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SMA Sunny Tripower CORE1 Inverters: Repowering Ready

Part II: Maximize and Protect

In the first installment of this series, we focused on MPP voltage. This post will explain how to maximize the number of strings connected to a string inverter and protect the inverter from damage. The strings are limited by the number of terminals and the maximum short-circuit current of each individual maximum power point tracker (MPPT).

CORE1 multiple strings

There are ultimately two advantages of checking the short-circuit current: to maximize the number of strings per inverter and to prevent inverter damage in the event of a string fault with a high DC current. Compared to 600VDC systems, modern PV systems have longer strings with higher MPP voltage, requiring fewer strings in parallel to reach the same capacity. Contemporary inverters can, as a result, handle a comparatively higher voltage with limited current capacities.

Still, a new inverter placed into an existing system must match the current requirements. There are two numbers to check to ensure that’s the case:

  1. Maximum operating input current
  2. Maximum short-circuit current of the inverter/MPPT

First, system age is an important consideration since older modules may not reach their maximum operating input current, even under the best conditions. In most cases, the DC/AC ratio has more influence on clipping than the maximum operating input current. Customers have, however, in some repowering projects, experienced up to a 20% higher module MPP current than the inverter’s maximum operating input current without a loss in production.

It’s also important to focus on the maximum short-circuit current of each inverter MPPT. As mentioned above, there are two reasons to investigate this value. Let’s dive into the specifics of how and why to ensure you’re ready for repowering.

Ready to Repower?

One reason to repower is to protect the MPPT of the inverter from damaging current. These elements include the maximum short circuit current per MPPT, the safety factor and the short-circuit current of the chosen module of two parallel strings.

Let’s look at an example using the SMA CORE1:

  • Module type: Sunmodule Plus SW290 MONO from SolarWorld
  • Standard safety factor: 1.25
  • Maximum short-circuit current: 9.97A

The maximum short-circuit current of the PV design is then calculated by multiplying the short-circuit current of the module (9.97A) by the number of strings (2) and by the safety factor (1.25). Multiplying these values equals 24.93A. The total must be less than the maximum short-circuit current of one MPPT of the CORE1, which is 30A.

Thus, this design works and matches the inverter limits, allowing connection of two strings directly to one MPPT. Three strings would risk permanent damage to the inverter.

The second reason to check the maximum short-circuit current per MPPT is so you can calculate the maximum number of strings that can be connected to each MPPT. In the aforementioned scenario, two strings are the maximum allowed per MPPT. Some installed modules in older designs, however, have a lower short-circuit current. In such cases, the maximum short-circuit current per MPPT must be divided by the safety factor and by the maximum short-circuit current of the modules installed.

When determining the maximum number of strings to connect to one MPPT in parallel, you can round the results down. Let’s look at an example:

  • Module type: Ultra 175-PC from Shell
  • Maximum short-circuit current: 5.43A

And here’s the math: The maximum short-circuit current of the MPPT (30A) divided by the safety factor (1.25) and by the short-circuit current of the module (5.43) results in 4.42 strings. Once rounded down, it shows that a maximum number of four strings can be connected in parallel to one MPPT.

string inverters formula

Why calculate the maximum number of strings, especially when repowering?

The existing strings are typically very short (about 10 to 14 modules), which results in a low string voltage. Combined with a low current, those strings have a low power output. Using the example above with the Shell modules, a string length of 12 modules with two strings per MPPT puts out 25.2kWp of total power under test conditions. The SMA CORE1, 33-US can handle up to 50.0kWp (DC).

Adding more strings until the chosen DC/AC ratio has been reached makes full use of the inverter capacity—underscoring why this is the second important reason to check on the maximum short-circuit current of the MPPT. Keep in mind, though, when more than two strings operate in parallel, each string requires protection, which is achieved by adding string fuses.

Now that you know how to correctly check both numbers, your repowering is set up for success—ensuring your system will be safe and efficient.



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Central American Clothing Manufacturer Decks Out Its Facilities with Solar Energy

Pinehurst MFG, a distinguished textile manufacturing company, is trusted with clothing production by world-renowned brands such as ADIDAS. The company now powers its operations using a solar system with SMA inverters.

Commercial solar Honduras

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Hilton Hotel Upgrades to Energy Independence

Nestled in the exclusive Villa Fontana area of Managua, Nicaragua, lies the modern DoubleTree by Hilton hotel. Guests have long relaxed in the spacious rooms featuring elegant décor and breathtaking views of Managua Lake. With the new solar installation, guests now also know they are supporting a business that isn’t dependent on fossil fuels.

Solar system Managua

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A Sunny Upgrade for Our Four-Legged Friends

Tucked into the northeast tip of Long Island lies the town of Southold. It’s a picturesque waterfront region with beaches, vineyards and now the first animal shelter in the state to be powered by solar energy.

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SMA Sunny Tripower CORE1 Inverters: Repowering Ready!

Would you like to discover a new level of PV performance? Then this blog post series on SMA Repowering is for you! In this article, our repowering expert Thorsten Hoefer shares insights on which aspects to consider when choosing an inverter for a repowering project and explains which SMA inverters are repowering ready.

Sunny Tripower CORE1 commercial inverter

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Cattle Ranch Beefs Up Savings with Solar Energy

Argentina’s first solar energy plant for self-consumption earns attention!

Sistema solar comercial con SMA

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Solar Spotlight: Naghtaneqed School Graduates to a Cleaner, Quieter Campus

Hakai Energy Solutions Delivers a Solar Hybrid Integration Project for Students in Canada!

solar school projects

The Naghtaneqed Elementary School sits nestled in the expansive Nemaiah Valley, three hours southwest of Williams Lake, British Columbia. In this First Nations reserve and ranching community, the school has—until now—been fully powered by diesel electric gensets for more than 30 years.

High operating costs associated with fuel purchase and ongoing maintenance motivated the district to explore solar power. The reliance on diesel also introduced pollution and noise to the campus. Thanks to clean, renewable energy, those issues are drastically reduced concerns today. The Cariboo-Chilcotin district hired Hakai Energy Solutions to install a solar project expected to save the school $50,000 CAD, roughly $37,000 USD, in annual diesel costs.

In July 2019, the school district invested in a hybrid energy system that integrated solar energy production, advanced energy storage and an expandable inverter platform. Utilizing 140 high-output solar panels, 118 kilowatt-hours of lithium energy storage and SMA inverter technology, this system was designed to offset diesel consumption by reducing generator operation by 6,900 hours each year.

Impressively, Naghtaneqed School is expected to recoup its investment in roughly seven years through reduced fuel consumption of approximately 38,400 L every year, plus generator maintenance and replacement cost avoidance. Not to mention, emissions reductions are also estimated at 2,534,000 kilograms of CO2 over the 25-year lifespan of the system, equivalent to 19,500,000 kilometers driven by a car.

“We’ve used SMA products from day one, and they’re simply unbeatable in terms of reliability, functionality and serviceability,” said Jason Jackson, energy system designer with Hakai Energy Solutions. “Working in remote areas makes product selection vitally important. Over the years, we’ve worked with every major manufacturer of inverters, and these experiences have only reinforced our confidence in SMA products. Every employee in this company—from the installation crews to the finance department—is on the same page. From a team perspective, SMA offers the most dependable and bankable suite of products on the market.”

In November 2019, the solar hybrid integration project was completed at the school. The total size is 57.6-kilowatt PV with 120 kwh lithium (LiFePo)-based energy storage and features 45 and 60 kW gensets. Every year, an estimated 72 megawatt-hours will be generated. What kind of impact does that have on energy consumption? A full 80% of the school’s energy will now come from the sun.

This PV array includes Longi Solar72 cell Mono bi-facial solar panels, six Sunny Islands, 1 SMA multi-cluster box and one 50 kW SMA CORE1. The district received funding for the entire project through the Ministry of Education’s program for carbon neutral funding via a community improvement award from Clean Energy B.C. for the project.

“This project has helped us meet our goal of reducing our environmental impact and improved the quality of experiences students have on our campus,” said Alex Telford, manager of facilities and transportation for the Cariboo-Chilcotin district. “When you factor in the cost savings, it’s a win-win-win!”

Visit our photo gallery to enjoy more pictures of this project!

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SMA Solar Academy and SMA Sunbelt Partner to Bring In-Depth Trainings to Florida Installers!

SMA will host three days of training at the Florida Solar Energy Center in Cocoa, Florida from February 18-20. If you are in the Southeast and are interested in learning about residential, commercial and off-grid solar and storage, then you don’t want to miss these seminars with the best resources in the industry!

SMA Solar Academy Training

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Interconnect Your Residential and Commercial Projects Faster with Less Risk

Don’t get left behind when mandatory compliance of California Rule 21 Phase 2 and 3 goes into effect on March 22, 2020.

SMa commercial solar project. View from top.

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Solar Spotlight: Sustainability is at the CORE of Spraying Systems’ Values and Business Strategies

GRNE Solar recently installed a new solar system powered by SMA Sunny Tripower CORE1 inverters and monitored with the SMA Data Manager M at the headquarters of Spraying Systems, a spray technology company in Illinois.

Solar system featuring SMA Sunny Tripower CORE1 inverters at Spraying Systems

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The Top Three Reasons Why Installers Love the CORE1 Commercial Solution from SMA!

Since its introduction, SMA’s Sunny Tripower CORE1 has been taking the commercial market by storm. Now with expanded features and functions, installers have even more reasons to appreciate this truly unique commercial PV solution. We compiled the top three reasons that have installers shouting their praise from the rooftop. 

Sunny Tripower CORE1

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Solar Spotlight: Pistachio and Almond Grower Invests in Solar for a Harvest of Savings

The ground-mounted system installed by JKB Energy located in Kettleman City, California, is the second largest net-metered solar project in PG&E territory and has a projected annual savings of $435,490.


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3.67 avg. rating (78% score) - 3 votes