diy solar

diy solar

AC coupled recommendation?

Setting/limiting EVSE current yes, but I can't graph the actual current/wattage.

The EVSE broadcasts amperage, but not measured voltage or wattage. I could multiply current that by 240 to get a rough wattage number. But I already had a current sensor and one spare input on the PI.

Graphing the command wouldn't work either as it's always sending the available current even when the car is fully charged or isn't connected.

Edit: added words to clarify...
 
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Setting/limiting EVSE current yes, but I can't graph the actual current/wattage.

The EVSE broadcasts amperage, but not measured voltage or wattage. I could multiply that by 240 to get a rough number. But I already had a current sensor and one spare input on the PI.

Graphing the command wouldn't work either as it's always sending the available current even when the car is fully charged or isn't connected.
Oh, your just adding another CT sensor to the Pi (for actual EV charging power). I thought you meant you were going to connect a CT sensor directly to the EVSE charger so that it could determine its own charge power…
 
Setting/limiting EVSE current yes, but I can't graph the actual current/wattage.

The EVSE broadcasts amperage, but not measured voltage or wattage. I could multiply current that by 240 to get a rough wattage number. But I already had a current sensor and one spare input on the PI.

Graphing the command wouldn't work either as it's always sending the available current even when the car is fully charged or isn't connected.

Edit: added words to clarify...
Hey, one question I have about your Conext XW-based rig is how it handles balancing.

I know it is a low-frequency inverter with a large Autotransformer, but is that Autotransformer always connected in a way that export or import to grid is always balanced?

Specifically, I the case that 240VAC solar power is more than enough to offset mains load, but that mains load is 75% on one leg and 25% on the other, will the XT put out power in a 75%/25% L1/L2 split so that both L1 and L2 are neither importing or exporting?

I don’t have any questions about the function of the transformer when grid is down and backup power is being used for critical loads panel, but I’m confused about whether it is always balancing house/mains load when the grid is connected.
 
I think an autotransformer will only balance to some extent when it sees a voltage differential.

A transformer typically has 10% voltage sag between open circuit and rated wattage, so if L1 is 250V, I think L2 would have to be 225V for transformer to transfer its rated watts from one leg to the other.

This of course implies power dissipation when transformer output voltage sags. Some types (toroid) may be rated at higher efficiency, which would suggest less voltage sag.
 
I think an autotransformer will only balance to some extent when it sees a voltage differential.
I thought Autotransformers balanced based on the Neutral voltage.

As long as Neutral is at Ground / midpoint, no balancing occurs but as soon as one leg has greater load and starts dragging Neutral closer to it, the Autotransformer provides balancing current from the other leg to get Neutral closer to Ground / midpoint.
A transformer typically has 10% voltage sag between open circuit and rated wattage, so if L1 is 250V, I think L2 would have to be 225V for transformer to transfer its rated watts from one leg to the other.
If loads are dragging L2 down to 225V, I believe that means Neutral is being pulled 12.5V up in the direction of L2 (so L2 to Neutral is 235.5V and L2 to Neutral is also 235.5V, at least for your example of 250/225V).

So what you are saying is that an Autotransformer delivering it’s full rated wattage will have something like a ~10% difference between the peak-to-peak differential voltage of the loaded leg (lower) versus the unloaded leg (higher).

I’m just trying to understand what that means in terms of import / export.

If you are just consuming from grid, imbalance can cause one leg to be lower than the other but peak voltage of the unloaded leg can never exceed the voltage leaving the transformer at the pole.

If you are self-consuming 240VAC power you are generating from solar, with no Autotransformer, the unloaded leg will increase above pole transformer voltage by the same amount that the loaded leg will decrease below pole transformer voltage (so kW measured at 240V by the meter will be zero).

From what you are saying, connecting an Autotransformer to that same solar-with-unbalanced-load will reduce the voltage difference to ~10% of what it would be without any Autotransformer, but the meter will still see an unloaded leg at a higher voltage than it was leaving the pole transformer…

This of course implies power dissipation when transformer output voltage sags. Some types (toroid) may be rated at higher efficiency, which would suggest less voltage sag.
My main interest is in understanding whether the utility smart meter can detect any difference between a customer consuming only a small amount of power versus a customer self-powering from generated solar energy.

Sounds like there will always be some distinguishable difference with a low-frequency inverter (Autotransformer) and that is one benefit to a dual-120V high-frequency architecture…

Of course, if the smart meter can only measure L1-versus-L2 voltage, and not L1-versus-pole-Neutral and L2-versus-pole-Neutral voltages, the difference is immaterial.
 
Hey, one question I have about your Conext XW-based rig is how it handles balancing.

Specifically, I the case that 240VAC solar power is more than enough to offset mains load, but that mains load is 75% on one leg and 25% on the other, will the XT put out power in a 75%/25% L1/L2 split so that both L1 and L2 are neither importing or exporting?
I'm pretty sure when connected to the grid the "auto transformer" isn't going anything. I'm pretty sure I have seen one leg pulling power from the grid while I'm pushing power out on the other leg.

It doesn't matter to me, the power company just looks at L1 + L2. So, +500 watts and -500 watts, would be grid zero.

I don’t have any questions about the function of the transformer when grid is down and backup power is being used for critical loads panel, but I’m confused about whether it is always balancing house/mains load when the grid is connected.

I'm pretty sure I've seen this situation work great too. Again positive on one leg and negative on the other.
And it will start my central AC.


I say "auto transformer" because I'm not sure it's quite the same. It's good coils in there, but I think it's just the actual transformer.

I'm not familiar with auto transformers on a grid connected system, but I'd think you would not want to connect it to the grid or you might end up balancing the entire neighborhood!
 
If loads are dragging L2 down to 225V, I believe that means Neutral is being pulled 12.5V up in the direction of L2 (so L2 to Neutral is 235.5V and L2 to Neutral is also 235.5V, at least for your example of 250/225V).

My bad, nominally 120/240V, so if one phase is 125 relative to neutral and the other is 112.5V (180 out of phase), that's a 10% difference and I would expect balancing transformer to carry about its rated current.

Yes, this would try to balance the neighbor's imbalance as well. Wire resistance to loads will determine which causes how much balancing.

If you instead used an isolation transformer, 240V on grid side and 120/240V split phase on your side, grid current would be perfectly balanced.
 
My bad, nominally 120/240V, so if one phase is 125 relative to neutral and the other is 112.5V (180 out of phase), that's a 10% difference and I would expect balancing transformer to carry about its rated current.

Yes, this would try to balance the neighbor's imbalance as well. Wire resistance to loads will determine which causes how much balancing.
Al least on my pole, the pole transformer puts out L1, L2, and a grid neutral tied to ground at the pole.

So I believe any imbalance by your feed and your neighbor’s feed is being balanced by the pole transformer.

If you have an Autotransformer, your house is putting out a balanced 240V load and leaving less work for the pole transformer to do.

But your puny Autotransformer is unlikely to balance your neighbor’s imbalance if the much larger pole transformer wasn’t able to achieve that beforehand…
If you instead used an isolation transformer, 240V on grid side and 120/240V split phase on your side, grid current would be perfectly balanced.
Yes, with an isolation transformer, you’d be perfectly balanced. As you would also be with two 120V inverters that each maintain zero export / zero import…
 
I am going to chime in here. I think you may understand most of this already. I got an enphase microinverter system installed with the idea that I would eventually add AC couple backup system.

While I really like the Enpase backup solution each 10KWH module only has about 3.3 KW of inverter power. So to really have something like full home backup would be around $40,000 even as DIY installation.

So assuming you want something like full home backup where you can at least decide which loads you want to run by turning off breakers, you have several problems to solve.

The first is what will be your maximum expected load in a ON GRID situation. If the inverters you choose cannot handle switching your max loads on and off the grid then you will need an external transfer switch. These alone can cost around $2000-2500 for a 200 amp transfer switch. This is why many people go with a "critical loads panel".

One of the huge benefits of the Sol-Ark 15K Is that they are rated to pass through 200 amps meaning you get your full 200 amp service power when running on grid.

So decision 1 is do I want an inverter that be placed between the meter and the main panel or do I want an inverter that will be placed after the air panel and use it to supply only critical loads.
Hi everyone,

I've currently got a 8kW system with enphase micro inverters. Works great, but being in Texas, with the big storm this past year, I wanted to upgrade to being off-grid capable. So, I've added 30 more panels with a Sol-ark 12k inverter and batteries. It's working great. Now, I've got a buddy with a matching 8kW enphase setup, and he's looking to do something similar with an AC coupled inverter, but doesn't want to spend the $7k for the Sol-ark12k.

So, he's looking at adding 5kW more solar panels with an AC coupled inverter and batteries. He's got the solar panels and batteries lined up, I'm just trying to determine the best inverter/charger to use. He really like the idea of AC coupling to be able to use his larger array when power goes off again, and dumping power into the batteries if he's not consuming that much at the time.

I like Schneider, but I don't think they're quite big enough. Outback is also not big enough. I see some interesting info on Growatt, but I don't know their history. And it seems their 'larger' systems are on paper-only, I've not seen them for sale. So, getting back to my question, what inverter/charger combos would you recommend to keep his costs down?
Thanks.
 
Well that's one way of bumping a 10 month old thread...

Nice to see that the "I have an 8kW Enphase setup and wanting to upgrade to whole house battery" question has been around this long. This should be a FAQ at this point I think...
 
I'm going to crime in here. There is one very important question yiu have not answered. Do you intend to build a system as "whole home back up" or with a "critical loads panel".

If you are doing a whole home back up, then then inverter will sit between the meter and your main panel. If you are doing a critical loads panel then the inverter will sit between the main panel and the critical loads panel. If you are planning whole home backup then the ability to handle pass through current (and switch it safely) becomes a limiting factor in how much power yiu can use even when operating on grid.

Any grid tied inverter needs to be disconnected from the grid before it can begin operating in off grid mode. This is done with a relay that disconnects the grid input.

The tricky thing about AC coupling is that Grid tied inverters have basically. one speed, full blast. When operating on the grid thos is fine. Any power not used by your loads goes back to the grid. MPPT charge controllers on the other hand are designed to charge a battery using specific charging curves. When the battery is not full the inverter attempts to balance AC from your micro inverters with your loads. Excess power goes into the batteries.

There is some ability to throttle back the output of micro inverters, but there are ramp up and ramp down curves with this that do not react instantaneously. So the charge rate of the MTTP controller is not critical for your situation. It is the AC charger. If a large load shuts down, the AC charger much be able to absorp that excess power until the inverters either are able to ramp down or be shut off. Once shut off the inverters will wait for a time before they reconnect.

On a sol-ark they typically will set it up to cycle between maybe 70 and 90%

Does this sound complicated enough for you?

Let me suggest something simple and cheap. Get an off grid inverter. If you are running motors (like your heat pump), find one that is a low frequency inverter with a transformer in it. Something like a 12K growatt. They are around $2000.00. Then buy an inverter generator that can run on propane. To operate off grid yiu will need a way to disconnect. A generator breaker interlock would allow this.

The power from the new DC Coupled panels will still work. You will spend thousands more to build a system to capture the output of those AC coupled solar panels during an outage. If you have 4 sun hours on a 10 KW array. At .20 a kilowatt hour that is $8.00 a day in lost solar generation. How many outage days do you expect? Charging at 5 KW it would take 8 hours to charge the batteries up.
 
I of course will suggest SMA Sunny Island :) (see my avatar picture)
That will manage GT PV inverters smoothly, using frequency-shift to adjust their power output (assuming they have that feature.) The shift from 0% up to 100% or back down takes a couple seconds, and Sunny Island will source or sink power from/to battery in order to make up the difference.

Other brands (SolArk, Outback, Schneider) have similar function, may or may not perform as well at this.
Sunny Boy GT PV inverter is best for the application because it can be set to "offgrid" where wider voltage and frequency are tolerated (good when using generator input), but any UL-1741-SA GT PV inverter that supports frequency-watts should work.

With two 120V Sunny Island configured for 120/240V split-phase, you can have up to 56A, 6.7kW per phase pass through to/from grid. So up to 13.4kW of micro- or string inverters, and loads. This could be for a protected loads panel, leaving larger loads on your 200A main panel. For double the pass-through current, four battery inverters could be installed.

You aren't likely to power electric furnace or range from the battery system, so not a big deal to not have whole house on backup. You can manually flip interlocked "generator" breaker to backfeed whole house panel during a power failure, just avoid using the electric furnace (which I have done inadvertently; I only have enough battery for an hour of that.)

The Enphase battery solution as you noted is expensive per kW of output (and kWh of storage).
Sunny Island and many others can use 48V lead-acid batteries, or lithium. For Sunny Island, particular model BMS allows communication. Some battery models are expensive, but others are more reasonable (maybe with a bit of DIY)

Sunny Boy Storage (an HF inverter) is 6kW with 9kW surge. Paired with an available (add-on) 200A transfer switch and auto-transformer, it can store power from your Enphase microinverters, pass through 200A for whole house, and provide backup. Of course, what it can power while grid down is limited. The catch is expensive 400V battery.

So assuming you want something like full home backup where you can at least decide which loads you want to run by turning off breakers, you have several problems to solve.

Let me suggest something simple and cheap. Get an off grid inverter. If you are running motors (like your heat pump), find one that is a low frequency inverter with a transformer in it. Something like a 12K growatt. They are around $2000.00. Then buy an inverter generator that can run on propane. To operate off grid yiu will need a way to disconnect. A generator breaker interlock would allow this.

With an inverter/charger, it can be fed by a breaker from main panel, keeping battery charged and connected to a critical loads panel, so things like alarm/communication are always powered.

With a backfed interlocked "generator" breaker, main grid breaker is turned off and inverter output fed through "generator" breaker to panel. Also, manually turn off the breaker which had been feeding the inverter/charger. You now have an off-grid system. If the inverter supports AC coupling, your Enphase or string inverters operate, supplying loads and charging battery.

I set up mine like that previously. First, GT PV. Then, with Sunny Island powered by main panel and manually feeding main panel (my multiple GT PV inverters were already on a separate breaker panel.) Then I moved the input breaker onto a line-side tap, so battery inverter + GT PV inverters + protected loads are always fed from grid. Main panel always fed from grid, except if I manually switch it to be fed from battery inverter.
 
The tricky thing about AC coupling is that Grid tied inverters have basically. one speed, full blast.
That is correct about older GT inverters. That spec is UL1741. The newer spec, UL1741SA, requires that the GT inverter be able to modulate in response to frequency Watt. That spec is the same as CA Rule 21. It makes AC coupling work smoother as loads increase and.decrease. I have done it with an Outback Skybox for three years.
My arrangement works much better than a generator because I use it for load shifting to avoid high TOU rates. If you want to talk about generators versus AC coupling, start a new thread about that subject with the appropriate title.
 
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Asking a general question I’m hoping one or more of you on this thread will know the answer to.

I’m trying to understand which budget hybrids or AC-coupled battery inverters will pass-through AC-coupled power from output to input.

Whether that AC power is coming from a Microinverter during the day or one of the new V2H bidirectional chargers connected to an EV at night, I’m looking for hybrid options to essentially behave in ‘pass-through’ mode as well as to offset Critical Loads while the feud is up.

And ideally, I’d like to find a hybrid such as the Schneider Conext SW or the MPPSolar LV2424 that operates off of a 24V battery (power requirements are modest),
 
Asking a general question I’m hoping one or more of you on this thread will know the answer to.

I’m trying to understand which budget hybrids or AC-coupled battery inverters will pass-through AC-coupled power from output to input.

Whether that AC power is coming from a Microinverter during the day or one of the new V2H bidirectional chargers connected to an EV at night, I’m looking for hybrid options to essentially behave in ‘pass-through’ mode as well as to offset Critical Loads while the feud is up.

And ideally, I’d like to find a hybrid such as the Schneider Conext SW or the MPPSolar LV2424 that operates off of a 24V battery (power requirements are modest),
I’ll let you all decide if I’ve hjacked the thread and should start a new thread for my question, but I’m having a second look at the Multiplus 2: https://www.solar-electric.com/lib/wind-sun/Datasheet-MultiPlus-II-12V-3kVA-120-50-2x-120V.pdf

The big negative is that it only inverts to 120VAC so one one leg of critical loads can be offset when it is on-grid.

On the other hand, it has two 50A transfer switches and will passively pass-through and power generated on the AC output to the AC input (as long as below that current limit).

So it’s not perfect for what I’m looking for but it is pretty close:

One leg can be offset off of 24V battery power and a split-phase no-directional charger can offset the other leg overnight.

When sufficient AC-coupled PV power is being generated to power the EV charger (1.44kW minimum), 240VAC power will ‘flow through’ the Multiplus II on one leg and the Multiplus II will offset the 720W consumed by the other leg).

I’d need to use another small inverter such as the GTILs I’m using currently if I want to offset overnight consumption on the second leg, but this would allow a bidirectional EV charger to be connected to the output side of a hybrid inverter that is pretty much ‘pass-through’ as I’m seeking.

Any other options to consider that are also in the $1000-2000 price range appreciated.
 
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