Confused about rapid shut down requirements

[physicsguy]

I am thinking of installing a critical loads subpanel and some battery storage and later maybe some solar to directly charge the batteries. (I already have a grid-tie 3.5kw solar array with micro inverters). Meanwhile, I'll use wall grid AC in battery EPS mode to keep the batteries topped off. The battery (e.g., an EcoFlow Delta Pro) will automatically switch to battery upon grid failure. Here are my questions.
1. Even without new DC solar coupling to the battery, don't firefighters need to be protected from live AC from the battery inverter going thru the subpanel distribution? Do I have to have some kind of labeled shutoff button/switch near the outdoor main panel to disconnect the indoor subpanel's output from any circuits?
2. If I add DC coupled (to the battery only) solar later (roof top or ground mount) do I need some kind of module level rapid shutdown (which if triggered by grid shutdown would seem to defeat the purpose of the whole system) or would a manual DC shutoff switch in some conspicuous location suffice? (I assume I'd still need some kind of shutoff for the AC subpanel output if I needed it for question 1 above.) Thanks for any help.

 

[zanydroid]

1. Even without new DC solar coupling to the battery, don't firefighters need to be protected from live AC from the battery inverter going thru the subpanel distribution? Do I have to have some kind of labeled shutoff button/switch near the outdoor main panel to disconnect the indoor subpanel's output from any circuits?

I know some AHJ require an external shutoff for grid forming batteries, and I wouldn't be surprised if this was standard.

There is probably some rule on the number of throws that you are required to stay under to de-energize the house. I haven't installed a grid forming / emergency power system.

2. If I add DC coupled (to the battery only) solar later (roof top or ground mount) do I need some kind of module level rapid shutdown (which if triggered by grid shutdown would seem to defeat the purpose of the whole system) or would a manual DC shutoff switch in some conspicuous location suffice? (I assume I'd still need some kind of shutoff for the AC subpanel output if I needed it for question 1 above.) Thanks for any help.

Ground mount does not need module level rapid shutdown.

Roof mount needs it for most sane string voltages.

Typically the RSD are connected to something that turns off if the inverter is shut off.

Things are a lot easier with grid tie since inverters are grid-interactive and automatically shutdown. And you can connect the RSD transmitter to the grid.

With equipment that stays up when grid is down you either make the inverter accessible (so that the switches on the inverter can be pressed) or plumb a button to the outside that will trigger the shutdown.

For some anecdotal flavor you can search the forum about some drama related to how the original iterations of 18kpv did not ship with remote button. I don't remember if headers had to be soldered onto some boards by the customer, or if it was just a missing cable.

And on SolArks there is not enough power in the external RSD power supply to start up something as thirsty as a Tigo CCA, which means customer has to provide a second power supply powered either with a DC-DC converter from battery or via AC-DC from the CLP.

As you might imagine dark start needs extra planning if there is an RSD. Since it will be a bad day if you can't power up the RSD because something in the chain broke. At least one forum member here keeps a small standalone UPS just in case the RSD needs to be bootstrapped.

 

[Hedges]

My visible blade knife switch uses 2 poles to isolate PV system from the grid.
I plan to use 3rd pole (3-phase switch) or handle position indicator (add-on microswitch) to perform rapid shutdown. One switch handle to rule them all.
Could potentially also use it to disconnect a load-shed relay for AC output of my battery inverters (which don't have a shutdown function.)

If someone used Lithium BMS with external relay, that could be used for total shutdown.

RSD-keep-alive is typically either an external box powered by 12V, or GT PV inverter powered by its PV strings. So some voltage like 6V needed.
I've contemplated a 12V panel feeding spare MPPT input. Or 12V panel of at least as much current, in series with the HV string that has RSD boxes.
PV feeding voltage regulator could supply stand-alone box.

If only Tigo RSD not optimizer, then just keep-alive not CCA, should be within SolArk's output capability.

 

[physicsguy]

I know some AHJ require an external shutoff for grid forming batteries, and I wouldn't be surprised if this was standard.

There is probably some rule on the number of throws that you are required to stay under to de-energize the house. I haven't installed a grid forming / emergency power system.

Ground mount does not need module level rapid shutdown.

Roof mount needs it for most sane string voltages.

Typically the RSD are connected to something that turns off if the inverter is shut off.

Things are a lot easier with grid tie since inverters are grid-interactive and automatically shutdown. And you can connect the RSD transmitter to the grid.

With equipment that stays up when grid is down you either make the inverter accessible (so that the switches on the inverter can be pressed) or plumb a button to the outside that will trigger the shutdown.

For some anecdotal flavor you can search the forum about some drama related to how the original iterations of 18kpv did not ship with remote button. I don't remember if headers had to be soldered onto some boards by the customer, or if it was just a missing cable.

And on SolArks there is not enough power in the external RSD power supply to start up something as thirsty as a Tigo CCA, which means customer has to provide a second power supply powered either with a DC-DC converter from battery or via AC-DC from the CLP.

As you might imagine dark start needs extra planning if there is an RSD. Since it will be a bad day if you can't power up the RSD because something in the chain broke. At least one forum member here keeps a small standalone UPS just in case the RSD needs to be bootstrapped.

The whole purpose of off-grid solar modules (let's say they are on the roof) connected directly to batteries is to charge them during a long grid failure. So if (module level?) RSDs has to be triggered by a grid shutdown, that would defeat the purpose. Are you sure that off-grid roof mounted solar modules connected only to battery charging inputs have to have automatic RSD devices that are triggered by grid failure?

 

[zanydroid]

The whole purpose of off-grid solar modules (let's say they are on the roof) connected directly to batteries is to charge them during a long grid failure. So if (module level?) RSDs has to be triggered by a grid shutdown, that would defeat the purpose. Are you sure that off-grid roof mounted solar modules connected only to battery charging inputs have to have automatic RSD devices that are triggered by grid failure?

That's not what I said. I realize my prose was poor up top but please take another shot at it. I tried to split it into grid tie and EPS (emergency power system) cases. In the EPS case you can design it to not have this property, and it requires a separate shutoff switch from AC grid interactive trigger. Since grid-interactive (go down when grid goes down) is obviously not what you want. (I also called out that one solution is to put a code compliant Hybrid or off-grid outside -- if it has direct RSD integration the appropriate off switch should turn off the RSD).

 

[zanydroid]

Did you look at a high quality install manual yet? 18kpv or SolArk. It's probably in there.

 

[John.DS99]

Is this still a DIY forum? Have I entered the solar twilight zone? Just kidding.

 

[zanydroid]

EDIT: FWIW this took 2 min to find as a non-SolARk owner... I guess I already had the domain knowledge on what strings to search for.

 

[zanydroid]

Is this still a DIY forum? Have I entered the solar twilight zone? Just kidding.

Huh?

 

[physicsguy]

That's not what I said. I realize my prose was poor up top but please take another shot at it. I tried to split it into grid tie and EPS (emergency power system) cases. In the EPS case you can design it to not have this property, and it requires a separate shutoff switch from AC grid interactive trigger. Since grid-interactive (go down when grid goes down) is obviously not what you want. (I also called out that one solution is to put a code compliant Hybrid or off-grid outside -- if it has direct RSD integration the appropriate off switch should turn off the RSD).

Ok, I guess when you said "with equipment that stays up when the grid is down" you also meant the solar panels for dc charging, and not just the battery inverter and critical loads subpanel. Thanks.

 

[physicsguy]

That's not what I said. I realize my prose was poor up top but please take another shot at it. I tried to split it into grid tie and EPS (emergency power system) cases. In the EPS case you can design it to not have this property, and it requires a separate shutoff switch from AC grid interactive trigger. Since grid-interactive (go down when grid goes down) is obviously not what you want. (I also called out that one solution is to put a code compliant Hybrid or off-grid outside -- if it has direct RSD integration the appropriate off switch should turn off the RSD).

Got it! If I do roof mount, I'll attach the RSD transmitter to the subpanel AC out (thru a DC supply if needed), and then when I hit the outside off button for the subpanel, that will take care of everything. Thanks!

 

[zanydroid]

Got it! If I do roof mount, I'll attach the RSD transmitter to the subpanel AC out (thru a DC supply if needed), and then when I hit the outside off button for the subpanel, that will take care of everything. Thanks!

Awesome.

Here is the thread about the dark start UPS, which integrates into the most impressive home setup I've seen so far. It is a bit extra and overkill but pulling it back 50-66% will probably end up in a solid place for most people.

My experiences finding the right black-start UPS for an off-grid solar system

I would like to share my experiences in finding the right black/dark start UPS for a solar system. It might be helpful for someone to avoid making the same mistakes as me. First, you only need to take care about a dark-start situation if you have some sort of emergency shutdown relays or...

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