europe-Western Europe, USSR-USA, and USSR-Japan.They also suggested further enhancement and development of technologies and equipment for the transmission of large power volumes by DC transmissions to long distances, as well as the development of the concept of a global super grid.

The problem of creating a global super grid has been raised again in [2,70], considering electric energy megaprojects as the main components.The Desertec and Medgrid projects intended to convert solar energy into electricity for further transportation from North Africa to load hubs in the Mediterranean and Europe by DC TLs are among them.

The development of these projects together with the implementation of the Gobitec and Atlantic Wind projects,and construction of energy interconnections in South East Asia and Asia as a whole, Scandinavian and North Sea interconnections, Iceland-Britain-continental-European interconnections, and others would result in the formation of a global super grid [70].

The Global Energy Interconnection Development and Cooperation organization, which was initially created in China and later recognized internationally, actively promoted the idea of creating a global super grid.It undertakes studies on the formation, development, and operation of the grid, and discusses and publicizes this idea at different international meetings by involving new members in the discussion, including experts, research institutions, and state bodies from different countries as well as international organizations.These activities promote the idea of creating a global super grid, its realization, as well as changes in specific proposals and practical steps.

7 Conclusion

Electric power integration is a process that occurs worldwide and contributing to achievement of the Sustainable Development Goals.Despite the expansion of distributed generation, this process is ongoing, and the transition from the formation of separate regional ISPGs to the creation of interregional and continental interstate interconnections is underway.Outlines of the first intercontinental power interconnections are currently being tracked, and the concept of creating a global super grid is being investigated.

ISPGs are gradually formed, starting from separate interstate interconnections and bilateral electric power trade and continuing with multilateral relations between participants as the electric network infrastructure develops.

The involvement of RES in power balances, varying conditions of electricity consumption in different countries of the region, enhanced use of available generating capacities, and mutual assistance by emergency power flows, among others serve as catalysts for ISET development and the formation of ISPGs.

There is no need to create a single dispatching center for ISPG control.The horizontal coordination of the actions of the system operators of subregional power interconnections is sufficient.For small ISPGs, the creation of a single dispatching center is desirable and useful.It is advisable to create supranational structures that coordinate decisions on ISPG development.

Interstate electric power integration occurs as a rule,together with the formation of other energy ties, ensuring the trade of fuel and energy resources among countries.

ISETs are implemented based on AC TLs, DC transmissions, and back-to-back links.To enhance the controllability and reliability of complex ISPGs or in cases wherein AC technologies cannot be used (EPSs of different current frequencies must be connected, or extended water obstacles must be overcome), DC back-to-back links or DC transmissions are considered to be suitable.Political differences between countries impede and complicate the development of electric power integration and other integration processes.

Interstate power grids account for a significant share of fossil-fuel power plants, ranging from 40% in European ISPGs to 80% in South and South East Asian interconnections.Coal-fired power plant generation accounts for 50% of the total TPP generation in Europe, and up to 85%-90% in South Asia and South Africa.Gas-fired TPPs account for 75%-80% of the total fossil-fuel power plant generation in the North American Western Grid, South American, and East African ISPGs.The South and Central American ISPGs are hydro-dominated.Solar and wind renewables are not common yet, accounting for 10-15% in power generation and installed capacity in European and North American Western ISPGs.However, renewables are assumed to be further developed globally to mitigate the impact of human activities on the environment and to facilitate achievement of net zero target.

Different rates of energy reforms and the creation of different forms of national power markets do not create obstacles for electric power integration.

A new level of electric power integration between significantly large ISPGs (super grids) that may cover entire continents is expected to result in the formation of a global super grid.

Acknowledgements

This research was conducted under the State Assignment Project (No.FWEU-2021-0001) of the Fundamental Research Program of the Russian Federation 2021-2030.

The authors thank the anonymous reviewers for their valuable comments that helped improve the manuscript.

Declaration of Competing Interest

We declare that we have no conflict of interest.