SINVERT PVM Inverters under test Offprint from PHOTON International April 2011, Pages The SINVERT PVM inverters Answers for the environment.

Transcription

1 SINVERT PVM Inverters under test Offprint from PHOTON International April 2011, Pages The SINVERT PVM inverters Answers for the environment.

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3 science & technology inverters test A new frontrunner The Solar Power Magazine International Siemens Sinvert PVM20 A 97.7 % at high irradiation 2/2011 Siemens Sinvert PVM20 identical in construction to Refu s Refusol 20K surges to the top of the pack in PHOTON Lab s inverter test The Solar Power Magazine 97.5 % at medium irradiation Highlights International Siemens Sinvert PVM20 A 2/2011 The three-phase transformerless Sinvert PVM20 has a DC nominal power of 19.6 kw and is identical in construction to the Refusol 20K from Refu Elektronik The device s MPP range stretches from 480 to 850 V, but cannot be fully utilized The maximum conversion efficiency is 98 percent, while its European efficiency is 97.8 percent and its Californian efficiency is 97.9 percent Its PHOTON efficiency at medium irradiation is 97.5 percent, and at high irradiation it achieved 97.7 percent Despite its transformerless topology, the PVM20 is also approved for use with First-Solar Inc. s thin-film modules Anyone looking at a Sinvert PVM inverter from Siemens AG would never know they are seeing double when comparing it to products from Metzingen-based Refu Elektronik GmbH. But, in fact, though the outer casings differ completely, the insides are exactly the same. The Refusol range is kitted out with Siemens covers, but otherwise sells with the same parts; the Sinvert PVM10, PVM13, PVM17 and PVM20 models with AC nominal powers between 10,000 and 19,200 W correspond to the Refusol 10K, 13K, 17K and 20K models. And this partnership is a smart move, as it adds four top products to Siemens range. Back in January, the Sinvert PVM10 received two A grades from PHOTON Laboratory, placing it among the top 10 inverters tested thus far (see box, p. 147). And the test results for the remaining three members of this product range don t disappoint either. The results for the most powerful of the three, the PVM20, are presented in full in the following pages, while shorter reports for the other two models are found on p. 134 and p Siemens Sinvert PVM20 was sent to PHO- TON Lab in September 2010 as part of the usual test agreement. While all of the other Refu counterparts have been tested, the PVM 20 s twin, the Refusol 20K, hasn t undergone PHOTON Lab s inspection as yet. In some ways, that s a shame for Refu, since now the honor of holding the top spot in PHOTON Lab s tests goes exclusively to Siemens. At 97.5 percent for medium irradiation, the unit s efficiency is a tenth of a percentage point higher than the previous frontrunner, the Refusol 17K (see PI 12/2010, p. 146), and Siemens version of that model, the Sinvert PVM17 (see article, p. 134). Construction Like all of the devices in the Sinvert PVM range, the PVM20 is a three-phase transformerless device. Although it has a complex design, the components are neatly arranged and facilitate simple manufacturing. The device makes a good impression, and is exceptionally light and small for a three-phase inverter in this power class. The internal structure is split into several layers: at the front is the control circuit board and the DC filter plate with the switching power supply for auxiliary power; at the back is a large power element circuit board. Seven chokes are cast into a separate section of the housing: three sinusoidal filter chokes and four storage throttles in the boost converter. The display circuit board is mounted on the housing s cover, behind a layer of transparent foil. The power element circuit board holds all the components for the input-side DC converter, the intermediate circuit with electrolytic capacitors and the output bridges. The power semiconductors are located in three separate modules, soldered to the bottom of the circuit board and installed on a large cooling element without forced ventilation, which is mounted on the back of the housing. This element, together with the side frame and front cover, form the device s housing. The Sinvert PVM20 has an IP 65 protection type and can therefore be installed outdoors. 126 International April 2011

4 Romana Brentgens / photon-pictures.com (2) The Sinvert PVM20 has a very compact internal structure. Thermal imaging shows no irregularities, although the power element is hidden away behind the circuit boards. A large fan is located under the circuit board, which provides internal ventilation and prevents heat pockets from forming. The fan has a lifespan of 80,000 hours at 40 C. However, if it malfunctions, it can be replaced relatively easily. The electrolytic capacitors used in the power element and the control electronics have a temperature class of 105 C and are therefore wellsuited to handle ambient temperatures. An automatic grid-monitoring unit ensures safe operation, monitoring the grid for proper voltage and frequency. In addition, the unit performs an insulation test to check the resistance between the solar generator s connections and the ground. It also monitors the grid-side leakage current. The Sinvert PVM20 also has a DC circuit breaker under the frame, next to the DC connector. The solar generator attaches to the inverter using six pairs of Multi-Contact AG MC4 connectors; a five-pole connector from Phoenix Contact is used for grid connection. After assembly, the connector can be attached to the housing with two screws. Moreover, the inverter offers an array of other options such as the connection of an irradiation and temperature sensor, a relay (230 V / 2 Ampere AC), as well as three communication ports RS485 (input and output), USB and Ethernet. The device s status is shown in the display and four LEDs. Data can be exported, and updates made to the firmware via the USB or Ethernet ports. The Sinvert inverter also has an internal datalogger that can hold a total of 40 measurements. These have to be individually activated and the parameters set. Additional optional equipment includes a larger grid connector, alternative connectors for attaching the generator and remote monitoring via different external devices. Operation The PVM20 arrives at the customer s home well-packaged and protected in thick cardboard. It comes with a bracket for wall mounting, which is also facilitated by its light weight for this power class, weighing in at just 41 kg. If the solar generator is properly designed and the DC disconnect is active, the inverter requires about 126 seconds to run a number of tests before connecting to the grid. The unit s operation can be monitored on an easily readable display with white backlighting; it is flush with the front cover. The display can show information in Czech, English, French, German, Italian or Spanish. Parameters are set using eight buttons. In addition to various status and error messages, there is a default display with current values for AC power and voltage as well as DC voltage and daily energy yield. An additional menu provides current values for DC power, voltage and current, AC power, voltage and current, and AC frequency. Users can also view information on the temperature of the cooling element and the inside of the inverter. If the appropriate sensors are connected, the display also shows irradiation and module temperature information. The display can also provide the absolute or standardized yield for the day, month, year or since operation began. The amount of power fed in daily can also be displayed in a bar diagram. All in all, the Sinvert provides a large number of measurements in a clear, accessible form. Instruction manual The device is accompanied by an instruction manual, both as a booklet and on CD-Rom; it also includes a number of different certificates. The instruction manual is available in the display languages listed above, as well as Greek, Korean and Portuguese. A quick guide for hooking up the inverter is also included, and that contains technical information about installation, connection and operation as well as general explanations. A chart explains how the display s menu is organized, and describes the operation, as well as the grid and DC connection. The quick guide and the comprehensive instruction manual, as well as technical data, can be downloaded from the manufacturer s website. Circuit design The circuit design is, in principle, two-stage, but it doesn t have a classic topology. First, energy from the PV generator reaches the power stage via an EMI filter. The device has a bifurcated intermediate circuit capacitor, the midpoint of which is connected with the grid s neutral conductor. Two three-phase output bridges are connected in parallel on the output side; the first International April

5 science & technology inverters test Conversion efficiency The PVM20 maintains a conversion efficiency of 97 percent or higher in a more consistent manner than the two other test candidates, the PVM17 and PVM13. MPPT adjustment efficiency When it comes to MPP tracking, the larger model in the PVM series has a slight advantage very slight even over the other devices. = Overall efficiency As the product of conversion efficiency and MPPT adjustment efficiency, the PVM20 s overall efficiency remains at a consistently high level. 129 International April 2011

6 science & technology inverters test Weighted conversion efficiency The European and Californian efficiencies follow an almost horizontal course and are always above 97 percent. The manufacturer s specified European efficiency of 97.8 percent was confirmed. Overall efficiency at different V MPP voltages The overall efficiency courses at different voltages progress better for the larger PVM20 model too; even the weakest (green) line at 850 V starts at 92 percent. It increases efficiency very quickly and then remains relatively high. Accuracy of inverter display The PVM20 s power measurements and power display leave no room for complaints: The level of deviation is at most 0.6 percent. 131 International April 2011

7 science & technology inverters test Manufacturer s response The high end of the MPP range was primarily designed for concentrating PV or highefficiency modules (with fill factors of 80 to 85 percent). Moreover, there are a few older module types, for example from Siemens, that have fill factors higher than 80 percent, which makes an MPP range of up to around 820 V essential. Irradiation peaks caused by cloudy weather will only affect performance if the inverter is insufficiently dimensioned. It is not considered economically viable at this time to offer a version of the device with a split MPP range. The efficiencies measured by PHOTON Lab were also validated by the Austrian Institute of Technology (AIT), taking measurement tolerances into consideration. Accounting for these measurement tolerances, your results are correct. is directly attached to the DC input, while the second is fed by two boost converters located in the DC input s positive and negative conductors, which in turn feed into another bifurcated intermediate circuit capacitor. The modulation of the sinusoidal waves is therefore divided between these two output bridges, so that both are responsible for just a portion of the voltage boost for the production of the sinusoidal current in the output chokes. This reduces losses in the power transistors and in the output chokes. Furthermore, there s a freewheeling path in the output for every phase, which prevents energy stored in the output chokes from flowing back into the intermediate circuit capacitor, thereby causing additional losses. A subsequent filter smoothes the modulated voltage blocks into sinusoidal voltage with a frequency of 50 Hz. An output filter, installed directly in front of the grid clamp, eliminates any radio interference. Measurements All of the following measurements are based on a grid voltage of 230 V. The Sinvert PVM20 s maximum DC voltage is 1,000 V. The DC nominal power and therefore the maximum generator power that can be connected is 19,600 W. During measurements, the simulator s opencircuit voltage had to be limited for MPP voltages above 790 V, since it would be higher than 950 V, and therefore too close to the PVM20 s maximum DC voltage at a fill factor of 75 percent. Locating the MPP: The DC and AC sides were switched off when measurements began. At a predetermined IV curve with nominal power and an MPP voltage of 655 V, the inverter needs about 126 second to connect to the grid, and another 28 seconds to reach its MPP. The switch from 655 V to the next lower MPP range (636 V) takes 10 seconds, while switching to the next higher range (675 V) took about 8 seconds. MPP range: The MPP range stretches from 480 to 850 V, which is a wide range. The maximum MPP voltage of 850 V is too close to the maximum input voltage of 1,000 V considering today s fill factors. That s why there s a hatched area in the diagrams for conversion efficiency, MPPT adjustment efficiency, and overall efficiency. These hatched areas represent limitations at about 800 V when used with crystalline modules and at about 740 V when used with thin-film modules. Conversion efficiency: In the diagram, the vertical line at 50 percent of nominal power and the horizontal line at an MPP voltage of 597 V meet at a maximum efficiency of 98 percent. Therefore, measurements fell short of the manufacturer s specification of 98.2 percent. The area with similar efficiencies forms a plateau between MPP voltages of 558 and 655 V, within the nominal power range of around 37 to 65 percent. Over the vast majority of the operating range, the values were 97 percent and higher, and the reduction in efficiency at higher MPP voltages was around 0.5 percentage points and just 0.3 percentage points at lower MPP voltages. Efficiency didn t fall significantly until nominal power was less than approximately 15 percent, but even then it didn t drop more than 3.5 percentage points. The power factor cos φ at nominal power was about one. MPPT adjustment efficiency: The MPPT adjustment efficiency is consistently high over the entire operating range. Only at lower powers in the upper voltage range are there two small areas in which the MPP power sinks below 99 percent of available power. Overall efficiency: As the product of conversion efficiency and MPPT adjustment efficiency, overall efficiency also takes a consistent, high course. In the diagram, the vertical line at 50 percent of nominal power and the horizontal line at an MPP voltage of 597 V meet at the overall maximum efficiency of 98 percent. Weighted conversion efficiency: The PVM20 s European efficiency reaches its highest value at an MPP voltage of 597 V. At 97.8 percent, it matches the manufacturer s specifications. The difference between the maximum conversion efficiency and maximum European efficiency is just 0.2 percentage points. The Californian efficiency also reaches its peak at an MPP voltage of 597 V, though it is 1 percentage point higher at 97.9 percent. Course of overall efficiencies, average overall efficiency and PHOTON efficiency: The PHOTON efficiency at medium irradiation is 97.5 percent, while the PHOTON efficiency at high irradiation is 97.7 percent. Both correspond to an A grade, and represent the best values recorded for any of the inverters tested thus far by PHOTON Lab. Feed in at nominal power: The inverter feeds in 100 percent of its nominal power over the entire input voltage range of 480 to 850 V at an ambient temperature of 25 C. Displayed output power: At a constant MPP voltage of 655 V so in the medium range the PVM20 s measured and displayed power for a range between 5 and 100 percent of nominal power only deviates slightly from the values measured by a power analyzer. At low powers, the deviation is around -0.6 percent, while at powers above 20 percent of nominal power, the deviation is -0.4 to -0.5 percent. Therefore, the display s accuracy is equivalent to that of a class B meter (previously known as precision class 1). Operation at high temperatures: The inverter feeds 100 percent of its nominal power into the grid at ambient temperatures of up to 56.4 C. After that point, it reduces its power, and efficiency drops slightly by around 0.1 percentage points. This reduction in power occurs outside of the temperature range stated, which stretches between -25 and 55 C, and so need not be taken into account when selecting an installation site for the PVM20. The very wide temperature range and the 132 International April 2011

8 IP 65 protection type make installation at a potentially warm site feasible for example, under a roof or outdoors. Overload behavior: If the Sinvert PVM20 is offered an overload of 1.3 times its nominal input power, so 25,480 W, at an MPP voltage of 655 V and an ambient temperature of 25.1 C, the device limits power to 19,820 W. This corresponds to percent of its DC nominal power of 19,600 W; the inverter s overload range is therefore very small. When power limitations take effect, the device pushes the operating point on the IV curve toward higher input voltages. The DC voltage adjusts itself to a value of around 733 V. Own consumption and night consumption: The PVM20 s own consumption in its tested construction is around 0.5 W on the AC side and at most 28 W on the DC side. The manufacturer offers no specifications for that. At night, the inverter consumes around 0.5 W of real power from the grid; the manufacturer specifies»less than 0.5 W.«Thermography: Thermographic images show the inverter from above while it is operating at nominal power and at an ambient temperature of 22.8 C. Due to its multi-layer construction, the power element is mainly hidden under a circuit board. As a result, only insignificant temperature increases were observed. The maximum surface temperature was 59.5 C. Summary The Sinvert PVM20 takes the top spot among all the inverters tested by PHOTON Lab thus far; an honor that actually should go to Refu Elektronik GmbH as the device s true developer and manufacturer. The Refusol 20K, with its identical construction, has yet to be submitted for testing, though. The PVM20 s construction is compact and production-friendly, and it s a very lightweight unit for a three-phase device in this power class. It also has a large number of integrated communications options. With an internal datalogger and graphic display, it offers the option of statistical analysis. The measurement and display of output power is also very precise. The maximum conversion efficiency is 98 percent, and the course is very consistent over the entire voltage and power range. The unit s very consistent, high MPPT adjustment efficiency produces an overall efficiency course that is very similar to the course of conversion efficiency. The only minor weaknesses are recorded at lower powers in the upper MPP voltage range. As a result of the device s consistent operating behavior, the PHOTON efficiency at medium irradiation is very good at 97.5 percent, despite the wide voltage range. The PHOTON efficiency at high irradiation is even slightly higher at 97.7 percent. The MPP voltage range is very wide, but shows limitations in the upper section, since the distance between the maximum DC voltage and the maximum MPP voltage is too narrow. When selecting the MPP of a PV system, an MPP range of up to around 740 V can be chosen. The inverter has hardly any overload capabilities. The temperature range, by contrast, is very wide and results in no power limitations. The conversion efficiency s temperature dependency is very low at just -0.1 percent. As a transformerless device, the PVM20 is chiefly designed for use with crystalline modules. However, it has been approved for use with First Solar Inc. s thin-film modules, and additional approval for use with modules from United Solar Ovonic LLC (Uni-Solar) will apparently follow. Text Heinz Neuenstein, Jochen Siemer Further information Contacts page 276 International April

9 science & technology inverters test Romana Brentgens / photon-pictures.com (2) The PVM17 is the same as the other models in this series, both inside and out. Thermographic imaging once again showed little reason for concern, although it s difficult to take an accurate image since the power element is hidden from view. The Solar Power Magazine Highlights A 97.7 % at high irradiation The Solar Power Magazine International Siemens Sinvert PVM % at medium irradiation 2/2011 International Siemens Sinvert PVM17 A 2/2011 The Sinvert PVM 17 from Siemens AG, identical to Refu s Refusol 17K, is a three-phase transformerless inverter with a DC nominal power of 16.8 kw The MPP range stretches from 460 to 850 V The unit s maximum conversion efficiency is 98 percent, while the European efficiency comes in at 97.7 percent and the Californian efficiency is 97.8 percent The PHOTON efficiency at medium irradiation is 97.4 percent, while the PHOTON efficiency at high irradiation is 97.7 percent The construction, characteristics and test results differ little from those of the Sinvert PVM20 and PVM13 Meeting expectations PHOTON Lab tested Siemens Sinvert PVM17 identical in construction to the Refusol 17K to see if its performance would match up The PVM17 arrived at PHOTON Laboratory together with the Sinvert PVM20 and the PVM13 last September. The device, like the others from the PVM range, was provided by the manufacturer as part of the usual test agreement. The lab expected the Siemens inverter to perform just as well as its twin, the Refusol 17K from Refu Elektronik GmbH, indeed it did. Construction The unit s construction is exactly the same as that of the Sinvert PVM20 (see article, p. 126). Operation The operation is exactly the same as that of the Sinvert PVM20 (see article, p. 126). Instruction manual The instruction manual, too, is the same as that of the Sinvert PVM20 (see article, p. 126). Circuit design The circuit design is identical to that of the Sinvert PVM20 (see article, p. 126). Measurements All of the following measurements were based on a grid voltage of 230 V. The Sinvert PVM17 s maximum DC voltage is 1,000 V. The DC nominal power and therefore the maximum accepted generator power is 16,800 W. For MPP voltages above 788 V, the simulator s open-circuit voltage had to be limited, since it was higher than 970 V, meaning it was too close to the PVM17 s maximum DC voltage, based on a fill factor of 75 percent. Locating the MPP: At the start of measurements, the DC side and the AC side were switched off. At a predetermined IV curve at nominal power and an MPP voltage of 679 V, the inverter required about 126 seconds to connect to the grid and another approximately 33 seconds to reach the MPP. The switch from 679 V to the next lower MPP range (662 V) took 8 seconds, while the switch to the next higher range (696 V) took around 5 seconds. MPP range: The MPP range stretches from 460 to 850 V, which is a wide range. Considering today s fill factors, the maximum MPP voltage of 850 V is too close to the maximum input voltage of 1,000 V. Therefore, in the diagrams covering conversion efficiency, MPPT 134 International April 2011

10 science & technology inverters test adjustment efficiency and overall efficiency, there are hatched areas representing limitations above approximately 800 V for crystalline modules and above around 740 V when used with thin-film modules. Conversion efficiency: In the diagram, the vertical line at 55 percent of nominal power and the horizontal line at an MPP voltage of 645 V meet at the maximum efficiency of 98 percent. Therefore, the test results didn t quite reach the manufacturer s maximum efficiency specification of 98.2 percent. The area with similar efficiencies formed a small plateau in the diagram between the MPP voltages of 563 and 665 V, and between 40 and 75 percent of nominal power. Over most of the operating range, the efficiency was 97 percent or higher. The reduction in efficiency at higher MPP voltages was only around 0.5 percentage points and at lower voltages around 0.3 percentage points. At powers below 15 percent of nominal power, efficiency decreased more significantly, but even then no more than approximately 3.5 percentage points. The power factor cos φ at nominal power was about one. MPPT adjustment efficiency: The MPPT adjustment efficiency is consistently high across almost the entire operating range. The inverter s MPP power was more than 99 percent of available power between 10 and 100 percent of nominal power. The only deviations were at low powers in the upper half of the voltage range. Overall efficiency: As the product of conversion efficiency and MPPT adjustment efficiency, overall efficiency also maintains a consistently high level. In the diagram, the vertical line at 55 percent of nominal power and the horizontal line at an MPP voltage of 645 V meet at the maximum overall efficiency of 98 percent. Weighted conversion efficiency: The PVM17 s European efficiency reached its peak of 97.7 percent at an MPP voltage of 604 V and is therefore very close to the manufacturer s specification of 97.8 percent. The difference between the maximum conversion efficiency and the European efficiency was just 0.3 percentage points. The Californian efficiency also reaches its maximum at an MPP voltage of 604 V, though it came in slightly higher at 97.9 percent. Course of overall efficiencies, average overall efficiency and PHOTON efficiency: The PHOTON efficiency at medium irradiation is 97.4 percent, while the PHOTON efficiency at high irradiation is 97.7 percent. Both correspond to an A grade. Only at higher voltages (represented by the green line in the diagram for 850 V) does the efficiency begin much lower at around 86 percent before reaching 97 percent above about 40 percent of nominal power. Feed-in at nominal power: The inverter feeds in 100 percent of its nominal power over the input voltage range of 460 to 850 V at an ambient temperature of 25 C. Displayed output power: At a constant MPP voltage of 679 V so in the medium range the power measured and displayed by the PVM17 in the range between 5 and 100 percent of nominal power deviates only slightly from the values measured by a power analyzer. At lower powers, the deviation is around -0.5 percent, while beyond 20 percent of nominal power the deviation is around -0.8 percent. Therefore, the display s accuracy is equivalent to that of a class B meter (previously known as precision class 1). Operation at high temperatures: The inverter feeds 100 percent of its nominal power into the grid up to an ambient temperature of 51.2 C. After that point, it reduced power, and efficiency fell slightly by around 0.2 percentage points. This power reduction should be taken into account when selecting an installation site for the PVM17. Otherwise, the wide temperature range of -25 to 55 C and the IP 65 protection type make the inverter suitable for installation in warm locations under a roof, for instance or outdoors. 136 International April 2011

11 Conversion efficiency Beyond 25 percent of nominal power and even earlier at voltages below 700 V the PVM17 operates consistently at a conversion efficiency of more than 97 percent. MPPT adjustment efficiency The MPP tracking only shows slight weaknesses in the lower power range at high voltages. = Overall efficiency As a result, the overall efficiency is high and very consistent. International April

12 science & technology inverters test Weighted conversion efficiency The European and Californian efficiencies follow a very consistent course near the maximum overall efficiency of 98 percent. Overall efficiency at different V MPP voltages At high MPP voltages (the green line, representing 850 V), the overall efficiency struggles a little, but otherwise the PVM17 reacts quickly and maintains a high level with remarkable consistency all of this forms a good basis for the unit s impressive PHOTON efficiency score. Accuracy of inverter display The only major discrepancy between the performance of the Sinvert and its Refu twin is found when testing the display s accuracy. While the Refusol inverter showed deviations at lower powers, the Siemens version took consistently accurate measurements. 138 International April 2011

13 Overload behavior: If the Sinvert PVM17 is offered an overload of 1.3 times its nominal input power, so 21,840 W, at an MPP voltage of 679 V and an ambient temperature of 25.4 C, the device limits power to 17,102 W. This corresponds to just percent of its DC nominal power of 16,800 W, meaning this inverter s overload range is very small. Power limitations push the operating point on the IV curve toward higher input voltages. The DC voltage adjusts itself to a value of around 758 V. Own consumption and night consumption: The PVM17 s own consumption in its tested construction is around 0.5 W on the AC side and up to 31 W on the DC side. The manufacturer provides no specifications for this. At night, the inverter consumes around 0.6 W of real power from the grid, while the manufacturer specifies»less than 0.5 W.«Thermography: Thermographic images show the inverter from above while it is operating at nominal power at an ambient temperature of 23 C. As a result of its multi-layer design, the power element is mainly hidden under a metal sheet. Therefore, no significant temperature increases were observed. The maximum surface temperature recorded was 59.9 C. Summary Our results achieved by Siemens Sinvert PVM17 differ just slightly from those of the PVM20, and the manufacturer s response is the same (see box, p. 132). The PVM17 delivers almost identical results to its twin, the Refusol 17K, and is therefore one of the best devices to be tested by PHOTON Lab. The PHOTON efficiency at medium irradiation, despite the wide voltage range, is a very good 97.4 percent, while the PHOTON efficiency for high irradiation is somewhat higher at 97.7 percent. The inverter has a quite limited overload capacity. The temperature range, by contrast, is very wide, but there are power restrictions that take effect beyond an ambient temperature of 51.2 C. All of the other significant characteristics are practically identical to those of the PVM20. Text Heinz Neuenstein, Jochen Siemer Further information Contacts page 276 International April

14 science & technology inverters test Romana Brentgens / photon-pictures.com (2) The Sinvert PVM13 is identical to its big brother, the PVM20. As the PVM13 has practically the same components but deals with lower power levels, thermographic readings were even less of an issue at least in those parts of the inverter that can be seen. The Solar Power Magazine International Siemens Sinvert PVM13 A 97.6 % at high irradiation 2/ Small, but impressive Siemens Sinvert PVM13 delivers impressive results just like its twin, the Refusol 13K from Refu The Solar Power Magazine A 97.3 % at medium irradiation International Siemens Sinvert PVM13 Highlights 2/2011 The Sinvert PVM13, identical in construction to the Refusol 13K from Refu Elektronik, is a three-phase transformerless inverter with 12.6 kw of DC nominal power The MPP range stretches from 420 to 850 V The unit s maximum conversion efficiency is 98 percent, while the European efficiency is 97.6 percent and the Californian efficiency came in at 97.9 percent The PHOTON efficiency at medium irradiation is 97.3 percent, while the PHOTON efficiency at high irradiation reaches 97.6 percent The construction, characteristics and test results differ little from those of the Sinvert PVM20 and PVM17 The PVM13 arrived at PHOTON Laboratory together with the Sinvert PVM20 and the PVM17 last September. This device was also provided by the manufacturer as part of the usual test agreement. Construction The unit s construction is exactly the same as that of the Sinvert PVM20 (see article, p. 126). Operation The operation is exactly the same as that of the Sinvert PVM20 (see article, p. 126). Instruction manual The instruction manual, too, is the same as that of the Sinvert PVM20 (see article, p. 126). Circuit design The circuit design is identical to that of the Sinvert PVM20 (see article, p. 126). Measurements All of the following measurements were based on a grid voltage of 230 V. The Sinvert PVM13 s maximum DC voltage is 1,000 V. The DC nominal power and therefore the maximum accepted generator power is 12,600 W. For MPP voltages above 790 V, the simula- tor s open-circuit voltage had to be limited, since it was higher than 950 V, meaning it was too close to the PVM13 s maximum DC voltage, based on a fill factor of 75 percent. Locating the MPP: At the start of measurements, the DC and AC sides were switched off. At a predetermined IV curve at nominal power and an MPP voltage of 624 V, the inverter required about 126 seconds to connect to the grid and another approximately 24 seconds to reach the MPP. The switch from 624 V to the next lower MPP range (601 V) took 7 seconds, while the switch to the next higher range took around 10 seconds. MPP range: The MPP range stretches from 420 to 850 V, which is a wide range. Considering today s fill factors, the maximum MPP voltage of 850 V is too close to the maximum input voltage of 1,000 V. Therefore, in the diagrams covering conversion efficiency, MPPT adjustment efficiency and overall efficiency, there are hatched areas representing limitations above approximately 800 V for crystalline modules and above around 740 V when used with thin-film modules. Conversion efficiency: In the diagram, the vertical line at 60 percent of nominal power and the horizontal line at an MPP voltage of 624 V meet at the maximum efficiency of 98 percent. This matched the manufacturer s specifications exactly. The area with similar efficiencies formed a small plateau in the diagram between the MPP voltages of 578 and 646 V, and in the nominal 140 International April 2011

15 Conversion efficiency At high MPP voltages, the PVM13 s performance was not as good as in the voltage range below around 700 V. Still, overall performance was very consistent. MPPT adjustment efficiency The MPP tracking diagram shows just two small areas, at the top left and bottom right, where values drop below 99 percent. = Overall efficiency Logically, the resulting overall efficiency maintains a consistently high level. International April

16 science & technology inverters test Weighted conversion efficiency The lines representing European and Californian efficiency remain almost horizontal and even exceed the manufacturer s maximum specs slightly. Overall efficiency at different V MPP voltages Like the PVM17, the PVM13 also shows slight difficulties in the start-up phase (the green line, representing 850 V), and efficiency falls slightly at low voltages (blue line, representing 420 V) in the upper power range. Accuracy of inverter display The inverter s power measurement and display are exemplary. The slight deviation over the entire range is negligible. 142 International April 2011

17 science & technology inverters test power range of 55 to 85 percent. Over most of the operating range, the efficiency was 97 percent or higher, and the reduction in efficiency at higher and lower MPP voltages was only around 0.5 percentage points. At powers below 15 percent of nominal power, efficiency decreased significantly by 4 to 5 percentage points. The power factor cos φ at nominal power was about one. MPPT adjustment efficiency: The MPPT adjustment efficiency is consistently high across almost the entire operating range. There are small zones where the MPP power drops below 99 percent of available power, but only in the lower power range at high voltages, and in the upper power range at low voltages. Overall efficiency: As the product of conversion efficiency and MPPT adjustment efficiency, overall efficiency also maintains a consistently high level. In the diagram, the vertical line at 70 percent of nominal power and the horizontal line at an MPP voltage of 601 V meet at the maximum overall efficiency of 98 percent. Weighted conversion efficiency: The PVM13 s European efficiency reached its peak of 97.6 percent at an MPP voltage of 624 V and is therefore even higher than the manufacturer s specification of 97.5 percent. The difference between the maximum conversion efficiency and the maximum European efficiency was just 0.4 percentage points. The Californian efficiency also reaches its maximum at an MPP voltage of 624 V, though it comes in slightly higher at 97.9 percent. Course of overall efficiencies, average overall efficiency and PHOTON efficiency: The PHOTON efficiency at medium irradiation is 97.3 percent, while the PHOTON efficiency at high irradiation is 97.6 percent. Both correspond to an A grade. Only at higher voltages (represented by the green line in the diagram for 850 V) does the efficiency begin much lower at around 90 percent before reaching 97 percent above about 45 percent of nominal power. At lower voltages (the blue line, representing 420 V), there is a slight drop beyond about 90 percent of nominal power. This could also be an explanation for why the PVM13 performed slightly worse than the PVM17. Feed-in at nominal power: The inverter feeds in 100 percent of its nominal power over the input voltage range of 420 to 850 V at an ambient temperature of 25 C. Displayed output power: At a constant MPP voltage of 624 V so in the medium range the power measured and displayed by the PVM13 in a range between 5 and 100 percent of nominal power deviates only slightly from the values measured by a power analyzer: the deviation was around -0.8 percent. Therefore, the display s accuracy is equivalent to that of a class B meter (previously known as precision class 1). Operation at high temperatures: The inverter feeds 100 percent of its nominal power into the grid up to an ambient temperature of 59.8 C. After that point, it reduced power, and efficiency falls slightly by around 0.1 percentage points. This power reduction need not be taken into account when selecting an installation location for the PVM13 since it occurs outside the specified temperature range of -25 to 55 C. Otherwise, the wide temperature range and the IP 65 protection type make the inverter suitable for installation in warm locations under a roof, for instance or outdoors. Overload behavior: If the Sinvert PVM13 is offered an overload of 1.3 times its nominal input power, so 16,380 W, at an MPP voltage of 624 V and an ambient temperature of 25.3 C, the device limits power to 13,010 W. This corresponds to just percent of its DC nominal power of 12,600 W. Power limitations push the operating point on the IV curve toward higher input voltages. The DC voltage adjusts itself to a value of around 695 V. Own consumption and night consumption: The PVM13 s own consumption in its tested construction is around 0.4 W on the AC side and up to 28.5 W on the DC side. The manufacturer provides no specifications for this. At night, the inverter consumes around 0.5 W of real power from the grid, while the manufacturer specifies»less than 0.5 W.«Thermography: Thermographic images show the inverter from above while it is operating at nominal power at an ambient temperature of 24.9 C. Due to its multi-layer design, the power element is mainly hidden under a metal sheet. Therefore, no significant temperature increases were observed. The maximum surface temperature recorded was 57.1 C. Summary PHOTON Lab s appraisal of Siemens Sinvert PVM13 differs only slightly from that of the PVM20, and the manufacturer s response is the same (see box, p. 132). The PHOTON efficiency at medium irradiation, despite the wide voltage range, is a respectable 97.3 percent, while the PHOTON efficiency at high irradiation is somewhat higher at 97.6 percent. Though that s somewhat lower than the PHOTON efficiencies of the other models in the range, it suffices for two A grades. As a result, even the PVM13 can be counted among the best inverters tested by PHOTON Lab thus far. There are slight differences in the product range, for instance, when it comes to overload capacity, which isn t quite as low as was recorded for the PVM20. All other significant characteristics are practically identical to those of the PVM20 and PVM17. Text Heinz Neuenstein, Jochen Siemer Further information Contacts page International April 2011

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20 Siemens AG Industry Sector Control Components and Systems Engineering P.O. Box Fürth, GERMANY Subject to change without prior notice 06/2011 Order No. E80001-A2180-P300-X-7600 Dispo WÜ/34641 MI.CE.PV.XXXX SD Printed in Germany Siemens AG 2011 The information provided in this brochure contains merely general descriptions or characteristics of performance which in actual case of use do not always apply as described or which may change as a result of further development of the products. An obligation to provide the respective characteristics shall only exist if expressly agreed in the terms of contract. All product designations may be trademarks or product names of Siemens AG or supplier companies whose use by third parties for their own purposes could violate the rights of the owners.