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battery grid feedback

With your rates in SoCal, solar is a no-brainer You are positive that 6848 can export battery power to the grid, right? To be fair, I have to agree with you that $3,000 is not an arm and a leg. However, to make time-shifting work, the cost of the equipment is crucial. If I don't use the inverter for solar (which I might but with only 1,800W), this investment will never pan out. Not even just a matter of a long time.
Getting the Schneider XW-Pro for $3,000 was a good deal, and I waited a few months to hit the sale and also got free shipping, which is a big deal when the pallet weighed in about 200 pounds. The current price right now at Real Good is $3,234.60 with the free shipping deal. But you also need to get the Insight Home box to be able to configure and monitor the system. The Sol-Ark 8K which is pretty comparable, but includes the MPPT and the monitoring is going for $6,588.00 or about double the price. The OutBack SkyBox used to be a bit more expensive as well, but I am now seeing it listed for around $3,600 at several locations, and one as low as $3,276 at "The Powerstore". If it was at that price when I got mine, I would have bought the SkyBox instead. For that price, it has the internet monitoring and a DC solar charge controller, all built in the same box.

The Schneider is a downright bargain, if only their software would allow fully automated time shifting in an AC coupled setup. One of the other guys on here did get a Raspberry Pi to be able to send the commands to start the charge cycle in the morning. I am working on a Triangle Research Nano10 PLC to send the commands, and I think I am close, by my program has some timing issues and keeps losing connection. Since work has picked back up, I have not had time to troubleshoot it. I just click it to start a bulk charge cycle before I head to work. If I miss a day, it's $2.00 so no big deal.

I have now had 3 power fails since the system was setup and it works perfectly in that mode. On two of the outages, we didn't even know it had gone out. We didn't really have anything on that was not on the backup panel, so everything was still working. Didn't even notice a glitch. I did have to reboot the Enphase inverters as a few of them did lock out due to "grid instability" but I think the new firmware and the Rule 21 grid code seem to have fixed the problem. On the last outage they all stayed working just fine, but we new something happened because our internet router rebooted and it assigned different ip address to a few devices. That normally would not be a problem, but I access a few devices by ip address, and I had missed setting them a fixed address. The Schneider XW-Pro was one of them. And now my PLC does not see it either. Oops. My network has over 40 devices on it.
 
Can you think of a model? I have an agreement to export so the limiter part is not even very relevant.
Your agreement to export may refer to a list or a specification for acceptable Grid Tie inverters. In California the CEC maintains that list. GT inverters do not cost "an arm and a leg" but are more expensive than non listed ones.
NOTE:
After rereading the thread, I now understand that what you want is a true hybrid. The less expensive GT inverters do not run off batteries.
 
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I have the Schneider XW-Pro 6848 6,800 watts at 120/240 volt split phase. And I now have a usable 36 KWHs of Chevy Bolt battery modules wired in a 14S12P arrangement of 60 amp hour cells LG cells. That makes 720 amp hours at a nominal 51.8 volts. It's about 58% of a complete Chevy Bolt battery pack. Yes, I am following the recall news.

Since you want to run your pool heater during the day, I would just add more solar with microinverters. That is by far the most efficient, to use the power as it is being produced. Charging is 95% efficient, at best, and inverting is also about 93% efficient, and the batteries lose a little as well. I lose a full KWH when I move 10 KWH from solar to peak rate evening time here.
The problem with just adding Microinverters is that he stated his 6kW load is intermittent - than means when the heat exchanger turns off he be blasting an additional 6kW to the grid.

Aside from that likely taking peak export power beyond the terms of the NEM agreement, there is a safety issue - when the utility approves a NEM agreemebt, that is in the context of reviewing upstream capacity of all transformers - if you push more peak power out to the grid than you agreed you would, it can cause damage and possibly even a safety hazard.

We can argue about whether your NEM agreement gives you the freedom to put out a square wave of power at agreed-upon peak versus the usual solar ‘hill/mountain’ around midday, but pushing out 6kW above your peak limit without review/permission first is a very bad idea.

And my rates go from 17 cents a the cheap time to 43 cents at the peak rate. Moving that 10 KWH in theory saves me 10 x 0.42 - 10 x 0.17 = $2.50 cents a day. I figure I average moving about $2.00 a day for 300 days a year to account for days of weak sun or other reasons I can't push the full 10 KWH in the peak window. I may actually do better than that. But that still means I am saving $600 a year by time shifting the power. But I spent $3,000 on the inverter, and probably something like $5,000 on the batteries. Maybe a little more with the cases, BMS units, and wiring etc. So taken totally separate from the solar power, the battery system will take 15 years to pay off. But I am only expecting the batteries to last about 10 years. So yup, at the peak to off peak rate here, it won't pay off, but it sure does cut down on the cost of having backup power.
Yeah, the batteries are the killers, aren’t they? I was planning a Hybrid install much like yours (Magnum PAE instead of Schneider Conext) but the infinite path to break even as well as the cost/complexity of rewiring my mains panel into a critical loads panel scared me into looking for another alternative.
But if you take the entire cost of my solar installation into the equation, and figure on what I am saving, then my system pays off in about 11 years. My Enphase solar PV system has already produced 16.9 MEGA watt hours. And it has just been running a bit over 2 years. In the full year of 2020, it made 7.9 MWHs. If I just figure that half of it was used at peak, and half off peak, so we average the value of the electricity, that is 30 cents per KWH x 7,900 = $2,370 per year chopped off of my electric bill, but that is with the battery doing the time shifting. Adding up everything I spent on the solar panels, inverters, installation, and my battery system, I spent $26,000 over a span of 2.5 years. Divide by the 2,370 per year = 10.97 years to cover the whole cost of everything just from electric bill savings. Production may fall off some, but I also expect So Cal Edison to jack the rates more. So that may end up a wash.
I’ve got a 4kW Microinverter-based system under NEM that was covering 100% of consumption until the TOU peak hour changes. That ended up costing me ~30% of my generation credits on an annual basis and added another ~5% to the cost of my consumption on an annual basis. So I need to add another ~1.4kW of production if I want to continue to cover my electrical bill.

I would have had to modify my NEM agreement to increase my peak output from 3.5kW to 4.75kW and would be subject to new rules adding taxes that I wanted to avoid.

So the DC-coupled GTIL system I added is to offset self-consumption and preserve generation credits so that I essentially consume 35% less from the grid (and keep my grid-tied generation credits where they were before the TOU changes.

I spent only $420 on 1.14kW of new panels and $500 on two GTIL inverters, plus another ~$500 for racking, wiring, and combiner boxes, so let’s say $1500 all-in or ~$1150 after tax credits.

I’d probably be charged over $250/year without that new system so on purely the solar generation front, the break-even is not bad (<5 years).

The rub is that to make the system work, I need to store up unused PV power until it is consumed, and that requires a battery and a charger, which cost me $1500 and $250 (or a total of $1350 after tax credits).

So the whole new system has cost me $2500 after tax credits and break even is back up to ~10 years (assuming the 3 cheap Chinese boxes I purchased last that long ;)).

I built this ‘platform’ with a plan to expand it once we get an EV (~2023).

If I add a single 500W panel (costing $200-250) to the DC array, it’ll offset another ~500kW of consumption annually which will allow me to preserve enough additional generation credits to drive ~1700 miles (worth $100/year).

So as my consumption increases, break even drops under 10 years.

This grand plan only works out if these cheap Chinese boxes last, but I figure my worst-case downside is to purchase higher-quality more expensive products when they crap out (this market is evolving so fast right now).

But back to the OP, I don’t think he can use Microinverters without exceeding his NEM cap so charging a battery at 20% / 95% cost = 21% at night then draining it to power his 6kW load during the day at 93% efficiency translates to ~77.4% savings (or at least 75% savings even if we throw in another 10% loss cycling energy through the battery).

The 6kW output peak is going to put him up into the higher-cost inverter category but between a hybrid such as the SolArk (or a 240V Deye if his heat exchanger takes 240V, as I suspect) or a Schneider Conext if it provides the charge-time control he is seeking is going to be the cheapest way to achieve what he is after.
 
Getting the Schneider XW-Pro for $3,000 was a good deal, and I waited a few months to hit the sale and also got free shipping, which is a big deal when the pallet weighed in about 200 pounds. The current price right now at Real Good is $3,234.60 with the free shipping deal. But you also need to get the Insight Home box to be able to configure and monitor the system. The Sol-Ark 8K which is pretty comparable, but includes the MPPT and the monitoring is going for $6,588.00 or about double the price. The OutBack SkyBox used to be a bit more expensive as well, but I am now seeing it listed for around $3,600 at several locations, and one as low as $3,276 at "The Powerstore". If it was at that price when I got mine, I would have bought the SkyBox instead. For that price, it has the internet monitoring and a DC solar charge controller, all built in the same box.

The Schneider is a downright bargain, if only their software would allow fully automated time shifting in an AC coupled setup. One of the other guys on here did get a Raspberry Pi to be able to send the commands to start the charge cycle in the morning. I am working on a Triangle Research Nano10 PLC to send the commands, and I think I am close, by my program has some timing issues and keeps losing connection. Since work has picked back up, I have not had time to troubleshoot it. I just click it to start a bulk charge cycle before I head to work. If I miss a day, it's $2.00 so no big deal.

I have now had 3 power fails since the system was setup and it works perfectly in that mode. On two of the outages, we didn't even know it had gone out. We didn't really have anything on that was not on the backup panel, so everything was still working. Didn't even notice a glitch. I did have to reboot the Enphase inverters as a few of them did lock out due to "grid instability" but I think the new firmware and the Rule 21 grid code seem to have fixed the problem. On the last outage they all stayed working just fine, but we new something happened because our internet router rebooted and it assigned different ip address to a few devices. That normally would not be a problem, but I access a few devices by ip address, and I had missed setting them a fixed address. The Schneider XW-Pro was one of them. And now my PLC does not see it either. Oops. My network has over 40 devices on it.
Yes $3000 for a Schneider may be the most economical way to get this capability with listed equipment.

The alternative is to purchase a 48V AC batttery charger (no idea what those cost) control it through a lamp timer (or relay if higher power is needed) and then use 4 2kW GTIL inverters currently coating $470 each: https://www.amazon.com/Inverter-Limiter-DC50-90V-AC185-265V-SUN-2000GTIL2-H/dp/B08F9Y6WKJ

The sensors of the GTIL inverters can be connected to one of the 240V wires supplying the heat exchanger and they will drain the 48V battery to supply the 6kW whenever the heat pump turns on (until the battery is drained at which point he grid will supply the needed power).

Probably under $2000 + battery cost all-in and no rewiring of anything needed…
 
Just to make it clear, I have no desire to export power to the grid with this setup. I am not necessarily even adding solar panels to the inverter I am after. If a kW escapes by accident, it's OK as I have an agreement but that's not my goal. The reason I need an inverter able to export battery power to the grid is I want to power my own loads connected in front of the inverter, which loads happen to be grid-connected of course. There will be no export though beyond what my current grid-tied system does occasionally.
 
Yes $3000 for a Schneider may be the most economical way to get this capability with listed equipment.

The alternative is to purchase a 48V AC batttery charger (no idea what those cost) control it through a lamp timer (or relay if higher power is needed) and then use 4 2kW GTIL inverters currently coating $470 each: https://www.amazon.com/Inverter-Limiter-DC50-90V-AC185-265V-SUN-2000GTIL2-H/dp/B08F9Y6WKJ

The sensors of the GTIL inverters can be connected to one of the 240V wires supplying the heat exchanger and they will drain the 48V battery to supply the 6kW whenever the heat pump turns on (until the battery is drained at which point he grid will supply the needed power).

Probably under $2000 + battery cost all-in and no rewiring of anything needed…
Let me see if I understand that. I can control the charger easily, let's say by a wifi relay. So that will allow me to time the battery charge. How do I control when the battery is discharged? The inverter? And I would be connecting the battery as a solar panel? Is that a good idea? The inverter will MPPT the battery. I also don't see an AC pass-through option. Where do I connect the grid if I connect my load to the AC-out ports?
 
Just to make it clear, I have no desire to export power to the grid with this setup. I am not necessarily even adding solar panels to the inverter I am after. If a kW escapes by accident, it's OK as I have an agreement but that's not my goal. The reason I need an inverter able to export battery power to the grid is I want to power my own loads connected in front of the inverter, which loads happen to be grid-connected of course. There will be no export though beyond what my current grid-tied system does occasionally.
Generally, that’s not what the term ‘export battery power to grid’ is interpreted to mean.

The common term would be a ‘zero-export grid-tie inverter’.

And I’ve understood that your use case requires charging a battery from a time-controlled AC charger and then powering your 6kW heat exchanger from battery power.

Your two obvious choices are to either:

1/ install a true all-in-one hybrid inverter such as a Solark between your mains panel and the feed to your heat exchanger. You’ll need to determine what your battery charger power needs to be (kWh daily consumption / low-cost grid power window) to be sure any all-in-one you get can charge your battery during the window you have available.

2/ install a GTIL inverter (or a bank of several if you cannot find one powerful enough) with sensors tied to one of the heat-exchanger supply wires )no rewiring needed) powered by a battery large enough to supply your daily heat-exchanger energy and charged by a separate AC charger sized to fill the battery during off-peak hours (or several in parallel if you can’t find one big enough).

If you need to control the GTILs to supply the heat-exchanger only during peak hours, you’ll need to use a suitably-sized lamp timer or a timer controlling suitably-sized relays (possibly a single disconnect relay connected to the battery).

And for charging, same thing - either a suitably-rated lamp timer to control when the charger is active or a suitably sized relay controller by a lamp timer or possibly the same disconnect relay connected to the battery.

The battery only needs to be connected when you want the battery to be supplying the heat exchanger and when you want the AC charger to be charging the battery, and since those two time windows do not overlap, a single 200A relay connected to a 48V battery should work to connect both inverters and charger…

Do you know what daily hear-exchanger consumption in kWh you are trying to supply from a battery?
 
Generally, that’s not what the term ‘export battery power to grid’ is interpreted to mean.

The common term would be a ‘zero-export grid-tie inverter’.
I am afraid you misunderstand. I don't need a zero-export inverter. I need an inverter that is capable of grid-export, though not planning to export. I don't need to prevent exporting. I could export but my consumption is larger enough. I do need the functionality though as my heat pump is not behind the inverter.
 
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Do you know what daily hear-exchanger consumption in kWh you are trying to supply from a battery?
That varies and I am not after covering it all. It will run on the grid at night and I need about 2h at peak time.
 
Let me see if I understand that. I can control the charger easily, let's say by a wifi relay. So that will allow me to time the battery charge.

How do I control when the battery is discharged? The inverter?
There are 2 ways to control a GTIL - disconnect the DC supply (battery) or disconnect the grid.

I started off using lamp timers to control my AC grid signal / output and that worked well, but I’m not sure they make 240V lamp timers and I’m not sure they would be rated for 6kW…

Then I discovered that my solar charger controller includes DC dry contacts that can be scheduled. So I bought some DC relays that can switch 120-240V AC and now use that to control when the grid signal reaches the GTILs.

Your biggest issue will be the 6kW (which is why I suggested a DC battery cut-off as another alternative you might consider.
And I would be connecting the battery as a solar panel?
You’ve convinced me you do not want to use solar power to charge your battery, so for your case, you’d just need a suitably-sized AC charger..,
Is that a good idea? The inverter will MPPT the battery.
The GTIL inverters I have are designed to work off of batteries or solar (they just don’t advertise and document the battery-driven capability as well as they should). The MPPT of the DC input just settles in the battery voltage.

I also don't see an AC pass-through option. Where do I connect the grid if I connect my load to the AC-out ports?
Here is what I did when I first tested my GTIL:

1/ opened an extension cord so that I had access to the hot wire.

2/ placed clamp sensor of GTIL around the hot wire or the extension cord.

3/ plugged AC cable of the GTIL into the extension cord (turns on but no output).

4/ plugged in a space heater into the end of the same extension cord (OFF).

5/ turn on the space heater and the GTIL initially reports grid consumption and then increases output until grid consumption is reduced to ~10W.

So when the space heater was set to 500W, GTIL puts out 490W and the grid supplied 10W,

when space heater increased to 750W, GTIL puts out 740W and the grid supplied 10W,

and when space heater increased to 1000W, GTIL maxes out at 850W and the grid supplied 150W.

A GTIL is connected completely in parallel with the grid - there is no ‘pass-through’ (like there is for a hybrid inverter) because nothing is passing through.

The sensor gets clamped around the wire whose consumption you want to offset.

The GTIL output is connected to any outlet on the same 240V leg as the one with the sensor.

I’m running 120V x 2 so I just made a new dedicated socket on a new 10A the-phase breaker with docked on both L1 and L2. BecausevI only have a maximum of 850W / 7.1A per phase, standard AC wiring and 10A breakers were sufficient.

You’re looking for 6kW @ 240V, so you’ll need breakers and wiring rated to easily handle your 25A (at least 30A, probably higher - check with an electrician).

Plugging in a GTIL is like plugging in a toaster oven except is emits rather than consumes power. It does not need to be connected to the wiring supplying your heat exchanger (only the clamp sensor does, though it’s just clamped around the wire, so not really a connection).
 
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I am afraid you misunderstand. I don't need a zero-export inverter. I need an inverter that is capable of grid-export, though not planning to export. I don't need to prevent exporting. I could export but my consumption is larger enough. I do need the functionality though as my heat pump is not behind the inverter.
We’re speaking past each other. You do not need export capability. You do need grid-tie imitation and you do need grid pass-trough (ability for the grid to power your heat exchanger).
 
That varies and I am not after covering it all. It will run on the grid at night and I need about 2h at peak time.
2h x 6kW = 12kWh, but you said it is not on 100% over those two hours. You need to estimate duty cycle to size your battery (50% duty cycle would need 6kWh but since GTILs are only ~80% efficient, your battery would need to store 7.5kWh in order to generate 6kWh over your 2-hour peak window.

And how many hours long is your cheap $0.05 off-peak window?
 
There are 2 ways to control a GTIL - disconnect the SC supply (battery) or disconnect the grid.

I started off using lamp timers to control my AC grid signal / output and that worked well, but I’m not sure they make 240V lamp timers and I’m not sure they would be rated for 6kW…

Then I discovered that my solar charger controller includes DC dry contacts that can be scheduled. So I bought some DC relays that can switch 120-240V AC and now use that to control when the grid signal reaches the GTILs.

Your biggest issue will be the 6kW (which is why I suggested a DC battery cut-off as another alternative you might consider.

You’ve convinced me you do not want to use solar power to charge your battery, so for your case, you’d just need a suitably-sized AC charger..,

The GTIL inverters I have are designed to work off of batteries or solar (they just don’t advertise and document the battery-driven capability as well as they should). The MPPT of the DC input just settles in the battery voltage.


Here is what I did when I first tested my GTIL:

1/ opened an extension cord so that I had access to the hot wire.

2/ placed clamp sensor of GTIL around the hot wire or the extension cord.

3/ plugged AC cable of the GTIL into the extension cord (turns on but no output).

4/ plugged in a space heater into the end of the same extension cord (OFF).

5/ turn on the space heater and the GTIL initially reports grid consumption and then increases output until grid consumption is reduced to ~10W.

So when the space heater was set to 500W, GTIL puts out 490W and the grid supplied 10W,

when space heater increased to 750W, GTIL puts out 740W and the grid supplied 10W,

and when space heater increased to 1000W, GTIL maxes out at 850W and the grid supplied 150W.

A GTIL is connected completely in parallel with the grid - there is no ‘pass-through’ (like there is for a hybrid inverter) because nothing is passing through.

The sensor gets clamped around the wire whose consumption you want to offset.

The GTIL output is connected to any outlet on the same 240V leg as the one with the sensor.

I’m running 120V x 2 so I just made a new dedicated socket on a new 10A the-phase breaker with docked on both L1 and L2. BecausevI only have a maximum of 850W / 7.1A per phase, standard AC wiring and 10A breakers were sufficient.

You’re looking for 6kW @ 240V, so you’ll need breakers and wiring rated to easily handle your 25A (at least 30A, probably higher - check with an electrician).

Plugging in a GTIL is like plugging in a toaster oven except is emits rather than consumes power. It does not need to be connected to the wiring supplying your heat exchanger (only the clamp sensor does, though it’s just clamped around the wire, so not really a connection).
I guess the resistance of the grid is higher than the resistance of the battery. But then how do you prevent using the battery when you don't want to use it?
 
2h x 6kW = 12kWh, but you said it is not on 100% over those two hours. You need to estimate duty cycle to size your battery (50% duty cycle would need 6kWh but since GTILs are only ~80% efficient, your battery would need to store 7.5kWh in order to generate 6kWh over your 2-hour peak window.

And how many hours long is your cheap $0.05 off-peak window?
Whole night. 7-8h. I am setting up 14kWh storage, 48V
 
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We’re speaking past each other. You do not need export capability. You do need grid-tie imitation and you do need grid pass-trough (ability for the grid to power your heat exchanger).
So, the whole issue is I did not want to put the heat pump behind the inverter as a critical load. I could but I rather reserve that for actual critical loads to power in the case of an outage.
IF I settled for that solution, any "hybrid" inverter will do.
 
I guess the resistance of the grid is higher than the resistance of the battery.
I’m not sure what you mean by that.

The inverter needs power which it gets through the DC inputs. When you cut out the battery, it stays on but reports ‘Liw Voltage Disconnect’ pans outputs no AC power.

The inverter needs the grid signal to run, so when you cut the AC input (which is the grid signal feeding into it’s output power cord), it instantly shuts down (as does any grid-tied inverter).

But then how do you prevent using the battery when you don't want to use it?
If you cut off the battery supplying the inverter, hopefully it’s clear how it’s not using the battery energy (since that energy is not available).

If you cut off the AC output (essentially ‘unplug’ the inverter) it shuts down like any other AC appliance would. It needs to be connected to the grid to function.
 
Whole night. 7-8h. I am setting up 14kWh storage, 48V
14kWh will give you more than enough storage to run your 6kW heat exchanger for 2 hours straight (100% duty cycle).

Are you sure you need that much?

First-off, the battery will be the most expensive component, so half as big will cost ~half as much.

Secondly, if you are actually consuming 14kWh during your 2-hour peak window, you’ll need a 2kW charger to charge the battery back up over 7-8 hours..,
 
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14kWh will give you more than enough storage to run your 6kW heat exchanger for 2 hours straight (100% duty cycle).

Are you sure you need that much?

First-off, the battery will be the most expensive component, do half as big will cost ~half as much.

Secondly, if you are actually consuming 14kWh during your 2-hour peak window, you’ll need a 2kW charger to charge the battery back up over 7-8 hours..,
That'll be alright. It just happens to be a s16 280Ah pack.
 
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