Evolution Opportunitie and Critical Issues for Pan European Transmission

40 ieee power & energy magazine march/april 20141540-7977/14/$31.002014IEEE

Digital Object Identifier 10.1109/MPE.2013.2294813

Date of publication: 19 February 2014

SSeveral initiativeS have been launched in the laSt decade in the european union (eu) to align pan-european power grid development with the eus policy targets, particularly in the energy and climate change fields. the building of new infrastructures, initially driven mainly by the need for increased cross-border trading and integration of the wholesale electricity markets, is nowadays also strongly supported by the demand for integrating diversified, low-carbon energy sources (e.g., renewable wind and solar sources).

the shape of the power grid in the medium- to long-term future (to 2050) depends greatly on different potential scenarios for the following items: renewable energy deploy-ment (primarily in terms of technologies, performance, and geographical siting); exten-sion of the european electricity network toward neighboring power grids (e.g. those of northern africa, the Middle east, and russia); and the penetration of distributed energy sources that require the development of a smarter power system, especially at lower volt-age levels. these factors, by defining preferential patterns for cross-european and inter-continental power flows, will outline the critical structural and operational needs of the european power grid of the future.

this article discusses the emerging challenges facing the european transmission grid as it contributes to meeting the eus energy and climate change policy goals. We

Its a Bird, Its a Plane, Its a Supergrid!

Evolution, Opportunities, and Critical Issues for Pan-European Transmission

By Ettore Bompard, Gianluca Fulli, Mircea Ardelean, and Marcelo Masera

march/april 2014 ieee power & energy magazine 41

Digital Object Identifier 10.1109/MPE.2013.2294813

Date of publication: 19 February 2014

Transmission: isTockphoTo.com/kharlamova Bird & plane: image licensed By ingram puBlishing

42 ieee power & energy magazine march/april 2014

focus on the european ultra-high-voltage system, which is already considered to be a smart system but is expected to evolve toward architectures offering higher transfer capaci-ties (a so-called supergrid). We address the challenges of making power distribution systems smarter only insofar as transmission-distribution interfaces are concerned, in the course of illustrating the tensions and complementarities within the smart grid and supergrid concepts.

in this light, the article presents the main policy objec-tives and visions for electricity in the european union, key figures and trends relating to the european energy and electricity systems in a worldwide context, and technologi-cal options and design challenges for the pan-european transmission grid. the article ends by summarizing various needs and potential solutions for the eu transmission grid in view of its long-term evolution.

EU Policy Objectives and Vision for Electricity the eus energy and climate change policies aim to concur-rently confront challenges related to:

security of energy supply (by ensuring a reliable and uninterrupted supply of energy and electricity)

competitiveness as electricity markets are restruc-tured (by reducing the energy bill for households and businesses and maximizing market efficiency)

sustainability (by limiting the environmental impact of energy production, transport, and use).

in 2009, the third internal energy market package was one of the major eu policy initiatives. it was aimed at accel-erating infrastructure investments, with the goal of ensur-ing the proper functioning of the eu electricity market. the europe 2020 growth strategywith its so-called 20/20/20 agendais the current starting point for europes energy and climate change policies. it aims to reduce cO2 emis-sions by 20% compared with 1990 levels, raise the share of renewable sources in the overall eu energy mix to 20%, and increase energy efficiency by 20%.

as far as energy grid development is specifically con-cerned, the medium-term policy was first outlined in the eus communication on energy infrastructure priorities for 2020 and beyond and then detailed in the guidelines for trans-european energy networks (ten-e), which identified three eu infrastructure priority areas (electricity highways, smart grids, and cO2 networks) and nine infrastructure pri-ority corridors (on electricity, gas, and oil).

as a first step in the implementation of ten-e, the euro-pean commission (ec) adopted a list of projects of common interest (Pcis) in electricity, gas, and oil infrastructure. the guidelines provide a new way to identify infrastructure proj-ects of common interest and to accelerate their implementa-tion through enhanced regional cooperation, streamlined permit-granting procedures, adequate regulatory treatment, and through european financial assistance under the proposed connecting europe Facility. the list of Pcis is to be reviewed

on a regular basis so as to implement the long-term vision of pan-european market integration and a low-carbon transition.

as for the longer-term perspective, the ec has issued the energy roadmap 2050, which outlines scenarios lead-ing up to 2050 and following a path toward a low-carbon economy, assuming a greenhouse gas emissions reduction target of at least 80%. all of the scenarios share the follow-ing key elements:

the share of renewables in energy will grow, covering more than 40% of gross final energy consumption in 2050, compared with the 20% expected in 2020.

energy savings will be crucial, with a 3241% reduc-tion in energy demand by 2050, compared with the 20052006 peaks.

the share of electricity in final uses will increase from 22% in 2009 to 37% in 2050.

capital investments in infrastructure assets will increase, and the fossil fuel bill will decrease.

decentralized power, i.e., power generation connected to medium- and low-voltage distribution systems, will grow, accounting for up to 35% of total generation capacity by 2050.

European Energy: Figures and Trendsthe final uses of energy in the eu and some other key areas in 2009 are reported in table 1. europe accounts for 14% of the final uses of energy in the world, almost the same level as china and the united States (17%). electricity represents 20% of the final uses of energy in the eu, basically the same as in the united States.

in 2009, the total eu energy consumption for final uses was covered mainly by oil and oil products (44%), gas (22%), and electricity (20%). this mix varies widely across countries and over time depending on the availability of resources, national policies and regulations, decarbonization requirements, and internal market developments. in turn, the production of electricity in the eu in 2010 was based mostly on traditional fuels (more than 50%), while nuclear produc-tion was still remarkable (27%) and renewables accounted for 21%, according to eurostat.

the general eu energy scenario has been character-ized by an increase over the last two decades in oil and gas imports, which are set to exceed 80% of the total oil and gas consumption by 2030. in contrast, other major countries like the united States are well on their way to becoming net gas exporters, thanks to the shale gas production boom. this is anticipated to widen the gap between eu and u.S. energy and electricity prices and at the same time increase the use of coal in europe for electricity production. eu coal imports increased by some 10% in 2012 relative to 2011. it is expected in some optimistic scenarios that indigenous unconventional gas could replace declining conventional production, reducing import dependence to the 60% level. rising global demand for energy resources may directly affect europe. in 2012, eu imports of liquefied natural gas (lnG) dropped by 30% with


respect to 2011 because Japan and Korea attracted more lnG with higher buying prices. the international energy agency (iea) anticipates global energy demand growth of about 35% over the period leading up to 2035, with china, india, and the Middle east accounting for 60% of the increase.

Gas and electricity bills for consumers account for a growing share of household expenditures, ranging from 7% to 17% across the eu member states. nevertheless, over the last decade, while prices for crude oil, gas, and coal have increased annually by 14%, 10%, and 8%, respectively, the average eu wholesale electricity price has risen by less than 4%. the moderate increase in electricity pricesas compared with the steeper growth of fossil fuel pricesis attributable to the ongoing introduction of competition in the electricity sec-tor. the electricity prices for residential customers (consumers of 2,5005,000 kWh annually) are not homogeneous in the eu member states; they range from 0.10/kWh to 0.30/kWh.

along with this relatively high level of prices there is an aging and not always adequate generation and transmission infrastructure. the european electricity transmission infra-structure is composed of seven major synchronous subsys-tems, as shown in table 2. the european electricity sector has been evolving from a regulated structure dominated by vertically integrated utilities to an unbundled and liberal-ized system organized into various regional markets. in each european country, one or more transmission system opera-tors (tSOs) are responsible for operating, maintaining, and developing the power grid.

the european network of transmission System Opera-tors for electricity (entSO-e) was founded in 2008 and is made up of 41 tSOs from 34 european countries, as laid down in the ecs third electricity and gas liberalization pack-age. entSO-e incorporates the former european transmis-sion System Operators association (etSO) and five tSO

organizations (atSOi, baltSO, nOrdel, ucte, and uKtSOa). entSO-es mission is to promote cooperation among tSOs on important aspects of energy policy relating to security, adequacy, market needs, and sustainability.

a geographic overview with some key figures on the dif-ferent synchronous systems in europe is given in Figure 1, draw-ing on the information reported in entSO-e documents and a ucte-iPS/uPS study for the synchronous interconnection of the european continental grid with the power systems of the commonwealth of independent States. the electricity networks of cyprus and Malta are independent and presently not connected to the continental system.

the security of supply, sustainability, and competitive-ness goals of the eu energy policies, driven by new trends including increased distributed generation penetration, mas-sive deployment of renewable sources, and decarboniza-tion targets, are expected to greatly affect the design and operation of european electricity networks. in particular, the target of a 20% share of renewable energy in final eu energy consumption corresponds to a 35% share of renew-able energy sources in electricity consumption by 2020 (compared with only 21% in 2010).

it has been estimated that the total investment required in the eu in energy generation, transmission, and distribution infrastructure through 2020 is on the order of 1 trillion. this investment should ensure greater diversification of energy sources, cleaner energies, and competitive prices within an integrated energy market. as far as the power transmission grid is concerned, the new investment needed (including stor-age facilities) is foreseen to amount to about 200 billion through 2020. On the generation side, almost a fifth of the eus total coal capacity is to be retired in the period leading up to 2020. due to low energy demand and increasing renewable electricity production, some 65 GW of gas and coal power

table 1. The final uses of energy in 2009. (Source: IEA, 2009 with completions.)

Consumption by Source

EU-27 United States China Russia Rest of the World World

Mtoe % %W Mtoe % %W Mtoe % %W Mtoe % %W Mtoe % %W Mtoe %

Solid fuels/coal and peat

36 3.1 4.3 23 1.6 2.8 517 36.1 62.1 18 4.3 2.2 238 6.1 28.6 832 10

Petroleum and products

505 43.7 14.6 740 50.6 21.4 336 23.5 9.7 106 25.1 3.1 1,775 45.7 51.3 3,462 41.5

Gases 258 22.3 20.4 312 21.3 24.6 50 3.5 3.9 128 30.3 10.1 518 13.3 40.9 1,266 15.2

Geothermal, solar, etc.

2 0.2 11.1 2 0.1 11.1 9 0.6 50 0 0 0 5 0.1 27.8 18 0.2

Biofuels and waste

71 6.1 6.6 65 4.4 6 202 14.1 18.7 2 0.5 0.2 740 19.1 68.5 1,080 12.9

Electricity 234 20.3 16.2 313 21.4 21.7 263 18.4 18.3 60 14.2 4.2 571 14.7 39.6 1,441 17.3

Heat 49 4.2 19.4 7 0.5 2.8 55 3.8 21.7 108 25.6 42.7 34 0.9 13.4 253 3

Total 1,155 100 13.8 1,462 100 17.5 1,432 100 17.1 422 100 5.1 3,881 100 46.5 8,352 100

NOTE: %W = % from world.


tab

le 2

. Po

wer

tra

nsm

issi

on

sys

tem

s in

Eu

rop

e.

Subs

yste

mR

egio

n,

Cou

ntri

esEU

TSO

sN

o. o

f B

uses

1Li

nes

(no.

)1Li

nes

(km

)Po

pula

tion

(m

il.)

Are

a (t

h.

km2 )

Peak

Po

wer

(G

W)

Con

sum

ptio

n (T

Wh)

Inst

alle

d C

apac

ity

(GW

)

Inte

rcon

nect

ed

to

1U

CTE

: APG

, VU

EN, N

OS

BiH

, Elia

, ES

O, S

wis

sgrid

, Cyp

rus

TSO

, CEP

S,

Tran

snet

BW, T

enne

T G

ER, A

mpr

ion,

50

Her

tz, E

nerg

inet

.dk,

Ele

ring

AS,

R

EE, F

ingr

id, R

TE, N

atio

nal G

rid,

SON

I, SH

ETL,

SPT

rans

mis

sion

, IP

TO, H

EPO

PS, M

SVIR

ZR

t, Ei

rGrid

, La

ndsn

et, T

erna

, Litg

rid, C

reos

Lu

zem

bour

g, A

ugst

sprie

gum

a tk

ls,

Crn

ogor

ski e

lekt

ropr

enos

ni s

iste

m,

MEP

SO, T

enne

T N

L, S

tatn

ett,

PSE

S.A

., R

EN, T

rans

elec

tric

a, E

MS,

SV

ENSK

A K

RA

FTN

T,

ELE

S SE

PS

Con

tinen

tal

Euro

pe, W

est

Den

mar

k

Yes

417,

306

222,

402

374,

053

434.

93,

294.

238

72,

600

671

NO

RD

EL

UK

TSO

A

IPS/

UPS

Not

in

oper

atio

n

TEIA

S

Mag

hreb

Wes

tern

U

krai

ne

2N

OR

DEL

: Ene

rgin

et.d

k, F

ING

RID

, ST

ATN

ETT,

SV

K; L

ands

net (

Icel

and)

ob

serv

er

Finl

and,

Nor

way

, Sw

eden

, Eas

t D

enm

ark,

Icel

and

Yes

578

436

,532

44,3

4022

.71,

206.

261

412

97BA

LTSO

UC

TE

IPS/

UPS

3BA

LTSO

: AT,

ELE

RIN

G, L

ITG

RID

Esto

nia,

Lat

via,

Li

thua

nia

Yes

379

5,47

717

,147

6.4

17.5

4.5

2610

NO

RD

EL

IPS/

UPS

4A

TSO

I: EI

RGR

I, SO

NI

Irela

nd, N

orth

en

Irela

ndYe

s2

562,

687

8,81

96.

484

.46.

535

.49.

7U

KTS

OA

5U

KTS

OA

: NG

ET, S

HET

L, S

PTR

AN

Engl

and,

Wal

es,

Scot

land

Yes

31,

743

28,8

2736

,170

63.2

229.

853

.536

575

ATS

OI

UC

TE

6IP

S/U

PS: E

CO

Cen

ter,

ECO

Sou

th,

ECO

Nor

th-W

est,

ECO

Mid

dle

Vol

ga,

ECO

Ura

ls, E

CO

Sib

eria

, Ukr

ener

ego,

B

elen

ergo

, Mol

dele

ctric

a, G

SE a

nd

Sakr

usen

ergo

, Aze

rene

rgy,

KEG

OC

, B

arki

, Toj

ik, E

lect

riche

skie

Sta

ncii,

M

ongo

lian

Cen

tral

Ene

rgy

Syst

em

Russ

ia, U

krai

ne,

Bel

arus

, M

oldo

va,

Geo

rgia

, A

zerb

aija

n,

Kaz

akhs

tan,

Ta

jikis

tan,

Ky

rgyz

stan

, M

ongo

lia

No

152

,000

165

,000

1,6

0024

8.4

2,26

67.4

210

1,26

032

7BA

LTSO

Sync

hron

ous

UC

TE

Not

in

oper

atio

n

NO

RD

EL

7TE

IAS:

TEI

AS

Turk

eyN

o1

707

40,8

261,

022

75.6

783.

536

230

53U

CTE

1 Onl

y bu

ses

13

2 kV

.


plant projects have been postponed or cancelled in the last three years. it is also worth noting that european investment in renewable energy sources dropped in the first quarter of 2013 by 25% (with respect to the same period of the previous year), with an almost complete halt in countries like France, italy, and Spain.

The Pan-European Transmission Grid: Options and Challengesamong the main challenges faced in the design and develop-ment of the evolving european transmission system, one can highlight the following:

Public acceptance and permitting: the bulk power system expansion is curbed by environmental and social issues. Social acceptance of electricity infra-structures is always a concern, as the resistance of local authorities and/or public opinion to new lines is persis-tently high. the time required to get permits for grid facilities is generally much longer than the time needed to build new power plants. One in three planned invest-ments by entSO-e faces delays in implementation due to long permitting processes, and some sections of new overhead lines have had to be replaced with under-ground cables. in Germany, as of mid-2012, only 214 km of 1,834 km of urgent transmission grid expansion projects were completed. to overcome these delays, the new ten-e guidelines include binding time limits for the permit process, the establishment of a national one-stop shop for permit granting, and a streamlined public consultation.

Renewable energy inte-gration, unplanned flows, and capacity markets: the ongoing liberalization pro-cess and the massive deploy-ment of renewable energy sources (reSs)which was not coupled with adequate or timely grid developmenthave led to increasing or unplanned interarea power exchanges through cross-border interconnectors. a high share of renewable energy in the electricity mix also raises the question of the adequacy of generation capacities and grids. this has a direct impact on the costs of ensuring security of supply (in terms of remedial

actions) and the interconnection capacity available for cross- border trade. according to entSO-e scenarios for 2020, 80% of the bottlenecks are related to reS integration, either because direct connection of reSs is at stake or because the network section or corridor is a keyhole between reSs and load centers. in addi-tion, entSO-e market studies show larger, more vola-tile power flows over larger distances across europe. investment on the grid is needed to avoid the worsen-ing of present congestion and new congestion. Other signs of the need to adjust market rules come from the increasing number of frequency deviations caused by short-term mismatches between power consumption and power generation experienced in the european synchronous regions. Several measures to cope with these issues have been proposed or deployed, including enhanced coordination among tSOs, innovative con-trol devices, investing in cross-border infrastructure, demand response measures, storage, and paying for the availability of generation capacityoften based on fos-sil fuelsat the national level. the latter solution, how-ever, is currently stirring up the ecs concerns about the risks associated with market inefficiencies.

Technological options and coordinated operation of intelligent devices: advanced technologies other

figure 1. The power transmission systems in Europe and beyond.

Power TransmissionSystems in the EU

UCTENORDELBALTSOATSOIUKTSOAIPS/UPSTEIAS

HVdc CableHVac CableHVdc B2BInterconnections


than conventional high-voltage ac (hvac) infrastructure are being deployed more and more at the transmission level. high-voltage dc (hvdc) lines, already mature for long-distance and undersea applications, have now been included in several on- and offshore transmission grid projects, particularly the voltage source converter (vSc)-based hvdc system, which offers greater flexibility of operation and easier expandability to multiterminal con-figurations. Phase-shifting transformers (PSts) and flex-ible ac transmission systems (FactS) devices, thanks to their ability to offer targeted active and/or reactive power control, are being deployed to reduce unplanned flows. new types of conductors, such as gas-insulated lines (Gils) and high-temperature superconducting (htS) wires, so far installed mainly in pilot projects, promise to increase transfer capacities. and a host of information and communication technology (ict) solutions are being adopted to increase the adequacy and robustness of the system, augmenting its monitoring capabilities and con-trollability (e.g., wide-area monitoring and control sys-tems that let operators optimize the power flows across very large systems thanks to satellite-based measurements and dynamic thermal power-rating techniques that take advantage of low temperatures to temporarily overload conductors without the risks of mechanical and thermal stress). it should be noted that in a highly meshed network like the european one, if intelligent control devices are extensively deployed they will deliver real benefits only when subjected to coordinated operation; since these technologies mutually influence each other, if sophisti-cated coordination and investment-sharing mechanisms are not put in place, grid operators face the risk that these devices will not deliver their full potential. they could even contribute to unwanted system behaviors.

International expansion and the regulatory frame-work: there is a tendency in europe (and indeed worldwide) to plan extensions of the transmission system beyond continental borders. Several initiatives focus on interconnecting the power systems along the shores of the Mediterranean; preliminary feasibility studies have been conducted to interconnect the euro-pean power system with iPS/uPS; and even china has expressed interest in performing planning studies to interlink the chinese power grid with europe through other international power systems. the first list of Pcis already includes links to non-eu countries. Some of the main regulatory and market obstacles in advancing this process are found in the lack of sound financing frame-works and business models, the need to develop sup-port schemes for reS generation in some countries; a lack of shared and harmonized rules for network access, capacity allocation, congestion management, and inter-tSO compensation; and a need for allocation and remu-neration mechanisms for the backup reserve and storage capacity necessary to cope with reS volatility.

Super transmission grids and smart distribution grids: in general, tSOs and distribution system opera-tors (dSOs) still have to implement strategies to address in a systematic way the interfacing issues originating from smart distribution grid developments. Many of the renewable-based generating units connected to distri-bution systems are only able to operate within limited frequency ranges and can find themselves disconnected just when they are needed to support system stabil-ity. according to entSO-e, if [they are] simultane-ously applied to a large number of units, such unique frequency thresholds can jeopardize the security of the entire interconnected system. to make the transmis-sion and distribution grids work together efficiently and safely, increased coordination in their development and operation must be pursued. both transmission and dis-tribution need to be further developed, not necessarily just in terms of carrying capacity but also via advanced ict infrastructure and communication and control plat-forms. networks and markets must adapt to the coexis-tence of centralized and decentralized power generation. entSO-e warns that the more active role of the net-works themselves, as well as the expected more active participation of loads and generation embedded in the distribution systems, will impact on the forecast of the load as well as, in the long run, the design of the mar-ket models. Several stakeholders (including regulators, system operators, and power producers) are calling for closer coordination between transmission and distribu-tion systems, especially for issues concerning demand and generation observability but also for interoperabil-ity and controllability, so as to ensure a suitable contri-bution of local resources to global system security.

A Possible Future Pan-European Transmission Networkthe main transmission grid projects agreed to by network stakeholders and supported by eu legislative and financial instruments can be grouped into four clusters:

1) north Sea offshore grid2) Southwestern europe and the Mediterranean area3) central and southeastern europe4) baltic energy Market interconnection Plan.the ongoing and planned activities in these four extended

areas are described below.

North Sea Offshore Gridthe north Seas countries Offshore Grid initiative (nScOGi) was launched in 2009 by ten nations (belgium, denmark, France, Germany, ireland, luxembourg, netherlands, nor-way, Sweden, and the united Kingdom). the underlying objective of the initiative is the exploitation of the huge wind power potential of the north Sea via an offshore transmis-sion network connected to the mainland grid. according to nScOGi scenarios, the countries belonging to the initiative


expect to host a total wind generation capacity of between 120 and 180 GW by 2030; the offshore portion should make up 40 to 60 GW of this total. the initiative obviously represents a multinational effort, with shared cost and benefits. appropri-ate technical and market regulation of all relevant aspects of the initiative (grid planning, permitting procedures, offshore generators grid connections, reS incentives, and market design) is therefore crucial.

this grid, which will connect offshore wind farms in dif-ferent countries in northern europe, also aims to enhance cross-border capability and the cross-border electricity trade by exploiting the large pumped hydro storage potential exist-ing in norway. a prerequisite, however, is the parallel rein-forcement of the grid in northern and central eastern europe. From a grid design standpoint, several topological solutions are being studied, with a preference for the meshed multi terminal networks built with modular multilevel converters (MMcs), vScs, and hvdc converters. there are connections already in place between Germany and norway (norGer and nord.link), the netherlands and norway (norned 1 and

norned 2), denmark and the netherlands (cobra), and the netherlands and the united Kingdom (britned). Others are planned to link Germany, the netherlands, norway, and the united Kingdom. Some vSc-based hvdc (vSc-hvdc) links for offshore wind connection to the German shore (including the borWin 1, borWin 2, SylWin 1, helWin 1, and dolWin 1 projects) have recently been commissioned or begun construc-tion. in the baltic Sea, the hvdc interconnections between eastern denmark and Germany at Kriegers Flak are impor-tant for offshore wind integration and cross-border trade.

Southwestern Europe and the Mediterranean AreaPlanned reinforcements in this area include the cross-border links between France and Spain (320-kv, 2x1000-MWvSc-hvdc) and between italy and France (500-kv, 2x600-MW vSc-hvdc). Other short- and medium-term plans in the region call for reinforcements and new interconnections at the Portugal-Spain border as well as connecting islands with the continental grid: a 2x200-MW current source converter

figure 2. The evolution of the European power transmission grid.

19902010 20102020

Beyond 2030

UCTE 2 Disconnected from UCTE 1 in Autumn 1991 Due to War in Former Yugoslavia Reconnected in November 2004


hvdc (cSc-hvdc) link for the balearic islands and a 220-kv, 250-MW ac link to Malta.

Furthermore, the southwestern european systems play a key role in connecting europe to north africa, where con-ventional, solar, and wind energy are all available. the con-tinental european network is synchronously coupled with the northwestern Maghreb countries (algeria, Morocco, and tunisia) via a single interconnection between Morocco and Spain (2x700-MW ac). Other systems in the region include the northeastern Maghreb countries (egypt and libya); the Mashreq countries (Jordan, lebanon, and Syria); israel and the Palestinian territories; and turkey (teiaS).

two main groups of grid developments in the Mediter-ranean area are planned. the first consists of projects needed to complete the so-called Mediterranean ring (Medring) that will interconnect most of the power systems of the countries around the Mediterranean. the second is the cross-Mediter-ranean undersea interconnection of selected power systems on the northern and southern shores of the Mediterranean.

closing the Medring in hvac mode remains complex, as demonstrated by the failure of the latest attempt (april 2010) to synchronize tunisia (and the european continental net-work) with libya. the problems have to do with dynamic and stability issues. the option of closing the Medring using full hvdc lines or back-to-back (b2b) hvdc systems seems more feasible; in fact, this would allow for higher net transfer capac-ities and less difficult operation of the interconnected systems. in this way, when turkish grid synchronization with the con-tinental european network is achieved, the two sections of the Medring that are still not synchronously interconnectednamely, the tunisia-libya and turkey-Syria bordersmay be directly interlinked via full or b2b hvdc schemes.

a number of initiatives and plans, such as the deSertec industrial initiative and Medgrid, foresee at different levels and under various time horizons and scenarios a large reS-based electricity exchange between the two Mediterranean shores. the first cross-Mediterranean hvdc interconnec-tion is a link planned between tunisia and italy. additional potential hvdc interconnections, such as algeria-Spain, algeria-italy, and libya-italy, have been investigated in recent years. Many factorstechnical, regulatory, finan-cial, market, socioenvironmental, and politicalhinder the implementation of such projects in the short to medium term.

Central and Southeastern Europein central and eastern europe several grid upgrades are needed, especially in the czech republic and Poland and at the interfaces with eastern and northeastern Germany, as well in the grids of austria, hungary, and Slovakia. at the same time, considering that generation capacity in Germany is concentrated in the northeast while load is increasing mostly in the south, considerable north-south transfer capac-ities should be planned. in the medium and long term, there is the need for additional generation connection and inter-connection capacities within and between the southeastern

european countries and also for increasing transfer capacity with central europe. Other axes to be expanded are the east-west corridor between the adriatic and black Sea countries as well as the corridors at the borders of italy with austria and Slovenia. as far as interconnections with non-eu coun-tries are concerned, the most ambitious plan concerns the potential coupling of the european continental zone (the for-mer ucte) with the iPS/uPS system in the former Soviet countries. the latest studies maintain that a synchronous connection may be feasible only as a long-term option, due to technical, operational, legal, and regulatory issues. For these reasons, nonsynchronous system coupling by hvdc (in full or b2b links) is thought to be the safest short-term solution. it is also worth mentioning that there are a number of old 750-kv extra high-voltage (ehv) a cover head lines that are currently out of operation or partly disconnected at the border between the continental european system and the iPS/uPS system that could be reused as the future back-bones of a potential pan-european supergrid.

BEMIPin 2009, eight baltic Sea eu member states (denmark, estonia, Finland, Germany, latvia, lithuania, Poland, and Sweden), along with norway as an observer, issued the baltic energy Market interconnection Plan (beMiP). beMiPs main priority is strengthening the interconnections between the baltic states and the other eu countries. the baltic states are still synchro-nously connected with the power systems of the republic of belarus and the russian Federation (iPS/uPS); the 2006 tie-line between estonia and Finland (estlink 1,350-MWvSc-hvdc) is the only link with the eu power systems to date. Other interconnections are planned between lithuania and Poland (litPol, 400-kv, 2x500-MWb2bhvdc), between lithuania and Sweden (nordbalt, 700-MWvSc-hvdc), between estonia and Finland (estlink 2, 650-MWcSc-hvdc), and possibly between latvia and Sweden. additional reinforcements, especially in latvia and lithuania, as well as cross-border interconnections between latvia and lithuania and between estonia and latvia are also planned in the short and medium term. new nuclear power plant proposals, like the one in the area of the russian enclave of Kaliningrad, will also be included in the planning studies for the grid due to their impact on the baltic power system.

Figure 2 depicts the main changesboth those that have already occurred and those that are anticipatedin the inter-connection of the different electricity subsystems that make up the european power grid, as described above in detail.

in summary, a prospective pan-european supergrid may in the long run include an enlarged hvac continental network that synchronously interconnects with the baltic countries, Moldova, turkey, and possibly ukraine and further asynchro-nously links up with the british isles and Scandinavia, along with the presence of a closed Mediterranean ring and inter-connections between the north and south shores of the Medi-terranean. in this system, islands like cyprus and iceland (via


potential hvdc links) and Malta (via an hvac link that has already been planned) would be electrically linked; belarus and russia would be asynchronously interconnected as well. Further extension of the interconnected power system to remote electricity grids (such as that of china) could represent a very long-range option to explore beyond 2030.

another interesting aspect of pan-european grid develop-ment concerns the historical evolution of the european high-voltage grids density (measured in terms of power line km per land km2). Grid density increased steadily until the beginning

of the 21st century; over the last decade, however, a rather seri-ous standstill has been recorded in transmission grid develop-ment, mainly associated with socioenvironmental opposition to new installations and related permitting issues.

the maps in Figure 3 depict the grid density in 2010 and the potential density occurring beyond 2030. the maps of grid density were created by combining several electrical power system spatial data sets from commercial and ec Joint research centre (Jrc) databases of ehv transmission lines. in a business-as-usual scenario, it is probable that most of the

North Seas Offshore Grid North Seas Offshore Grid

Baltic EnergyMarket for Electricity


Central Eastern andSoutheastern Europe


Southwestern Europe Southwestern Europe

Grid Density km/100 km2011.0133.0155.017.5

7.511010.011515.012020.01100

Grid Density km/100 km2

1.0133.0155.017.5

7.511010.011515.012020.01100

North Seas Offshore Grid



Southwestern Europe

Grid DensityIncreasing Transfer CapacityCoupled with Decreasing DensityIncreasing Transfer CapacityCoupled with Increasing Density

(a)

(c)

(b)

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figure 3. The current power transmission grid density in Europe and the density under two different scenarios for 2030 and beyond. (a) The line density in Europe 2010. (b) The potential evolution of line density in Europe business as usual scenario beyond 2030. (c) The potential evolution of line density in Europe alternative scenario beyond 2030.


currently planned transmission grid infrastructure would be successfully built without dismantling other adjoining power infrastructure; this scenario therefore entails additional growth in power grid density. an alternative post-2030 scenario could instead include the construction of more long-distance ehv backbonesto interconnect generation and consumption cen-ters located far apart from each otheraccompanied by the dismantling of adjoining hv infrastructure. this could occur for the following reasons. First, it would provide environmen-tal benefits and compensation to the populations whose lands are crossed by such new infrastructure (e.g., the construction of a new 380-Kv line could be compensated for with the dismantling of other 220-kv or 150-kv lines). Second, the upward trend in distributed generation diffusion produces a greater need for locally improved and upgraded medium- and low-voltage networks than for high-voltage grids. the areas where this trend may become more visible will probably be those where a higher penetration of distributed generation is occurring, e.g., the central parts of western europe.

The Way AheadMeeting the energy and climate change policy objectives of the eu requires a major transformation of the electric-ity infrastructure, from both the structural and operational points of view, along with sizable volumes of investment. the evolution of the power grid in the medium to long term depends greatly on which scenarios are adopted for renew-able energy deployment, extension of the european elec-tricity network toward neighboring power grids, and the penetration of distributed energy sources that require devel-opment of a smarter system.

even with the advent of more decentralized power tech-nologies and systems, it is expected that the transmission grid will still have a crucial role in wheeling power over long distances and serving as a backup to local distribution grids. it is probable that neither of the different and, to a certain extent, conflicting architecturessupercentralized transmission and smart and decentralized distributionwill prevail over the other, but they will need to be integrated and combined.

in europe, there is a need to start today to build the electricity networks planned for the next decades, at both the transmission and distribution levels. at the transmis-sion level, the implementation of a pan-european supergrid requires addressing and solving several technological, regu-latory, market, and socioenvironmental issues.

in summary, a pan-european supergrid can be envisioned as an electricity grid infrastructure based on mixed hvac and hvdc onshore and offshore backbones (highways) interconnecting renewable energy sources and storage technologies and trans-porting bulk power to load centers across the whole european continent and beyond. Whereas an increase of the long-distance transfer capacity is expected in most of the transmission grid, some areas could experience (contrary to what happened so far) a decrease of total grid density in the future. this trendlinked to socioenvironmental needs, distributed energy resource pen-etration, and strategic planning decisionscould also be sup-ported by technological breakthroughs providing higher transfer capacity in narrower corridors.

the Jrc, as an independent science provider, is tasked with monitoring the ongoing developments in and assess-ing the costs and benefits of the different technological and architectural evolutions of the european power system to provide scientific support to the relevant eu energy policies. For more information, visit http://ses.jrc.ec.europa.eu/.

Acknowledgmentsthe authors would like to acknowledge the contributions and comments of angelo labbate of rSe, italy.

For Further Readinge. bompard, et al., classification and trend analysis of threats origins to the security of power systems, Int. J. Electr. Power Energy Syst., 2013.

e. bompard, et al., Market-based control in emerging dis-tribution system operation, IEEE Trans. Power Delivery, 2013.

c. brancucci Martinez-anido, et al., Medium-term demand for european cross-border electricity transmission capacity, Energy Policy, 2013.

FP7 SeSaMe Project. tools and regulation framework for european power grid security. [Online]. available: https://www.sesame-project.eu/

iee Gridtech Project. integrated assessment of new grid-impacting technologies. [Online]. available: http://www.gridtech.eu/

BiographiesEttore Bompard is with the european commission, Joint re-search centre, institute for energy and transport (ec Jrc-iet).

Gianluca Fulli is with the ec Jrc-iet.Mircea Ardelean is with the ec Jrc-iet.Marcelo Masera is with the ec Jrc-iet.

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In Europe, there is a need to start today to build the electricity networks planned for the next decades, at both the transmission and distribution levels.

Evolution Opportunitie and Critical Issues for Pan European Transmission

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