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Rated output of Panel i am getting it all?
#1
I Have 8 Pieces 10W Solar Panels Connected in Series and Parallel to achieve higher voltage for my 24V Battery Bank. I am only Getting 55W / 1.8A of power and 60W / 1.9A peak is this all the panel it can produce? Given that 0.56A Max for each String multiply by 4 i should be getting 2.24Amps. or my computation is wrong?
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#2
What angle are the panels mounted at? For ideal sun this time of year, you would need the angle to be close to whatever latitude you are at. Flatter than that and less current is highly likely. Also, what voltage are you reading at your charge controller? There's likely a drop there as well due to the long run at relatively low voltage.
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#3
Positioning and panel angle can make a huge impact… there are inefficiencies associated with less than idea installations, along with any losses in long runs for conductors. Without looking at the entire installation, its hard to comment, but 60 out of 80 watts sounds like you are close to where you should be at 75%, and if those panels can produce the full 100%, 25% can easily be lost in the above mentioned items.

Are you measuring this as the panel to the charge controller, or from the power going into the cells as you could also see losses based on the charge controller selected.
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#4
(04-24-2019, 02:32 PM)hazSolar Wrote: What angle are the panels mounted at?  For ideal sun this time of year, you would need the angle to be close to whatever latitude you are at.  Flatter than that and less current is highly likely.  Also, what voltage are you reading at your charge controller?  There's likely a drop there as well due to the long run at relatively low voltage.

The sun passes on top of my roof @ maybe 70-80 degrees . Solar panel are mounted 16-18 degrees. The charge controller reads 30-31v(55W @ 1.8A) when charging the 24v battery

(04-24-2019, 06:18 PM)Crimp Daddy Wrote: Positioning and panel angle can make a huge impact… there are inefficiencies associated with less than idea installations, along with any losses in long runs for conductors.  Without looking at the entire installation, its hard to comment, but 60 out of 80 watts sounds like you are close to where you should be at 75%, and if those panels can produce the full 100%, 25% can easily be lost in the above mentioned items.

Are you measuring this as the panel to the charge controller, or from the power going into the cells as you could also see losses based on the charge controller selected.
i'm measuring it using the software of the charge controller, here it is 1.9A from solar panel going to controller and 2.22A going to the battery,
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#5
Temperature? Losses in cables? Losses in Charger?
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#6
Panel Rating is at 1000w per sq metre of sunlight and at 25 degrees celsius.
Any deviation from these parameters will yield less power.
Right now You are getting 77%, that is not that bad.
However, as Dromer stated, check cabling.

With a clamp amperemeter You could check that all 4 clusters of 2 panels give power, one may be missing.

Best of luck Smile

ChrisD
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#7
Unfortunately you (almost**) never get the output on the label.
Like ChrisD5710 & others are saying, the main reason is temperature rise of the panel in the sun, it gets hot & the output drops.
** if the sun pops out from behind some clouds on a cold day you'll get better numbers for a bit until the panels heat up again.

A typical panel's output drops like this:
Temperature coefficients of Pmax = -0.40%/℃
Temperature coefficients of Voc = -0.30%/℃
Temperature coefficients of Isc = 0.06%/℃
So if the label spec is at 25degC (called STC) & the panel runs at 45 degC (called NOCT, might be hotter at your place) then 20 x 0.40% is 8% less output power right there.

Re the wiring, you've got a 10m run of AWG16 cable which has a resistance of about 0.0132ohms per m (from an online look-up chart).
The total "round trip" length is probably about 23m (bit extra at panel end?) so 0.0132 x 23 = 0.3036 ohms at 25degC
The cable losses are from current & go like this:
so Imax = (0.56A x 4 strings of panels) = 2.24A at 25degC (ie STC)
so at your place assuming 45degC operating temp it's 20 x 0.06/100 = 1.2% less current = 2.21A (ie at NOCT)
So on your cable with 0.3036 ohms, at 2.21A current you're getting about 0.67V loss which is not much vs about 32.45V (see below) ie that's about 2% loss of voltage.

Now some voltage numbers:
Spec says 17.83 max power voltage at 25degC test conditions
Assuming the MPPT unit tracks this properly....
At 45degC operating temp the max power voltage drops by about 8.9% (typical panel spec sheet STC vs NOCT)
So each of the 2 panel strings should be putting out about 17.83 x 2 x .909 = 32.45V at the panels

At 2.21A, you'd see about 32.45 - 0.67 = 31.78V at the controller

So expected power would be 2.21A x 31.78V at the controller's input = 70.23W

You've got a 7s Li-ion battery so assuming full voltage = 7x 4.1V = 28.7V, that's only about 3V difference to the controller's input?

From the controller pic, your numbers look close to this but voltage is up a little & the current a bit down.
The MPPT unit may tracking a different point or not able to pull enough current from the panels with only a small voltage difference?
Running off solar, DIY & electronics fan :-)
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#8
(04-25-2019, 03:02 AM)rhedbatt Wrote:
(04-24-2019, 02:32 PM)hazSolar Wrote: What angle are the panels mounted at?  For ideal sun this time of year, you would need the angle to be close to whatever latitude you are at.  Flatter than that and less current is highly likely.  Also, what voltage are you reading at your charge controller?  There's likely a drop there as well due to the long run at relatively low voltage.

The sun passes on top of my roof @ maybe 70-80 degrees . Solar panel are mounted 16-18 degrees. The charge controller reads 30-31v(55W @ 1.8A) when charging the 24v battery

(04-24-2019, 06:18 PM)Crimp Daddy Wrote: Positioning and panel angle can make a huge impact… there are inefficiencies associated with less than idea installations, along with any losses in long runs for conductors.  Without looking at the entire installation, its hard to comment, but 60 out of 80 watts sounds like you are close to where you should be at 75%, and if those panels can produce the full 100%, 25% can easily be lost in the above mentioned items.

Are you measuring this as the panel to the charge controller, or from the power going into the cells as you could also see losses based on the charge controller selected.
i'm measuring it using the software of the charge controller, here it is 1.9A from solar panel going to controller and 2.22A going to the battery,

I dont consider that a valid test... use an inline amp power meter or clamp meter to test the actual yield of the panel without a load.  Short circuit current and open circuit voltage and compare that to the spec sheet.

Test each panel individually first, then as a system.

Anything else in the chain of production is going to have loss and inefficiencies.
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#9
(04-25-2019, 08:00 AM)Redpacket Wrote: Unfortunately you (almost**) never get the output on the label.
Like ChrisD5710 & others are saying, the main reason is temperature rise of the panel in the sun, it gets hot & the output drops.
** if the sun pops out from behind some clouds on a cold day you'll get better numbers for a bit until the panels heat up again.

A typical panel's output drops like this:
Temperature coefficients of Pmax =  -0.40%/℃
Temperature coefficients of Voc =  -0.30%/℃
Temperature coefficients of Isc = 0.06%/℃
So if the label spec is at 25degC (called STC) & the panel runs at 45 degC (called NOCT, might be hotter at your place) then 20 x 0.40% is 8% less output power right there.

Re the wiring, you've got a 10m run of AWG16 cable which has a resistance of about 0.0132ohms per m (from an online look-up chart).
The total "round trip" length is probably about 23m (bit extra at panel end?) so 0.0132 x 23 = 3.036 ohms at 25degC
The cable losses are from current & go like this:
so Imax = (0.56A x 4 strings of panels) = 2.24A at 25degC (ie STC)
so at your place assuming 45degC operating temp it's 20 x 0.06/100 = 1.2% less current = 2.21A (ie at NOCT)
So on your cable with 3.036 ohms, at 2.21A current you're getting about 0.67V loss which is not much vs about 32.45V (see below) ie that's about 2% loss of voltage.

Now some voltage numbers:
Spec says 17.83 max power voltage at 25degC test conditions
Assuming the MPPT unit tracks this properly....
At 45degC operating temp the max power voltage drops by about 8.9% (typical panel spec sheet STC vs NOCT)
So each of the 2 panel strings should be putting out about 17.83 x 2 x .909 = 32.45V at the panels

At 2.21A, you'd see about 32.45 - 0.67 = 31.78V at the controller

So expected power would be 2.21A x 31.78V at the controller's input = 70.23W

You've got a 7s Li-ion battery so assuming full voltage = 7x 4.1V = 28.7V, that's only about 3V difference to the controller's input?

From the controller pic, your numbers look close to this but voltage is up a little & the current a bit down.
The MPPT unit may tracking a different point or not able to pull enough current from the panels with only a small voltage difference?
Great explanation thanks.So i also read that monocrystalline panels tend to become hotter than polycrystalline. Since this is a monocrystalline panels and my roof is very hot when there is no passing clouds maybe 50-60degC so there is 10%-14% loss there and I've confirmed this i tested every panel with 12V battery when the panels are warm it can produce 8-9Watts i leave each of them for 10minutes under the sun and the panels produce only 7.0-7.8Watts, 1 panel even produce 6.9Watts w*f. So i'm thinking maybe they are sh*t panels.

7S Li-ion = I boost charge them up to 28.35V(4.05 per cell) , 28V Float. (batteryuniversity says you can get more cycles at lower charged voltage)

So if we assume that MPPT unit are tracking different point, what do you suggest i will do? connecting 3 panel strings?
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#10
Not all MPPT is created equal, but brands like Victron and Genasen seem to be VERY fast in tracking and optimizing that powerpoint.

Alternately, series panel setups are great and MPPT and absolutely take advantage of it, you also need to be aware of any possible panel shading as it will effect all panels in series.

Quality of the panel might come into play as well, but sometimes its easier to over provision by a small amount to deal with any issues like that.
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