There are currently no new, groundbreaking

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1 photovoltaics Inverters: progress in detail Devices for use with thin-film modules are now available from almost all inverter manufacturers. Today, manufacturers are tending to focus on specific improvements. Inverter bridge with H5 topology: This technology reduces losses to a minimum. Photo: SMA Sunmaster XL: The Europeanstandard efficiency is greater than 95 %. Photo: Mastervolt There are currently no new, groundbreaking topologies for grid-connected inverters. It tends to be smaller optimisations an amendment here to the switching, a software update there which succeed in raising the efficiency even further, according to Andreas Schlumberger from Kaco-Gerätetechnik. Here experience has shown that merely replacing a component with an improved version can bring about astonishing improvements. Along with the improvements in thin-film technology, there has been increasing discussion in the past as to whether all inverters are equally compatible with CIS, CdTe & Co. Most manufacturers seem to have found an answer, if an answer was at all necessary, and the issue does not seem to be providing any problems anymore. The same cannot be said, however, when it comes to implementing a new medium voltage directive or the Directive for the connection and parallel operation of power generators in the low voltage grid planned in Germany. According to this directive, inverters should be capable in future of, for example, generating reactive power in order to allow them to automatically relieve temporary overcapacities in the grid. But all the manufacturers spoken to pointed out that it is simply not possible to develop technologies overnight and then integrate them in all products. According to the current plans, inverters for the medium and low- voltage range must be redesigned from scratch and expanded, confirms Rainer Brohm from the German Solar Industry Association (BSW-Solar). Following a hefty debate, the directive for the low-voltage range now will no longer come into force at the beginning of 2009 already, as initially planned in the first draft. The companies believe that series-produced products can only be expected in 2010 at the earliest. It has only recently become common practice to specify the MPPT efficiency. This is probably because companies are only now beginning to realise that customers are ultimately only interested in the energy yield of their PV systems and here the efficiency of the MPP tracking is just as important as other characteristics. According to company specifications, the MPP tracking efficiency (dynamic), which is determined under dynamic conditions with changes in the solar radiation, exceeds 99 % with some devices. With the MPPT efficiency steady, the value is frequently around 99.9 %. Although these specifications sound very impressive from a marketing point of view, they are not based on any measurements under realistic conditions but on the statistical distribution of solar radiation throughout the year. Studies have shown that while practically all the tested devices lie between 98.5 and 100 % under steady conditions, some devices drop back to around 92 % when there is fluctuating radiation. New inverters Not all companies responded to enquiries from Sun & Wind Energy about new topologies or the MPPT efficiency. There were also manufacturers who did not provide any specific information on the aforementioned aspects. 116 Sun & Wind Energy 6/2008

2 The sun fills us with energy The sun transmits light, heat and energy Ingeteam provides innovative solar plant solutions to convert this unlimited power source into electricity. We are designers and manufacturers of a wide range of easy-to-install, highly reliable gridconnected inverters for maximum solar energy output. Harnessing the power of the sun. Visit us at: Lyon Salon des Energies Renouvelables: Feb Bad Staffelstein OTTI PV Symposium: 4-6 March Verona Solar Expo: 7-9 May Madrid Genera: May Munich Intersolar: May solar.energy@ingeteam.com Avda. Ciudad de la Innovación, 13 - E Sarriguren-Spain - Tel

3 photovoltaics The triple-phase TripleLynx from Danfoss Solar Inverters is designed for high AC rated powers. Photo: Danfoss Efficiency The Dutch manufacturer Mastervolt presented its new Sunmaster XL and Sunmaster XS models. The devices in the Sunmaster XL series cover a power range between 10 and 15 kw; the European-standard efficiency exceeds 95 %. The DC voltage range for the solar input side is specified at between 100 and 600 V DC, with a nominal power of 400 V DC. A class II highfrequency transformer ensures galvanic isolation between the DC and AC side; this should make it possible to use the device in all thin-film solar power systems without any problems. In the event of a single-phase AC fault or a grid outage, all three power modules are immediately disabled to protect against islanding. Mastervolt is hailing its new Sunmaster XS inverters as multi-talents. The XS2000, XS3200 and XS4350 versions have power outputs of 1,500, 2,500 and 3,300 W. The company emphasises that the individual Input voltage Fronius IG Plus with transformer switching Inverter without transformer switching Inverter without transformer The Fronius IG Plus s automatic transformer switching creates three efficiency peaks and thus consistent efficiency across a broad input voltage range. Source: Fronius components in the XS series are designed for maximum efficiency. The powerful MPP trackers achieve remarkable yields even when there is little solar radiation: even at just 2 to 8 W, the inverter switches on in the early morning and does not switch off again until the end of the day. At 5 % of the PV output capacity, the devices achieve an output performance of more than 90 %. Even with ambient temperatures of up to 45 C it maintains the full output. Danfoss Solar Inverters has its roots in constructing frequency converters and now benefits from more than 40 years of acquired expertise. The company from Sonderborg in Denmark has both single- and triplephase inverters in its product range (UniLynx and TripleLynx). The triple-phase TripleLynx is designed for high AC rated powers (10/12.5/15 kw) and, according to the company, is the first of its kind with a maximum DC voltage of 1,000 V. Further features highlighted by Danfoss include the MPP voltage, which ranges from 430 to 800 V and a maximum efficiency of 98 %, which is still above 97 % when weighted according to the European climate. How was it possible to achieve such excellent values? They were the result of a construction designed to achieve maximum output performance, according to Allan Pilgaard-Jensen, Marketing Manager at Danfoss Solar Inverters. This required a combination of many different features: the transformerless design, cutting edge electronics with CoolMOS and silicon carbide diodes, optimised internal connection to reduce unnecessary losses, and special digital algorithms to ensure a high MPPT efficiency across a wide voltage range. Even the internal construction has been designed to achieve maximum efficiency. Each component has been so precisely located that the power flows the shortest and most rational route from the PV module to the supply grid. A special cooling system made from die-cast aluminium fixed to the housing frame ensures that heat is effectively dissipated via a fan and the best possible ambient temperature is created for the high-performance electronics. The power capacitors are housed in the coolest area of the inverter, which helps to reduce the operating temperature and can considerably lengthen the service life. As with Danfoss Solar Inverters, LTi Reenergy in Germany also did not gain its initial experience in the solar power industry. The company originally became known for its inverters for wind turbines and its drive systems for electrically adjusting rotor blades. It now claims to be one of the world s leading companies in this market, having supplied more than 5,000 systems and components (as of 2007). This existing expertise encouraged Reenergy to also develop and produce solar inverters. The first devices central inverters in the PVmaster 450 series were rolled out at the end of 2007; they were presented to the general public for the first time at the Intersolar 2008 in Munich. These central inverters with rated powers of 33/47/68/100/200 kw are not only suitable for modules made of crystalline silicon cells but, in particular, for thin-film modules. For the transformerless PVmaster series, a maximum efficiency of 98 % and a European-standard efficiency of 97 % are specified. 118 Sun & Wind Energy 6/2008

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5 photovoltaics For high-power solar generators: The PVmaster 450 solar inverter series from LTi Reenergy. Photo: LTi Reenergy These values apply when connecting to a transformer with a 3~290 V output voltage. The values are lower with the topologies PVmaster with transformer with electrical isolation between the DC input and AC output and PVmaster without electrical isolation between the DC input and AC output. The MPP voltage ranges between 450 V and 850 V for all devices. Although we asked, they were not forthcoming on the efficiency of the MPP tracking. Nor are they prepared at the moment to tell Sun & Wind Energy about any current new developments and optimisations. We can only wait in anticipation. It will also be interesting to see what lies ahead with the German market leader, SMA Solar Technology. Although SMA claims to have a lot going on in development at the moment, they say that it is not all ready to be made public, whereby it points out that many new innovative products were, of course, already presented at the Intersolar 2008 and that there is anyway no really new technology at the moment. When interviewed, SMA preferred to highlight once again its innovations from the recent past: the H5 topology, which enables the efficiency of the transducer to be considerably increased via a fifth semiconductor switch, has proved extremely effective over the years; the same applies to the OptiTrac process for optimising the MPP tracking. According to SMA, more recent studies have shown that OptiTrac increases efficiency not just with crystalline silicon (c-si) but also with systems with thin-film modules. Contrary to frequently made presumptions to the contrary, explain SMA developers Gerd Bettenwort and Joachim Laschinski, we were able to prove that no cell-specific MPP tracking is necessary for thinfilm systems, but one that guarantees high efficiency in dynamic operation. It was also possible to make considerable improvements to the efficiency with the Electronic Solar Switch (ESS). This is a DC load circuit breaker, which is integrated in the inverters and works completely without loss. Highly functional grid-connected inverters that work wonderfully with all solar modules is how the Austrian manufacturer, Fronius, describes its IG and IG Plus series of inverters. They cover a rated power between 1.5 and 40 kw. The latest development work is aimed, amongst other things, at optimising the devices for use in thin-film solar power systems. In this context, the focus has been on the efficiency and the problem of earthing, explained Thomas Mühlberger, Head of PV system technology at Fronius. 120 Sun & Wind Energy 6/2008

6 PHOTOVOLTAICS Fuse triggered The module earthing concept used in the Fronius IG Plus Source: Fronius According to Mühlberger, there are several re quire ments that need to be met with inverters for thin-film modules. Firstly, for a good annual solar yield it is desirable to have a high conversion efficiency that occurs not only with an input voltage dependent on the string length, but which remains almost constant across the entire MPP voltage range. Fronius has solved this problem by optimising the transformer switching in line with the respective input voltage so that the decline in efficiency, which can otherwise be observed across the entire voltage range, is minimised, explained Mühlberger. With its special module earthing concept, Fronius is responding to demands made by several thinfilm module manufactures to earth the negative pole of the solar generator in order to prevent corrosion on the TCO layer. However, that can only be realised sensibly, according to Mühlberger, when the solar generator and the load circuit are galvanically isolated; in other words if the inverter does not have a transformer, it must be equipped with a special topology. This functions as follows, whereby in the event of an earth leakage there are two possible situations that can occur with a solar generator that is galvanically isolated by a transformer from the load circuit: if the solar generator is not earthed, there is no leakage current thanks to the galvanic isolation; if the generator is earthed, a residual current flows via the earth to the earthed generator pole. Protective measures are required for the latter case. Fronius solves this safety problem in its IG Plus inverters with a special concept for earthing the modules (diagram above): Should, despite the protection class II installation, a leakage current occur between the The power of energy in your hands. Elettronica Santerno, leading company in solar technology, manufactures 2.6Kwp to 730Kwp photovoltaic inverters for all types of use. SANTERNO GRUPPO CARRARO Elettronica Santerno S.p.A - Via Strada Statale Selice Imola (BO) - Italy - t f sales@elettronicasanterno.it -

7 Got Efficient Electro nics? Highest efficiency in power electroni cs pays off: Lower silicon cost, lower effort for cooling, higher energy yield and extended lifetime. Proprietary technologies like SoftSwi ng and AutoCommutation allow us to avoid most of the switching losses of conventional designs and realize power electronics with efficie ncy in excess of 99%. Typical application s are - power inverters - power DC/DC convert ers - precisely controll ed electric drives and generator s If you feel your products will benefit from even higher efficiency, thereby creating outstanding value for your customer and strengthening your market position: Profit from our expertis e and experience! Call us today for a proposal The Stecagrid ph is the new UniString inverter for grid feeding Photo: Steca non-earthed conductor and the earth, the earth fuse on the earthed pole is triggered and transforms the system into a PV system that is earthed in the opposite direction until the fault has been rectified. This means that despite the existing leakage current, the inverter can continue to operate without any increased safety risks; the fault is shown on the inverter. In order to protect the module from possible TCO corrosion, the earth leakage must be rectified and the faulty fuse replaced with a new one. In addition to the module earthing concept and the transformer switching, there is yet another technical device that can help guarantee annual solar yields: in the connection part of the Fronius IG Plus, fuse elements are installed to secure six module strings. Should a string fail as a result of surge current, this is displayed or reported via the internal communication interface. This makes it unnecessary to install a separate fuse box. In the middle of the year, Steca Elektronik from Germany presented among other things the Stecagrid ph triplephase inverter for grid feeding. StecaGrid is primarily intended for use on industrial roofs, agricultural buildings and ground-mounted systems, in each case with identical module orientation and without shadow problems. Particularly noteworthy is the three-phase symmetrical grid feeding and the large input voltage range. The device is suitable for indoor or outdoor installation and has an integrated DC disconnect. It has a rated power of 9 kw and, according to the specifications, the input voltage ranges from 350 to 800 V. The maximum efficiency is specified to be 96.2 % and the European is 95.3 %. The device is scheduled to come onto the market at the beginning of The triple-phase design is very much in the interest of the power supply companies, explains Steca Product Manager Roland Burge, highlighting one of the advantages of the new inverter. This ensures that the solar power produced is always distributed symmetrically on all three line conductors to the public grid, and in particular across the entire power range. The triple-phase system also prolongs the service life, as Burger explains as follows: During zero crossing in singlephase operation, single-phase inverters have to temporarily buffer the entire energy supplied by the solar modules in the device. This is generally performed by electrolytic capacitors. Because they can dry out, these components have an impact on the service life of electronic devices. With triple-phase inverters, on the other hand, energy is fed into the grid on at least two phases at any time, Burger goes on to explain. This considerably reduces the necessity to buffer the energy in the

8 PHOTOVOLTAICS device and this has a positive effect for the system operators, given that it prolongs the service life. With systems with thin-film modules, Steca recommends using the inverter family StecaGrid because they guarantee galvanic isolation with a high-frequency transformer. However, one thin-film module is not necessarily the same as another thin-film module, points out Burger. If in doubt, it is worthwhile asking the module manufacturer for approval before using the planned inverter. When asked about the directives under discussion, Burger said that they have not yet been forced to react to the new medium voltage directive, since the vast majority of their devices feed into the low voltage grid. However, we are very closely monitoring the debate at FNN about revising the directive on parallel operation in the low voltage grid. Studer Innotec manufactures a wide range of sine wave inverters. Since 2007, the Swiss manufacturer has been producing the Xtender series of sine wave inverters/chargers. These products are designed for hybrid systems and can be stacked together for use in rural power plants (up to 72 kw). One of Xtender s main features is its smart-boost function, which adds power to the AC source according to the input limit current. Another brand new function offered by this series is the ability to give priority to renewable energy in hybrid systems. This function adjusts the instantaneous power consumed from the source in accordance with the battery voltage, thus enabling maximum yields to be achieved from the renewable energy. This requires the smart-boost function. The solar priority function is achieved through automatic modification of the input limit current. The input limit current is decreased from the initial value (given by the user) if there is enough energy available on the DC side the lower the input current, the greater the DC power provided to the load by the smart-boost function. This enables the power from the DC side to be integrated into the system and the input consumption is limited. The RCC-02 programming unit makes it possible to set the input limit current and several hundred other parameters. Photo: Studer Innotec Sun & Wind Energy 6/

9 photovoltaics Grid Control and monitoring Solar generator HERIC with fixed potential (FP) switching Graphic: Sunways The Studer XTH inverter with smart-boost function. One of its new features is the ability to give priority to renewable energy in hybrid systems. Photo: Studer Innotec DC regulator The German manufacturer Sunways premiered its first-ever central inverter before an international public at the PVSEC 2008 in Valencia. The transformerless device, called the Solar- Inverter PT 30k, has been on the market in Germany since April 2008, has triple-phase grid feeding and an output power of 30 kw. PT stands for Performance Technology and refers both to its high efficiency, which exceeds 97.5 %, and its very wide MPP voltage range from 420 to 800 V. The maximum DC voltage is specified at 1000 V. The transformerless HERIC topology, which has been used by Sunways for years, has been adapted for use with the PT 30k. Also available since June is the NT 8000, which was specially designed for crystalline modules with five-inch cells. It has an output power of 8 kw and an input voltage range between 350 and 850 V. Three MPP trackers enable flexible use with differently sized solar generators. The advantage of transformerless inverters such as the NT 8000 and the PT 30k is that they have a potentially greater efficiency. Since, however, dispensing with a transformer also means that there is no galvanic isolation, negative voltages against the earth potential at the negative pole can cause irreversible TCO corrosion with thin-film modules. Furthermore, slightly increased leakage current can occur with modules with a metallic rear side, which would be in violation of the relevant safety standards. Thin-film modules do not have sufficient voltage resistance and have made this aspect an issue in the first place, emphasises Christian Buchholz, Product Management Team Leader at Sunways. That s why we recommend to our customers that they obtain approval from the module manufacturer before using any devices for thin-film solar power systems. This fundamentally applies to all inverter types, including the AT series, even if these are based on a special topology. Together with specialist HERIC inverter colleagues from the Fraunhofer ISE, Sunways engineers already developed the Heric with fixed potential (FP) switching topology some years ago, in which the negative pole of the solar generator is galvanically connected to the neutral conductor. This means that no potential differences can develop at this point. The voltage flow at the positive pole against the earth potential corresponds to that of transformer inverters with an earthed negative pole, so that no significant leakage current flows. The DC regulator in the inverter converts the variable input voltage from the solar generator into constant DC voltage. It is only then that it is converted into alternating voltage. The connection through the device between the negative pole of the The triple-phase SolarMax central inverters with rated powers from 20 to 300 kw are ideal not just for medium-sized solar power systems with outputs of 30 kw and more but also for large-scale systems in the megawatt range. Photo: Sputnik Engineering 124 Sun & Wind Energy 6/2008

10 solar generator and the neutral line in the grid creates a DC voltage, as is shown in the diagram (see figure on the left). The latest SolarMax S string inverter series from Sputnik Engineering in Switzerland was already presented in The four models have rated powers between 1.8 and 4.6 kw. Instead of deploying the previously used device for mains monitoring with impedance measurements (MSD), Sputnik is using with this series the oscillator method known from the USA in order to prevent unwanted islanding. In order to optimise the overall performance, further technical details were improved: a digital controller reduces the distortion factor, undesired harmonics and the DC component on the AC current. Thanks to an improved cooling concept, the devices now store their entire power even with ambient temperatures up to 45 C. The MPP voltage on the transformerless devices ranges between 100 and 550 V; depending on the model, the European-standard efficiency lies between 95.4 and 96.2 %. In comparison to devices in the C-series, the S-series is up to 2.3 kg lighter for the same rated power. Sputnik Engineering has also, of course, focussed on the issue of inverters for thinfilm technology. The company has announced that the US solar module manufacturer, Unisolar, has officially given its seal of approval for combining the transformerless inverters in the SolarMax-S string inverter series with its a-si modules. The new string inverters in the VS series are the result of Voltwerk s many years of experience in developing PV inverters, reported Voltwerk electronics, a subsidiary of Voltwerk s new VS inverter series will be available from the first quarter of 2009 in the output classes 3, 4 and 5 kw. the German Conergy Group. The devices are available in the output classes 3, 4 and 5 kw, and can be used in system sizes ranging between 3 and 100 kwp. The quality of these devices is based on innovative improvements in three areas, explains Senior PR Manager Christoph Lapczyna: Optimising the software has enabled us to achieve MPP tracking with 99 % accuracy and a response time to the nearest second almost throughout the entire working range; furthermore the new inverters have a newly patented switching topology and work with a new cooling concept. All three factors ensure durable devices with efficiencies greater than 98 %. A further feature of the devices that will particularly delight installers is their ability to identify wiring faults during installation. Lapczyna reported on a concept that has been developed with the new inverters: When selecting components for PV systems, the most important criteria are reliability, efficiency and cost. Reliability and cost are always determined by the number of components used, especially in inverter design. Components have to be kept within a limited range of temperatures. A 10 K temperature reduction typically doubles the service life of most electronic components. Thus the inverter s efficiency and cooling concept are crucial for the inverter s lifecycle. For this reason they have developed and realised a concept for a single-phase 5 kw inverter with a reduced number of components, high efficiency and an advanced cooling system. Lapczyna: The concept has been verified by measurements that show a peak efficiency of more than 98 %, with an MPP tracking efficiency of 99.9 %, and the ability to work at an ambient temperature of 50 C at full load. Y Further information: Photo: Voltwerk Wilhelm Wilming PV OFF GRID PV GRID CONNECTED SOLAR THERMAL Simple as that. TR 0603mc * Analysis Software TS Analyzer 1 * One PC and the system controller TR 0603mc with SD-card will do to control your solar energy system! Steca TR 0603mc saves operating data and balance values directly on SD-card, TS Analyzer 1 visualizes the system results. w ww.steca.com