Best commercial solar inverter options

Goodwe, Kuga’s Number 1 commercial solar inverter for rooftop applications

Kuga Electrical’s very first commercial solar installation was a 200kW at Spa Industries back in 2017. The installation won a Master Electricians award for best commercial project of the year. 4 x 50kW Goodwe MT series inverters were used and the team at Kuga has never been back for a warranty claim on the inverter. Since then, hundreds of installations at Kuga have used Goodwe MT Series and SMT Series solar inverters. Some notable installations are the 525kW installation at Della Rosa using 11 x 50kW MT Series inverters and the 300kW installation at Maxton Fox using 4 x Goodwe 80kW MT Series inverters.

Kuga Electrical has been installation Sungrow commercial inverters for 2 years now. Sungrow early in the market launched a 110kW inverter called Sungrow SG110CX model. For the past 2 years, Kuga Electrical has been installing 2 – 3 Sungrow SG110CX inverters per week. The major advantages of this inverter are:

• Up to 146kW of PV can be installed on this inverter
• In-built DC Isolators
• Factory-built DC isolator cover to protect and also improve the visual appeal of the installation

In January 2021 Kuga Electrical installed a 450kW commercial solar installation at Medline located in Marsden Park, Sydney, NSW Australia. The project used 4 of the 110kW Sungrow SG110CX inverters.

Kuga Electrical has reviewed 2 years of installation data and the team has worked out to get the best performance only 6 MPPTs are used and the string length has 17 panels.

Why not use all 9 trackers on the SG110CX Inverter? It’s simple. It’s rare that commercial solar installations have more than 3 arrays or are impacted by shading. Usually, optimising for shade or 9 different roof orientations isn’t required.

Here is the reason why Kuga Electrical typically uses only 6 trackers on the Sungrow SG110CX Inverter:

• The more panels that are installed in a single string the higher the voltage. The higher voltage will produce more electricity throughout the year.
• Sungrow SC110CX MPP voltage range for nominal power is between 550V to 850V. The is important because:
  • Installing 17 panels per string will typically operate between 550V to 750V keeping the string in optimal voltage range for longer throughout the year compared to;
  • Installing 14 panels per string will typically operate between 400V to 600V. The string voltage is outside the optimal voltage range therefore the inverter efficiency drops dramatically. This will ultimately produce less electricity.
• Keep in mind that installing 17 solar panels per string isn’t possible to do all the time but it’s important to optimise the design as much as possible.

Good Sungrow Inverter options for Ground Mount systems

Sungrow is also a really good choice for ground-mount projects and AC coupled battery storage projects. The most commonly used inverters for ground mount systems are:

Sungrow SG110CX inverter – This inverter is suitable for 1100V system designs for a behind-the-meter three-phase project. This inverter is IP66 rated, the largest capacity three-phase inverter from Sungrow and has been used in projects across Australia. Ground mount solar installations from 0kw to about 1.7mW that are low voltage would typically use the Sungrow inverter.

Sungrow SG250HX inverter – This inverter is used for ground-mount systems up to 2mW and where there is a high voltage connection. Its important to note that the ACThe advantage of this inverter is:

• The string can be designed up to 1300V as the nominal power range for voltage is between 860V to 1300V.
• The higher string voltage will result in:
  • Lower DC cable cost because a smaller cable will be required. Example – Cable run of 200m. Voltage drop under 3%. 1100V inverter with a string design at 600V would need a 10mm DC cable. The Sungrow SG250HX 1500V inverter with a string design of 1100V would need a 4mm DC Cable. 4mm DC cable is over 70% cheaper than 10mm.  Jcalc is a good entry-level calculator to play around with for cable sizing.
  • Max efficiency of 99% or 98.8% euro efficiency.
  • Increased solar production.
  • High power output of 250kW is one of the largest inverter options in the market. With Sungrow, the project will have fewer inverters than a competitor.

Sungrow Central inverters

The central inverter range from Sungrow is available up to 6.8mW capacity. Central inverters aren’t viable on projects that are small or under 2mW. When considering central inverters, the engineers at Kuga would consider Distributor approval requirements and costs. Often the Distributed Network Service Provider (DNSP) would make applications under 1.5mW AC easier and cheaper vs applications up to 5mW. At project feasibility phase Kuga include the best size and inverter recommendation for your project objectives.

Fimer inverters (formerly ABB), made in Italy

In Australia, it’s a one-horse race for SMA in the Utility market specifically. Reports suggest 95% of all Australian utility-scale solar projects use SMA inverters. For solar farm project below 5mW Kuga Electrical typically recommend the SMA MV Power Station. The capacity ranges between 2.2mW and goes up to 4.6mW. The range also includes a low voltage option that may be used for some “behind the meter” projects. For example, a business that is a high user and roof top isn’t an option or has been exhausted, but has empty land next to their building. The minimum size of land that would suit a 2.2mW central inverter with solar panels is around 25,000sqm.

The range of SMA Medium Voltage Power stations are:

SolarEdge commercial solar optimisers and inverters

In this article, we have talked a lot about string design and voltage. Along with DC and AC Cable selection, string design and voltage are the most important elements in commercial solar installations. It’s the reason why you use Kuga Electrical over XYZ solar company. Like Kuga Electrical, SolarEdge optimisers and inverters exceed in performance in long cable runs, complete roof orientations, for example, shopping centres, schools or Aged Care facilities and rapid shut down safety features.

Kuga Electrical has an example of a SolarEdge installation. The Kuga team installed a 100kW solar system at St Francis of Assisi Primary School in Tarniet Victoria. On this job, SolarEdge had to be used because:

Optimisers were required:

• Multiple short roof arrays meant the number of panels on a string varied and couldn’t be optimised for a string inverter. For example, the Sungrow inverter needs 17 panels on a string with the same orientation for the string to be in the inverter optimal inverter range. That wouldn’t be possible on this roof.
• The SolarEdge DC optimisers meant regardless of the solar panel mismatch the optimiser will optimise the specific panel to 750V – 830V therefore reducing the impact of solar panel mismatch.
• Kuga Electrical could design string to the maximum panels with SolarEdge as the orientation of the panels can vary as SolarEdge has DC optimisers.
• About 10% of the solar panels were impacted by shading in the afternoon.

Rapid shut-down:

• There is a lot of issues with DC isolators. SolarEdge will automatically shut down the PV system when an arc issue is detected and reduce voltage to 1V.

Kuga Electrical installed a meter and a solar schools program

The students can do modules to learn about solar while looking at the actual solar production from the school’s PV system (as explained by Clement).

When designing large commercial solar rooftop projects, SolarEdge can dramatically decrease DC cable costs.  Kuga Electrical currently has a 1.4mW project on a complex roof and the upgrade to SolarEdge will save over $60,000 in DC cable cost. The Kuga team finds that SolarEdge products are the best option when optimisers or rapid shutdown are required.