Performance analysis of PV plants: Optimization for improving profitability

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<ul><li><p>iz</p><p>ezEscu</p><p>l PVexpovenswawie impro</p><p>et penndouslts thathanismch, theegionsligedminimin man</p><p>market. PV module prices have fallen by 22% each time the cumu-lative installed capacity (in MW) has doubled [2]. For large ground-mounted systems, the generation costs in 2010 ranged fromapproximately 0.29/kWh in the north of Europe to 0.15/kWh inthe south of Europe and were as low as 0.12/kWh in the MiddleEast. According to EPIA (European Photovoltaics Industrial Associ-ation) estimations, these rates will fall signicantly over the nextdecade. Expected generation costs for large, ground-mounted PV</p><p>systems in 2020 are likely to be in the range of 0.070.17/kWhacross Europe [2].</p><p>from the changing scenario brought about by Royal Decree (RD)1578/2008 [4], which introduced a signicant decline in produc-tion premiums, and by Order ITC/3353/2010 [5], which placed lim-itations on production times at feed-in tariff prices and introducedthe obligation to produce at the ordinary tariff at other times. Thesame situation occurs in other countries like France [6], Italy [7] orGermany [8], where the entry into force of the new regulated rateswas a major turning point in the protability of the facilities.</p><p>Studies of PV systems in Germany [9], California [10] and Japan[11], have revealed performance problems associated with suchissues as shading, equipment and installation defects, inverter</p><p> Corresponding author. Tel.: +34 947 258925; fax: +34 947 258910.</p><p>Energy Conversion and Management 54 (2012) 1723</p><p>Contents lists available at</p><p>n</p><p>lseE-mail address: (C. Alonso-Tristn).Austria, France, Denmark, Germany, Greece, Italy, Netherlands,Portugal, Spain, Switzerland and the state of California (USA),among others. Table 1 summarizes the electricity price of PVkWh in different countries [1] in 2009.</p><p>High demand and an exponential increase in the supply of com-ponents for photovoltaic systems have led to a very signicantprice drop per kW installed, and economic incentives have encour-aged a large number of small investors to enter the photovoltaic</p><p>ponents, many installation companies and more than 15,000 directpermanent jobs and a further 25,000 casual jobs at peak activity[3]. However, mechanisms to ensure the quality of facilities inSpain, from an energy standpoint, have not been implemented inany single instance. The economic returns are guaranteed even ifthe installation is not optimized.</p><p>The protability of the investments made so far has become apriority for both government and industry. In Spain, this is evident1. Introduction</p><p>Over the last decade, global mark(PV) technology has increased tremedriven by the environmental benenology, but also by the incentive meccountries; the most common of whiintroduced in many countries and rmodel, electricity companies are obfrom renewable energy sources at aFeed-in tariffs have been adopted0196-8904/$ - see front matter 2011 Elsevier Ltd. Adoi:10.1016/j.enconman.2011.09.013etration of photovoltaicy. This trend is not onlycharacterize this tech-s developed in variousfeed-in tariff, has beenin recent years. In thisto purchase electricityum price xed by law.y countries including:</p><p>In the Spanish case, this has meant more than 3350 grid con-nected MW distributed across more than 50,000 installations.Spain is a world leader in solar penetration per capita (75.19W/person) and coverage of electricity demand by this technologywas 1% in 2008 and approximately 1.5% in 2009. The technologyhas already won widespread social acceptance, is no longer mar-ginal, and will be the basic standard in a very short time. The Span-ish PV market in 2008 reached a value in excess of 16,000 M, withover 40 identied companies engaged in the manufacture of com-Performance analysis of PV plants: Optim</p><p>M. Dez-Mediavilla, C. Alonso-Tristn , M.C. RodrguResearch Group SWIFT (Solar and Wind Feasibility Technologies), University of Burgos,</p><p>a r t i c l e i n f o</p><p>Article history:Received 29 March 2011Received in revised form 15 September2011Accepted 16 September 2011Available online 4 November 2011</p><p>Keywords:System performancePV systemGrid-connectedOptimization</p><p>a b s t r a c t</p><p>A study is conducted of reasame area, both of whichproduction were collectedof radiation. The installatiotem, and the power supplywere also employed for thenomic terms, highlight thparameters for maximum</p><p>Energy Conversio</p><p>journal homepage: www.ell rights reserved.ation for improving protability</p><p>-Amigo, T. Garca-Caldern, M.I. Dieste-Velascoela Politcnica Superior, Avda. Cantabria s/n, 09006 Burgos, Spain</p><p>production from two 100 kWp grid-connected installations located in theerience the same uctuations in temperature and radiation. Data sets onr an entire year and both installations were compared under various levelswere assembled with mono-Si panels, mounted on the same support sys-s equal for the inverter and the measurement system; the same parametersring, and electrical losses were calculated in both cases. The results, in eco-portance of properly selecting the system components and the design</p><p>tability. 2011 Elsevier Ltd. All rights reserved.</p><p>SciVerse ScienceDirect</p><p>and Management</p><p>vier .com/ locate /enconman</p></li><li><p>Hence, the two facilities are subject to the same environmental</p><p>Fig. 1. Aerial photograph of System 1 and System 2, at Torquemada (Palencia,Spain), portraying the panels and the inverter systems of both facilities.</p><p>Fig. 2. Panel support system. Detail of mechanical support.</p><p>ersioconditions in terms of temperature, radiation, humidity and windspeed. The area benets from very favourable atmospheric condi-tions. Solar irradiation is estimated at approximately 1450 Kwh/m2 year [12]. The ambient temperature range is between 4 Cand 20 C and the number of cloudy days is very low [13]. Fig. 1presents an aerial photograph of both installations.</p><p>2.1. Description of the PV-panelsfailure, and deviations frommanufacturers specications in the PVmodules.</p><p>In this work, the importance of an appropriate choice of ele-ments for the installation is studied. The inuence of the qualityof the panels used, the location of the protection and measurementsystem, the design of the wiring and the choice of the inverter sys-tem have all been analysed in economic terms, using real produc-tion data taken from two 100 kWp grid-connected installations.</p><p>2. The facilities</p><p>Both facilities (System 1 and System 2) in this case study arelocated at Torquemada (Palencia), at the centre of the autonomousregion of Castilla y Len in Spain. Their geographical coordinates are42010280 0 N latitude and 4180280 0W longitude, situated at an alti-tude of 740 m above sea level. The facilities are located in neigh-bouring plots, with no barriers between them, occupying a totalsurface parcel of 8000 m2. They stand on a gentle, south-facingslope that is conducive to natural air circulation, one of the mostbenecial aspects for improving the panels electrical productionin summer time.</p><p>Table 1Indicative installed PV prices per kWh in variouscountries in 2009. Tariff depends on type and installedpower of facilities. Data from [32].</p><p>Country Price (/kWh)</p><p>Austria 0.460.30Canada 0.820.42France 0.570.32Germany 0.430.31Greece 0.450.40Italy 0.400.36Japan 0.220.20Portugal 0.450.32Spain 0.300.24Switzerland 0.560.30USA 0.240.18</p><p>18 M. Dez-Mediavilla et al. / Energy ConvSystem 1 can generate 101.01 kWp with 546 PV panels (modelBP-7185S [14]), the technical specications for which are 185 Wp,5.1 A of IPM and 36.5 V for VPM. Electrical performance is between14% and 15% and the tolerance value is 2.5%. The panels integrateIntegraBus technology, which limits partial shading losses. They arearranged in groups of 14 panels in series to work with a voltage of511 V (within the voltage range of the inverter). The current foreach group is 5.1 A. Panels are arranged in 12 rows with threegroups in each one and a further two rows with two groups andone group, respectively. This means that the distance between therst and the last row is 60 m and the width is approximately42 m, as portrayed in Fig. 1.</p><p>A mobile structure was designed which adjusts the position ofthe panels according to the time of year, in order to optimize elec-trical production, which also helps to minimize the visual impactof the facilities. The maximum height of the panels (1.80 m) usu-ally occurs during winter time and they can be lowered at othertimes of the year, using a manual system that allows the angle ofn and Management 54 (2012) 1723inclination of the panels to be varied between 5 and 50. Thismodication is performed approximately every 26 days. Fig. 2 pre-sents the panel support system and Fig. 3, their highest and lowestpositions.</p><p>The second facility, System 2, can generate 108.36 kWp with602 panels (model CEEG-180 24/s [15]). Their technical specica-tions are 180Wp, 5 A of IPM and 36 V for VPM. Electrical perfor-mance is 16.8% and the tolerance value is 5%. They are arrangedin groups of 14 panels in series functioning at a voltage of 504 V(valid range for the inverter). Current for each group is 5 A. The plotdistribution has been arranged in 10 rows with different numbersin each group as presented in Fig. 4. The distance between the rstand the last row is 50 m with a maximum width of 100 m.</p><p>Fig. 3. Panel support system. High and low panel positions.</p></li><li><p>in System 1 and panel adjustments are performed simultaneously.</p><p>cooling installation as employed in System 1.</p><p>crosses the centre of the installation from north to south. Thereare only three protection boxes, in the rst, fth and seventh rows.Fifteen groups are wired into the rst box (row one) and fourteengroups are wired into each of the other two boxes (rows ve andseven). All wiring has a cross-section of 10 mm2. Two wires emergefrom each protection box to the inverter conducting a maximumcurrent of 70 A. There are three positives and three negative inputwires to the inverter, which facilitate this type of connection.</p><p>2.4. The measurement system</p><p>For System 1, the connection to the measurement system is a6 m long section of wire able to conduct a maximum current of146 A, corresponding to the maximum output of the inverter. ForSystem 2 the connection is 50 m long. The section of wiring isthe same as that employed in System 1, since the maximum output</p><p>tions of both installations.</p><p>ersion and Management 54 (2012) 1723 192.3. The protection boxes2.2. Description of the inverters</p><p>Only one 100 kW inverter was selected for System 1: IngecomSun 100model [16]. Its technical specications are 100 kWnominalpower and 110 kW maximum power, input voltage range of405750 V and input current of 286 A; output voltage is 3 400 Vand output current 187 A; harmonic distortion is less than 3% andenergyefciency is higher than96%. Theworking temperature rangeis 10 C to 65 C. In order to prevent unwanted disruptions due toany adverse effects of temperature, a ventilation system that elimi-nateswarmair in summerhasbeendesignedand installedalongsidethe inverter in a stall, located 5 m from the front row.</p><p>As in System 1, an SMA Sunny Central inverter (100 kW Indoor)[17] was the sole choice for System 2. Its technical specicationsare 100 kW nominal power and 110 kW maximum power, inputvoltage range 480820 V and input current 235 A; output voltageis 3 400 V and output current 145 A; harmonic distortion is lessthan 3% and energy efciency higher than 97.6%. The working tem-perature range is 20 C to 50 C. The stall of the inverter is located10 m from the front row and has been tted with the same type ofThe mobile structure on which to place the panels is the same as</p><p>Fig. 4. Panels distribution in System 2.</p><p>M. Dez-Mediavilla et al. / Energy ConvThe protection system for System 1 is structured in rows. Onebox, containing the protection elements fuse and switch foreach group in the row is placed in its respective position. The pro-tection system structure is as follows: the 14th row, at the north-ernmost point of the facility, formed of a single group, within theenclosure, consists of a fuse and a 10 A switch. Output from thisbox goes to the box in the adjacent row (the 13th), where thereare two 10 A switches and two 10 A fuses. Each group goes throughthe fuse and the switch, and the output is added to the previousrow. The output wiring of the 13th row protection box containsthe necessary section for the three groups. Following the same de-sign philosophy, the output wiring section of each protection box issufcient to carry the current from the groups of previous rows.Thus, the output section of the rst line, the southernmost andclosest to the inverter location, supports a current of 198.9 A, com-ing from the 39 groups of the installation. This output wiring is at-tached to the DC input inverter, located approximately 5 m fromthe enclosure of the rst row.</p><p>Distribution of System 2 is as follows: the wiring for each of the43 groups in System 2 runs along the tables into a ditch that3. Factors inuencing the performance of PV plant</p><p>In recent years, PV-plants in Spain have become a very attrac-tive investment product, almost within reach of any small investor.The economic incentives for PV production, soft loans and subsi-dies for small power plants have meant that facilities of up to100 kW proliferate throughout the country. There have been anumber of installation companies that offer turnkey solutions inorder to cover the high demand. They handle all administrativeprocedures, carry out the project, install the plants, and even par-ticipate in their maintenance. But mechanisms have not beenimplemented which would ensure the quality of installation, nei-ther has optimal plant design and the best conditions for theiroperation been assured.</p><p>Table 2Technical specications of panels and inverter used in System 1 and System 2.</p><p>Panels System 1 System 2BP-7185S CEEG-180</p><p>VPM (V) 36.5 36IPM (A) 5.1 5WP (W) 185 180Performance (%) 1416 16.8Tolerance value (%) 2.5 5No of panels 546 602No of groups 39 43Vgroup (V) 511 504Facility power (kW) 101.01 108.36</p><p>Inverter Ingecom Sun 100 SMA- Sunny Central 100 Indoor</p><p>Vcc (V) 405750 480820Icc (A) 286 235Vca (V) 3 400 3 400I (A) 187 145current of the System 2 inverter matches that in System 1. Theelectrical company which buys and distributes the electricity stip-ulates a requirement that the signal should pass through a stan-dard fuse and switch and three current transformers with thevalues that are sufcient for the measurement system, at the pointat which production measurement occurs. The measurement sys-tem is the same for both Systems 1 and 2, since technical andmechanical specications are common to both.</p><p>Since its start up on 5th July 2006, until 30th June, 2010, System1 has produced 518,076 kWh, which amounts to 240,000, sur-passing its expected performance by more than 5%. Since 25th Sep-tember 2008, until 30th June, 2010, System 2 has produced258,028 kWh, the estimated cost of which, at 121,273, is 2.6%higher than predicted. Table 2 summarizes the technical specica-ca</p><p>Temperature range 10 to 65 C 20 to 60 CPerformance...</p></li></ul>