Part 1: Commercial PV System Sizing and Design with SMA CORE1 Inverter

From on 08/08/2018 in Category Technology with 11 Comments

PART I

In view of the increasing number of PV commercial installations across the U.S., installers and contractors find themselves under constant pressure to complete more projects in less time. In order to achieve this, they must streamline the installation process while maintaining safety and quality standards.

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The first step of the process starts with design. While most of the time the objective is to maximize roof space in order to fit as many modules as possible, it is essential to plan ahead for service and maintenance, leaving enough space between strings of modules in order to allow easy access. Once the system layout has been determined, the equipment for the project must be selected. When choosing the right inverter for the job, one must consider more than just technical specifications. It is also important to keep he installation process in mind, under what conditions the inverters will be working, and all other major requirements of a commercial PV plant, including; monitoring systems, weather stations, string aggregation, shade mitigation, racking structures, and additional BOS.

When considering all these factors it is often difficult to find an inverter that can meet all of the required metrics for the integration. Fortunately, we have the tools and the solutions to help you design a successful project that can be carried out and completed within a tight deadline.

First, SMA’s free sizing and simulation tool, Sunny Design, allows you to size systems correctly by matching SMA inverters with PV curves, and to compare design alternatives with different inverters in order to be able to make the right decision not only based on energy yield but also on economics and architectures.

As an example, we sized a 67-kWp rooftop commercial system with Sunny Design. We designed two alternatives for this project; one with the Sunny Tripower TL-US and one with the Sunny Tripower CORE1 – the latest addition to our commercial solutions portfolio.  For this project, we designed a roof-mounted array with an East/West configuration and a 15o inclination.

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When used in the automatic design mode, Sunny Design will do all the calculations and can offer options based on profitability or energy yield. For the first alternative we have selected a design with two STP 30000 TL-US inverters. The suggested configuration for the array has three strings in parallel connected to each input of the inverter, meaning that we will need to incorporate DC combiner boxes in order bring the six strings into the two MPPT channels of the STP inverters. The results of the simulation, including current and voltage values, can be seen below:

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It is important to note the 1.1 DC/AC ratio of the design. High DC/AC ratios account for module degradation and potential higher energy yields during a calendar year.

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The higher integration of the CORE1 allows you to connect up to 12 strings to the inverter eliminating the need for additional BOS like DC combiner boxes. Thanks to its higher power rating of 50kW it is possible to reduce the number of inverters and the number of connections, improving the overall installation time.

When considering the specification of the PV plant it is clear that the advanced features of the CORE 1 align better with the requirements of the project.

Multiple communication channels allow for easier monitoring and commissioning. Although best practices for monitoring involve using a physical communications channel like Speedwire (SMA’s Ethernet based protocol) because of its reliability and higher speeds, WLAN is the better option when commissioning the inverter on site. It will allow direct communication between the inverter and any smart device that can connect to a wireless network and access the WebUI through a web browser.

In part two of our series, we will outline the benefits of the CORE1 for weather data integration as well as the advantages of using Sunny Design.

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The Author

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Alex Avellaneda is a technical training specialist for the SMA Solar Academy.

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11 Comments

  • avatar

    Andykaufmantony

    08/22/2018 at 11:04 am

    Alejandro, thanks so much for the post.Much thanks again. Really Cool.

    Reply »
  • avatar

    Sharif Ahmed

    11/07/2018 at 12:08 pm

    can cor 1 inverter to deliver power for my load after utility gird failure ? in other words can i use it for export the access power to the utility but when the utility grid is shut down because failure the cor 1 well be still to feed my loads or cut off

    Reply »
    • avatar

      Alejandro

      11/07/2018 at 2:14 pm

      The Core1 inverter is designed for Grid-tied operation, meaning that if the grid fails the inverter will disconnect and stop producing power as per anti-islanding requirements.

      Reply »
  • avatar

    Armando

    11/25/2018 at 8:18 am

    Do we have to balance the PV input to the amount of MPPTs like in the example? 12 strings of 20, 40 panels per MPPT?

    We could reduce the amount of PV wire by increasing the amount of panels per string in some cases and reducing the amount of strings.

    Reply »
    • avatar

      Mike

      11/26/2018 at 10:33 am

      Armando – no, you do not need to balance the inputs. Often it simplifies the installation, but it is not required. However, you must ensure that all inputs do not violate the electrical limits of the inverter, on both the coldest and the sunniest days.

      Reply »
  • avatar

    Jose Antonio Woo

    11/26/2018 at 1:09 pm

    Armando

    Hi

    We are looking the spec for a 1000 kw system

    Do you can help with this information

    My BR

    JAW

    Reply »
    • avatar

      Alejandro

      11/28/2018 at 11:16 am

      Hi, we recommend that you take a look at this recorded webinar on Sunny Design https://bit.ly/2vdp0dK . This is our sizing and dimensioning tool for PV systems, and it can be helpful when trying to spec a commercial system.

      Reply »
  • avatar

    Mario

    11/28/2018 at 8:29 am

    Tengo un inverso SMA sunní Boy 7000wac y tiene un error 8206

    Reply »
    • avatar

      Alexandra

      11/29/2018 at 9:34 am

      ¡Hola Mario! Debes comunicarte con nuestro departamento de soporte técnico. Ellos podrán ayudarte.

      Reply »
  • avatar

    Jon

    11/30/2018 at 3:37 pm

    Hi,

    Reading the inverter manual, I saw, there are cases where the neutral is not needed. When are those cases?

    And should the Ground be sized same as the Lines A,B, and C in that case?

    Thanks.

    Reply »
    • avatar

      Mike

      12/06/2018 at 9:35 am

      Hi Jon! If allowed by the authority having jurisdiction, the neutral wire does not need to be run to the neutral terminal in the CORE1. There is a jumper installed from the inverter body ground to the neutral terminal. If required, this jumper will be removed and a neutral wire will be run to each inverter. Either way it is wired, the CORE1-US must be attached to a 277/480 grounded wye utility service. A 480 delta service connection is not allowed. The ground wire should be sized in accordance with all applicable local and national standards.

      Reply »

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