Grid Tied + Hybrid in one system

HecThor

Member
Location
Philippines
Hello All,

As stated above, one client of ours wants a grid-tied system with a hybrid system for resiliency. I don't have yet the rating of the distribution panel that we are about to install. The plan is to do a supply/line side tap for the grid tied system and do a load side tap with the hybrid system. Is there a code reference prohibiting to do grid tied and hybrid in one system? Thanks in advance.
 

GoldDigger

Moderator
Staff member
There is no code prohibition against having both types of system at one site.
But a high quality hybrid system will allow you to incorporate as high a grid tied power total as you want. That is why it is called a hybrid system.
It is true that the ATS component of the hybrid system will limit the amount of power to be sold back to the grid, but I still have the feeling that a single integrated system will be both more cost effective and more efficient than two independent systems.
This may be either an AC coupled or a DC coupled system. I suspect that an AC coupled system such as the Sunny Boy/Sunny Island system will be better able to accommodate a large amount of grid tied power.

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HecThor

Member
Location
Philippines
There is no code prohibition against having both types of system at one site.
But a high quality hybrid system will allow you to incorporate as high a grid tied power total as you want. That is why it is called a hybrid system.
It is true that the ATS component of the hybrid system will limit the amount of power to be sold back to the grid, but I still have the feeling that a single integrated system will be both more cost effective and more efficient than two independent systems.
This may be either an AC coupled or a DC coupled system. I suspect that an AC coupled system such as the Sunny Boy/Sunny Island system will be better able to accommodate a large amount of grid tied power.

Sent from my XT1585 using Tapatalk
With that regard, Can I combine the inverter output circuit of let's say (4)grid-tied inverter and the AC output of (1)hybrid inverter and connect it as supply/line side tap? By the way we are using Solax SK-TL5000E hybrid inverter with Emergency Power Supply(EPS) function. Thanks for your input!
 

jaggedben

Senior Member
With that regard, Can I combine the inverter output circuit of let's say (4)grid-tied inverter and the AC output of (1)hybrid inverter and connect it as supply/line side tap? By the way we are using Solax SK-TL5000E hybrid inverter with Emergency Power Supply(EPS) function. Thanks for your input!
I don't believe there's any problem with that.
 

pv_n00b

Senior Member
Location
CA, USA
You have to have some type of ATS to isolate the local system from the grid when in backup mode. You can interconnect the grid-tied inverters to the service supply side and the hybrid inverter to the backup input to an ATS. How you connect the ATS into the system depends on what you want to backup and if you want the ATS to be the service disconnect.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
You have to have some type of ATS to isolate the local system from the grid when in backup mode. You can interconnect the grid-tied inverters to the service supply side and the hybrid inverter to the backup input to an ATS. How you connect the ATS into the system depends on what you want to backup and if you want the ATS to be the service disconnect.
Don't hybrid inverters usually have their own ATS with separate terminals for connecting to the grid and to the protected loads? And yeah, I know we're not supposed to call them protected loads any more, but you know what I mean.
 

GoldDigger

Moderator
Staff member
Don't hybrid inverters usually have their own ATS with separate terminals for connecting to the grid and to the protected loads? And yeah, I know we're not supposed to call them protected loads any more, but you know what I mean.
Yes, in general they do. That is necessary to both allow grid interaction and provide islanded power when the grid is down. Some have an additional set of AC input terminals for a local generator and may include generator control circuitry.
 

jaggedben

Senior Member
Strictly speaking the switches in these inverters don't typically have a 'transfer' function. They only disconnect the 'island' from the grid to let it operate on its own. The code term is 'micro-grid interconnect device'.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Yes, in general they do. That is necessary to both allow grid interaction and provide islanded power when the grid is down. Some have an additional set of AC input terminals for a local generator and may include generator control circuitry.
I'm not current on PV technologies except for what I read in the general press and surfing the Web, but If you're in island mode, don't you need batteries or some other storage to smooth the demand/supply response of the system?
 

pv_n00b

Senior Member
Location
CA, USA
Don't hybrid inverters usually have their own ATS with separate terminals for connecting to the grid and to the protected loads? And yeah, I know we're not supposed to call them protected loads any more, but you know what I mean.
You are correct and the hybrid inverter will then have two outputs, one for the utility interconnection and one for the protected load panel. The OP stated they were connecting the hybrid inverter to the service panel with no other connection so it is unclear if the inverter they are using has two outputs and internal switching. If it only has one output intended to back up a load then there needs to be an ATS.

I must have missed the memo, what's wrong with using "protected loads"? "Critical load is worse and I hear people using that.
 

PWDickerson

Senior Member
Location
Clinton, WA
With that regard, Can I combine the inverter output circuit of let's say (4)grid-tied inverter and the AC output of (1)hybrid inverter and connect it as supply/line side tap? By the way we are using Solax SK-TL5000E hybrid inverter with Emergency Power Supply(EPS) function. Thanks for your input!
When you connect the output of a grid-tied inverter (or 4 of them) to the output of a hybrid inverter (a.k.a. grid-tied battery inverter), this is known as AC coupling. It is important to understand that you can over-charge the battery with this type of system if you don't include design features to prevent it. Specifically, in the event that the grid is down, the sun is shining, and the backup loads are small, the grid-tied inverter(s) will send an unregulated charge back through the hybrid inverter and over-charge the battery bank. Design features to prevent this scenario from occurring should be inherently fail safe. For instance, a voltage sensing relay, using the upper limit of battery voltage as the set point, can be used to drive the coil of a power relay that opens the grid-tie inverter output circuit. If the "normally open" contacts of both relays are used, the system will shut down the grid-tie inverters in the event of a component failure. Or better yet, use SMA inverters that take care of this problem for you automatically.

If you do use relays to prevent over-charging, you will want to set the disconnect voltage at the upper limit of the battery voltage, and the re-connect voltage low enough to prevent the system from cycling on and off continually.

You mentioned connecting the hybrid inverter as a supply side tap. This is confusing. I assume that your hybrid inverter has an AC input that connects to the grid, and an AC output that connects to a backup loads panel. If you connect the grid-tied inverter(s) to the AC output of the hybrid inverter, you cannot also connect them as a supply side tap. You can connect the AC input of the hybrid inverter as a supply side tap, but not the AC output. You need to make sure that your hybrid inverter has the capacity to pass all of the grid-tied inverter current through from its output terminals to its input terminals.
 

jaggedben

Senior Member
I'm not current on PV technologies except for what I read in the general press and surfing the Web, but If you're in island mode, don't you need batteries or some other storage to smooth the demand/supply response of the system?
Pretty much yes, although a few inverters have a feature where they power a single 15A receptacle as long as there's enough sun.

...
I must have missed the memo, what's wrong with using "protected loads"? "Critical load is worse and I hear people using that.
I'm guessing that ggunn mistyped. I agree that 'critical' is the term to stay away from. (For similar reasons, the name of that receptacle I referred to above got change from 'emergency power supply' to 'secure powr supply' early on.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I'm guessing that ggunn mistyped. I agree that 'critical' is the term to stay away from. (For similar reasons, the name of that receptacle I referred to above got change from 'emergency power supply' to 'secure powr supply' early on.
Not exactly; I was speaking from (my apparently erroneous) memory.
 

HecThor

Member
Location
Philippines
You mentioned connecting the hybrid inverter as a supply side tap. This is confusing. I assume that your hybrid inverter has an AC input that connects to the grid, and an AC output that connects to a backup loads panel. If you connect the grid-tied inverter(s) to the AC output of the hybrid inverter, you cannot also connect them as a supply side tap. You can connect the AC input of the hybrid inverter as a supply side tap, but not the AC output. You need to make sure that your hybrid inverter has the capacity to pass all of the grid-tied inverter current through from its output terminals to its input terminals.
You assumed correctly, it has two AC ports, an AC input that connects to the grid which can also output energy from the battery at night time as long as the grid is on and an AC output for selected loads which supplies energy from the battery only when the grid is down. Different workmode can also be done with this inverter such as load priority battery>load> grid or load>battery>grid to name a few also choosing when the battery discharges. Initially the plan is to connect the AC input of the hybrid inverter together with grid tied inverters but due to design limitation, it will now be load side.
 
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