- Email: [email protected]
Performance Analysis of a 3.5 kWp CPV System with Two-axis Tracker
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 61 (2014) 220 – 224
The 6th Innternational Conferencee on Applied Energy – ICAE2014
Perform mance an nalysis off a 3.5 kWp k CPV V system m wiith two-aaxis tracker M. Renzzia*, M. Sanntolinib, G. Comodib b
a Facoltà di Sccienze e Tecnologgie, Libera Univeersità di Bolzano Dip ipartimento di inggegneria industriale e science mattematiche (DIISM M), Università Politecnica delle M Marche
Abstract This paper prresents the preliiminary operatiional results of two 3.5 kWp CPV C systems ussing triple juncttion III-V solarr cells and a tw wo-axis trackinng mechanism. The plant is iinstalled in the campus of thee Università Poolitecnica dellee Marche (Anccona, Central Italy). I The con ncentration opttics consists of a primary Fresnel F lens annd a secondary y reflective opttics with an ovverall geometriical concentrattion ratio of 47 76 X. An expeerimental meassurement setup p acquires the m main plant opeerating and amb bient quantities ; the paper reports the first months m of plant operation with h particular foccus on the influuence of the av vailable radiatioon and the amb bient temperatu ure on the perfo formance of thee system. The eelectric output has a linear treend with the avvailable direct normal radiatio on while ambieent temperaturee has a minor eeffect on the perrformance of th he CPV systemss; also the influeence of the Air Mass coefficieent is reported. © by Elsevier Ltd. an open access article under the CC BY-NC-ND license © 2014 2014Published The A Authors. Publis hedThis by isElsevier r Ltd. (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection andd/or peer-review w under responssibility of ICAE E Peer-review under responsibility of the Organizing Committee of ICAE2014 Keywords: CPV V; solar energy; experimental e data; solar concentrration; real opera ation
1. Introducction In the conntext of the growing deman nd of renewabble energy to mitigate the effect e of the ellectric energy y production ssystems [1], silicon s PV systems have acchieved a larg ge market pen netration mainnly driven by y favorable inncentive pays in many Coun ntries and duee to a good reeliability and bankability b [22]. Among thee alternative ssolar energy technologies, t the Concentrration PhotoV Voltaic techno ology (CPV) is considered d one of the m most promisinng solar energ gy conversionn devices both h on the economic [3], the technical [4]] and the envvironmental point p of view [5]. CPV tecchnology involves three basic componeents: tracking g mechanism, concentratioon optics, and d triple-juncttion (3J) solaar cells that allow to expploit a largerr on. Converselyy, because of the t use of lenses, the solar concentration n spectrum off the available solar radiatio technology can use only a fraction of the whole avvailable solar radiation, the Direct Norm mal Irradiation n nents of the CPV C systems oor some short-(DNI). Evenn though theree are several sttudies on the ssingle compon time monitooring on protootype units [6 6], there is laack of experim mental data in n continuous real working g operation [77]. In fact, thee effect of the ambient condditions, the efffect of the environmental ffouling on thee *Correspondingg author: Massim miliano Renzi; e-m mail: [email protected]; tel: +39 0471 017816; fax: +39 00471 017009 Libera Universsità di Bolzano, Facoltà di Scienze e Tecnologie, Piiazza Università 5, 5 39100 Bolzano o, Italy
1876-6102 © 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review under responsibility of the Organizing Committee of ICAE2014 doi:10.1016/j.egypro.2014.11.1075
M. Renzi et al. / Energy Procedia 61 (2014) 220 – 224
lenses and the imprecise alignment of the tracking mechanism are all sources of losses that must be taken into account to evaluate the real efficiency of CPV systems [8, 9]. Therefore, the aim of this work is to report the preliminary performance results of two 3.5 kWp CPV systems that are installed inside the campus of the Engineering Faculty of Università Politecnica delle Marche (Ancona, central Italy), a location where the average annual DNI is about 1500 kWh/(m2 year). 2. CPV system description and monitoring apparatus Each monitored CPV system consists of eight 420 W-modules having a total number of 768 3J cells with a total net area of 11.05 m2. Modules are installed on a chassis and tracking is realized with an azimuth-elevation system that uses electric motors. An embedded electronic board controls the motors to track the sun by means of a differential light-intensity sun sensor. The rated tracking accuracy is 0.2°. The optics consists of a plastic PolyMethylMethAcrylate (PMMA) primary Fresnel lens. The two installed systems have a different solution for the Fresnel lenses: the first one has a constant pitch of 0.5 mm of spacing in the Fresnel grooves; the second one, which is a newer version, presents a differential pitch having larger grooves in the center of the lens and smaller ones in the external part. Both of the Fresnel lenses have an aperture of 120x120 mm and a focal length of 130 mm. In addition to the primary lens, a simple reflective secondary optics is used: it consists of a frustum pyramidal cone installed in correspondence of the focus of the primary optics, close to the solar cell. The geometrical concentration ratio of the optical system is 476 and its acceptance is 0.4°. In our system, the 3J cells have an active area of 5.5x5.5 mm; their performance at the flash test with a concentration ratio of 520 suns is 37.5% while the modules have a rated efficiency of 26% with a direct normal irradiation of 850 W/m2. The cells are soldered on an Insulated Metal Substrate (IMS) to spread the non-converted radiation flow; each receiver is then connected in series to form the modules that are then coupled with a traditional solar inverter. The performance of each CPV system is monitored using a measuring apparatus that allows to evaluate the conversion efficiency of the plant and the main working parameters. All the monitored data are collected in a data logger and stored each 5 minutes. The sensors that are installed in the plant are: i) Pyrheliometer (first class accuracy, installed on the tracker on a side of the CPV modules); ii) ambient temperature sensor (accuracy r1.5 °C); iii) wind speed (cup anemometer that supplies data to evaluate the cooling effect of the ambient air on the modules and also serves as a security control for the wind effect on the trackers); iv) AC electric power produced (accuracy r3%). 3. Results and discussion Results reported in this paper were acquired from July 2013 to March 2014 for both the systems. One of the aims of the present paper is to show the performance of a CPV system in real working conditions, also taking into account the effect of lens fouling and soiling. For this reason, the surface of the lens was not cleaned during the test campaign. In Figure 1a the trend of a typical clear day (in this case September the 14th) is reported. Irradiance starts after 8:00 AM due to the shadowing effect of the surrounding hills and buildings in the early hours of the morning; DNI peaks at over 900 W/m2 at noon and the corresponding AC power production is over 2.5 kW for the constant pitch Fresnel lens system. The power output is flat over a large range of the day time (except for some transient clouds) thanks to the use of the tracking system that allows to maximize the exploitation of the available solar radiation. Figure 1b reports the trend of the ambient temperature and the corresponding efficiency of the CPV system: efficiency trend shows an opposite concavity, with higher values in the early morning and late in the afternoon (about 26%), and lower efficiency (about 25%) in the central day hours: this trend can be ascribed to the higher ambient (and receiver) temperature around the noon and thus a slightly lower CPV system efficiency.
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M. Renzi et al. / Energy Procedia 61 (2014) 220 – 224
Fig. 1 a, b. Pow wer-Irradiance (a)) and Efficiency- Ambient temperaature (b) daily treend on Septemberr the 14th 2013
In Figuree 2a the valuee of the poweer productionn as a function n of the availlable DNI is reported. Thee power produuced by the CPV C system iss clustered in three sets of ambient temp perature: <10 °C; 10-20 °C C and 20-30 °°C. Power prooduction almo ost linearly foollows the treend of the DN NI as depictedd by the trend d lines. In adddition, the inflluence of the ambient tempperature on th he CPV outputt is negligiblee meaning that the heat disssipation proceess and the cell performancee is not strong gly affected by y the ambient cconditions. Figure 2bb reports the electric efficiency of the syystem depend ding on the DNI availability ty, also in thiss case clustereed for three levels of ambiient temperatuure. The trend d of the electrric efficiency is almost flat with the DN NI and the efffect of the ambient temperaature is minim mal on the perrformance of tthe monitored d plants. Onlyy in presence of high ambieent temperatuure and high irrradiation it iss possible to ffigure a slight reduction oof the efficienncy which must m be confiirmed with further f experiimental data; anyhow thiss ms. dependence is far lower thhan that reporrted in traditioonal PV system a the graph h in Figure 33b reports thee Figure 3a shows a piicture of the two monitorred systems and i the primaryy optics, on a comparison of the perforrmance of thee CPVs havinng two differeent solutions in y production iss very similarr for both systems and, withh the availablee selected dayy of Novembeer. The energy data, a significant advantaage of the new w optics solutiion over the olld one cannot be observed. t CPV sysstems and thee Another interesting reemark is the time lag bettween the prroduction of the p of eaarly morning dew over thee availability of DNI. Thiss behavior is mainly ascribbable to the presence out half an hou ur to dry the llenses. lenses becauuse of the strong night humiidity. Sun rayys required abo
Fig. 2 a, b. Elecctric power - DNII (a) and Efficien ncy - DNI (b) trennd clustered for th hree levels of amb bient temperaturee
M. Renzi et al. / Energy Procedia 61 (2014) 220 – 224
Fig. 3 a, b. Pictture of the two monitored systems (a) and comparisson of their poweer production (b)
Figure 4aa reports the electric e powerr production ffor some seleected days as a function off the Air Masss (AM) coeffiicient for the system with constant c pitch Fresnel lens. The value off the daily max aximum powerr production aalways correspponds to the lowest value oof the AM, wh hen the sun haas the smallestt zenith angle. In a single dday the trend is not symmeetrical, as it m might be expected, because in the morninng the system m suffers from m some shaddowing effect, as abovem mentioned; in n addition, th he installationn location iss characterizeed by a higherr morning amb bient humidity ty which often n reduces the DNI. The tren end of three off these days w were highlightted with a solid line referrinng to those casses when the DNI D was simiilar both in thee morning andd in the afternnoon; thus the power producction almost overlaps o for th he same value of the AM, at least in the central hours of the day. In n Figure 4b th the upper grap ph shows the trend of the eelectric powerr M for the 3rd oof Septemberr: efficiency iss steady at 255% throughout and efficienncy as a functiion of the AM all the day. IIn the lower graph g also the trend of the D DNI is reporteed showing a clear c overlap w d with the trend of the electric power exceept for the morrning hours duuring the starttup of the plan nt. Table 1 reporrts the compaarison of the m monthly DNI irradiated en nergy per squaare meter, thee Finally, T monthly eneergy producedd and the correesponding moonthly averagee efficiency (calculated on D DNI basis) forr the system w with a constaant pitch lens. Data for the month of Jan nuary are not available duee to reliability y issues whilee in the monthh of July the plant p was startted and only few f days of op peration couldd be collected. Efficiency iss almost consttant throughou ut the monitorred period; du uring fall and winter w monthss the availablee DNI is veryy poor and, as a consequencce, also the prroduced energ gy is scarce; this t outcome highlights thee importance oof installing thhe CPV system ms in those loocations wheree the DNI is particularly inttense.
Fig. 4 a,b. Pictuure of the two moonitored systems (a) and comparis on of their powerr production (b)
223
224
M. Renzi et al. / Energy Procedia 61 (2014) 220 – 224
Table 1. Monthly values of the DNI energy, the production and the performance of the CPV system with a constant pitch lens
Month
DNI energy [kWh/m2]
Total Energy [kWh]
Mean Efficiency
Month
DNI energy [kWh/m2]
Total Energy [kWh]
Mean Efficiency
July
62.8
175.7
25.3%
August
190.2
509.3
24.8%
September
155.1
430.7
25.1%
October
47.8
143.0
26.1%
November
28.0
78.3
25.3%
December
44.9
134.3
26.0%
February
44.8
134.2
26.1%
Total
573.6
1605.5
25.3%
4. Conclusions In this paper the preliminary experimental results of two 3.5 kWp CPV plants operating in real working conditions are reported. Data confirmed that the CPV power output is linearly dependent on the DNI radiation while the influence of ambient temperature and AM coefficient on the efficiency is minimal. The project will be carried on with the implementation of additional sensors: a back-cell temperature probe; inclinometers to evaluate the tracking system accuracy; global solar radiation probe. A deeper evaluation of the influence of the cell temperature will be carried out as well as a comparison of the performance of CPVs and traditional PVs as a function of the ratio between the DNI and the global radiation. References [1] U. Desideri, J. Yan. Clean energy technologies and systems for a sustainable world. Applied Energy 2012;97: 1–4. [2] Carlos J. Sarasa-Maestro, Rodolfo Dufo-López, José L. Bernal-Agustín. Photovoltaic remuneration policies in the European Union. Energy Policy 2013;55:317–28. [3] W. Nishikawa, S. Horne. Key advantages of concentrating photovoltaics (CPV) for lowering levelized cost of electricity (LCOE). 23rd European PV solar energy conference; September 2008; Valencia. [4] P. Pérez-Higueras, E. Muñoz, G. Almonacid, P.G. Vidal. High Concentrator PhotoVoltaics efficiencies: Present status and forecast. Renewable and Sustainable Energy Reviews 2011;15:1810–5. [5] K. Menoufi, D. Chemisana, J. I. Rosell. Life Cycle Assessment of a Building Integrated Concentrated Photovoltaic scheme. Applied Energy 2013;111:505–14. [6] B.D. Tsai, Y.T. Hsu, T.T. Lin, L.-M. Fu, C.H. Tsai, J.C. Leong. Performance of an INER HCPV Module in NPUST. Energy Procedia 2012;14:893–8 [7] E. F. Fernández, P. Pérez-Higueras, A. J. Garcia Loureiro, P. G. Vidal. Outdoor evaluation of concentrator photovoltaic systems modules from different manufacturers: first results and steps. Progr in Photovolt: Res and Appl 2013;21:693-701. [8] M. Piliougine, C. Cañete, R. Moreno, J. Carretero, J. Hirose, S. Ogawa, M. Sidrach-de-Cardona. Comparative analysis of energy produced by photovoltaic modules with anti-soiling coated surface in arid climates. Applied Energy 2013;112: 626–34. [9] M. Vivar, R. Herrero, I. Antona, F. Martinez-Moreno, R. Moreton, G. Sala, A.W. Blakers, J. Smeltink. Eơect of soiling in CPV systems. Solar Energy 2010:84;1327–35.
Biography of the presenting author Massimiliano Renzi received his PhD in Energy in 2011; at present he is assistant professor in fluid machines and energy systems at the Faculty of Science and Technology, Bolzano, Italy. His research direction includes cogeneration systems, both traditional and fed by alternative fuels, and concentration solar energy (CPV and CSP).
ScienceDirect Energy Procedia 61 (2014) 220 – 224
The 6th Innternational Conferencee on Applied Energy – ICAE2014
Perform mance an nalysis off a 3.5 kWp k CPV V system m wiith two-aaxis tracker M. Renzzia*, M. Sanntolinib, G. Comodib b
a Facoltà di Sccienze e Tecnologgie, Libera Univeersità di Bolzano Dip ipartimento di inggegneria industriale e science mattematiche (DIISM M), Università Politecnica delle M Marche
Abstract This paper prresents the preliiminary operatiional results of two 3.5 kWp CPV C systems ussing triple juncttion III-V solarr cells and a tw wo-axis trackinng mechanism. The plant is iinstalled in the campus of thee Università Poolitecnica dellee Marche (Anccona, Central Italy). I The con ncentration opttics consists of a primary Fresnel F lens annd a secondary y reflective opttics with an ovverall geometriical concentrattion ratio of 47 76 X. An expeerimental meassurement setup p acquires the m main plant opeerating and amb bient quantities ; the paper reports the first months m of plant operation with h particular foccus on the influuence of the av vailable radiatioon and the amb bient temperatu ure on the perfo formance of thee system. The eelectric output has a linear treend with the avvailable direct normal radiatio on while ambieent temperaturee has a minor eeffect on the perrformance of th he CPV systemss; also the influeence of the Air Mass coefficieent is reported. © by Elsevier Ltd. an open access article under the CC BY-NC-ND license © 2014 2014Published The A Authors. Publis hedThis by isElsevier r Ltd. (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection andd/or peer-review w under responssibility of ICAE E Peer-review under responsibility of the Organizing Committee of ICAE2014 Keywords: CPV V; solar energy; experimental e data; solar concentrration; real opera ation
1. Introducction In the conntext of the growing deman nd of renewabble energy to mitigate the effect e of the ellectric energy y production ssystems [1], silicon s PV systems have acchieved a larg ge market pen netration mainnly driven by y favorable inncentive pays in many Coun ntries and duee to a good reeliability and bankability b [22]. Among thee alternative ssolar energy technologies, t the Concentrration PhotoV Voltaic techno ology (CPV) is considered d one of the m most promisinng solar energ gy conversionn devices both h on the economic [3], the technical [4]] and the envvironmental point p of view [5]. CPV tecchnology involves three basic componeents: tracking g mechanism, concentratioon optics, and d triple-juncttion (3J) solaar cells that allow to expploit a largerr on. Converselyy, because of the t use of lenses, the solar concentration n spectrum off the available solar radiatio technology can use only a fraction of the whole avvailable solar radiation, the Direct Norm mal Irradiation n nents of the CPV C systems oor some short-(DNI). Evenn though theree are several sttudies on the ssingle compon time monitooring on protootype units [6 6], there is laack of experim mental data in n continuous real working g operation [77]. In fact, thee effect of the ambient condditions, the efffect of the environmental ffouling on thee *Correspondingg author: Massim miliano Renzi; e-m mail: [email protected]; tel: +39 0471 017816; fax: +39 00471 017009 Libera Universsità di Bolzano, Facoltà di Scienze e Tecnologie, Piiazza Università 5, 5 39100 Bolzano o, Italy
1876-6102 © 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review under responsibility of the Organizing Committee of ICAE2014 doi:10.1016/j.egypro.2014.11.1075
M. Renzi et al. / Energy Procedia 61 (2014) 220 – 224
lenses and the imprecise alignment of the tracking mechanism are all sources of losses that must be taken into account to evaluate the real efficiency of CPV systems [8, 9]. Therefore, the aim of this work is to report the preliminary performance results of two 3.5 kWp CPV systems that are installed inside the campus of the Engineering Faculty of Università Politecnica delle Marche (Ancona, central Italy), a location where the average annual DNI is about 1500 kWh/(m2 year). 2. CPV system description and monitoring apparatus Each monitored CPV system consists of eight 420 W-modules having a total number of 768 3J cells with a total net area of 11.05 m2. Modules are installed on a chassis and tracking is realized with an azimuth-elevation system that uses electric motors. An embedded electronic board controls the motors to track the sun by means of a differential light-intensity sun sensor. The rated tracking accuracy is 0.2°. The optics consists of a plastic PolyMethylMethAcrylate (PMMA) primary Fresnel lens. The two installed systems have a different solution for the Fresnel lenses: the first one has a constant pitch of 0.5 mm of spacing in the Fresnel grooves; the second one, which is a newer version, presents a differential pitch having larger grooves in the center of the lens and smaller ones in the external part. Both of the Fresnel lenses have an aperture of 120x120 mm and a focal length of 130 mm. In addition to the primary lens, a simple reflective secondary optics is used: it consists of a frustum pyramidal cone installed in correspondence of the focus of the primary optics, close to the solar cell. The geometrical concentration ratio of the optical system is 476 and its acceptance is 0.4°. In our system, the 3J cells have an active area of 5.5x5.5 mm; their performance at the flash test with a concentration ratio of 520 suns is 37.5% while the modules have a rated efficiency of 26% with a direct normal irradiation of 850 W/m2. The cells are soldered on an Insulated Metal Substrate (IMS) to spread the non-converted radiation flow; each receiver is then connected in series to form the modules that are then coupled with a traditional solar inverter. The performance of each CPV system is monitored using a measuring apparatus that allows to evaluate the conversion efficiency of the plant and the main working parameters. All the monitored data are collected in a data logger and stored each 5 minutes. The sensors that are installed in the plant are: i) Pyrheliometer (first class accuracy, installed on the tracker on a side of the CPV modules); ii) ambient temperature sensor (accuracy r1.5 °C); iii) wind speed (cup anemometer that supplies data to evaluate the cooling effect of the ambient air on the modules and also serves as a security control for the wind effect on the trackers); iv) AC electric power produced (accuracy r3%). 3. Results and discussion Results reported in this paper were acquired from July 2013 to March 2014 for both the systems. One of the aims of the present paper is to show the performance of a CPV system in real working conditions, also taking into account the effect of lens fouling and soiling. For this reason, the surface of the lens was not cleaned during the test campaign. In Figure 1a the trend of a typical clear day (in this case September the 14th) is reported. Irradiance starts after 8:00 AM due to the shadowing effect of the surrounding hills and buildings in the early hours of the morning; DNI peaks at over 900 W/m2 at noon and the corresponding AC power production is over 2.5 kW for the constant pitch Fresnel lens system. The power output is flat over a large range of the day time (except for some transient clouds) thanks to the use of the tracking system that allows to maximize the exploitation of the available solar radiation. Figure 1b reports the trend of the ambient temperature and the corresponding efficiency of the CPV system: efficiency trend shows an opposite concavity, with higher values in the early morning and late in the afternoon (about 26%), and lower efficiency (about 25%) in the central day hours: this trend can be ascribed to the higher ambient (and receiver) temperature around the noon and thus a slightly lower CPV system efficiency.
221
222
M. Renzi et al. / Energy Procedia 61 (2014) 220 – 224
Fig. 1 a, b. Pow wer-Irradiance (a)) and Efficiency- Ambient temperaature (b) daily treend on Septemberr the 14th 2013
In Figuree 2a the valuee of the poweer productionn as a function n of the availlable DNI is reported. Thee power produuced by the CPV C system iss clustered in three sets of ambient temp perature: <10 °C; 10-20 °C C and 20-30 °°C. Power prooduction almo ost linearly foollows the treend of the DN NI as depictedd by the trend d lines. In adddition, the inflluence of the ambient tempperature on th he CPV outputt is negligiblee meaning that the heat disssipation proceess and the cell performancee is not strong gly affected by y the ambient cconditions. Figure 2bb reports the electric efficiency of the syystem depend ding on the DNI availability ty, also in thiss case clustereed for three levels of ambiient temperatuure. The trend d of the electrric efficiency is almost flat with the DN NI and the efffect of the ambient temperaature is minim mal on the perrformance of tthe monitored d plants. Onlyy in presence of high ambieent temperatuure and high irrradiation it iss possible to ffigure a slight reduction oof the efficienncy which must m be confiirmed with further f experiimental data; anyhow thiss ms. dependence is far lower thhan that reporrted in traditioonal PV system a the graph h in Figure 33b reports thee Figure 3a shows a piicture of the two monitorred systems and i the primaryy optics, on a comparison of the perforrmance of thee CPVs havinng two differeent solutions in y production iss very similarr for both systems and, withh the availablee selected dayy of Novembeer. The energy data, a significant advantaage of the new w optics solutiion over the olld one cannot be observed. t CPV sysstems and thee Another interesting reemark is the time lag bettween the prroduction of the p of eaarly morning dew over thee availability of DNI. Thiss behavior is mainly ascribbable to the presence out half an hou ur to dry the llenses. lenses becauuse of the strong night humiidity. Sun rayys required abo
Fig. 2 a, b. Elecctric power - DNII (a) and Efficien ncy - DNI (b) trennd clustered for th hree levels of amb bient temperaturee
M. Renzi et al. / Energy Procedia 61 (2014) 220 – 224
Fig. 3 a, b. Pictture of the two monitored systems (a) and comparisson of their poweer production (b)
Figure 4aa reports the electric e powerr production ffor some seleected days as a function off the Air Masss (AM) coeffiicient for the system with constant c pitch Fresnel lens. The value off the daily max aximum powerr production aalways correspponds to the lowest value oof the AM, wh hen the sun haas the smallestt zenith angle. In a single dday the trend is not symmeetrical, as it m might be expected, because in the morninng the system m suffers from m some shaddowing effect, as abovem mentioned; in n addition, th he installationn location iss characterizeed by a higherr morning amb bient humidity ty which often n reduces the DNI. The tren end of three off these days w were highlightted with a solid line referrinng to those casses when the DNI D was simiilar both in thee morning andd in the afternnoon; thus the power producction almost overlaps o for th he same value of the AM, at least in the central hours of the day. In n Figure 4b th the upper grap ph shows the trend of the eelectric powerr M for the 3rd oof Septemberr: efficiency iss steady at 255% throughout and efficienncy as a functiion of the AM all the day. IIn the lower graph g also the trend of the D DNI is reporteed showing a clear c overlap w d with the trend of the electric power exceept for the morrning hours duuring the starttup of the plan nt. Table 1 reporrts the compaarison of the m monthly DNI irradiated en nergy per squaare meter, thee Finally, T monthly eneergy producedd and the correesponding moonthly averagee efficiency (calculated on D DNI basis) forr the system w with a constaant pitch lens. Data for the month of Jan nuary are not available duee to reliability y issues whilee in the monthh of July the plant p was startted and only few f days of op peration couldd be collected. Efficiency iss almost consttant throughou ut the monitorred period; du uring fall and winter w monthss the availablee DNI is veryy poor and, as a consequencce, also the prroduced energ gy is scarce; this t outcome highlights thee importance oof installing thhe CPV system ms in those loocations wheree the DNI is particularly inttense.
Fig. 4 a,b. Pictuure of the two moonitored systems (a) and comparis on of their powerr production (b)
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224
M. Renzi et al. / Energy Procedia 61 (2014) 220 – 224
Table 1. Monthly values of the DNI energy, the production and the performance of the CPV system with a constant pitch lens
Month
DNI energy [kWh/m2]
Total Energy [kWh]
Mean Efficiency
Month
DNI energy [kWh/m2]
Total Energy [kWh]
Mean Efficiency
July
62.8
175.7
25.3%
August
190.2
509.3
24.8%
September
155.1
430.7
25.1%
October
47.8
143.0
26.1%
November
28.0
78.3
25.3%
December
44.9
134.3
26.0%
February
44.8
134.2
26.1%
Total
573.6
1605.5
25.3%
4. Conclusions In this paper the preliminary experimental results of two 3.5 kWp CPV plants operating in real working conditions are reported. Data confirmed that the CPV power output is linearly dependent on the DNI radiation while the influence of ambient temperature and AM coefficient on the efficiency is minimal. The project will be carried on with the implementation of additional sensors: a back-cell temperature probe; inclinometers to evaluate the tracking system accuracy; global solar radiation probe. A deeper evaluation of the influence of the cell temperature will be carried out as well as a comparison of the performance of CPVs and traditional PVs as a function of the ratio between the DNI and the global radiation. References [1] U. Desideri, J. Yan. Clean energy technologies and systems for a sustainable world. Applied Energy 2012;97: 1–4. [2] Carlos J. Sarasa-Maestro, Rodolfo Dufo-López, José L. Bernal-Agustín. Photovoltaic remuneration policies in the European Union. Energy Policy 2013;55:317–28. [3] W. Nishikawa, S. Horne. Key advantages of concentrating photovoltaics (CPV) for lowering levelized cost of electricity (LCOE). 23rd European PV solar energy conference; September 2008; Valencia. [4] P. Pérez-Higueras, E. Muñoz, G. Almonacid, P.G. Vidal. High Concentrator PhotoVoltaics efficiencies: Present status and forecast. Renewable and Sustainable Energy Reviews 2011;15:1810–5. [5] K. Menoufi, D. Chemisana, J. I. Rosell. Life Cycle Assessment of a Building Integrated Concentrated Photovoltaic scheme. Applied Energy 2013;111:505–14. [6] B.D. Tsai, Y.T. Hsu, T.T. Lin, L.-M. Fu, C.H. Tsai, J.C. Leong. Performance of an INER HCPV Module in NPUST. Energy Procedia 2012;14:893–8 [7] E. F. Fernández, P. Pérez-Higueras, A. J. Garcia Loureiro, P. G. Vidal. Outdoor evaluation of concentrator photovoltaic systems modules from different manufacturers: first results and steps. Progr in Photovolt: Res and Appl 2013;21:693-701. [8] M. Piliougine, C. Cañete, R. Moreno, J. Carretero, J. Hirose, S. Ogawa, M. Sidrach-de-Cardona. Comparative analysis of energy produced by photovoltaic modules with anti-soiling coated surface in arid climates. Applied Energy 2013;112: 626–34. [9] M. Vivar, R. Herrero, I. Antona, F. Martinez-Moreno, R. Moreton, G. Sala, A.W. Blakers, J. Smeltink. Eơect of soiling in CPV systems. Solar Energy 2010:84;1327–35.
Biography of the presenting author Massimiliano Renzi received his PhD in Energy in 2011; at present he is assistant professor in fluid machines and energy systems at the Faculty of Science and Technology, Bolzano, Italy. His research direction includes cogeneration systems, both traditional and fed by alternative fuels, and concentration solar energy (CPV and CSP).