A team at the US Department of Energy’s Oak Ridge National Laboratory has developed a utility-scale solar and storage project that can provide power to both AC and DC high-voltage lines, and thus shore up grid stability – here’s how it works.

Most of the US power grid uses alternating current, or AC, which constantly switches the direction of electron flow. But solar and battery storage uses direct current, or DC, that flows in a single direction.

The US power grid includes a smaller number of high-voltage DC lines that are more efficient at delivering bulk power over long distances or to remote regions. 

Converting current between DC and AC requires specialized power electronics. So researchers at Oak Ridge National Laboratory have developed a design and control system and architecture for a solar and storage plant that can provide power to both AC and DC high-voltage lines. As a result, renewable power can be more easily and reliably transmitted.

The project is called MARS, or “multi-port autonomous reconfigurable solar power plant.” It’s an all-in-one package that includes power electronics, electrical architecture, and cybersecurity software. And because it’s plug-and-play, it’s easier and cheaper for utilities to get it online.

Case simulations in hardware that were based on two California sites revealed that MARS achieved up to 50% reduction in power loss, a 16% improvement in stabilizing AC voltage frequency, and 100% detection of cyber intrusions.

MARS can also reconfigure itself based on available energy. For example, when the solar panels weren’t generating electricity at night, MARS could continue to connect the AC and DC transmission systems and use stored battery power to supplement its operation.

The researchers found that MARS reduced electrical costs by up to 40%, as they developed an algorithm to fine-tune plant size and energy storage to maximize annual revenue.  

MARS also includes an innovative type of inverter that can maintain grid stability and jumpstart the  grid after a disturbance.

Team lead Suman Debnath team explained:

You do not want the power grid to have significant losses of power when disturbances happen.

Traditional renewable plants may disconnect from the grid or stop sending power, but we did not see that happen with MARS. It could cope better with failures in the external grid and  continue to operate, supporting the broader power system.

Oak Ridge National Laboratory is working with such industry partners as Southern California Edison, Opal-RT, Hitachi Energy, and the Georgia Institute of Technology. The Oak Ridge team and its partners are working together to roll out an initial field demonstration of either MARS components that support grid stability, or a scaled-down version of the full design.

Southern California Edison’s senior engineer for grid technology innovation, Md Arifujjaman, said:

From the point of view of a good algorithm to track down cybersecurity problems and technology we can use on the DC side,  MARS is very helpful.

The DC technology is also promising for scaling down DC voltage for electric vehicle charging stations.  

Photo: Existing and potential high-voltage direct current lines in states with the greatest solar potential, and prospective sites for MARS/Oak Ridge National Laboratories

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