BP Solar Module

LeighC

Hello
I have a BP 275 module that is about 13 yrs old & still works OK that I want to put in series with my other BP 3165S modules & a SunnyBoy SB2500 grid connect inverter, my question is it has a maximum system voltage written on it of 380 volts & my system is running at about 450v, do you think it will be electrically safe? The BP 280 of today that replaces it has max 600 v on it & it looks the same. The panels are on my roof well out of the way & are connected by MC leads. Whats the worst that can happen as the short circuit currents are within 10% of each other & it is sitting around not being used. The inspectors never check on any thing here in Australia either.
I wouldn't hold any to any views but would like some feedback.
Thanks - Leigh

BB.

Re: BP Solar Module

Well... Obviously you would be operating the panel above its maximum rated voltage so anything that I type below is by definition is unsafe. Also the hipot testing itself, if done wrong (or even right) can damage equipment and even kill the person doing the test. Assuming that you wish to continue:

You need to "hipot" the BP 275 module. It has been many years--so the Numbers that I am using are from memory--but I would suggest that you get a power supply (recommend adjustable, low current of a few 100 milliamps maximum) that can go up to about 1,500 VAC (or 2,100 VDC) and two good DVMs.

To test the panel, I would take some aluminium foil and wrap the (wetted with salt water) edges of the panel(s) or--if the panels have a metal frame, skip the foil. Next connect the two output leads of the panel together (shorted). Now, take your two meters and connect one across the supply (for voltage) and the other in series (for current). Take the "tester" leads and connect one to two panel leads (previously shorted together) and the other lead to the panel frame (or foil). Place the whole thing on dry wooden blocks or some other insulated surface. (salt water to make sure the glass seams are well sealed and insulated--not required for hipot testing but a good idea for something exposed to rain).

Crank up the voltage to 1,500 VAC (or 2,100 VDC) and monitor the current flow for 1 minute. If you have less than 5 milliamps of current flow, the panel(s) have passed hipot testing. Be aware that while both AC and DC tests are equivalent, the large area of a solar panel could cause the AC hipot test to fail due to leakage current (AC capacitive coupling)--that is why DC hipot is also allowed (AC voltage times square root of 2 for DC rating). Also, if doing (especially) DC hipot, make sure that the panels are discharged before touching them.

You have now hipot tested the panels which is what UL and others would require. It is a big assumption that the new panels have the same construction as the old panels--but if you look through the face of the panel and see that the distance from the edges is the same between the two models and the rest of the contruction is the same (insulation on the back, wires are marked the same, etc.)--you have done about all you can to prove that the panel(s) will probably work OK in your string.

Alternative Solution:

Now, another possible solution for your problem that is reasonably safe and sound engineering... If the SunnyBoy inverter (I have no idea about the SunnyBoy's internal grounding) grounds one side of the string (say negative ground), you can pretty safely just add the 380 volt rated panels to the ground referenced side of the string (negative in this example).

If you know what you are doing, just open the DC safety panels (danger--danger--danger--even if the AC mains are turned off power will be present) on the SunnyBoy solar panel connections and measure the "+" and "-" connections hard referenced to ground. If one of them reads very close to zero volts (using both AC and DC settings on your meter) that is the lead you should add the new panel connection to. If the reading is much above 5-10 Volts, you may have a ground reference issue or a floating DC bus and there is no correct side of the string to add the 380 Volt rated panel.

Ideally the ground reference is either a hard ground (copper to copper) or through a fuse (Xantrex uses a 1 amp fuse and a ground fault--blown fuse?--detection circuit). Ideally, you should either measure the resistance to ground (during the night--no sun and sunnyboy AC power off--or during the day with a small resistive load)--if you don't know what I am talking about--don't try it (you can hurt yourself and/or damage equipment if done wrong).

Possible Failures

The possible failures of the panels would be a short between ground and insulated sections. That could cause early failure of the panel (arc punches through insulation allows water into the panel) and if short occurs just right, you could start a fire at that point (there are typically no fuses in the DC side of each panel--so the short would be powered by the sun).

You could also, if there was a short to ground, create a shock hazard in rain. Walking on a wet roof (or working on a pole mounted array) would shock somebody touching the wrong place at the wrong time. It only takes 15 milliamps or so of current, properly applied through the human body across the heart (say left arm to right leg) to stop the heart.

The chances that you would destroy more than the one panel or the SunnyBoy is relatively low (<20% chance?). The chances that any of the other bad things (fire) that I warn about happening is, overall, also pretty low. Shock hazard is real--but would probably require a failure in insulation to occur first and ungrounded metal in the area for someone to touch (same issue as if you had a cracked panel).

And, in the end, this is all up to your personal choice and comfort level in (possibly) violating you local building codes and electrical requirements. Australia is known for its "difficult" electrical mains environment for us design engineers. Generally we try to error on the side of caution as risking life and property to save a few hundred dollars (US or AUS) is not usually considered a smart play.

In any case, if you can identify that one side of the SunnyBoy string is (hard) grounded (or grounded through a 1 amp fuse like the Xantrex with ground fault indicator) and you can add the 380 volt rated panels to that side of the string--I would feel pretty confident that it is safe installation and you have met the spirit of the code.

However, given that I am 1/2 a world away, don't know anything about your installation or your (probably very knowledgable) electrical skills and equipment that you have available, I cannot guarantee anything about your particular situation. You must take the responsibility for anything that you do. And if you are not sure of what you are doing, either get somebody who does (an electrician and/or electrical engineer) or don't do the work.

Sincerely,
-Bill

niel

Re: BP Solar Module

it would be easier, better, and safer to just sell the old pv and apply the profits towards another identical pv for the string and be done with it.

LeighC

Re: BP Solar Module

Thanks for your replies Bill & Niel
I will get an electrical engineer to check the module out, as this could be an insurance problem as well. My brother has low voltage off grid so I will sell it to him if there is any doubt.
Another query that you may be able to help me with - The higher voltage that flashes up on the Sunny Data screen because of the edge of cloud effect, it seems to be a magnifying senario, would it damage my SunnyBoy SB2500 which is rated at 600v? It seems to be only momentary but it does show up on the 7 second scan time & can be an extra 50 volts above what it is running at the time. A lot is figured into the system design on higher voltages as the temperature drops but not edge of cloud voltage rise.
I have 10 X BP3160 modules series Grid tied at the moment & have bought 2 more BP3165 S to go up this weekend. I use the GenAu_7-24.xls program out of SMA in Germany to work out design parameters & this is the max on 1 string for my temps. -5'C in Victoria Australia - 588 Voc - It gives an OK for 12 modules in series.
Thanks - Leigh