Question About Preventing Grid Backfeed

[timselectric]

There is no blending of grid power when using a battery charger

It does blend.
The loads are split among whatever sources are available.
In the morning, when the sun is rising.
My loads would be completely powered from the charger.
As solar production ramps up, the loads gradually switch to being partially fed from both, and then completely fed from solar.

 

[zanydroid]

It does blend.

It is blending in DC which is fine

What settings do you put on the chargeverter to encourage the inverter to pull from the solar and guarantee 0W when MPPT can supply the whole load?

 

[timselectric]

It is blending in DC which is fine

What settings do you put on the chargeverter to encourage the inverter to pull from the solar and guarantee 0W when MPPT can supply the whole load?

48v

 

[dougbert]

Don’t install ESS Assistant, don’t use PowerAssist.
No feedback, no problem. Great UPS solution.

that is Option 1

Option 2 is to (charge batteries/run house loads) when needed from the grid is by using a Chargeverter. Only the CV is connected to the grid with no grid connection to the inverter (breaker off). There is no Netmetering

 

[dougbert]

Not without double conversion, no.

My system is off grid.
No connection to the grid, except for a charger.
I can blend grid and inverter (battery and/ or solar) , when needed.

same here - I CAN connect the grid to the XW Pro if needed, but my normal operation is, is that that breaker is OFF. I don't netmeter, don't want to, too much trouble to me

 

[timselectric]

same here - I CAN connect the grid the XW Pro if needed, but my normal operation is, is that that breaker is OFF. I don't netmeter, don't want to, too much trouble to me

I don't even have a connection or breaker to turn on. lol

 

[dougbert]

I don't even have a connection or breaker to turn on. lol

I installed the breaker back BEFORE the CV came out. Once it did come to market and I learned about it, I just flipped the breaker - my lol as well

 

[zanydroid]

I’m not sure double conversion will reliably “blend” in the expected sense.

It will guarantee that there is zero hiccup if the grid has to provide a shortfall.

If you set 5kW charge rate on a 48V 100Ah battery you should reliably be able to feed a 10kW load while battery floats at 100%, however there is no guarantee how battery at a lower SoC will be maintained.

I think the output of the charger needs to be regulated to be able to control how Solar, Battery, and Charger distribute the work among themselves. That is needed for paralleled DC power supplies and parallel inverters (IE they have analog or digital communications cables)

Anyway I hope the answer here for original post is that 1741 off grid inverters aren’t allowed to backfeed, or the manuals make it clear which modes are parallel/require interconnection agreement. And documenting the pre purchase questions confirming this with a reputable vendor would hedge against issues.

 

[timselectric]

I’m not sure double conversion will reliably “blend” in the expected sense.

It worked perfectly for me, for the entire month of January.
Which was when the solar production couldn't cover everything.
Solar took care of everything it could, and the charger covered everything else.

 

[timselectric]

I think the output of the charger needs to be regulated to be able to control how Solar, Battery, and Charger distribute the work among themselves.

Voltage is the only communication necessary.
Whichever is providing the higher voltage, does the most work.

 

[cs1234]

I think the output of the charger needs to be regulated to be able to control how Solar, Battery, and Charger distribute the work among themselves. That is needed for paralleled DC power supplies and parallel inverters (IE they have analog or digital communications cables)

He's doing it by simple voltage though? He just sets the chargeverter to a lower static voltage (or at least doesn't let it go as high) as his other chargers. Only when his DC bus dips below that voltage setting does the chargeverter kick anything into the mix. If anything with a higher voltage comes along, it gets to do the lifting unless a load drops it back down below the chargeverter set point.

 

[cs1234]

Voltage is the only communication necessary.
Whichever is providing the higher voltage, does the most work.

Don't even need a fancy closed loop! It's like some type of weird laws governing electricity handle it.

 

[zanydroid]

Voltage is the only communication necessary.
Whichever is providing the higher voltage, does the most work.

Got it. What is different about this from other cases of paralleling power supplies, because I’m familiar with somewhat complex articles on the matter, EG

Learn to connect power supplies in parallel for higher current output. - Technical Support Knowledge Center Open

 

[cs1234]

Got it. What is different about this from other cases of paralleling power supplies, because I’m familiar with somewhat complex articles on the matter, EG

Learn to connect power supplies in parallel for higher current output. - Technical Support Knowledge Center Open

I would guess they are trying to maintain a more even distribution of current, stable voltage and quality of electricity between all those power supplies than a chargeverter and the solar chargers on @timselectric system can provide with simple voltage set points.

 

[timselectric]

Got it. What is different about this from other cases of paralleling power supplies,

The battery being in the system.
It's the buffer of all sources.
And keeps the voltage stable.

 

[zanydroid]

Ok. I still don’t see how fixed voltage control alone can guarantee EG holding the SOC at a particular level or not over drawing grid if it isn’t needed.

Let’s suppose a 6000XP with 6kW-AC inverter and 6kW CC setting on charger

Imagine 80% SoC, what stops the charger from going to full CC current when the load is smaller than the available solar. Most people would not want that. I believe your personal setup has some kind of disconnect switch to turn it off in states like this.

If a disconnect switch on the charger is present to manage SoC. I can see how we can stably have 6kW of loads. But I don’t see how we can use double conversion grid assist to do 12kW of loads.

The double conversion UPS folks would keep their loads below the 6kW that the inverter can carry on its own.

 

[Brucey]

Ok. I still don’t see how fixed voltage control alone can guarantee EG holding the SOC at a particular level or not over drawing grid if it isn’t needed.

Let’s suppose a 6000XP with 6kW-AC inverter and 6kW CC setting on charger

Imagine 80% SoC, what stops the charger from going to full CC current when the load is smaller than the available solar. Most people would not want that. I believe your personal setup has some kind of disconnect switch to turn it off in states like this.

If a disconnect switch on the charger is present to manage SoC. I can see how we can stably have 6kW of loads. But I don’t see how we can use double conversion grid assist to do 12kW of loads.

The double conversion UPS folks would keep their loads below the 6kW that the inverter can carry on its own.

Tim has the charger voltage threshold set to 48V. It will only start supplying power when his battery is down to 48V and below. During normal solar conditions voltage would be above that threshold.

 

[timselectric]

Ok. I still don’t see how fixed voltage control alone can guarantee EG holding the SOC at a particular level or not over drawing grid if it isn’t needed.

Let’s suppose a 6000XP with 6kW-AC inverter and 6kW CC setting on charger

Imagine 80% SoC, what stops the charger from going to full CC current when the load is smaller than the available solar. Most people would not want that. I believe your personal setup has some kind of disconnect switch to turn it off in states like this.

If a disconnect switch on the charger is present to manage SoC. I can see how we can stably have 6kW of loads. But I don’t see how we can use double conversion grid assist to do 12kW of loads.

The double conversion UPS folks would keep their loads below the 6kW that the inverter can carry on its own.

Has nothing to do with SOC.
Voltage is the only factor.
The charger is set to 48v. If the voltage falls below that, the charger adds whatever current is needed to float at 48v.
If the voltage goes above 48v, it just sits idle , providing zero current.
The SCC is set to a much higher voltage. When producing, it takes over.

 

[zanydroid]

Tim has the charger voltage threshold set to 48V. It will only start supplying power when his battery is down to 48V and below. During normal solar conditions voltage would be above that threshold.

Right, so that to me sounds like it is not designed to grid assist. I imagine the threshold is picked to trigger the charger if the battery sags beyond a certain point.

I messed up the parameters in my previous message, let’s pretend there’s a second 6000XP to give 12kW-AC. To reliably support a load up to 12kW the battery has to be able to supply 250A.

While a grid assist 6000W inverter with 50a bypass can get away with 125A battery, pulling 6 kW from grid

 

[ChrisG]

Has nothing to do with SOC.
Voltage is the only factor.
The charger is set to 48v. If the voltage falls below that, the charger adds whatever current is needed to float at 48v.
If the voltage goes above 48v, it just sits idle , providing zero current.
The SCC is set to a much higher voltage. When producing, it takes over.

@timselectric 48v is pretty low, what if there is a grid outage where CV can’t charge with battery already that low. Assume other manual efforts to supply power?

 

[timselectric]

@timselectric 48v is pretty low, what if there is a grid outage where CV can’t charge with battery already that low. Assume other manual efforts to supply power?

48v still leaves me plenty of capacity to survive for a while.
Especially if I conserve power.
Grid is just the simplest backup option. So, it's currently the first backup.
I can have a generator step in, if the grid is down. But, it would be more efficient to run the generator at 70% load. So, it's the second backup option. Because it would work best with a wider operating window, instead of just carrying the minimum loads (floating).

 

[Brucey]

Right, so that to me sounds like it is not designed to grid assist. I imagine the threshold is picked to trigger the charger if the battery sags beyond a certain point.

I messed up the parameters in my previous message, let’s pretend there’s a second 6000XP to give 12kW-AC. To reliably support a load up to 12kW the battery has to be able to supply 250A.

While a grid assist 6000W inverter with 50a bypass can get away with 125A battery, pulling 6 kW from grid

Yes so if his bank is down to 48V then he could potentially be limited to an output of 100A to the inverter, assuming no battery contribution. Solution is more chargeverters if such a load needs to be supported during grid down.

 

[timselectric]

Right, so that to me sounds like it is not designed to grid assist.

It wasn't designed for grid assist, it was designed for charging.
But, it works perfectly for this purpose.

I imagine the threshold is picked to trigger the charger if the battery sags beyond a certain point.

Exactly

I messed up the parameters in my previous message, let’s pretend there’s a second 6000XP to give 12kW-AC. To reliably support a load up to 12kW the battery has to be able to supply 250A.

While a grid assist 6000W inverter with 50a bypass can get away with 125A battery, pulling 6 kW from grid

It doesn't have anything to do with the size of the battery. (Assuming that it's not wildly undersized for the system)
The charger just needs to be large enough to cover the average loads.
A 5kw charger can supply over 200 120kwh a day.

Edited

 

[zanydroid]

It wasn't designed for grid assist, it was designed for charging.
But, it works perfectly for this purpose.

Exactly

It doesn't have anything to do with the size of the battery. (Assuming that it's not wildly undersized for the system)
The charger just needs to be large enough to cover the average loads.
A 5kw charger can supply over 200kwh a day.

OK, yup that makes sense.

But it wasn’t clear to me if the OP was interested in grid assist to boost the capacity of the inverter and battery or just having grid there to back things up if the battery or solar runs dry, without risking problems with POCO.

For grid assist double conversion doesn’t seem to make sense to me, you would probably need something smarter than just hooking up a Chargeverter. Which might just end up costing more than a grid tie hybrid

For grid as backup your system works well.

 

[cs1234]

A 5kw charger can supply over 200kwh a day.

I was following along nicely until that one.. what planet do you live on?

Edit.. I'm all confused.. I thought I had the kw to kwh conversion thing down. I've got to look it up.