Series / Parallel - 6500EX Questions

[dmkjr]

Good evening community --
I have two strings of 8 panels in series, roughly 230v per string.

I have each of those strings paralleled together to go into MPPT_1 on the 6500ex.

- However, after adding the second string, I've noticed the amps really have not increased -- maybe slightly from just having the first string plugged in. Why would adding a second set of 8 panels in parallel to the first string of 8 not really improve the performance? I installed the second string of 8 on Thursday (6/22), so you can see it improves, but incrementally I think.







Total of 16 250w Trina panels 2S1P is what I have.

Any ideas on what to check? Is that all I'm going to get out of these? Better way to wire them together? Full sun most of the day, facing due South.

 

[sunshine_eggo]

Good evening community --
I have two strings of 8 panels in series, roughly 230v per string.

When stating string voltage, you should use Voc.

EDIT: incorrectly stated current.

I have each of those strings paralleled together to go into MPPT_1 on the 6500ex.

Not likely an issue with your panels, but any PV current above 18A is wasted.

- However, after adding the second string, I've noticed the amps really have not increased -- maybe slightly from just having the first string plugged in. Why would adding a second set of 8 panels in parallel to the first string of 8 not really improve the performance? I installed the second string of 8 on Thursday (6/22), so you can see it improves, but incrementally I think.

Total of 16 250w Trina panels 2S1P is what I have.

Assume you mean 8S2P?

Any ideas on what to check? Is that all I'm going to get out of these? Better way to wire them together? Full sun most of the day, facing due South.

If your batteries are fully charged you won't get any more power than you need.

Try each string independently with a > 2000W load at high noon in clear skies. Confirm they perform similarly. Once confirmed, parallel the strings and confirm you get near 2X performance with a 4000W load.

 

[dmkjr]

When stating string current, you should use Voc



Not likely an issue with your panels, but any PV current above 18A is wasted.


View attachment 154388



Assume you mean 8S2P?



If your batteries are fully charged you won't get any more power than you need.

Try each string independently with a > 2000W load at high noon in clear skies. Confirm they perform similarly. Once confirmed, parallel the strings and confirm you get near 2X performance with a 4000W load.

@sunshine_eggo Your comment about not producing more than is needed is interesting here. I have my mode on Solar, Utility, Battery right now, but I do have 20KWH of battery. Should I change to 'SBU' and see if it will allow it to produce more? My batteries are sitting at near 100% (I notice it fluctuates from 96%-99% typically.

Correct, I did mean 8S2P. Is that the better way here? I just ran 8 panels on one row together and then added another row this past weekend.

 

[sunshine_eggo]

@sunshine_eggo Your comment about not producing more than is needed is interesting here. I have my mode on Solar, Utility, Battery right now, but I do have 20KWH of battery. Should I change to 'SBU' and see if it will allow it to produce more? My batteries are sitting at near 100% (I notice it fluctuates from 96%-99% typically.

Correct, I did mean 8S2P. Is that the better way here? I just ran 8 panels on one row together and then added another row this past weekend.

A 100,000W array will only deliver as much power is needed. If you're pulling 100W, that's all the array will produce. if you're simply powering loads, and those don't vary much from day to day, that's probably what you're seeing.

Deliberately induce a > 4000W load on the inverter and evaluate array performance.

 

[dmkjr]

@sunshine_eggo Thank you for the words. I just changed the mode of the inverter to run the batteries down a bit. I'm on the east coast (USA), so my sun is gone for the day, but will evaluate tomorrow.

 

[sunshine_eggo]

@sunshine_eggo Thank you for the words. I just changed the mode of the inverter to run the batteries down a bit. I'm on the east coast (USA), so my sun is gone for the day, but will evaluate tomorrow.

You may find that the batteries are fully charged again before you can test the performance. If you can't confirm near doubled array performance, deliberately induce a 4000W load at high noon.

 

[dmkjr]

You may find that the batteries are fully charged again before you can test the performance. If you can't confirm near doubled array performance, deliberately induce a 4000W load at high noon.

I’m not 100% sure I can put a 4kw load. I have 10 circuits on a “solar sub panel”, most of which is powering our backup business datacenter. We usually have about 1.3kw load at any time on the inverter and it spikes to about 2.3kw.

I do plan on adding another inverter and putting some 240v loads on them. However, I’m just trying to justify the install right now and kind of proof the concept (to myself really).

Those panels should be generating much more than 10-12kw a day I would think.

 

[sunshine_eggo]

I’m not 100% sure I can put a 4kw load. I have 10 circuits on a “solar sub panel”, most of which is powering our backup business datacenter. We usually have about 1.3kw load at any time on the inverter and it spikes to about 2.3kw.

If that's the case, then you may want to disable solar until noon-ish.

I do plan on adding another inverter and putting some 240v loads on them. However, I’m just trying to justify the install right now and kind of proof the concept (to myself really).

Those panels should be generating much more than 10-12kw a day I would think.

Only if you use that much power.

 

[dmkjr]

If that's the case, then you may want to disable solar until noon-ish.



Only if you use that much power.

Lets say the load is 1.2kw. And the batteries are at 30%. Will the panels bring in enough juice to start charging the batteries and provide for the 1.2kw load? I'm just curious if there is another setting that needs to tell the inverter to charge the batteries. I have it set to 30amp charge rate on the 6500ex.

 

[Adam De Lay]

Lets say the load is 1.2kw. And the batteries are at 30%. Will the panels bring in enough juice to start charging the batteries and provide for the 1.2kw load? I'm just curious if there is another setting that needs to tell the inverter to charge the batteries. I have it set to 30amp charge rate on the 6500ex.

Why do you have the charge current set to 30a? That's the max current going to the battery, so 30ax51.2v (nom) would give you a max of 1536W going into the battery at peak time.

You said you have around 20kw of battery storage, so I'm guessing 4 server rack batteries? Each one can typically charge from 50-100a a piece (depending on manufacture settings) so you should easily be able to have your max charge value set (option 2) to the max the inverter can support (120a) because the current will be split between each battery.

 

[dmkjr]

Why do you have the charge current set to 30a? That's the max current going to the battery, so 30ax51.2v (nom) would give you a max of 1536W going into the battery at peak time.

You said you have around 20kw of battery storage, so I'm guessing 4 server rack batteries? Each one can typically charge from 50-100a a piece (depending on manufacture settings) so you should easily be able to have your max charge value set (option 2) to the max the inverter can support (120a) because the current will be split between each battery.

That's correct, I have 4 server rack batteries (EG4).

Max charging was set to 120a. Max AC charge was set to 30a. I just increased that. Waiting for full sun to see if I generate more than what I have been generating.

 

[Adam De Lay]

That's correct, I have 4 server rack batteries (EG4).

Max charging was set to 120a. Max AC charge was set to 30a. I just increased that. Waiting for full sun to see if I generate more than what I have been generating.

AC charging won't affect your solar panel charging.

Like @sunshine_eggo said, 18a is the max each MPPT will allow, anything over that will be clipped. The inverters will only draw the power they need once the batteries get full.

I agree with the tests suggested above. Disable solar till around noon and see if your results change. I would also disconnect the first string of 8 and make sure everything's working with the "new" string of 8.

Aside from having to run more cabling, is there a reason you didn't just wire up the second set of 8 to the second MPPT on the inverter?

 

[sunshine_eggo]

Lets say the load is 1.2kw. And the batteries are at 30%. Will the panels bring in enough juice to start charging the batteries and provide for the 1.2kw load? I'm just curious if there is another setting that needs to tell the inverter to charge the batteries. I have it set to 30amp charge rate on the 6500ex.

Should work.

PV charge current set to max.

 

[dmkjr]

Should work.

PV charge current set to max.

Well, it appears you were correct. When I changed the mode, now I'm getting about 3000w from solar on the 16 panels. Max appears to be 4000w, is 3000-3100 reasonable? Of course there are factors, but its primarily faced due south at a pretty decent angle (not sure the exactly angle).

 

[Adam De Lay]

Well, it appears you were correct. When I changed the mode, now I'm getting about 3000w from solar on the 16 panels. Max appears to be 4000w, is 3000-3100 reasonable? Of course there are factors, but its primarily faced due south at a pretty decent angle (not sure the exactly angle).

4000W would be perfect conditions. In my case in MI, spring and fall (because temps are cooler outside) are the times I see closer to max output. On a perfectly sunny day you might get close, but temperature and angle play a big role in panel output.

I used an app on my phone "PV Optimizer" to help figure out the proper direction and angle that my panels should be facing. You could also try the "pop-can" method...wait, your in SC...."soda-can" method to figure out the best angle at solar noon. ?

 

[sunshine_eggo]

Well, it appears you were correct. When I changed the mode, now I'm getting about 3000w from solar on the 16 panels. Max appears to be 4000w, is 3000-3100 reasonable? Of course there are factors, but its primarily faced due south at a pretty decent angle (not sure the exactly angle).

70-80% in summer heat is typical. I don't know what you mean by "decent angle", but you should actually have a pretty shallow angle this time of year - about 10% from horizontal. If you are tilted around your latitude of 33°, then the sun is off perpendicular by about 23°, and you would see a performance hit.

3100/4000 = 78%, so it's within reason.

As we approach the autumnal equinox in September, with the sun entering a more favorable angle (assuming panels around 33°) and cooler temps, you might see more production.

 

[dmkjr]

@sunshine_eggo / @Adam De Lay

Thank you for the input today. Changing the inverter form to utilize batteries when not at 100% was the problem. After changing, I've generated over 23kwh of solar today so far and even at 6:30pm on the east coast, producing 2200w still. I'm impressed.

 

[dmkjr]

Here is the breakdown after today. Even the voltage was lowered after changing to SBU.

 

[sunshine_eggo]

Here is the breakdown after today. Even the voltage was lowered after changing to SBU.



View attachment 154540

View attachment 154541


View attachment 154542

That's how it works. If you don't pull anything, you get something close to Voc. If you pull max power, you get something close to Vmp. If you pull less than max power, you get something between Vmp and Voc.

 

[dmkjr]

That's how it works. If you don't pull anything, you get something close to Voc. If you pull max power, you get something close to Vmp. If you pull less than max power, you get something between Vmp and Voc.

Well thank you for the advice. I'm newer to the solar world, but have learned a ton since starting. Installed the system myself.

I have some more panels to install and looking forward to getting the remainder of them installed.