Solar panels connected to subpanel - How does this work to power things on the main panel?

[run-the-joules]

Hey team,

My Tesla solar panels were supposed to be installed earlier this month but were delayed a few weeks so I can get a small roof repair done. I just had a thought regarding how they were/are going to install that I realized I don't quite understand how part of it works, and wanted to figure this out before the install happens.

My main service panel has two slots on it, occupied by a 100-amp dual-pole breaker and a 50-amp dual-pole breaker.

The 50a goes to the roughed-in for my AC/heat pump that will be installed later.

The 100a goes to a subpanel about 20 feet from the main panel, in the garage, which is currently full but the install team intends to replace some of the smaller circuits with tandem breakers or something to that effect, and free up space to connect the PV system.

I can more or less understand that the inverter does some magic with the incoming grid power when connected to the main panel to make the downstream devices feed off of the solar supply, but how the heck is the 50a breaker that feeds the AC going to draw from the subpanel?

Am I just missing something, or did Tesla miss something and I'd have ended up with my HVAC always drawing grid power if I hadn't thought of this?

 

[BrettS]

The short version is that power can flow in both directions. If your solar system is producing more power than the devices in that sub panel are using then power will flow from the sub panel into the main panel and your AC will be able to use solar power. If your solar system is producing more power than all of your loads are using then power will flow from your house back to the grid and will be used by your neighbors.

 

[run-the-joules]

The short version is that power can flow in both directions. If your solar system is producing more power than the devices in that sub panel are using then power will flow from the sub panel into the main panel and your AC will be able to use solar power. If your solar system is producing more power than all of your loads are using then power will flow from your house back to the grid and will be used by your neighbors.

Yeah, I guess I'm just kinda confused on how exactly that works. I've gotta do some reading up on how power actually flows through the system, I had thought that the inverter needed to do some sort of handwaving at the point of the power delivery chain closest to the power company

 

[cwied]

One helpful analogy is to just think of the electrical wires as water pipes. The solar inverter is pumping water into the pipes. If it pumps fast enough that it is generating more water than is being used by all the devices in the house, the excess will flow out to the grid.
If you think about this model, you can see that if both the grid and the solar panels are providing energy to your house it's not very meaningful to say that one device is powered by the grid and another by solar. All that you really can tell is that the total energy from all sources is being used by the combination of your devices in the house. Where the energy that powers a specific device is coming from is unclear.

 

[run-the-joules]

One helpful analogy is to just think of the electrical wires as water pipes. The solar inverter is pumping water into the pipes. If it pumps fast enough that it is generating more water than is being used by all the devices in the house, the excess will flow out to the grid.
If you think about this model, you can see that if both the grid and the solar panels are providing energy to your house it's not very meaningful to say that one device is powered by the grid and another by solar. All that you really can tell is that the total energy from all sources is being used by the combination of your devices in the house. Where the energy that powers a specific device is coming from is unclear.

Right on, that makes sense.