SMA does not specifically recommend one PV manufacturer's panels over another, nor does SMA recommend one specific model of panel from a manufacturer over any other. However, no matter which panel you are using, we do recommend that you try to use the same model of panel for each entire string. Further, we recommend that if you are using parallel strings that each string have the same number of panels. We also strongly recommend that every panel in each string have the same orientation.
For further details of this issue please read the PV Overcurrent Protection Letter from SMA America's President John Berdner. Please also contact your local inspector and utility for further details.
The Sunny Boy Inverters have the widest DC voltage window of any grid-tied PV inverter on the market. Depending on the module, there may be many series/string combinations of panels that will work with each SB Inverter. There are many factors to consider when deciding how many modules are best for your installation. These factors include: min/max ambient temperature, angle of incidence to the sun, optimized time-of-year and time-of-day power output, space limitations, partial shading, and other seasonal impacts on system performance. It is not possible for SMA to recommend a "Best" module number for every installation.
SMA American has available a String Sizing Program on this web site. This program allows you to choose module manufacturer, module model, the peak irradiance for the site, and the high and low temperatures that the site will experience. It assumes all other performance parameters are optimized for peak system performance. This tool is provided to assist in designing PV systems to work with Sunny Boy Inverters, and does not guarantee actual system performance due to the large number of site specific operating parameters that are not considered. When using the SMA String Sizing Program be sure to wait for the page to re-load after you make a selection in the inverter, manufacturer, and panel drop down menus. When you are using this program you must ensure that you have a Windows compatible browser. These include, Netscape 6.0 and higher, Mozilla 1.0 and higher, and Internet Explorer 5.0 and higher. The program may not work properly with Macintosh operating systems.
Ideally, every PV panel connected to one Sunny Boy Inverter should be installed in the same plane-of-array orientation (facing the exact same direction). You should not place PV panels in different orientations. Every module should also be installed in a location to avoid shading, no matter how small. If the orientation is mixed or partially shaded, the weakest panel(s) in the system will limit the output of the entire PV array. Other orientation considerations should be made to optimize time-of-day and/or time-of-year performance.
Yes according to the NEC code in section 690.13 the PV conductors must have a disconnecting means to isolate the inverter from the PV power source. Because SMA inverters are high voltage systems, the disconnecting means have to be rated for 600 Vdc, for the SB 2500U, and 400 Vdc, for the SB 1800U. There are two 600 Vdc disconnect switches that SMA America recommends. The first is GE part number THN-2261-RDC, the other is the Square D part number HU361RB. These switches are widely used in the PV community. Note that for the GE switch that the two outer poles of the disconnect switch must be wired in series to achieve the 600 Vdc rating. Refer to the manufacturers' data sheets for further detail. Depending on local code and local utility requirements, the equipment and configuration may change. SMA always recommends contacting your local inspector and utility for specific local requirements.
The Sunny Boy Inverters have been tested by Sandia National Laboratories and shown incapable or back-feeding the PV array in the event of an internal inverter failure, per the PV Overcurrent Protection Letter. The NEC Article 690-9 also requires individual AC protection for each inverter, which protects the system from the possibility of an AC to DC short within the inverter. In short, there is no need to fuse the array to prevent back-feeding from the inverter.
The NEC Article 690-41/42 requires that one conductor of the PV DC circuit be grounded. NEC Article 690-14 states the grounded conductor may not be disconnected unless as a means of ground fault protection. The Sunny Boy Inverters all have the negative conductor grounded within the inverter. Therefore, only the positive conductor may be opened by the DC disconnect switch. Ungrounded arrays require fusing on both the positive and negative conductors as well as having provisions to disconnect both conductors.
The size of the cabling on the DC side depends on the distance between the PV array and the Inverters, as well as the short circuit rating of the PV string. SMA America recommends sizing the PV wired to keep the voltage drop below 1%. Please look at table 310-16 of the NEC code for cable sizing requirements. Use 125% of parallel module rated short circuit current. In any case, the DC terminals in the Sunny Boy Inverter will only accept up to 10 AWG wire.
The best place to mount the Sunny Boy Inverters is outside, in a shady location (usually on the North wall of a building). In some cases this is not possible or is undesirable to the equipment owner. if this is the situation, you may install it anywhere you wish, but please consider the following: The inverter must be shaded from the sun The inverter must have adequate airflow over the heat sink The inverter must be placed in an area where the ambient temperature remains below 160°F. Failure to account for these factors may cause the inverter to operate in "derating mode" and will reduce the output power of your PV system. For more on derating mode and how to prevent it please see this discussion of Derating Mode.
This depends on the length of the run, and what model of Sunny Boy Inverter you are using. In all cases, the total voltage drop on the run to the AC distribution panel should be less than 1.5% (3.6Vac) for then entire run. The 1.5% voltage drop must include cabling, but also switches, sub-panels, and so forth (all components between the Inverter and the point of interconnection to the utility). If the AC wire voltage drop is too large, the inverter may shot down with Vac High faults during power production. Please look at table 310-16 of the NEC code for cable sizing requirements. The AC terminals in the Sunny Boy 1800U and 2500U will only accept up to 10 AWG wire.
According to the NEC code in section 690-64 the inverter shall have an AC disconnecting means. This may either be a breaker in a distribution panel, or a fusible switch. In some cases the local utility will require both, so it is up to the installer to be familiar with the local requirements. For the SB 2500U the breaker(s) and/or fuse(s) should be rated for 250V and 15A, with breakers being 2-pole. For the SB 1800U the breaker(s) and/or fuse(s) should be rated for 120V and 20A, single pole.
SMA recommends going directly to Underwriters Laboratories for information on the listing of our products. All of the inverters that SMA America sells have been UL listed, and our UL file number is E210376. Specific information relating to the UL tests performed may also be found on the UL site with our file number.
Yes you can. In general, the Sunny Boy Inverters may be connected to any 3-phase system, regardless of configuration or grounding scheme, provided the AC voltage is correct for the model of inverter that you are using. For more details on all of the design considerations please contact our technical support department at techinfo@sma-america.com or call us at (916) 625 0870.
