By Chris Meehan | Nov 09, 2020
String inverters for solar panel arrays
BREK Electronics uses bleeding-edge technologies in innovative ways to design utility-scale inverters -- which convert the DC electricity produced by solar panels into the AC electricity used in homes and businesses -- that are much less expensive, smaller, and lightweight than those in the market now.
The company is developing three-phase DC string inverters capable of handling 250 kilowatts of power from solar panels. Currently, most string inverters are limited to 125 kilowatts because of the silicon components used in them. The BREK technology uses a design architecture that is based on silicon carbide components.
"It's the technical design that uses this new silicon carbide power transistor technology that is becoming available," Erickson explains. "We've shown how to use that to greatly reduce the size and weight of the big magnetics and capacitors that are the big, bulky and expensive components in an inverter."
BREK's prototype inverters now cost roughly 4 cents per watt. "We're working on further refining it, but that's a good number for today," says Erickson, a professor at University of Colorado Boulder. "That's maybe 2 cents lower than the best string inverters today and on par with the least expensive, big, central inverters, the 5-megawatt-type inverters. But then we have a path to lower costs as well."
Adds Majeti: "We're actually blurring the line between central inverters and string inverters when it comes to size because string inverters -- at higher powers -- were unheard of before, and we're approaching the size of central inverters with our scalable architecture."
While the costs of silicon carbide components are more expensive, the power densities BREK has achieved through their design architecture overcome those more expensive costs. "We've achieved roughly four times the power density," touts Erickson. "That's measured in kilowatts per kilogram and today's string inverters are about one kilowatt per kilogram. We're at about five kilowatts per kilogram . . . so for the same weight, we could get five times the power out of it."
That results in a utility-scale string inverter that's the size of a typical residential inverter, or about 100 pounds, versus the status quo, a 125-kilowatt string inverter that often requires heavy equipment to move and install. Central inverters for utility-scale solar installations are even bigger and heavier, often the size of small tractor-trailer container.
"Our 250-kilowatt design is highly modularized. We can actually scale up to higher powers by simply adding more modules in," Erickson says. "We have a path to easily scale up to 500 kilowatts and higher."
A 5-megawatt solar farm would require 20 of BREK's units, compared to 40 125-kilowatt string inverters. At the same time, the company anticipates the functional life of its devices will be 20 years, compared with 10 years for most current string inverters.
Notes Majeti: "This allows for easy installation and maintenance and even fast swap outs when needed without much downtime. The higher power density also means that you require fewer inverters in the field."
The designs and prototypes were developed at CU Boulder based on patents the university has licensed to BREK, according to Majeti, and the technology is based on work done at the university sponsored by ARPA-E and the U.S. Department of Energy. The company has already won grants and recognition for the designs from CU Boulder, the Department of Energy's Office of Energy Efficiency & Renewable Energy, and the American-Made Solar Prize, and has received support from the Colorado Office of Economic Development & International Trade -- all of which helped the company get started and into testing its designs.
"We completed a first round of testing at the National Renewable Energy Laboratory," Erickson says. The initial tests showed BREK's devices were more than 98 percent efficient at converting DC electricity into AC electricity and he anticipates reaching even higher conversion efficiencies. "The silicon carbide transistors can operate at a higher voltage with, lower switching loss and conduction loss, so basically at higher efficiency."
BREK had planned to do additional testing at NREL in 2020, but it was hampered by COVID-19. Still, Erickson is hopeful that the company will seek UL certification for its units in 2022.
As for market interest, it's already there, according to Majeti. "We're in talks with companies, that's all we can say at this time," she says. "We're going to start with pilot applications and then we'll ramp up gradually. I think the first half a year to year would be our pilot installations."
The company also is looking ahead to its flagship technology's price dropping and has designed its products to take advantage of factors that will lead to price drops. Though silicon carbide technology was developed in the U.S. and has been studied for about 20 years, it's only in the last few years that they have become commercially available, says Erickson.
"Their prices really are a function of the manufacturing volume," he notes. "We're seeing them used in other industries. I think the most interesting one is the electric vehicle industry is adopting these devices. That can drive the volume up and drive the price down of these devices. We're actually trying to choose our inverter architecture so that we can use the same devices that the automotive industry would use, and then we can piggyback and benefit on the high volume."
The inverters are also designed for highly automated manufacturing in Colorado or elsewhere in the U.S. "It's a very simple assembly and does not require a lot of manual labor to build," Erickson says.
Challenges: "First we need to, to demonstrate a working unit that's been fully tested," Erickson says. "I think after that the challenges are the usual, funding to ramp up production and then . . . there are questions of bankability and establishing sales channels."
Opportunities: "I believe this technology will help the U.S. become a leader again in solar inverter technology, because there are not very many U.S. inverter manufacturers," Majeti says.
Needs: Capital. "I think all startups need more funding to keep growing and we're no different than that," Erickson says. "I think with more funding, we could grow faster and maybe get to market faster, but we do have a good path as it is."