As more distributed energy resources (DER) — primarily solar — are connected to grids, the equipment that makes it all work safely and reliably is under increasing stress. Compounding this, much of this equipment — conductors, transformers, relays, breakers, etc. — is reaching or even beyond its intended end of life.
As solar generation is installed in distributed locations, traditional planning and grid management assumptions are being challenged. Additionally, increased load in traditionally off-peak times from electric vehicle (EV) charging is adding complexity. Bidirectional power flows on aging infrastructure are causing thermal overload of the primary conductors farthest from the source station, limiting the hosting capabilities of the lines.
Increasing Complexity
For many decades, electric distribution grids could be designed and managed with a great deal of predictability. Historically, most distribution grids have been configured in a radial pattern, with circuits of power lines originating at distribution substations. Grid planners were able to assume that power would flow predictably one way over the lines and that voltage would decrease as it moved farther away from the substation. In this model, transformers and other equipment would cool overnight as load could be expected to decrease.
Now, as new DER sources are connected to the grid, those assumptions are no longer as valid. Voltage will be higher near a source of solar generation, and this power is likely to fluctuate multiple times each day as cloud cover and other factors come into play. Further, EV charging shifts demand from the more traditional load curves.
As the penetration level of DER rises, it causes a couple of issues that potentially lead to grid instability. The first is that voltage levels are increasing beyond the limits set by safety codes and standards. When power reaches the meter at homes or businesses, voltage levels must be consistent to be sure all mechanical systems, appliances, motors and devices are not damaged. Voltage regulation is now increasingly required throughout the distribution grid.
The second issue is that sudden upsurges or losses of solar power can affect frequency of the alternating current, creating power quality issues. These sudden fluctuations can knock power out of phase.
Grid planners increasingly must assume that power supply and load can appear anywhere, requiring protective devices and voltage settings to be adaptive to fluctuations that can sometimes move up to 100 times a day on a single circuit. Phase imbalances can appear and disappear in minutes as sources of DER come online.
Supply Chain Challenges
Of course, many utilities undertaking system upgrades are facing the same supply chain and labor challenges that are slowing projects in many other sectors. For example, a 10-mile distribution system upgrade now underway for one of our clients will take at least eight months to build, but the schedule is further delayed as cable material lead times have increased from eight weeks to roughly 22 weeks, with equipment and components up to six months out. With many thousands of miles of circuits needing upgrades, this pace will certainly become problematic as many distribution grid sections already are facing stress.
The obvious solution will be a staged approach, with projects addressing the most urgent needs first and including upgrades that will enable system planners to anticipate and manage sectors that are likely to experience the most DER connections and load growth.
As utilities grapple with the surge in needed upgrades for both transmission and distribution grids, some adjustments in filings for regulatory approvals for large capital programs will be needed.
Thinking Long Term
The need for a broader, holistic planning approach is gaining momentum as more utilities begin to realize the full scope of today’s challenges. Still, these long-term planning needs are sometimes taking a back seat to other priorities.
For one Midwest utility currently undergoing a large capital program to harden existing distribution assets against severe weather impacts, the budget does not allow capacity additions that could truly prepare this grid for the future. Though the program will reduce duration and number of customers impacted by outages, the grid will be ill-prepared for DER connections and the inevitable increase in EV charging demand. In order to alleviate issues like these, utilities will need to work closely across departments and functions, communicating clearly with their regulators about the relatedness of various in-flight programs.
As grid modernization efforts ramp up, wireless and broadband telecommunications will increasingly become the critical communications link. Billions of dollars in funding is now available under the Infrastructure Investment & Jobs Act to help utilities get started.