Nonprofit Group Aims to Expand Use of DC Microgrids that Integrate Renewables

Pushing power from rooftop solar into DC devices

Connolly’s company aims to maximize the use of clean energy by connecting variable speed electric motors straight onto the DC output point of nearby solar panels, he said. This avoids some investment in expensive equipment such as power electronics and uses solar energy more efficiently.

“This is machinery inside a small electrical apparatus that can push power from rooftop solar into batteries and electric motors,” he said.

For the foreseeable future, moving power, say, from the north to the south part of a city using high voltage transmission lines will likely be alternative current (AC).

“But if a campus, university or hospital has lots of DC machines—wind, solar and EVs—then instead of trying to adapt all those DC machines to synch with the big AC grid, it’s better to loop them together in a microgrid and for that microgrid to sit independent of the grid and sometimes be connected to it,” Connolly said.

Moving to this type of model would require economic incentives. For example, microgrids at the grid edge could be paid for providing demand response, he said.

Nonprofit aims to create standards for DC microgrids

To help enable these DC microgrids, the nonprofit group is creating standards that would allow different DC devices to work together. “That way, circuit breakers from Schneider and EV chargers will work together, plug and play,” Neyret said.

In interviews with Microgrid Knowledge, U.S. storage and microgrid companies said that DC power can be more efficient, but numerous challenges must be addressed before it can be widely deployed.

“Unlike traditional AC systems, DC microgrids offer higher energy efficiency, greater conversion efficiency, lower-cost converter systems and improved power reliability,” said Mike Wietecki, senior vice president of strategy and regulatory affairs at Powin, which offers utility-scale energy storage systems.

Avoiding the lengthy interconnection process 

“These advantages make them an increasingly attractive option for utilities and organizations looking to integrate multiple energy sources while keeping costs down,” he said. Just as important, off-grid DC microgrids create a way to avoid the lengthy and often uncertain interconnection process, he said. 

But upfront costs and longer project timelines can be barriers to adoption in part because of limited market visibility and industry familiarity, he added.

In addition, retrofitting traditional AC systems to accommodate DC infrastructure can be complex and costly.

“As adoption increases and technology matures, these implementation challenges are expected to diminish, but they remain important considerations today,” Wietecki said.

Pete DiSanto, executive vice president, engineering power solutions for data centers at Enchanted Rock, said that DC in general is more efficient and has fewer losses. “All your PV and solar battery storage is in native DC and there are benefits to that.” For example, with DC systems, there aren’t frequency challenges like those that Texas encountered during Winter Storm Uri, when grid frequency dropped.

Remote areas might be a good place to begin deploying DC microgrids, he said

Focusing on locations with high deployment of DC devices

“If I’m going to launch a DC microgrid, I would stack the deck in my favor and pick an area with high use of EVs and buses, a place that has a high density of DC already,” he said.

Jeff Barber, vice president for global data centers sales at Bloom Energy, whose fuel cells are DC architecture, said that DC architecture can be especially helpful to data centers. It can avoid the industry’s supply chain delays acquiring the inverters and transformers needed to change DC electricity to AC electricity and back.

“For data centers, with a typical architecture, there are multiple levels of inversion and rectification. When electricity flows into a data hall, it’s inverted to AC and when distributed, it goes back to DC,” he said. That involves a lot of equipment and creates an 8% to 12%  loss in efficiency, he added.

“I think we’ll start seeing some data halls or rows going all DC,” Barber said.

For Neyret, the benefits of DC architecture will be best realized through an approach that flows from utility customers to the grid. For example, utility customers would use their solar panels to meet their own needs and then send only the surplus to the grid.

“The AC system has been top down–big production plants down to lightbulbs. DC will be a bottom-up approach,” he said.