Where Are We Going? Two experts weigh in on the effect of DERs and EVs on PQ

By Richard P. Bingham | Jun 14, 2024
In business as in life, it is helpful to plan for the future by learning from the past. The power quality industry is no exception. 

In business as in life, it is helpful to plan for the future by learning from the past. The power quality industry is no exception. 

Instrument companies and practitioners in the PQ monitoring and troubleshooting business must focus on moving forward. In my May column, I explored how changes in the supply and use of electricity affected the power quality. Now let’s consider how monitoring and analysis of PQ data has been changing and where it seems to be heading.

Problems with DERs

To dive into this topic, I enlisted the assistance of two long-time friends, colleagues and well-known experts in the power quality world. I posed the question from last month’s article to them: Have you seen a negative effect from the deployment of distributed energy resources (DERs), specifically on photovoltaic (solar) panels and wind turbines? 

Dave Mueller, vice president of energy systems studies at EnerNex, Knoxville, Tenn., has expertise in conducting PQ studies on large-megawatt DER sites and working with utilities on solving grid PQ problems. He has seen some isolated incidents, such as harmonic resonance at a wind farm, but from his perspective, the higher-source impedance issue raised by some hasn’t made a significant impact on grid stability, so far. 

Bruce Lonie entered the power quality realm over 40 years ago as one of the founders of PowerCET, a consulting, education and training company that dealt with common (as well as extremely complex) PQ problems. Lonie is still very active in the PQ world, doing troubleshooting and monitoring programs for many different industries as the president of his new company, POWERetc Corp., Santa Clara, Calif.

I posed the same question to Lonie. His observations and studies are in agreement with Mueller’s. He is aware of the concerns that such sources don’t have the inertial stability capabilities that generators in nuclear, hydropower and oil/gas/coal generating systems do. However, the changing loads are a different story. 

Data that Lonie collects from numerous facilities suggest harmonics on the grid or within a facility are not as big a concern as 20–30 years ago. Short-duration sags (6–10 cycles) don’t cause as many problems as in the past, as many electrical equipment manufacturers have made their power supplies more robust to ride through the common utility-source sag caused by a fault on a distribution circuit cleared in 6–10 cycles by the substation breaker.

EV charging brings other issues

The effect of charging electric vehicles on the distribution grid, especially in residential areas, is a significant concern to Lonie and many others in the industry. It was the sole topic of the November/December 2023 issue of IEEE Power and Energy Magazine. 

Before the EV sales began to accelerate, Lonie was contacted to do a study on how the residential distribution system would respond to EV charging requirements. A typical situation is a pole-mounted transformer that takes 13 kilovolts or similar to 120/240V to four houses. One Level 2 EV charger would probably be OK, but it is unlikely that even two EVs could be supported. Electric demand from Level 2 chargers is 2–4 times the typical demand of the household. Multiple Level 1 chargers on the same transformer are feasible, but most people don’t want to wait overnight to charge their vehicles. 

It turns out that the 10-vehicle public charging stations also can’t be fully electrically supported in many cases and use time-­division-multiplexing to swap the power between them to appear to be servicing the chargers all at the same time. A similar technique is used in some residential chargers with the HVAC system to keep the current at sustainable levels.

Another frequent problem is one that has been the topic of several recent articles and has generated a number of reader calls: LED lighting. The power supplies in LED bulbs or multiple LED fixtures are often improperly designed by some manufacturers. 

Lonie has also seen problems with AFCI breakers tripping, as discussed in a recent article (see “Follow the Current,” ELECTRICAL CONTRACTOR, October 2023). He recommends using ferrite cores at the point of common coupling to keep the high-frequency noise (100 kHz) from getting into the electrical system. 

The second question: How has the PQ monitoring instrumentation evolved, and where is it heading? One trend is more affordable instruments, which would make it more practical for electrical contractors to get involved in PQ monitoring programs. More on this topic in next month’s article!

About The Author

BINGHAM, a contributing editor for power quality, can be reached at 908.499.5321.





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