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New class of zero-export AC-coupled battery inverter (Huayu)

fafrd

Solar Wizard
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I just stumbled onto this, and as far as I know, it is the first example of the new product class I have been pineing-for / predicting: https://m.huayu-solar.com/Content/uploads/2021694206/PDF/AC-Coupled-Quick-Installation-Guide.pdf

This AC-Coupled battery inverter being introduced by Huayu, the HYH-3K/3.6K/5K-AC, supports 2 CT sensors, one for incoming grid energy (grid load) and a second for incoming PV generation.

This should allow it to be programmed for zero-export by charging the battery with all excess PV generation beyond that needed to serve loads (so Pcharger = Psolar - Pload).

Here is a bit more detail about the 5K version: https://m.huayu-solar.com/ac-couple...r/5kw-lv-ac-coupled-solar-power-inverter.html

I’m hoping this product proves to deliver the capability I am hoping for and will be offered in configurations compatible with the US grid (single-phase 240V or split-phase 120/240V).

My current battery-system is DC-coupled but a smart battery inverter like this supporting zero export would allow me to use microinverters on my 1kW PV array, monitor that production through a CT sensor connected to this battery inverter, and program the inverter to consume as much of that 240VAC production as needed to charge the battery in order to maintain grid consumption at zero.

Dawn of a new era if I’m right about what this product represents…
 
Found this AC-coupled battery inverter from TSUN that seems very similar to the ‘HV’ (90-400VDC) version of the Huayu AC-coupled battery inverter: http://www.tsun-ess.com/datasheet/TSUN-AC-Coupled-Inverter-TSOL-A-H.pdf?=v1.0.1

And here is the manual: http://www.tsun-ess.com/products/TSOL-A/UserManual-TSOL-A-HSeries-AC-Coupled-Inverter-EN-V1.0.pdf

Page 11 shows Section 3.2 Work Modes including Work Mode: Self-Use which sets priority for Load > Battery > Grid, meaning generated power from PV array irate goes to supplying house loads to point of zero-export, then remaining energy goes to charging battery and only if there is sufficient solar energy to both serve home loads and charge battery at maximum power (or battery is full) is excess solar energy exported to grid.

As long as maximum battery charge power exceeds maximum PV power generation and battery is drained nightly and sized large enough that it never fully-charges during the day, this will achieve zero-export.

But export can happen if the battery can become fully-charged and the inverter has no way to communicate with the PV inverter to throttle it back (like the Enphase system has…).
 
, it is the first example of the new product class I have been pineing-for / predicting
Excellent. Although my prediction is that the inverter will become the only source of power for the home. The grid will only augment the battery.
The data sheet shows shows a 10ms switchover,,,isn't it possible for a home solution to avoid this..to seamlessly mix ac/ac?
 
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Excellent. Although my prediction is that the inverter will become the only source of power for the home. The grid will only augment the battery.
I think you are confusing the backup capability of this AC-coupled inverter with it’s ability to serve self-consumption from an existing (and seperate) AC-coupled PV generator.

(Look at the wiring diagram here: https://m.huayu-solar.com/Content/uploads/2021694206/PDF/AC-Coupled-Quick-Installation-Guide.pdf)

During the day, when the solar inverter is generating power, the battery inverter will allow the solar energy to power the house first and if there is remaining solar generation after that (which otherwise would be exported to grid), it will drive the AC battery charger with just enough energy to offset remaining solar production (so grid export is zero).

In the case that solar generation plus battery generation is insufficient to power the home loads, then yes, grid energy will be imported to cover the gap.

But as long as solar generation plus battery generation is sufficient to serve all home loads, grid consumption will remain at zero (no import, no export) meaning the grid is just being held there on standby in case there are loads needing more power than can be delivered from the combination of solar generation + battery generation (such as might be the case for startup surge for a motor, for example).

The data sheet shows shows a 10ms switchover,,,isn't it possible for a home solution to avoid this..to seamlessly mix ac/ac?
I don’t really understand your question.

The home loads are served through the AC input (as well as the solar generator). There is no backup power for home loads when the grid goes down (since the solar generator is grid-tied and goes down with the grid).

Only the EPS AC output switches over from AC (grid + solar geberator) power to emergency battery power when the grid goes down.

So for a computer connected to the main panel, it will go down when the grid goes down, but a computer connected to the EPS output will switch from grid/solar power to battery power 10ms after the grid goes down (well within the time constant of any computer power supply, so the computer is powered continuously without interruption).

10ms is pretty ‘seamless’ for the Emergency Power Supply (Critical Loads Panel) and there is no ‘mixing’ to speak of on the mains power when the grid goes down.
 
I don’t really understand your question.
Just something to avoid CT1 and CT2.
Every other feature of this Huaya box but without the 10ms delay and not the conversion to DC and back to AC as other small ups do to achieve this.
 
Just something to avoid CT1 and CT2.
Every other feature of this Huaya box but without the 10ms delay and not the conversion to DC and back to AC as other small ups do to achieve this.
Oh, sure if you are only interested in UPS (EPS) and don’t care about offsetting consumption when the grid is up, you don’t need any CT sensors.

The 10ms delay is no big deal as far as UPS so I’m not understanding why you keep harping on that.

And as far as avoiding ‘the conversion to DC and back to AC’, by definition AC-to-DC for storage and DC-to-AC for consumption is inherent to the definition of an AC-coupled battery.

The only way to avoid that is to use a DC-coupled SCC to charge a battery directly (DC-to-DC).

There are plenty of Hybrid inverters combining DC-coupled SCCs with AC inverters for UPS, that’s just not really anything new and not the subject of this new thread I’ve started…
 
Oh, sure if you are only interested in UPS (EPS) and don’t care about offsetting consumption when the grid is up, you don’t need any CT sensors.

The 10ms delay is no big deal as far as UPS so I’m not understanding why you keep harping on that.

And as far as avoiding ‘the conversion to DC and back to AC’, by definition AC-to-DC for storage and DC-to-AC for consumption is inherent to the definition of an AC-coupled battery.

The only way to avoid that is to use a DC-coupled SCC to charge a battery directly (DC-to-DC).

There are plenty of Hybrid inverters combining DC-coupled SCCs with AC inverters for UPS, that’s just not really anything new and not the subject of this new thread I’ve started…
There's nothing really new about this inverter. The deye, sol-ark, gsl inverters have been doing this since they came out 4 years ago. Other than the grid CT, all the inputs to the inverter have integrated CTs so the system "just works"
 
There's nothing really new about this inverter.
I agree and take issue with the title of this thread as well. Zero export is simply one of many features of any well designed hybrid inverter. To me a well designed hybrid inverter includes an automatic transfer switch and the ability to have several modes of operation including load shifting, off grid, self consumption and maximum independence. Some of those modes include zero export and most of those modes require internal or external CTs to operate those modes.

I see this as a growing field and the recent offerings of larger capacity hybrids by Outback, SolArk and others says to me that the manufacturers and building products to satisfy the growing demand.
 
There's nothing really new about this inverter. The deye, sol-ark, gsl inverters have been doing this since they came out 4 years ago.
Solark inverters are rebranded Deye’s, but I’ve never heard of GSL - do you have a link?
Other than the grid CT, all the inputs to the inverter have integrated CTs so the system "just works"
As far as internal CTs, that’s obviously straightforward and not the functionality being discussed.

The only way to control export from grid-side AC-coupled PV is with a variable-power battery charger and an external CT sensor (or energy monitor).

When zip started this thread, so did not realize that Deye/Solark already supported that capability.

So does the Conext XW+ and I’m still trying to understand whether the Victron Multiplus II supports variable charging power or not.

So yes, the capability of the Huayu inverters is not as new as I thought it was when this thread was started…
 
The only way to control export from grid-side AC-coupled PV is with a variable-power battery charger and an external CT sensor (or energy monitor).
I am not clear what you are referring to when you say, "AC coupled PV"?
PV by its nature is DC. Are you referring to a simple GT inverter that cannot operate unless it has an AC signal provided by the grid or a grid forming hybrid inverter?

I am also not sure I understand what a battery charger has to do with controlling export? Most battery chargers vary power during the constant voltage stage by varying current to keep voltage constant. So by definition all battery chargers could be called variable power.
Nothing described earlier in this thread is new as @Vjv mentioned.
 
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I am not clear what you are referring to when you say, "AC coupled PV"?
PV by its nature is DC. Are you referring to a simple GT inverter that cannot operate unless it has an AC signal provided by the grid or a grid forming hybrid inverter?
Yes, I’m talking about a legacy string inverter or Microinverter-based array that is tied to the mains panel (the AC input of the hybrid inverter, not the AC output / critical loads/EPS AC output.
I am also not sure I understand what a battery charger has to do with controlling export?
If AC-coupled solar is connected to the AC-input/grid, the only way to prevent export is to consume the excess generation. Solark, Schneider and supposedly Huayu all support a variable-power AC battery charger that can be programmed to co dime any excess AC-coupled PV power on their AC input before it gets exported (at least as long as the battery is in bulk).
Most battery chargers vary power during the constant voltage stage by varying current to keep voltage constant. So by definition all battery chargers could be called variable power.
Nothing described earlier in this thread is new as @Vjv mentioned.
Once the battery nears full charge and goes out of bulk, this ‘zero export’ function stops working.

It only works while the charger is in bulk charge mode.

A DC-coupled SCC will charge at whatever power the PV array can supply (assuming it has not hit its power limit).

Using a CT-sensor or energy monitor connected to the power main wires, variable-power battery chargers support the capability to charge a battery with exactly the necessary power needed to avoid import or export (with grid-tied solar generation on the AC input).
 
I'm not digging into the part where this product is nothing revolutionary.

But, most importantly: IT IS NOT SPLIT PHASE.
It is not suitable for US use. And with a single grid side current sensor, you can't see half of the current you are using.
 
Doesn't look like US split phase compatible. It looks only 230 vac with neutral - hot across 230vac.

RCD breakers is Residential Circuit Disconnect breaker and is rest of world name for 230vac GFI breakers.

Assume box labelled 'inverter' is grid tied PV inverter.

The diagram does not show any AC coupling of GT inverter to hybrid inverter and doesn't appear to have a way to disconnect from grid mains. Without a relay to release from grid mains there can be no GT PV inverter when grid goes down.

Believe pass-through '>= 40A' should really be '<= 40 amps' maximum pass through. It is amperage limit of pass-relay to Aux panel backup breaker panel.

CT1 & CT2 is taking responsibility for shutting down PV GT inverter if it begins to export to grid. No control line shown to PV GT inverter. Very risky to expect the hybrid inverter has proper data communications control to modulate a random model PV GT inverter output power level.
 
Doesn't look like US split phase compatible. It looks only 230 vac with neutral - hot across 230vac.
First, I started this thread before I understood that Solark/Deye as well as Schneider already supported this capability.

Second, Huayu is rumored to be planning both single-phase 120VAC or 240VAC versions of this product as well as a 120/240 split-phase offering.

Talk is cheap and rumors are even cheaper, so we’ll just need to wait and see what materializes.
RCD breakers is Residential Circuit Disconnect breaker and is rest of world name for 230vac GFI breakers.

Assume box labelled 'inverter' is grid tied PV inverter.

The diagram does not show any AC coupling of GT inverter to hybrid inverter and doesn't appear to have a way to disconnect from grid mains. Without a relay to release from grid mains there can be no GT PV inverter when grid goes down.
The documentation is clearly a work in progress. I believe the intent is to support grid-down power through the EPS/AC output only when the grid goes down…
Believe pass-through '>= 40A' should really be '<= 40 amps' maximum pass through. It is amperage limit of pass-relay to Aux panel backup breaker panel.
For sure.
CT1 & CT2 is taking responsibility for shutting down PV GT inverter if it begins to export to grid. No control line shown to PV GT inverter. Very risky to expect the hybrid inverter has proper data communications control to modulate a random model PV GT inverter output power level.
No, this is not shutting down a legacy grid-tied PV inverter (that’s impossible without rewiring it from grid to AC output. The intent is to use the CT sensors to determine excess PV production after loads have been served and to consume exactly that amount of AC-coupled power to charge the battery rather than allowing it to be exported. It’s ‘zero export through modulated consumption’ rather than ‘zero export by throttling solar production’ or ‘zero export by modulated production from battery’.

Again, Deye/Solark as well as Schneider Conext XW+ already support this capability.
 
I'm not digging into the part where this product is nothing revolutionary.

But, most importantly: IT IS NOT SPLIT PHASE.
It is not suitable for US use. And with a single grid side current sensor, you can't see half of the current you are using.
As I just posted, Huayu has said they will make a split phase version of this battery inverter, but even a single-phase 120V option delivers some interesting possibilities:

2 inverters on a single battery will support split-phase operation when on grid (by being connected to separate legs) and wil support true zero export better than either Solark/Deye or Schneider Conext XW+ will (since each leg will be zero export & zero import rather than only 240VA net export being zero as Solark and Conext deliver).

If you don’t mind having one leg exporting and one leg importing and you can get by with only single-phase 120VAC for backup, you can get by with just a single 120VAC single-phase battery inverter.

You’’ll consume excess 24VAC production on one 120VAC leg, so that leg will import while the other leg will export, but the sun will be zero.

When offsetting consumption, the situation will be reversed and the leg withdrew the inverter will export while the other leg will import (but the sun will again be zero kW).

When the grid goes down, only the one leg with the battery inverter connected to it will have power.

Victron is offering something similar with their Multiplus II for US market but they have a pair of transfer switches to pass through both legs of 240VAC while the grid is up and then pass the same 120VAC output to both legs when the grid is down (so all 120VAC loads are powered in backip mode, but not 240VAC loads…):

 
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I am not clear what you are referring to when you say, "AC coupled PV"?
PV by its nature is DC. Are you referring to a simple GT inverter that cannot operate unless it has an AC signal provided by the grid or a grid forming hybrid inverter?

I am also not sure I understand what a battery charger has to do with controlling export? Most battery chargers vary power during the constant voltage stage by varying current to keep voltage constant. So by definition all battery chargers could be called variable power.
Nothing described earlier in this thread is new as @Vjv mentioned.
I have a Enphase grid coupled system but I do not want to pay the big $s for their batteries. What I want is for a inverter charger that will use the CTs to use the inverter for when power is coming off the grid (commonly available) but also use the charger when excess power is being generated on the grid tied micro inverters. The inverter/charger 's that I am aware of only throttle the charger based on PV energy supplied THROUGH the inverter/charger.
Does anyone know of a device that does 0 grid based on CTs and NO attacked PVs?
 
Does anyone know of a device that does 0 grid based on CTs and NO attacked PVs
If all you want is zero exportn and you have an Envoy, just buy the CTs and configure your micros for zero export.
Also there are lots of hybrid inverters that can be configured for maximum independance or self consumption and are capable of AC coupling to your micros. The hybrid generally have an automatic transfer switch and the AC out and micros are wired to the same sub panel. My Outback Skybox does that. SolArk, some Schneider, SMA and other brands do that. Each have their own limits on how much AC coupled capacity they can handle.
I am of the opinion that only a building permit is needed to add to you system since it is behind the meter. If you want to add additional PV solar to the hybrid you can limit the export to the amount in your PTO and not have to ask permission from your utility.
 
I do not just want just 0 export. I want to store that excess energy in a set of agnostic batteries. Using the envoy will just throttle back the production on my micro-inverters. I want to generate that extra energy, I just do not want to ship it off to our utility. I want to use that stored energy later to offset demand when my loads exceed what the micro-inverters are producing.
An option that I have been looking at is running the micro-inverters through a SolArk 12K ($7,000). The problem there is if you do that then you can not run a generator at the same time. Also they need to have PV generated energy that runs through there inverter in order to establish a stable system(another $5,000). All they can do with the Microinverters is turn then on and off through frequency shifting. Not really a good solution unless you buy a bunch of PVs and run them through THEIR inverter/Charger. What I am hoping is out there, is a more simple solution where one set of CTs can look at inflow and out flow and consume or supplement it to get me to a 0 grid situation (pending SOC of the batteries).
 
The issue is that it is a complex problem to be solved. It requires a complex piece of hardware with complicated firmware. The least expensive solutions in the Tier One offerings are from Outback, SolArk and others.
You are correct that some of them run better with a minimal DC coupled array of solar panels. I wanted that extra capacity anyway and had room on a patio cover to install some used Sunpower panels. Earlier in this thread there is some discussion of less expensive solutions.
If those don't work for you then my suggestion is that you start a new thread with a title specific to your use case. I think the Skybox and SolArk can accomodate generator input but not concurrent with AC coupling. My guess is that is a simple workaround that could be done with a manual set of switches and/or breakers.
 
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