Where is the Power Going

In this episode, Where is the Power Going? . . .

Have you ever wondered where the electricity generated by a PhotoVoltaic (PV) Solar system goes when the system is shut down? Stay tuned for the answer.

On Thursday, February 16, 2023, about 22 attendees from the Cenergy Power staff attended a carport system project tour of a One MegaWatt-DC (1MW-DC) PV solar array at Long Beach Memorial Hospital, in Long Beach, CA. hosted by Eilroma Sarkis, Cenergy's Project Manager. For many, this was the first time visiting a commercial solar installation. As expected, there were a lot of questions from the guests.

To get an idea of the scale of this project, each carport section spans about 45 feet in width and is 200 feet long. There are five such arrays. The tour lasted about one hour; our host explained every aspect of system construction; module layout, system orientation, electrical components, wiring, inverters, shutdown panel boards, interconnection to the hospitals' main electrical service, system monitoring, electrical grounding, and much more. Click the YouTube link to view a few attendees' photos, reactions, and comments.

However, one nagging question kept coming to my mind: "We are standing under a connected 648.72 kW-DC PV Solar Array that is generating DC Power. The system is turned off. Where is the electricity being generated by the modules going?

After discussions with one of our electrical engineers and studying a few physics videos on YouTube, I was reminded that PV solar modules are passive devices. This means the over 1,224 - 530 Watt PV modules only produce a current (electrical flow) when connected to a load. Translation; A load occurs when Power is requested by lighting in the hospital, air conditioning, possible battery storage, or any other on-demand electricity requirements.

Since this system's inverters were turned off, this is considered an open circuit. The 10-50kW string inverters were not fulfilling the demand for a load. Therefore no power (voltage x current) was generated by the system.

However, another fundamental principle applies, the "Conservation of Energy." During a shutdown, the modules will continue to convert sunlight into DC electricity. The electricity generated by the PV modules will dissipate as heat.

The system will simply "idle" until turned on, then the inverters convert the DC electricity into AC electricity that can be used or stored. It's important to note that even when a PV solar system is turned off, there can still be some residual voltage, which can be dangerous. Therefore, it's necessary to follow proper safety procedures when working on or around a PV solar system, even when it is turned off.

Now you know the rest of the story!

I'm Patrick Ball; thanks for listening. See you in the next episode.

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