input voltage drop
hillside
Registered Users Posts: 132 ✭✭
After several years of trouble free use my downstairs system is showing a marked drop in input voltage from the panels. And it may have happened further back than I realized. Early on one string of 4 235W panels would show up to 90 volts at the controller--now it shows in the low-mid 60's, to 67V. Panels are mixed, purchased new and used (very limited supplies here on the island at the time)
Is it possible some have degraded to this point?
The other string next to it shows an average of 65 Volts at the CC.
Both strings are series/parallel, both sets of panels are new/used and each feed 40A MPPT controllers to one set of 4 370AH Deka fld. batts.
I know I'll need to measure open circuit voltage on each panel and did so when set up, marked each one with a sharpie and the ink has disappeared! If I recall all were in the 33-37Voc. range.
Appreciate any advice!
Is it possible some have degraded to this point?
The other string next to it shows an average of 65 Volts at the CC.
Both strings are series/parallel, both sets of panels are new/used and each feed 40A MPPT controllers to one set of 4 370AH Deka fld. batts.
I know I'll need to measure open circuit voltage on each panel and did so when set up, marked each one with a sharpie and the ink has disappeared! If I recall all were in the 33-37Voc. range.
Appreciate any advice!
8- 235Watt panels, 2 strings in series/parallel, 4L16 Deka 6Volt, 370AH FLA. batteries, 3000W Cotek pure sine inverter, SRNE ML2440 40Amp Controller & 40 Amp Renogy controller, 24 Volt system.
5 stand alone PV arrays; 12V gate opener, 24V Dankoff rain water pumping system, 12V Shurflo rain water garden pumping, 12V bathroom LED lighting and fan.
4- 450 Watt panels with 4 L16 6 volt batts./ 2-Renogy Tracer 40 Amp controllers/ Xantrex 1800W PSW Inverter.
4- 450 Watt panels with 4 L16 6 volt batts./ 2-Renogy Tracer 40 Amp controllers/ Xantrex 1800W PSW Inverter.
Honda EU3000W generator for backup.
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- If you have a circuit breaker combiner box, you can turn off one string and then the other... Record the string current and voltage. Frequently, things fail one at a time, and the "weak string" can be identified and you can then do further testing (i.e., disconnect panels and check Voc/Isc numbers). If you have, for example, fuses/fuse holders, generally not a good idea to use the "fuses" as a functional quick disconnect as it is (quite) likely that you will have DC arcs which can ruin the holders or even set a holder on fire. Depending on how easy to get to the panels, you could try covering one string at a time with dark tarps/blankets to see if the "dark string" is carrying "its share" of voltage/current.
- Get an AC+DC Current Clamp meter. You need the DC function of the meter and can quickly check the current from each string--Again, double check operation of each string.
It sounds like you have a failed panel with 30 volt drop (Vmp~30 volts?)... MPPT controllers "track for maximum power point"--But with a "failing panel", you don't know if it is tracking the "lower voltage or higher voltage power peak (i.e,. 60 volt peak of both string, or 90 volt peak of one string).Examples of AC+DC current clamp DMMs (digital multi meters):
https://www.amazon.com/UNI-T-Digital-Handheld-Resistance-Capacitance/dp/B0188WD1NE (lower cost, "good enough")
https://www.amazon.com/Auto-Ranging-Resistance-Klein-Tools-CL800/dp/B019CY4FB4 (higher function, mid priced)
When doing your checks, crimp connections fail--You may see melting of plastic, or the wire may pull from crimp connections). Or you may see corrosion from water intrusion.
Look closely at panels... You may see streaks on cells/glass, water intrusion, corrosion, browning of cells, cracked cells, etc. I had failed panels due to j-box overheating (see some browning--"Coffee Stains"--on glass side of panel over j-boxes).
When testing panels--Try to do all checking quickly under "same sun, same direction wrt sun--With multiple panels, they should all be very close to each other (Vmp/Imp/Voc/Isc)--With in 10% or so of each other. Any panels that are 50% or greater deviation are probably "bad".
-Bill
-Bill
BTW, I have no idea how old or used the panels were when I bought them (from a solar biz but I think it was the owner or an employee.)..
Will report back. Thanks
4- 450 Watt panels with 4 L16 6 volt batts./ 2-Renogy Tracer 40 Amp controllers/ Xantrex 1800W PSW Inverter.
2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.
If you can come up with New or newer larger panels easy enough you might just run a new array.
2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.
When panels were $10-$30 a Watt... Saving old but otherwise OK panels was more of an economic decision.
When you can purchase panels at $0.50-$1.00 per Watt (shipping is always a big question), then it becomes an issue of how much time and energy you wish to expend working around the "old" (and the mix&match Vmp/Imp issues) vs just installing new panels and (hopefully) getting 20+ years out of the new set.
-Bill
I'm hoping I find a failed MC4 conection. I noticed one of the panel's 10ga. wires gets warm at times during peak sun...
And, the other kitchen array needs a 40 Amp fuse and I can't find one anywhere. Store here is out as is Platt Electric. I bought a 3 pk of these for lighting and would like to know what you think. Thanks
https://www.ebay.com/itm/114056620173
4- 450 Watt panels with 4 L16 6 volt batts./ 2-Renogy Tracer 40 Amp controllers/ Xantrex 1800W PSW Inverter.
- Don't know mfg and ratings (Starpoint? No details I could find)... Typically this type of fuse is rated for "automotive" use and 32 VDC max voltage
- Fuses really don't do much for lightning which took a trip of mile(s) to reach your system. Another 1/2 inch is not doing much.
- Where are the fuses installed... Typically for series strings of panels, need one series protection fuse (typically around 10-20 amps depending on panel specs). If used for controller to battery bus connection, that is less than 32 VDC, they could work as wiring protection fuses.
- When designing for lightning--Grounding design is critical. And a good quality surge suppressor helps too (i.e., clamp voltage to ground vs just "opening a switch/fuse/breaker".
Surge Suppressor (our host):https://www.solar-electric.com/search/?q=midnite+surge+mnspd
Scroll down for Documents/Video buttons for detailed information:
https://midnitesolar.com/productPhoto.php?product_ID=283&productCat_ID=23&sortOrder=1&act=p
-Bill
But back to my voltage drop.
I could buy the clamp on multi meter but amazon will take 2-3 weeks to get here. Or I could drive around for a couple hours searching locally but if I could check the panels with my regular multi meter it would save serious time.
But, in a 4 panel string that is series/parallel (no j-box) how to go about checking each panel seperately? Tarp all 4, disconnect all wires and uncover one panel at a time?
Thanks
4- 450 Watt panels with 4 L16 6 volt batts./ 2-Renogy Tracer 40 Amp controllers/ Xantrex 1800W PSW Inverter.
As a start, I would, in the middle of the day, with a discharged battery bank (or put, for example, and electric heater as a load on the system to ensure lots of current/power draw from the array)... Cover one panel at a time and see what the charge controller array voltage/current is.
Since all the panels are similar, then covering each panel separatly and logging the results--My guess is that a weak panel (or string) you will find (at least) one panel that "behaves" differently than the rest (most likely, that one covered panel does not drop the array power as much as any of the other panels).
You have "identical" panels, and are looking for any that do not behave the same as the rest.
Regarding the 40 amp fuses... I suggest that you "oversize" the wiring and fuses/breakers by 1.25x ... For example, in North America, fuses (breakers) are designed to no trip at 80% or less of rated current, and trip at 100%+ of rated current (may take hours, or never for 101%--They are not that accurate).
For example, if these were for the 40 Amp MPPT charge controllers, I would suggest the fusing (and wiring) be rated for:
40 amps * 1.25 NEC derating = 50 amps "branch circuit"
The idea is to avoid trips for otherwise normal operation (i.e., MPPT controller outputting rated current for several hours into a discharged battery bank).
-Bill
https://www.nist.gov/news-events/news/2020/03/nist-study-uncovers-potential-driver-premature-solar-panel-failures
The premature cracking has largely been attributed to the widespread use of certain plastics, such as polyamide, but the reason for their rapid degradation has been unclear. By closely examining cracked polyamide-based backsheets, researchers at the National Institute of Standards and Technology (NIST) and colleagues have uncovered how interactions between these plastics, environmental factors and solar panel architecture may be speeding up the degradation process. These findings could aid researchers in the development of improved durability tests and longer-lived solar panels.
Cracks in backsheets often show up first near certain features — such as the grid-shaped space in between the blue or black electricity-producing solar cells — and can eventually propagate through the entire thickness of a sheet. These defects make way for oxygen and moisture to infiltrate and damage the interior where the cells lie and also allow electrical current to escape, increasing risks of electrocution.
If left outside for long enough, any plastic-based backsheet will start to fall apart, but not all backsheets are created equal. Some plastics deteriorate much more rapidly than others.
“In the 2010 to 2012 timeframe, many modules were deployed containing polyamide-based backsheets, which presented dramatic cracking failure in as little as four years despite meeting standard requirements,” said Xiaohong Gu, NIST materials engineer and co-author of the study.
PV panel failures are not uncommon, with most of these defective modules using non field-proven materials. Even more, defects are seen among systems in use less than five years.
As early as 2010, DuPont tests revealed significant weaknesses in PET, polyamide, and PVDF-based backsheet materials, which are currently used in a large volume of solar panels in the field. Single-stress and sequential stress tests were conducted, revealing PV panel failures such as yellowing/embrittlement and cracking, caused by exposure to UV, extreme temperatures and humidity over time.
A Global, Growing Concern
What was once thought to be isolated cases of failures is proving to be a more prevalent occurrence around the world, with many of those failures found in backsheets.
Globally, PV panel failures are growing.
All of these cases have experienced backsheet failures at extremely young ages – an alarming statistic given the importance of performance and durability over the long haul.