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1620w worth of panels producing a maximum of 1000w.


profa
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I am a noob at this and by no means even slightly an expert so please keep that in mind and please ask for any info I have failed to provide for you to help me solve this issue. 

I have a 3kva/3000w Synergi PWM (yes PWM not MPPT) 24 volt (yes twenty four volt) inverter installed. Connected to this, I have two 12 volt 200 amp/hour AllGrand gel batteries installed in series. I then also have six 270w Enersol solar panels installed in parallel (this is how the manual says the panels should be installed). 

Now here is my problem. This should be producing a theoretical maximum of 1620w, but only ever does a maximum of 1000w and averages in the 800-900w region. Accoring to the inverter display, it does this at around 25-27volts and 36-40amps.  Basically I am losing around 40% of theoretical solar power. Roof is north facing. Not sure of the angle of the roof, but it is a "standard" angle of what I estimate to be about 30-40 degrees slope. 

I am at work now, but will happily provide pictures or whatever else info I have missed when I get home after work. Installer blames the fact that it is a PWM inverter and not MPPT. Same guy also promised at least 1200w of solar production, so go figure. 

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Another quick question(s).....am I correct to assume the following:

1. There MUST be a fuse between battery and inverter?

2. The DC cabling from the solar panels should not share a conduit with the AC cables? And thus, the solar panel fuse should not be located in the same DB as the home's DB (the AC DB)?

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5 minutes ago, Vassen said:

What is the specifications of the panels. What’s the normal operating voltage. A pwm inverter will basically need a voltage of just over the battery voltage, so in this case probably around 28V. Anything over that is basically wasted. If your panels have a voltage of 40V, then that’s already a 30% loss.  Then there’s the efficiency losses on the pwm itself. 
 

with an mppt, I am getting around 85-90% of the max power. 
 

so in this case your installer may be right. 

I think this is what I have installed

Spec sheet

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10 minutes ago, Bloubul7 said:

1. Correct

2. Correct

Additional items, check to ensure that you have an inline fuses close to panels as well

Thanks for this. More school fees to pay I guess. I definitely do not have another fuse close to the panels either. Only a fuse in the AC DB board for the solar panels. No fuse from battery to inverter. AC and DC sharing same conduits.  

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9 minutes ago, Vassen said:

Okay that’s actually not bad. Max power is achieved at 31.1V and at 8.67A. 
 

so losses should not be as high as I mentioned. 
 

if all are in parallel, it should be easy to connect them 1 at a time to check what the power is. You should however NOT disconnect them when they are under load. So turn off the DC breaker first and then disconnect all and then connect 1 at a time. Breaker on, check power, breaker off and repeat. 
 

30v is not too high but best to be safe. 

Stupid question, but I dont have a breaker, but only one of those glass fuses that fits into a breaker type housing. So I remove the fuse, disconnect all but one, then put the fuse back in. Repeat. 

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On 2020/10/09 at 1:16 PM, Vassen said:

Yes, you can do that as well. If you open that fuse house, it will disconnect.  Again, seeing that it’s 30v it should be safe. The dc breakers used for solar are no-ark type 
 

you should actually get the breaker though. I take it then that you also don’t have the surge protector on the solar panels. You get  a combiner box that includes the fuse, breaker and surge protector. That’s the correct way to do it. It’s often cheaper to just buy the components separately instead of the complete prebuilt box. Just wondering if your panels are earthed. 

Correct on all accounts. No surge protector on the solar panels. Also no earthing on the solar panels as far as I know. 

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On 2020/10/09 at 9:41 AM, profa said:

No fuse from battery to inverter. AC and DC sharing same conduits.

 

6 hours ago, profa said:

No surge protector on the solar panels. Also no earthing on the solar panels as far as I know.

Not to be judgmental or anything, but I think you need someone professional to check your whole system over. It sounds to me like someone has taken a few shortcuts.. 

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Is this  grid tie system? What are the loads? Once the batteries are charged, and there is no load, there is no current drawn from the panels. If you want to get the theoretical maximum out of the panels, switch on a kettle at midday on the 21st of December. 

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So it seems it has to do with the inefficiency of a PWM inverter. Tested yesterday, by connecting 3 panels only (out of the total of 6). Put at least 1500w of load on the system, and the 3 panels produced 590-600w (25v and 24amps) which makes sort of sense as the panels are rated at about 8 amp each. So the amp rating makes sense as panels are in parallel (the voltage is very low from the rated voltage of about 31V the panels are supposed to provide). Then did the same experiment with the other 3 panels. Same exact result. However when all 6 are connected, I get about 1000w total from the panels (higher volts at about 27-28 but not double the amps or even close to double the amps at about 37-38). 

Lesson learn. School fees paid I suppose. Only good thing about this is that I am learning. And am in the solar thing now with zero debt. All paid for cash. Wouldve pissed me off if my R150k system I took a loan to get was doing this LOL. 

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On 2020/10/12 at 3:33 PM, Solaris said:

 

Not to be judgmental or anything, but I think you need someone professional to check your whole system over. It sounds to me like someone has taken a few shortcuts.. 

With all due respect, I thought it was someone professional that did the installation. And that is the reason I have been so hesitant to do this for so long. All the "professionals" out there. Will try my best to sort out the issues myself as best I can. The rest will just have to stay non-compliant until I have school fees to spare again.  

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5 hours ago, profa said:

However when all 6 are connected, I get about 1000w total from the panels (higher volts at about 27-28 but not double the amps or even close to double the amps at about 37-38).

24 V inverters sometimes have very weak solar charge controllers. Some are 600 W max, some are 1500 W. Maybe yours is 1000 W max. Does it give the solar charge controller specs on the side of the inverter? Axperts and their clones usually do.

That could explain the higher panel voltage; it has to PWM the panels to bring the charge power down to around 1000 W (perhaps it's 40 A max). So the panel voltage will be stepping between battery voltage and Voc; I could believe that the average is around 27-28 V if the battery voltage is around 25 V.

PWM charge controllers are pretty simple.

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5 hours ago, profa said:

So the amp rating makes sense as panels are in parallel (the voltage is very low from the rated voltage of about 31V the panels are supposed to provide).

That's the nature of PWM charge controllers. Your battery voltage is around 25 V, so your panel voltage (when running flat out) is around 25 V. The extra 6 V is just wasted. If you had  an MPPT charge controller, it could make use of the extra 6 V ("transforming" the panel power from 31 V @ 8 A per panel to ~25 V @ 10 A (ignoring losses, which are typically only 2% for a charge controller anyway).

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19 hours ago, Vassen said:

There is a ton of information available on various platforms on the internet with regards to anything that one needs to do. 
 

Whenever I need to do anything at home, I will always try to research what needs to be done and how to do it.  Being hands-on, I often try to do things by myself and if I can’t, I will get a “professional” in to do the task. If I seem to know more than the “professional” he needs to leave. 

For people that are not hands-on, it still helps to have an idea what needs to be done so that you know you are getting value for the money that you spend and that the job is being done correctly. 

I am generally the same. I try to do my research as best I can. But sometimes that information contradicts what the experts tell you in reality (just as an example, every expert will tell you that you never skimp on tyres. I try to buy the cheapest tyres I can (from reputable dealers who wont sell "chinese crap") and in 15 years of buying my own tyres since owning a vehicle of which I now have 3, I have never ever had a single tyre failure due to quality).

I have a pretty good relationship with the electrician that did the work. He is a good electrician, but clearly isnt clued up on solar despite having done MANY installations. So yeah, like I said, I will get hands on and try to sort out the problems myself as best I can. 

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15 hours ago, Coulomb said:

That's the nature of PWM charge controllers. Your battery voltage is around 25 V, so your panel voltage (when running flat out) is around 25 V. The extra 6 V is just wasted. If you had  an MPPT charge controller, it could make use of the extra 6 V ("transforming" the panel power from 31 V @ 8 A per panel to ~25 V @ 10 A (ignoring losses, which are typically only 2% for a charge controller anyway).

Installer told me the MPTT inverters break easily and many have been returned to the supplier, and the supplier recommends the PWM one because they havent had a single return. He also promised me the difference in performance wouldnt be that big. *insert foot in mouth emoji*

I now realise the PWM probably wasn't selling, hence selling them to idiots like me. 

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15 hours ago, Coulomb said:

24 V inverters sometimes have very weak solar charge controllers. Some are 600 W max, some are 1500 W. Maybe yours is 1000 W max. Does it give the solar charge controller specs on the side of the inverter? Axperts and their clones usually do.

That could explain the higher panel voltage; it has to PWM the panels to bring the charge power down to around 1000 W (perhaps it's 40 A max). So the panel voltage will be stepping between battery voltage and Voc; I could believe that the average is around 27-28 V if the battery voltage is around 25 V.

PWM charge controllers are pretty simple.

Mine is rated at 50AMP @ 30V which amounts to 1500w it should in theory be able to handle from panels. I have seen it on very rare occasions jump to 44amps for a few minutes without issue so I think it can handle at least the rated 50 amps. Highest I have seen its voltage is about 28.5 or thereabout. So I think it can get close to 1500w in terms of amps, just not in terms of voltage. And I think it would need about 2200w worth of panels to do it. 

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6 minutes ago, profa said:

Installer told me the MPTT inverters break easily and many have been returned to the supplier, and the supplier recommends the PWM one because they havent had a single return. He also promised me the difference in performance wouldnt be that big. *insert foot in mouth emoji*

I now realise the PWM probably wasn't selling, hence selling them to idiots like me. 

never ever ask nor trust to the seller. their only goal is to sell their  stock 

Edited by ibiza
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One last quick question, the cable length from the panels to the inverter is about 15m give or take. The cable used according to the invoice, was 6mm DC cable. Would that affect the amount of amps coming through to the inverter? I have felt the cable before as it comes into the fuse, and it is warmish. Not hot by any means, but definitely warm to the touch so that it is noticable. 

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3 hours ago, Vassen said:

I guess that’s why places like this are so important where people offer advice based on own experience without actually having any vested interest in what you buy. 

Thank you very much. That's what I have being trying to achieve since 2013. This really makes me happy. 

Sincerely

Jason

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1 hour ago, Vassen said:

I’m no expert in this this but yes it does affect the current as well as the voltage to an extent. 
 

However, more importantly is that this becomes a hazard. Cables should not get warm to the touch under normal operation. 
 

googling some calculators, for a 32v system, operating at 40A (which is less than the 6x9A), over 15m with a 5% loss, you will require around 20mm2 of cable. 
 

Do you just have 1 cable coming from the panels to the inverter?

So im busy chatting to the installer, he used 74m of cable from panels to inverter. 37m positive (going through fuse) and 37m negative going straight to inverter. 74m total. 

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So......i just did a very unscientific measurement from where i know the panels are on the roof and took huge (1m estimate) steps from within the house where the panels are, to the garage where the inverter is. counted 17 steps. now wondering how the hell that could remotely even get close to 37m worth of cable 🤔🤔

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6 mm² cable is about as thick as PV cable gets. But is it really 6 mm²? It should be printed on the side of the cable.

6 mm² cable should be good for nearly 40 A. Same as 6 mm² AC cable, neglecting skin effect, and the fact that any voltage drop has 9x the effect at 26 V (compared with 230 V).

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24 minutes ago, Coulomb said:

6 mm² cable is about as thick as PV cable gets. But is it really 6 mm²? It should be printed on the side of the cable.

6 mm² cable should be good for nearly 40 A. Same as 6 mm² AC cable, neglecting skin effect, and the fact that any voltage drop has 9x the effect at 26 V (compared with 230 V).

I went and checked and removed some covers but dont see any writing on the cables from the panels. However, on the battery cables to the inverter it says 25.00mm2. And those cables look to me like 4 gauge car sound cable thickness which I know pretty well. The cables from the solar panels look to me like 8 gauge car sound cable or about half as thick as the battery cables. Does this help?

 

Also, according to the inverter, the panels are happily producing between 28-30v now at about half load (500w being drawn from house and to charge batteries). At full load (well when I draw more than they can produce) they produce about +-28v but obviously not near the amps they should be producing (38-39 instead of 46-47).   

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