August 26, 2019

Tool Could Keep Solar Power From Going Off The Grid

PNNL research creates new approach to managing solar power transmission and distribution



Zbynek Burival

Utility engineers have the difficult task of integrating the growing demands of solar power as a result of rising electricity costs and stricter requirements for renewable energy.

A handful of PNNL researchers are developing the only tool that can control large-scale distributed energy resources (DERs) like rooftop solar panels in real time.

PNNL recently published research demonstrating the Coordinated Real-time Sub-Transmission Volt-Var Control Tool’s (CReST-VCT) effectiveness in coordinating and distributing solar energy.

A powerful tool

PNNL has been working on the simulation prototype with researchers from North Carolina State University, the University of Texas, GE Global Research, One-Cycle Control, and Duke Energy. CReST is designed to improve grid voltage stability, reduce system losses, and secure grid operations.

CReST is funded by DOE’s Office of Energy Efficiency and Renewable Energy through the SunShot Initiative.

The proposed tool determines how to increase power system resilience for any given grid. The goal of the prototype is to improve grid voltage stability by coordinating the operation of DERs in real time. This coordinated operation uses an algorithm that operates in real time at every five-minute interval. Frequent updates minimize fluctuations in voltage. The CReST-VCT tool calculates the upper and lower limits of the “virtual power plant,” or aggregated DERs, and coordinates them to minimize grid voltage fluctuations.

When the operational condition of the distribution system and transmission system are unknown to each other, there are operational issues for distributing solar power. The proposed tool allows missing information about the DERs in the transmission and distribution systems to be exchanged. The prototype can eliminate potential operational issues for distributing solar power, including blackouts, voltage instability, and shorter life spans.

The CReST-VCT is the only tool that has been simulated successfully on a full-scale utility model, the PNNL research team reports.

The grid-dy demands

PNNL researchers say renewable energy will play a more important role worldwide because solar power is becoming more affordable while electricity costs continue to rise. Additionally, there are tighter requirements for providing sustainable power. Notably, California’s Renewables Portfolio Standard requires half of the electricity sales be sources from renewable sources like solar, wind, geothermal, and biothermal by 2030. The CReST-VCT tool accommodates the expected solar power demands and provides a way to mitigate power supply interruptions. In the study, CReST-VCT provides voltage support for users in real time.

“The prototype CReST-VCT improves the ability of electricity grid to integrate diverse distributed renewable resources from electricity consumers into common operational assets for managing system reliability, and building resiliency at the grid level,” PNNL senior power system research engineer Xinda Ke said. “The proposed tool will allow customers to consistently deliver reactive power in response to grid needs, maintain power quality, and grid reliability.”

Since the prototype is under development, the next step is to test CReST-VCT in the field and then to market it commercially, Ke said. The field tests will be offered to local solar farms that can use the tool in realistic conditions.


About PNNL

Pacific Northwest National Laboratory draws on its distinguishing strengths in chemistry, Earth sciences, biology and data science to advance scientific knowledge and address challenges in sustainable energy and national security. Founded in 1965, PNNL is operated by Battelle for the Department of Energy’s Office of Science, which is the single largest supporter of basic research in the physical sciences in the United States. DOE’s Office of Science is working to address some of the most pressing challenges of our time. For more information, visit For more information on PNNL, visit PNNL's News Center. Follow us on Twitter, Facebook, LinkedIn and Instagram.

Published: August 26, 2019


Xinda Ke | Nader Samaan | Jesse Holzer