Adding grid tie inverter to existing off grid (Axpert hybrid inverter) system

[Mikenr]

I have been doing a lot of research about this and have yet to come up with a good answer - I hope the community can help. . .

At the moment I have a 24v 3kW Axpert OMEGA UM v3 (it is branded as a 'Master Power') with approx a 5kW home built lithium battery and 1.3kW of panels - which has been more than enough for our needs.

Having bought an electric car this year, I have bought eighteen 450w Canadian Solar panels, to be able to charge the car - What I would like to do, if it's possible, is to keep my existing hybrid inverter and battery, add a grid tie inverter to charge the car, run heating etc in the house when the car doesn't need charging/isn't at home, and charge the battery.

The existing 1.3kW of panels will have to go, but it would be good to avoid having to replace the battery, also from what I understand a grid tie inverter would be more efficient and economic than a higher capacity hybrid inverter.

I am looking at 8kW single phase inverters to be able to charge the car at 7.4kW

Many thanks in advance with thoughts/opinions/advice on the matter ???

 

[meetyg]

I'm not sure I understand exactly your proposed setup.

AFAIK, You should not connect a grid-tie inverter to the output of an off-grid inverter!
That's because the grid tie will try to push as much current as possible, available from solar. In order to do this, it will raise the voltage (as current flows from a high potential to a lower potential). If there aren't enough loads, this can raise the AC voltage on the off-grid too high and effectively blow up your Axpert inverter.
If your grid tie inverter has export limiting via a CT clamp, that might be fine, but I would still be reluctant to do so.

If you will connect the grid tie to your grid, that's OK. If any power is not used by house loads, it will flow back to the grid (unless again it has export limiting functionality). You should check with your local regulations if that's legal.

Then, you can set your Axpert to charge battery via the grid (AC IN) and some/all of that will be powered by the grid tie.

 

[timselectric]

I wouldn't bother with a grid-tied inverter. These days it's not worth the hassle. And getting worse every day.
But there are a few believers left, who might be able to help you. If you are dead set on pursuing it.
I would recommend increasing your off grid setup. With the grid as backup.

 

[Mikenr]

I'm not sure I understand exactly your proposed setup.

AFAIK, You should not connect a grid-tie inverter to the output of an off-grid inverter!
That's because the grid tie will try to push as much current as possible, available from solar. In order to do this, it will raise the voltage (as current flows from a high potential to a lower potential). If there aren't enough loads, this can raise the AC voltage on the off-grid too high and effectively blow up your Axpert inverter.
If your grid tie inverter has export limiting via a CT clamp, that might be fine, but I would still be reluctant to do so.

If you will connect the grid tie to your grid, that's OK. If any power is not used by house loads, it will flow back to the grid (unless again it has export limiting functionality). You should check with your local regulations if that's legal.

Then, you can set your Axpert to charge battery via the grid (AC IN) and some/all of that will be powered by the grid tie.

Many thanks! I am 100% off grid, the nearest connection to the grid is several kilometers away . . .

Thank you again for your thoughts/advice ??

 

[Mikenr]

I wouldn't bother with a grid-tied inverter. These days it's not worth the hassle. And getting worse every day.
But there are a few believers left, who might be able to help you. If you are dead set on pursuing it.
I would recommend increasing your off grid setup. With the grid as backup.

Thanks for your thoughts ??? Grid as a backup - not an option for me the nearest connection to the grid is several kilometers away . . .

 

[timselectric]

Thanks for your thoughts ??? Grid as a backup - not an option for me the nearest connection to the grid is several kilometers away . . .

Ok so, grid-tied is not even an option.
Just expand your existing system.
I assume that your "home built battery" is diy from cells. I would recommend reconfiguring to a 48v system. It's more efficient and wiring can be smaller/cheaper.

 

[timselectric]

It looks like you have a 230v single phase system.
If you are wanting to increase your solar and daytime AC output. Without adding batteries.
You can use a Growatt SPF-5000-ES in SUB mode.
If you can charge the EV during the day.

 

[timselectric]

You could also add a 24v separate AC charger to charge your existing battery.

 

[meetyg]

Many thanks! I am 100% off grid, the nearest connection to the grid is several kilometers away . . .

Thank you again for your thoughts/advice ??

So you are totally off-grid with only a 3kw inverter?
Impressive...

 

[Mikenr]

It looks like you have a 230v single phase system.
If you are wanting to increase your solar and daytime AC output. Without adding batteries.
You can use a Growatt SPF-5000-ES in SUB mode.
If you can charge the EV during the day.

That would be an option - but I'd really like to charge my car at 7.4kW on bright sunny days - which are many here ?

 

[Mikenr]

So you are totally off-grid with only a 3kw inverter?
Impressive...

Yep - for more than 10 years we made do with a lot less ?

 

[pollenface]

Don't add grid tie to an off grid system unless you have sufficient loads to soak up the power or use a power limiting inverter with a current sensor, otherwise you may destroy your primary "off grid" inverter.

 

[meetyg]

Yep - for more than 10 years we made do with a lot less ?

Did you have the Axpert for the whole ten years? Any major problems?

It would be tough charging an EV with only 3kw (probably less due to home loads).
In your case I would get a larger off-grid inverter that can run off of solar only (maybe a small battery just as a buffer for some clouds). I think some of the larger MPP and maybe EG4 can do that. Just to save you the expense of a large new battery (probably 48v).

See this for example:

Also, make sure you get an EV charger with adjustable current setting to match your new inverter's max output (or say 80% of that for longevity).

 

[timselectric]

That's why I suggested the Growatt SPF-5000-ES.
Because it can be used without batteries.
For 7.2 kw you'll need two. But still a reliable cheap option.
With SUB mode, it can be placed after your existing system and increase the power for your other loads as well. This will let your existing system be more dedicated to the batteries that you already have. And take over at night.

 

[Mikenr]

Did you have the Axpert for the whole ten years? Any major problems?

It would be tough charging an EV with only 3kw (probably less due to home loads).
In your case I would get a larger off-grid inverter that can run off of solar only (maybe a small battery just as a buffer for some clouds). I think some of the larger MPP and maybe EG4 can do that. Just to save you the expense of a large new battery (probably 48v).

See this for example:

Also, make sure you get an EV charger with adjustable current setting to match your new inverter's max output (or say 80% of that for longevity).

I don't charge it off the 3kW inverter, and I have only had the Axpert for a couple of years, no problems apart from that I have to play games with it to make it charge from my generator, most likely because the generator is a cheap one. I plan to use an EV charger that will work with the excess power adjusting itself accordingly ???

 

[timselectric]

I plan to use an EV charger that will work with the excess power adjusting itself accordingly

Have you already figured out how to accomplish this?

 

[Mikenr]

That's why I suggested the Growatt SPF-5000-ES.
Because it can be used without batteries.
For 7.2 kw you'll need two. But still a reliable cheap option.
With SUB mode, it can be placed after your existing system and increase the power for your other loads as well. This will let your existing system be more dedicated to the batteries that you already have. And take over at night.

So I could have 2 Growatt SPF-5000-ES connected in parallel, to the output of my existing inverter, a 24v charger to charge my existing battery and have the existing inverter giving me power at night/bad weather days - am I getting that right?

 

[timselectric]

So I could have 2 Growatt SPF-5000-ES connected in parallel, to the output of my existing inverter, a 24v charger to charge my existing battery and have the existing inverter giving me power at night/bad weather days - am I getting that right?

Correct
You may not need the extra 24v charger. Because during the day, the Growatt's will cover all loads and the original setup will probably easily charge the batteries on its own. Since that's all that it will have to do. But, it could come in handy for cloudy days.

 

[Mikenr]

Have you already figured out how to accomplish this?

There's a company Orbis Energy (https://orbis.es/) who I have already been in contact with about this - they assure me that it's possible with their Viaris UNI charger plus another piece OB709800 Viaris Solar, if it can work then it would be ideal ?

 

[Mikenr]

Correct
You may not need the extra 24v charger. Because during the day, the Growatt's will cover all loads and the original setup will probably easily charge the batteries on its own. Since that's all that it will have to do. But, it could come in handy for cloudy days.

That's great news - I will need a 24v charger because I don't have room on my roof to keep the existing panels ?
I'm gonna have to figure out how to arrange my eighteen 450w panels, I was planning on 2 strings of 9 panels, but I guess with 2 Growatt inverters I would need 4 strings, right?