The state-of-the-arts of the study on grid interconnection between Iberian Peninsula and West Maghreb region

1 Introduction

In the current world, environmental pollution and greenhouse gas emission have become more prominent with the rapid growth of energy consumption. however energy supply of traditional fossil fuels is facing increasing shortage. In this situation, ensuring the safety and sustainable development of energy supply has become an important direction for global energy development research [1].

In March 2007, the EU proposed a resolution on energy and climate integration. Its core content is “20-20-20” campaign. This plan promised to reduce the EU’s greenhouse gas emissions of EU by 20% on the 1990 level by 2020, and set a binding target of increasing the share of renewable energy in total energy consumption to 20%. This campaign also promised to increase energy efficiency by 20%. Driven by the goals of “20-20-20” plan,a lot of European countries have successively formulated policies on reducing carbon emissions and promoting renewable energy development. At the same time, Europe countries have taken extending its scope of energy use to the surrounding areas in account, such as “Mediterranean Solar Plan [2-3]” (MSP) which plans to develop 20GW solar power in South and East of Mediterranean Countries(SEMC) and transfers 5GW to Europe [4].

In support of the MSP, a research project called“MEDGRID” was launched in February 2011 by more than 21 companies, including the transmission operators, power companies, technology companies and investors which in Europe and the eastern and southern Mediterranean.The aim is to analyze the feasibility of building a trans-Mediterranean Europe-Africa interconnected power grid which ensures the power transmission between Europe and Africa promoted by MSP. The project also hopes to mobilize the enthusiasm of countries which in the northern,southern and eastern Mediterranean for developing renewable energy sources. The project was completed in May 2014 and proposed a series of solutions for the trans-Mediterranean Europe-Africa power grid interconnection.These findings have been reflected in some European planning project research such as the completed EU project“e-Highway 2050”, as well as the ongoing EU project MEDTSO project.

According to the research results of the MEDGRID project, due to the limit of the depth of trenches and the topography in the Mediterranean Sea [5] (topographic map of the Mediterranean trench is shown in Fig. 1), the possible routes which can achieve interconnection of Mediterranean power grids are in the area between Morocco, Algeria and Portugal, Spain, in the area between eastern Algeria,Tunisia and the Italian islands shallow sea region. Therefore,the project proposes a scheme interconnecting the northsouth power grid in the Mediterranean region, which has three corridor routes including the eastern, central and western routes shown in Fig. 2.

Western corridor： maritime and land paths from Algeria and Morocco, via Portugal and Spain to central Europe(namely France) by the Pyrenees interconnections.

Center corridor： maritime and land routes from Algeria and Tunisia, via Italy (possibly via Sicily, Corsica or Sardinia) to central Europe through the northern Italy interconnections.

Fig. 1 Topographic map of the Mediterranean trench

Fig. 2 The interconnection of MEDGRID

East corridor： terrestrial routes from Libya to Europe,via Egypt, Jordan, Syria and Turkey (and Lebanon,Palestine and Israel). There are also some alternative paths through Cyprus. However, these alternatives need further studies to assess the impact of the current geopolitics at these areas.

The Iberian Peninsula described in this article is mainly targeted at Portugal and Spain. The West Maghreb is mainly targeted at Morocco and Algeria. The power grid interconnection plan mainly refers to the western route mentioned above. At present, in the Western corridor program, Morocco and Spain have synchronized interconnection through two 400kV AC lines and jointly participated in the EU electricity market transactions.This paper researches on the electricity development in the Iberian Peninsula and the West Maghreb, analyzes the current status and future trends of power grid interconnection in these two regions, and introduces the MEDGRID project in the Iberian Peninsula and the Western Maghreb grid interconnection program, and then identifies the technical problems needed to be solved in the next stage.

2 Iberian Peninsula power grid development

2.1 General situation

The Iberian Peninsula includes Spain, Portugal,Andorra and the British Gibraltar. Most of the territory belongs to Spain, a small part of the southwest corner of the territory belongs to Portugal. This article focuses on the grid situation in Portugal and Spain.

Portugal is located in the southwest Iberian Peninsula,and the southwest is near the Atlantic Ocean. Portugal has an area of 92,000 square kilometers with a total population of about 10 million. In 2015, Portugal’s GDP totaled$1989.23 billion and its per capita GDP was $19,222. It is a medium-sized developed country in the EU with weak industrial base. Textile, wine-making and tourism industries are the pillar industries of the national economy. By the end of 2015, the national power generation was 49TWh and annual maximum load was 8.6GW.

Spain occupies most area of the Iberian Peninsula. It has an area of 506,000 square kilometers and a population of about 46 million. In 2013, Spain’s GDP totaled $1,398.63 billion and its per capita GDP was $30,147. It is a mediumdeveloped capitalist industrialized country with a total economic output ranking the fifth in the EU. By of the end of 2015, the national power generation was 254TWh and annual maximum load was 41GW.

2.2 Power source structure

2.2.1 Portugal power source status

From the beginning of the 21st century, under the guidance of EU related environmental protection targets and Portuguese supporting laws and regulations, renewable energy has been rapidly developed in Portugal. The Portuguese power generation system has been developing steadily towards a carbon-free hybrid power generation system. By of the end of 2015, the total installed capacity of Portugal’s power grid was 18,533MW and the installed capacity of renewable energy was 11,014MW, accounting for 64.8% of the total installed capacity. Table 1 shows the specific installed power resource capacity.

Table 1 Power source capacity in Portugal by 2015

Generation type Power capacity（MW）Power generation（GWh）Hydropower 6146 9613 Wind power 4826 11334 Thermal power(Biomass, Waste) 613 2633 PV 429 755 Coal 1756 13677 Gas 4698 9810 Other non-renewable 65 343 Total 18533 48165

2.2.2 Spain power resource status

In Spain, the installed power generation mainly consists of combined cycle units, thermal power and hydropower.By of the end of 2015, the total installed capacity of Spain's power grid was 101027.17MW, with wind power accounting for 22.6%, solar power accounting for 6.7%and hydropower accounting for 20.1%. Table 2 shows the specific installed power generation capacity.

Table 2 Power source capacity in Spain by 2015

Genaration type Genratoin capacity(MW)Power generation(GWh)Hydropower 20351.72 30815 Nuclear 7572.58 54755 Coal 10468.02 50924 Combined cycle 24947.71 25334 Wind power 22864.24 47707 PV 4420.39 7839 CSP 2299.527 5085 Other renewable energy 741.69 4615 Cogeneration 6683.89 25076 Waste 677.41 1886 Total 101027.17 254036

2.2.3 Iberian Peninsula power development

According to the relative organization forecasting, the installed power generation capacity of Iberian Peninsula in 2030 [6] is shown in Table 3.

Table 3 The prediction of installed capacity of Iberian Peninsula in 2030

Power capacity（MW） Portugal Spain Thermal power（Coal） 568 9335 Thermal power（Gas） 4746 33914 Thermal power（Oil） 996 3513 Nuclear 0 6982 Hydropower 4738 15073 CSP 613 10000 PV 5000 6945 Onshore wind power 8000 30000 Offshore wind power 324 5707 Other 1431 1836 Total 26416 123305

2.3 Load demand

The load centers in Portugal are mainly located in the northern part of Porto, central Lisbon and Setubal, and the southern Algarve. The central region accounts for the largest share about one third of the national load. In addition, Portugal and Spain send power to each other through nine tie-in lines to ensure system power balance during load peak and valley season, when wind and solar power is fluctuating. In 2015, the maximum load of the power grid in January was about 8,620MW, which is 790MW higher than the maximum load in 2010.

The power load of Spain is mainly concentrated in the central Madrid region and the eastern Barcelona region,mainly in industrial and commercial services, residential electricity consumption, and accounting for more than 90%of total electricity consumption. The maximum load in 2015 was 40,726 MW.

2.4 Power grid structure and interconnection

The backbone network of Iberian Peninsula power grid consists of 400kV and 220kV lines. The total length of the transmission line in Portugal is about 8800km. The length of 400kV line is about 2600km and the length of 220kV line is about 3600km in Portugal. The length of transmission line in Spain is 42986km, including 21179km for 400kV line and 21807km for line of 220kV and below.

Spain and Portugal are interconnected by 6 circuits of 400 kV and 3 circuits of 220 kV. The exchange power is 2200-2800 MW, interlinked with Morocco via 2 lines of 400kV, and 2 lines of 220kV AC and 2 lines of ±320kV DC are interconnected with France. Iberian Peninsula power grid structure is shown in Fig. 3.

Fig. 3 Power grid structure of Iberian Peninsula[7]

3 West Maghreb power grid development

3.1 General situation

The Maghreb region is in the combination area of Africa and Europe which is the throat that connects the Mediterranean and the Atlantic with an important geostrategic position. Morocco’s economic strength ranks fifth in Africa. Its main industries are the food industry sector, the chemical industry and the mining industry. Among them, phosphate reserves rank first in the world and are the main source of GDP. Morocco lacks energy resources, especially oil and gas. As the economy continuously growing, energy issues become increasingly prominent. Algeria is located between Morocco and Tunisia. It has rich oil and natural gas resources that are the economic pillar of Algeria, accounting for about 60% of the total income. Its agricultural development lags behind and some daily necessities and food crops need to be imported.

3.2 Power structure

3.2.1 Power resource development status

Table 4 Power source capacity in northwest power grid in 2012

Installed capacity（MW） Algeria Morocco Hydropower 228 1770 Thermal power（Oil） 297 202 Thermal power（Combined cycle） 3252 850 Thermal power（Gas） 6686 1215 Thermal power（Steam） 2487 600 Thermal power（Coal） 0 1785 Wind power 0 255 Total 12950 6677

The power generation of Morocco consists of hydropower, thermal power and a small amount of wind power. The electricity production is run unified by the Moroccan Power Group (ONE). The power generation of Algeria consists of hydropower and thermal power. Table 4 shows the current status of power capacity in the Western Maghreb region in 2012.

3.2.2 Power development trend

Morocco and Algeria are located in North Africa,where have abundant solar and wind energy resources [8].The renewable energy resources in this region are shown in Table 5, which has a great development potentiality in the future.

Table 5 Renewable energy resources in the Western Maghreb region

Index Morocco Algeria Light area (km2) 1400 6000 Wind area (km2) 2500 2800 Wind speed (m/s) 4.6-6.5 5.1-6.2 GHI(W/m2) 1950-2150 1800-2150 DNI(W/m2) 2250-2600 2300-2350

It is estimated that by 2030 Morocco will have a total installed power generation capacity of 23,391MW, of which renewable energy will account for 43.6%. Algeria will have a total installed capacity of 30,975MW, of which 38.7% is renewable energy. The forecast of installed power generation capacity in the West Maghreb in 2030 [6] is shown in Table 6.

Table 6 The prediction of installed power generation capacity of West Maghreb in 2030

Installed capacity（MW） Algeria Morocco Thermal power(Oil) 405 446 Thermal power(Gas) 18150 9000 Thermal power(Coal) 0 1745 Hydropower 418 2000 Renewable energy 12002 10200 Total 30975 23391

3.3 Load forecasting

According to the analysis of the historical electricity consumption data in the Western Maghreb region as well as Arabian Union data, the forecasting data of load and electricity of the Western Maghreb region in mid-2020 and forward-2030 are given [6], which is shown in Table 7.

Table 7 Load forecasting in Western Maghreb region from 2020 to 2030

Algeria Morocco 2020 2025 2030 2020 2025 2030 Generation consumption /TWh 120.4 176.9 243.5 52.2 70.5 95 Load/GW 23.5 34.5 47.5 8.7 11.8 15.9 Utilization /h 5127 5123 5126 5986 5989 5994

3.4 Power grid structure and interconnection

In the process of regional integration, the power grid interconnection has been basically completed in the West Maghreb region, laying a good foundation for establishing a renewable energy power market in the future. The voltage level of power grid in the Western Maghreb region is mainly rated at 400kV and 220kV. The Moroccan power grid is formed along the Atlantic coast. The north transmission network covers the entire country. The total transmission line length is about 22,209 km. The total transmission line length of the Algerian power grid is up to 23,802km. Fig. 4 shows the structure of the West Maghreb grid.

Morocco interconnects with Spain via two 400kV submarine cables with a link capacity of 1,400 MW.Morocco and Algeria are interconnected via a single 400kV line and two 220kV lines with a tie line capacity of 1,500MW. The electricity supply of Morocco is mainly imported from Spain.

Fig. 4 The Western Maghreb grid structure [7]

In addition, Algeria is also connected to Tunisia via two 90kV, one 220kV, and one 150kV AC lines, while the interconnection project with Spain is still under study.Algerian power grid basically can maintain the power balance by itself.

The current status of interconnection between the Western Maghreb Region and the Iberian Peninsula is shown in Table 8.

Table 8 The present interconnection between the Western Maghreb and the Iberian Peninsula

Interconnected countries Tie line capacity /MW Voltage level / kV Status Spain - Algeria 2000 500 DC Unfinished Morocco - Spain I 700 400 AC Completed Morocco - Spain II 700 400 AC Completed Morocco - Algeria 1400 400 Completed

4 Future networking programs

4.1 Driving force for power grid interconnection

4.1.1 MSP

Mediterranean countries have great potential in development of solar energy, especially in the desert regions of North Africa and the Middle East, with long sunshine periods. These regions have abundant solar energy resources and unique conditions for the development of renewable energy such as solar energy.

MSP is an important part of energy cooperation between EU and Mediterranean countries and involves 43 countries including EU countries. This program will require 38 billion to 46 billion euros in investment in the next 20 years and will develop 20 GW of power generated by solar energy in southeastern Mediterranean countries,of which 5GW capacity will be sent to Europe. There are several challenges during developing solar energy： first,the high cost; second is to establish a stable and resourcesharing system conducive to investment; third is to remove the legal barriers to the development of solar energy; fourth is to construct infrastructures and the Mediterranean North-South grid interconnection [9].

4.1.2 Resource sharing

The power grid interconnection between the Iberian Peninsula and the West Maghreb is determined by the complementarity of energy supply and demand in these two regions.

Renewable energy sources in Portugal and Spain are abundant. About 60% to 70% of Portugal's electricity comes from renewable sources. The installed capacity of wind power in Spain accounts for more than 22%. In 2016, Portugal set a record that the power supply of the whole country was supplied by renewable energy for four consecutive days. However, due to the scale of the power grid, a large number of PV resources exploited in the Iberian Peninsula are idle. However, the installed capacity of photovoltaic power generation in the Portuguese power grid is only 450MW currently.

On the other hand, although the MSP depicts a huge development space for renewable energy in the Western Maghreb region, its electricity shortage is still a big problem in the short term. At present, about 20% of Morocco’s electricity supply is from Spain.

Therefore, the power grid interconnection can realize the sharing of power resources on both sides, promote the development of solar photovoltaic power generation in Portugal, and solve the electricity supply problem in Morocco.

4.1.3 Power trading diversification

The power grid interconnection not only realizes the power transmission but also promotes the formation of the electricity trading market of both parties in the network that ensures the security and sustainability of the energy supply.For example, one day in 2015, the Portuguese power grid is short of 3,000 MW of power within 12 hours. Due to Spain’s emergency power support, Portugal grid can be survived in such a sudden power loss. Another example, in May 2016, the Portugal’s surplus electricity was delivered to Spain via electricity transmission.

Due to the benefits of power grid interconnection,these countries are even more urgent to strengthen power grid interconnection, especially the connection between Portugal and Morocco. Both Morocco and Portugal hope that interconnection benefits will be directly accessed through the interconnection and the power transactions is with diversified characteristics a. if this interconnection projects is built, the Morocco’s dependence on electricity transactions between Spain and Algeria will be reduced,and the safety of energy supply of Morocco will be increased.

4.2 Key technical issues on power grid interconnection

4.2.1 Transmission line capacity Through the comparison on the power source capacity of Morocco in 2012 and 2030, it can be seen that capacity of gas-fired thermal power plants and renewable energy will be raised almost 10 times. However, Morocco is short of gas and oil, and this problems will become more outstanding especially as the economic growth. It is assumed that the power resource will be a half slowdown,and the conservative installed capacity of Morocco will be 15822.5MW in 2030. According to the power demand prediction, the load in Morocco in 2030 is 15.9GW.Considering the reserve capacity, the power capacity is short of 1 or 2GW in Morocco.

On the other side, according to the e-Highway 2050 research work, there is an enormous power shortfall in the part areas of Portugal, Spain, and France under the renewable energy concentrated development strategy. The electricity demand shortage in Spain will be 4.5TWh.

In conclusion, it maybe in recent years the power will be sent from the Iberian Peninsula to West Maghreb Region. In the future, the power will be sent from the West Maghreb Region to Iberian Peninsula as the development of the solar power in North Africa. A new power transmission line will be established, and its capacity is mainly focused on the following two options [10]：

a. West Maghreb delivered 1,000 MW to the Iberian Peninsula, vice versa;

b. West Maghreb delivered 2,000 MW to the Iberian Peninsula, vice versa.

4.2.2 Power transmission technology

In order to satisfy the interconnection of large-scale power grids and the large-scale centralized development of renewable energy sources it may also bring new changes and problems for the system operation, such as frequently reversal power flow. In addition, with the rapid development of power electronics technology and modern control technology, the light HVDC technology based on VSC inverter is growing rapidly [11]. Besides, submarine cables have enabled the interconnection lines to reach a depth of 1,650 meters across the sea floor, exceeding the depth limit of 1,500 meters for Portugal and Moroccan interconnection.

There are several ways to achieve the above interconnection transmission capacity, as following：

a. Using existing or new AC cable;

b. Transforming part of the existing lines into conventional or light HVDC transmission systems;

c. Constructing a new conventional or light HVDC transmission system.

4.2.3 Identify the best interconnection terminals

It is important to determine the best nodes to place the terminals of an interconnection projects. Hence, to the calculating of the limits of nodal injections in a power system is become very necessary

4.2.4 Internal reinforcements

According to the transmission capacity and terminals of the power grid interconnection the project may need to take into consideration the reinforcement plan including the Spanish grid, the Portuguese grid and the Spain-French tie line respectively, which will not be described in detail in this article.

4.3 Interconnection program

Fig. 5 Sketch map of the Iberian Peninsula-West Maghreb interconnection scheme

According to the research results of the MEDGRID project, the paths of interconnection between the Iberian Peninsula and the West Maghreb region are shown in Fig. 5.

Table 9 shows the power grid interconnection solutions in detail between the Iberian Peninsula and the West Maghreb region proposed by the MEDGRID project.

Table 9 Interconnection scheme and economic comparison

No.Capacity(MW) Technical solutions Investment cost(Million Euros)1 Morocco-Spain Use the current 2×700MW AC lines 930 2 1000 Morocco-Spain Construct 1×700MW 400kV AC line 1070 3 Morocco-Spain Construct a single line at ±350kV VSC-HVDC to transfer 1GW 1130

Continue

No.Capacity(MW) Technical solutions Investment cost(Million Euros)4 Morocco-Portugal Construct a single line at ± 500kV VSC-HVDC to transfer 1GW 1386 1000 5 Algeria-Spain Construct a single line at ± 500kV VSC-HVDC to transfer 1GW 1259 6 Morocco - Spain Construct 1×700MW AC additional line 2165～2320 7 Morocco - Spain Convert current 2×700MW AC into 1×700MW AC and 2GW HVDC bipolar link 2310～2465 8 Morocco - Spain Construct a single line at 350kV bipolar HVDC 2215～2370 9 Morocco - Spain Convert current 2×700MW AC into 3000MW VSC-HVDC 2480～2635 10 2435～2590 2000 Morocco - Spain Use current 2×700MW AC Morocco-Portugal Construct 1GW HVDC link 11 Morocco - Spain Construct 1×700MW AC additional line 2×700MW AC Morocco - Spain Construct 1GW HVDC link 2600～2755 12 Morocco- Spain Use current 2×700MW AC Algeria-Spain construct 1GW HVDC link 2245 13 Morocco - Spain Construct 1×700MW AC additional line 2×700MW AC Algeria-Spain Construct 1GW HVDC link 2400

The Moroccan-Spain interconnection can adopt the following solutions as seen in Table 9：

a. AC line 400kV;

b. 1GW HVDC LCC 400kV or 500kV;

c. 1GW or 2GW HVDC VSC 350kV

Morocco-Portugal interconnection solutions：

a. 1GW HVDC LCC 500kV;

b. 1GW HVDC VSC 400kV or 500kV

Algeria-Spain interconnection solutions：

a. 1GW HVDC LCC 500kV;

b. 1GW HVDC VSC 400kV or 500kV

4.4 Research direction for the next stage

This article describes the 13 kinds of interconnection programs that can be summarized as Morocco-Portugal,Morocco-Spain and Algeria-Spain interconnection project.The time of project construction depends on the power resource construction and the motivation of the relevant countries’ government. The following aspects need further research in the next step.

1) The optimization for the layout of the interconnection terminal points and the solutions of internal reinforcements;

2) The unified power trading mechanism;

3) The control strategy to ensure the safety and stability of the interconnection power grids.

5 Conclusions

The Power grid interconnection between the Iberian Peninsula and the Western Maghreb region is one of the key steps in supporting the MSP and also one of the means to ensure the sharing of electricity resources on both sides.

According to the research results of the MEDGRID project, the main interconnected routes connecting the Iberian Peninsula and the Western Maghreb include Morocco-Portugal, Morocco-Spain and Algeria-Spain.On the one hand, it can be retrofitted on the basis of the original networked lines. On the other hand, a new AC or DC submarine transmission system can be taken into account.

Based on the proposed power grid interconnection plans of some projects, it is recommended that further research should focus on the optimization of terminals of sides,the solution of internal reinforcement, the mechanism of market trading, and the safety and stability of operation.