New 6KW Setup - Basic Questions

[jainsushant]

existing setup without solar.jpg

Hi

I am a new to this forum. What I wish to ask may be too elementary for you all, but please excuse me for this.

I have attached the image of my existing setup here. This is the setup of my factory unit where the total AC load (Including all machines, lights, fans, ACs, computers etc.) is 30 KVA or a little more. As you can see that in my setup, I have a DG connected of 32.5KVA. Now, in summers, when we use the ACs, the connected load is much more than the capacity of our DG, so, we are forced to switch off some of the machines/ACs during grid unavailability so we can use the DG for other machines and load. So, before the summers, we were considering to upgrade the DG to support more load. And the only way to do that is replace it with higher capacity. Now, I have come up with the bright idea of installing solar panels and doing away with DG replacement expenditure. So, to go about it, I have a few questions. I request you all to please answer them for me and help me accomplish this project without errors. I wish to use Grid Tie Inverters. My questions are:

1. Since my distribution is of 3 Phase, I am planning to buy a 3 Phase Inverter. Is this right? Or should I use 3 smaller Inverters; one for each phase?

2. What is the best place to connect the output of the Inverter? Should it be put after the switch? If yes, my concern is that the capacity of my Inverter will be 6 KW, but additional 24 - 25 KW of power will be running through the Inverter. Will this not burn the Inverter?

3. Please see the below image:

Proposal 1.jpg

Is this looped kind of connection possible? i.e. inward connection from the bus bar and giving back to the bus bar again?Or will it just burn everything?

4. Finally, I want to keep my system upgrade friendly. i.e. if I wish to increase the capacity of the solar, I wish that to be as easy as possible without making my existing investment redundant.

Please advice me how can I achieve this? Thanks in advance

Regards

Sushant

[SunEagle]

[ATTACH=CONFIG]3872[/ATTACH]

Hi

I am a new to this forum. What I wish to ask may be too elementary for you all, but please excuse me for this.

I have attached the image of my existing setup here. This is the setup of my factory unit where the total AC load (Including all machines, lights, fans, ACs, computers etc.) is 30 KVA or a little more. As you can see that in my setup, I have a DG connected of 32.5KVA. Now, in summers, when we use the ACs, the connected load is much more than the capacity of our DG, so, we are forced to switch off some of the machines/ACs during grid unavailability so we can use the DG for other machines and load. So, before the summers, we were considering to upgrade the DG to support more load. And the only way to do that is replace it with higher capacity. Now, I have come up with the bright idea of installing solar panels and doing away with DG replacement expenditure. So, to go about it, I have a few questions. I request you all to please answer them for me and help me accomplish this project without errors. I wish to use Grid Tie Inverters. My questions are:

1. Since my distribution is of 3 Phase, I am planning to buy a 3 Phase Inverter. Is this right? Or should I use 3 smaller Inverters; one for each phase?

2. What is the best place to connect the output of the Inverter? Should it be put after the switch? If yes, my concern is that the capacity of my Inverter will be 6 KW, but additional 24 - 25 KW of power will be running through the Inverter. Will this not burn the Inverter?

3. Please see the below image:

[ATTACH=CONFIG]3873[/ATTACH]

Is this looped kind of connection possible? i.e. inward connection from the bus bar and giving back to the bus bar again?Or will it just burn everything?

4. Finally, I want to keep my system upgrade friendly. i.e. if I wish to increase the capacity of the solar, I wish that to be as easy as possible without making my existing investment redundant.

Please advice me how can I achieve this? Thanks in advance

Regards

Sushant

I am sure there is grid tie equipment that uses solar pv to generate the 3 phase power you need. The big issue is that the safety systems built into a grid tie solar system will keep it from producing any electricity if the Utility grid goes down. You will be forced to use your DG to provide all power as you do now.

You can build a solar battery off grid system to provide extra power although that would be much more expensive than upgrading your DG to a size to handle all your needs.

[inetdog]

1. Since my distribution is of 3 Phase, I am planning to buy a 3 Phase Inverter. Is this right? Or should I use 3 smaller Inverters; one for each phase?

I have not yet seen a three phase grid tie inverter for sale that does not actually consist of three separate inverters, each one wired either phase to phase or phase to neutral depending on the design.
If you have a particular brand and model three phase inverter in mind, please let us know about it. (But no click-able links please.)

[SunEagle]

I have not yet seen a three phase grid tie inverter for sale that does not actually consist of three separate inverters, each one wired either phase to phase or phase to neutral depending on the design.
If you have a particular brand and model three phase inverter in mind, please let us know about it. (But no click-able links please.)

I was thinking of a company called Advanced Energy. They make all types of grid tie inverters for small residential, commercial and utility systems. I have actually seen a couple of their 500kw inverters at a school that has a 1MW solar farm but I just don't remember if they make a small 3 phase inverter in the range the OP was looking for.

[Naptown]

Fronius, power 1, both make them in the three phase versions
Problem comes in with using in tandem with a generator. Not going to happen.

[jainsushant]

I have not yet seen a three phase grid tie inverter for sale that does not actually consist of three separate inverters, each one wired either phase to phase or phase to neutral depending on the design.
If you have a particular brand and model three phase inverter in mind, please let us know about it. (But no click-able links please.)

Well, a lot of companies make 3 phase grid tie inverters. The one I am considering is Delta and SMA (Makers of Sunny boy). But this decision is smaller. My bigger concern is how to connect the Inverter to my existing setup. Is creating a loop as shown by me in the image wise enough? Or is it that I have to separate the distributions ahead.

Someone please advice

[jainsushant]

Fronius, power 1, both make them in the three phase versions
Problem comes in with using in tandem with a generator. Not going to happen.

Hi Naptown

Even my DG is three phase. And since I have a manual switch over, I see no problem in that. Can you please explain where am I going wrong?

And what do you suggest about where to connect the Inverter?

[SunEagle]

Hi Naptown

Even my DG is three phase. And since I have a manual switch over, I see no problem in that. Can you please explain where am I going wrong?

And what do you suggest about where to connect the Inverter?

It doesn't matter where you connect the inverter. If the grid goes down the inverter for the solar panels will also shut down. You will only have your DG to provide the electric needs.

[jainsushant]

It doesn't matter where you connect the inverter. If the grid goes down the inverter for the solar panels will also shut down. You will only have your DG to provide the electric needs.

Why cannot DG act as the grid? I am not feeding anything to the grid. I just wish to reduce the load on DG.

[SunEagle]

Why cannot DG act as the grid? I am not feeding anything to the grid. I just wish to reduce the load on DG.

The inverter is looking for specific electrical parameters that a generator will not provide. Only a Utility power grid can do that. That is how the inverter is designed. No grid power means no solar pv power.

[inetdog]

Why cannot DG act as the grid? I am not feeding anything to the grid. I just wish to reduce the load on DG.

A grid tied inverter has no way to throttle back its output if the load decreases, and if it tries to backfeed the generator there will be problems.

A hybrid off grid system designed for "generator support" can effectively limit its output to keep a non-zero load on the generator, but the inverter has to have battery storage connected to do that. There are very robust but very expensive systems that can do this well (notably from Xantrex).
Or the SMA Sunny Boy GTIs can be associated with a single Sunny Island off grid inverter to supply the grid function that the SBs need, while providing feedback that lets the SBs generate less than their maximum output. But the SI will not synchronize its output to a generator, making the whole process unworkable in that case.

Note that I am not saying that it cannot be done, just that nobody does it in a commercial unit that passes UL and NEC requirements for use in the US AFAIK.

[jainsushant]

A grid tied inverter has no way to throttle back its output if the load decreases, and if it tries to backfeed the generator there will be problems.

A hybrid off grid system designed for "generator support" can effectively limit its output to keep a non-zero load on the generator, but the inverter has to have battery storage connected to do that. There are very robust but very expensive systems that can do this well (notably from Xantrex).
Or the SMA Sunny Boy GTIs can be associated with a single Sunny Island off grid inverter to supply the grid function that the SBs need, while providing feedback that lets the SBs generate less than their maximum output. But the SI will not synchronize its output to a generator, making the whole process unworkable in that case.

Note that I am not saying that it cannot be done, just that nobody does it in a commercial unit that passes UL and NEC requirements for use in the US AFAIK.

Thanks for all the inputs. So, I understand now that if there is no grid, there is no generation. But if the DG is still giving input on the Inverter, will that be a problem?

And can the output of the inverter feed back the same phase line from where it is drawing power, creating the loop? Or is it too stupid to do?

[inetdog]

Thanks for all the inputs. So, I understand now that if there is no grid, there is no generation. But if the DG is still giving input on the Inverter, will that be a problem?

And can the output of the inverter feed back the same phase line from where it is drawing power, creating the loop? Or is it too stupid to do?

Depending on the exact design of the anti-islanding circuitry in a particular model GTI, it may or may not accept a well controlled generator output as being a grid.
If it does not accept it, there will be no harm. If it does accept it, then you run the risk of burning out the generator rather than harming the GTI.
The GTI will not try to deliver power into a short circuit or into any similar condition caused by feedback.
A GTI can only deliver power into the phase line that it is connected to, so I am not sure I see your point.
It will NOT however, deliver power into a resonant circuit where it is the only power source. That is a requirement of the anti-islanding protection design.

[jainsushant]

Depending on the exact design of the anti-islanding circuitry in a particular model GTI, it may or may not accept a well controlled generator output as being a grid.
If it does not accept it, there will be no harm. If it does accept it, then you run the risk of burning out the generator rather than harming the GTI.
The GTI will not try to deliver power into a short circuit or into any similar condition caused by feedback.
A GTI can only deliver power into the phase line that it is connected to, so I am not sure I see your point.
It will NOT however, deliver power into a resonant circuit where it is the only power source. That is a requirement of the anti-islanding protection design.

Thanks inetdog for the reply. This has made the most sense to me till now. Can you please answer one very basic question? The reason for asking the basic is because I have never seen a GTI physically myself.

What I wish to ask if is whether there are 2 connection between the circuit breaker panel and the GTI i.e. one being input of AC and another being output? Or just one connection that senses and passes current?

Thanks

Sushant

[DreInMD]

Thanks inetdog for the reply. This has made the most sense to me till now. Can you please answer one very basic question? The reason for asking the basic is because I have never seen a GTI physically myself.

What I wish to ask if is whether there are 2 connection between the circuit breaker panel and the GTI i.e. one being input of AC and another being output? Or just one connection that senses and passes current?

Thanks

Sushant

There is just the one AC connection. At least on my inverters.