Research and comprehensive evaluation on delivery schemes of the Grand Inga hydropower station

0 Introduction

The Congo River,with a basin area of 3.7 million km2,is a prominent river in Africa and around the world.The main channel is 4,640 km long,the average annual flow of the Congo River estuary is approximately 41,000 m3/s,and the annual runoff flow is approximately 128 billion m3[1-4].As one of the richest rivers in the world in terms of hydropower resources,the Congo River has a technical hydropower potential of up to 150 GW [5-6].The lower reaches of the Congo River are located in the territory of Democratic Republic of (D.R.) Congo,and the borders with the Republic of Congo are suitable for large-scale,cascade hydropower development.The idea of constructing a largescale hydro-project such as the Grand Inga was proposed in the 1850s [7].The capacity of the Grand Inga hydropower station could be as large as 60 GW with an annual electricity production of approximately 37 TWh [1].However,the currently developed infrastructure on the lower reach of the Congo River generates only 1,770 MW,which is less than 3% of the technical potential [8].The main reason for the serious delay in the development of hydropower on the Congo River is the volatile political and economic situation in D.R.Congo,and the lack of effective investment and financing mechanisms for the development of large-scale projects.

The economy of D.R.Congo is very weak,with a total annual electricity consumption of approximately 7.2 TWh.Accordingly,it could not consume the total output of the Grand Inga if it runs at full capacity [9].Although the economy of R.Congo has been developing steadily in recent years,the scale of the economy is even smaller,with only 1.6 TWh of annual electricity consumption.Therefore,cross-border and inter-regional power delivery is the main future direction of the hydropower consumption of the Grand Inga.South Africa has signed an agreement with the government of D.R.Congo expressing its willingness to purchase hydropower in the range of 2.5-5 GW from the Grand Inga to replace the unsustainable power from it saged coal-fired plants [10].However,given the long transmission distance and limited capacity,the proposed project is not economically competitive.Moreover,there is still a need to seek a larger power consumption market for the Grand Inga.

With the continuous progress of ultrahigh voltage(UHV) transmission technology,long-distance and largecapacity transmission has become very mature,and has been extensively applied in China,Brazil,and India.It has also become an important technology for the widearea and large-scale allocation of clean-energy resources[11].Given the large-scale transmission capacity,per-unit economy of ultrahigh voltage direct current (UHVDC) is more advantageous than high voltage direct current (HVDC).With UHVDC technology,the downstream hydropower of the Congo River could be delivered to load centers in West Africa and Southern Africa,fully tapping the electricity consumption market.

The complex political situation in Central Africa,as well as the huge investment scale of the Grand Inga project makes it difficult for investment institutions and policy makers to fully assess the project feasibility.A method to comprehensively evaluate the impact factors and identify the potential cross-border power delivery options is essential.Therefore,a comprehensive assessment model covering six classes of impact factors,including social economy and business environment,infrastructure situation,development potential,electricity market space,transmission pathway condition,as well as tariff competitiveness,are proposed.The model uses the best-worst method to determine the weights of all impact factors and conduct comprehensive evaluation of all candidates based on experts cores.With the proposed model,all the inter-regional power delivery options for the Inga III project are assessed,and the relatively competitive options are recommended for future investors and decision makers.

The study is organized in four sections.Section 1 analyzes the hydropower development situation of the Grand Inga station.Section 2 derives the proposed comprehensive assessment model for large-scale,long distance,cross-border power interconnection projects.Section 3 presents the evaluation results of potential interregional power delivery options for the Inga 2 project with the proposed assessment model,and the most applicable transmission schemes are recommended.Section 4 concludes the paper.

1 Grand Inga hydropower development and delivery

1.1 Basic information and development plans of the Grand Inga hydropower plant

The Livingstone Falls on the lower reach of the Congo River consist of 32 rapids and waterfalls with a total drop of 280 m over 200 km;the hydropower technical potential is up to 100 GW.To promote the development of industries,the government of D.R.Congo funded the construction of the Inga I hydropower station with an installed capacity of 350 MW in 1972.In 1982,the Inga II hydropower plant was operated with an installed capacity of 1,420 MW;power was delivered to the mines in the southern province of Katanga through the ±500 kV HVDC Inga-Kolwezi line that was the longest HVDC transmission project in the world at that time [1].According to relevant studies [1,5],the subsequent Inga hydropower cascade stations could be developed from phase III to phase VI.The installed capacity of the Inga III hydropower station could reach 11 to 12 GW,and the annual utilization could reach 6,500-7,500 h.In 2018,China and Spain formed a consortium and signed an exclusive agreement with the Grand Inga Development and Promotion Agency,and jointly completed the development plan of the Inga III hydropower station.In the next phase,the Chinese and Spanish consortium focused on the identification of the outbound electricity consumption market as well as the feasibility report preparation.Construction of the Inga III project is expected to be initiated by 2023,and will be operable by 2030.

1.2 Power delivery options of the Inga III hydropower station

The distribution of Inga III hydropower will prioritize industrialization and electrification of D.R.Congo,and will consider the electricity consumption requirement of neighboring countries,such as R.Congo,Zambia,as well as the inter-regional areas,including West and Southern Africa.The power delivery plan should also make reasonable provision for subsequent phases IV to VI development of the Grand Inga.The economy scale and electricity consumption of D.R.Congo and neighboring potential electricity recipients are listed in Table1 [9,12].

Table1 Economic and electricity consumption indicators of countries targeted for Inga III hydropower supply

Countries GDP in 2017(billion USD)GDP annual growth(2012-2017)/%Electricity consumption in 2017/TWh Electricity annual growth(2012-2017)/%D.R.Congo 37.2 9.3 7.2 -0.4 R.Congo 8.7 -8.6 1.6 14.9 Nigeria 375.8 -4.0 25.8 0.5 South Africa 349.4 -2.5 194.5 -0.4 Ghana 47.3 2.4 10.2 6.3 Zambia 25.8 0.2 12.2 3.4 Guinea 10.5 6.9 1.0 7.6

The following analysis focuses on the consumption potential and market space of the targeted power delivery markets.The future power demand is affected by a range of unpredictable factors,such as political stability,global economic environment,technology innovations,etc.[13].In this study,we conducted the following power demand forecast in typical scenarios.

·dD.R.Congo

D.R.Congo owns rich mineral resources,with 75 million tons of copper ore—accounting for 15% of the total production worldwide—and 4.5 million tons of cobalt ore—accounting for half of the global total [14].As the largest economy in Central Africa,D.R.Congo is committed to taking advantage of its mineral resources and promoting industrialization.Based on its current economic development trend,as well as the requirement of industrialization and universal access to electricity,the peak demand of the D.R.Congo is expected to increase from 2 to 3 GW by 2030.If the co-development of electricity,mining,metallurgy,manufacturing and trade could be achieved,industrialization would be accelerated,and the peak load would reach 6 GW by 2030.Specifically,2 GW requirement is expected to be from industrial development and electricity consumption in the southern mining areas,and 1 GW will be from the capital city,Kinshasa.Besides the downstream hydropower of the Congo River,other local power generation will supply around 1 GW of electricity.

·R.Congo

R.Congo is rich in mineral resources,with reserves of approximately 6 million tons of phosphate ore and 25 million tons of iron ore,currently exported mainly as raw ore [14].Pointe-Noire is one of the three largest seaports on the west coast of Africa,and industrial parks have been built with well-developed supporting infrastructure.Following its current economic developmental trends,as well as the requirement of industrialization and universal access to electricity,the peak demand of R.Congo is expected to increase from 300 MW to 500 MW by 2030.Considering the co-development between mineral processing,industrial parks and port trade,as well as the accelerated development of electrolytic aluminum and steel industries in Pointe-Noire,the peak demand would reach 5 GW by 2030.More than 3 GW will be consumed in Pointe-Noire,and 1 GW will be consumed in Brazzaville.In addition to the downstream hydropower of the Congo River,local gas generation will supply electrical power of approximately 500 MW to 1 GW.

·West Africa

The industrial structure of West African economy is dominated by agriculture and primary services with a weak industrial base.West Africa is rich in energy and mineral resources with bauxite ore (45 billion tons) and iron ore reserves (64 billion tons) constituting 60% and 8% of the global total,respectively [14].In the future,accelerating infrastructure construction and co-development of electricity,mining,metallurgy,manufacturing and trade is expected to accelerate development of the economy [2].Considering the two scenarios of business as usual and the co-development of electricity,mining,metallurgy,industry and trade,it is expected that by 2030,the peak demand of West Africa would reach 52 and 62 GW,respectively.Therefore,the scale of power import would be 8 and 16 GW,respectively.Nigeria,Ghana,Cote d’Ivoire and Guinea are the major load centers,with peak demands in the ranges 26 to 29 GW,6 to 7.5 GW,4 to 6 GW,and 1 to 7.5 GW,respectively.

·Southern Africa

Southern African Region is the most industrially developed region in sub-Saharan Africa,led by the Republic of South Africa.It is rich in mineral resources with large reserves of coal,oil,gas,and other fossil energy resources.Additionally,the population of Southern Africa grows quite fast;the region still has a great potential for future development.Southern Africa is projected to have a peak demand that will range from 82 to 92 GW by 2030,with imported power ranging from 5 to 8 GW.Southern African Power Pool (SAPP) has included the transmission from Inga III to South Africa in the regional power pool planning [10].

In summary,to support the industrialization of D.R.Congo and R.Congo,hydropower (4 to 5 GW) of Inga III can be consumed.Inter-regionally,the Inga III hydropower could be delivered to Western and Southern Africa,and the scale of the inter-regional power delivery is approximately 8 GW,as shown in Fig.1.

Fig.1 Inter-regional and intraregional power delivery directions of the Inga III hydropower station

1.3 Inter-regional and intraregional power delivery schemes of the hydropower of the Congo River

·Intraregional Power Delivery Schemes

Based on the analysis in Section 2.2,considering both the short-term and long-term power consumption requirement,a double circuit 765 kV transmission line shall be built from Inga III to Kinshasa;the corridor for the third line shall be allocated for future development.Considering the electricity requirement of the highly populated cities in the central area,such as Kindu,and the mining zones in the eastern area,a ±660 kV HVDC transmission line shall be built between Inga III and Kindu.

Cross-border wise,a double circuit 765 kV transmission line between Inga III and Pointe-Noire could be built to supply power to the industrial parks.The Inga-Matadi-Moanda 400 kV transmission corridor should be extended to Cabinda,Angola,to meet the electricity demand in Cabinda.The intraregional power delivery schemes of Inga III are illustrated in Fig.2.

Fig.2 Intraregional power delivery scheme of the Inga III hydropower station

·Inter-regional Power Delivery Schemes

After meeting the local electricity demand of D.R.Congo and neighboring countries,Inga III could still export approximately 8 GW.UHVDC technology could be exploited to deliver this huge amount of power to load centers in Western and Southern Africa regions.With the electricity market analysis in Section 2.2,the candidate inter-regional power delivery options include delivery to Southern African countries,such as Zambia and South Africa,as well as interregional power delivery to West African countries,such as Nigeria,Ghana,Guinea,etc.The seven options for longdistance,large-scale,inter-regional power delivery of the Inga III hydropower are illustrated in Fig.3.

2 Comprehensive evaluation model development for long-distance,large-scale power transmission schemes

Research papers and reports have presented some classic ways associated with the evaluation of large-scale power

Fig.3 Illustration of seven candidate inter-regional power delivery projects of the Inga III hydropower station

interconnection project feasibility [16-23].Few research results have been published regarding comprehensive political,technical,and economic evaluation of largescale,cross-border power interconnection projects.The latest research published by Ahmed et al.[16]proposed a multilevel evaluation model for intercontinental power project evaluations.However,the method is calculation intensive and could not effectively differentiate multiple options for one project from economic and technical perspectives.Other research studies regarding cross-border interconnection mainly focuses on specific aspects,instead of comprehensive evaluations.For example,a report [17]released by the Asian Development Bank focused on the influences on and risks of cross-border power trading.Other research studies [18-21]focused on the business model development or economic evaluation of crossborderand large-scale power interconnection projects.Rama [22]reviewed six dimensions of the social impact of the international interconnection of the power grid.The study by Puka and Szulecki [23]focused on political and economic aspects of cross-border power projects.Therefore,we propose a comprehensive evaluation framework to evaluate the cross-border and inter-regional power delivery options of Inga III from the viewpoints of political,social,economic,and technical dimensions.

2.1 Framework design of the comprehensive evaluation model

To comprehensively evaluate the feasibility of longdistance,large-scale,power-delivery schemes,such as the inter-regional power delivery of the hydropower of Grand Inga,a comprehensive evaluation model is proposed.The model covers six classes of evaluation indicators,including social economy and business environment,infrastructure situations,development potential,power market space,transmission-path conditions,as well as tariff competitiveness.The comprehensive set of indicators could fully reflect the technical and economic feasibility,as well as the comprehensive benefits of the project.

As shown in Fig.4,the comprehensive evaluation model consists of 17 sub-indicators classified in six dimensional indicator classes.The dimension of social economy and business environment is assessed in terms of the evaluations of the economic volume and growth trend,political environment,and business environment evaluation issued by the United Nations [20].The dimension of the infrastructure was assessed in terms of roads,railways,airports,communications,electricity,education,science and technology,health care,etc.The dimension of the development potential was assessed in terms of the economic growth rate,total population and structure,government management capacity,regional advantages,etc.In addition,the dimension of market space was assessed in terms of the current electricity demand and forecasted future power demand.Furthermore,the dimension of transmissionpath conditions was assessed in terms of transmission path geography,countries crossed,transmission distance,etc.Finally,the dimension of tariff competitiveness was assessed in terms of the net present value (NPV) of the project as well as the price difference between the feed-in tariff of the power delivered and the local tariff.

To assess tariff competitiveness,it is necessary to calculate the investment required for each transmission project followed by the calculation of the corresponding transmission tariff of the project based on assumptions,such as the financial net present value,payback period,internal rate of return (IRR),etc.

Fig.4 Schematic of the comprehensive evaluation indicator system for long-distance,large-scale power transmission projects

Net present value (NPV) reflects the profitability of the project during the evaluation period.It represents the net income obtained during the entire life cycle of the project,with net cash flows of different times converted to the initial stage subject to specified discount interest rates.The project is economically feasible only if the NPV is not less than zero.The NPV can be calculated as follows.

where CI is the cash inflow,CO is the cash outflow,n is the calculation period,ic is the discount rate of the power industry or base rate of return,and t is the time in the calculation period.After the NPV is assessed,the levelized cost of transmission has to be calculated.The feed-in tariff(FIT) is calculated by adding the levelized cost of energy(LCOE) of the generation and the levelized transmission tariff.The lower the transmission tariff is,the lower the FIT is,and the more competitive the project’s tariff will be.

The levelized transmission tariff (LCOE_T) in USD/MWh is calculated as follows,

where α is the capital recovery factor;r is the weighted average cost of capital assumed to be equal to 10%;I denotes the investment costs,including the finance cost for construction at interest I;C denotes the capital costs,excluding the finance cost for construction.To calculate the cost for construction,the share of capital cost is assumed to be 20%,and the finance costs are assumed to be equally distributed over the construction period,d represents the decommissioning cost,and OM are the net annual operation and maintenance costs that summarize the fixed OM (FOM)and variable OM (VOM).Additionally,E is the electricity produced annually,calculated by multiplying the capacity P with the number of full load hours (FLH).Regarding the delivery of the Congo River hydropower,the FLH is assumed to be equal to 7000 [1,5,6].

With (2)-(6),the transmission tariff of all the interregional power delivery schemes of Inga III is calculated,and the results are listed in Table2.

Table2 Calculated transmission tariffs for various inter-regional power delivery schemes of Inga III

No.Project Voltage/kV Capacity/GW Transmission Distance/km Investment/(Billion USD)Transmission Tariff/(US cents/kWh)1 Inga-Boké,Guinea ±800 8 4500 7 1.7 2 Inga-Kumasi,Ghana-Boké,Guinea ±800 4,4 4600 7.4 1.8 3 Inga-Benin City,Nigeria±800 8 2000 3.8 0.9±660 4 2000 2.25 1.1 4 Inga-Benin City,Nigeria-Kumasi,Ghana ±800 4,4 2800 5 1.2 5 Inga-Kumasi,Ghana ±800 8 2800 4.5 1.1 6 Inga-Lubumbashi-Lusaka,Zambia ±800 4,4 2200 4.4 1.1 7 Inga-Cape Town,South Africa±800 8 3400 3.4 1.3±800 5 3400 3.4 2.2

2.2 Evaluation methodology and application in assessing the inter-regional power transmission projects of Inga III

The evaluation model proposed is a multidimensional decision-making problem.The model implementation consists of two steps.The first step is to determine the weights of each dimensional indicator,and the second step involves the determination of the value of the indicators.

·Determination of Weights of Dimensional Indicators

Subjective weighting,objective weighting,and combined subjective and objective weighting methods are commonly used to determine weights.This study applies the latest multi-attribute decision method,namely the bestworst method (BWM) [25-27],to determine the weights of various secondary indicators.The BWM selects the best and worst indicators first and then compares them with other indicators,taking into account the views,experiences and knowledge of the experts involved in the evaluation process.The weights optimization method is as follows.

In the set of indicators {C1,C2,…,Cn},the optimal indicators CB and CW are selected.The optimal and inferior indicators are selected without considering the values of the indicators;only the degree of importance of the indicators is taken into account.The most important indicator with a high preference is the optimal indicator,and the relatively unimportant indicator with a low preference is the inferior indicator.

Subsequently,using the scale of 1 to 9,the selected optimal indicator is compared with other indicators,and the optimal comparison vector AB=(AB1,…,ABn) is constructed based on the comparison results,where ABi represents the degree of preference of the optimal indicator compared with other indicators i.The larger the value is,the more important the optimal indicator is compared with indicator i,ABB=1.

Similarly,using the scale of 1 to 9,the selected worst indicator is compared with other indicators,and the worst comparison vector AW= (AW1,…,AWn) is constructed based on the comparison results,wherein AWi represents the degree of preference of the worst indicator compared with other indicators i.The larger the value is,the more important the indicator i is compared with the worst indicator,AWW=1.

Finally,the mathematical planning problem is constructed and solved,and the optimal weights (W1*,…,Wn*) are obtained.To obtain the optimal weight for each indicator,the maximum value among {|WB-ABiWi|,|Wi-AiwWw|} for all indicators needs to be minimized.The planning problem could be expressed as follows.

Where ξ is the conversion factor.Equation (7) is a linear function and has only one solution.By solving the function,the optimal weights (W1*,…,Wn* ) and ξ* are obtained.The BWM uses the consistency ratio (CR) to test the consistency of the results compared among the evaluation indicators to verify the validity of the weights obtained for the evaluation indicators.

where CI is the consistency indicator.The smaller the value of ξ* is,the smaller the CR value is,the more consistent the results are,and the more valid the compared results are.

·Value Determination of Dimensional Indicators

We recruited 30 electrical planning and design experts to evaluate the sub-indicators associated with the six dimensions.Their evaluation results are averaged and applied.The evaluation process adheres to the following scoring principles.

In the case of the dimension of social economy and business environment,the candidate scheme with political,economic,and social stability,abundant energy resources,as well as a good business environment scores 80-100 points;50-80 points are awarded if local conflicts or investment risks exist in the business environment,whereas 0 points are scored for unstable political situations and huge risks in investment returns.

In the case of the dimension of the infrastructure situation,80-100 points are awarded for a well-developed infrastructure system,50-80 points are awarded for infrastructure with a specific foundation with clear planning,but with constraints on industrial development,and 20-50 points are awarded for poor infrastructure and unclear planning.

In the case of the dimension of the development potential,80-100 points are awarded for good economic base and development trend,50-80 points are awarded for weak economic base or uncertain development prospects,and 0-50 points are awarded for weak economic base,ineffective planning and poor development prospects.

In the case of the dimension of market space,80-100 points are awarded for high-electricity demand with fast growth rate;50-80 points are awarded for medium electricity demand with a moderate growth rate,0-50 points are awarded for low-electricity demand and low-growth rate.

In the case of the dimension of the transmission-path condition,considering the project synergy difficulties and risks in the countries along the transmission route,80-100 points are awarded for less than two routing countries and no political disputes between the countries,60-80 points are awarded for routes across 3-4 countries,and 40-60 points are awarded for routes across more than four countries.Scores are adjusted accordingly based on various factors,such as the transmission distance and path geography.

Under the dimension of tariff competitiveness,if the feed-in tariff is 5 US cents lower than local tariff per kWh,100 points are awarded;60-100 points are awarded if the feedin tariff is 2-5 US cents lower than the local tariff.If the feed-in tariff is higher than local tariff,zero points are awarded.If the tariff of the receiving grid exhibits a continuous rising trend,the points could be increased appropriately.

3 Evaluation of inter-regional power delivery options of the Inga III hydropowerstation

The seven candidate inter-regional power delivery options of the Inga III hydropower are evaluated with the methods described in Section III.The thirty Chinese and foreign experts submitted scores for all six indicators,selected the best and worst indicators,and scored the degree of importance of the best and worst indicators compared with other indicators.The experts scored each of the subindices on their own,and applied the weighted average method to obtain the final score of the six indicators.The planning model was solved with the software LINGO,and the optimal weights of all the six dimensional indicators were obtained.

The consistency test showed that the inter-indicator comparisons for all 30 experts differed by less than 0.05.This indicates that the decision results given by the experts have a high-degree of reliability and consistency.By averaging the calculated optimal weights of the six dimensional indicators for the 30 experts,the final weights for the six indicators are obtained as shown in Table3.

Table3 Optimal weights of the six dimensional indicators for Inga III inter-regional power delivery projects

Indicator Weight Social economy and business environment 0.1 Infrastructure cases 0.1 Development potential 0.1 Electricity market space 0.2 Transmission-path conditions 0.2 Tariff competitiveness 0.3

With the weights and evaluation of the six dimensional indicators calculated based on the scores from the 30 experts,the seven candidate inter-regional power delivery projects could be comprehensively evaluated and scored.The scores of each project in each dimension and the final comprehensive scores are listed in Table4.

Table4 List of scores for the evaluation of the inter-regional power delivery schemes of Inga III

Project Social Economy and Business Environment Infrastructure Situation Development Potential Market Space Transmission Path Conditions Tariff Competitiveness Final Score 1 Inga-Guinea 80 40 80 50 50 100 70 2 Inga-Ghana-Guinea 90 60 80 60 50 100 75 3 Inga-Nigeria 3.1 8 GW 80 80 90 90 75 100 88 3.2 4 GW 80 80 80 70 75 100 83 4 Inga-Nigeria-Ghana 90 70 85 90 60 100 84.5 5 Inga-Ghana 100 60 80 70 60 100 80 6 Inga-Lubumbashi-Zambia 90 70 80 80 75 100 85 7 Inga-South Africa 7.1 8 GW 100 100 80 80 75 80 83 7.2 5 GW 100 100 70 70 75 50 71

Fig.5 illustrates the comparison of the candidate interregional power delivery schemes of Inga III in six different dimensions.

According to the evaluation results,the Inga-Nigeria project scores are the highest.This is attributed to the fact that Nigeria has the largest electricity market space and the government is willing to import electricity.In 2016,the peak demand of Nigeria was approximately 6 GW,and a demand of approximately 7 GW was suppressed owing to unavailable power [28].The peak demand was forecasted to reach 26 to 29 GW in 2030,with amarket space of 5 to 8 GW,which could accommodate the import of hydropower from Inga III.The transmission distance between Inga III and Nigeria is approximately 2,000 km across two countries,and a ±800 kV,8 GW UHVDC transmission technology could be applied.The feed-in tariff of Inga III in Nigeria is approximately 4 US cents/kWh,which is much lower than the local tariff of Nigeria.Hence,the tariff is very competitive.

Fig.5 Multidimensional comparison of candidate inter-regional power delivery schemes of Inga III hydropower station

Considering the forthcoming large-scale generation projects,such as the Mambilla hydropower station rated at 3.05 GW,there is still uncertainty about the electricity market space of Nigeria.Given that both the ±660 kV HVDC and±800 kV UHVDC projects are economically competitive,either transmission technology could be selected.

Regarding the Inga-South Africa transmission option,the feed-in tariff for the ±800 kV,8 GW transmission option is approximately 4.3 US cents/kWh,which is much lower than the local tariff of 6 US cents/kWh;the tariff is quite competitive.However,regarding the ±800 kV,5 GW transmission option,the feed-in tariff will exceed 5 US cents/kWh,and the tariff competitiveness will be significantly reduced.Therefore,a UHV transmission with larger capacity is recommended.

The options of Inga-Ghana,Inga-Nigeria-Ghana,and Inga-Lubumbashi-Zambia score relatively similarly,with total scores of approximately 80-85 points.The basic conditions for all these options are in place to achieve the inter-regional power delivery with the Inga III power station.Among them,the Inga-Nigeria-Ghana could deliver Inga III hydropower to both Nigeria and Ghana.Inga-Lubumbashi-Zambia could deliver hydropower to both the southern mines of D.R.Congo and the copper-belt of Zambia.Therefore,these two options have more secure market spaces.

The options of Inga-Guinea and Inga-Ghana-Guinea had relatively low scores mainly owing to the transmission route that passed seven countries in total,making it difficult to coordinate the project with a long transmission distance over 4,000 km.In addition,the economy and infrastructure of Guinea is quite weak.This poses additional difficulties on project implementation.However,the feed-in tariff of Inga III is very competitive compared with the local grid tariff in Guinea.

As an underdeveloped continent,the cross-border energy and power project investment is more complicated compared with projects in more integrated and developed areas,such as Europe.The evaluation of economic and political stability is important for the success of the project;we have tried to quantify this indicator but it is sensitive to numerous unpredictable factors.To make wise investment decisions,the political situation must be monitored closely.Moreover,the investment of the energy and power infrastructure shall be tied up with other industries,such as mining,metallurgy,manufacturing,trade,and others,to guarantee the success of the project [1,4,29,30].

4 Conclusions

The development of the Grand Inga hydropower is of great significance for the industrialization of Africa.The identification of politically,economically,and technically feasible intraregional and inter-regional power delivery schemes is of great importance to facilitate project implementation.Taking into account the potential electricity market and reasonable transmission options,D.R.Congo and surrounding countries will consume approximately 4 to 5 GW of Inga III hydropower.Thus,the remaining 8 GW hydropower of Inga III has to be consumed interregionally.This study proposes a comprehensive evaluation model to assess the feasibility of large-scale,long-distance power delivery schemes in six dimensions,including social economy and the business environment,infrastructure situation,potential for development,electricity market space,transmission-path conditions,as well as tariff competitiveness.The evaluation results of the candidate interregional power delivery schemes of the Inga III hydropower station can assist investment institutions and policy makers in policy making and potential market targeting.

Acknowledgements

This work was supported by National Key Reaearch and Development Program of China (2016YFB0900400).

Declaration of Competing Interest

We declare that we have no conflict of interest.