Utility-scale solar projects are getting bigger and bigger, with the largest project approved in the United States (as of August 2021) reaching a whopping 690 MWAC. Choosing the best inverter is becoming increasingly important in order to produce the huge amount of energy these projects strive for.
Project developers select inverters even before submitting an interconnection application. Utility companies need to know these details in order to conduct studies that will determine the impact of solar projects on the grid.
“The inverter is one of the very important components of the studies and basically enables us to see the project at a very early stage of development,” says Vishrut Bhatt, Industry Segment Manager Renewable Energy Systems at TMEIC.
Manufacturers of modules, racks and inverters usually work together at the beginning of a project's life cycle to give developers the best plan for their projects, according to Maren Schmidt, general manager of the utility division at Fimer.
“We all have to work together,” said Schmidt. “We have the project developers, the EPCs, the technical consultants – we have to think in terms of the system together with the module manufacturers and the tracker manufacturers, because the goal must be to optimize yields.”
During this planning period, developers will review utility needs, financial targets, and product projections, said Brian Taddonio, VP of engineering at Blue Ridge Power, the newly formed EPC arm of Pine Gate Renewables. Developers need to be sure that the inverter they choose is about two or three years in the future when the project actually lays the foundation stone.
“It's about the past of these manufacturers and where we believe they are, how healthy their company is at this point in time and their forecast for the quarters ahead,” said Taddonio.
Choice between string and central
Power solar project developers have more options than ever for the type of inverter that best suits each location. It is no longer just a choice between central and string inverters – manufacturers are now producing “central” string inverter solutions in which several string inverters are combined in one housing. String inverters offer several MPPT (Maximum Power Point Tracker) to reduce shading effects and are easier to replace in the event of a fault in order to minimize power loss. If a central inverter fails at one location, much more energy is lost before the O&M teams can fix the problem.
Fimer recently launched two new solutions for utility projects: a traditional stand-alone string inverter and a skid solution with multiple string inverters centralized in one place. Schmidt said the company had pushed the new centralized design as the cost of string inverters is now close to that of central offices.
TMEIC also offers central string inverter solutions with nominal powers between 730 and 920 kW through its Solar Ware Ninja product line. These inverters are integrated on a skid, with up to three ninjas on each side of a centered medium voltage transformer. The inverter manufacturer previously only produced central inverters, but saw the value of string solutions for projects in the supply sector. Now the modular ninja line is TMEIC's main offering for the US market.
Nevertheless, some contractors in the utility sector stick with real central inverters. Blue Ridge chooses control panels for most of its projects because of their ease of installation, lower cost, and additional storage options.
“While there is always the argument that you can repair a string inverter much faster than you can replace an entire control panel and that your system does not break down as it should [long], I think some of the other considerations outweigh some of the other considerations. And we are still able to properly inventory the spare parts that would be needed for these larger central inverters, ”said Taddonio.
Installation of large inverters
It is important to choose the right location to mount the inverters when an installer is putting them together. The inverters should be easily accessible and hazard-proof for O&M technicians, said Taddonio. Flood zones should be avoided or the land should at least be built on so that water can run off. Blue Ridge also makes sure that inverters are carefully installed away from inhabited buildings, as inverters emit some noise.
Once the correct location has been determined, it is time to bring in the inverters. Although moving large central inverters requires some heavy machinery, installation is a relatively straightforward process, according to Taddonio.
“Assuming you have this space on the job site and you can handle this equipment properly on the job site then it becomes very efficient to install these units, especially when they come on the packaged skid assemblies,” said Taddonio.
Blue Ridge Power cranes the inverters onto the construction site and then sets them down on pre-drilled screw systems to fix them in place.
“You put the screws in, then you put them straight on, weld, fasten and you're good to go,” said Taddonio.
Cantsink works with Blue Ridge to manufacture skid mounting equipment for inverters. After working on refurbishing sinking solar inverter mounts for some time, Cantsink came up with the porch solution to install spiral piles under skid mounts to prevent future soil disturbances.
“The floors are all very, very different. This is not always taken into account and you run the risk and high chance that problems will be resolved over time. You don't want that with your project, ”says Dara Macias, Sales Manager at Cantsink.
After the runners are attached, the picking process is pretty straightforward. Inverter systems like those from TMEIC are pre-wired so installers simply need to feed the DC inputs to each inverter, connect the AC cables to the transformer, and set up any fiber optic or control networks they need, Bhatt said.
“You come to this unit, you get your test equipment out, you sit right there. Whether it's a large unit or small units in a cluster, they can do all of their work right in that one place, and it really creates some efficiency in their movement around the site, ”said Taddonio.
The design and installation of inverters on large projects sounds daunting, but the right planning, engineering, and collaboration between manufacturers all help to make the process as easy as possible.