Prospects for wider energetic utilization of subgeothermal waterresources: eastern Serbia case study

ZORAN STEVANOVIĆ1, ALEKSANDAR SALJNIKOV2, DEJAN MILENIĆ1, †MIĆA MARTINOVIĆ1,DARKO GORIČANEC3, MIRKO KOMATINA2, PETAR DOKMANOVIĆ1, DRAGI ANTONIJEVIĆ4,

ANA VRANJEŠ1 & SAVA MAGAZINOVIĆ1

Abstract. Extensive worldwide usage of fossil energy sources causes high pollution and contributes toglobal warming. Hence, achieving energy independence by stimulating efficient use of energy and environ-mentally friendly exploitation of renewable sources is a main orientation of European countries.

Geothermal energy is generally treated as a renewable and inexhaustible energy source. Nonetheless, directuse of low enthalpy subgeothermal resources, i.e. groundwater of 30ºC or lower, for heating is commonlyviewed as economically unjustified. To enable its usage, large panel surfaces or a high-temperature heat pumpwith excellent efficiency is required. The development of a cascade type heat pump and its wide applicationwould enable more efficient utilization of widely available and easy replenished groundwater sources withtemperatures of 10–30ºC.

The hydrogeological conditions in eastern Serbia are particularly favourable for exploitation of subgeother-mal resources due to rich aquifer systems and notable terrestrial heat flow formed into the main geo-structuresof the region (Carpathian-Balkan arch and Dachian basin). More intensive exploitation of subgeothermalsources additionally justifies the existence of a number of urbanized small and medium-size cities with a heat-ing infrastructure already developed and centralized. Sustainable use of groundwater resources should be fol-lowed by thermal reconstruction of the previously constructed buildings as well as new legislation which sup-ports and encourages development of renewable energy sources. It is estimated that the total potential thermalpower which can be generated from subgeothermal waters in the study area is around 33 MWt, which corre-sponds to some 16 % of the total heat requirements.

Key words: subgeothermal source, groundwater, heat pump, energy efficiency, eastern Serbia.

Апстракт. Интензивно коришћење фосилних горива широм света узрок је озбиљних загађењаприроде и утиче на глобално загревање. Отуда је један од главних циљева енергетске политикеевропских земаља коришћење ефикасније “зелене” енергије из обновљивих и сопствених извора.

Генерално, геотермална енергија представља вид обновљивих извора енергије. Ипак, и даље се сма-тра да коришћење субгеотермалне енергије ниске енталпије (температуре подземних вода од 30°C иниже) за потребе грејања није у потпуности економски оправдано. Стандардна технологија за применуовог вида енергије захтева велике површине под панелима са цевима које проводе топлу воду и/илиупотребу топлотних пумпи са високим степеном искоришћења. Развој каскадне топлотне пумпе и њенашира примена омогућила би далеко ефикаснију употребу “лако” доступних подземних водних ресурсатемпературе између 10–30°C и стога је у више пројеката реализованих последњих година анализиранаи развијана ова технологија.

Хидрогеолошки услови у теренима источне Србије, су веома повољни са аспекта експлоатације суб-геотермалних ресурса. Подручје се одликује значајним количинама подземних вода и терестичним

GEOLO[KI ANALI BALKANSKOGA POLUOSTRVA

ANNALES GÉOLOGIQUES DE LA PÉNINSULE BALKANIQUE72 131–141 BEOGRAD, decembar 2011

BELGRADE, December 2011

1 Department of Hydrogeology, Faculty of Mining & Geology, University of Belgrade, Djusina 7, Belgrade, Serbia,E-mail: zstev@eunet.rs

2 Faculty of Mechanical Engineering, University of Belgrade, Kraljice Marije 16, Belgrade, Serbia.3 Faculty of Chemistry and Chemical Engineering, University of Maribor, Smetanova 17, Maribor, Slovenia.4 Faculty of Applied Ecology, Singidunum University, Bul. M. Pupina 12a, Belgrade, Serbia.

DOI: 10.2298/GABP1172131S

Introduction

The utilisation of low-enthalpy ground source heatfor space-heating (or cooling) is widespread in the USAand in Canada, with recent growing interest through-out Europe (BANKS 2008). The heat pump technologywhich supports low-enthalpy sources would help toachieve the objectives of the Kyoto protocols on “green-house” gas emissions. The thermal input for thosepumps can be provided either directly by groundwaterextracted from wells or tapped springs, or indirectlyby water injected into the ground and then pumpedout (rock and soil heat release) afterwards. Groundsource heat pumps (GSHP) can be regarded as com-plementary technology inasmuch as they require a“driving” mechanical or thermal power input (com-monly, electrical power to a compressor) that is usedto extract renewable heat from the ground.

The heat effect delivered by a GSHP is typically 3–4times the electrical power input. This means that itdelivers heat 3–4 times more cheaply, with up to 75 %less CO2 emission, than direct use of electrical resist-ance elements. This, in turn, allows GSHPs to delivermore CO2-efficient space-heating than even the mostefficient combustion of fossil fuels. Fossil energysources are especially limited in European countries,and their dependence on import will be even more crit-ical in the near future. Moreover, ground source heatcan also compete effectively in terms of marginal costswith coal or gas (YOUNGER et al. 2007). The energy ofthe geothermal water could be exploited to the maxi-mum before it is returned to the ground through a rein-jection well (as already required by legislation of theEuropean Union). With reinjection an ecological prob-lem is also minimized, as utilized geothermal watermust not be released into local water courses.

Although the initial high capital cost of GSHPschemes is a potential weakness, within the EuropeanUnion the uptake of ground source heat technologyhas dramatically increased (ALLEN et al. 2003). InSweden, for example, which has few native fossil fuelresources and an energy economy that is founded on

nuclear/hydroelectric electricity, there has been astrong political motivation to develop technologiesthat utilise electrical energy as efficiently as possible.Moreover, the strong environmental and centralist tra-ditions of the Swedish government have stimulatedthe uptake of technology since the early 1990s by agenerous subsidy programme. In 2007, it was assum-ed that 185,000 GSHPs were installed in Sweden, pro-viding some 1700 MW of power (BOUMA 2002;YOUNGER et al. 2007; BANKS 2008).

In central and SE Europe there is also growinginterest in introducing, widely applying and promot-ing this kind of “green energy”. In 2000, fewer than1000 GSHP were functional within Czech Republic orPoland, while just five years later the number of pro-cured and installed systems had increased tenfold.Rapidly growing interest in GSHPs is also noticed inItaly and in Slovenia, but the less powerful economiesof the Balkan countries are still waiting for the en-couraged legislation and the deduction of fees fortheir wider application. However, concerning ground-water resources and availability most of the countriesthat belong to the Balkan region are strong prospects.The efficient use of thermal potential of existing flu-ids would thus prevail over the possible alternative i.e.exploitation of rock and soil petrothermal resources.

Subgeothermal water sources

In most relevant references the geothermal fluidswith a temperature lower than 100º C are classified as“low enthalpy”: only the direct generation of electricalenergy from water heat at a temperature higher than100º C is considered to be fully feasible (NICHOLSON

1993; LUND & FREESTON 2001; HUTTRER 2001). Due primarily to the “young Alpine geology” of the

Balkan countries, there are insufficient geothermalfields to generate electrical power under existing tech-nologies. However, the number of thermal occur-rences is very large. For example, in Serbia alone over230 springs or wells with thermal or mineral waters

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топлотним током у оквиру геолошких формација у основним гео-структурним јединицама овогрегиона (Карпато-Балканиди и Дакијски басен). Близина урбанизованих насеља и мањих градова ипостојање развијеног и централизованог грејања су чињенице које повољно утичу на могућностексплоатације субгеотермалних водних ресурса. Одрживо коришћење подземних водних ресурса по-дразумевало би и потребну термалну реконструкцију и бољу изолацију постојећих грађевинскихобјеката, као и доношење нових законских прописа у Србији у циљу подстицаја коришћења обновљи-вих извора енергије. У подручју источне Србије, процењене количине енергије које се могу добити изсубгеотермалних вода износе око 33 MWt, што би представљало око 16% укупних енергетских потребанеколико одабраних већих насеља за које је ова анализа вршена. И поред чињенице да се не очекујепотпуно искоришћење овог потенцијала, евидентно је да је он далеко већи од 4 % колико је у плано-вима енергетског развоја предвиђено да би могло износити учешће геотермалних водних ресурса нанивоу целе Србије.

Кључне речи: субгеотермални извори, подземне воде, топлотне пумпе, енергетска ефикасност, ис-точна Србија.

are registered, 2/3 of them with water temperaturesover 20ºC. Most of the thermal waters are used forbalneology and just a few for heating purposes. Incontrast, in neighboring Hungary thermal flows aretapped for heating purposes in many locations. A goodexample is Hodmezovasarhely where 50000 inhabi-tants get their heat from the thermal waters at 80ºC,tapped at a depth of 2000 m (75 % of utilized watersare reinjected into the ground).

Recently conducted studies aiming to assess the ther-mal potential of lower temperature ground sources inSerbia introduced the term “subgeothermal resources”(STEVANOVIĆ et al. 2008). It has been proposed thatwaters with a temperature of 30ºC or lower are to beclassified in this group whereas those with a tempera-ture of 30–100ºC belong to “geothermal resources”.One of the explanations is very practical: althoughGSHP is necessary for water with lower temperatures,the panel radiator systems allow direct use of waterwith a temperature of 30ºC or more without GSHP.However, as temperatures are lower, heating panelswith larger surfaces are required.

Subgeothermal fluids in the territory of Serbia aretypical of complex geology as well as of a moderatecontinental climate. They are classified as follows(Таble 1):

Brief physio geography, geology andhydrogeology of the study area

There were several reasons to choose the Car-pathian region in eastern Serbia (Fig. 1) as a studyarea: abundant groundwater reserves, considerablesubgeothermal flow, a good number of small industri-al towns with developed centralized heating infrstruc-ture, and moderate continental climate. The northernboundary is the Danube River, the eastern/northeast-ern boundary is the state border with Bulgaria (towardwhich the Carpathian-Balkan mountain range contin-ues), and its western border runs along the edges ofthe Velika Morava and Južna Morava valleys (Fig. 2).The main settlements are (from north to south): DonjiMilanovac, Kladovo, Negotin, Majdanpek, Bor, Zaje-čar, Sokobanja, Knjaževac, Pirot (all with between10000–60000 citizens). Further west in an adjacentarea of central Serbia (Velika Morava valley) there are

several large cities such as Niš, Paraćin, Ćuprija, Po-žarevac and others that are also envisaged as possibleconsumers of geothermal energy produced either fromlocal sources or from eastern Serbia (MILIVOJEVIĆ &MARTINOVIĆ 2005; MARTINOVIĆ et al. 2008).

The mountains of the Carpathian-Balkan arch aremostly unpopulated and used by the local villagers forspecific crop cultivation or grassland during the sum-mer months. Most of the hills are covered by forests orpastures. The demographic trend in the region is nega-tive: the younger population is gravitating towardsnearby industrial centers such as Bor or Zaječar.

The area is a prospect for the development of tou-rism. It is unpolluted and accessible by many roads, isrich in clean waters, and boasts beautiful landscapesand features such as caves, waterfalls and springs,including several spa and medical centers.

Annual average rainfall ranges from 600 mm to 750 mm for most of the cities, while the annual averageair temperature for the entire region is around + 9ºC.

The complex geology of eastern Serbia comprisestwo main geo-structures: the Carpathian-Balkan archand the Dachian basin, both characterized by hydro-geological heterogeneity and a variety in aquifer sys-tems and groundwater distribution. Thus, the region ischaracterized by the presence of formations withsmall groundwater reserves but also Mesozoic carbo-nate rocks, Tertiary or Quaternary alluvial and terracedeposits that could be very rich in groundwater(STEVANOVIĆ 1994).

The study area consists of several mountain massifs,the majority of which are built from carbonate rocks(Fig. 2). Precambrian rocks are not often exposed to thesurface and can be found in anticline cores, often corre-sponding with mountain central parts and peaks. Theyare commonly overlaid by Paleozoic rocks (Ordovici-an, Silurian and Devonian age). Paleozoic formations,magmatic and metamorphic rocks are mostly aquitardsor aquifuges.

The major part of the study area was invaded by theMiddle Jurassic marine transgression, and the sedi-mentation cycle continued until the end of the Lower

Prospects for wider energetic utilization of subgeothermal water resources: eastern Serbia case study 133

Таble 1. Energetic potential of subgeothermal sources.

Fig. 1. Location maps of eastern Serbia.

Cretaceous (Albian). Throughout this period, thickdeposits, primarily of carbonate rocks, were formed toa total thickness of about 1300 metres. Carbonaterocks are characterized by the non-uniformity of the

facies with prevalent limestone but also by ”impure”varieties in lower sections, such as sandy limestonesof the Dogger, or Oxfordian-Kimeridgian chert lime-stones. The carbonate complex was formed mostly

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Fig. 2. Hydrogeological sketch map of eastern Serbia and main groundwater sources (based on Hydrogeological digital mapof Serbia, Stevanovic & Jemcov 1995).

during the Tithonian, Valanginian, Hauterivian, Barre-mian and Aptian and it contains predominantly purecarbonates or magnesium carbonates.

The karst aquifer formed in carbonate rocks is richin groundwater, and is recharged mainly from rainfalland from sinking flows which gravitate from imper-meable rocks at higher altitudes. Carbonate rocks arewell-karstified and contain very large groundwaterreserves (STEVANOVIĆ 1994, 2009).

The karstic groundwater is used mostly for drink-ing purposes or for small industry supply; almost allthe cities in the region are consumers. Although thetotal dynamic reserves in karst often surpass by far theexploitation capacities, most of the tapping structuresare constructed simply to tap the natural discharge ofthe springs and thus depend solely on the natural flowregime. Aiming to overcome this problem, during thelast three decades several successful aquifer controlprojects have been completed (STEVANOVIĆ et al.2007). Karstic groundwater is extracted in a verysmall amount for irrigation purposes.

In the Timok tectonic trough on the eastern part ofCarpathian arch, a volcanogenic-sedimentary seriesover 2000 meters thick (andesites, pyroclastics, tuffa)was formed during the Senonian and the Paleogene(Fig. 2). Fissured aquifer of this complex containsseveral important thermal and thermomineral occur-rences with the water temperature ranging from30–40ºC (Brestovačka spa, Gamzigradska spa, Soko-banja, Nikoličevo, Šarbanovac).

Clastic sediments, marls, clays, and sands were de-posited in a number of the intermountain depressionsfilled with lake waters during the Neogene (e.g. Žagu-bica, Bogovina, Sokobanja, Babušnica, Pirot). Thesandy water-bearing layers could have an artesianpressure (confined aquifers) and are tapped in severallocations (e.g. Negotin, Zaječar).

Most recent are alluvial sediments which followmajor streams in the region (Nišava, Timok, Resavaetc.) and are used mostly to supply local villages. Theexception is Niš where a large amount of alluvialwater is tapped (Mediana source) for Niš itself, thethird largest city in the country.

Utilizing geothermics by cascade heatpump - Discussion

For heating purposes three basic types of heatpumps are used (GORIČANEC et al. 2008):

– a single stage heat pump,– a two stage heat pump with a flash vessel, – a two stage heat pump with a heat transmitter.Using a single stage heat pump for heating build-

ings, the temperature of the secondary carrier canreach 55°C maximum, which is quite a bit too low forthe heating of buildings with a “classical” radiatorheating system. Therefore, single stage heat pumps

are primarily used for low-temperature heating sys-tems, with the temperature of the secondary carrier upto 45°C. In high temperature heating systems, thetemperature of the secondary carrier must be evenhigher than 60°C. With an appropriate refrigerant, atwo stage heat pump with a flash vessel could be usedfor high temperature heating systems. But it is diffi-cult to find a refrigerant which allows the exploitationof the temperature of geothermal water by cooling itto 10° C and at the same time reach a high tempera-ture in the condenser of the second stage in the heatpump (GORIČANEC et al. 2009).

This problem has initiated research for a two stageheat pump with a heat transmitter (heat exchanger),schematically shown in Figure 3. The heat pump infact consists of the two single stage heat pumps whichare connected by a heat transmitter. The advantage ofsuch a cascade heat pump is that, according to theirphysical-chemical characteristics, different refriger-ants can be used at each stage. In choosing the refrig-erant considerable attention must be paid to its physi-cal-chemical characteristics, ecological acceptability,and use of recognized brands.

The heat transmitter between the two stages repre-sents a condenser for the first stage and an evaporator

Prospects for wider energetic utilization of subgeothermal water resources: eastern Serbia case study 135

Fig. 3. Scheme of two stage heat pump with a heat trans-mitter (Goričanec et al. 2009)

for the second (GORIČANEC et al. 2008). The use oftwo stage heat pumps with a heat transmitter is sug-gested in the existing district heating system of build-ings in the city of Lendava in Slovenia (TORHAČ et al.2005). The heat source for the heat pumps is geother-mal water of 42°C. The principle of exploiting heatfrom geothermal water in an individual facility isshown in Figure 4. With such a system it would bepossible to exploit the heating of geothermal water toa temperature of even 10°C.

The coefficient of profitability of a two stage heatpump and the period of time for the investment to berecovered show these to be good prospective solutions.In the case of the Lendava thermal source, the coeffi-cient of profitability has been calculated on 1.19, andthe investment will be returned in 3.2 years (KOZIĆ etal. 1994; TORHAČ et al. 2005). The coefficient of per-formance (COP) of a heat pump is between 3.5 and4.4. Tests and calculations for water at lower temper-atures, different refrigerants and equipment used re-sulted in a longer period for investment recovery, butstill justifiable in terms of both economy and ecology.

At present, almost 50 % of total energy productionin EU countries is spent in buildings. In Serbia evenmore, almost 2/3 of the energy is utilized for domes-tic heating, which is quite logical given that more than50 % of buildings in Serbia were built before 1970.when application of thermal insulation was not oblig-atory. According to some estimates, the annual energy

output is in the range of 150 tо 250 kWh/m2. This is2–3 times more than optimal.

Moreover, the application of active and passive re-newable energy for space and water heating is still notproperly regulated in Serbia: it is only recommendedin different state or local government strategies. How-ever, central heating systems exist in numerous citiesand can be used for conveying energy from alternativethermal sources.

Eastern Serbia - subgeothermal potentialand prospect

Several conducted studies (STEVANOVIĆ 1994,2009; MILIVOJEVIĆ & MARTINOVIĆ 2005, 2010; MAR-TINOVIĆ et al. 2008; STEVANOVIĆ et al. 2008) have con-cluded that eastern Serbia is one of the regions in thecountry with the greatest prospect for groundwaterand subgeothermal energy extraction due to: richnessof the aquifer, developed heating infrastructure withinmoderately populated cities, proximity of the sourcesto the end-users.

In practical terms, most important is the karstictype of aquifer in Jurassic and Cretaceous limestones,which covers about 30 % of this region. The regionfeatures a considerable number of karstic springs, ofwhich 16 have a minimum yield of more than 0.1 m3/s(STEVANOVIĆ 1995). All major cities use water fromkarstic aquifers; however, available reserves are sev-eral times higher than the water demand of this andneighboring regions, and will remain so for a longtime to come. There is also good potential for ground-water utilization from alluvial sediments and Neogeneformations in Intra-Carpathian basins. Regarding thetotal groundwater resources available there are somecontradictions in their estimates. The Water MasterPlan of Serbia from the year 2000 indicated dynamicgroundwater reserves in the amount of 4.27 m3/s,while some other studies found that even the reservesof karst aquifers are considerably higher, reaching12.6 m3/s. The karst and fissured aquifers are also richin thermal water occurrences: there are 6 registeredwith temperatures over 30°C and some 20 with tem-peratures over 20°C. In addition, average water tem-peratures of artesian and subartesian waters fromNeogene sediments are in the range of 10–18°C whichalso classifies those aquifers as ones with high poten-tial for geothermics utilization (Table 2).

According to the preliminary assessment, some 1.7m3/s of groundwater in eastern Serbia can be extract-ed and sustainably used for heating/cooling systems(STEVANOVIĆ et al. 2008). This potential flow resultedfrom the calculation which took into considerationprioritized water utilization for drinking and industri-al water supply, ecological flow for downstream waterdependent eco-systems, and the average water tem-perature ranging from 10–30° C. The subthermal flow

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Fig. 4. Scheme of heating of building by a two stage heatpump and reinjection of utilized waters

can be separated into three categories as presented inTable 1. Total potential heat capacity is calculated bythe formula:

Q = m * c * ∆Twhere,

Q – total potential heat capacity (MWt),m – mass (kg),c – specific water thermal capacity J/(kg°C) i.e.0.004184,∆T – differential temperature (°C).

Differential temperatures are in the range of 6–18°Cdepending on geothermal categories (e.g. ∆T = 18°C forthe waters with T 22–30°C). Available heat power isbased on available water resources and tolerable COP,and is assumed to be around 49.20 MWt (Table 2).

The next step in the calculations considered the ther-mal heat power from sources which are located in thevicinity of the urban areas. Most of the water resourcesare at a viable distance from the consumers. The calcu-

lation is based on apartments with an average surface of60 m2 and required average heat of 100 kWh/m2. Thelatter figure takes into consideration the implementa-tion of some other energy efficiency measures to beimplemented at the same time (thermal reconstructionand insulation of the buildings). Complete and sys-tematic insulation would additionaly improve the sit-uation and reduce required heat, but at this stage justpart of these activities are envisaged. Table 3 containsdata concerning the total power required to heat theapartments in major towns, the potential subgeother-mal flow available in their vicinity (for each of de-fined three categories), the potential thermal powerwhich can be produced by heat pumps, and the per-centage of heat demands that can be met by heatpower generated in such a way.

The total potential thermal power which can begenerated from subgeothermal waters for large settle-ments is assumed to be around 33 MWt, which corre-sponds to some 16 % of their total heat demands.While it is clear that not all potential energy can beefficiently exploited, this figure indicates that the

Prospects for wider energetic utilization of subgeothermal water resources: eastern Serbia case study 137

Table 2. Available subgeothermal resources and calculated heat power in the Eastern Serbia.* = Temperature of groundwater resources: 10–30°C

Table 3. Potential of subgeothermal water resources and heat power in vicinity of urban areas of Eastern Serbia.* = Flow of subgeothermal categories: 10–16 / 16–22 / 22–30°C.

potential of subgeothermal energy in this region ismuch higher than the 4 % contribution from that kind

of energy source to the Serbian energy balance recent-ly announced in the national energy plans.

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Fig. 5. The settlements - Main potential consumers of subgeothermal energy in eastern Serbia, their heat demands and pos-sible cover

Between 11 % and 29 % of heat demands of select-ed towns are covered (Fig. 5). The latter figure char-acterizes the town of Negotin where a relatively largegroundwater resource is located near a small urbansettlement.

Such promising geothermal potential requires fur-ther systematic research as well as the development ofa new strategy and legislation. Therefore, greater gov-ernmental support for “green” energy production isexpected. Sustainable groundwater extraction shouldalso be followed by controlled extraction (by the pro-vision of permits for exploitation rights) as well aspermanent monitoring aiming to prevent over-exploitation and potential technogenic processes.

The implementation of new legislation similar tothat of the European Union is also required particular-ly for utilized waters which have to be regularly rein-jected into the ground. A sound practice applied indeveloped countries suggests that reinjection shouldtake place in the layers regularly overlying the mainaquifer (Fig. 4) in order not to cool the existing tem-perature of the tapped waters [The heat pumps pro-duce thermal energy by significantly decreasing initialwater temperature (∆T)]. A new approach also requ-ires intensive public promotion of energy efficiencydemands and achievements. And last but not least, thereconstruction of old buildings and thermal insulationshould systematically be undertaken.

Conclusions

Among the main advantages of subgeothermalenergy extraction from groundwater (temperature30°C or less) are:

• Easy tapping (once the groundwater resource isproperly explored and defined);

• Renewable energy resource which is cheap todevelop;

• Inexpensive heating pumps and equipment (willbe even less costly with wider application andfurther commercialization);

• Conservation and guarding non-renewable ener-gy sources for future generations (in accordancewith sustainable development principles);

• Energy independence of the country; • Lesser emission of CO2, CO, along with numer-

ous other ecological benefits;• Prospect for alternative economic development

including tourism, recreation and the develop-ment of spa centers.

The two stages (cascade) heating pumps enable theexploitation of low enthalpy sources with tempera-tures over 10°C. However, every additional tempera-ture degree makes this exploitation more feasible.Some regions such as eastern Serbia are a good exam-ple to demonstrate the feasibility and advantages ofthe development of subgeothermal resources and

wider application of cascade heat pumps. One of themain advantages is the existence of a centralized heat-ing infrastructure in most of the small or mediumsized cities in the region.

Acknowledgements

The authors gratefully acknowledge the financial andadministrative support provided by EUREKA Programmeof the European Union and the Ministry of Science andTechnological Development of Serbia for the implementa-tion of the R&D projects !EUREKA 4117, SGTE 18008,and OI 176022. We are also acknowledging valuable com-ments provided by the reviewers Dr HANS ZOJER (WATER-POLL, Graz) and Dr ALEKSEY BENDEREV (GeologicalInstitute of Bulgarian Academy od Science, Sofia) whichhelped to improve quality of our work.

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Резиме

Потенцијал субгеотермалнихводних ресурса за ширe енергетскоискоришћавање - пример источнеСрбије

Геолошки услови на подручју Србије и балкан-ских земаља не омогућују формирање хипертер-малних вода у плићим структурама (до 2000 m),самим тим ни постојање геотермалне енергије којаби се могла користити за производњу електричнеенергије. Међутим, потенцијал за коришћење тер-малних вода и водних ресурса различите темпера-туре за грејање је велики. Само у Србији регистро-вано је преко 230 извора и бунара са термалним иминералним водама. Од тога 2/3 ових вода су сатемпературом већом од 20°C. Већина термалнихвода се користи у балнеологији, а само мањи број

појава за потребе грејања. Насупрот томе, у су-седној Мађарској геотемална енергија се користиза потребе грејања у многим местима. У суседномХодмезовасархелy, преко 50 000 становника доби-ја топлотну енергију из термалних вода темпера-туре од 80°C, захваћене на дубини од 2000 m (75 %искоришћене воде се реињектира назад у геоло-шку средину).

Спроведене новије анализе усемерене на про-цену потенцијала субгеотермалних водних ресур-са у Србији, увеле су термин „субгеотермалниресурси” (СTЕВАНОВИЋ и др. 2008). Овој категоријиби припадале воде температуре 30°C или ниже,док би воде температуре од 30 до 100°C предста-вљале “геотермалне ресурсе”. Док су геотермалнетоплотне пумпе (ГТП) неопходне за подизање тем-пературе хладније воде, панелни систем грејањадозвољава директно коришћење вода температура30°C или више, и то без употребе пумпи. Наравно,површина панела за грејање мора бити већа што сутемпературе ниже.

Коришћење геотермалне енергије ниске ентал-пије за потребе грејања (или хлађења) простора јешироко распрострањено у САД и Канади, а од не-давно је приметан пораст интересовања и широмЕвропе (BANKS 2008). ГТП се могу сматрати ал-тернативном технологијом, пошто им је потребнодовођење механичке или топлотне енергије (оби-чно електричне енергије до компресора), како бисе геотемална енергија “извукла” за коришћење.При том, топлотни ефекат добијен радом ГТП јеобично 3–4 пута већи од утрошене електричнеенергије потребне за њен рад. Произведена то-плота је уједно и 3–4 пута јефтинија, са до 75 %мање емисије CO2, у односу на најефикасније си-стеме за грејање са сагоревањем фосилних горива.

Иако су почетна инвестициона улагања у ГТПвисока, касније уштеде и еколошке предностиусловиле су да посебно у земљама Европске Унијезначајно порасте интерес за коришћење овог вида“зелене“ енергије. Илустративни пример су Чешкаи Пољска у којима је током 2000. године било не-што мање од 1000 оперативних ГТП, а само петгодина касније број инсталираних система се по-већао десетоструко.

Тренутно, у земљама ЕУ скоро 50 % укупне про-изводње енергије троши се на стамбене објекте. УСрбији је овај проценат знатно већи, готово 2/3 це-локупне потребне енергије се користи за грејањедомаћинстава. То је и логично ако се има у виду даје више од 50 % стамбених објекта у Србији изгра-ђено пре 1970, када термоизолација у станоградњиније била обавезна. Према неким проценама,годишњи утрошак енергије је у распону од 150 до250 kWh/m2, што је 2–3 пута више од оптималног.

Постоји неколико разлога због чега је областКарпато-балканида источне Србије разматрана каоподручје у коме би се могли активније користити

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ресурси субгеотермалне енергије: обилује значај-ним резервама подземних вода које нису у потпу-ности искоришћене за друге намене, има значајанброј термалних и субгеотермалних природнихводних појава, у овој области се налази и значајанброј мањих индустријских градова са развијеноминфраструктуром централног грејања, и има ре-лативно специфичан умерено-континетални типклимата. Ова област је перспективна и за развојтуризма. Природни амбијент је релативно очуван,богата је чистом водом, и разноврсним природнимпојавама (пећине, водопади, извори), укључујућинеколико бања и медицинских центара. Све то јепотенцијал чијој би већој валоризацији могли до-принети и ефикаснији системи грејања.

У неколико раније спроведених студија (STEVA-NOVIĆ 1994, 2009; MILIVOJEVIĆ & MARTINOVIĆ 2005,2010; МАРTИНОВИЋ и др. 2008; СTЕВАНОВИЋ и др.2008) закључено је да је источна Србија један одрегиона у земљи са највећим потенцијалом за екс-плоатацију подземних вода и субгеотермалнеенергије. У практичном смислу, најзначајнији јекарстни тип издани формиран у оквиру јурских икредних кречњака, који заузимају око 30 % овеобласти и у којима су акумулиране резерве водапроцењене на преко 12 m3/s.

Према прелиминарној процени, око 1,7 m3/sподземних вода источне Србије из различитихгеолошких средина, могло би се експлоатисати иодрживо користи за потребе система за греја-ње/хлађење (СTЕВАНОВИЋ и др. 2008). Тај потенци-јални капацитет резултат је прорачуна који је узеоу обзир да су приоритет воде које се користе запиће и индустријско водоснабдевање, као и да семора обезбедити и еколошки проток воде за низ-водне екосистеме. Субгеотермални ресурси суподељени у три категорије (табела 1).

Процењено је да је укупни потенцијал термалнеенергије, која се може добити из субгеотермалних

вода око 33 MWt за већа насеља. То би пред-стављало око 16 % њихових укупних енергетскихпотреба. Проценат покривености топлотног конзу-ма за одабране градове се креће између 11 и 29 %.Највеће учешће субгеотермалних вода за грејањемогло би се остварити у Неготину, где су рела-тивно значајни ресурси подземних вода у близининешто мањег урбаног насеља.

Иако је познато да се субгеотермални потен-цијал не може практично никада искористити употпуности, анализа указује и да је потенцијалсубгеотермалне енергије у источној Србији далековећи од 4%, колико је у плановима енергетскогразвоја предвиђено да би могло износити укупноучешће геотермалних ресурса на нивоу Србије.

Значајан геотермални потенцијал захтева даљасистематска истраживања, као и развој нове стра-тегије и законодавства у енергетици. Према томе,очекује се већа државна подршка за производњу“зелене” енергије. Одрживо коришћење подзем-них вода треба да буде праћено и контролисаномексплоатацијом (обезбеђивањем експлоатационихдозвола), као и сталним мониторингом, са циљемда се спречава прецрпљивање издани и могућапојава пратећих техногених процеса.

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Табела 1. Енергетски потенцијал субгеотермалнихизвора