Conway, Ark., APPA-Funded Study Finds No Harmful Harmonics From Residential Solar

May 4, 2022

by APPA News
May 4, 2022

A study of residential solar power installations by Conway Corp. in Arkansas found that they did not generate harmonic patterns harmful to the public power utility’s electric system.

The study was done with financial support from the American Public Power Association’s Demonstration of Energy & Efficiency Developments (DEED) program.

“Our staff became aware of solar system harmonics while working on a 1-megawatt distributed energy resource solar project in 2019-2020,” Ronson Smith, electric systems engineer at Conway Corp., said via email.

Irregular loads, such as computer and solar power equipment, can create harmonic patterns that interfere with the smooth sine curve of non-linear loads and can damage the distribution grid by causing equipment to overheat or by creating the risk of disruptions or fires.

The utility’s engineers and technicians began to wonder if residential solar installations would also produce harmonic distortion. In particular, they were concerned that a large number of grid-connected solar photovoltaic inverters on a distribution network could cause power quality problems, especially since utility professionals know little about the effects of harmonics-generating equipment when it is widely distributed on a power grid.

For the study, 2021-Case Study: The Presence of Residential-Class Photovoltaic Induced Harmonics on the Distribution Network, Conway Corp. worked closely with E2C Engineering’s Electrical Consulting Engineers and hired two interns from a local university to test the individual harmonic distortion and total harmonic distortion limits on single phase residential houses with solar panels, as well as residential homes with solar panels and LED lighting.

Monitoring equipment collected data at various net metering test sites at varying degrees of magnitude on the electrical network.

The workers measured the harmonics in the same conditions while the solar system was turned off and then, during a similar period under similar conditions, with the solar system turned on to determine whether the solar system was creating harmful harmonics.

“We found that the harmonics generated are within the limits of the national standards such as IEEE-519 no matter the size PV solar system installed,” the utility said in its DEED report.

More specifically, the study showed that the typical total voltage distortion level from a house with a solar system was around 1.5 percent while the same house without the solar system connected had total voltage distortion of about 1.3 percent.

APPA’s DEED program awarded $45,520 to Conway Corp. on Oct. 2, 2020, and the project concluded on March 31, 2022. Conway Corp. contributed $71,531 to the cost of the project.

“This study will be a foundational building block for our knowledge and approach to power quality related to residential loads, as well as solar projects in general,” and it “will serve as a template for other possible power quality studies if needed in the future,” Smith said.

Conway is a quickly-growing city where more and more homes are installing solar power systems. While the utility does not have any current plans to make any changes to its net metering program based on the study results, it said it would continue to monitor the harmonics produced in different circumstances, as well as the harmonics from existing and new solar farms.

The data and analysis that came out of the study “will be helpful going forward with planning and operations,” Smith said. “It also enhanced the staffs’ understanding of net metering, solar power, and power quality.” And, Smith said, “we were able to engage local university students with a valuable internship experience at a municipal utility.”

The APPA-funded study will also provide other utilities with insight into the operational characteristics of residential solar, Smith said. “It could also give them a leg up on data and analysis strategies for similar challenges they may encounter in their own parts of the power grid.”