Xiaomeng Lei,Dawei Wang,Wei Wang
1.China Electricity Council,Beijing 100761,P.R.China
2.Global Energy Interconnection Development and Cooperation Organization,Beijing 100031,P.R.China
Abstract: Electric interconnection is an essential trend for future large-scale development and utilization of renewable energy.China has proposed the concept of Global Energy Interconnection to realize the clean utilization of energy through the interconnection of power grids and optimize the allocation of global energy resources.This study proposes the Kazakhstan-China-Republic of Korea networking scheme,analyzing the characteristics of power supply and demand in these countries.Based on the regional economic analysis and power development,four interconnection schemes are proposed utilizing UHVDC technology.Accordingly,existing problems and favorable factors are fully considered.The investment analysis of ±1100 kV and ±800 kV lines,configuration scheme of the converter station,and investment estimation of four interconnection schemes are given.
Keywords: Global Energy Interconnection,Renewable energy source,Interconnection schemes,Cost and benefits analysis.
The interconnection of electric power is an integral trend for the large-scale development and utilization of global renewable energy.It is also a vital aspect of energy infrastructure cooperation in the Belt and Road Initiative.The expansion of cross-border power grid interconnection and the deepening of trade can effectively motivate countries worldwide to eliminate barriers,deepen integration,change the geopolitical state and pattern of energy,and achieve more innovative,coordinated,green,and open shared regional development[1-2].
From a global perspective,the distribution of energy resources and energy demand among countries and regions is unbalanced.Generally,the energy base is located far away from the load center.As a result,large-scale,longdistance transmission and large-scale optimal allocation of electricity should be implemented.The centralized,largescale development and long-distance transmission of nonfossil energy,such as wind and solar power,have attracted increasing attention as an effective solution to the problem of energy shortage[3].Global Energy Interconnection (GEI)is a global grid solution to provide electricity generated from renewable energy sources to load centers over a long distance.Chinese President Xi Jinping proposed the GEI initiative at the UN Sustainable Development Summit on September 26th,2015.The GEI initiative aims to develop a modern energy supply system,realize clean energy utilization,and optimize the allocation of energy resources on a global scale[4].
First,following the interconnection of power grids,interconnected power grids can enhance the reliability of power grid operation by sharing spare capacity,which reduces the need for spare capacity construction.Second,the interconnection between power systems provides a more diverse combination of generator sets from fuel to power generation technology[5].Third,the interconnection of power grids can increase load diversity and smoothen the load change.From an economic perspective,in addition to achieving economies of scale and reducing the costs of investment,the interconnection between different power grids also realizes the scheduling of power generation resources in a large system,which can optimize resource allocation and protect the environment[6].
Transnational power interconnection and power trade are the physical and economic manifestations of the GEI initiative.Currently,the interconnection level of power grids in Europe,North America,and the Russia-Baltic region is relatively high.Central America,South America,Middle East,Southeast Asia,and other regional power grid interconnections have a preliminary development foundation,a relatively clear regional interconnection plan,and several interconnection lines have been developed[7].However,the interconnection of regional power grids in Northeast Asia,South Asia,Africa,etc.is still in its infancy,which highlights the significance of promoting the interconnection of regional power grids[8].
Northeast Asia is the most economically developed region in Asia,with close economic ties among countries and a strong complementarity of energy resources.The primary energy consumption of Northeast Asia accounts for approximately 30% of the net global energy consumption,making it the region with the largest energy consumption in the world.More specifically,the People’s Republic of China(China),Japan,and Republic of Korea (ROK) are the main energy consumers in this region,and energy consumption is still dominated by fossil energy.Implementing regional energy cooperation,establishing transnational networking channels in Northeast Asia,and realizing power interconnection are conducive to further promoting regional economic development.
The potential of international high-voltage connections and their impact on the environment have been reviewed[9].In reference[10],the reserve power was obtained for future power shortages faced by the metropolitan areas of the Korean Peninsula and southeastern area of ROK in North-East Asia.Technical and market considerations for the power system interconnection in Northeast Asia(NEA) were proposed in reference[11].Attempts have been made to evaluate the possibility of power cooperation by conducting a simulation analysis of electricity markets in Northeast Asian regions using Generation-Transmission Maximization modeling[12].A comparative study of the changes in CO2emission performance of state-owned fossil fuel power plants between China and ROK was conducted in reference[13].The adverse environmental effects associated with the traditional ways of generating electricity necessitate accurate and extensive planning for renewable and sustainable energy generation systems.Reference[14]analyzes solar data in Asia to support the utilization of large-scale renewable power plants.The complementary features of the cross-time zone load demand and new energy power output were quantified,and the peak-shaving benefits brought by the cross-time zone interconnections were calculated in reference[15].
In general,China’s interconnection with neighboring national power grids can be divided into two stages.The first stage is from the 1990s to 2015.This is the stage of cross-border line construction and power trade under the promotion of power exchange between China and neighboring countries.The second stage refers to the energy internet construction stage with the goal of realizing a low-carbon power system.This stage entails transnational interconnection to promote long-distance transmission of renewable power and realize a low-carbon power system following the construction of Global Energy Interconnection and Asian Super Grid in 2015.
The International Green Technologies and Investment Centre (IGTIC) in Republic of Kazakhstan (Kazakhstan)proposed the feasibility of a project called Silk Road Super Grid (SRSG) the aim of which is to explore the possibility of promoting the trade of affordable renewable energy along the New Silk Road by generating renewable energy at low costs in Central Asian countries and exporting the energy to load centers in China and ROK.As the pilot project,the power system interconnection between Kazakhstan,China,and ROK is feasible because these three countries have complementary characteristics in production and consumption of renewable energy,load curve patterns,generation mix,and climate change mitigation targets agreed to under the Paris Climate Agreement.The present analysis initiated a scoping study to investigate renewable energy trade among Central and Northeast Asian countries.
With the concentration of load to the east and large renewable energy sources (RES) and coal mines located in remote areas,large amounts of electricity transmission over long distances have become increasingly common.Ultrahigh voltage direct current (UHVDC) projects have been developed successfully and rich operational experience has been accumulated[15].China trades electricity with other counterparts,which includes transmitting electricity and constructing transmission lines.Studies have analyzed transmission scenarios from the perspective of costs and transmission prices based on feasible economic and technical concepts.
In addition to requiring technological progress,the interconnection of the Northeast Asian power grid also requires synchronization and coordination of the political environment,policies,and markets.
1.1 China
1.1.1 Adequacy Assessment of Generation in China
In 2021,the power supply adequately satisfied the national demand.By the end of 2021,the total generation was 8395.9 TWh,an increase of 7.8%,of which the proportion of non-fossil fuel generation was 34.5%,an increment of 12.1% compared to that of the previous year.Generally,power generation continues the green and low-carbon development trend.The installed capacity of non-fossil fuel accounts for 41.9% of the total installed capacity,an increment of 1.1% compared to that of the last year,and has exceeded the target of 39% of the non-fossil fuel capacity in 2020.The investment,installation,and production of coal-fired power generation,as well as the growth rate and proportion of power generation,decreased compared to those of the previous year.
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Fig.1 National installed capacity from 2012 to 2021 (GW,%)
1.1.2 Transmission systems
With the concentration of loads in the eastern and southern areas along the coast and coal mine deposits and renewable energy resources in remote western and northern areas,it is common to transmit a large amount of electricity to promote transmission system development and regional interconnections.The two national transmission system operators (TSOs),namely the state grid corporation of China (SGCC) and China southern power grid company(CSG) have developed substantial transmission systems covering the entire country.The highly meshed regional and provincial transmission systems and interconnections among them are conducive to optimizing energy use in different provinces and even in a larger area.
By 2020,SGCC completed and put into operation 26 UHV projects of “Fourteen Crossings and Twelve Strains”.There are 31 UHV transmission projects under construction,which cover a line length of 41,000 kilometers and a power transformation (conversion)capacity of over 450 million kVA.The UHVDC voltage level currently in operation in China has reached ±1100 kV with a capacity of 12000 MW.
1.2 Kazakhstan
1.2.1 Generation mix
Owing to its abundant renewable energy resources,Kazakhstan is considered as one of the main parts of the GEI initiative.Kazakhstan proposed the initiative of SRSG.The Association of ecological organizations of Kazakhstan,together with the IGTIC,developed a roadmap to promote the SRSG project.As of 1st January,2020,the total installed capacity of power plants in Kazakhstan is 22,936.6 MW and the available capacity is 19,329.7 MW[17].Moreover,the total installed capacity of renewable energy facilities reached 1700 MW in 2020,with 933 MW of wind power plants,467 MW of solar power plants,290 MW of hydro power plants,and 10 MW of biogas power plants[18].Natural gas production volumes have been increasing,and Kazakhstan became a net gas exporter in 2003.Kazakhstan also has the largest recoverable coal reserves in Central Asia,which is used to power most of its electricity generation.In 2012,the government adopted the Kazakhstan 2050 Strategy,which specifies the directions for long-term national economic development.In May 2013,the concept for the Kazakhstan’s transition to a green economy was adopted with the ambitious goal of a 2050 generation mix that comprises 50% of alternative energy sources,including gas,nuclear,and renewable energy.The government plans to achieve this by gradually decommissioning aging infrastructure,implementing broader use of alternative fuels,installing energy-efficient equipment,and complying with strict environmental standards.
The green economy concept specifies the renewable energy sector development targets in Kazakhstan: 3% share of RE in the total electricity production by 2020;10% share of RE in total electricity production by 2030;50% share of low-carbon alternatives;and RES by 2050.Over the last decade,generation by non-hydropower renewables has risen by an average of 9.7% per year in Kazakhstan,increasing the output from 0.65 TWh in 2018 to 1.48 TWh in 2028[19].
Fig.2 Locations of power plants in Kazakhstan [20]
1.2.2 Renewable Energy Source (RES) potential
Wind and solar power are the focus of the renewable sector.The European Bank for Reconstruction and Development (EBRD) is planning on investing approximately USD 244.2 million in developing the RES of Kazakhstan,which has attracted private and international financial investments[21].The hydroelectric facilities in Kazakhstan are primarily located along the Irtysh River,which flows from China across northeast Kazakhstan.The Syr Darya river flows from the western Tianshan Mountains on the southern shore of the Issyk-Kul Lake,spanning 2212 km,with a drainage area of 219000 km2and a technical potential of 14.5 GW.Its main tributaries include the Naryn River and Qaradaryo River[21,22].
Wind power resources: Wind power has the highest potential among all RES in Kazakhstan.The average annual wind speed of all sites at a height of 80 m is equal to 7.5 m/s.According to the Republic of Kazakhstan 2030 Concept of the Fuel and Energy Complex Development,power wind potential equals 1,820 billion kWh per year.Depending on the location,the capacity factor varies from 30 to 40%.
Fig.3 Wind resource map at 50m of Kazakhstan [23]
Hydro power resources: Hydropower is the secondlargest energy source in Kazakhstan.The annual hydropower potential of medium and large rivers is 55 billion kWh,whereas small rivers have a capacity of 7.6 billion kWh.
Solar power resources: Solar energy can generate approximately 2.5 billion kWh per year,with approximately 2,200-3,000 hours of sunlight annually (2,500-3,000 hours annually in the southern regions) out of 8,760 hours[24].
Geothermal: 4.3 GW.Geothermal resources with temperatures of 40°C to more than 100°C are estimated at 10,275 billion cubic meters (water rate) and 680 billion GCal (heat rate).
Biogas: Kazakhstan is a major producer of grain and other agricultural products,which produces a significant amount of agricultural wastage.Livestock waste is a stable source of biomass for energy production.Besides,household solid waste is another source.
Fig.4 Solar resource map of Kazakhstan [24]
Kazakhstan is capable of providing 3 GW of export considering the import limitation of 3 GW of ROK.
1.3 ROK
The energy sector of ROK is characterized by the dominance of fossil fuels,which in 2018 accounted for 85% of the total primary energy supply (TPES),strong dependence on energy imports at 84% of TPES,and the dominance of industrial energy use at 55% of the total final consumption[25].
The national power grid of ROK is an isolated system.There are no cross-border transmission lines,and the load distribution of the power grid of ROK is uneven,with the load centers being distributed in Seoul and its surrounding areas in the northeast and industrial areas in the southeast.The main directions of the power grid are the northeast,southwest,and central power supplies to deliver power to the capital area and southeast industrial areas.
In 2019,the transmission system of ROK had a line length of 34,402 km and 862 substations.The majority of transmission lines in the country are 154 kV (67% of the network);however,transmission voltages are also 765 kV and 154 kV or lower for local networks.The frequency of the power grid is 60 Hz[26].
There are increasing concerns in ROK regarding local air pollution and fine dust.The Seoul metropolitan area is among the most polluted cities in the world.In December 2017,the government of ROK announced the renewable energy 3020 implementation plan.It set a goal to generate 20% of its energy from renewable sources by 2030 and increase relevant job opportunities[27].
ROK is the 14th country to legislate carbon neutrality by 2050,with an interim target of a 40% reduction inemissions by 2030 compared to 2018 levels.ROK retains industries that are considered highly energy-intensive and imports over 90 percent of energy resources given that the country lacks sufficient domestic energy resources.In 2021,ROK generated 576,316 GWh of electricity,which included 18 percent and 15.3 percent increases in renewable(43,085 GWh) and gas (168,262 GWh) power generation,respectively.Admittedly,there was a significant decrease in coal power generation.However,coal still accounts for approximately 34 percent of the total electricity generation.Additionally,almost 27 percent of electricity is generated from nuclear power,which is targeted to reach at least 30%by 2030.In 2020,CO2emissions from fuel combustion were 570.74 million tons (Mt),compared to 432 Mt in 2000[28].
2.1 Selection of sites for the UHVDC stations and market changes
From a technical and economic standpoint,HVDC stations should ideally be located near the RES areas in the energy exporting country and load centers concentrated areas in the importing countries.It is apparent that the site in ROK may be close to its capital,Seoul,while the site in Kazakhstan is close to RES-concentrated areas.Site selection in China is based on the adequacy assessment of generation supply to the regional systems to determine the locations of the HVDC stations[29-30].
The central and east regions have relatively developed economies with high demand for electricity.In 2017,59.3%of the newly increased electricity consumption in China was concentrated in the east and central regions.For the foreseeable future,the eastern and central regions are likely to remain the main regions of China’s power consumption.In 2030,the proportion of electricity consumption in the eastern and central regions is predicted to reach 62.5%.To meet user demands in the central and eastern regions,it is expected that by 2020,the cross-provincial and regional transmission capacity will reach 300 GW.
The three provinces,Henan,Jiangxi,and Hunan,lack energy resources.Moreover,there is a relatively long distance to transport coal,while the provinces in the east coastal region can transport coal via sea transportation at a cheaper price.The Henan province would be one of the recommended UHVDC station sites.Shanxi is an energy exporting province in China,so the site in Shanxi was chosen for exporting electricity to ROK.Another site has been chosen in the Liaoning bordering with the Democratic People’s Republic of Korea (DPRK).
Coal-fired power plants (CFPPs) will still be dominant in the generation mix for the foreseeable future,even if the development of CFPPs will be limited.Based on a study conducted by the China Electricity Council (CEC) on the report of the 14th 5 year PDP,the capacity of CFPPs will reach 1250 GW by 2025.with 150 GW to be added compared to the capacity of CFPP in 2020.The annual growth rates of demand in the Central regional system are predicted to be 5.7% in 2021-2025 and 3.6～4% from 2026 to 2030.Consequently,China’s power sector is still a substantial market for electricity exported from Kazakhstan,and some of the CFPP capacity will be replaced by electricity imported from Kazakhstan.
2.2 Scenario A
2.2.1 Scenario A-1
Scenario A-1 includes two HVDC lines,one from Kazakhstan in the RES area and Xinjiang in China,and another from Shanxi in China to the site close to Seoul in ROK.
Based on both technical and economic analysis of existing HVDC projects in China,the ±500 kV HVDCs are suitable for 1.5～3 GW with 1000～1500 km transmission lines as indicated in table 6.
(1) KZ-CN(Xinjiang) 3GW HVDC project
The Rectifier station was chosen to be located at the RES area,which is 200 km to China’s border,and the inverter station was chosen to be located near the capital city of Xinjiang and the rectifier station of Guquan UHVDC±1100 kV project.The distance of the KZ-CN (Xinjiang)transmission line is 900 km with a nonlinear factor of approximately 1.1.
(2) CN-ROK 3GW HVDC project
The rectifier station was chosen in the Shanxi province of China,and the inverter station at a site close to Seoul.
2.2.2 Scenario A-2
Scenario A-2 includes two HVDC lines.The line distance of the KZ-CN 8GW UHVDC project is 3600 km from the RES area in Kazakhstan to Henan province in China.The CN-ROK project is a 3-terminal HVDC project.The rectifier station is located in the west of Liaoning province in China,330 km away from the border of DPRK,and the two inverter stations are located near the capital cities of Pyongyang in DPRK and Seoul,respectively.The distance of the transmission line is 750 km with a nonlinear factor of approximately 1.1.The capacity of the three stations is as follows: 3 GW in China,0.5 GW in the DPRK,and 3 GW in ROK.
2.3 Scenario B
2.3.1 Scenario B-1
Currently,there are no ±800 kV UHVDC submarine cables in operation or planned worldwide,and the voltage of the western link HVDC project in operation since 2018 is ±600 kV,which is the maximum worldwide[31].Consequently,the voltage of the submarine cable was chosen to be ±500 kV.Two independent transmission lines are suggested;the KZ-CN line with ±800 kV and CN-ROK line with ±500 kV.The ±800 kV inverter station in China and the ±500 kV rectifier station may be constructed on the same site in China.
The 8 GW UHVDC stations: The rectifier station may be located close to the RES in Kazakhstan with a capacity of 8 GW,and the inverter station should be at a site in Henan province in China.
Fig.5 Suggested scenarios[32]
The 3 GW HVDC stations: The rectifier station in Henan province of China was chosen to be located on the same site as the UHVDC inverter station with an AC connection to it and the inverter station at the site close to Seoul with a capacity of 3 GW.
The three sections of the transmission line: section 1,from the rectifier station in Kazakhstan to the inverter station in China,is 3600 km long;section 2,from the ±500 kV rectifier station in China to the connection point between the overhead line and submarine cable,is 880 km;and section 3,is a submarine cable with a distance of 350 km.
2.3.2 Scenario B-2
A three-terminal UHVDC project,the line of the rightof-way via China and the DPRK to the site close to Seoul.
The voltage of the KZ-CN-ROK UHVDC project is±800 kV.
3 UHVDC stations: The rectifier station is located close to RES areas in Kazakhstan with a capacity of 8 GW;inverter station 1 is located at the site close to Shenyang in Liaoning province in China with a capacity of 3 GW;and inverter station 2 is located at the site close to Seoul with a capacity of 5 GW.
There are two sections of the transmission line: Section 1 spans a distance of 4000 km from the rectifier station in Kazakhstan to the inverter station in China.Section 2 spans a distance of 580 km from the inverter station in China to the station in Korea.
As mentioned above,KZ-ROK direct electricity transmission via China is possible,but the Yellow Sea poses some technical difficulties owing to the problems with the±800 kV submarine cable.However,theoretically,direct electricity transmission is still possible via China and the DPRK.Scenario B-3 is derived from B-2 by removing the inverter station in Liaoning province in China to realize KZROK direct electricity transmission over a distance of 4580 km.
3.1 Voltage Choice for the HVDC Project
Referring to existing HVDC projects in China,the voltages of the existing projects are summarized in Table 3.
Table 1 Generating capacity installed in China by 2021 [16]
Table 2 Transmission network of the Korea Electric Power Corporation,2019
Table 3 Power industry status of ROK (December 2018)
Table 4 Power generation capacity (GW) ratio based on the 9th basic plan for Long-term Electricity Supply and Demand 2020-2034
Table 5 Renewable Portfolio Standard ratio
Table 6 Voltages of the existing HVDC projects in China
The power of ±600 kV DC transmission reaches 4.6 GW,and the economical transmission distance reaches 1100 km,the power of ±800 kV DC transmission exceeds 8.0 GW,and the economical transmission distance reaches 2300 km.The distance between the power supply end-load center and the load center-load center in Northeast Asia is approximately 400-1900 km.Using the current mature ultra-high voltage transmission technology,energy from Mongolia and the Russian Far East can be sent to the load center in Northeast Asia[32].
Based on the technical and economic analysis of existing HVDC projects in China,the ±500 kV HVDCs are suitable for 1000～1500 km of transmission lines as indicated in Table 6.The KN-CN and CN-ROK sections in A-1 are chosen as ±500 kV.
Some major cost parameters are obtained from the The Design index of Transmission Projects Cost Estimation in 2018 published by the Electric Power Planning and Engineering Institute (EPPEI)[33].Since 2019,the Guquan UHVDC project in China has been put into operation with a capacity of 12 GW.The line cost of the KZ-CN section and the stations in scenarios A-2,B-1,and B-2 in China may take the line cost of the Guquan UHVDC project as a reference,and the line cost is recommended to be 80%of the line cost of the Guquan UHVDC project.The cost parameters have been converted from CNY to US dollars at an exchange rate of 1 USD = 6.8462 CNY on August 23rd,2022.The estimated costs are as follows:
±1100 kV transmission line: 786878.97 USD/km
±800 kV transmission line: 524543.37 USD/km (typical geographical condition)
±1100 kV UHVDC station: 89.45 USD/KW (Guquan UHVDC project)
±800 kV UHVDC station: 76.25 USD/KW
The voltages for the KZ-CN sections of scenario A-2,B-1,and B-2 are chosen by comparing the costs of±1100 kV and ±800 kV projects (Table 7)
Table 7 Cost comparison of KZ-CN UHVDC sections between ±1100 and ±800 kV (in million USD)
Referring to Table 7,the project cost of ±1100 kV is much higher than that of the ±800 kV project.Thus,the voltage of ±800 kV is highly recommended even if the transmission loss exceeds that of ±1100 kV to some certain extent.Otherwise,±1100 kV might be chosen if the transmission capacity roughly exceeds 10 GW.
3.2 Technical Specifications of the HVDC systems
3.2.1 Power systems of the provinces where the sites located
Xinjiang has 2 UHVDCs with ±800 kV/8 GW and ±1100 kV/12 GW exporting electricity to Henan in the central region and Anhui in the eastern region,respectively,and the AC voltages of the Xinjiang system are 750/330/220/110 kV,Henan and Liaoning 500/220/110 kV.Table 8 lists the generation mix of the Xinjiang,Henan,and Liaoning power systems,where the HVDC sites were selected by referring to 3.1.
Table 8 Generation mix of Xinjiang,Henan,and Liaoning in 2019 (MW)
3.2.2 HVDC converter stations
Based on the technical and economic analyses of existing HVDC projects in China,the ±800 kV UHVDCs are suitable for 4～8 GW with more than 2000 km of transmission lines.Similarly,±500 kV HVDCs are suitable for 1.5～3 GW with 1000～1500 km according to Table 3.The capacity of ±800 kV converter stations was chosen as 5 and 8 GW and the capacity of the ±500 kV converter stations was chosen as 3 GW in the relevant scenarios.
Table 9 ±800 kV/8 GW stations in China and Kazakhstan
Table 10 ±500 kV/3 GW stations in China,Kazakhstan,and ROK
Table 11 Transmission lines and submarine cables
It is proposed that the HVDC converter station in Kazakhstan should be connected to the 500 kV AC system in Kazakhstan for stable power system operation and better electricity collection and distribution.The converter stations in China are recommended to be connected to the 750 kV AC system in Xinjiang and the 500 kV AC system in Henan.Finally,the three-terminal converter stations of the CN-DPRK-ROK HVDC project are recommended to be connected to the 500 kV AC system in the Liaoning province of China,220 kV in the DPRK,and 500 kV in ROK,respectively.The specifications are as follows[33].
As for the ±800 kV/5 GW and 3 GW UHVDC stations,the main differences from the UHVDC 8 GW stations are the fewer number of AC lines and the smaller sizes of the DC lines and major devices,and the others,such as main configuration,etc.,are the same.Therefore,the specifications are not listed and the costs may be estimated by the cost of 8 GW per unit in the next chapter.
The specifications of the 500 kV 500 MW inverter station in DPRK are not listed and the cost may be estimated to be 25% of that of the 3 GW station.
3.2.3 Transmission lines and submarine cables
Specifications of the HVDC transmission lines and submarine cables[33],[34].
China implemented the national standardGuideline for system planning of HVDC transmission projectin July 2018,which stipulated the selection process and method for HVDC project scheme.The analysis of power system security and stability will be made in the feasibility study stage.[35,36]
4.1 Cost estimation of the scenarios
Globally,there are no 3 GW ±500 kV submarine cables in operation or under construction.The cost of 3 GW±500 kV submarine cables is referred toThe Study Report of Power Transmission Planning from China to Korea[34].The cost estimated per km is 71971427CNY.All the other cost parameters are chosen fromThe Design index of Transmission Projects Cost Estimation in 2018[33].The cost of a 5 GW ±800 kV line is assumed to be 80% of the cost of the 8 GW line.The cost parameters are converted from CNY to US dollars at the exchange rate of 1 USD =6.8462 CNY on August 23rd,2022 (the same below).
±800 kV line: 524543.36 USD/km (6*1000 conductor bundle,8GW)
±800 kV line: 419634.696 USD/km (6*630 conductor bundle,5 GW)
±800 kV station: 75.96 USD/KW
Earth electrode: 6354635.79 USD,Earth line:5272268.91 USD (50 km)
±500 kV line: 309855.58 USD/km
±500 kV station: 71.64 USD/KW
Earth electrode: 3633227.54 USD,Earth line:4536976.62 USD (50 km)
±500 kV 0.5 GW station cost: 25% of 3 GW station
±500 kV submarine cable: 9011817.06 USD/km
Table 12 describes the sizes and major parameters of all the scenarios.
Based on the cost parameters above,the costs of the scenarios are estimated in Table 13.
Table 12 Major parameters of the scenarios
Table 13 Costs estimated of the scenarios in million USD
The investment cost can significantly differ from project to project.Some of the main causes for differences between costs of individual projects are:
· Customised specifications for individual projects.
· HVDC technology market situation (e.g.market power of technology suppliers).
· Prices of raw materials (e.g.steel and copper).
· Location related aspects
· Differences in risk perception.
The availability of reliable cost reference data and the validity of investment model cost parameters need continuing attention in the future.[37]
4.2 Transmission Levelized Cost of Energy(LCOE) Prices and Wheeling Charges
4.2.1 Transmission cost estimated
Based on the cost estimate,there are still some crucial assumptions that need to be determined beforehand.Some of these assumptions are based on the existing HVDC projects in China.The losses of HVDC stations are assumed to be 1.5%of the total electricity transmitted[38].The total transmission losses of each HVDC project is referred to some similar existing HVDC projects in China.Some LCOE calculation tools are used,providing an economic assessment of the cost of the energy-generating system including all the costs over its lifetime: initial investment,operations and maintenance,cost of fuel,cost of capital and etc.[39]
Tianzhong ±800 kV UHVDC project: 2210 km,7.2% of transmission loss.
Longzheng ±500 kV HVDC project: 860 km,7.5% of transmission loss
The LCOEs,in cents/kWh,are calculated on different annual capacity factors based on the assumptions in Table 14.Table 15 lists the results of the LCOEs calculation[40].The cost of interest rates in construction periods is not calculated in detail because the construction period of the transmission projects is only approximately three years.The LCOEs in Table 15 do not include profits and tax.
4.2.2 Transmission prices estimated
The transmission project’s pricing needs to involve some more financial parameters,such as the return of the investment and tax.The analysis does not include the cost changes over time,e.g.inflation correction for the cost parameter sets[38].
The assumptions to be used in transmission prices are 20%of capital,10% of return on capital (ROC),6.3% of return on investment (ROI) with just 2 percentage points of interest added and 13% of VAT.The prices of transmission projects are based on the LCOEs in Table 15[40].The prices with 10%ROC and 6.3% ROI are presented in Tables 16 and 17.
Table 14 Assumptions chosen for the LCOE calculation of the HVDC projects.(In years,%)
Table 15 LCOEs of the HVDC projects.(In cents/kWh)
Table 16 Transmission prices of the HVDC projects based on LCOEs.(10% ROC,In cents/kWh)
Table 17 Transmission prices of the HVDC projects based on LCOEs (6.3% ROI,In cents/kWh).
Table 17 Transmission prices of the HVDC projects based on LCOEs (6.3% ROI,In cents/kWh)
The transmission price of scenario B-3 with 4580 km,±800 kV,8 GW,and 13.31% losses is 1.13 cents/kWh at capacity factor of 0.6,ROC of 10 % and VAT of 13 %.
4.2.3 Wheeling Charges in China
The wheeling charges include HVDCs and the regional grids the power trade passes through in China,as shown in Fig.2.As for scenario A-1,the KZ-CN HVDC project may have opportunities to utilize the existing UHVDCs in Xinjiang to transmit electricity to the eastern provinces of China.For the two UHVDCs,the price of Tianzhong±800 kV (1) is 0.943 cents/kWh approved and that of Guquan±1100 kV (2) will be 1.188 cents/kWh for approval.The twopart tariff was chosen for wheeling charges of regional grids in China and the capacity tariffs of the provinces are different.In 2019,wheeling charges were approved by the national development and reform committee of China (NDRC),as shown in Table 15[41].The stamp methodology was chosen for calculating the wheeling charges.
In 2019,the capacity factors of UHVDC 1 and 2 are 0.592 and 0.14,respectively.Thus,UHVDC1 is only available for wheeling in off-peak hours,and UHVDC2 may be available for wheeling for the time being within 2 or 3 years from now because the planned CFPPs are not installed yet.The transmission capacity of AC grids for the wheeling will be available in non-rush hours for shortterm trading.Nevertheless,the wheeling charges are still estimated from Kazakhstan to ROK.Based on Table 15,the wheeling charges from KZ to ROK via UHVDC2 and some AC grids are 5.264 and 6.52 cents/kWh by DPRK and submarine cables,respectively.It may not be necessary to consider the possibility of power wheeling through AC grids from China to ROK because the costs of AC grids are not economically feasible when compared with the investment of HVDC transmission.
Table 18 Wheeling charges of the five regional girds in China in cents/kWh
4.3 Benefit Analysis
Based on the preliminary research conclusions in the early stages of the project,it is concluded that the construction of an intercontinental transmission channel has technical and economic feasibility as well as remarkable comprehensive social and environmental benefits.
First,regarding the technical and economic feasibility,the ultra-high-voltage long-distance and large-capacity transmission technologies have matured,and with the further development of technology,the cost can gradually decrease.Second,regarding the promotion of energy conservation and emission reduction,a line with a transmission power of 11000 MW can provide 60 billion kW·h of clean energy annually,replacing 20.52 million tons of standard coal,reducing emissions by 57.05 million tons of CO2and 410,000 tons of SO2,and promoting the transformation of the energy development mode to low-carbon and green.The third involves realizing energy mutual assistance.It can realize the benefits of trans-regional surplus and deficiency adjustment,peak shifting,peak avoidance,and mutual backup.The fourth is to promote common development.It is conducive to giving full play to the resource advantages of Kazakhstan,which includes narrowing regional disparities,increasing social employment,and promoting healthy economic development[42].
4.3.1 Scenario A
Scenario A-1 is a 3 GW interconnection with a short distance between RES areas in Kazakhstan and the Xinjiang power system in China.Xinjiang is an energy-concentrated region and the energy curtailment of wind farms and PVs has occurred seriously in recent years because of the rapid development of RES and a lack of flexible capacity.The curtailment rates of wind farms and solar PV are 13.9%and 7.3%,corresponding to an energy curtailment of 6605 GWh and 1021 GWh,respectively.The hydro power plants(HPPs) of Kazakhstan could be operated in collaboration with the renewable energy sources to eliminate the intermittency and reduce the energy curtailment.It could also replace some CFPPs planned.
A benchmarking price for CFPPs was chosen for each province in accordance with the fuel costs and transportation conditions of the provinces.The benchmarking prices were approved by the government.The governments may make adjustments based on the changes of the fuel cost,particularly if it exceeds a predefined level.The feed-in tariff for RES installed in 2019 and 2020 has been reduced significantly.Thus,Table 19 presents the electricity sell prices of CFPPs and RES in 2018 for reference in power trading between Kazakhstan and China.
Table 19 Electricity prices in Xinjiang,Henan,Liaoning,and Shanxi in 2018 (USD cents/KWh)
The transmission prices with capacity factor of 0.6(Table 16) are listed below.
Kazakhstan to Xinjiang in China: 0.6 cents/kWh (A-1);
Shanxi in China to ROK: 3.108 cents/kWh (A-1);
Kazakhstan to Henan in China: 1.006 cents/kWh (A-2);
Kazakhstan to Henan in China via existing HVDC to Henan (Xinjiang to Henan ±800 kV/8 GW):0.6+0.943=1.543 cents/kWh (A-1).
Electricity sell price from Liaoning in China to ROK is 5.37+0.644=6.014 cents/kWh;
Electricity sell price from Shanxi in China to ROK is 4.76+3.108=7.868 cents/kWh.
In summary,scenario A-2 is more economical than utilizing the existing HVDC if Kazakhstan sends electricity to Henan in China.The electricity prices in the Northeastern regional system in China are extremely competitive compared to the electricity market of the ROK if scenario A-2 could be implemented,passing through DPRK.The selling price to ROK from Shanxi in China is still acceptable,referring to ROK’s electricity market.
4.3.2 Scenario B
As for Scenario B-1,there are 2 separate HVDCs,±800 kV 8 GW and ±500 kV 3 GW.Specifically,5 GW will remain in Henan province in the Central China regional system with acceptable transmission LCOE prices on reasonable capacity factors.Coal generation accounts for a large portion of the generation mix in the Henan provincial system.Thus,importing RES from Kazakhstan will still be significant even if the price is higher than coal generation.The CN-ROK project has a high transmission price due to submarine cables;however,it is still the only solution to import electricity to ROK because of the uncertainty of DPRK participation.The transmission prices from Kazakhstan to ROK with a capacity factor of 0.6 (Table 16)are listed below.
Scenario B-1: 1.006+3.085= 4.091 cents/kWh
Scenario B-2: 0.87+0.306=1.23 cents/kWh
Scenario B-3: 1.13 cents/kWh
Scenario B-2 and B-3 still have the critical problem of uncertainty in the participation of DPRK.
4.4 Financing Issues and Business Model
Since 2018,SGCC has introduced social capital for UHVDC projects.On December 25,2018,the State Grid issued ten measures to deepen the reform,including the introduction of social capital in the field of UHVDC projects.The state grid will actively introduce social capital,such as insurance companies,large funds,and investment platforms owned by local governments,to invest in new UHVDC projects in the form of joint venture project companies.On November 19th,2019,the Qinghai-Henan±800 kV project was determined to be participated in by China People’s Insurance Group Co.,Ltd.,with an initial planned share of 40%.Thus,the KZ-CN-ROK power interconnection project may have a high probability of attracting private investors from China if the project is economically and technically feasible.
(1) The countries in Northeast Asia,including China,Japan,ROK,Mongolia,and Russia,convened the first meeting of the Northeast Asia Regional Power Interconnection Forum (NEARPIC) on 26-27 October,2016 in Beijing,China.As an initiator,China electricity council (CEC) jointly with some international organizations organized and established the forum as a platform together with the countries.The CEC proposed that the steering committee be chaired by the United Nations Economic and Social Commission for Asia and Pacific (UNESCAP),and the forum was held annually.Political tensions in the region remain the biggest obstacle to cooperation on regional power grid connectivity.
(2) The power systems of the Central Asian Republics(CARs) were designed by considering the need to take advantage of the available fuel and energy resources and the seasonal interchange of electricity between countries.Kazakhstan"s power generation industry has undergone a challenging and painful transformation.
(3) CEC created statistics for all the HVDC projects in China and published annual results of the reliability index.Referring to the statistics of 12 ±800 kV projects,the availabilities were from 84.147% to 96.519%.The extremely long distance transmission line of the KZ-CNROK UHVDC project is not a substantial problem for operational reliability.
(4) Reviewing the historical development of the worldwide regional power interconnection,all the related countries have reached a consensus on the huge benefits of sharing diversity of generation mix,load profiles,and reserve capacity,reducing energy cost,and increasing security of power supply via regional power interconnection.Numerous regional power pools have been formed and have covered most countries worldwide.However,most Asian countries have not established a regionally interconnected system.
(5) Most regional power pools are supported by regional economic communities,such as ENTSO-E in Europe,five regional power pools in Africa,SAARC in South Asia,etc.Some international institutions have played crucial roles in promoting regional power connectivity,such as the World Bank in Africa and Asia Development Bank in Asia,particularly in establishing a regional power trading coordination committee in the Greater Mekong subregion,and UNESCAP supports NEARPIC in Northeast Asia.Most regional power cooperation frameworks have been based on intergovernmental MOUs.Inter-government agreements are one of the most crucial steps in implementing regional power interconnection.
(6) China has accumulated vast expertise in planning,engineering,and operation.A series of UHVDC national standards and guidelines,including planning,engineering,and operation,have been announced recently.For example,Code for the design of ±800 kV DC overhead transmission line(GB 50790 2013) and theCode for the design of ±800 kV DC converter station(GB/T 50789 2012) have played crucial roles in the engineering phase of±800 kV UHVDC projects in China.Standards of HVDC equipment have been related to system aspects that will be prepared in close collaboration and in joint responsibility with the relevant technical committees and subcommittees.TC115 has published 10 standards since 2008.Most HVDC submarine cables are operated in Europe,and the European standards for HVDC submarine cables are recommended to be chosen[29].
(1) The scenarios are listed based on the priority recommended by analyzing the technical,economic,and political features of each scenario in the following.
Scenario A-1.It is the first recommended scenario with fewer business difficulties and low risks.The two HVDCs can be independently developed by bilateral cooperation.RES from Kazakhstan may provide flexible capacity to the Xinjiang system to obtain acceptable trading prices.The power trade from China to ROK via China and the Yellow Sea is still economically feasible compared to the power market of ROK and can avoid political uncertainty along the transmission line,even if the transmission cost is high.
Scenario B-1.B-1 can realize 3 GW of electricity transmission from Kazakhstan to ROK via China and submarine cables at a high transmission cost without political uncertainties and obstacles.RES importing from Kazakhstan is significant for areas that lack energy,such as the central regional system in China for the coming decades of energy transition.
Scenario A-2,B-2.Electricity prices in China’s power markets are highly competitive if ROK could import electricity from China.However,the problem of political remains uncertain.
(2) A road map for promoting regional power interconnections is suggested.Bilateral cooperation may be easier than multilateral frameworks.Therefore,Scenario A is preferentially recommended.A working group might be organized for joint planning study of power connectivity as the initial step;multilateral framework shall be established to be prepared for exchanging information and gradually increasing the mutual trust;a multilateral agreement between governments on the cooperation of power development is crucial for building trust and political consensus on the common vision of power interconnection.
(3) From technical and economic perspectives,there are no substantial problems in implementing regional power interconnections.Accordingly,HVDC technology is the best solution for power interconnections among the three countries,with no impact on the stable operation of transmission systems,and the economic benefits can be realized by regional power interconnection,particularly by sharing the green energy,diversity of generation mix,demand profiles,generation reserves,etc.The detailed studies for hydro and RES optimization in Kazakhstan and the power market analysis in ROK is required to promote feasible power trading among the three countries.Hydro generation may not only balance the intermittency of RES but also provide stable power to keep the acceptable capacity factor of transmission lines.
This paper addresses the preliminary feasibility study of power system interconnection.In this paper,we estimated the system specifications and performed a preliminary feasibility study by considering the technical,economic,and financial perspectives as well as energy security problems.Some necessary implifications and assumptions are made.
(1) Fundamentally,it is economically and technically unreasonable to transmit 3 GW only from Kazakhstan to ROK through China.The UHVDC must be chosen for very long-distance transmission between the two countries.
(2) The concept of “swapping” RES from Kazakhstan to ROK by substituting coal generation in China could be considered.It means that RES imported from Kazakhstan to China will replace coal generation in a province and could build the same capacity of CFPP in another province for exporting electricity to ROK without changing the total coal generation in China.Upon selecting scenario A-1,the electricity price to ROK is 4.76 (Shanxi province in China)+3.108 (transmission price) =7.868 cents/KWh.It is the main reason why A-1 is recommended.
As for Kazakhstan,the electricity export of 3 GW to Xinjiang (A-1) is recommended and 5 GW to Henan (B-1)may be also considered provided that Kazakhstan can collect sufficient generating sources.Because of high transmission costs,transmitting 3 GW of power from Kazakhstan to ROK is not recommended,passing through China with a new UHVDC line or wheeling through China’s existing transmission grids.
The solution suggested might be that both Kazakhstan and ROK may engage bilateral power trading with China,primarily because China may have the possibility to provide electricity at competitive prices to ROK without any limitation on importing electricity ranging from 3-8 GW from Kazakhstan if it can provide a competitive cost of electricity.
The benefit-sharing mechanism established by power interconnection can promote cooperation between countries.Countries can increase the income of clean energy and electricity via power interconnections and realize the response to global climate change at a lower cost.For power transmission,countries with an investment ability,based on the premise of ensuring normal financial profitability of the project,can achieve a mutually beneficial and sustainable development via reasonable negotiation of the transmission price.The land resources occupied by the state through transmission projects can be considered as shares at a certain price,sharing the benefits of transmission projects and participating in the operation and maintenance services of transmission lines to stimulate local employment.Acceptance of clean electricity by electricity recipient countries can promote the development of renewable energy and reduce greenhouse gas emissions at a lower cost,ensuring the security of electricity supply on a larger scale.
Acknowledgements
This work is supported by the Technical Assistant 9690 project of Asian Development Bank (ADB).As the term of reference of the author’s consulting assignment outlined in the TA9690,Integrated High Impact Innovation in Sustainable Energy Technology-Energy System Analysis,Technology Road Maps and Feasibility Studies for Pilot Testing,the authors has completed the scoping study report of power transmission scenarios interconnecting Kazakhstan,China and ROK and cooperated with other two experts from Kazakhstan and ROK who focused on collecting RE generation and importing capability analysis in their countries respectively.The contents of the paper do not reflect the views and policies of ADB or its Board of Governors or the governments they represent.Many thanks to Mr.Jingmao Xu,energy specialist of ADB and his colleagues for supporting the study.
Declaration of Competing Interest
We declare that we have no conflict of interest.
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