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Sol-Ark 15K AC coupled setup to reduce grid supplied power

M

Msg822

New Member
Joined
Dec 25, 2021
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14
I'm about a day away from starting up a new 15K installation and am curious about what the right configuration should be to achieve my goals (see below). Any thoughts from experienced Sol-Ark users is greatly appreciated.

GOALS
PRIMARY: Use as little grid power as possible, and use solar when available as source for topping up the batteries and running household electrical
SECONDARY: Have enough battery backup to power critical loads for 24 hours (typical critical load for 24 hours is approximately 10kW)
TERTIARY: Generate income/credit from utility by selling power back to the grid

MY SETUP:
  • Sol-Ark 15K inverter
  • 15kW of Signature Solar EG4 LL batteries (3 batteries in a cabinet, 48V, 300AH),
  • Load-side AC coupled solar of 7.9kW connected to Sol-Ark thru a 100amp subpanel that is connected to the 200amp main breaker panel (diagram 4 in Sol-Ark manual). I cannot direct connect from panels to Sol-ark because the Fronius inverter is in a barn a long way from the main panel, so I have to AC couple as described
  • Backup PTO (from tractor) generator connected to the Sol-Ark thru the GEN connection
Thanks
 
So you have no DC coupled panels, just AC
Do you have a net metering agreement? 1:1, .2:1 ect.
What is your evening load? 300Ah at 80% may be a little low if you want to cover your loads the whole night. I have to TOU my battery power to make it last till morning and I have a 720 Ah bank.
 
Bottom of page 37 of manual to make batteries 2nd priority for power (time of use settings).

Be careful about battery charge level when grid down. You need some margin to dump excess production for a few seconds until the solar can be turned off.
 
I am not 100% on this, but I was under the impression that with solarks, there was a dc/ac ratio for panels that was recommended. You may want to check with solark to make sure its aok to have no dc coupled solar panels.
 
mgdean said:
So you have no DC coupled panels, just AC
Do you have a net metering agreement? 1:1, .2:1 ect.
What is your evening load? 300Ah at 80% may be a little low if you want to cover your loads the whole night. I have to TOU my battery power to make it last till morning and I have a 720 Ah bank.
Click to expand...
Just AC coupled, connected to the Main panel (not the GEN panel on the Sol-Ark), My net metering agreement is 1:1, Average nightime use is very modest as heat is wood, estimated at between 6 and 10 kW.
 
DIYrich said:
Bottom of page 37 of manual to make batteries 2nd priority for power (time of use settings).

Be careful about battery charge level when grid down. You need some margin to dump excess production for a few seconds until the solar can be turned off.
Click to expand...
Good info. Thanks
 
Msg822 said:
Just AC coupled, connected to the Main panel (not the GEN panel on the Sol-Ark)
Click to expand...
When you say connected to your main panel, do you mean the sol ark or main electrical panel? If you are not bringing your ac coupled through your Gen breaker are you bringing it in through your grid breaker? To the point of balancing AC couple load with DC, I thought any AC coupled energy goes to Grid with the Sol Ark, but may be wrong
 
mgdean said:
When you say connected to your main panel, do you mean the sol ark or main electrical panel? If you are not bringing your ac coupled through your Gen breaker are you bringing it in through your grid breaker? To the point of balancing AC couple load with DC, I thought any AC coupled energy goes to Grid with the Sol Ark, but may be wrong
Click to expand...
PV from array goes to Fronius inverter, converts to AC and goes to 100 amp subpanel via a breaker in the panel, then from 100 amp subpanel to the 200 amp main breaker panel. The 100 amp subpanel gets AC input from BOTH the 200 amp main AND when the sun is shining, from the PV array. This subpanel also powers other equipment in or near the barn--lights, tools, EV charger, etc.
 
GuyG said:
I think Sol-Ark discourages, maybe even prohibits, using both of these AC sources simultaneously. Maybe it’s too many waves to synch up, idk.
Click to expand...
You are correct. If you look at their wiring diagram they for AC coupling on the load side, they state "Do not use" for the generator input. The issue is that if PV inverters are outputting more power than your loads, the PV inverters will attempt to back feed the generator. The work around for this is to use a 4 pole contactor with 2 NO and 2 NC contacts. Place the 2 NC poles inline with the PV and the generator inline with the NO. Use a contactor with a 240 V AC coil. Use the generator line side to power the coil. The contactor should be sized to handle 125% of your max PV, so 40 amps should be sufficient.

So when the generator is powered up, it will energize the contactor. This will disconnect the PV and connect the generator. . This is fool proof, but the generator and and PV inverter would need to be at the same location for this to work. It sounds like you don't have this. You could just turn the PV off before turning the generator on, but if you forget? Also, you could never do a generator auto start without some type of interlock.

One might think that there is fancy electronics in the inverter that manages the flow of power between the various components that are AC coupled. This isn't the case. Basically there is an AC bus and breakers. The only thing the inverter can control is the power going to and from the battery. So they can limit the power pulled from the generator by controlling the battery charge rate. The generator must cover 100% of the loads first. Then the leftover generator capacity can then be used to charge the battery. The inverter has not way to control the power that would flow between the PV inverter and the generator. Some inverters have a generator support mode where the inverter can supplement the generator to handle large load peaks, but it basically still controlling generator load by controlling battery charge / discharge.

The other issue here as stated by some other people is that AC coupled the battery inverters have limited control over the PV inverters. It can adjust their output by frequency shifting. This means when there is a sudden reduction in load or increase in PV, the battery inverter must absorb that load and send the power to the battery. If the battery is full, you have a problem. This is why Sol Ark recommends a 50 50 mix of AC and DC. The MPPT chargers can respond instantly to changing conditions. They will never overcharge the battery. Now all this will operate perfectly fine when you are grid connected, but when off grid AC coupling frequency shifting takes time to kick in. Until it does there is 158 amps of DC that the batteries need to absorb. As batteries get more full, they can absorb less current. Since you never know when a power failure might occur, you can't keep your batteries too full.

I have an AC coupled system. So far I can't get it to produce power off grid. It is basically a giant UPS. I can charge from a generator, but the inverters won't come on and stay on. Enphase IQ8+ don't seem to work off grid unless you pair them with the full Enphase battery system. They might work with the correct grid profile, but so far I haven't found one that works. I got the "Latest Greatest" assuming they would work better, but apparently the older micros (the ones they made before they were selling batteries) work better off grid. I'm sure they aren't deliberately making it so if you have Enphase micros, you can only use Enphase batteries, right?
 
Msg822 said:
PV from array goes to Fronius inverter, converts to AC and goes to 100 amp subpanel via a breaker in the panel, then from 100 amp subpanel to the 200 amp main breaker panel. The 100 amp subpanel gets AC input from BOTH the 200 amp main AND when the sun is shining, from the PV array. This subpanel also powers other equipment in or near the barn--lights, tools, EV charger, etc.
Click to expand...
You have an issue with this configuration. The problem is with the panel buses. You have PV rated at 7900 watts. That is 32.9 amps. For a continuous load your breaker and wire should be sized for 125%. So you could probably use a 40 amp breaker. The problem then is that your panel allows 100 amps from the main breaker and 40 amps from the PV breaker. 140 amps is too much for a 100 amp bus. Now as a practical matter if you have only a few small loads on the 100 amp panel, you would probably won't burn anything down.

You mention the fact that you have an EV charger on this panel, and this is a high wattage continuous load. The correct solution would be to upgrade this sub panel to a 200 amp panel. You would still feed the new panel with a 100 amp breaker from the main panel. So the total power into the sub panel couldn't exceed 140 watts. The bus in the 200 amp panel will easily handle that. Some of the current generated by the PV inverters can be consumed right on the subpanel. So if your PV is generating 25 amps and your EV charger is using 40 amps, then the sub panel will draw 15 amps from the main panel.

You also need to consider the back feed into your 200 amp main panel. I'm not an electrician so don't take my word for this. I think you are OK, on this one. One thing you should do is place the breaker feeding the sub panel on the opposite end from the main breaker. So if your loads do exceed 48,000 watts on the main panel the breakers in the middle will be drawing some current from both ends of the bus and the overall current flowing through the bus is reduced. The code allows for a 20% overrating on the bus when you use this configuration. The maximum back feed should be the 32.9 amps that your PV can generate. You should use the rating of the PV Inverter for this. Often the solar panel watts will be higher than the PV inverter watts. The problem could be that if the sub panel is back feeding the main panel is the inspector only going to look at the size breakers connecting the panel and sub panel together or will they look at the PV breaker which will limit the back feed.

It would be unusual for a typical house to actually exceed the 48,000 watt limit of the main breaker, but you still want to comply with the code. I believe that insurance company may not have to cover fires resulting from shoddy DIY non-code compliant electrical work.
 
Last edited:
wheisenburg said:
You have an issue with this configuration. The problem is with the panel buses. You have PV rated at 7900 watts. That is 32.9 amps. For a continuous load your breaker and wire should be sized for 125%. So you could probably use a 40 amp breaker. The problem then is that your panel allows 100 amps from the main breaker and 40 amps from the PV breaker. 140 amps is too much for a 100 amp bus. Now as a practical matter if you have only a few small loads on the 100 amp panel, you would probably won't burn anything down.

You mention the fact that you have an EV charger on this panel, and this is a high wattage continuous load. The correct solution would be to upgrade this sub panel to a 200 amp panel. You would still feed the new panel with a 100 amp breaker from the main panel. So the total power into the sub panel couldn't exceed 140 watts. The bus in the 200 amp panel will easily handle that. Some of the current generated by the PV inverters can be consumed right on the subpanel. So if your PV is generating 25 amps and your EV charger is using 40 amps, then the sub panel will draw 15 amps from the main panel.

You also need to consider the back feed into your 200 amp main panel. I'm not an electrician so don't take my word for this. I think you are OK, on this one. One thing you should do is place the breaker feeding the sub panel on the opposite end from the main breaker. So if your loads do exceed 48,000 watts on the main panel the breakers in the middle will be drawing some current from both ends of the bus and the overall current flowing through the bus is reduced. The code allows for a 20% overrating on the bus when you use this configuration. The maximum back feed should be the 32.9 amps that your PV can generate. You should use the rating of the PV Inverter for this. Often the solar panel watts will be higher than the PV inverter watts. The problem could be that if the sub panel is back feeding the main panel is the inspector only going to look at the size breakers connecting the panel and sub panel together or will they look at the PV breaker which will limit the back feed.

It would be unusual for a typical house to actually exceed the 48,000 watt limit of the main breaker, but you still want to comply with the code. I believe that insurance company may not have to cover fires resulting from shoddy DIY non-code compliant electrical work.
Click to expand...
Excellent advice, thanks. I plan to upgrade the 100 amp subpanel to 200 amp, but keep the feed to the panel from the main at 100amp. As you state, this 200 amp subpanel will address the issue of 140 amps coming in (100/main, 40pv).

As far as the location of the 100 amp breaker on the main breaker that is feeding the subpanel, this is the way it is configured already.
 
wheisenburg said:
You are correct. If you look at their wiring diagram they for AC coupling on the load side, they state "Do not use" for the generator input. The issue is that if PV inverters are outputting more power than your loads, the PV inverters will attempt to back feed the generator. The work around for this is to use a 4 pole contactor with 2 NO and 2 NC contacts. Place the 2 NC poles inline with the PV and the generator inline with the NO. Use a contactor with a 240 V AC coil. Use the generator line side to power the coil. The contactor should be sized to handle 125% of your max PV, so 40 amps should be sufficient.

So when the generator is powered up, it will energize the contactor. This will disconnect the PV and connect the generator. . This is fool proof, but the generator and and PV inverter would need to be at the same location for this to work. It sounds like you don't have this. You could just turn the PV off before turning the generator on, but if you forget? Also, you could never do a generator auto start without some type of interlock.

One might think that there is fancy electronics in the inverter that manages the flow of power between the various components that are AC coupled. This isn't the case. Basically there is an AC bus and breakers. The only thing the inverter can control is the power going to and from the battery. So they can limit the power pulled from the generator by controlling the battery charge rate. The generator must cover 100% of the loads first. Then the leftover generator capacity can then be used to charge the battery. The inverter has not way to control the power that would flow between the PV inverter and the generator. Some inverters have a generator support mode where the inverter can supplement the generator to handle large load peaks, but it basically still controlling generator load by controlling battery charge / discharge.

The other issue here as stated by some other people is that AC coupled the battery inverters have limited control over the PV inverters. It can adjust their output by frequency shifting. This means when there is a sudden reduction in load or increase in PV, the battery inverter must absorb that load and send the power to the battery. If the battery is full, you have a problem. This is why Sol Ark recommends a 50 50 mix of AC and DC. The MPPT chargers can respond instantly to changing conditions. They will never overcharge the battery. Now all this will operate perfectly fine when you are grid connected, but when off grid AC coupling frequency shifting takes time to kick in. Until it does there is 158 amps of DC that the batteries need to absorb. As batteries get more full, they can absorb less current. Since you never know when a power failure might occur, you can't keep your batteries too full.

I have an AC coupled system. So far I can't get it to produce power off grid. It is basically a giant UPS. I can charge from a generator, but the inverters won't come on and stay on. Enphase IQ8+ don't seem to work off grid unless you pair them with the full Enphase battery system. They might work with the correct grid profile, but so far I haven't found one that works. I got the "Latest Greatest" assuming they would work better, but apparently the older micros (the ones they made before they were selling batteries) work better off grid. I'm sure they aren't deliberately making it so if you have Enphase micros, you can only use Enphase batteries, right?
Click to expand...
At some point I'm going to bite the bullet and decommission the Fronius inverter, run an additional PV line from the panel so I have 3 MPPTs instead of the current two, and then direct feed DC from the array into the Sol-Ark. That should take care of all of the hassle of dealing with AC coupling. There is already a relay installed that opens the circuit from the PV to the subpanel when the generator is turned on, so the generator can't backfeed to the PV inverter. Frankly, I don't plan to have to use the generator at all in the future, as I'll keep adding battery capacity to cover grid down periods.
 
Msg822 said:
At some point I'm going to bite the bullet and decommission the Fronius inverter, run an additional PV line from the panel so I have 3 MPPTs instead of the current two, and then direct feed DC from the array into the Sol-Ark. That should take care of all of the hassle of dealing with AC coupling. There is already a relay installed that opens the circuit from the PV to the subpanel when the generator is turned on, so the generator can't backfeed to the PV inverter. Frankly, I don't plan to have to use the generator at all in the future, as I'll keep adding battery capacity to cover grid down periods.
Click to expand...
I suppose it depends on exactly where you live. 10 months of the year I would have plenty of solar. In Dec and Jan the solar just doesn't produce enough to run my house. Part of the issue is my HOA doesn't want panels on the south roof which faces the street. I have east and west facing panels. In winter especially, south facing panels work better. Also, buying a $2000.00 generator vs another $10,000 in batteries makes sense to me. I would not plan to use a generator frequently, but there may be times when there are several days in a row with weak sun. How many batteries do you buy for a just in case senario?
 
Last edited:
I’m finding out right now. 31 inches of snow on Tuesday and our grid power is down. Batteries down to 42% this AM, but the sun is coming up and solar is starting to recharge them. 15K battery backup seems adequate, as long as someone is available to brush the snow off the PV array.
 
AC coupling on SolArk is best done using Generator input port. This changes the function setup on Gen port so it cannot be used for generator.

AC coupling toughest risk is when grid is down, or you have grid export disallowed, with house consumed large amount of PV generation, then a large house load is switched off. Suddenly there is significant PV excess power that can only be dumped to battery until the frequency shifting reduces PV output to match your loads. Frequency shifting has a slow reaction time and takes several seconds before GT inverter reduces output.

Frequency shifting is not fast enough to react to a sudden PV overload when you switched off a large house load. It can result in inverter damage, or at least an immediate inverter shutdown to protect itself.

Using the generator input on SolArk gives the SolArk the safety out of opening the generator pass-through relay to disconnect from GT inverter if it gets into trouble with too much excess AC coupled PV power to swallow.
 
Last edited:
Msg822 said:
At some point I'm going to bite the bullet and decommission the Fronius inverter, run an additional PV line from the panel so I have 3 MPPTs instead of the current two, and then direct feed DC from the array into the Sol-Ark. That should take care of all of the hassle of dealing with AC coupling. There is already a relay installed that opens the circuit from the PV to the subpanel when the generator is turned on, so the generator can't back feed to the PV inverter. Frankly, I don't plan to have to use the generator at all in the future, as I'll keep adding battery capacity to cover grid down periods.
Click to expand...
I like the simplicity and efficiency of using micro-inverters. I actually have very reliable underground utility power here. So 99.9% of the time I expect to be grid tied. Unfortunately getting my PV to actually work during that 0.1% of the time when the grid is down, is proving troublesome. I'm pretty sure I don't want to go to a full DC coupled system. So for now I'm thinking the best choice is to recharge using a generator and hope Enphase fixes their IQ8s so they work off grid. In a true SHTF scenario, well I guess I'm just SOL.
 
Last edited:
wheisenburg said:
hope Enphase fixes their IQA8s so they work off grid. In a true SHTF scenario, well I guess I'm just SOL.
Click to expand...
I don't think the issue is with Enphase. I have a SolArk with Enphase IQ7s and have the same issue. Previously the IQ7s worked off grid with an Outback Skybox. I am in the process of adding more DC coupled solar to see if that helps the SolArk manage the AC coupling process.
 
wheisenburg said:
I'm pretty sure I don't want to go to a full DC coupled system.
Click to expand...
If your primary use case is supplementing or backfeeding grid you should stick with AC coupling.

PV DC coupling to batteries then having sinewave inverter convert battery power to grid AC, puts a large continuous ripple current on batteries. The batteries are effectively a large filter capacitor for illumination based constant DC PV controller output to convert the smooth PV DC supply current to the sine squared power ripple profile of inverter DC input to AC single-phase output.

It usually has more PV conversion power loss with PV controller efficiency followed by AC inverter efficiency.
 
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