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Part 2: Commercial PV System Sizing and Design with SMA CORE1 Inverter

PART II

In part one, we introduced the features of SMA’s free sizing and simulation tool and outlined how the CORE1 is designed to provide easier installation, commissioning and monitoring. In part two, we will discuss the benefits of the CORE1 for weather data integration as well as the advantages of using Sunny Design.

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For weather data integration, the CORE1 communications card allows the installation of a sensor module that can integrate temperature, irradiance, and wind speed sensors, reducing the amount of connections, cable runs, and additional external monitoring devices needed.

If we look at the East/West configuration of the array, it is important to account for any possible shading effects. Fortunately, SMA inverters include the Opti Trac Global Peak algorithm, which reduces the effects of shade on the system by allowing the inverters to optimize the Maximum Power Point Tracking of the PV array. Additionally with the CORE1, it is possible to monitor independent strings in order to check for any differences in energy production on each of the channels of the inverter. As it occurs in this case where we have strings of similar size, it is possible to configure two groups (East and West) to compare currents and identify any failures or potential problems on the strings.

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One nice feature of Sunny Design is the possibility of doing a side-by-side comparison of design options. In the image above, we can see the results and overview of both options. Although for alternative 1 there is a higher AC capacity by having two 30kW inverters, the annual energy yield and the performance ratio of both designs is almost the same. The CORE 1 design has a higher DC/AC ratio.

Depending on the characteristics and conditions of the installation site, it might make more sense to adopt the alternative one with two Sunny Tripower TL-US inverters. Even though these devices do not have the high integration of the CORE 1, they are lighter, more flexible, and allow installations in high-pitched roofs.

The last step in the design process involves selecting the option that makes the economic sense. Fortunately, Sunny Design offers the possibility of customizing values and settings to perform a profitability analysis, so that costs and payback periods can be visualized. This enables an integrator to make the right decision not only based on technical specifications, but also on financial metrics.

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In summary, if you want to complete successfully a PV project on time, there is no need to cut corners, just make sure that you have the best tools for the job. You can count on SMA, we have the solution for any PV project offering the best support and providing the answers, you need every step of the way.

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

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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Sunny Design: Polystring Configuration

Sunny Design
What happens if I have an east-facing PV array and a west-facing PV array connected to the same string inverter with one MPP tracker?

This is a fairly common question that SMA Technical Support receives from customers and installers. There is only one answer that is correct 100% of the time: Do the design!

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