Sol-Ark Whole-Home, how handle Generator stop

[seldon]

I'm planning a system for a utility building with 400A service, following the Sol-Ark 'Whole-Home Generator' diagram on page 51 of the manual (to allow > 19.2kW from the generator), screenshot below. We will require 2x Sol-Ark in parallel to allow for 400A passthrough. The generator will be a Kohler, with their RXT Automatic Transfer Switch.

In this setup, when the Grid goes down, the Sol-Ark will sense grid-down and start the generator when the batteries reach some lower state of charge. The ATS will switch when it senses stable voltage from the generator. This all seems fine.

My question is what happens with the Grid comes back up. The ATS will switch back to Grid, but the Sol-Ark won't know this. Eventually when the batteries reach 95% state of charge the Sol-Ark will stop the generator, but this could be some time after the ATS has switched, meaning the generator is running with effectively no load.

How have others dealt with this?

 

[seldon]

After finding this thread, it may be a better approach: https://diysolarforum.com/threads/sol-ark-with-generator-ats-on-load.83711/

 

[DIYrich]

Put an AC controlled relay on the Gen Start line. Power it from grid before the ATS. When the grid comes back, the switch opens (or closes) and the generator stops.

 

[Bkord]

use the solak relay and the ATS relay in series. Both have to be closed to start the gen but only one needs to be open to stop the generator. Many ATS have multiple relays. But you could always add one like DIYrich said.

 

[dreancestere]

I don't know what kind of disconnect switch is in there. But, be careful of a generator on the Grid terminal. If you're selling power back, the grid goes down and the generator kicks on, if your PV is generating enough power, you'll end up feeding all that power back into the generator (the inverter sees power coming from the grid side (though it's the generator that's producing it), so it keeps selling PV back).

I tried a lower-tier version of your setup and never could figure out how to stop the backfeed to the generator. Had to have my installers move the generator to the GEN input. The ATS is nothing but a glorified, manual switch now. Hopefully, someone smarter than me can help with this.

 

[LyvWyr]

If the sol ark has a built in ats and all loads are powered through the sol ark, get rid of the kohler ats and wire the generator to the gen port of the inverter. Use the 2 wire start diagram for your generator and let the inverter manage the generator.

 

[Bkord]

If the sol ark has a built in ats and all loads are powered through the sol ark, get rid of the kohler ats and wire the generator to the gen port of the inverter. Use the 2 wire start diagram for your generator and let the inverter manage the generator.

I think he wants 200a per solark on gen. I’m not sure if the gen port can handle that much?

 

[dreancestere]

Good point. 90A rated terminal. 80A continuous. From the manual:

"Generators Smaller than 19.2kW → On “GEN” Input
1. ONLY Supports 120/240V Split-Phase generators.
2. 90A rated “GEN” terminal. 80A continuous.
3. A THD (Total Harmonic Distortion) of less than 15% is preferred.

Generators Greater than 19.2kW → On “GRID” Input
1. Supports 220V Single phase, 120/240V Split phase, 120/208V 3-Phase (2 of 3 phases). The correct grid type must be selected before
connecting the generator.
2. Programming “GEN Connect to Grid Input” is required: → Limiter → Other → 🗹 GEN Connect to Grid Input .
3. DO NOT use “Grid Sell” in Off-Grid systems. Potential to damage the generator. Installation of CT sensors on generator lines is
only required if “Peak Shaving” is intended to be used."

EDIT: I just checked my Settings > Battery > Charge setting and even though the manual says the GEN terminal is rated only to 90A (80A continuous), it happily let me set the Gen Charge rate to 100A. I just knocked that down to 80A. If I ever have to use that generator, I'll just be using it to charge up the batteries and run the house from them.

 

[Cmiller]

EDIT: I just checked my Settings > Battery > Charge setting and even though the manual says the GEN terminal is rated only to 90A (80A continuous), it happily let me set the Gen Charge rate to 100A. I just knocked that down to 80A. If I ever have to use that generator, I'll just be using it to charge up the batteries and run the house from them.

That Gen Charge rate setting is the DC amp rate that the Sol-Ark will charge from gen input terminals. 100A x 52V would be 5,200w or roughly 22A at 240V.

@seldon Since you are planning on using 2x 15K inverters, I would recommend using the gen port for the gen. Each inverter can handle 80A of input. This would let you go up to 160A total. 160 x 240V would be 38.4kW. In order to comfortably draw that much you should probably have a 40-45kW rated generator. Do you plan to have one that big?

The ATS issue that you brought up can definitely be taken care of using a relay, as others mentioned. But realistically, I find it hard to believe that you need more gen than what the gen port can handle. And also, the ATS option just plain opens a few cans of worms.

• Stop parameter vs. grid coming back online. (As you brought up.)
• Potential for ATS to switch back to grid out of phase and potentially cause issues in the Sol-Ark's. (Sol-Ark insists that the inverters can detect when it switches, and disconnect quickly enough. But I have yet to hear someone say they did it that way and tested and it works.)
• Potential solar backfeeding to gen. (Again, Sol-Ark insists that the inverters can tell when it's a gen, and won't backfeed.... I question this!)

 

[dreancestere]

That Gen Charge rate setting is the DC amp rate that the Sol-Ark will charge from gen input terminals. 100A x 52V would be 5,200w or roughly 22A at 240V.

I've got to start paying more attention to the voltage differences in different parts of the inverter. I should have thought of that.

Looking at that manual reference to the Grid terminal, for generators less than 19.2kW, it's rated at 80A continuous. So, with 240V coming from the generator, everything matches (80A x 240V = 19.2kW). My batteries (15 cell, not 16 cell) charge at 53.2V. So, the full 80A continuous from the Grid terminal could theoretically push 19,200w / 53.2V = 360A into my batteries. My batteries are rated for 400A, but the 15k inverter maxes the battery charge rate to 275A. So, since the inverter's 275A maximum battery charge rate is less than 1) what the batteries can do, 2) what the Gen terminal can feed to the batteries, and 3) what the grid can feed to the batteries, I guess I'll head back out and change the Settings > Battery > Charge > Gen Charge and Grid Charge settings to both be 275A (assuming I haven't made yet another mistake).

Anyway, thanks for setting that straight.

 

[Cmiller]

Anyway, thanks for setting that straight.

You are welcome! That grid charge and gen charge setpoint can definitely throw you for a loop.

I am in the solar industry, so I work with inverters all the time. I often know, without thinking about it, what the settings "mean" or do, anymore. I'm happy to be of help to other people when I can be.

 

[mikee]

That Gen Charge rate setting is the DC amp rate that the Sol-Ark will charge from gen input terminals. 100A x 52V would be 5,200w or roughly 22A at 240V.

@seldon Since you are planning on using 2x 15K inverters, I would recommend using the gen port for the gen. Each inverter can handle 80A of input. This would let you go up to 160A total. 160 x 240V would be 38.4kW. In order to comfortably draw that much you should probably have a 40-45kW rated generator. Do you plan to have one that big?

The ATS issue that you brought up can definitely be taken care of using a relay, as others mentioned. But realistically, I find it hard to believe that you need more gen than what the gen port can handle. And also, the ATS option just plain opens a few cans of worms.

• Stop parameter vs. grid coming back online. (As you brought up.)
• Potential for ATS to switch back to grid out of phase and potentially cause issues in the Sol-Ark's. (Sol-Ark insists that the inverters can detect when it switches, and disconnect quickly enough. But I have yet to hear someone say they did it that way and tested and it works.)
• Potential solar backfeeding to gen. (Again, Sol-Ark insists that the inverters can tell when it's a gen, and won't backfeed.... I question this!)

I agree that having the ats is a can of worms but I am also in the design stage of a system similar to the the original post. I am an electrical contractor and this is for a customer. Most of the systems I have done are grid tied only so battery systems are relatively new to me, having only done one very basic sol-ark 15 with homegrid battery. I have used sol-arks wiring diagram for whole home generator. It seems like the simple way to shutoff the generator is to have a N.C. relay inline with the 2 wire start that opens when utility power returns. PSP products also has a 2 wire start convertor
( ktws-1 ) that would also integrate with this. I can post my design here, would love to have critique of it, or I can start a new thread. Moderators ? let me know what would be preferred. For back feeding, I think the solark "should" know when the generator is running as it is the one calling for it to run with the 2 wire start. Once it reaches 95% charge it is supposed to shutoff the genset. It also looks like in their install tips page 41 that it needs to be "limited power to load" so I would assume that it won't/can't be net metered. For the ats switching back to utility the KTWS-1 has up to 30 sec delays built in which would (theoretically) allow the inverter to switch to backup mode first and then resync once the ats does switch back to utility.

 

[Cmiller]

For the ats switching back to utility the KTWS-1 has up to 30 sec delays built in which would (theoretically) allow the inverter to switch to backup mode first and then resync once the ats does switch back to utility.

Most transfer switches will delay when switching back to grid. However, once it switches, there is only a slight flicker as they transfer. In other words, there is only milliseconds of "open" time frame. The transfer switch is either on grid or on gen, never in an "off" position. The question is whether the Sol-Ark can "see" the short "open" state during transfer, respond to it, drop voltage to it's contactor ("transfer relay") coil, and have the relay open, all before the transfer switch hits the "grid" side. If not, there is a high risk of the inverter getting hit with an out of phase grid input! This would risk letting the magic smoke out!

During a normal relay disconnect scenario, it doesn't matter how slow that relay opens. The inverter stays sync'd to the grid source until it disconnects. Therefore the opening happens while it is still sync'd.

Some transfer switches wait to transfer back to grid until the gen and grid are sync'd. (They transfer right in a "sync'd" moment, so to speak.) This makes for a very clean transfer. But, I'm pretty sure most ATSs don't worry about being sync'd... So then it's all a gamble of whether or not the gen will be in sync, and if not, how quickly the Sol-Ark is actually able to respond.