Solar PV’s intermittency, in combination with other factors, leads to voltage variability on distribution feeders, yet utilities have an obligation to maintain voltage within 114 to 126 volts all along those lines to meet ANSI standards. Voltage variability triggers the operation of electro-mechanical devices designed for voltage regulation (and that act based on voltage changes, not timers) – from load tap changers (LTCs) at the substation, to voltage regulators out on the feeder – far more frequently than intended by their original design. In turn, that higher number of operations dramatically shortens those devices’ lifecycles, without necessarily resolving the variability, leading to unanticipated costs and a search for mitigating technologies. 

This domino effect of high-penetration solar PV on voltage variability and voltage regulation devices’ reduced lifecycles has been identified and is being addressed at San Diego Gas & Electric (SDG&E) in Southern California and Arizona Public Service (APS) in central Arizona. Yet there’s reason to believe these effects are also taking place at utilities that simply aren’t examining feeder voltage data in highly granular form and remain unaware of the issue.

 

In any case, the high-penetration of solar PV – aided by federal and state policies and the declining cost of PV panels – and its aforementioned effects is a nascent trend that will inevitably become more widespread in the United States. It behooves utilities to understand and anticipate these impacts prior to addressing the symptoms, because many factors affect the selection and application of mitigating technologies. While the effects may be generalized, the solutions and their precise applications are likely to be specific to each utility. (It’s worth noting that the trend is already commonplace in Europe, where the policy framework that encourages high-penetration of solar PV also requires inverters that provide reactive power compensation.)

 

The search for mitigating technologies ranges from the conventional, such as re-sizing feeder lines and installing dynamic VAR (Volt-Ampere Reactive) devices, to the unconventional, which includes energy storage and the application of power electronics to technologies that today rely on electro-mechanical means of operation. In fact, the overall subject highlights why, in my view, the currently separate disciplines of power electronics and power system automation ought to be integrated.