Elektrotechnik & Informationstechnik (2013) 130/8: 241–246. DOI 10.1007/s00502-013-0166-9 ORIGINALARBEITEN

New age with renewable energy sourcesM. Babuder OVE, G. Omahen, Z. Bregar

The article gives an insight into the Slovenian electric power system observed during its adapting to the intensified use of renewableenergy sources. Some critical phases in this process are discussed, particularly the impact of massive introduction of photovoltaic powersources on the long term development of the power system. It pays careful attention to the characteristics of power sources in orderto assess and evaluate the replacement of conventional sources with renewables.

Keywords: energy; renewables; power system; acceptability

Alles neu durch erneuerbare Energieträger.

Der Beitrag gibt einen Einblick in das slowenische elektrische Energiesystem, das während seiner Anpassung an die verstärkte Nutzungerneuerbarer Energiequellen beobachtet wurde. Einige kritische Phasen in diesem Prozess werden diskutiert, insbesondere die Auswir-kungen der Stromerzeugung aus den zahlreichen Photovoltaikanlagen auf die langfristige Entwicklung des Stromnetzes. BesonderesAugenmerk wird auf die jeweiligen Eigenschaften der einzelnen Energiequellen gelegt, um den möglichen Ersatz von konventionellenEnergiequellen durch Erneuerbare entsprechend bewerten zu können.

Schlüsselwörter: Energie; Erneuerbare; Energiesystem; Akzeptanz

Received October 16, 2013, accepted November 14, 2013, published online December 3, 2013© Springer Verlag Wien 2013

1. IntroductionThe total installed power of the electric power system amounts tosome 3000 MW having an annual production of 12000 GWh. Onethird of generating units are hydroelectric power stations, two thirdsare thermal plants.

The hydro power plants are using the water power of three mainrivers: Drava, Sava and Soca and are of the run-of-river type ofplants. The water of the Soca river is used for one reversible unit(RU) having small storage capacity.

The thermal power plants include coal fired units, gas fired unitsand a nuclear power plant.

The structure is shown in Table 1.

2. The transition from conventional to renewable energysources

With the purpose to follow the Directive 2009/28/EC of the Euro-pean Parliament and Council from April 2009, that gave the incen-tives to introduce and use the renewable energy sources, it was im-posed to the member states to prepare an Action plan (AP RES) forthe period 2010–2020. The objectives and aspirations were set to

Table 1. Electric power generation in Slovenia

Hydro power plants [MW] Thermal power plants [MW]

Sava river 183 Šoštanj 779Drava river 599 Trbovlje 168Soca river 316 TE-TO Ljubljana 112Mura river No plants

built yetBrestanica 318

Soca (RU) 185 Krško 696

Total Hydro 1283 Total Thermal 2073

Fig. 1. Planned growth of renewable electric energy generation forthe period 2011–2020 set in the Action Plan

influence the electric power generation, heating, cooling and trans-portation. Figure 1 shows the planned contribution of renewablesto the electric power generation.

Action Plan established the following principal targets:

– Obtaining 25 % participation of all RES in the final energy con-sumption and 10 % RES for transportation by the year 2020, that

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Nach einem Vortrag bei der 51. Fachtagung der Österreichischen Gesellschaft fürEnergietechnik im OVE, die am 10. und 11. Oktober 2013 in Graz stattfand.

Babuder, Maks, Elektroinštitut Milan Vidmar, Hajdrihova 2, 1000 Ljubljana, Slovenia(E-mail: Maks.Babuder@eimv.si); Omahen, Gregor, Elektroinštitut Milan Vidmar,Hajdrihova 2, 1000 Ljubljana, Slovenia (E-mail: Gregor.Omahen@eimv.si); Bregar,Zvonko, Elektroinštitut Milan Vidmar, Hajdrihova 2, 1000 Ljubljana, Slovenia(E-mail: Zvonko.Bregan@eimv.si)

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Fig. 2. The total power of RES by November 2012

Table 2. Target and achieved values of the Action Plan

Savings Target Obtained[GWh] [%] [GWh] [%]

Savings of final energy (FE)2008–2016

4.261 9,0

Intermediate savings of FEup to 2010

1.184 2,5 1.174 2,5

– Savings 2008–2010 831 1,7* Households, Tertiarysector, Intersectorialmeasures 2008–2010

726 1,5 531 1,1

* Transport and Industry 458 1,0 300 0,6* Early activities1995–2007

343 0,7

requires to double the energy generation from renewables takingthe year 2005 as basis

– stop the increase of final energy consumption– introduce the efficient energy consumption and use of RES as a

priority in economic development– increase the share of RES in final energy consumption up to the

year 2020

With this purpose the government has undertaken the obligationto provide for a suitable support.

The experience gained during one third of the action plan’s timespan is showing a less promising reality. Discrepancies in photo-voltaics growth, less security of supply, remarkable slow-down of in-vestments in hydroelectric plants and uncertainties in the CO2 mar-ket reflect the most significant features of the immediate past. Theinstalled power of RES was expanding rapidly as shows Fig. 2.

3. Energy efficiency on the demand sideAccording to agreements within the EU and specifically to obey theDirective 2006/32/EC of the European Parliament and Council fromApril 2006, the Slovenian Government triggered the Second na-tional action plan for energy efficiency for the period 2011–2016.The Directive imposed to the member states to prepare an Actionplan in 2007, 2011 and 2014 respectively. The target of the secondAction plan for the period 2008–2016 is to obtain 9 % of energysavings after implementing of suitable instruments. The target andachieved values are given in the Table 2.

4. Smart Grid pilot projects and advanced ICT introductionThe Slovenian Smart Grids Development Program completed in April2012 provided a firm foundation and defined the concept of smartelectric power grids of the country. Main goal of smart grids is to op-timize investments in the infrastructure. New concepts of power gridplanning, design, construction and operation shall be developed andapplied in pilot projects, before mass implementation begins. Thispilot project should be carried out as an interdisciplinary project in-volving numerous participants from technology, economics, regula-tory and sociology fields. To allow for an efficient participation ofall involved, it should be suitably managed. Industry is expected touse this opportunity and integrate their most recent achievements inorder to obtain needed advantageous references. It has been fore-seen that the project should embrace five geographical locations. Anemphasis will be put on advanced ICT been aware of necessity to in-troduce the latest achievements in this technology. The operationalplan shows a promising approach towards the mass integration ofSmart Grids.

5. Readjustment of the distribution and transmissionnetwork

The structure of the electric power network is changing due to in-troduction of new technical solutions caused mainly by restructuringof the generating part of the system. The power flow is modified bynew sources; particularly dispersed small generating units have animportant impact in this sense. Both, the transmission part and thedistribution require a new paradigm in planning and structuring ofthe system. Let us consider and present some of prevailing argu-ments showing and reflecting this process:

– In some cases the energy flow will change the direction—fromlow voltage to higher voltage levels

– This needs a new operating procedure– There is often a justified need for the use of advanced metering– There is often necessary to compensate the capacitive load on

higher voltage levels– New material and technique is asking for new codes and stan-

dards– It is frequently necessary to overcome problems with voltage qual-

ity and high interferences– The free market and dispersed generation need newly developed

services.

The dynamics of this process was unexpectedly high and was pro-gressing in such a way that made difficult or almost impossible tomatch the growth of renewables with the changes and readjustingof the distribution network. These consequences were less impor-tant in the transmission system in our country although we knewthat this is crucial in some other European countries.

6. Solving of vital environmental problems by use of RESIt is necessary to point out an important basic precondition which issignificant and in some cases essential for a stable operation of theelectric power system:

In the energy conversion process from any source into electric en-ergy, a permanent balance between the generated and consumedportion must be kept. This is practically valid for the majority ofpower systems but particularly for the Slovenian Electric Power Sys-tem. The characteristics of available renewable energy sources to beused for electric power generation in Slovenia are as follows.

6.1 Small hydro power plants– The better part o the water flows are torrential

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M. Babuder et al. New age with renewable energy sources ORIGINALARBEITEN

– The water in smaller rivers frequently drains away during the sum-mertime

– During rainy weather they do operate with full power otherwisethey generate low power or do not operate at all

6.2 Windmills– The wind force in Slovenia is much lower than in Northern Europe– Average value of wind power is lower– The wind-speed is unstable and its direction is frequently chang-

ing too– Consequently, the wind turbine generated power is changing ac-

cordingly

It may be illustrated by means of a simple equation that relatesthe wind speed to the output windmill power P = f (v3). If the windspeed goes down to 1

2 , the output power falls down to 1/8

6.3 Biogas– The gas production technology requires its permanent and stable

consumption and consequently a constant output power– The generating and conversion systems necessitate major surfaces

and usage of the soil surface being formerly available for foodproduction

– It needs very high government subsidies– It isn’t environmentally friendly to the nearest neighborhood and

that brings quite often resistance from the sensible interestedpublic

6.4 Cogeneration– The generation of electric power is of secondary importance in

the whole process– The output power and the operating time are subordinated to

the heat output (district heating and supply of heat and steam forindustrial use)

– The operation is seasonally depending

6.5 Run-of-river and accumulative hydro power plants– Hydro power in Slovenian power system is the unique power

source suited to balance the power but by a limited amount be-cause of a relatively small available accumulations

– Their investment cost is considerably high but they are never theless the most advantageous renewable energy source

– Regarding the national economy at large they represent the bestsolution but require comprehensive effort and time needed toovercome all political and other obstacles impeding the obtain-ing of construction permits

6.6 Photovoltaic power plants– The output power obtained is very volatile and difficult to predict

(seasonally unsuitable)– The cost price is very high– They cause additional cost in the distribution system– They produce additional cost for system services– They lower the competitiveness of the national economy and may

trigger the social problems– They are macro economically highly unsuitable (major part of the

invested money is spent for the imported equipment and services)

7. The development of photovoltaic power in recent yearsThe revolutionary breakthrough of the photovoltaic power in thecountry surprised everyone who played part in this process. Thegrowth of the total electric power of erected renewable energysources in Slovenia as shown in Fig. 2.

Fig. 3. The Energy Regulator impact to the subsidizing process

Fig. 4. The Declarations issued by the National Energy Regulator(given in MW)

The photovoltaic power development notably during recent twoyears took an unexpected and wrongly predicted course because:

– This power subdivision was very successful in the countries wherewe frequently follow the examples from

– The investors rapidly reacted on generously offered subsidies– The responsible bodies reacted with time delay (see the flow-

diagram Fig. 3) that caused oscillatory course of the controlledevaluation process

– The price dynamics of photovoltaic modules was high and unpre-dictable (dumping of Chinese Manufacturers) see Fig. 5

The National energy regulator followed the targets from theabove cited Directive and issued a considerable number of Decla-rations as shown in Fig. 4.

It seems reasonably to believe that energy regulator couldn’t replyquickly enough to the fast changes of PV system price (see Fig. 5).

8. The amount and impact of subsidiesWith the purpose to clarify the amount and effect of subsidizing ananalysis was carried out. The results are shown in the Table 3.

The unsuitable control of the subsidizing process didn’t initiallyproduce as big damage as it was the case in 2011 and 2012. Figure 6clearly shows this faithfull disproportion. The curve marked with thetriangle dots shows the prediction given in the Action Plan. Similarcourse was predicted in the National energy outlook as a moderatesolution marked with the rotated squares. Finally, there was anotherprognosis put in the National energy outlook called intensive option,

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Fig. 5. PV system price since February 2006

Table 3. Amount and impact of subsidies

Type of thegenerationunit

Producedenergy(kWh)

Subsidy(EUR)

Share ofenergy(%)

Share ofsubsidy(%)

Hydro PowerPlants

75.517.679 4.354.366 18,06 7,36

PhotovoltaicPlants

98.223.239 27.419.602 23,49 46,37

Windmills 598 57,05 0,00 0,00Biogas Plants 62.934.194 7.853.981 15,05 13,28Biomass Plants 46.082.611 5.372.884 11,02 9,09Cogenerationbased on fossilfuel

135.044.801 14.038.230 32,29 23,74

Other 362.272 87.390 0,009 0,15

Total 418.165.394 59.126.510 100 100

which foresaw an even more intensive PV growth (the curve markedwith horizontal squares).

This disproportion became critical during last two years repre-sented in Fig. 6 by the red curve marked with crosses. The real causethat led to this faulty process was the wrongly adjusted subsidies.The cost price per MWh of energy produced in Germany publishedby BSW Solar shows the blue curve in Fig. 7, the red curve showsthe cost price per MWh of PV unit category 3.1.1. In Slovenia. Thedifference was evidently too high.

9. The random behavior and the reliably available power ofRES

Considering the system operation after having introduced a rela-tively high amount of RES, it was useful to focus on and take intoaccount practices obtained abroad in one of neighboring systems. Itwas worrying to see the total amount of reliably available power asillustrated by Fig. 8.

Regrettably, the media are frequently reporting on the achieve-ments in reducing of environmental impact by introduction of RES,by pointing out the installed power, but rarely mention the totalgenerated energy and reliably available power.

Moreover, the power of FV sources is difficult to predict. Very fastunpredictable power changes are possible (see Fig. 9).

To steadily keep continuous balance between the demand andsupply side the TSO has to provide for satisfactory additional sec-ondary back-up. There are several possibilities to fulfill this condition:very expensive short term storage in hydro pump plants or engage-

Fig. 6. Disproportion in PV power growth

Fig. 7. Subsidized price comparison

Fig. 8. Reliably available power from RES

ment of several conventional plants reducing their efficiency andincreasing cost.

10. Consequences of dispersed RES introduction in thedistribution grid

The distribution grid was planned to allow for the energy flow fromhigher voltages down to the lower voltage levels. The generationunits connected in the medium and frequently in the low voltagegrid may require a new paradigm in network planning.

The power electronics needed to connect the PV sources pro-duces:

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Fig. 9. Prediction of FV sources

– harmonic components of the voltage– radiofrequency interferences– changes of reactive power need– worsening of voltage control– Impact on protection and short circuit conditions.

Practicing of massy implementation of RES will bring about an es-calation of problems to be solved and hence additional investmentsin adaptation of the medium and low voltage grid.

11. Conclusions(a) Prices on the Slovene energy market strongly correlate with

prices on EEX energy market. Large number of PV and windpower plants had been erected in the last decade in the areacovered by EEX. Variable costs of PV and wind power plants arepractically zero and their production has a priority dispatch in theelectric power system.

(b) Although there are more than 30 GW of wind power plantsinstalled all over Germany, the reliably available capacity is lowerthan few % of the installed power. Production from PV plants

is high in clear and sunny days only (Fig. 8). To ensure reliabledemand it is necessary to provide for 100 % coverage by classicalsources, despite huge installed capacity of renewables.

(c) Priority dispatching of PV and wind power brings the need forquick changes in the production of other power plants in thesystem. Those consequences have not being felt yet in Sloveniaby such a margin because of frequent congestions in the trans-mission system on the Slovenian—Austrian border. However, byintensive introduction of PV plants in the last couple of years,Slovenia will certainly face similar problems very soon.

(d) Priority dispatch of PV and wind power plants lowers operatinghours of “classical” units and raises their cost price. “Close tozero” variable costs of PV and wind power plants are changingthe conditions on the electric power market. Market prices haveseen a decrease in the last couple of years and are currently onsuch a low level that there is no economic interest for buildingnew (conventional) power plants necessary to keep electric en-ergy supply reliable.

(e) It may be supposed, that these circumstances in the energy mar-ket will not change even if all future subsidies stop. Currentlyinstalled units of RES already have large enough share and willoperate according to contractual agreements for next 15 years.Without an intervention from market regulator, the reliability ofthe system is expected consequently to be lower. At this point,it is necessary to remember that the most important aim of re-structuring the power system is to maintain and keep its requiredreliable operation.

References

1. Babuder, M. (2013): Renewable energy sources—reality and opportunities. In Yearlyconference on energy policy organized by WEC Slovenian committee and energy indus-try chamber, Ljubljana, Slovenia, September 2013.

2. Bregar, Z. (2013): Assessment of photovoltaic energy in Slovenia. In Proc. of the na-tional CIGRÉ committee conference, paper C1-15, May 2013, Lasko, Slovenia.

3. Omahen, G. (2013): RES impact on the long term power system development. In Proc.of the national CIGRÉ committee conference, paper C5-05, May 2013, Lasko, Slovenia.

Authors

Maks Babuderreceived his B.S.E.E. degree from University ofLjubljana, Slovenia, in 1964 and the Ph.D. de-gree from University of Zagreb, Croatia. Hestarted his professional career as Research En-gineer at the High-Voltage Laboratory of the„Milan Vidmar“ Electric Power Research Insti-tute in Ljubljana. Later on he became its Headand is currently the Institute’s Assistant Man-aging Director. During the period from 1987

to 2008 he had also an academic career at the Faculty of ElectricalEngineering of Ljubljana teaching students high-voltage engineer-ing. He is a Member of IEEE Dielectrics and Electrical Insulation Soci-ety, Distinguished Member of CIGRÉ and Member of OVE.

Gregor Omahenwas born in Ljubljana, Slovenia, in 1978. Hereceived his B.Sc. econ. degree from the Fac-ulty of Economics, University of Ljubljana in2003 and his M.Sc. degree from the same in-stitution in 2010. He has been employed asa researcher at EIMV since 2003 and dealswith CBA analysis of different investments inthe electric power system. In the last yearshis interest is mainly on smart grids, especially

smart metering and demand side management. He is co-author ofthe Smart grid development program in Slovenia and the Opera-tional plan of the national smart grid demonstration project as wellas of main documents in the field of smart grids in Slovenia. Since2011 he has also been the Secretary of the Technology platform forsmart grids with the main task of the creation and organization of anational smart grids demonstration project.

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Zvonko Bregarwas born in Novo Mesto, Slovenia, in 1964.He received his B.Sc. Math. degree from theFaculty of Mathematics and Physics, Univer-sity of Ljubljana in 1988 and his M.Sc. degreein Computer Science from the same Univer-sity in 1998 respectively. In 1988 he joinedthe Milan Vidmar Electric Power Research In-stitute. He is a member of Slovenian CIGRÉ.

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