Hi,

I need some recommendations. A year ago, I installed 30 x 280W solar panels with 2 x OGT5.0-1P grid tied inverters. It seemed like a good Idea at the time. It produces more than enough power during the day but the moment the grid goes down so does the inverters.

Currently our municipality is in arrears with Eskom and we are getting daily power cuts.

I have a small 3kva Axpert inverter with 4 x 100Ah batteries that is now 3 years old that I use for essential necessary systems. I have a LPG gas powered generator for rainy days. I can not run other devices until I start the generator.

I got 4 x 100Ah batteries two weeks ago with the idea that I want to connect a second Axpert inverter for my crypto mining machines. Not done yet.

Now with this municipality throwing a spanner into the works I have ordered 2 x Axpert 5kva inverters to replace the Omnipower ones as they are the cheapest. I am going to setup them in parallel. If the municipality do not come to agreement with Eskom in the next week we will have power cuts from 6 am until 8pm.

As a small computer retail store owner, I am not worried about power after hours. I would like to do AC coupling and use the 2 x OGT5.0-1P to produce AC power for the inverters if possible.

The plans were to replace them in another 2 years with a full hybrid system.

The question is what is the minimum battery bank that I can get away with? I plan to replace it with lithium in the future and go off grid completely.

How will I direct the electrician to install the system? Minimum system requirements without compromising safety.

35 minutes ago, Slowpoke said:

As a small computer retail store owner, I am not worried about power after hours. I would like to do AC coupling and use the 2 x OGT5.0-1P to produce AC power for the inverters if possible.

Can't do that with Axperts. When the grid goes down the grid-tied units go down too. You cannot tie them to the output of the axpert without blowing things up either.

Your only options are 1) install axpert as a plain UPS and write off the power from the grid-tied inverters, 2) get rid of the grid-tied inverters and tie the PV panels via MPPT to the battery bank, 3) get an inverter that supports the GTIs on the output, like a Victron Multiplus for example.

Hi plonkster,

Lets go with option 2.

What is the minimum battery bank that I will need?

Do I need to change the solar panel setup from the  2 x OGT5.0-1P  to work with the Axperts? . I have been reading up on the setup and have confused myself over the weekend.

Why do you have a Commodore 64 badge? The Commodore 64 were one of the first computers I ever worked on.

16 minutes ago, Slowpoke said:

Hi plonkster,

Lets go with option 2.

What is the minimum battery bank that I will need?

Voltronic recommend 200Ah minimum. With 2 Axperts the recommendation would then be 400Ah which is a sizable bank. I have seen folk squeak in with 100Ah per inverter but if they are lead acid batteries be prepared for some voltage overshoots. I have 200Ah of Lithium which is a completely different beast. Plus I do not have a full complement of PV so its not balls to the wall and my batteries have a breather.

21 minutes ago, Slowpoke said:

Do I need to change the solar panel setup from the  2 x OGT5.0-1P  to work with the Axperts? . I have been reading up on the setup and have confused myself over the weekend.

Yes you probably will have to GTIs generally have high voltage MPPTs so you probably have those panels in 2 to 4 strings. The Axpert MPPT max is 145V DC and so I recommend max three 60 cell panels and two 72 cell panels in series.  In warmer parts of the country you may be able to get away with three 72 cell panels in series.

27 minutes ago, Slowpoke said:

Why do you have a Commodore 64 badge? The Commodore 64 were one of the first computers I ever worked on.

It is in recognition of Plonky's contribution to the forum. @plonkster is our resident IT, electrical guru with a affinity for history and philosophy hence the Commodore reference. 

5 hours ago, Slowpoke said:

Hi plonkster,

Lets go with option 2.

What is the minimum battery bank that I will need?

Do I need to change the solar panel setup from the  2 x OGT5.0-1P  to work with the Axperts? . I have been reading up on the setup and have confused myself over the weekend.

Why do you have a Commodore 64 badge? The Commodore 64 were one of the first computers I ever worked on.

Commodore 64 badge! haha. Love it!!! I try my best to think up the best names I can. I will get to everyone who is frequent on the forum. :>>

Thanks that made my day. All my crazyness :>

12 hours ago, Chris Hobson said:

hence the Commodore reference.

You may call me El Commodore :-)

19 hours ago, plonkster said:

Can't do that with Axperts. When the grid goes down the grid-tied units go down too. You cannot tie them to the output of the axpert without blowing things up either.

Your only options are 1) install axpert as a plain UPS and write off the power from the grid-tied inverters, 2) get rid of the grid-tied inverters and tie the PV panels via MPPT to the battery bank, 3) get an inverter that supports the GTIs on the output, like a Victron Multiplus for example.

More a question. If you use a pure sine wave 600W inverter as the "base" generator. A relay activates this standby unit then the grid tie inverter should work 100% or am I wrong?

I have replaced the 2 Axpert inverters with one SOL-I-IS-5M. I send the Axpert ones back this morning with the same courier that delivered them.  If the grid go down then I will have one inverter running from solar.

The idea is to unplug one Omnipower grid tied inverter and plug this one in. In a few months or more I will replace the other Omnipower with a SOL-I-IS-5M.

In true space kadet form I think the one SOL-I-IS-5M will start the Omnipower inverter. I do not think it will be wise to do that because what will happen with the excess power if I do not use it. Last December it produced about 45 to 54kWh per day. The monthly yield is 816.5kWh up to now.

Any suggestions would be welcome. 

2 hours ago, Erastus said:

More a question. If you use a pure sine wave 600W inverter as the "base" generator. A relay activates this standby unit then the grid tie inverter should work 100% or am I wrong?

Unless the inverter is designed to expect extra power on the output, it won't work. It will not only not work, it will blow up, set your house on fire, and cause you to run with scissors in a way that is not safe.

Just a silly question but as the OGT5.0-1P is grid tied inverters they will produce what ever the grid voltage is. Now if you run the Axpert in grid mode with the grid tie inverters supplying the solar if eskom goes down your will use the Axpert as a UPS and can charge the batts once the grid comes back. Not perfect but I cant see it not working. 

1 hour ago, plonkster said:

Unless the inverter is designed to expect extra power on the output, it won't work. It will not only not work, it will blow up, set your house on fire, and cause you to run with scissors in a way that is not safe.

tnx

 

1 hour ago, plonkster said:

Unless the inverter is designed to expect extra power on the output, it won't work. It will not only not work, it will blow up, set your house on fire, and cause you to run with scissors in a way that is not safe.

Should grid tie not follow the 220V of the grid?  I will see in the next day or three. Customs must release my stuff then I can see.  Tnx

2 hours ago, Erastus said:

Should grid tie not follow the 220V of the grid?

Yes, but it is actively pushing power into it, the current waveform is out of phase with the voltage as it forces the power vector into the opposite direction. For example, the Fronius unit on my test bench, it easily raises the voltage by a good 10V in order to force current in the opposite direction. Now the Victron Multiplus is designed to deal with this, and to charge the battery "in reverse" from this power, but any unit not designed to be bi-directional in this way will either have adverse effects (as in stuff blowing up) or the voltage will be very high and it might even cause the grid-tied unit to repeatedly shut down as things just go out of bounds continually.

If you do try it, please film it :-)

4 hours ago, plonkster said:

Yes, but it is actively pushing power into it, the current waveform is out of phase with the voltage as it forces the power vector into the opposite direction. For example, the Fronius unit on my test bench, it easily raises the voltage by a good 10V in order to force current in the opposite direction. Now the Victron Multiplus is designed to deal with this, and to charge the battery "in reverse" from this power, but any unit not designed to be bi-directional in this way will either have adverse effects (as in stuff blowing up) or the voltage will be very high and it might even cause the grid-tied unit to repeatedly shut down as things just go out of bounds continually.

If you do try it, please film it :-)

tnx.  Nothing will happen. I can control the current from 250mA up wards. The invertor I am refering to is an of grid with a nice FAT transformer.

4 hours ago, plonkster said:

Yes, but it is actively pushing power into it, the current waveform is out of phase with the voltage as it forces the power vector into the opposite direction. For example, the Fronius unit on my test bench, it easily raises the voltage by a good 10V in order to force current in the opposite direction. Now the Victron Multiplus is designed to deal with this, and to charge the battery "in reverse" from this power, but any unit not designed to be bi-directional in this way will either have adverse effects (as in stuff blowing up) or the voltage will be very high and it might even cause the grid-tied unit to repeatedly shut down as things just go out of bounds continually.

If you do try it, please film it :-)

Your "test system" the inverter set to follow the of grid unit is it high or low Freq?

3 hours ago, Erastus said:

The invertor I am refering to is an of grid with a nice FAT transformer

Aaah, low frequency setup with the "wisselrigtiger" on the other side of the transformer. Yeah that might work.

3 hours ago, Erastus said:

Your "test system" the inverter set to follow the of grid unit is it high or low Freq?

It's a Fronius Primo. It has a high frequency DC/DC boost stage.

Hi there

I am no expert on this but let me tell you my idea. AC coupling requires high voltage batteries and the cost of batteries are still to the roof. Just recently Voltronics (http://www.voltronicpower.com/oCart2/index.php?route=product/product&product_id=196) developed Axpert VMIII hybrid 5KVA/5KW output solar inverter for 48VDC systems, that can handle max PV input of 500Vdc, max 80A MPPT solar charger, max Solar Power 4000W. If your existing Grid-tied system has an existing two PV string of 500VDC each, then there is no need to rewire, all you need is to hook in one string to the inverter or you can invest to SATS (Solar Array DC Transfer Switch). You still have an option of keeping your grid-tie system working.

Another option is to purchase a 5500w Hybrid Solar inverter 48v 230vac PV input 500v , Grid tied solar +off grid form MPP solar (https://www.ebay.com.au/itm/5500w-Hybrid-Solar-inverter-48v-230vac-PV-input-500v-Grid-tied-solar-off-grid/132427185943). Check the details on the attached file. The same inverter is also made by Votronics InfiniSolar E 5.5KW (http://www.voltronicpower.com/oCart2/index.php?route=product/product&path=24&product_id=180). This has a multiple power operations: Grid-Tie with battery backup,Grid-Tie feedback or Off-Grid, Support Max Solar Power 6500w, Pure sine wave with max 5500w output, Supports parallel up to 6 units, 2 PV input,PV input up to 500Vdc each, Built-in Max 60A battery charger.

Axpert VM III_DS.pdf

InfiniSolar E_DS.pdf

It is all about fooling the grid tied inverters thinking that the grid is still working. Then it will produce power.

Can anyone recommend a watt meter for the whole system?

I have Dlink smartplugs for my mining rigs that show the power usage on the plug. I want something like that for the whole system. Something stupid that display only.

So that I can put it where the guys in the workshop can see it and know their power usage and not trip the inverter with over usage.

3 hours ago, Slowpoke said:

It is all about fooling the grid tied inverters thinking that the grid is still working. Then it will produce power.

It's a bit more than that. You also have to frequency shift when you want it to stop. Ideally you also need somewhere to put surplus power because adjusting it down is never an instant thing, so your pipeline needs to be sufficiently bidirectional so that such surplus can go into the batteries. If the generated power has nowhere to go the voltage will rise and the GTI will disconnect.

3 hours ago, Slowpoke said:

Can anyone recommend a watt meter for the whole system?

I'm not anywhere near qualified, but would a Carlo Gavazzi ET112 not give you what you want?

https://www.gavazzionline.com/pdf/broemeng.pdf

 

I think you should go with plan 2nd. lithium battery gives excellent battery backup.

 

Air Conditioning Installation Service

yeah, you should surely go with the 2nd plan

Android app development