Grid tie inverter with off grid system?

[saggys]

Hi,

Was wondering if adding a small 1000 watt 120 volt grid tie inverter to an existing 1100 watt off grid inverter would be worth it? I was thinking of keeping my existing off grid system charging my batteries and for overnight loads and using the grid tie for sunshine daytime loads, supplement A/C, washing machine, etc.
What would happen if you have more power available than usage? Does the grid tie throttle back the panels? I know it would probably be more efficient to add to my off grid system, but this separate addition might be easier and cheaper.

 

[Ampster]

It would work if the GT inverter had external current transformers to limit power so nothing is exported. I am only referring to functionality. Building permit is another issue.

 

[saggys]

No export happening, off grid system only.

 

[Ampster]

No export happening, off grid system only.

If you don't have a grid connection then an inexpensive GT inverter won't work. Your off grid inverter probably can't AC couple to it.
Are you constrained by inverter capacity or solar panel capacity? Trying to figure out the most cost effective way to get you a kW for a few hours during the day.

 

[saggys]

That is what I was wondering? Why would it not sync? It is a true sine wave inverter.

 

[Ampster]

Why would it not sync? It is a true sine wave inverter.

GT inverter goes through a series of tests to verify that there is a true grid. It is not just 60 Hz it is looking for. It needs to see infinite impedance and a few other things the grid presents. What that means in real terms is the grid presents an infinite load to a GT inverter which then sends all the energy the GT inverter can pull from the solar panels. Without that buffer, when the loads drop there is no place for the energy to go and the result is the smoke gets out of the device that may have tried to fool the GT inverter. That is what AC coupling is about and what a good hybrid inverter can do. Hope that helps.

 

[fromport]

Hi,

Was wondering if adding a small 1000 watt 120 volt grid tie inverter to an existing 1100 watt off grid inverter would be worth it? I was thinking of keeping my existing off grid system charging my batteries and for overnight loads and using the grid tie for sunshine daytime loads, supplement A/C, washing machine, etc.
What would happen if you have more power available than usage? Does the grid tie throttle back the panels? I know it would probably be more efficient to add to my off grid system, but this separate addition might be easier and cheaper.

Really depends on the inverter you currently have. Eg a sunnyboy Island is able to use frequency control the power of an AC coupled inverter.
If you would have to buy a new inverter better get a larger one and hook all current & future PV to that.

 

[Ellcon123]

Checkout thebackshed forumn. I believe the big issue is controlling output from GTI. They are designed to push all available Watts into the grid so you need a method to divert or stop.

 

[saggys]

Thank you for the replies, I have little knowledge of grid tie inverters. The explanations have helped clear this up.

 

[Ampster]

I believe the big issue is controlling output from GTI. They are designed to push all available Watts into the grid so you need a method to divert or stop.

Yes that is the issue. As mentioned above, a hybrid inverter which can AC couple can manage a GT inverter,

 

[Ellcon123]

https://www.thebackshed.com/forum/ViewTopic_mobile.php?FID=4&TID=14747

 

[saggys]

Thanks for the link.