3 Phase grid tie solar system issue

[Tigerdim]

I have just installed a 7.5 kwh solar system in my house.
The house has a 3 phase system.

The technician installed a 3 Phase Sofar inverter. After a few days of use, during daytime, Im only getting 4kW total per day from the solar system, and still 30kW from the grid. (7 hours of full sunshine) My consumption without solar was around 30kW during day time.

The technician explained that the way the inverter works is that is always takes the lowest producing phase, and applies this power to the other 3 phases.
So while my AC is consuming 4kWh on Phase 1, the fact that Phase 2 is only pulling 40W, means that the inverter will only produce 40W on each phase.
This seems quite incredible, and can't see why a system would be designed to work like this.

The goal of the solar system was for me to reduce my daily consumption to close to 0.
The technician tells me that the only solution is to replace my inverter by 3x single phase inverters.

Is this the only solution? Also, I have been told that PEA no longer allows excess solar power to be sent back to the grid to reverse the meter. Is this correct?

[BritManToo]

Sounds more like the installer doesn't know how to install a 3 phase inverter.

PS

7.5 kwh solar system doesn't mean anything.

Did you mean 20x 400w solar panels?

[007 RED]

3 hours ago, Tigerdim said:

Also, I have been told that PEA no longer allows excess solar power to be sent back to the grid to reverse the meter. Is this correct?

As @BritManToo has indicated in his response above, it is highly likely that the installer has little, if any, experience of setting up a 3 phase system, hence his response to your concern.

 

I'm sorry but I'm not qualified to give advice regarding your 3 phase grid tied installation.  3 phase is way above my pay grade.  The man with the answers is @Crossy and no doubt he will be along shortly to provide you with some good pointers/advice.

 

Regarding your question above.  Yes you have been informed correctly.  It is deeply frowned upon by the local PEA (or MEA if you live in BKK) to connect your solar system in such a manner as to make the meter disc spin backwards. 

 

If they (PEA/MEA) discover the meter spinning backwards e.g. the meter reader sees it whirring backwards when he/she takes your reading, or you have negative meter reading e.g. the current reading reading is less than previous one, they will take action against you.  It is highly likely that they will replace your meter with a digital one which does not run backwards so you are no longer able to 'dump' excess electricity back to the grid.  They can also cut your supply off and instruct you to disconnect/remove the solar system.  They can also fine you for lost revenue.  So be warned.

 

It becomes imperative when running a grid tied system that has not been officially approved by the PEA/MEA that you are aware of the day(s) when the meter reader is most likely to visit and take steps to ensure that your system does not export on that day.  I have set my small scale solar system to automatically not export on the day before the meter reader is due to visit, but last month I nearly got caught out as he arrived a couple of days earlier than I predicted.  Have a look at my post "Saved by a Cloud"

 

Hope that you are able to resolve your new installation problem.

 

[Crossy]

Actually I don't really know what's going on, but I've found Sofar support very responsive with good English, the address should be in the manual.

 

Personally I wouldn't have used a 3-phase inverter and would have gone with 3 x single-phase units my reasoning being that a 3-phase unit will shut down fully if one of the input phases fails (our most common failure mode) whereas if you have 3 single-phase units two of them will still be operating.

 

Any way to get your inverter swapped out?? 

[Tigerdim]

Thanks all for your replies. 

I indeed have 18 panels, so must be 18 panels of 400W.

 

My installer is trying to swap my 3 phase inverter for 3 single. 

I just wanted to check the forums to see if this was correct. I indeed think my installer doesn't know what he is doing so prefer to be sure now, before I install 3 inverters and discover it still isn't the right solution. 

 

The explanation I got from the installer for the 3 phase inverter still sounds crazy. 

[tjo o tjim]

FWIW, the meter will only see the kWh in aggregate, so exporting on two phases and importing on one might not spin the meter backwards. 

[Tigerdim]

At this stage I would rather not send anything back at all to the grid if there is another solution.

 

Sofar replied the following:

While we have had a new firmware to support unbalanced load. Buy electricity for a certain phase and sell electricity for a certain phase to achieve the maximum power generation.

For example: Load Power 2.5K/1K/2K  --------  Reality output of inverter (2.5+2+1)/3=1.833KW : 2.5K(1.833+0.6..)/1K(1.833-0.833)/2K(1.833+0.167)

 

 

So my understanding in the case above, as Im not sending back to the grid, I would only get 1.8*3 = 5.5kW total.

 

My goal is still to be able to reduce my day time grid consumption to 0 and still really cant see how this is possible.

 

If I use 3 single phase inverters, i guess it will be split 3 * 2.5 kw. So if one phase requires 5 kw, I will again be pulling 2.5 kw from the grid. is this correct?

What is the best solution to be able to use the full solar capacity I have?

 

[BritManToo]

1 hour ago, Tigerdim said:

What is the best solution to be able to use the full solar capacity I have?

Batteries, around 30Kbht for 5kWhr of storage.

[Crossy]

11 hours ago, Tigerdim said:

If I use 3 single phase inverters, i guess it will be split 3 * 2.5 kw. So if one phase requires 5 kw, I will again be pulling 2.5 kw from the grid. is this correct?

What is the best solution to be able to use the full solar capacity I have?

 

I have no direct experience of exporting into a 3-phase meter. But knowing how the conventional disc meters work I would suggest that exporting 2kW into one phase whilst importing 2kW from another should result in zero movement of the meter. Of course the meters aren't actually designed to work like that, it's just a fact of physics. Note that the inverter on the "exporting" phase would think it is actually exporting so would need the "no-export" function turned off.

 

3 x 3-4kW inverters would be the way I would go, possibly make them grid-tie hybrids so batteries are a possible option.

 

If one phase is more heavily loaded during the day you could have more panels on it's respective inverter or even run two inverters on that phase.

 

[Tigerdim]

4 hours ago, Crossy said:

I have no direct experience of exporting into a 3-phase meter. But knowing how the conventional disc meters work I would suggest that exporting 2kW into one phase whilst importing 2kW from another should result in zero movement of the meter

I have read in a few places that indeed there will be a net zero to the grid. I will explore this solution for now as would be the easiest.

3x inverters would mean I would need to check all the phase loads and would need quite a bit of playing around with. (and I ve lost patience with my technician...)

 

Thanks all again. Will keep you posted on how things pan out.

[BritManToo]

How much did you pay for this system?

200Kbht?

[Will B Good]

I always thought ac electricity was generated as three phase, but domestic supply was only single phase.........is that incorrect?

[Tigerdim]

54 minutes ago, BritManToo said:

How much did you pay for this system?

200Kbht?

yeah 210k

[Crossy]

58 minutes ago, Will B Good said:

I always thought ac electricity was generated as three phase, but domestic supply was only single phase.........is that incorrect?

 

Thailand is 3-phase 4-wire at the distribution level.

 

Your single-phase house supply is between one phase and neutral. Larger homes hook on to all three phases and the neutral, it works like 3 single-phase supplies.

 

If you look at the pole outside it will have 4 wires, the top one (usually bare) is the neutral the lower three are the phases. Your meter will come from the neutral and one phase.

 

[Tigerdim]

On a side note, I contacted PEA who told me they would have a new solar program in May apparently, with a new tarif for sending back to the grid.

 

In the meantime my inverter will be changed for 3x single phase this friday.

 

Again thanks all for your input.

[Tigerdim]

My 3 single inverter is definitely working much better now.

 

I do have one last question though.

If I disable antireflux, I will be sending excess back to the grid. My installer says that this can also be dangerous for PEA workers as can cause sparks.
I havent understood it all, but guess he is referring to the anti islanding. THis should be separate from the anti reflux right and anti islanding shouldnt be available as a setting to be switched on/off?

[Crossy]

1 hour ago, Tigerdim said:

I havent understood it all, but guess he is referring to the anti islanding.

 

All domestic class GTIs have anti-islanding as standard, there is no danger to PEA workers (and you are correct, it's not an option that can be turned off).

 

What type of inverters do you now have just to verify??

 

I suspect that your man is misunderstanding what anti-reflux and anti-islanding are.

 

It is important to understand the difference between exporting energy into a live grid (OK) and back-feeding into a dead grid (very not OK).

[Tigerdim]

14 hours ago, Crossy said:

What type of inverters do you now have just to verify??

I have 3x SOFAR 3300TL-G3

I have seen they are on the PEA approved list.

[Crossy]

19 minutes ago, Tigerdim said:

I have 3x SOFAR 3300TL-G3

I have seen they are on the PEA approved list.

 

Yeah, we have the 6kW version, excellent inverters.

 

PEA approved so no issues with islanding.

[Tigerdim]

I noticed the country code on the inverters is set to 22. Should I change this to 40 (thailand PEA)?

[Crossy]

2 hours ago, Tigerdim said:

I noticed the country code on the inverters is set to 22. Should I change this to 40 (thailand PEA)?

 

22 is "Europe General", try 40, it can't do any harm and might have broader limits for voltage and frequency.

[007 RED]

2 hours ago, Tigerdim said:

I noticed the country code on the inverters is set to 22. Should I change this to 40 (thailand PEA)?

It appears that the Sofar inverters are set to #22 "Europe General" as the default.  I changed my 2200TL-G3 to #41 "Thailand MEA" (although I live in a PEA area) during initial commissioning in October last year and the beast has been working well since then.

 

The only problem was the changing the settings.  The one push button, plus having to enter the password almost every step of the way, is a preverbal pain in the rear.

[007 RED]

@Tigerdim  Has your installer fitted and connected a CT (Current Transformer) device to the inverter which is connected to the supply line connected to your meter?

 

If not, then it may well be advisable to get one fitted plus a simple switch and the "Reflux Power" setting on your inverter set to 0 (zero).  The switch can be left open and this will allow any excess power to be fed back to the grid for reclaim later.  With the switch closed the inverter will stop sending power back to the grid - meter disc will not spin backwards.

 

Remember, if your system is grid tied, the last thing that you want is for the meter reader to see the disc spinning backwards.  (see my original comments in post #3 above). 

 

[Crossy]

Good point @007 RED although our OP has 3 x single-phase inverters so will have 3 x CTs (one on each incoming phase) so he will need to arrange to switch all three.

 

My ESP8266 based unit could be modified to drive a 3-pole relay to do the job automagically.

[BritManToo]

4 hours ago, 007 RED said:

Remember, if your system is grid tied, the last thing that you want is for the meter reader to see the disc spinning backwards.

My meter readers never cared, and it was running backwards for 2 years.

[Crossy]

25 minutes ago, BritManToo said:

My meter readers never cared, and it was running backwards for 2 years.

 

But some do, @Thaifish can confirm ????

 

Note that there's an important difference between it running backwards (ours does) and it being seen going backwards by the meter reader (ours isn't).

 

[Tigerdim]

On 4/2/2022 at 12:29 PM, 007 RED said:

Has your installer fitted and connected a CT (Current Transformer) device to the inverter which is connected to the supply line connected to your meter?

I havent seen anything like this.

 

For now I was just going to manually stop sending back the last week of the month. Though as you mentioned it's a pain going through the settings with that one button. Also inputting PIN and then setting the reflux to 0.00. And I need to do that x3 ????

[Tigerdim]

On 4/2/2022 at 5:50 PM, Crossy said:

Note that there's an important difference between it running backwards (ours does) and it being seen going backwards by the meter reader (ours isn't).

I havent understood this. How can you run backwards without it being seen?

[Crossy]

3 minutes ago, Tigerdim said:

I havent understood this. How can you run backwards without it being seen?

 

We know when the meter reader comes, he's pretty consistent. Earliest he's been is the 16th (only in February), latest is the 19th. So we disable export between the 16th and 19th automatically, of course if he comes on the 16th then export gets turned on as soon as his motorcycle is out of sight ???? 

 

As it happens he usually turns up at about 7AM so we're not generating much anyway.

 

I know we will eventually get a "smart" meter so I'm constantly upgrading so that we never actually export energy anyway (more batteries Igor, more batteries!).

 

[Photoguy21]

It may sound a silly question but why would you have a 3 phase supply to your house?