Volume 7 / Issue 2 MAY 2014 www.fe.um.si/en/jet.html Journal of ENERGY TECHNOLOGY ✓—____л Ш VOLUME 7 / Issue 2 Revija Journal of Energy Technology (JET) je indeksirana v naslednjih bazah: INSPEC©, Cambridge Scientific Abstracts: Abstracts in New Technologies and Engineering (CSA ANTE), ProQuest's Technology Research Database. The Journal of Energy Technology (JET) is indexed and abstracted in the following databases: INSPEC©, Cambridge Scientific Abstracts: Abstracts in New Technologies and Engineering (CSA ANTE), ProQuest's Technology Research Database. /_____ ш JOURNAL OF ENERGY TECHNOLOGY Ustanovitelj / FOUNDER Fakulteta za energetiko, UNIVERZA V MARIBORU / FACULTY OF ENERGY TECHNOLOGY, UNIVERSITY OF MARIBOR Izdajatelj / PUBLISHER Fakulteta za energetiko, UNIVERZA V MARIBORU / FACULTY OF ENERGY TECHNOLOGY, UNIVERSITY OF MARIBOR Odgovorni urednik / EDITOR-IN-CHIEF Andrej PREDIN Uredniki / CO-EDITORS Jurij AVSEC Miralem HADŽISELIMOVIĆ Gorazd HREN Peter VIRTIČ Izdajateljski svet in uredniški odbor / PUBLISHING COUNCIL AND EDITORIAL BOARD Zasl. prof. dr. Dali ĐONLAGIĆ, Univerza v Mariboru, Slovenija, predsednik / University of Maribor, Slovenia, President Prof. dr. Jurij AVSEC, Univerza v Mariboru, Slovenija / University of Maribor, Slovenia Zasl. prof. dr. Bruno CVIKL, Univerza v Mariboru, Slovenija / University of Maribor, Slovenia Prof. ddr. Denis ĐONLAGIĆ, Univerza v Mariboru, Slovenija / University of Maribor, Slovenia Prof. dr. Danilo FERETIĆ, Sveučilište u Zagrebu, Hrvaška / University in Zagreb, Croatia Doc. dr. Željko HEDERIĆ, Sveučilište Josipa Jurja Strossmayera u Osijeku, Hrvatska / Josip Juraj Strossmayer University Osijek, Croatia Izr. prof. dr. Miralem HADŽISELIMOVIĆ, Univerza v Mariboru, Slovenija / University of Maribor, Slovenia Doc. dr. Gorazd HREN, Univerza v Mariboru, Slovenija / University of Maribor, Slovenia Prof. dr. Roman KLASINC, Technische Universität Graz, Avstrija / Graz University Of Technology, Austria Prof. dr. Ivan Aleksander KODELI, Institut Jožef Stefan, Slovenija / Jožef Stefan Institute, Slovenia Prof. dr. Alfred LEIPERTZ, Universität Erlangen, Nemčija / University of Erlangen, Germany Prof. dr. Branimir MATIJAŠEVIČ, Sveučilište u Zagrebu, Hrvaška / University of Zagreb, Croatia Prof. dr. Borut MAVKO, Institut Jožef Stefan, Slovenija / Jozef Stefan Institute, Slovenia Prof. dr. Matej MENCINGER, Univerza v Mariboru, Slovenija / University of Maribor, Slovenia Prof. dr. Greg NATERER, University of Ontario, Kanada / University of Ontario, Canada Prof. dr. Enrico NOBILE, Università degli Studi di Trieste, Italia / University of Trieste, Italy Prof. dr. Andrej PREDIN, Univerza v Mariboru, Slovenija / University of Maribor, Slovenia Prof. dr. Aleksandar SALJNIKOV, Univerza Beograd, Srbija / University of Beograd, Serbia Prof. dr. Brane ŠIROK, Univerza v Ljubljani, Slovenija / University of Ljubljana, Slovenia Doc. dr. Andrej TRKOV, Institut Jožef Stefan, Slovenija / Jožef Stefan Institute, Slovenia Izr. prof. dr. Peter VIRTIČ, Univerza v Mariboru, Slovenija / University of Maribor, Slovenia Prof. dr. Koichi WATANABE, KEIO University, Japonska / KEIO University, Japan Prof. dr. Mykhailo ZAGIRNYAK, Kremenchuk Mykhailo Ostrohradskyi National University, Ukrajina / Kremenchuk Mykhailo Os-trohradskyi National University, Ukraine, Tehniška podpora / TECHNICAL SUPPORT Tamara BREČKO BOGOVČIČ, Janko OMERZU izhajanje revije / PUBLISHING Revija izhaja štirikrat letno v nakladi 150 izvodov. Članki so dostopni na spletni strani revije -www.fe.um.si/si/jet.html / The journal is published four times a year. Articles are available at the journal's home page - www.fe.uiri.si/en/jet.htiTil. Cena posameznega izvoda revije (brez DDV) / Price per issue (VAT not included in price): 50,00 EUR Informacije o naročninah / Subscription information: http://www.fe.um.si/en/jet/subscrip-tions.html Lektoriranje / LANGUAGE EDITING Terry T. JACKSON Oblikovanje in tisk / DESIGN AND PRINT Fotografila, Boštjan Colarič s.p. Oblikovanje revije in znaka revije / JOURNAL AND LOGO DESIGN Andrej PREDIN Ustanovni urednik / FOUNDING EDITOR Andrej PREDIN Izdajanje revije JET finančno podpira Javna agencija za raziskovalno dejavnost Republike Slovenije iz sredstev državnega proračuna iz naslova razpisa za sofinanciranje domačih znanstvenih periodičnih publikacij / The Journal of Energy Technology is co-financed by the Slovenian Research Agency. Odkupne cene električne energije, proizvedene iz OVE virov in SPTE v Sloveniji v letu 2014 Borzen, organizator trga z električno energijo d.o.o. je izdal dokument Določanje višine podpor električni energiji proizvedeni iz OVE in SPTE in višine podpor v letu 2014, ki veljajo za elektrarne, ki vstopijo v sistem podpor. Opredeljen je bil z novim Energetskim Zakonom (veljaven od 22. 3. 2014). Dokument predstavlja neuradni izračun višin podpor za leto 2014 (uradni izračun opravi Javna Agencija RS za energijo). Splošno je razviden padec povprečnih odkupnih cen od leta 2009, ko je le-ta znašala 65 €/MWh, na 43,31 €/MWh, ki velja v letošnjem letu. To pomeni znižanje odkupnih cen na 66,6 % cene iz leta 2009. Navkljub padcu cen veliki proizvajalci električne energije v Sloveniji tarnajo, da te subvencije zajedajo njihov dobiček in tako posredno ogrožajo delovna mesta na področju energetike. Ponovno se torej odpira stara dilema ali subvencionirati proizvodno ali investicije na področju OVE in SPTE virov, seveda v manjših enotah. V kolikor v Sloveniji resno mislimo na pot večjega koriščenja OVE virov, potem seveda ni dileme, da so subvencije potrebne kot vzpodbuda potencialnim investitorjem. Vendar samo to ne bo dovolj. Hkrati bi morali posodabljati električno omrežje v smeri razvoja pametnih omrežij, ki lažje (ustrezno) vključujejo in upravljajo z manjšimi proizvodnimi enotami. Tu pa seveda trčimo ob problem investicijskega denarja, ki ga praviloma za omrežje vedno zmanjka. Investicija je visoka, povrnitev vloženih sredstev pa dolgoročna. To seveda ni zanimivo za investitorje, ki želijo čim prej in čim bolje povrniti vložena sredstva. V vmesnem obdobju, na prehodu iz ogljične v nizko-ogljično družbo, pa seveda brez velikih trajno-stnih energetskih postrojenj še ne bo šlo. Andrej PREDIN The prices of electricity produced from renewable sources and cogeneration in Slovenia in 2014 Borzen, the electricity market company, has issued a report entitled Determination of the level of support for electricity generated from RES and CHP and the level of support in 2014, which applies to plants in the support system defined by the new Energy Act (in force since March 22, 2014). This document presents an informal calculation of the level of support for the 2014 (the official calculation is performed by Public Agency for Energy). It shows that there has been a decrease in average purchase prices since 2009, when it stood at €65/MWh, to €43.31/MWh in 2014, which means a reduction in feed-in tariffs to 66.6%. Despite the fall in prices, large producers of electricity in Slovenia complain that subsidies have parasitic effect on their profits and thus indirectly threaten jobs in the energy sector. Therefore, once again, the old dilemma of whether to subsidize production or investment in the field of RES and cogeneration sources has been raised. If in Slovenia we intend to continue on the path of greater use of renewable sources, then, of course, the dilemma is that subsidies are necessary as an incentive to potential investors. However, they will not be enough. The incentives should simultaneously update the electricity grid towards the development of smart grids, which are better (properly) included and manage small production units. Here, of course, is the issue is the problem of investment money which, as a rule, the network still handles. The investment is high, and return on investment is long-term. This is not interesting for investors who want to recover their funds invested as soon as possible. In the meantime, the transition from a carbon society in a low-carbon society will not work without major sustainable energy plants. Andrej PREDIN Table of Contents / Kazalo Current-temperature analysis of the ampacity of overhead conductors depending on applied standards / Analiza tokovno-temperaturne preobremenljivosti vodnikov daljnovodov glede na uporabljene standarde Ivica Petrovič, Hrvoje Glavaš, Željko Hederić..............................11 Small hydropower plants in Slovenia / Male hidroelektrarne v Sloveniji Primož Mavsar...............................................29 Global trends and the thermal energy capacities greater than 10 MW in Slovenia / Svetovni trendi in stanje termoenergetike nad 10 MW v Sloveniji Dušan Strušnik...............................................39 A case study of exergy analysis of waste heat recovery in refrigeration system / Analiza eksergijskih tokov v hladilnem sistemu z izkoriščanjem odpadne toplote Ivana Tršelič, Jurij Avsec..........................................53 Renewable energy potential and opportunities for organic farming in the region of the Šalek valley / Obnovljivi energetski potenciali in sonaravno kmetijstvo širšega območja Šaleške doline Natalija Špeh, Nataša Kopušar......................................67 Instructions for authors..........................................79 i Journal of Technology Energy JET Volume 7 (2014) p.p. 11-28 Issue 2, May 2014 www.fe.um.si/en/jet.html CURRENT-TEMPERATURE ANALYSIS OF THE AMPACITY OF OVERHEAD CONDUCTORS DEPENDING ON APPLIED STANDARDS ANALIZA TOKOVNO-TEMPERATURNE PREOBREMENLJIVOSTI VODNIKOV DALJNOVODOV GLEDE NA UPORABLJENE STANDARDE Keywords: Transmission capacity, Ampacity, Conductor Temperature, Overhead Power Line The opening of the electricity market is accompanied by new market participants whose requirements need to be fulfilled in order for the electricity market to function. To do so, transmission capacity is of significant importance. As the building of new overhead lines is an expensive and long-term investment, increasing the transmission capacities of existing lines is an unavoidable necessity. The transmission capacity of overhead power lines is commonly determined by limitations on the conductor's temperature, characterized by its ampacity. The conductor's temperature, and therefore the ampacity, is dependent on weather conditions. This fact enables increasing the transmission capacity according to calculations based on current weather conditions and forecasts, as opposed to static and conservative values. This paper discusses the application of different standards and comparison of results for transmission capacity value, with particular reference to Croatian legislation on transmission overhead power lines. Calculation of sensitivity on input parameters is also examined because of the changes in the weather that change transmission capacity. As an extreme case of unfavourable weather R Corresponding author: Ivica Petrovič, PhD, Tel.: +385 91 766 17 87, Fax: +385 31 21 31 21, E-mail address: ivica.petrovic@hops.hr Ivica Petrovič* Hrvoje Glavaš, Željko Hederič Abstract conditions, an example is given of transmission capacity value trends during the hottest recorded day Croatia. The conclusion is that increases of the transmission capacity on particular power lines is possible but, for the safe and secure operation of the transmission grid, a seasonal regime of operation or ampacity zones depending on the time of the year could be made. Povzetek Odpiranje trga z električno energijo spremlja vstop novih udeležencev na trg, kateri morajo izpolniti določene zahteve, da trg z električno energijo lahko nemoteno deluje ob upoštevanju prenosne zmogljivosti prenosnega omrežja. Gradnja novih daljnovodov je finančno zahtevna ter predstavlja dolgoročne naložbe in je žal neizogibna zaradi želenega povečanja prenosnih zmogljivosti obstoječih daljnovodov. Maksimalna tokovna zmogljivost in temperatura vodnikov omejuje zmogljivost prenosa daljnovodov. To dejstvo omogoča povečati prenosno zmogljivost v skladu z izračuni, ki temeljijo na trenutnih vremenskih razmerah in napovedih, v nasprotju s statičnimi in klasičnimi vrednostmi. Ta članek obravnava uporabo različnih standardov in primerja rezultate vrednosti prenosnih zmogljivosti prenosnih daljnovodov z upoštevanjem hrvaške zakonodaje. Analiziran je vremenski vpliv na vhodne parametre, kar vpliva na prenosne zmogljivosti in posledično na občutljivost izračuna. Kot ekstremni primer neugodnega vremenskega vpliva je v analizi zajet tudi najbolj vroč dan na območju hrvaškega prenosnega sistema. V zaključku dela je predstavljeno, da je možno povečati zmogljivosti prenosnega omrežja oziroma posameznih daljnovodov, vendar za varno in zanesljivo obratovanje omrežja je potrebno upoštevati sezonski režim delovanja. 1 INTRODUCTION The transmission capacity of electric grid elements is significantly defined by deterministic safety criteria. Therefore, certain categories of failures or breakdowns are of great importance for the assessment of an electric grid and electric power system safety. If a physical quantity (allowed current, voltage, etc.) exceeds the defined and allowed range of values in the case of failure, the situation before the fault is considered to be unsafe. According to the safety criteria, the grid configuration must be designed in such a manner that it is able to ensure, in all operating conditions, that the failure of any power line does not lead to operational restrictions of its own and/or neighboring regulation areas. For the same reason, regulations for power lines treat and determine the highest ampacity of overhead conductors in individual systems. From that, the timely determination of the available transmission capacity must follow, as is the most urgent task to be perform in order to increase both the safety and efficiency of the electricity system. Due to a significant number of cases in which the transmission capacity is determined by the highest allowed conductor temperature, such determination or calculation of the conductor temperature during operation is becoming increasingly important. Therefore, the conductor temperature values are calculated with regard to regulations and all factors that affect heating and cooling. Specific research is conducted on the mathematical impact of each factor on the determination of the conductor temperature calculation. 2 VALID STANDARDS IN CROATIA FOR CALCULATION OF AMPACITY IN OVERHEAD CONDUCTOR Designing overhead power lines in Croatia is subjected to the Ordinance of technical standards for the construction of overhead power lines of nominal voltage from 1 kV to 400 kV (Croatian Official Gazette (COG) 53/91, 24/97). The valid ordinance is taken from the Official Journal of SFRY 65/88 in which the conductors and protecting wires are calculated for a range of temperatures from -20°C minimum to +40°C maximum, and for the temperature at which there is an additional load, i.e. -5°C. Article 16 states that the cross section of the conductor lines must be large enough that the overall temperature of the conductor due to the heating from the current does not exceed +80°C, whereby the calculation is conducted with an ambient temperature of +40°C. The article remains unchanged, apart the amendment in 1997 for classic conductor ropes, while for special conductors it allows exceeding the earlier specified conductor temperature if there is proven mechanical stability for a specific conductor. The final result of the maximum conductor temperature corresponds to the most adverse weather conditions, i.e. a small or negligible influence of wind (up to 0.6 m/s) and continuous ambient temperature of +40°C. The value of ampacity determined by this method, in most cases, even in the summer under maximum temperatures, remains below the possible ampacity limit with regard to the temperature limit and regulated safety heights, COG No. 24/97, [1]. 3 CALCULATION OF TEMPERATURE ACCORDING TO THE IEEE STD 738-2006 Calculation of the temperature of bare, non-insulated overhead power lines is made with various methods that serve for the calculation of heat transfer and allowed current load of transmission power lines. The mathematical basis of the calculation used is the House and Tuttle method altered and adjusted according to the ECAR (East Central Area Reliability). The method takes into account all the relevant weather factors (influence of the sun and wind) without simplifications, which are made in some other calculations, IEEE [2]. The conductor temperature at a specific location is a function of more variables that have different impacts on the calculation. In the first place, there are weather conditions and their variability in space and time. Other important factors are solar flux, power line orientation in relation to the position of the sun and the direction of the wind motion, the type of the terrain (hilly, forested, etc.), cross-section and the percentage of aluminum in the cross-section, characteristics of materials including steel core, conductor geometry and 'air pockets', current, connected equipment, the density and viscosity of air, surface and external conditions (coefficient of emission and absorption) and corrosion, IEEE [3]. Potentially the greatest mistake possible in the temperature calculation involves a variable that takes into account direction and wind motion. This is because the wind motion is subjected to frequent changes. In the upper atmosphere, wind motion is relatively laminar, but closer to the surface, due to the influence of the terrain and the thermal effects, the motion of the wind becomes turbulent. Therefore, it is necessary to distinguish the still air flow from the turbulent air flow. The House and Tuttle method uses two different equations for forced convection or heat transfer with large air flow. Since the turbulence begins at a certain wind speeds and reaches its peak at higher speeds, the transition from one curve to another is a curve, not a discontinuity. A single value is Issue 2 selected as a suitable value for the calculation of permissible conductor loads; the individual value of transfer results in a discontinuity of current, when this value is reached. Therefore, to avoid this discontinuity, which occurs in House and Tuttle method, ECAR makes a change from still air motion into forced, turbulent air flow at the point or place where the curves are the result from the crossing of two equations (4.1 and 4.2). This method is primarily intended for calculating thermal values at a fixed state and transient occurrences, and conductor temperatures at fixed, constant weather conditions. In the given circumstances of widely available computers, the method for calculation bypasses certain simplifications, which can be recommended when speed or complexity of calculation, is of great importance. Weather conditions often vary along power lines; therefore, the temperature of the conductor varies from one section to another of the same power line. The proper evaluation and calculation of the conductor temperature via IEE Std 738-2006 should take into account local weather conditions along the sections of the power line. 3.1 Calculation at fixed (constant) state If there is data available for the maximum temperature of a non-insulated, intertwined conductor (Tc) and weather parameters for constant (unchanging) conditions (Vw Ta etc.), it is possible to calculate heat losses due to convection and radiation (qc and qt), gain of heat by insolation (qs) and conductor resistance R(Tc) using the equations in the third chapter. Corresponding conductor current (I), which produced this temperature under these weather conditions can be found from the heat balance equation of an unchanging state, according to Equation 3.1. While this calculation can be done for each conductor temperature and under all weather conditions, the maximum allowed temperature of the conductor (e.g. 75°C to 150°C) and moderate weather conditions (e.g. 0.6 m/s to 1.2 m/s wind speed, 30°C to 45°C in summer weather conditions) are often used to calculate the thermal values of conductors at a constant state. Since heat losses by radiation and convection are not linearly dependent on the conductor temperature, the heat balance equation (3.2) yields conductor temperature expressions for current and weather variables by iteration, i.e. by taking into account electrical current of the conductor: a) Conductor temperature is assumed, b) Corresponding heat losses are calculated, c) Conductor current that generates this temperature is calculated according to Equation 3.2, d) Calculated current is compared with given conductor current, e) Conductor temperature is then increased or decreased, until the calculated current does not reach the set current. 4c + 4r = 4s +12 ■ K(Tc) (3.1) (3.2) 3.2 Calculation at transient state Thermal evaluation of a transient state is regularly calculated by repeating the previous calculations Tc(t) in the range of f values, and then selecting If value, which causes the conductor temperature to raach its maximum value in agiven time. The temperature of the overhead |uower line is conatantly changing, in accordance with chagges of the current and the weatger conditions. It is assumed that the weather parameters (speed agd direction ol wiud, ambient temparature, etc.) are not changed and that every change of current is limited by h gradual rteu clange, from the initiel current Ii to the Unal current If, as shown in Figuce 3.1. Shortly before the step o r gradual clange of cuenent (t=0- ), i t i s aashmed that the cond ucro r is in thenm al equilibrium, i. e. that t he sum of thg heat produced by ohmic losses and heat of the sun is equal te the heat loss by convection and radiation, [10]. Immediately after the gradual, step change of the current (t=0+), the conductor temeerature is enchanged (as conductor resistance and heat losses due to convectien and radiation), but there is aa increase in heat generation due to ohmic losses. Therefore, at momaat t=0+ tit e conductor temperature begins to increase, the increase Is given in the leat balance eqgetion for transient state (3.3 ), as follows: ? = + (3.3) that is qc + qr+ mCp ^ = (3.4) After a period of time, At, the conductor temperature increases with temperature change, ATC. Increased conductor temperature leads to greater heat losses due to convection and radiation, and a greater ohmlc resisUance of tie conductos due to iacreased huat gageratioc. Tihe; aonductor temperature continues to rise from At to 2At, but with a smaller increase. After ai farge number of sgcC time Inteevale, tha conductor temperattee approaches ies Unal temperature of constant state, Tf. The acsurncy of the iterative calculatian off thu sransient state requires thaf the snt time of the step or gradual change is sufficiently short compared to the thermal time constant. It is always prudent to sepeat the calculation with a shortet interval of change, in order to check the change oU the calcalateU valtes. 4 EQUATIONS FOR CALCULATION OF THERMAL VALUES (STATES) AND RESISTANCE OF THE CONDUCTOR Previously, equations for the thermal equilibrium of the fixed state and transient state from 3.1 to 3.4 have been given. Heat losses due to forced convection is described in Equation 4.1, which is used for weak winds, while Equation 4.2 is used for high-speed winds [9]. 4a - 4c2 - 1,01 + 0,0372 ■ f^1)0'52] * kf ■ Kangle ■ (Tc - Ta) 0,0119 ■ 6 ■ kf ■ Kangle ■ (Tc - Ta) (4.1) (4.2) At any wind speed, the higher value of the two calculated heat losses due to convection is taken. The loss of heat due to transmission by the wind is multiplied by the wind movement factor, where ф is the angle between the wind direction and axis of the conductor (see Equation 3.3). Kangle = l-l94 " C0S(P + °Д94 ' COs(2) -1 sin(Lat)cos(a>)-cos(Lat)tan(5)J The constant of the solar azimuth C (in degrees), is the function of hour angle w, and the solar azimuth variable x, as shown in Table 3. Table 3: Constant of the solar azimuth C, as a function of hour angle, and the solar azimuth variable x Hour angle w [°] C if x>0° C if x<0° -180 ^ Type of ACSR conductor Figure 3: Comparison of ampacities by applied standard on 7.5.2013 at 20 h Figure 3 shows the compared results of allowed ampacity depending on the applied standard, for typical constructions of ACSR conductors according to the HRN N.C1.351 standard. It can be seen that the ampacity in the case of IEEE Std 738 is 25% to 40% higher than the results according to the COG No. 24/97, [1]. In conclusion, it can be said that ACSR conductors are loaded under the limit most of the time. The ampacity that is considered as a standard is valid for a very short time period of the year. The most unfavourable day in 2012 was 6 August, on which the temperature reached 40°C throughout Croatia, but only between 10:00 and 17:00. This fact is significant because of the possibility for a particular power line to become overloaded for a definite time interval beyond the limits set by legislation, in order to meet the requirements of demanding market participants. 7 CALCULATION SENSITIVITY ON INPUT PARAMETERS According to IEEE Std 738-2006, described in previous chapters, calculation of ampacity considering input parameters is (beside ambient temperature and the time of the day) is most sensitive when the speed and direction of the wind are taken into account. The accuracy of the method according to the applied standard has been the subject of discussion, but there were determined minimum deviations in regard to the actual situation, Strobach, Straumann, Franck, [4], and Lindberg, [5]. For example, the ACSR conductor, type 490/65 on the relation between Zagreb and Osijek is taken. In this account, the initial data of conductor characteristics, the location of the power line and the weather conditions of the meteorological stations are taken for 12 May 2013 at 13:00. The most unfavourable factor in the calculation is the analysis of wind motion. Fluctuations in air motions are continuous and constantly changing. Figure 4 shows the impact of the incident angle between the wind flow and power line direction on the final result of the maximum allowed current. An error that can be entered in the calculation is not significant if it is an angle between 70° and 90°. However, for angles up to 30°, errors can amount to 20% of the total allowed current value. The differences are more pronounced as the wind speed increases. 0 0 10 20 30 40 50 60 70 80 90 ni1 Гп-а! 0 1950 1960 1970 1980 1990 2000 2100 Years Figure 1: Global trends of fuel consumption, EIA [4] The Kyoto protocol is an international treaty that attempts to reduce the emission of carbon dioxide and five other greenhouse gases. This protocol has been valid since February 2005. By 2009, the treaty had been ratified by 183 countries and the European Union. At the time of signing the protocol, 37 developed countries and 15 member countries of the European Union agreed to the obligations of reaching the Kyoto aims, [5]. In Article 17 of the Kyoto protocol, the trading of emission quotas is defined. Consequently, in the case of emissions of greenhouse gases that are higher than allowed, the signatory countries have to buy emission quotas on the market. These greenhouse gas emission quotas, which are granted to the member states, will be reduced in the course of time, which means that the countries will have to buy quotas on the market or invest into new technologies. As a result of this treaty, we can expect further decreases of coal technology, as the technology for natural gas will be economically more favourable. There has been a decrease of emissions of carbon dioxide produced by burning coal and an emission increase of carbon dioxide produced by burning gas since 2006 (Fig. 2). This trend should also continue in the future. ш Electric Power, by Major Source "П 1ППЛ Coal 1950 I960 1970 1980 1990 Years 2000 2010 Figure 2: Emission of gas CO^ EIA [4] A negative trend of coal usage is evident in thermoelectric plants, as modern gas technologies for producing electricity are becoming increasingly effective, efficient and profitable. If the progressively demanding ecological restrictions are also considered, gas has massive potential. Global energy usage trends also indicate a decrease of coal technology and an increase of gas technology (Fig. 3). Figure 3: Production of electricity, EIA [4] From a global perspective, in 2002 50% of electricity was produced by burning coal and 18% by burning gas. By 2012, the production of electricity obtained from coal had been reduced by 37%; the production of electricity obtained from gas had increased by 34%. It is notable that the increased gas consumption is matched with the beginning of gas production from unconventional sources (e.g. slate) in 2009. The trend of energy consumption in Europe is decreasing, because of the financial crisis; both trends (the energy trend and financial crisis) are simultaneous. There is a decrease in economic activity, including industry, production, and purchasing power; consequently, the need for energy is also decreasing. Nevertheless, increased consumption of gas can be observed, because of the lower usage of coal (Fig. 4). European consumption trends are compatible with global trends and are based on cleaner technology. 140 Gross inland consumption of coal and gas, 1955-2012 (1995-100%) 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 Years Figure 4: Usage of coal and gas [6] In March 2007, The European Commission for a Lower Carbon Society accepted additional commitments [7]. These commitments are: • Emissions decrease of greenhouse gases by 20% and, according to special conditions, even by 30%, in the period from 1990 to 2020, • increase of renewable energy sources by 20%, and • improvement of energy efficiency by 20%. 1.2 Long-term trends Long-term global trends indicate a steady increase of energy needs, which will be provided by increased usage of already known fuels. Of key importance to fuel usage are economic guidelines. The International Energy Agency, [8], has presented two anticipated scenarios: the Basic and the Blue courses of events. They represent a basis for further economic development strategy and are based on implementation of low carbon technologies to 2050, [9]. According to the Basic Scenario, any new energy or environmental policy will not be accepted. The average anticipated global economic growth is per 3.1% yearly. The Blue Scenario is based on a low carbon society. It anticipates that by the year 2050 the global emissions of carbon dioxide will decrease to a level of 50% of the current amount and that global temperatures will not rise by more than 2°C or 3°C. This goal can only be achieved when there will also be a decrease of the emission of other greenhouse gases, in addition to the measures for reductions of carbon dioxide, [9]. To achieve the aims defined in the Blue Scenario, significant reductions in emissions in all sectors will have to be achieved by 2050: electricity, industrial and building sectors. In this case, the difference between the produced and consumed energy will have to be substituted by alternative sources. Dušan Strušnik JET Vol. 7 (2014) Issue 2 Figure 5: Primary energy needs according to the energy source and guidelines scenario [9] The IEA's prediction of a consumption trend of coal and gas is shown in Fig. 6. Figure 6: Consumption trends of coal and gas, IEA [8] 2 STATUS OF THERMAL ENERGY IN SLOVENIA Slovene and European trends have no fundamental differences, because they are based on the same environmental and energy directives. Slovenia consumes solid fuel in thermoelectric plants for the production of electricity and thermal energy. Because the domestic production of solid fuel does not satisfy current needs, some fuel is imported (Fig. 7). Over time, the amount of imported solid fuel has been quite consistent, and it will gradually increase in the future, because of a decrease of domestic production. The largest deficiencies in the usage of coal are its greenhouse gases. Therefore, the usage of domestic coal is in the future will be limited to lignite from the Velenje coal mine, for the production of electricity. The Kyoto protocol goal is the long-term reduction of all coal usage. The gradual closing of the Velenje coal mine is predicted around the year 2054. The closing of the Trbovlje-Hrastnik mine is predicted to occur in 2015, in accordance with the law on the developmental restructuring of the region. With the gradual decrease of the amount of coal usage, coal remains an element of domestic energy supply because of its strategic reliability and the diversification of energy sources, [10]. By 2020, Slovenia will have gradually stopped importing coal for the production of electricity. 23,3 17,4- o 11,6 4 * 5,8 j I. I. I. I. I. I. Il I. I. I. I. I. I I II II II II II II II II II II II II I 2000 2001 2002 2OO0 2004 2006 2006 2007 20СЙ 200Э 2010 2011 2012 ■ Domestic Prodotion ■ Import ■ Consumption Figure 7: Consumption trends of firm fuels in Slovenia [11] Slovenia imports almost all its natural gas. The energy needs for natural gas are increasing, and its price is formed on the market. The global trend is based on increased consumption of gas; higher gas prices can thus be expected. As a consequence, there will be increased energy dependence and more expensive energy for the consumer. For the supply of natural gas, the gradual convergence with the neighbouring markets will be of key importance. The competitiveness of the natural gas market will improve. Gas consumption will depend on electricity production, especially in high-efficiency joint production in local supply and industry. The assurance of energy service from remote heating systems will have priority over the extension of gas networks to new regions, [10]. 11,6 9,ì U1 L. о 6,9 га L. - - ------- - - ■ ------------- DJ - 23- - - - - - - - - —._._._ _ - О ——LM— ————LM— ———— — 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 ■ Domestic prodction ■ Import ■Consmption Figure 8: Trend of natural gas in Slovenia [11] Fig. 9 shows the usage of energy sources, which is fairly stable. On average, Slovenia imports 51% of its energy resources (energy dependence), and this will increase in time. Most energy is produced by burning solid fuels. 9,3 2000 2001 2002 2003 2004- 2005 2006 2007 2003 2009 2010 2011 2012 ■ Firm Fell Consumption ■ Natural Gass Consumption Domestic Energy h Energy Spply ■ Final Energy Consumption Production Figure 9: Energy indicators in Slovenia [11] 2.1 Thermal energy facilities with more than 10 MW capacity in Slovenia Thermoelectric plant Šoštanj (TEŠ) With 779 MW of power, TEŠ produces one third of the energy in the country. The annual production of electricity ranges from 3500 GWh to 3800 GWh. The annual production of thermal energy for remote heating of the Šaleška valley is from 400 GWh to 450 GWh. For the abovementioned production of electricity and thermal energy, from 3.5 to 4.2 million tons of coal and around 60 million m3 of natural gas is used every year, [12]. Table 1: Specified power of generators [12] Block Fuel Specified power of generators Steam block 1 Lignite Permanently halted on 31 March 2010 Steam block 2 Lignite Permanently halted in 2008 Steam block 3 Lignite 75 MW (to be permanently halted in 2015) Steam block 4 Lignite 275 MW (to be permanently halted in 2015) Steam block 5 Lignite 345 MW (to be permanently halted in 2027) Two gas blocks Natural gas 2 X 42 MW (permanently halted in 2027) After the acceptance of the Strategic Development Plan of TEŠ in June 2004, Block 6, with 600 MW, power will gradually replace the technologically outmoded and economically unprofitable Blocks 1, 2, 3, 4 and 5. This is a nationally important project, which the government accepted on 12 October 2006 and amended in 2008. It is a part of the Resolution of the National Energy Programme and of the Resolution of National and Development Projects for the period from 2007 to 2023. For the same amount of produced energy, Block 6 will use approximately 30% less coal, thereby significantly lowering emissions, [12]. Thermoelectric plant Toplarna Ljubljana (TE-TOL) TE-TOL is the largest combined heat and power generation in Slovenia. It supplies more than 90% of the needs of the remote heating system of Ljubljana, which represents approximately 50% of such needs for Slovenia, [13]. The electricity produced represents 3% of the needs for electricity in Slovenia. Table 2: Specified power [13] Block Fuel Specified power of generators Specified thermal power Steam block 1 Brown coal 42 MW 94 MW Steam block 2 Brown coal 32MW 94 MW Steam block 3 Brown coal Biomass 50 MW 152 MW LPB Oil 150 MW Since 2002, only Indonesian coal (low sulphur content) has been used in TE-TOL, because of the requirements of ecological legislation. The coal must have a high heating value and low sulphur content (under 0.2%) and ash (1-3%), [13]. Otherwise, the company would have to invest in expensive technology for cleaning emissions. In the boiler of Block 3, wood chips also have been used since 2008, replacing 20% of the coal. From renewable energy sources, approximately 8% of thermal energy and electricity is produced. From 1 January 2016 onward, TE-TOL will not be able to achieve the allowed emission of carbon dioxide (200 mg/m3); its average annual concentration around 400 mg/m3. With the transitional national plan, in which TE-TOL was included in December 2012 and is valid until 1st July 2020, the company will change the primary fuel from coal with natural gas. This gasification phase (PPE-TOL) is one of the measures in the transitional national plan of Slovenia. Thermoelectric plant Trbovlje (TET) TET is the largest energy facility in the Zasavje region. Together with the Zasavje coal mines, it had been a key element for the development of many factories, industrial and craft plants, traffic and social services in Zasavje and Slovenia. TET currently has two units; the steam block produces electricity from brown coal from the Zasavje coal mines, while the two gas blocks use natural gas and oil for the production of electricity; they are a reserve in the electrical energy system of Slovenia. TET sells the remaining amount of electricity independently on the market, [14]. Table 3: Specified power of generators [15] Block Fuel Specified power of generators Steam block Brown coal 125 MW Two gas blocks Oil Complete power 63 MW The vision of TET is the construction of a gas-steam electric power plant that has the possibility of being upgraded with an integrated gas combination cycle, which requires the gasification of coal or fuel oil as remainder in the process of refining oil and the implementation of neutralization technology of greenhouse gases. This vision also requires the renovation of gas blocks with a combined coal and wooden biomass unit with the possibility of using the heat energy for the heating of Zasavje. With the renovation of the gas blocks, the extraction of coal from the Trbovlje-Hrastnik coal mine would be extended, or the coal would have to be substituted by imports. Thermoelectric plant Brestanica (TEB) TEB provides reliable and safe electricity production, with the aim of remaining the leading provider of systemic services of tertiary regulation while simultaneously being an indispensable reserve electricity source for the Krško nuclear power plant. With its services, TEB is a reliable reserve electricity source for the electrical system of Slovenia at its most critical moments. With its fast aggregates, the plant enables rapid intervention at times of system overload or a cut out of Slovene electric power plants or power lines, thereby preventing collapses of the electrical energy network with quick intervention, restructuring of the electrical energy network after a failure, and providing an independent and direct energy source for the Krško nuclear power plant, [16]. Table 4: Specified power of generators [16] Block Fuel Specified power of generators Three gas blocks Oil or natural gas 3 x 23 MW Two gas blocks Oil or natural gas 2 x 114 MW The policy of the company is to keep or to increase its share of the market of systemic services of tertiary regulation on the domestic and foreign electricity markets, to optimise business costs, to provide high start-up reliability and availability of company devices, to continue with its active role in the maintenance chain of hydroelectric power plants on the lower River Sava and to maintain a quality system according to the ISO 9001 standard. Its purpose is to continue with the substitution of gas blocks with 3 x 23 MW power with new blocks, which will correspond both to ecological standards and the technical demands of tertiary regulation, and quick start up in the case of a collapse of the electrical networks, [16]. 3 CONCLUSION With the increasing population, development and economic growth, the need for energy has also increased. From a global perspective, energy needs are currently very different from continent to continent. The largest increase is in the developing economies of China and India. The biggest energy needs but with rather moderate growth is seen in the USA. European needs are decreasing somewhat, which is connected with economic indicators. The world is becoming increasingly ecologically conscious; consequently, environmental legislation, which is based on decreased emissions of greenhouse gases and environment protection, is of key importance. From a global perspective, the human factor represents only 4% of carbon dioxide emissions into the atmosphere. The warming of the oceans represents the largest part, i.e. 90%, of the increase of carbon dioxide concentration in the atmosphere. When the oceans' temperature decreases, carbon dioxide is absorbed, but when the temperature rises, carbon dioxide is released. Human use of energy, therefore, contributes only a small part of greenhouse gases; the rest is a consequence of the natural warming of the atmosphere (solar radiation, protective ozone layer, etc.). Nevertheless, environmental legislation forces the energy industry to buy new and more expensive technologies or to buy emission quotas. The global, European and Slovene energy industries have adjusted to the environmental guidelines with lower coal usage and greater usage of natural gas. The thermal energy industry of Slovenia uses both energy sources for the production of thermal energy and electricity in rather old and obsolete systems. In the transitional period until 2020, fundamental changes must occur, which will be seen in the closing of coal thermoelectric plants and investments into gas thermoelectric plants. The reason for this is also the closing of coal mines in Slovenia, as from 2015 only the coal mine in Velenje will be in operation. This, however, means that Slovenia will be increasingly dependent on imports. We will be able to import the energy sources in the primary form (coal, gas, oil) or as a final product in the form of electricity. References [1] Wikipedia: [Online]. Access to: http://sl.wikipedia.org/wiki/Ogenj#Odkritje in zgodovina ognja [05.07.2013]. [2] M. Obrecht: Študij dejavnikov pri modeliranju razvoja trajnostne energije, Univerza v Mariboru, Ekonomsko-poslovna fakulteta Maribor, 2012, pp. 50-51, [Online]. Access to: http:// dkum.uni-mb.si/IzpisGradiva.php?id=22929 [04.07.2013]. [3] Državni zbor RS: Resolucija o nacionalnem energetskem programu, Predlog 6.11.2003, pp. 6, [Online]. Access to: http://www.vlada.si/fileadmin/dokumenti/cns/ doc/0311120737551 46v7.doc [02.07.2013]. [4] U.S. Energy Information Administration (EIA): [Online]. Access to: http://www.eia.gov/ [05.07.2013]. [5] Wikipedia: [Online]. Access to: http: http://sl.wikipedia.org/wiki/Kjotski protokol [06.07.2013]. [6] European Commission EUROSTAT: [Online]. Access to: http://epp.eurostat.ec.europa.eu/ portal/page/portal/eurostat/home [05.07.2013]. [7] European Commission of Climate Action, The 2020 climate and energy package: [Online]. Access to: http://ec.europa.eu/clima/policies/package/index en.htm [05.07.2013]. [8] International Energy Agency (IEA): [Online]. Access to: http://www.iea.org/ [06.07.2013]. [9] B. Pišotek: Tehnologija zajemanja CO2 ter preučevanje njihovega vpliva na delovanje energetskih sistemov, Univerza v Mariboru, fakulteta za strojništvo, 2013, pp. 3-8. [10] Nacionalni energetski program Republike Slovenije (NEP): Osnutek predloga Nacionalnega energetskega programa Republike Slovenije za obdobje do leta 2030, Institut "Jožef Stefan", Ljubljana, Slovenija, Center za energetsko učinkovitost (CEU), 2011, pp. 95-107, [Online]. Access to: http://www.mg.gov.si/fileadmin/mg.gov.si/pageuploads/Energetika/Zelena knjiga NEP 2009/NEP 2010 2030/NEP 2030 jun 2011.pdf [04.07.2013]. [11] Statistični urad Republike Slovenije (SURS): [Online]. Access to: http://pxweb.stat.si/pxweb/ dialog/statfile2.asp [04.07.2013]. [12] Termoelektrarna Šoštanj(TEŠ): [Online]. Access to: http://www.te-sostanj.si/si/ [05.07.2013]. [13] Energetika Ljubljana, enota TE-TOL: [Online]. Access to: http://www.te-tol.si/ [05.07.2013]. [14] Wikipedia: [Online]. Access to: http://sl.wikipedia.org/wiki/Termoelektrarna Trbovlje [05.07.2013]. [15] Access to: http://sl.wikipedia.org/wiki/Termoelektrarna Trbovlje [05.07.2013]. [16] Termoelektrarna Brestanica (TEB): [Online]. Access to: http://www.teb.si/ [04.07.2013]. Nomenclature CO2 Carbon dioxide EIA U.S. Energy Information Administration EUROSTAT European Commission Statistic GWh Giga Watt Hour IEA International Energy Agency MW Mega Watt Mtoe Million Tonnes of Oil Equivalent NEP National Energy Programme of Slovenia LPB Low Pressure Boiler PPE-TOL Toplarna Ljubljana gas-steam energy source RS Republic Slovenia SURS Statistical Office of Slovenia TEB Brestabica thermoelectric plant TWh Tera Watt Hour TE-TOL Toplarna Ljubljana thermoelectric plant TEŠ Šoštanj thermoelectric plant TET Trbovlje thermoelectric plant Dušan Strušnik JET Vol. 7 (2014) Issue 2 Journal Of JE1 Volume 7 (2014) p.p. 53-66 Issue 2, May 2014 Energy Technology www.fe.um.si/en/jet.html A CASE STUDY OF EXERGY ANALYSIS OF WASTE HEAT RECOVERY IN REFRIGERATION SYSTEM ANALIZA EKSERGIJSKIH TOKOV V HLADILNEM SISTEMU Z IZKORIŠČANJEM ODPADNE TOPLOTE Ivana TršeličR Jurij Avsec Keywords: exergy analysis, refrigeration system, waste heat recovery Abstract From an energy perspective, refrigeration systems employ a wasteful process; nevertheless, the food industry depends on refrigeration systems. To improve the efficiency of this process, a refrigeration system can be combined with a heating system, by using the waste heat from the condenser of the refrigeration system in the heating system. A case study of the application of a waste heat recovery system is considered in this paper. The conserved energy for three years is calculated, based on the literature, i.e. practical engineering articles. The numbers given are compared with the case study. The economic analysis reveals that the investment in an advanced refrigeration system is returned over a very short time. Two system models are discussed: a refrigeration system with no alternation and a refrigeration system that applies the recovery of waste energy. Exergy analysis has been developed for both models. The analysis shows an increase in the exergy efficiency of the advanced refrigeration system by 2%. Povzetek Z vidika porabe energije je hladilni sistem zelo potraten. Industrija hrane je odvisna od hladilnih sistemov. Proces hlajenja lahko naredimo bolj učinkovit tako, da izkoriščamo odpadno kondenzator- R Corresponding author: Ivana Tršelič, Tel.: +386-7-620-2217, Mailing address: University of Maribor, Faculty of Energy Technology, Hočevarjev trg 1, 8270 Krško, Slovenia, E-mail address: ivana.trselic@um.si ш sko toploto. Opazovali smo konkreten primer na katerem smo sistem izkoriščanja odpadne toplote inštalirali. Izračunali smo izkoriščeno odpadno toploto v zadnjih treh letih delovanja sistema. Enačbe za preračun izrabljene odpadne toplote smo našli v starejši literaturi. Ekonomska analiza pokaže, da se začetna investicija povrne v zelo kratkem času. Z eksergijsko analizo sistema brez izkoriščanja odpadne toplote in sistema z izkoriščanjem odpadne toplote smo ugotovili, da ima slednji za 2% boljši eksergijski izkoristek. 1 INTRODUCTION Refrigeration chambers maintain foodstuffs at a particular temperature in order to extend the shelf life of foods. This paper deals with an exergy analysis of cold storage intended for freezing fish. The refrigeration chamber cooling system maintains a constant temperature by supplying cold through evaporators, thus compensating for heat losses through the refrigeration chamber walls or due to the impacts of lighting fittings, occasional opening of the door, etc. The refrigeration system is wasteful in terms of energy consumption. From an energy perspective, the upgrading the refrigeration system, involving the capturing of waste heat from the condenser to use the hot side of the cooling system, results in a greater effect, lower energy consumption and, ultimately, financial savings. Modern refrigeration rooms and cold stores are designed to freeze the largest possible quantity of food in the shortest time possible. This case study involves the storage of fish; freshly caught fish, a highly perishable food, should be stored in a flake ice bath, while frozen fish is stored in frozen fish chambers until taken over by a customer. Refrigeration tunnels operate when necessary, but the storage rooms have to maintain a constant temperature throughout the year. In terms of energy consumption, contemporary systems include new compressor designs with a so-called integrated eco-system, reducing isentropic losses by cooling hot gases during compression and installing a sub-cooler on the condenser side to increase the evaporator cooling power, using little energy. The use of condenser heat is necessary in order to increase the efficiency of the refrigeration system. This article deals with the calculation of savings, whereby the amount of heat recovered from the condenser unit is based on the equations found in articles by Die Klima und Kaeltetchnik, published in 1987, [1]. The exergy analysis of the upgraded system proves the improvement of refrigeration systems to be reasonable. 2 REFRIGERATION SYSTEM DESIGN The refrigeration system observed consists of five refrigeration units, the first of which is designed to maintain the temperature of the chambers with the packaging, and a corridor designed for handling. The second unit maintains the temperature of the chambers containing frozen fish. The third cooling unit operates occasionally, as it ensures the functioning of the refrigeration tunnels, freezing approximately 10 tons of fresh fish to -28°C in nearly nine hours of operation. The fourth unit also operates occasionally, producing flake ice. The fifth refrigeration unit operates separately, when necessary. It allows the freezing of each fish separately, [2]. For waste heat recovery from condensers, only those systems that operate constantly throughout the year may be used. These maintain a constant temperature in the refrigeration chambers. The first system maintains a constant temperature in the fresh fish chambers and operates at an evaporation temperature of +3°C or -8°. A suction pressure regulator needs to be fitted to the suction pipes of the chambers with the evaporation temperature of +3°C. This system is referred to below as the 'plus system'. The second system, maintaining a constant temperature in the frozen fish chambers, operates at evaporation temperatures of -32°C or -13°C. In this case, a suction pressure regulator is also needed to maintain the evaporating temperature of -32°C in the suction pipe. This system is referred to as the 'minus system'. The plus system comprises six chambers connected to a compressor set with three compressors. These are four-piston compressors with a two-stage regulation of the operation. The regulation may be performed at six stages. The plus system's cooling capacity is 57 kW, and the condensation heat to be recovered from the system is 77 kW, [2]. The minus system comprises five chambers connected to a generator unit with 2 six-piston compressors, each capable of performing a three-stage regulation. The minus system's cooling capacity is 47 kW and the condensation heat 78 kW, [2]. 2.1 Waste heat recovery system While the condensation temperature of the designed system is 45°C, the hot gases exiting the compressor have a temperature of 76°C. It is established that tap water can be heated from 10°C to 50°C for sanitary use with an additional plate heat exchanger installed before the hot gasses enter the air-cooled condenser. In accordance with Die Kaelte und Klima Technik, [1], an analysis of possible waste heat recovery systems was made to select an appropriate plate heat exchanger. The decision was made to connect the pressure pipes from the plus system's multi-compressor unit and the minus system's multi-compressor unit with regard to the position of the engine and boiler rooms. A 40 kW plate heat exchanger is installed in the engine room, using part of the condensation heat of the refrigeration system in question for heating the sanitary water, presented in Fig. 1, before entering the condenser, placed on the roof. Water travels through the plate heat exchanger and transfers heat to the heating system in the boiler room as shown in Fig. 2. The selected condenser is of sufficient size to be able to evacuate condensation heat from the refrigeration system even when the waste heat recovery system is inactive. 2.2 Boiler room design The boiler room is located away from the engine room, which is a weakness of the system, as some heat is lost during distribution. The boiler room houses a 500-litre tank, receiving heat by the bottom coil from the waste condensation heat recovery system shown in Fig. 2. The tank is used only for sanitary water in toilets of the office part of the building, in the staff kitchen and bathroom. Tap water is used for the purposes of building cleaning. Figure 2: Waste heat recovery system combined with the heating system [2] 3 CALCULATION OF WASTE HEAT The plate heat exchanger, installed as indicated in (Fig. 1), initially recovers the heat occurring in hot gas cooling and then recovers a portion of the heat dissipated in the refrigerant condensation. To analyse the system, the equations for the calculation of the quantity of condensation waste heat that can be recovered were needed. The equations according to [1] were used, showing that the recovered condensation waste heat is calculated according to Equation 3.1, in which Ah, and Ah^ are the values from the diagram log p - h (Fig. 3). . _ . Ah2 Qw - Qcond ■ TT- (3.1) Figure 3: Values used for the calculation of waste heat [2] Given that the waste heat recovery system comprises both the plus and the minus system, separate calculations are required. 3.1 Calculation of waste heat for the plus system For the given state of operation, the values of enthalpy in the working points were read from the log p - h diagram for Freon R404A [3] and presented in Table 1. Table 1: Values of enthalpy used in the calculation for the plus system h (kJ/kg) h2 405 h2' 380 h3 265 Ah, 140 Ah2 25 Using (3.1), it was calculated that 13.7 kW of waste heat flow may be recovered from the plus system. 3.2 Calculation of waste heat for the minus system For the given state of operation, the values of enthalpy in the working points were read from the log p - h diagram, for Freon R404A, [3], and are presented in Table 2. Table 2: Values of enthalpy used in the calculation for the minus system h (kJ/kg) h2 418 h2. 380 h3 266 Ah1 152 Ah2 38 Using (3.1), it can be calculated that 19.5 kW of waste heat flow may be recovered from the minus system. The total waste heat flow that can be recovered for sanitary water heating purposes is 33.2 kW. As (3.1) was only found in older references and the use of condenser waste heat had become common knowledge over years of practice, the calculation of its amount with (3.1) became a useful instrument. 4 CALCULATION OF COST SAVINGS Waste heat recovered from a refrigeration system operating 3,900 hours per year amounts to 129,480 kWh, [2]. According to (4.1), the amount of heated water can be calculated. V = ■ Qu •At- p (4.1) Over a period of one year, the refrigeration system can heat approximately 2,774 m3 of taps water from 10°C to 50°C using the condensation heat. In order to heaS the rame amount of water, the quantity of 11,262 m3 natural gas would be requi red. In three ysars, the cost savin g would a ccou nt for €16,724 when calculated with the average natural gas price over the last six years, i.e. €0.495 for 1 m3. In view oO the fact that the conssmers in tOe building ncsd a lower quantity of waste heat, it is esOablishe d tSrt they do not need a ga s Uoiler for sanitary water heating. The riven refrigeration system contains a sufficiently high quantity of waste heat for heating the sanitary water. The price for one extra plate heat exchanger, extra valves, and tubes is approximately €7,500. The diagram presented in Fig. 4 shows the number of month s in which the investment repays its costs over savi ngs, taking in account the price varia ble for 1 m3 of natural gas over the previous six years. 25 20 15 10 5 0 20 Natural gas prices in EUR/m3 nll.1 0.4471 0.4744 0.3922 0.5195 0.6509 0.4868 2008 2009 2010 2011 2012 2013 Figure 4: The number of months to repay investment over savings 5 EXERGY ANALYSIS OF THE REFRIGERATION SYSTEM The cost-benefit analysis has revealed that upgrading; the refrigeration system is financially viable. Given that energy may be used for refrigeration and hyating, it may Ire argued that the; upgrading results in an increase in ghie exergy ofahe system. The exergy methed is a functional myans of promoting the effactiveness of energy-ranoagce use, [4]. To Tegin the calculation, the spaeific exergy was calculated using (5.1). e = (h-h0)-T0(s-s0) (5.1) where h0 and s0 are syecific enthalpy and enthrhpy at surroundings temperature, respectively [4]. For each state, the values in Table 3 were used. Table 3: Valu es ofspecific enthalpy, specific entropy [3] and calculated specific exergy calculation (5.1) for the plus system S tate h (kJ/kg) s (kJ/tgK) e ( kJ/kg) 0 Surroundingh 395 1.854 0 1 Compression start 368 1.636 37.17 2 Condensation start 405 1.659 67.13 3 Expansion start 260 1.198 57.03 4 Evaporation start 259 1.225 48.57 To calculate the exergy efficiency of the system, the equations according to [5] were used. 5.1 Exergy losses in a compressor Exergy losses in a compressor occur due toelectromechanical conversion and isentropic efficiency compression and can be calaulated using (5.2). ecomp = C1 — Лет) ' ein + Vi ' ein + el — e2 (5.2) For 90% electromechanical conversion efficiency anO 80% isentropio comprcesion efficienoy io a compressors a 21.7% loss was calculated regarding tine exergy when entering the system. 5.2 Exergy losses in an evaporator Evefnocators are units through which the supplied excrgy is loot due to the mass flow and is calculated using C.3). eevap = e4 — el — ecold (5.3) The exergy loss due to the mass flow rate accounts for 29.8% of the supplied exergy. An evaporator is a working unit that evacuates th e heat from a room. Therefore, the percentage of the exergy loss is reduced by t hermal exergy oft he he at which i s Iran sferre d from the chamber. Therm al exergy load of heat is cal culated u sinj;; (5.4), [6]. ^cold 4evap ' (1 ^ 1 (5.4) \ 'INsr ' Where the surroundings temperature T0 of 293 K and T|Nsr mean temperature of the air into which the evaporator dishipates ghe heat out of t Pie; chamber, the value of 270.5 K, were used. Thh total exergy loss thsough hhe evaforatar if s.5% of the alet exergy. Tf e exeegy aal1 heat inlet in tne evaco-rator is 24.3%. 5.3 Exergy losses in an expansion valve The exerge loss is calculated using (5.5) in an expansicn valve, where ap adiabatie syctem conversion ta kes plare. sule ly in terms oft Ce exe rgy sub pli ed aed hecovone d. Oexp = 03 0 04 (5.5) Thee c;a lcul^1:ed loss oSthe efergy supplied eo the axpansion valvo is; 221.196. 5.3 Exergy loss>es in a condenser The; lass ol chxei"gyy throfgh an air cooled condensar aomprises the supplieU and recoverifd exesgy flow throughh ghe conJeaner (5.6). 0cond = 02o 03 (5.6) It was saiculated that f6.4% of thh supplied exehgy is losr i n t he cocd enser. Exergy losses and gain are pres ented in Table 4and in (Fii. 5) acco rdi ng to Rant, f7] . Table 4: Values of exergy inlet losses and gains Exergy loss (%) Compressor 21.7 Expansion valve 22.1 Evaporator 5.5 Condenser 26.4 Heat outlet of the chamber Exergy gain (%) 24.3 Figure 5: Exergy Rant diagram for refrigeration system 6 EXERGY ANALYSIS OF THE REFRIGERATION SYSTEM UPGRADED WITH HEAT RECOVERY In the refrigeration system upgraded with a waste heat recovery, the percentage of the lost exergy through the condenser is changed, as a portion of exergy is recovered in the form of heat for heating purposes. The calculation of the exergy loss in the condenser was repeated, due to added state of calculation values to Table 3, and are presented in Table 5. Table 5: Values of specific enthalpy, specific entropy [3] and calculated specific exergy calculation (5.1) for the plus system upgraded with heat recovery State h (kJ/kg) s (kJ/kgK) e (kJ/kg) 0 Surrourdiogs 395 1.854 0 1 Compression stort 368 1.636 37.17 2 Heat recovery atart 405 1.659 67.13 2' Condensation stont 383 1.588 65.94 3 Ex pansion ste rt 260 1.198 57.03 4 Evaporatine sta rt 259 1.225 48.57 6.1 Exergy losses in a condenser of the system using waste heat The exergy losses in an air cooled condenser are calculated using (6.1). As before, exergy is lost due to the mass flow, but the losses are considered at the flow through state 2. econd = e2' _ ез (6.1) The exergy loss due to the mass flow amounts to 23.3% of the supplied exergy in the system. In a plate condenser, in which heat is recovered to the sanitary water heating system, a portion of exergy is ushd for heating. Given that a platee heat exchanger ih also n unit causing soecific exengy losses due to the muss flow, this portion of tSt l ost eatergy should also ten taCen ifto consideratioe. Thermal exergy load of heat calculated with (6.2) according to [6]. - r° \ eheat — 4w • I1 T I V 'ПЧТчг' (6.2) Where T0 is tOe surroundings temnernturi of 293 П and TOUTsr value of 30i K is median temperature of water into which the condens er dinsipates the heat. hhermel exerge threr gO th e fola te heat exchanger is 2% of the inlet exergy, whereas the exergy loss due to the mass flow through the plate heat exchanger, calculated with (6.3), is 3.1% of the exergy inlet. (6.3) Altogether, the exethy loss through the plete hear exclnanghi it 1.1% due to exergy loss eeeluction by 2%. The wante hear rtcavery system represents the possiltity of increasing rhe exetgy oi the refrige ration system. Exergy losses and gains are preaented in Table (5 and in (Fig. 6) according to [7f Table 6: Values of exergy inlet losses and gains for heat recovery Exergy loss (%) Compressor 21.7 Expansion valve 22.1 Evaporator 5.5 Condenser Plate heat exchanger 26.4 1.1 Heat recovery Heat outlet of the chamber Exergy gain (%) 2 24.3 Figure 6: Exergy Rant diagram for refrigeration system with heat recovery 7 CONCLUSION This case study shows the quality of refrigeration project applicable in all constant operating refrigeration systems with higher condensation temperatures. To avoid problems with Legionella infections, additional heaters need to be installed. The exergy calculations of both systems show that the exergy efficiency is increased in the waste heat recovery system. It is also more efficient from an energy perspective. The cost-benefit analysis shows that via a small additional contribution and a proper selection of components it is possible to influence the long-term efficiency of the system. The waste condensation heat recovery systems are simple, and it is reasonable to use them in a refrigeration system operating throughout the year. The investment pays off approximately in one year. References [1] Enthizungleistung, Die Kaelte und Klima Technik, 1987, Vol. 10 [2] I. Tršelič: Exploitation of waste heat in refrigeration, Master's thesis, 2nd level, Faculty of Energy Technology, University of Maribor, 2012 [3] Solvay, Chemicals Diagrams, 2011 [4] M. Farmahini-Farahani, S. Delfani, J. Esmaeelian: Exergy analysis of evaporative cooling to select the optimum system in diverse climates, Energy, 2012, Vol. 40 Issue 1, p.250-257 [5] T. Obersnu: Strojno hlajenje in gretje, Tehniška založba Slovenije, 1991 [6] R. Chengqin, L. Nianping, T. Guangfa: Principle of exergy analysis in HVAC and evaluation of evaporative cooling schemes, Building and Environment, 2002, Vol. 37 Issue 11, p. 10451055 [7] Z. Rant: Termodinamika knjiga za uk in prakso, Ljubljana, 2007 Nomenclature specific exergy specific enthalpy waste heat condensation heat specific entropy temperature difference environment temperature median temperature in the evaporator median temperature in the condenser volume flow electromechanical efficiency isentropic efficiency e h Qw Q cond s At T0 TINsr TOU1sr V n n, Ivana Tršelič, Jurij Avsec JET Vol. 7 (2014) Issue 2 ш JOUrnal Of JE1 Volume 7 (2014) p.p. 67-78 Issue 2, May 2014 Energy Technology www.fe.um.si/en/jet.html RENEWABLE ENERGY POTENTIAL AND OPPORTUNITIES FOR ORGANIC FARMING IN THE REGION OF THE ŠALEK VALLEY OBNOVLJIVI ENERGETSKI POTENCIALI IN SONARAVNO KMETIJSTVO ŠIRŠEGA OBMOČJA ŠALEŠKE DOLINE Natalija ŠpehR, Nataša Kopušar Keywords: food production, organic farms, renewable energy, rural landscape, sustainable farming, Šalek Valley Abstract The purpose of this research paper is to examine the rural area of the Šalek Valley and to determine what the potential for the promotion of organic farming is in an area that is traditionally better known as an electricity producer and industry supplier. The predominant agricultural activity is livestock, and there is almost no market-oriented horticulture. The farms included in the study were from three neighbouring municipalities: Velenje, Šoštanj and Šmartno ob Paki; 1218 farm owners were invited to participate, and the research was presented orally to 370 farmers. Only 40 surveys were returned and completed; nine of these were declared to be organic farms and four to farms in conversion. The average age of the surveyed farm owners was over 50 years and was not significantly different regarding the farms' orientation; 63% of family farms have already planned for a successor, less so with the organic agricultural holdings. Since organic farms also showed livestock to be the predominant agricultural activity, a good potential for the renewable (biomass) energy production, e.g. co-generation of electricity and heat, was assumed. R Corresponding author: Ass. Prof. Natalija Špeh, Tel.: +386 3 898 6417, Fax: +386 3 898 6412, Mailing address: Visoka šola za varstvo okolja, Trg mladosti 2, SI-3320 Velenje, Slovenia E-mail address: natalija.speh@vsvo.si As we were interested in the economic prospects of the farms, we wanted to know their attitude to energy supply as a supplementary farm activity or whether they had had any experience with renewable energy sources. With these input data, we want to check: a) agricultural holdings, especially those that were organic-oriented, which are expected to have the prominent role in the future food supply; b) how the owners plan the on-farm activities; and c) the current energy supply and openness of farmers to using other energy sources. Povzetek Uvodoma smo želeli preučiti lokalno ponudbo podeželja Šaleške doline in ugotoviti možnosti za pospešitev razvoja ekološkega kmetijstva na območju, ki je tradicionalno bolj znano kot območje termoenergetike in industrije. V raziskavo so bile zajete kmetije 3 občin: MO Velenje, občine Šoštanj in občine Šmartno ob Paki. K sodelovanju je bilo povabljenih 1218 nosilcev kmetijskega gospodarstva, od tega je bila 370-tim kmetijam raziskava predstavljena še ustno. V raziskavi je sodelovalo 40 kmetijskih gospodarstev, od tega 9 ekoloških in 4 integrirane kmetije. Povprečna starost nosilcev kmetijskega gospodarstva v Šaleški dolini je nad 50 let in se ne razlikuje pomembno med ekološko usmerjenimi in ostalimi kmetovalci. Na 63 % kmetijah je že znan naslednik, na registriranih ekoloških kmetijah je odstotek manjši. Ker tudi na ekoloških kmetijah prevladuje živinorejska usmerjenost, predvidevamo še neizkoriščene možnosti za uporabo biomase (organskih odpadkov) za namen proizvodnje obnovljive energije, tudi v obliki kogeneracije električne in toplotne energije. V nadaljevanju nas je zanimala ekonomska perspektiva kmetij, kako razmišljajo o energetski preskrbi kot dopolnilni dejavnosti kmetije, kakšno je njihovo mnenje ali že izkušnja z obnovljivimi viri. Z omenjenimi vhodnimi podatki želimo preveriti: a) usmerjenost kmečkih gospodarstev, predvsem ekoloških, od katerih se v prihodnje pričakuje vidnejša vloga v prehranski preskrbi, b) kako nosilci kmetij načrtujejo proizvodne dejavnosti na kmetijskem gospodarstvu ter c) aktualno energetsko oskrbo in odprtost kmetovalcev za koriščenje drugih energentov. 1 INTRODUCTION The transformation of conventional farms to organic farming is an appropriate goal, which also coincides with European agricultural directives and ensures a monitored food network, safe food, the revitalization and strengthening of rural areas and healthy ecosystems. Many potentials for organic farming and local food supply have been studied (Slabe et al., 2011): • to increase supply of Slovene organic products (especially vegetables and fruit), direct sales at farms and agricultural holdings of larger size should be encouraged, • obstacles to producers in terms of cooperation and market connections should be removed, • more knowledge transfer at production and market areas should be supported and realized. The goal of developing sustainable agriculture is the responsibility of all participants in the system, including farmers, workers, policy makers, researchers, retailers and consumers. Each group has its own part to play and its own unique contribution to strengthen the sustainable agriculture community (De Lauwere et al., 2004). The number of organic farms in Slovenia has been increasing; in 2005 1.6% of family farms declared themselves to organic; by 2010, that number has risen to 2.5%. In addition, 0.4% farms were in the process of conversion (Agriculture Census, 2010). Among gainful activities on family farms, renewable energy production is a promising supplementary activity, with regard to the increasing number of farm families in recent years (Table 1). Table 1: Complementary activities on family farms (in number), Slovenia, 2000-2010. Supplementary activity/year 2000 2010 IndeX (7010/70001 Meat processing 221 155 70.14 Milk processing 247 242 97.98 Fruit and vegetable processing 394 502 127.41 Farm tourism 692 642 92.77 Renewable energy production 38* 78 205.26 Handicraft 268 167 62.31 Aquaculture 75 28 37.33 Sale of wood products 104 28** 26.92 Forestry - 9078 - Wood processing 699 513 73.39 (Source: SORS, 2013) Legend: * data values for 2003; ** data values for 2007; - no data Further, we attempted to make some common findings between food production on agricultural holdings and their openness to using renewable energy sources. Before the project (European Agriculture Fund for Rural Development), there was no information on the food supply characteristics and the prevalence of organic farming in the Šalek Valley. The original idea of the research was to present it to the food-producing farms and help them in connecting and communicating with the local people who are interested in organic-produced and healthy food supply of local origin. We were following these project goals: 1. to check the farmers' marketing interests, collect data on farms' locations and their supply at home for potential buyers, 2. to enable farmers to sell their products directly to consumers interested in safe food consumption, 3. to connect the organic farmers with the potential clients, and 4. to verify the status of the use of renewable energy sources. The project was focused on organic food production and processing, in the local environment and directly accessible to local people. The research goals were to involve and promote farms that have already introduced the organic food production guidelines. The results should have encouraged the majority of farmers in the valley that use conventional work methods, i.e. following the European and national guidelines, and guiding producers and consumers to full local food self-sufficiency. Indirectly, we intended to educate young people, future consumers and potential actors in organic farming. At the same time, farmers were introduced to renewable energy production, and we noted that a workshop on this topic would be very welcome by them. We wished to inspire farmers for organic food production and the acceleration of sustainable farming with other supplementary activities, especially in the areas with limited factors for farmland (mostly steep terrain with a prevailing share of grassland), which would help to revitalize the agricultural landscape of the Šalek Valley. 2 AREA OF RESEARCH 2.1 Agriculture and land use in the researched area The Statistical Office of the Republic of Slovenia data, published in Statistical GIS land cover of Slovenia, showed the spatial distribution of the cover categories and the decreasing of the rural land between 1993 in 2001 (SORS, 2013). The precise structure of agricultural land database in 2001 reports that the biggest share in the Savinjska statistical region belongs to meadows (25.9%) and only 3.2% to arable land. In the evidence of the last observation period (2011), the share of forest land had the same value as in previous periods, the increase (+3.2%) of the agricultural area was surveyed and developed areas in the region expanded by 2.6%. The register of the actual land use of agricultural and forest land for 2005 and 2011 showed more extensive farming in the region (the meadows' share rose up from 22.3% of the total agricultural land in 2005 to 24.8% in 2011 (Table 2). Table 2: Land cover of the chosen categories in shares (%), Savinjska statistical region, 1993-2011. Year/Category Wooded areas All agricultural areas Developed areas 1993 55.2 39.8 3.1 1997 56.7 37.3 3.2 2001 60.9 32.9 3.3 2005 57.5 34.1 6.7 2011 56.7 36.1 5.9 (Source: Statistical Year book..., 2011; Analiza stanja ekološkega..., 2013) In 2007, approximately 4.9% of employed Slovenians worked in agriculture. In Table 3, we can see the data of the same period (2007) for the researched area; the municipality of Šoštanj (7.7%), Šmartno ob Paki (10.6%). Meanwhile, the municipality of Velenje had a strong focus on employ- ment in other sectors. A comparison with the surveyed data from 2002 showed a positive employment trend in agriculture, but not in Slovenia as a whole. Table 3: Share (in %) of the persons employed in agriculture. Municipality/Year 2002 2007 2011 Šmartno ob Paki 4.08 10.6 11.0 Šoštanj 5.71 7.7 5.5 Velenje 0.99 1.3 1.5 Slovenija (average) 5.5 4.9 3.6 (Source: Statistical Yearbook ..., 2011) Regarding the change of number of people employed in agriculture, between 2007 and 2011 a slight increase was recorded in Velenje and Šmartno ob Paki, whereas the value of the Šoštanj returned to the state in 2002 (Table 3). The average Slovene share was steadily declining. Considering the possibilities for more promising and profitable farming with sustainable methods, the availability and quality the land resources is important. The Statistical Office of RS data for the year 2000 confirms extremely dispersed agricultural land in Slovenia (SORS, 2013). The share of the smallest agricultural holdings was the highest. Only Šoštanj exceeded the Slovenian average with 6.1% in the largest agricultural holdings (over 10 ha) category; the other two municipalities were below average. By the year 2010 the share had dramatically changed; the lowest data were shown in Velenje whereas farms in Šoštanj had 60% in the largest size class (over 10 ha). Table 4: Share (in %) of the agricultural holdings by size classes of utilised agricultural area (UAA) in 2000 and 2010. Municipality/ size/year 0 - < 2 ha 2 - < 5 ha 5 ha - <10 > 10 ha 2000 2010 2000 2010 2000 2010 2000 2010 Šmartno ob Paki 36.9 9.42 36.9 23.5 20.0 26.9 6.25 40.07 Šoštanj 27.7 3.38 26.1 10.0 27.4 26.28 18.7 60.3 Velenje 28.4 5.8 38.3 29.9 25.0 40.25 8.3 30.8 Slovenija 26.6 4.6 35.2 17.5 25.5 25.9 12.6 51.9 (Source: Agriculture Census 2010; SORS; 2013) 3 METHODOLOGY After collecting and examining the statistics, the fieldwork provided basic input data for research, since we wanted to determine the actual characteristics that formed agriculture in Šalek Valley. Only the description questions in the interview yielded information about the opinion, values and points of view of the farms' owners. We planned to check the following topics: • Are organic farms in average smaller than conventional/in conversion farms? • Are the owners of the organic farms younger or more educated than owners of the conventional/in conversion farms? • Do organic farms practice electricity production from renewable sources on a larger scale than conventional/in conversion farms? The extensive content of the survey consisted of basic contact information of the farm, land use, livestock, evidence of the production of market vegetables, renewable energy production, persons in employment at family farms, forestry at farms, fish farming, tourism and other supplementary activities at farms, organic farming and biodynamic agriculture, permaculture and beekeeping. We attempted to include all fields of agriculture. There were no answers about fish farming, and very little interest was evident regarding beekeeping. Finally, we checked the farm managers' interest in renewable sources use. 4 RESULTS AND DISCUSSION 4.1 Agricultural holdings by size Nine organic farms were included in the survey. The total area of their farmland was 459.8 ha. We also interviewed four farms in conversion, with a total of 59.3 ha. The average organic farm size was 26.23 ha, excluding one extremely large farm with over 350 ha (with rented land outside the surveyed area). The farms in conversion had an average of 18.83 ha large, and the conventional farms had an average of 25.93 ha. Table 5 shows the administrative distribution of the family farms and the type of farming. Only some of them (15%) have registered the supplementary activities to their basic agricultural orientation. Table 5: The researched family farms considering the municipality affiliation and type of farming. Production/Municipality Šoštanj Šmartno ob Paki Velenje Total Vegetables /fruit 1 1 2 Meat/milk 1 1 Sheep 2 2 Mixed 2 2 4 Vegetables /fruit 2 2 4 Meat/milk Mixed Vegetables /fruit 1 2 3 Meat/milk 4 3 6 13 Tourism 3 2 5 Other farms beekeeping, winery, cereals -bakery products 2 solar cells 6 Total 14 10 16 40 Key conventional farms organic farms farms in conversion The average farm size in the research area was 24.23 ha; in contrast, the average Slovenian farm size in 2010 was 6.4 ha, i.e. 18.45 ha less than our researched farms. The average farm in the Savinjska statistical region had 5.9 ha in the same period (Agriculture Census, 2010). We recorded an organic farm owner that was distinct in its size, consisting of eight agricultural holdings located across the western part of the Savinjska statistical region. There were 45 ha of arable land, 5 ha of orchard and 300 ha of forest. Because it was such an extreme outlier, it was not considered in the calculation of average farm size, also because some parts were located outside the researched area. The average farm size with the largest area (43.89 ha) was surveyed in the Šoštanj municipality (Table 6). Table 6: Surveyed municipalities and their agricultural characteristics. Municipality Total Velenje Šoštanj Šmartno ob Paki Number of researched farms 16 14 10 40 Agricultural land (ha) 253 614.58 101.7 969.28 Average farm size (ha) 15.81 43.89 10.17 24.23 (Source: Agriculture Census 2010 in SORS, 2013) 4.2 Agricultural managers by age and education attainment We interviewed 40 farm owners and 92.5% provided their birth data. We wanted to determine how and whether the average age of farm owners would be reflected the actual state of agricultural holdings. The interviewed farm managers were on average 54.95 years old. Organic farms are managed by younger owners (in average 3.64 years younger) than the conventional farms were, where the owners were 55.77 years old in average (Table 7). The youngest farm owner was 31 years old, whereas the youngest farmer who ran a conventional farm was 40 years old. The oldest owner of an organic farm was 67 years old, and the oldest manager of a conventional farmer was 82. During the fieldwork survey, we established that additional administration needed for organic farming represented a kind of discouragement for organic farmers. The average age of a Slovene family farm manager was 57 in 2010 (Agriculture Census, 2010). The average age of Slovene farmers is probably also a reason that farmers and their products are hardly competitive on the agricultural market. New, younger farm managers are required. Our survey showed the 38% farms had no known successor. If we consider average age of conventional/in conversion farm owners and the sex indicator, male owners are an average of 6.37 younger than female farm managers (59.25 years). The organic farm managers are less different by age and it was vice versa; men are 1.3 years older than women (Table 7). Table 7: Average age of the researched family farm managers. Farm type conventional/in conversion organic Sex total male female total male female Average age 55.77 52.65 59.25 52.13 52.6 51.3 Regarding the education, the organic farms' managers were better educated; three managers had B. Sc. Degree, one was Ph. D., three had finished trade degrees and two had graduated from secondary school (Fig. 1). Conventional farms and farms in conversion were run mainly by farmers with finished professional and secondary school degrees. These differences proved that organic farming requires younger, well-educated managers with competences, skills, knowledge and courage for facing and coping with stringent environmental and other regulations relating more modern farming attitude. In comparison with the Slovene average, the majority (37.2 %, SORS, 2013) had basic school education. Figure 1: Interviewed family farm managers by educational attainment. 4.3 Family farms and renewable energy production Our research dound foer organic darms and Pour conventionel farms to be renewable energy producers, mostly with wood biomess. One integrated Parm had its own electeieity production Crom renewable sourreCi Using these datai, we cannot conclude that the exploitation of renewable sources had any signifiwant eorrelation with lhe farei orieptatien. Although renew/table energy production should be incorporated in suetainable farm management, most of the plants in the valley are owned by non-agricultural managers. There is one biogas plant (150 kW) and one small hydro power plant (35 kW) in the researched area. Solar plants are more common due to government subsidies, especially in recent years, because Slovenia has been following EU measures and is obliged to have a 25% share of renewable sources in final energy consumption by 2020. Table 8: Solar plants in number and by capacity (in kW) in Šalek Valley installed, 2009-2012. Municipality/Year 2009 2010 2011 2012 TOTAL Šmartno ob Paki 0 2 (18) 1 (116) 3 (124.62) 6 (258.62) Šoštanj 0 2 (98) 4 (847.05) 6 (442.91) 12 (1387.96) Velenje 2 (19) 10 (633) 8 (249.06) 15 (1710.24) 35 (2611.3) TOTAL 2 (19) 14 (749) 13 (1212.11) 24 (2277.77) 53 (4257.9) (Source: Geographical Information system for RES, Sončne elektrarne v ..., 2013) As a promising best practice case, renewable technologies or programs could play a significant role since they enable and are aimed to provide energy access to the poor in the "bottom of the pyramid" (BOP). Thus billions have been spent and will be spent on projects such as expensive line extensions or solar panels to the poor living in "last mile" communities (Santiago, Roxas, 2012). Renewables' exploitation also prove a sustainable and responsible community model, which corresponds not only with the poor at the BOP, their traditional responses to income and energy poverty. According to Klagge and Brocke (2012), decentralized electricity generation from renewable sources can become an important factor for local economic development in rural regions and their urban centers. Another advantage of regarding the internal resources is that local (pioneer) firms take up the business challenges associated with renewable energies and are successful in entering not only local, but also national or even international markets. Decentralized electricity generation from renewable sources can develop a region very dynamically. Based on the early activities of some pioneers, such regions introduce very specific organizational structures and enter development paths in which renewable energies are an important economic factor. However, special supporting conditions and constellations are needed to enable that type of development, including representatives of utilities/grid operators, local politics and administration, civil society, plant operators and other businesses involved in the renewable energy value chain. 5 CONCLUSIONS The fieldwork has revealed a small share of the farms engaged in organic food production. The main point of organic farming should be awareness for sustainable environmental management to maintain soil fertility, water sources and air quality when planning agriculture development. In addition, renewable energy production and energy self-supply should be incorporated. There are still many agricultural holdings with the owner is older than average, where the successor is known, but the actual manager has still not transferred the property and management rights to the descendant who would introduce innovations and manage the farm development. We determined that 38% of interviewed farms have not resolved the succession issue. The research discovered that on average organic farms are larger than conventional and integrated agricultural holdings. There are two extremely large organic farms: one 230 ha and another 350 ha with some areas out of the researched region. The last farm was too much of an outlier to be included in data analysis of average agricultural holdings' size. Organic farms' managers were younger and better educated than conventional farms' owners. We assumed that more skills and competences are required for running an organic farm (to obtain the organic farm certification, to edit all the documentation for application and farming after gaining the certificate, etc.). We cannot declare organic farming to be more energy efficient since the same number of conventional and organic farms used renewable sources for their own energy production. It would be very significant to encourage agricultural holdings and their successors (the Agricultural Census data for 2010 showed that the manager of a Slovenian farm was on average 57 years old, finished primary school and had no formal agricultural education). The average farm owner in the surveyed area was three years younger in comparison to the Slovene average (2011 data). The transfer from conventional farming methods to organic farming would assure the direct sale of the organic food to consumers, since demand for healthy food has been increasing, and the food without any chemical treatment is more perishable. According to the Agricultural Institute of Slovenia data, the country is only 68-75% self-sufficient in food production. We aim at 10% increase, which would reduce Slovenia's dependence on foreign food markets. However, first more incentives of Chamber of Agriculture and Forestry and the relevant ministries should persuade farmers to manage their agricultural holdings in a sustainable way. Availability of the land sources of adequate quality Interest in healty goods, new products, energy self-supply Legal framework and support for the wider social (political) environment Qualified human resources Figure 2: Sustainable farming factors. Moreover, the main agricultural constraints (inefficiency and lack of competitiveness due to fragmentation and small farms, a large amount of hired land and the uncertainty caused by the global economic cf sis) simply leads to the supplementary activities for Slovenian farmers, fenenrable eng ergy production is u highly appropriate supglement iter organic Warming and should tre elementary in the sustain able agricultural management. Since it demands quite an investment and because was a high national priority recently to follow the EU commitments of the obligatory share of re-newables, many solar plants were subsidized in the Šalek Valley. In 2012, there was more than half (53.5%) of total solar plants of the Šalek Valley were installed (total capacity from 2009-2012 amounted to 4.26 MW). Private investors were in the minority. In 2009-2012, 53 solar plants were built with a capacity of 4.26 MW; in 2013, no solar plant was constructed due to the abolition of favorable conditions of construction. Recently (August 2014) farmers are no longer supposed to produce energy and have solar/hydro plant as a complementary activity. According the newly adopted legislation the possibility of electricity produced from all renewable energy sources was removed except from biomass, manure, slurry and vegetable substrate. The action plan of European Commission until 2025 anticipates the sustainable growth and implementation of bio-economics, which means development of industries based on raw natural (biological) origin without fossil resources. It should be a promotion of a development guideline, which would connect different fields and activities, e.g. energy, chemistry, forestry with wood activity, agriculture etc. The case of agricultural activity should promote a sustainable farming with lower emissions, natural (renewable) sources stocks and biodiversity conservation. Acknowledgement First year students of the Environmental Protection College (class of 2010-2011) introduced the fieldwork to the subject of Protection and Evaluation of the Geographical Environment. They carried out a survey on the diversity of the Šalek Valley rural area and its potential for sustainable farming. Later, the survey was an opportunity for student placement. With their fieldwork on the use of renewable sources, the 1st year postgraduate students (2012-2013) in the subject of Sustainable Planning of Landscape Resources did a great job. References [1] Statistical Office of the Republic of Slovenia, Agriculture Census 2010 in SI-STAT data portal. http://pxweb.stat.si/pxweb/Dialog/Saveshow.asp. (cited 8.1.2013) [2] Ministrstvo za kmetijstvo in okolje (MKO), Analiza stanja ekološkega kmetijstva v Sloveniji 2013. http://www.mko.gov.si/si/delovna podrocja/kmetijstvo/ekolosko kmetovanje/ analiza stanja ekoloskega kmetovanja/ (cited 8.1.2013) [3] Chamber of Agriculture and Forestry of Slovenia. Internet: http://www.kgzs.si/. (cited 26.8.2012) [4] De Lauwere, C.C. Drost, H. de Buck, A.J. Smit, A.B. Balk-Theuws, L.W. Buurma, J.S. and H. Prins: To change or not to change? Farmers' motives to convert to integrated or organic farming (or not). Acta Hort. (ISHS) 655:235-243. (2004) [5] Geographical Information system for RES, ENGIS http://www.geopedia. si/?params=T1965#T1965 x509632 y134664 s12 b4 (cited 7.5.2013) [6] B. Klagge, T. Brocke: Decentralized electricity generation from renewable sources as a chance for local economic development: a qualitative study of two pioneer regions in Germany. Energy, Sustainability and Society, 2:5. Springer- Verlag 2012. [7] Pravilnik o ekološki pridelavi in predelavi kmetijskih pridelkov oziroma živil, Ur. l. RS, št. 71/2010 str.10462, (94/2010 str.14672 popr.) [8] A. Santiago, F. Roxas: „Identifying, developing, and moving sustainable communities through renewable energy", World Journal of Science, Technology and Sustainable Development, Vol. 9 Iss: 4, pp.273-281 (2012). [9] A. Slabe, B. Lampič, Juvančič: Potenciali ekološke pridelave za trajnostno lokalno oskrbo s hrano v Sloveniji. Dela. [Tiskana izd.], št. 36, str. 93-109, 2011. [10] Sončne elektrarne v Sloveniji, 2013. PV portal, Slovenski portal za fotovoltaiko, http://pv.fe. uni-lj.si/Seseznam.aspx (cited 3.5.2013) [11] SORS, Statistical office of the Republic of Slovenia, SI-STAT data portal, http://pxweb.stat.si/ pxweb/dialog/statfile1.asp (cited 15.5.2013) [12] Statistical Yearbook 2011, Statistical Office of the Republic of Slovenia (SURS), http://www. stat.si/letopis/LetopisVsebina.aspx?poglavje=30&lang=en&leto=2011 (cited 19.11.2012) ш\ Journal of Energy Technology Author instructions www.fe.um.si/en/jet.html MAIN TITLE OF THE PAPER SLOVENIAN TITLE AuthorsR, Corresponding author Keywords: (Up to 10 keywords) Abstract Abstract should be up to 500 words long, with no pictures, photos, equations, tables, only text. Povzetek (Abstract in Slovenian language) Submission of Manuscripts: All manuscripts must be submitted in English by e-mail to the editorial office at jet@um.si to ensure fast processing. 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