Back feed pool subpanel

[BlueMarblePA]

I am planning to have a local company install solar on part of my roof. I am planning on getting the solark 15k, so that I can add more panels via DC inputs myself later. They will pull permits and install the first 12kwatt roof panels.

One question I have is whether I can back feed into a pool subpanel? This is the subpanel. It is fed by a 100amp breaker at my house. I assume because of the 20% rule, I could add a 20amp breaker to feed this subpanel. I am waiting until net metering takes place, but the question I have is how to create a disconnect. If the grid power goes out, how do I prevent the solar power from back feeding down the line?

I was planning to add six panels on a mobile wheeled ground mount near the pool that would be rolled out of the way when the pool is in use. I would plan to do add a small portable mppt and 2000 watt inverter to the pool pump area and then send ac into the subpanel?

Is this completely wrong and unsafe?

 

[RCinFLA]

From the picture I highly doubt that subpanel is a 1000 amp backbone so 1000 amp input breaker would be a violation before talking about PV. I hope you meant 100A main breaker to subpanel.

20% rule means power fed from main panel and power fed from PV cannot exceed 120% of panel backbone rating.

If subpanel backbone is 100 amp panel you could add a 20 amp PV backfeed and that would be 120% maximum input power to panel backbone with a 100 amp main input breaker to subpanel. You also have the 120% that needs to be met in the main panel with the incoming 20 amp PV current from subpanel.

It also does not look like the two black backbone wires coming into subpanel can handle 100 amps. They look like aluminum wire and would have to be #3 gauge copper. #2 aluminum is 90 amps max at 75 degs C.

 

[Redflyer]

Not sure if this helps, but I have a 50 amp breaker for my pool sub. It originally ran Three 2hp pumps, the panel and lights.

I replaced the main pump for a variable speed updated model. The other two pumps never run. The are just for waterfall features (that burn a ton of power for the visual effects).

I plan on pulling the whole thing off the main house panel and put it on the new solar (off grid) sub. I think a 30amp for the one pump and the system requirements should work. Very rarely use the two pool lights too. But if I did, the pool pump would be off in the evening. I have it setup to run early in the morning for around 6 hours.

 

[BlueMarblePA]

From the picture I highly doubt that subpanel is a 1000 amp backbone so 1000 amp input breaker would be a violation before talking about PV. I hope you meant 100A main breaker to subpanel.

20% rule means power fed from main panel and power fed from PV cannot exceed 120% of panel backbone rating.

If subpanel backbone is 100 amp panel you could add a 20 amp PV backfeed and that would be 120% maximum input power to panel backbone with a 100 amp main input breaker to subpanel.

I accidentally added an extra zero to my original post. I corrected it.
Yes. It is a 100amp breaker going to the subpanel. Hence, I am planning for a 20amp breaker with solar feeding it.

Is there a way to disconnect the solar when the grid power goes out?

 

[BlueMarblePA]

Another question I have is how does any inverter at 60hz lock on to the grid frequency? What if the back feed inverter is out of phase with the grid?

 

[timselectric]

Grid-tied inverters are designed to sync up with the grid, so that's not an issue.
They are also designed to shut down, when they don't see the grid. So also not an issue.

 

[BlueMarblePA]

Grid-tied inverters are designed to sync up with the grid, so that's not an issue.
They are also designed to shut down, when they don't see the grid. So also not an issue.

Thank you. This is helpful. I have been playing in the RV/shed world with pure sine wave inverters, but if I am going to grid-tie, I need to get specific grid-tie inverters. Will continue my learning.

 

[SparkyJJO]

If I understand correctly, your SolArk and 12kW array is feeding into your MAIN panel in your house, and this pool sub panel is only coming into play because you're wanting to add a second, smaller array near your pool with its own inverter, correct?

If all you're wanting to do is grid tie this set and have it basically only operate while the grid is up, perhaps some micro inverters would be the way to go on this small extra array. Throw some Chilicon CP-720 micros behind your panels, wire it up, and call it a day. Could even put a 30A 240V genset cord on it if you wanted to make it really modular. Could just unplug it from the socket off your sub panel and move it anywhere you please.

Obviously, look into any legal stuff (permitting, permission to operate from utility, whatever is needed). Power companies don't like getting stuff backfed into the grid without their knowledge and consent for pretty obvious reasons.

Just make sure your mobile array can be tied down somehow in case of high winds. Last thing you want is a windstorm to rip through and smash a bunch of panels all up.