safety when connecting panels into strings

[Salts]

I always leave one of the MC4 connectors between panels in each string open. This way, when I'm stripping wires and installing connectors, the circuit is open and I can't get shocked.

Make sure the DC switch to the inverter is off, then wire up the DC pos and neg lines into the inverter. The last thing I do before flipping the DC Switch to the ON position is to go back in the string and connect that MC4 connector I left open.

Turn on the AC, turn on the DC.

I did mine under full sunshine. No tarps or cardboard required.

[J.P.M.]

post was held in moderation, released now

R.U.A.

Thank you.

J.P.M.

[RShackleford]

Having really looked at those MC4 connectors for the first time, I feel better. Seems pretty safe to:

1. Turn off DC connection to inverter, however that is done for your setup - built in to inverter, separate breaker or switch, whatever.
2. Do all non-MC4 connections first (that involve handling bare wire, such as into terminal blocks.
3. Don't work when it's at all wet.
4. Work during twilight.

[bcroe]

The AC outlets power my night work flood lights. The light intensity of these is far
too low to generate dangerous solar panel energy. Bruce Roe

[RShackleford]

No, I'm not. I'm simply reporting in good faith what my experience has been with respect to the apparent opaqueness of various tarping materials.

Geez man, this isn't a court of law. How about "you're suggesting ..." ?

[RShackleford]

There is enough generation from the back side of my panels to be dangerous.

Meaning, from bright lights one might put underneath the frame, to assist in wiring the panels ?

That is one reason AC outdoor outlets are mounted on my array frames, for the lights and everything
else.

Not following (how generation from backside of panels suggests mounting AC outdoor outlets on array frames).

[J.P.M.]

So you're saying that unless I acquire a (presumably expensive) fully-opague tarp like the tenters used, I'm better off with the cheap brown tarps than the cheap blue ones ? I think even that will be a pain though; I think I'll just do it in the dark; a good floodlight out there seems easier and cheaper.

No, I'm not. I'm simply reporting in good faith what my experience has been with respect to the apparent opaqueness of various tarping materials.

What you do with it, if anything, is for your engineering judgement to determine. It's simply information. Take it FWIW.

[bcroe]

There is enough generation from the back side of my panels to be dangerous. That is
one reason AC outdoor outlets are mounted on my array frames, for the lights and everything
else. Bruce Roe

[RShackleford]

The brown tarp transmitted 0 W/m^2. The blue tarp transmitted 105 w/m^2. The tarps appear to be of similar weight and material.

So you're saying that unless I acquire a (presumably expensive) fully-opague tarp like the tenters used, I'm better off with the cheap brown tarps than the cheap blue ones ? I think even that will be a pain though; I think I'll just do it in the dark; a good floodlight out there seems easier and cheaper.

[Mike90250]

post was held in moderation, released now

[J.P.M.]

SEIA once did a test in their solar lab of covering an array with one of those blue tarps and then measuring the open circuit voltage. Still plenty of DC voltage left to kill you....
Just leave one MC4 connection on an array to be the last thing connected and you'll be just fine.

I had my house tented about 4 yrs. ago. Aside from the adventures of keeping the tenters off the array (honest !), when the tent was over the array/house, the array measured zero output current and a fraction of a volt potential. That tarp was completely opaque.

At approx. 1200 - 1215 hrs. P.D.T. (11:09:26 to 11:24:26 solar time) today, under cloudless skies, I covered the solar sensor on my Davis weather station for 5 minute periods, first for 5 minutes with a sample of brown tarp, then uncovered for 5 minutes, and then covered for 5 minutes with a sample of blue tarp, both tarps are the std. stuff of the type you'll find at Big Box.

Both tarps are fairly new and not used much.

The uncovered GHI at the time varied from 1003 W/m^2 at 1200 hrs. PDT to 1013 W/m^2 at 1215 hrs., both readings uncorrected for instrument temp.

The brown tarp transmitted 0 W/m^2. The blue tarp transmitted 105 w/m^2. The tarps appear to be of similar weight and material.

Take the above FWIW.

[RShackleford]

SEIA once did a test in their solar lab of covering an array with one of those blue tarps and then measuring the open circuit voltage. Still plenty of DC voltage left to kill you....

Damn, as I suspected (from I-V curves above).

Just leave one MC4 connection on an array to be the last thing connected and you'll be just fine.

Not sure how that helps. We're talking open-circuit voltages.

[solarix]

SEIA once did a test in their solar lab of covering an array with one of those blue tarps and then measuring the open circuit voltage. Still plenty of DC voltage left to kill you....
Just leave one MC4 connection on an array to be the last thing connected and you'll be just fine.

[bcroe]

I reserve most panel electrical work till complete darkness, when they are no
longer dangerous. One method is break a string at several points so voltages
do not add up.

Curves above look like 0.53 to 0.59 volts per cell OC variation. Bruce Roe

[bob-n]

You're right. Open-circuit panel output voltage can be significant, even on a dreary day, and multiple panels add up. In this plot, at no load, even with 1/5th of STC, you still get 88% of the maximum output voltage from the panel.
solarcells2.png