SOLAR SKI LIFT PV CARPORT AND OTHER SOLAR WINGS CABLE BASED SOLUTIONS

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1 of the 27 th European Photovoltaic Solar Energy Conference, Frankfurt 25 st Sept. 2015; 4BV.1.60 SOLAR SKI LIFT PV CARPORT AND OTHER SOLAR WINGS CABLE BASED SOLUTIONS F. Baumgartner 1, A. Büchel 2, R. Bartholet 3 1 University of Applied Science Zurich, ZHAW, School of Engineering, Technikumstrasse 9, CH-8401 Winterthur, ; bauf@zhaw.ch; Tel Solar Wings AG, Oberweilerstrasse 36, , LI- Ruggell, Liechtenstein; info@solar-wings.li 3 BMF Maschinenbau AG, Lochriet, CH-8890 Flums,, ABSTRACT: Cable based mounting systems of solar modules offers several promising options of using existing infrastructure installations to apply PV application on top. This concept of double use of land was successfully applied to a 650kW Solar Wings PV plant two meters on top of a waste disposal site, or a 90kW PV plant eight meters above an industrial outdoor storage facility or on top of a skilift in. The analysis of the first three years of operation of the 650kW one-axis tracking installation in Southern Germany proofed a tracking gain of 23.5% of the irradiance relative to a standard fixed installation. Together with the measured excellent yearly AC performance ratio of 0.9 the average annual yields to 1325kWh/kW was measured due to the perfect cooling of the PV modules at their mounting position several meters above ground. New cable based PV installation on top of Carports and other light weight low cost cable based PV installation are discussed. Keywords: mounting solutions, PV carport, cabel based mounting 1 INTRODUCTION Photovoltaic could be more than only another envelope of buildings. There is a chance that some of the PV installations evolve into new architectural elements with additional features others than only producing electricity. Cable based PV mounting solutions offers this option to link the building with the surrounding space or mount the PV modules on top of carports.[1] In the last decade cost share of PV modules are declined from two third below one half of today s total PV plant costs. Further cost reduction of PV electricity will be done, by reducing primarily the PV mounting costs. The recently dramatic cost reductions of the PV modules economically faced out several two axis tracking systems due to their higher cost levels. The trends in the coming years toward higher module efficiency at much lower module costs make it unrealistic to bring back these traditional tracking systems. Also the high concentration PV tracking systems have to be aware of the relative high costs of the needed very stable mechanical mounting systems below their high efficiency cells. Several new mounting concepts of standard PV modules, beside the existing traditional systems will be developed in future. Here we will concentrate on mounting systems based on cables. First solutions of using cables to mount solar cells are proposed in some early patent applications.[2] In [3] the authors describe the Solar Wings solution to combine cable based PV mounting solutions with tracking of the PV modules together with extensions to also track low concentration optical mirrors mounted on the same cables. In this paper the different realized Solar Wings projects are described including their performance values and further development are discussed. Thirty years ago the pioneer Adolf Götzberger proposed the combination of PV modules mounted in about two meter heights above agriculture land to achieve nearly constant solar irradiance during the day, thus supporting also the growth of the plants below the modules.[4] Recently, Solar Wings thanks Prof. Götzberger for the promising discussions about using Solar Wings mounting system as a candidate for a future pilot Agrovoltaic installation. 2 CONCEPT AND SOLUTIONS OF CABLE BASED PV MOUNTING The main advantage of cable based mounting solutions on top of different existing infrastructure facilities is the function of double use of land. Solar Wings cable based PV mounting solutions have demonstrated this feature in several projects, attracting broad public interest.(see Fig. 1) Latest example is the 60kW Solar Wings recently installation on top of a skilift in, to be aware to use all the potential of PV power wherever it is possible.(see Fig. 2) Using cables as the main mechanical support of the PV modules offers the second advantage, to minimize the amount of used metal material within the mechanical support structure. Further total cost reduction of PV electricity will find their final limits in the material costs of the mounting structural elements. Other cost limits are given by the material costs of the PV module itself like semiconductor material, glass, encapsulation materials together with the electrical components like copper cables and connectors. An overview of the realized Solar Wings projects is found in Tab. 1. Solar Wings powering the world first solar skilift in Tenna,, (Fig. 2) 60kW PV modules installed in December 2011, nine meters above the ski-slope with a cable length of 320m; one-axis tracking, the annual grid connected PV production exceeds the electricity needs of the lift by a factor of three. In total 82 Solar Wings are mounted in a distance of about four meters each holding three standard 240W polycrystalline silicon modules on aluminium profile. Two inverters of 10kW and three of 13kW are used for grid-connection. The support cables are oriented East-West and the average slope of the hill is 18. The annual PV production should exceed the annual electricity consumption of the lift by more than a factor of five. Solar Wings span the outdoor storage facility in Flums, ; (Fig. 5) 94kW PV modules installed in December 2009 nine meters above the ground with a cable length of 200 meters, two-axis tracking of the PV modules, motor trucks can pass below the PV installation; In total of 50 Solar Wings are mounted in a

2 distance of about four meters each holding eight standard 235W polycrystalline silicon modules on o the aluminium mounting bar. Ten inverters each at a nominal n powerr of 10kW are used for grid-connection. 50 away from south direction. The anglee of The support cables are oriented the mounting bar for the two supportingg cables can be set with an additional linear drive motorr between +/-35 enabling full two axis tracking. The second axis is moved by the steering cable to perform the angle be controlled between +/-45. reduced. Another neww concept of light weight cable c based solar cell mounting is proposedd in [6]. Againn the whole mounting support of the PV modules is i reduced dramatically, by the fact, that inn case of strongg wind and snow, the PV modules will be parked in a safe position. Thus cost can bee saved not to be invested in materials of a heavy support structure. Similar systems as shown in Fig. 7 for PV modules m at a distance of several tens of meters are provenn for moving sun shading elements in the building sector onn the meter scale. Currently other solar wings projects are a in the development phase, like the 8 MW PV plant on the lake of Walensee,. There probably supporting cables with a length of 170 meters may spann the whole PV Generator inn front of hill with a slope of f about 60. Similar Solar Wings PV-installations could bee combined in future with large buildings. The market situation s and the analyses of the t costs of several Solar Wings solutions are given in [8]. Figure 1: top: Solar Wings Sketch (A. Büchel, Solar Wings), bottom: Solar Wings Prototype constructed in May 2009 see Tab. 1 Solar Wings PV plant on top of the waste disposal site Waldshut, Germany, 654kW PV modules were installed in December 2008 two meterss above groundd of the 22 sloped waste disposal site using supporting cables with 320 m length;(fig. 3) The one-axis tracking system is controlled by the steering cable between the limits s of +/-45 of the support bars. In total of 320 Solar Wings are mounted in a distance of five meters each holding eight standard 230W polycrystalline silicon modules on the aluminiumm mounting bar. Twenty-one inverters each at a nominal power of 30kW are used forr grid-connection. More technical details are given in.[1] Solar Wings span a parking area in Flums, ; 2kW PV modules installedd as the first Solar Wings prototype in May 2008 four meters above an industrial parking area with 40 m cablee length, one-axis tracking Next year the first large scale Solar Wings PV Carport will be installed. (Fig. 6) Similar to other Solar Wings projects the supporting cables are hold by intermediate pillows at a distance of about 40 meters. The PV modules are installed about 4 meters above the parking ground floor. No tracking is applied, but the PV modules can be moved in a parking position in case of strong snow fall.[5] Thus the end fundaments of the supporting cables have not to be designed to take over the additional snow load and the total mounting costs can be Figure 2: Solar Wings W Skilift installed in December 2011 (see

3 3 PERFORMANCE OF SOLAR WINGS CABEL BASED PHOTOVOLTAICS 3.1 One-axis tracking Waldshut plant Figure 4 gives the irradiance and temperature values measured during the 30 th of Aug at the Waldshut plant. In the morning at eight o clock and in the afternoon at half past four the irradiance is doubled due to tracking. The overall tracking gain during the whole day sum upp to 37% increase for the sensor mounted on top of the tracked modules, relativee to a second sensor s which was mounted in a fixed position 22 inclined oriented south. At noon when both sensor oriented parallel toward the sun, the difference of the sensor readings are below 2%. Starting in the late morning small amounts of foggy clouds were reduced continuously for f that weather situation, reaching the maximum irradiance close to 1000W/m2 of the tracked sensor after two t o clock in the afternoon. Figure 4: Measured Performance of the Solar Wings Waldshut Plant on o 30th Aug Nominal daily input irradiance of 7.00 hours and 9.6hours at average 1000 W/m2 for the fixed and tracked irradiance sensor (Data measured by Fraunhofer ISE E in an interval of five minutes) public performance data avalible at Figure 3: Solar Wings 650kW PV plant on top of the Lonza waste disposal site, Waldshut, Germany [1] On that nearly clear sky day with no relevant wind the module temperature was about 200 degrees higher, during most of the period when PV electricity was generated,, at an averagee daily ambient temperature of 21 C. In Fig. 3 the calculated absolute thermal losses relative to the STC power of the polycrystalline modules with a temperature coefficient of -0.43%/ C is shown for each 5 minutes. In average this gives daily thermal losses of 7.2% relative to STC efficiency values, contributingg to a daily Performance Ratio PR of 0.86 relative to the measured DC power of the PV generator. From April to October the gain in irradiance duee to tracking was within the limit of 25% +/- 2%.(Tab. 2) ) In the same period of the year the overall AC Performance Ratio of the plant was / as an average in the first threee years of operation. In thee remaining four month in the winter period only one quarter of the yearly PV production is reached with lower tracking gains of +17% +/- 4% and higher PR values of / (Tab. 2) The measured module temperature was in January about 5 degreess above ambient while in August an average of 15 degrees abovee average ambient daily temperature wass recorded. Due to the fact, that in summer there is more PV production, the annual energy weighted averagee daily module temperature off 27.4 was calculated. This was w 12.8 C above average daily ambient temperature. Thus the temperature losses compared to STC values in terms of annual energy production becomes only 1%. 1 This excellent cooling of the PV modules in the Solar Wings mounting system explains the very high yearly average Performance Ratio of Finally excellent yearly nominal working hours of 1325 kwh/kw of this one axis tracking plant was measured for thee first three years of operation. Similar nominal working hours are reached with fixed PV installations in southern Italy. Figure 5: Solar Wings parking (left 90kW two axis tracking, Flumroc,

4 3.2 Solar Skilift one- axis tracking Tenna plant In the first winter season of operation, starting 6 thh of December 2011, the electricity demand of the Skilift motor was 6147kWh.(Fig. 2) During the same period the Solar Wings PV installation on top of the Skilift produces kwh. Thus the solar surplus was about 170% during winter time. The total specificc solar electricity production from 6 th Dec 2011 to 13 thh May 2012 was 514kWh/kW according to the readings of the local utilities meters The AC performancee of the Tenna solar s ski lift on the clear sky day 25 th of May 2012 was 9.0kWh/kWp. 9 The AC performance of a roof mounted 28kW polycrystalline silicon module plant, oriented 55 toward west, inclinationn 23 and located several hundred meters away from the ski lift, was also recorded. Finally the one axis tracking solar ski lift showed 40% higher daily AC yield compared to the above fixed installation. A detailed precession monitoring program is planned at the Tenna plant to analyse the trackingg gain at that high elevation assuming higher amounts of direct irradiation compared to other installations like the Solar Wings Waldshut plant. Figure 7: New light weight cable based PV mounting solution [6]. In case of strong wind and snow the PV cells are parked in thee safe position inside the housing on the left part of the system 4 CONCLUSION Three years of operation o of the 654kW one-axis Solar Wings plant in Waldshut proved stable cable based mounting solutions at an excellent performance ratio of 0. 9 and annual specific yield of 1325kWh/kW at this location in Southern Germany. Further developments of cable based PV Carports and new light-weigh low cost solutions will be realised in the next months. ACKNOWLEDGEMENTS The support of the measured data of thee Waldshut plant, performed by Klaus Kiefer, Alfons Armbruster ISE Freiburg, Germany and the support of the measured data from the Tenna, Solar Skilift PVV plant performed by Edi and Uli Schaufelberger, Tennaa and Silvio Koller, from Hassler energia AG, Zillis all from are highly acknowledged. REFERENCES Figure 6: Solar Wings Parking solutions [3] 3.3 Two-axis tracking Flums plant A detailed performance analysis of the two-axis tracking installation (Fig. 5) together with the influence of the local shading of the nearby power transmission lines are given in [7]. The final specificc annual yield for 2011 was 1360 kwh/kw. For this installation in Flums, the yield was slightly higher than the one- located on the Swiss border to Germanyy (Tab. axis tracking Solar Wings installation in Waldshut, 2). [1] F. Baumgartner, A. Büchel, R. Bartholet, Proceedings, EUPVSEC 23 rd in 2008, 4DO.9.5; 24 th in Hamburg 2009, 4CO.8.6; 25 th in i Valencia 2010, 4BV.1.34 [2] patent S. Conger, C US B2, 2007 ; H. Zaloun, WO 2006/130892; k. Stein, EPO A1, 1988 [3] A. Büchel, F. Baumgartner, R. Bartholet; patent WO 2010/ A3 [4] A. Götzberger, A. Zastrow, Int. J. Solar Energy, 1982, Vol 1, pp55-69; On the Coexistence of Solar-Energy Conversion and Plant Cultivation [5] A. Büchel, F. Baumgartner, R. Bartholet, patent applicationn 2011 [6] A. Büchel, F. Baumgartner, iworks AG, patent applicationn May 2012 [7] F. Baumgartner et. al. Report of the Swiss Department of Energy BFE, Annual Photovoltaic Report 2011, [8] A. Büchel,, Thesis, Dec 2011, HSG University of St. Gallen

5 of the 27 th European Photovoltaic Solar Energy Conference, Frankfurt 25 st Sept. 2015; 4BV.1.60 Table 1 Main characteristics of Solar Wings Cable based PV plants Type mounted above Heights above ground [meter] total lengths cables [meter] Location Operation since Nominal Power [kwp] Mechanical Tracking Industrial area parking 4 20 Flums, May axis Waste disposal site Waldshut, Germany Dez axis Industrial outdoor storage facility Flums, 90 2 axis Skilift Tenna, Dec axis Carport 4 40 Germany Planned no tracking but snow/wind position Table 2 Performance of Solar Wings 654kW cable based PV plants in Waldshut, Germany, data measured by Fraunhofer ISE, Freiburg.(the combined measurement uncertainty values are estimated to be +/-3% at k=2) Monthly Solar Input not tracked at 22 south [kwh/m2] Tracked AC yield tracked Generator [Wh/Wp]] Tracking gain sensor Mean Mean Mean Mean Jan % 0.96 Feb % 0.95 Mar % 0.97 Apr % 0.92 May % 0.89 Jun % 0.88 Jul % 0.86 Aug % 0.87 Sep % 0.88 Oct % 0.92 Nov % 0.96 Dec % 0.92 YEAR % 0.90 PR