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Energy Currents
A Blog by Enerdynamics

Running a Grid with High Penetrations of DERs: It’s a Whole Different Animal

by Bob Shively, Enerdynamics President and Lead Facilitator

In most regions, distributed energy resources (DERs)[1] behind the customer meter are simply treated as “negative load.” This means transmission and distribution system operators simply attempt to adjust their load curve forecasts to account for any “loss of load” due to DERs rather than separately forecasting DERs as a supply resource.  

While this may work fine when penetrations of DERs remain low, it will become problematic for transmission and distribution system operations as penetrations grow. A few regions in the U.S. are already experiencing significant and growing penetrations of DERs. For instance, in California the capacity of DERs has already exceeded 10% of system peak demand, and this is expected to grow to 20% in the next decade. Portions of Hawaii have seen even more extreme penetration levels.

In many other regions with lower penetrations, now is the time to get ahead of the curve and prepare both transmission and distribution operators, planners, and designers for a changing future. To prepare, it is important to understand the significant differences between today’s transmission distribution systems. This is important because limitations on the distribution system including lack of visibility, control, situational awareness, and forecasting capabilities will make integrating DERs significantly challenging for those familiar with the more robust tools available on the transmission grid.

Forecast growth of DERs:

Forecast growth of DERs

Source: Distributed Energy Resources  – Technical Considerations for the Bulk Power System FERC Staff Report, February 2018

Key Contrasts Between Transmission and Distribution

The following table lays out key differences between the transmission and distribution systems:

Growing Penetrations of DERs Create Challenges

As you may have concluded from the above table, once DERs grow enough to be more than just a minimal load modifier, transmission and distribution operators, planners, and designers will need to develop and implement new tools and procedures to ensure a reliable grid.  Now is the time for utilities and system operators throughout North America to begin piloting and implementing these so that they will be prepared when large amounts of DERs begin appearing on their grids.


[1]Distributed energy resources (DERs) refer to demand side management, distributed generation, storage, and microgrid resources that are connected to the distribution grid.  DERs may be connected directly to the distribution system or may be located behind a customer meter.  In this discussion, we will only consider DERs located behind a customer meter.  Some consider electric vehicles (EVs) to be a fourth DER, but we consider them to be a type of load that offers demand side management capabilities through control of charging.

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DER , Distributed Energy Resources , Demand Side Manangement ,