6 minutes ago, SilverNodashi said:

I don't think she has Axpert's installed. They keep referring to 5Kw and 10Kw so I'm guessing she has Microcare or other 5Kw inverters which doesn't have built-in MPPT chargers. 

Agree with this, was just trying to explain how they should be fighting for control under the current setup

On ‎6‎/‎21‎/‎2015 at 4:34 PM, Mart-Mari said:

Hi, I have an Axpert MKS 5 K Inverter, twelve 250W 10A 48V DC Solar panels and twelve 100Ah Deep cycle batteries installed.

Just to get us all on the same page

Just now, viper_za said:

Agree with this, was just trying to explain how they should be fighting for control under the current setup

True, it could possibly very well be fixed, but the report is sketchy and IMO leans more in favor of the new installer than the client. 

I would:

#1 Replace all the cables with the correct cables. 

#2 Replace all fuses / isolators with the correct type and rating, i.e. DC fuses on the batteries / inverters and AC on the AC side

#3 Install more isolators / fuses where needed

#4 Add more solar panels, if possible, and move the ones that's in the shade, trim the trees if necessary. If it's behind another building, one would need to either move to another roof, 

#5 replace the MPPT chargers

#6 replace the batteries

#7 Obviously supply all the technical material, offer training, suggest regular maintenance, etc. 

#8 Get someone to sign a COC, preferably the same person / company who signed the original COC. If there's no COC, the client needs to understand that a whole new COC could cost a lot of money, depending on what needs to be fixed / replace in the rest of the house. My one friend spend R70K two years ago whey they sold their house, to re-wire the whole house as everything was sub standard. 

#9 supply & install battery cabinet, warning labels, instructions for safe disconnect, etc. 

#10 educate the client on the system, possible safe loads, run times, etc, etc. 

6 minutes ago, viper_za said:

Just to get us all on the same page

That's not the same system as the report..... 

 

The report says 2x 5Kw inverters and 2x battery banks. 

A single Axper inverter, 12x panels and 12x 250W panels and 12X 100Ah batteries would be at full capacity of the system. 

Perhaps the 4 independent experts don't really know too much about inverters and solar panels?

How do you mistake a single 4Kw axper for 2x 5Kw inverters?

12x 100Ah batteries would give 3x battery banks, not 2. 

 

 

12 hours ago, SBBS said:

you can not share the panels across all three  inverters

Others have said this already but let me add some technical background. Each inverter tries to track the maximum power point of the panels, but this is actually a little misleading. It doesn't just "track" it passively, it actually actively manipulates the panel voltage to be at the optimum. So when you write everything in parallel, you have three inverters all trying to manipulate the voltage. This could actually cause a kind of power flip-flopping between inverters. So this is the basics, but let me go into a bit more detail.

As we learned in school, V = IR (ohms law). A solar panel is a constant current device (well, that's somewhat of a simplificaiton, but it is true within the linear operating region, so we'll go with that). If we use a 300W panel as an example, it might mean that the current it can provide is 8 amps. It can do that at any voltage almost down to zero. Look up the specs on any panel, you will see that the short circuit current, in other words the current at zero volts, is quite close to the peak current.

You will see further that the panel has a V_mp, that is, the voltage at which it makes the maximum power. For our example 300W panel, it will be around 37.5 volts. In other words, for the panel to make 300 watts, it has to be connected to a bus (or battery) that is presently at 37.5.

If you connect it directly to a 24V battery, which you might do in an emergency, it will make only 8 * 24 = 192 watts.

Back to ohm's law. We know V=IR, or R = V/I, and we know V=37.5 and I = 8, so we want R = 4.7 ohms. This is the impedance we should aim for.

What an mppt controller does is create an adjustable "load" with a variable impedance. Once again, I'm simplifying a bit (and there is more than one way to do it), but in the simpler case it uses a method called perturb and observe, that is it increases the resistance a little, and measures the power (ie ampere times present panel voltage). If the power comes down, it goes the other way and decreases the resistance a little. It goes back and forth like this the whole time until it oscillates right around the maximum power point.

Now lets consider what happens when you have two (or more) MPPTs in parallel. One might be decreasing resistance in an attempt to see if it's going to result in a power increase. At the same time, the other one is increasing resistance to see if that will result in more power. Regardless of what the outcome is (more or less power) one of the mppt controllers will incorrectly think that it made a GOOD change, while in reality it made a bad change that results in less overall power.

If they fight each other hard enough, you may find that they never latch on to a proper power point. Instead, all the power is on one mppt... then all the power moves to the other mppt... and so it flip-flops between inverters.

At least, this is what I would expect.

On 6/22/2015 at 0:00 PM, Mart-Mari said:

Hi and thank you. Thing is that Eskom did not supply the power while the "bypass" sign was on. I checked that on my Smart Meter account. I think Chris Hobson is correct. He says:

"Bypass is enabled meaning that if overload occurs in battery mode the inverter will allow grid to bypass inverter. Page 19 program option 23 in the manual. May not be currently bypassing but the mode is enabled." Thanks again.

 

42 minutes ago, SilverNodashi said:

I don't think she has Axpert's installed. They keep referring to 5Kw and 10Kw so I'm guessing she has Microcare or other 5Kw inverters which doesn't have built-in MPPT chargers. 

 

34 minutes ago, viper_za said:

Agree with this, was just trying to explain how they should be fighting for control under the current setup

She asked about the "bypass" sign and acknowledged Chris' post regarding "bypass" in the Axpert manual. I'm pretty sure she had Axperts.

29 minutes ago, viper_za said:

Just to get us all on the same page

Thanks viper, missed that one.

17 minutes ago, SilverNodashi said:

That's not the same system as the report..... 

 

The report says 2x 5Kw inverters and 2x battery banks. 

A single Axper inverter, 12x panels and 12x 250W panels and 12X 100Ah batteries would be at full capacity of the system. 

Perhaps the 4 independent experts don't really know too much about inverters and solar panels?

How do you mistake a single 4Kw axper for 2x 5Kw inverters?

12x 100Ah batteries would give 3x battery banks, not 2. 

 

 

I think this is where the additional upgrades happened that they talked about.
What I quoted was the original install

14 minutes ago, SilverNodashi said:

That's not the same system as the report..... 

 

The report says 2x 5Kw inverters and 2x battery banks. 

A single Axper inverter, 12x panels and 12x 250W panels and 12X 100Ah batteries would be at full capacity of the system. 

Perhaps the 4 independent experts don't really know too much about inverters and solar panels?

How do you mistake a single 4Kw axper for 2x 5Kw inverters?

12x 100Ah batteries would give 3x battery banks, not 2. 

The installation was upgraded a few times.  More batteries and another inverter were added.

1 minute ago, superdiy said:

The installation was upgraded a few times.  More batteries and another inverter were added.

I would still expect to have seen the right equipment being quoted in the reports, by the experts. Surely the experts would then have said 2x 4Kw inverters and 3x battery banks? It sounds to me like Mart-Mari is being taken for a ride, yet again. 

2 hours ago, SBBS said:

For example, if one inverter draws 3500 watts beacuase the washing machine AND a few other appliances are drawing power, then the other two phases will have only 2000 watts between them

Also, this isn't necessarily the case, and it ties in into some conversations (jdp :-) ) we had earlier about how the Axpert uses the solar power "directly" without passing it through the battery (it actually doesn't, but it balances things so that it looks that way). The three MPPT controllers are connected to the same battery bank already, and because of the way the axpert manages its DC bus, it means a surplus on one string could be used by another inverter by passing it through the "battery", or the DC bus to be accurate. So there is no reason to parallel things up before the MPPT because you are worried that the power won't be shared properly.

To put that another way, if one inverter doesn't have enough solar to "use directly", it will draw the difference from the battery. If another inverter has a surplus at that moment, it will dump that into the battery. What will happen in reality, is one inverter will pass its surplus to the other on the DC bus, it won't even go "through the battery" at all... :-)

So the problem is already solved... well, as long as the individual inverters are each allowed to dip into the battery up to a point :-)

4 hours ago, SilverNodashi said:

which is why he should balance the panels out over the MPPT's. 

Can you please elaborate more on what you mean by "balance the panels out over the MPPT's". Do you mean (what other on the forum had also said) that I should split the 18 panels so that I have 6 panels going into each inverter

3 hours ago, plonkster said:

Also, this isn't necessarily the case, and it ties in into some conversations (jdp :-) ) we had earlier about how the Axpert uses the solar power "directly" without passing it through the battery (it actually doesn't, but it balances things so that it looks that way). The three MPPT controllers are connected to the same battery bank already, and because of the way the axpert manages its DC bus, it means a surplus on one string could be used by another inverter by passing it through the "battery", or the DC bus to be accurate. So there is no reason to parallel things up before the MPPT because you are worried that the power won't be shared properly.

To put that another way, if one inverter doesn't have enough solar to "use directly", it will draw the difference from the battery. If another inverter has a surplus at that moment, it will dump that into the battery. What will happen in reality, is one inverter will pass its surplus to the other on the DC bus, it won't even go "through the battery" at all... :-)

So the problem is already solved... well, as long as the individual inverters are each allowed to dip into the battery up to a point :-)

Please elaborate more on what you mean by "dip into a battery up to a point". Does this mean that if all three the inverters are setup to charge the batteries from solar, then it will use the DC bus that you referred too to send the surplus solar to the other inverter.

33 minutes ago, SBBS said:

Please elaborate more on what you mean by "dip into a battery up to a point". Does this mean that if all three the inverters are setup to charge the batteries from solar, then it will use the DC bus that you referred too to send the surplus solar to the other inverter.

I'm not an axpert expert (say that 10 times fast), but as I understand it they have different "programs" to prevent them from discharging the batteries. What I'm saying is that you will have to let the inverter discharge the battery for such a scheme to work, so you have to pick the right program here. It's a disclaimer so to speak... there might be reasons to completely ignore what I'm saying here because the equipment simply doesn't work that way... :-)

Essentially, you will allow one inverter to discharge the battery because another one (with surplus solar power) will recharge it again. What will happen in practice is that the two cancel each other out, as the one loads down the DC bus, the other notices the drop in voltage and picks it up... hence, passing power on the DC bus.

52 minutes ago, SBBS said:

Can you please elaborate more on what you mean by "balance the panels out over the MPPT's". Do you mean (what other on the forum had also said) that I should split the 18 panels so that I have 6 panels going into each inverter

Yup

 

39 minutes ago, plonkster said:

I'm not an axpert expert (say that 10 times fast), but as I understand it they have different "programs" to prevent them from discharging the batteries. What I'm saying is that you will have to let the inverter discharge the battery for such a scheme to work, so you have to pick the right program here. It's a disclaimer so to speak... there might be reasons to completely ignore what I'm saying here because the equipment simply doesn't work that way... :-)

Essentially, you will allow one inverter to discharge the battery because another one (with surplus solar power) will recharge it again. What will happen in practice is that the two cancel each other out, as the one loads down the DC bus, the other notices the drop in voltage and picks it up... hence, passing power on the DC bus.

Thank you to everyone in this forum, for explaining and the patience you had with my questions. I must confess that I did not understand the proper working of MPPT until Plonkster explain it, and now I also understand why you must split up the solar panels. If it was not for this forum I am certain that I also would have had damage in the long run on my inverters.

I will split the solar panels ASAP, and hope that I have not harmed the chargers (or batteries) yet. 

But I have one last question (Hopefully) that will put all this in perspective for me. 

 If I split the solar panels between the inverters to have 6 panels per inverter, then I will only have 1860 watts per inverter, and if one inverter starts to draw 3000 watt, then the inverter will switch to battery mode. What will happen to the 1860 watt from that inverter? Will it still be able to supplement the 3000 watt (meaning 1860 watt from the solar and only 1140 watt from the batteries)? If the surplus solar power from the other 2 inverters are more than 1140 watt, then the batteries will stay full, and the effect that Plonkster explain with the DC bus will happen?

Just now, SBBS said:

Thank you to everyone in this forum, for explaining and the patience you had with my questions. I must confess that I did not understand the proper working of MPPT until Plonkster explain it, and now I also understand why you must split up the solar panels. If it was not for this forum I am certain that I also would have had damage in the long run on my inverters.

I will split the solar panels ASAP, and hope that I have not harmed the chargers (or batteries) yet. 

But I have one last question (Hopefully) that will put all this in perspective for me. 

 If I split the solar panels between the inverters to have 6 panels per inverter, then I will only have 1860 watts per inverter, and if one inverter starts to draw 3000 watt, then the inverter will switch to battery mode. What will happen to the 1860 watt from that inverter? Will it still be able to supplement the 3000 watt (meaning 1860 watt from the solar and only 1140 watt from the batteries)? If the surplus solar power from the other 2 inverters are more than 1140 watt, then the batteries will stay full, and the effect that Plonkster explain with the DC bus will happen?

If the 3 inverters are linked together, the load will be split evenly (to a great degree at least) between the 3 inverters. 

1 minute ago, SilverNodashi said:

If the 3 inverters are linked together, the load will be split evenly (to a great degree at least) between the 3 inverters. 

Don't think it will as he mentioned he does have a 3 phase installation.

The PV should still work as plonkster explained

2 minutes ago, SilverNodashi said:

If the 3 inverters are linked together, the load will be split evenly (to a great degree at least) between the 3 inverters. 

Not in this case, the load will not be split because his inverters are not running in parallel, they are in 3 phase configuration.

13 minutes ago, SBBS said:

If I split the solar panels between the inverters to have 6 panels per inverter, then I will only have 1860 watts per inverter, and if one inverter starts to draw 3000 watt, then the inverter will switch to battery mode. What will happen to the 1860 watt from that inverter? Will it still be able to supplement the 3000 watt (meaning 1860 watt from the solar and only 1140 watt from the batteries)? If the surplus solar power from the other 2 inverters are more than 1140 watt, then the batteries will stay full, and the effect that Plonkster explain with the DC bus will happen?

If the load on any one of the inverters is more than what the panels (connected to that inverter) can supply at that point in time, that inverter will switch over to battery and use battery only - not partly battery and partly solar PV. As Plonkster has explained, the other inverters should then try to compensate for the drop in the battery voltage (on the DC bus) and start charging the batteries by using the PV connected to each of the other inverters.

1 minute ago, superdiy said:

Not in this case, the load will not be split because his inverters are not running in parallel, they are in 3 phase configuration.

The only time it will be out of balance in a 3phase configuration, is when the 3phases are used to run normal 220V appliances. But if he's using 480V / 3phase appliances, it will still balance out evenly between the inverters. 

1 minute ago, SilverNodashi said:

The only time it will be out of balance in a 3phase configuration, is when the 3phases are used to run normal 220V appliances. But if he's using 480V / 3phase appliances, it will still balance out evenly between the inverters. 

He specifically asked: "and if one inverter starts to draw 3000 watt, then the inverter will switch to battery mode."

 

3 minutes ago, SilverNodashi said:

But if he's using 480V / 3phase appliances

380 / 400V   

Just now, superdiy said:

380 / 400V   

yea, yea..

Just now, superdiy said:

He specifically asked: "and if one inverter starts to draw 3000 watt, then the inverter will switch to battery mode."

 

Fair enough. So let's assume in his setup, the red phase feeds all the plugs in the house, the blue phase feeds the pool pump, irrigation and garage, and the yellow phase feeds the stove, geyser and lights. Then, yes, the 3 inverters will be unbalanced and if one of them use more power than the PV  can produce, it would draw from the batteries. Or from Eskom. 

 

But in a normal 3phase setup, with 3phase equipment, it would have balanced out evenly.