Solar panels concern

[SilverNodashi]

2 hours ago, Fritz said:

Thank you for the all the responses.  

@superdiy My specs:    6 panels all in series. 

2 x amerisolar  150W  ,      12V   ,  18Vp max  and 21.4V open circuit. Imax = 8.33A

+

4 x omega 180W,   12V , 18Vp max and 21.4V open circuit,  Imax = 10A

* just a note these panels looks almost exactly the same , i think the amerisolar just got a stronger alu frame. 

So my inverter input PV show,   +-115V and +-6A

The MPPT controller will look for the max power point which should be at  18 x 6 = 108V but it runs at 115V

so surely it must get max power?

I wish the answer will be that i bought shit panels and thats it..... ?!! yes ? no ? maybe?

 

When you mix panels, the lower panel is used as reference - if that makes sense?

i.e. instead of trying to calculate 2x 150W + 2x 180W + 2x 180W, you have 2x 150W + 2x150W + 2x150W. 

Getting back to electronic basics:

 

When current sourced (i.e. batteries / panels / etc) are added in series, Ampere stays the same, but the Volts add. When added in Parallel, the Volts stay the same, but the Ampere adds up as 1+n, i.e. 2x 8A devices gives 16A. BUT, when doing the math, all devices will run at the lowest denominator. So, in your case you have 2x 8.33A and 4x 10A panels, everything will run on 8.33A. 

Why do you only see +-6A? Current is drawn, not pushed. i.e. it will take what it needs, depending on the settings on the MPPT charger and only use that. When your batteries are dead flat, you could possibly see 8.3A, but in your case your panel angle does play a role, so you may possibly only see it in summer, on a "perfect" day. 

[Guest]

Having been in the same corner, you have the options, seeing you have to fix the angle and seeing you have 5kva 48v inverters:
1) Sell the panels and get ones more suited for you inverter / batts.
2) Sell the 2 small ones and get same specs ones.
3) Keep the panels, fix the angles, and use them for separate 12/24v systems to power smaller loads, and get a larger array.

EDIT: Sorry what inverter do you have @Fritz

[Fritz]

2 minutes ago, The Terrible Triplett said:

Having been in the same corner, you have the options, seeing you have to fix the angle and seeing you have 5kva 48v inverters:
1) Sell the panels and get ones more suited for you inverter / batts.
2) Sell the 2 small ones and get same specs ones.
3) Keep the panels, fix the angles, and use them for separate 12/24v systems to power smaller loads, and get a larger array.

EDIT: Sorry what inverter do you have @Fritz

Thanks for the advice but i will stick to what i have for now. 

i think i will try to change the angle. ( will be difficult ). summer should also tell me more about angle efficiency. 

i have a 5kva 48V axpert with 4 x 105 ah.

But what i still dont understand is that the total string runs at 115V so lets say that is  +-19V avg over each panel which should give close to 8.33A in the string.

another question is when i upgrade can i add a string with same nominal voltage. ?  ( 12 x 6 = 72V)

i will add a pic soon. 

[Guest]

Just now, Fritz said:

have a 5kva 48V axpert with 4 x 105 ah

As long as you understand if you want to get to the full use of the inverter, you need to get more panels, a lot more.

It is all part of the school fees. I would have gone for higher voltage panels, that you can get as close as you can to the MPPT's optimal range, least amount of panels.

And the 105ah, I would gather they are maintenance free? If so, learn how to make them last as long as you can, excellent training batteries.

[Guest]

11 minutes ago, Fritz said:

But what i still dont understand is that the total string runs at 115V

On my small MPPT, I get 60+ volts. Amps, 0.9 = 54w
Then later in the day I get lower volts and higher amps, like 414w coming from 2 x 200w panels. The higher the amps, the lower the volts.

Now your array is angled too flat, so the panels are not getting optimal sunlight, ie. not enough amps. 

On top of this, what Silver said above.

Bottom line, you are stuck. 

You have to get the angle optimal, and summer and winter have different angles, IF you want to go there.

As simple as that. 

[Fritz]

i still believe Pt = P1+P2+P3+P4+P5+P6  which is in my case = 1020W 

maybe the angle then or the cheap quality panels. 

[___]

42 minutes ago, Fritz said:

i still believe Pt = P1+P2+P3+P4+P5+P6  which is in my case = 1020W 

Nopity nopity nope. When you mix panels, they don't add up. The max current for the string is as much as the smallest panel will pass (I believe 8.3 amps in this case), and the voltages remain the same. So you derated 4 of your panels by 30W each, so 120W will be lost. Max is going to be 900W, under ideal circumstances. I rarely see more than about 800W from my 900W array (made up of 6 x 150W panels), and my panels are at the correct pitch... so your numbers are exactly where they should be.

I don't see any way to rectify the situation. You can't take panels out of the string, then your voltage goes too low. If you can get more of the 180W panels, then get two more of those. Put the 150W panels on a separate string with a separate controller.

Also, the Axpert experts here will know better, but I believe the minimum charge current the Axpert can be configured for is too high for a 100Ah bank. I stand to be corrected, but I definitely remember it being said here. If you only charge from solar (and not from mains) it might be fine, don't know the specifics.

[___]

My panels are configured in strings of 3, with 18V Vmp each. So the peak should be at 54V, right? In practice I see it hang around 52V, as low as 50V towards late afternoon. It has to do with the light level. A PV panel is a constant current device (mostly) so in practice it tends to make more or less the same amps all the time, but it cannot always do it at the same voltage. That "fall off a cliff" bit at the end of the IV chart moves down on the V scale as the light level goes down. So the lower Vmp is almost certainly because of the panel angle.

Edit: Hang on, I see now your Vmp is higher than expected. Well, the MPPT is usually of the Perturb-and-Observe kind, so the peak is determined literally by playing with the voltage (by messing with the overall impedance of the charging circuit). What happens in the general case, is the MPPT takes the voltage up until it sees a reduction in power, and then it pulls back a quarter turn and parks the voltage right there at the detected peak. If it happens at 115V, there is some kind of inter-module impedance at play where the controller finds it advantageous to run things at a higher voltage. It would be interesting to measure individual modules to see which ones are driven above their normal Vmp in order to get more out of the others :-)

[Guest]

Someone a very long time ago told me lesser panels = more efficiency.

Now I wonder @plonkster, you have 900w, I have 930w max.

24v PWM controller, 3 x 310w panels parallel with Open Circuit of 45.35 / 36.3v max power. Short Circuit is 9a / 8.6a at max power.

With PWM and all that, I hover between 750-780, right.
My best EVER was 968.96watts.
PANEL_VOLTAGE at the time was 29.6662v
PANEL_AMPS was 32.6621v

Why don't I get that more often you may ask? Because some a__e did not THINK back when panels where installed and used too thin a wire for the distance back then. (facepalm)

 

@Fritz, as my case above, IF angle is as close as I can get, perfect cool sunny day, you can exceed the array's total watts with ease BUT then you MUST have the angle right, panels match as close as they can, panels are cool in full sunlight and you have the right thickness cable for the length of wire.

All the above are factors that are stealing your power from your array. And as Silver and Plonk said, and now I, you cannot calc as you do. Does not work that way. Sorry bud.

 

[Fritz]

27 minutes ago, plonkster said:

My panels are configured in strings of 3, with 18V Vmp each. So the peak should be at 54V, right? In practice I see it hang around 52V, as low as 50V towards late afternoon. It has to do with the light level. A PV panel is a constant current device (mostly) so in practice it tends to make more or less the same amps all the time, but it cannot always do it at the same voltage. That "fall off a cliff" bit at the end of the IV chart moves down on the V scale as the light level goes down. So the lower Vmp is almost certainly because of the panel angle.

Edit: Hang on, I see now your Vmp is higher than expected. Well, the MPPT is usually of the Perturb-and-Observe kind, so the peak is determined literally by playing with the voltage (by messing with the overall impedance of the charging circuit). What happens in the general case, is the MPPT takes the voltage up until it sees a reduction in power, and then it pulls back a quarter turn and parks the voltage right there at the detected peak. If it happens at 115V, there is some kind of inter-module impedance at play where the controller finds it advantageous to run things at a higher voltage. It would be interesting to measure individual modules to see which ones are driven above their normal Vmp in order to get more out of the others :-)

yes, i am glad you spot  that up. All 6 my panels are at Vpmax.  + 

how can i test each panel in the string?

will it be a painful exercise:

1 - disconnecting them

2 - make my own test load 

3 - measure current or total power with meter

4- running around on roof

?

 

[___]

11 minutes ago, The Terrible Triplett said:

My best EVER was 968.96watts.

1080W, one cold morning with cloud-edge effect.

4 minutes ago, Fritz said:

how can i test each panel in the string?

The idea would be to measure them on the roof while in circuit and connected. The point of the exercise is to measure the voltage distribution across the modules while the MPPT holds it to the optimum detected voltage. It will be a pain in the neck to get onto the roof and do it... doesn't matter, I just thought it might be interesting to know. I think it runs the 150W panels high because it loses less power on them while making more on the 180W panels. Basically, it's going to try and find a happy "medium" voltage where it gets the most power.

[Fritz]

pic of panels :

 

[cvzyl]

Solar generating potential must be directly proportional to the apparent solar panel area as seen by the solar rays. Something like this graph, horizontal axis is angle between solar panel surface and solar rays, vertical is potential for the given conditions.

[DeepBass9]

Back to Ballar's question, I don't think your batteries can soak up all of that power, so they could be the limiting factor. What happens at midday if you put a 5kw load on your system? Can the panels drive that? Not that you will be getting the full 4800W at this time of year. My panels are fixed at about 35 degrees true north, and I am now getting about 65-70% of their rated output at midday. In summer I have seen just over 2kW from my 1800W of panels briefly (Yingli 300W panels)

[Chris Hobson]

I try and maximise my load (within reason - I still want to charge my batteries) and therefore maximise production. At the moment I get between 2300W and 2500W from a 3kW array. In spring and autumn I go over 3000W on some days. This is important to me not for the momentary maximum but being able to achieve that shows that losses and inefficiencies are being kept to a minimum. In summer with the high temperatures it is difficult to achieve 3000W.