Renogy - Hit & Miss

[PNjunction]

3 panels reached 5.0amps... 1 panel would only reach 3.9 amps.

WHOA! Wait a minute. If these are 60 watt panels, then the IMP should normally be about 3.3A under best conditions. (60w / 18v).

Although one seems to have a high forward voltage drop, I'd say you are actually doing better than spec! How are you measuring the amperage? Is there an STC sticker on the back?

[inetdog]

WHOA! Wait a minute. If these are 60 watt panels, then the IMP should normally be about 3.3A under best conditions. (60w / 18v).

Although one seems to have a high forward voltage drop, I'd say you are actually doing better than spec! How are you measuring the amperage? Is there an STC sticker on the back?

OP probably measured I_SC but even that sounds a bit high.

[Shockah]

WHOA! Wait a minute. If these are 60 watt panels, then the IMP should normally be about 3.3A under best conditions. (60w / 18v).

Although one seems to have a high forward voltage drop, I'd say you are actually doing better than spec! How are you measuring the amperage? Is there an STC sticker on the back?

OP probably measured I_SC but even that sounds a bit high.

Yes,,, measured ISC... sticker says 3.67A

0527042128.jpg

I even used a 2nd DMM to verify all 8 panels
and 6 of them flat lined @ 5.0amps.

I know the low reading of 3.9A is still above sticker,
But I figured it would be better to have all 4 at the highest output since I am mounting these panels at low tilt.

Is it possible the voltage @ ISC is lower than the rated VMP?
i.e., If VMP is 12v @ ISC, then 60W/12V would produce the 5amp?

[PNjunction]

My only thought at this point is that perhaps that one panel is more sensitive to an inductive load like a fan, rather than a charge-controller / battery combo. Still that weird one has thrown up a red-flag.

While Renogy warns about not shorting panel leads together, the standard procedure for testing ISC and IMP with NO LOAD AND NOTHING ELSE ATTACHED, is to put a towel over the panel. Attach ammeter / multimeter across leads noting the proper multimeter jacks AND switch position to measure amps. (do this wrong and poof goes your fuse). Remove towel. Measure, throw the towel back on and disconnect the meter.

The same goes for measuring voltage, but again be sure you have the multimeter in the right jacks and switch positions first for voltage- do not change them while connected. First hand experience.

At this low a voltage and current level, we shouldn't have an issue, but lurkers beware of high-current / high voltage systems. The towel trick, especially if the wind blows it off is a personal safety hazard.

[bcroe]

While Renogy warns about not shorting panel leads together, the standard procedure for testing ISC and IMP with NO LOAD AND NOTHING ELSE ATTACHED, is to put a towel over the panel. Attach ammeter / multimeter across leads noting the proper multimeter jacks AND switch position to measure amps. (do this wrong and poof goes your fuse). Remove towel. Measure, throw the towel back on and disconnect the meter.

I would never bother with the towel routine for a single panel. YES don't disconnect your
MP4s with current flowing. OPEN the SWITCH you installed in series with the meter, THEN
disconnect your MP4s. Voltage capability gets a lot more demanding for multiple panels.
Bruce Roe

[inetdog]

Voltage capability gets a lot more demanding for multiple panels.
Bruce Roe

Which would then require multiple towels....

[PNjunction]

I would never bother with the towel routine for a single panel.

Ordinarily no. But for me, it develops a good safety habit for those times when I forget that instead of a 5 watt panel at the end of the cable, I've really got a 500 watt system. I setup and teardown portable and experimental systems a lot, and can get easily distracted or excited and forget.

I even found myself getting complacent about polarity with my digital voltmeter since it will read either way. Even though I know that, I try to make it a point to get the polarity correct. The reason here is to develop the habit of getting the polarity right on *other* stuff.

Almost took out my other gear when in a hurry, my mind was saying "go ahead and connect up, it doesn't matter". Stopped inches short of a reverse polarity mistake.

I know me - if I see a shortcut, I'll take it, but in the case of personal safety, I don't want my subconscious thinking about shortcuts.

[bcroe]

Ordinarily no. But for me, it develops a good safety habit for those times when I forget that instead of a 5 watt panel at the end of the cable, I've really got a 500 watt system. I setup and teardown portable and experimental systems a lot, and can get easily distracted or excited and forget.

I even found myself getting complacent about polarity with my digital voltmeter since it will read either way. Even though I know that, I try to make it a point to get the polarity correct. The reason here is to develop the habit of getting the polarity right on *other* stuff.

Almost took out my other gear when in a hurry, my mind was saying "go ahead and connect up, it doesn't matter". Stopped inches short of a reverse polarity mistake.

I know me - if I see a shortcut, I'll take it, but in the case of personal safety, I don't want my subconscious thinking about shortcuts.

I as well have worked up a fairly elaborate safety procedure, with 400 VDC at 40A on tap. I am
afraid to post it in great detail and then be accused of being liable for not doing enough. My
light bulb tester tells me if any real power is present; a DVM is fooled by static on big arrays.
But I don't trust covering panels, which will minimize current, but still produce the voltage
from light on the back. Sometimes I work at night, with a head mounted light. Bruce Roe

[Shockah]

.... Sometimes I work at night, with a head mounted light. Bruce Roe

I beg to differ with the head-light approach.

I have a post lamp in my driveway with a 20W panel.
One night my son was launching his baseball around, and BAM! ... landed right on the panel.
He ran in and told me about it and said it sounded like cracked glass.
I went out there with a ladder and head-mounted-light to check the panel.

When I got up the ladder and looked down at the panel, the post-lamp shut off...
For a second, I thought the panel was damaged, but then realized the panel was producing at least 5 volts from the head-light.
Hence, the load controller thought it was dusk, and turned the light off.
(BTW, the baseball did not damage the panel).

Small panel, small light... but the point is a PV panel with a light shining into it can produce some current at night.
Meaning working at night is not absolutely current-free either...

I've been meaning to measure ISC on a panel on a full-moon night.....

[pleppik]

I've been meaning to measure ISC on a panel on a full-moon night.....

Interesting question....I looked it up, and the illumination for a full moon at max brightness is about 1.4W/m2.

In round numbers, call that about 1/700th of what you get from the sun. So a 7KW array could give you, under ideal circumstances, about 10W under a full moon.

Except of course that a silicon PV cell needs a minimum amount of light to produce any power at all, so you're likely to just get zero.

[bcroe]

Interesting question....I looked it up, and the illumination
for a full moon at max brightness is about 1.4W/m2.

In round numbers, call that about 1/700th of what you get from the sun. So a 7KW
array could give you, under ideal circumstances, about 10W under a full moon.

Except of course that a silicon PV cell needs a minimum amount of light to produce
any power at all, so you're likely to just get zero.

Full moon is in 8 days. Guess it might be interesting to disconnect the panels
from the inverters, and see if there is enough output to overcome the cell
leakage loss, and actually generate some voltage. The test might do better
in Feb, since semi leakage generally varies exponentially with temperature.

At 1/700th, there wouldn't be enough power to start my inverters.

As for my head light, it might trip a light detector straight on. But powered
by a couple AAAs, the amount of power transferred to the back side of my
275W panel probably isn't measurable. Light from the night sky might
generate some voltage, but there won't be much current. Anyway, I open
the circuit in multiple places to avoid either voltage or current.

Maybe the real reason I work in the dark, is to avoid loss of production.
Bruce Roe

[bcroe]

Full moon power

Interesting question....I looked it up, and the illumination for a full moon at max brightness is about 1.4W/m2.
In round numbers, call that about 1/700th of what you get from the sun. So a 7KW array could give you, under ideal circumstances, about 10W under a full moon.
Except of course that a silicon PV cell needs a minimum amount of light to produce any power at all, so you're likely to just get zero.

For your entertainment, here is the NW IL full moon report. 2 days from full moon
the clouds blew away, so I did measurements just before midnight. Both systems
were near identical readings.

My 2 string inverters will run down to 27W. They were not running; they were not
trying to start, they were completely dead.

I opened the DC disconnect between the panels and inverters. 5 parallel strings
connected to an open circuit generated about 3V. I further went out and opened all
10 string fuses. These strings nominally run 360 VDC, the open circuit voltage is
higher. On the 6 newer panel strings (3 KW each), the open circuit voltage was 9 to
15 VDC. On the 4 older type panel strings (2.75 KW each), the open circuit voltage
was about 0.9 VDC. The leakage of these was apparently dragging down the others,
before being isolated.

The moon was detected, but zero useful power was generated. Bruce Roe

[Shockah]

So be it

[Shockah]

Well, subject 60W Panels are up and running...

I'm confident they will perform as expected.

0611041936.jpg

[pleppik]

For your entertainment, here is the NW IL full moon report. 2 days from full moon
the clouds blew away, so I did measurements just before midnight. Both systems
were near identical readings.

Not at all surprising results, but I think it's awesome that you actually went out and did this.