Low panel voltage on one inverter, normal on the other???? Could they have all failed?

Can you tell us a bit more about your setup? "Inverter"... Are these inverter-charger (combined) system? Or are you typing about MPPT Solar charge controllers? What brand/model Array Vinput voltage range (web links OK to your hardware)?

What brand/model of solar panels (i.e., Vmp and Imp ratings)?

How are the panels wired? 8 series panels * 2 parallel strings or 4 series * 2 parallel for eight total panels?

How is the second array wired? 8 panels on one roof plane and 6 panels on a second? (i.e., 8s * 1p; 6s * 1p, or 7s * 2p, etc.)?

Regarding having the house grid tied... Even though this is a "solar forum"--Always suggest looking at the cost/benefit of any solar system.

In the USA, I suggest that solar power costs on the order of $1 to $2+ per kWHr (more if you are using part time). There is one member here that through hard work, shopping for good deals, and managing energy usage in a relatively sunny location (using A/C in Summer) is down towards $0.50 per kWH... And you pay a lot of money up front (batteries, chargers, panels, inverters, etc.).

You can figure out your $/kWH costs... For example, add up your hardware costs (plus a new battery bank every 10 years) and divide by your 20 year planned energy usage.

The other issues include:

• Unplanned failures (money out of your pocket)
• Changes in zoning/government regulations
• Possible insurance issues (i.e., fire insurance may payoff if there are issues with code/wiring/etc.)
• As we get older, at 70+ years, not sure I want to change battery banks and crawl on the roof to debug/fix
• Marketing/service life for many electronics is 5-10 years--In 10+ years may need to find/integrate new hardware, etc.
• If you need to sell the property in the future--Would having Grid Power make your property more saleable?
• In USA, running utility power to remote locations can easily start at $10,000 to $20,000 and go up from there
• in "remote" locations, some utilities seem to be cutting service or declining to connect new customers (no more government rural electrification subsidies)

Right now, electric utility power is becoming unreliable and expensive--And Grid Tied Solar (solar->GT inverter->grid----No battery bank) is losing much of its green subsides (government and utility)--So that is becoming less financially viable (or downright prohibited in some locations now).

And the whole "oil/fuel/coal" decarbonization "green" issue and the "war"... Having an independent solar+battery power system sure looks tempting.

-Bill

Good Day Phil,

It looks like this inverter-charger:

(fixed incorrect first link. -BB)
https://www.photonicuniverse.com/en/catalog/full/371-Iconica-5000W-48V-hybrid-pure-sine-wave-inverter-with-80A-MPPT-solar-controller-and-60A-mains-battery-charger-with-parallel-capability.html
https://www.photonicuniverse.com/upload/file/Manuals/Iconica/IC-KMS/IC-KMS_user_manual.pdf
And these are your solar panels:

http://www.solardesigntool.com/components/module-panel-solar/Hareon-Solar/806/HR-240W/specification-data-sheet.html
It looks like you have 2 panels in series and 8-14 parallel strings...

Just a quick look the inverter-charger specifications...

First, having one inverter-charger that has some panels on one roof plane and another set in parallel (2sx4p, and 2sx3p) is less than ideal as this inverter charger appears to only have 1x MPPT input. That means you have two different set of panel strings that operate at different temperatures (i.e., some facing the sun directly and getting hot, while others are off angle to sun and not as hot). Because Vmp (voltage maximum power) is temperature sensitive, the "hotter panels" will be operating at a Vmp of some percentage (10% or so worst case) than the other cooler array).

Depending on how the panels are mounted/pointed, and the design of the MPPT system inside the inverter, the MPPT has possibly two Vmp "peaks" to choose from... There is no "optimum" in the sense that each roof string is operating at a different Vmp voltage--So Pmp=Vmp*Imp has two or three different solutions (lower voltage Vmp, higher voltage Vmp, and some answer in between).

I have not done any testing (I am not in the solar business), but you could lose a fair amount of energy (10% or more??? Could be worse--Pure guess) on that second setup (2x roof planes).

The second issue is a bit more speculative... Many (most? all?) MPPT designs these days require Vmp-array to be higher than Vbatt during charging... They are "buck type" circuits that only "drop" the Array Voltage to the Battery voltage.

In your case, you are in a cooler region, so Vmp-array-hot does not drop as much vs being in a desert climate... And this is winter, so Vmp-array on many days is probably closer to Vmp-array-std (standard test conditions).

Again, guessing a bit here, your Vmp Array is based on 2x panels in series or 2*29.7V=59.3v Vmp-array-std... And your battery charging voltage (depends on battery type and your setup) is probably around 59 volts... So with a "cold array", your Vmp-array is very near battery charging voltage (not including wire resistance and inverter-charger voltage drop)... And on a hot summer day, Vmp-array may be 80% of V,mp-std or below ~45 volts (hot day, wiring resistance voltage drop, and inverter-charger voltage drop may be another 3-5+ volt drop).

My first suggestion would be to check with your inverter-charger installer/supplier about the proper array configuration... My guess is that you should be running 3 panels in series for an Vmp-array-std=89.1 volts... That would make battery charging much more efficient and give you a better harvest.

You cannot run 4 panels in series as Voc-array can exceed inverter-charger's maximum solar input voltage of 145 VDC max.

I am not sure about this statement: "We have some issues regarding our panels. Testing them today and one complete set is down to around 7v (depending on cloud) whereas the string next to it (on the other inverter) is sat happily around 30v."

Your Vmp-array voltage should be somewhere around 59.4 to 47.5 volts (based on Vmp @ xxC temperature)... And may actually be Vbatt-charging + a few volts (i.e., Vbatt-charging=54 volts, Vmp-array may be 54-60 volts). Again, these numbers are pure guesses as I have no detailed knowledage of your inverter-chargers or your array setup, or where you are measuring voltages.

Why "it worked well earlier" vs not so well today... There are always possible issues with wiring connections, and differences in solar panel irradiation (sunny, cloudy, direction array faces, temperature of cells, etc.)... 

Some more information on how solar panels/systems work at this link:

https://forum.solar-electric.com/discussion/5458/two-strings-in-parallel-with-unequal-string-voltages

Does any of this help you?

-Bill

Hmmm.... Just to be clear, 8 panels in series * 2 parallel strings? The Vmp-array should be around:

• rn29.7 * 8 panels in series = 237.6 Volts Vmp-array-std (i.e., pretty cold weather)
• 29.7 * 8 panels in series * 0.81 hot weather derating = 192.456 Volts (i.e., hot/no-wind weather)

Voc (voltage open circuit:

• 36.9 volts * 8 series panels = 295 volts (cold array/weather)
• 36.9 volts * 8 series panels * 0.81 hot weather derating = 239 volts (hot weather)
  

290 volts would be if the inverter-charger was not significantly loading the array (i.e., not drawing current from the array).

If the panels were tested and found to have 7 volts Voc--The probably are fried.

There are several major ways that solar panels can fail in this way (guessing). One is that the panels were connected in reverse to a voltage source (second string?). Solar panels are just giant diodes. And when connected in reverse, they flow current just like diodes... And if connected to a large enough voltage/current source, the current following through the panel will overheat and kill the solar cells.

Another way would be to (for example) connect a (one or a few) panels in series (with a another string and a larger number of panels in series)... An example would be 2 panels in series and a second string with 8 panels in series. The "over voltage" to the 2 panels in series would exceed their reverse voltage limits being fed by the 8 panel series string. Again ruining the cells with high reverse voltage.

And there are bypass diodes in solar panels... These diodes are there to bypass current around "dark" cells (local shading of cells/whole panel in a series string of panels). The diodes are supposed to be able to carry the Imp (current maximum power) of the rest of the string around the "dark" cells (dark cells go "high resistance" and can be ruined by too much "voltage" because they are "high resistance" because of local shading). The bypass diodes are there to carry current "around" dark cells until the shading is removed. For your panels there are probably 3-4 bypass diodes per panel. And these bypass diodes can fail. They can fail shorted or they can fail open. Replacing failed shorted diodes can repair a panel (if you can access them in the J-Box of the panel).

Do you have lots of shading on the array in full sun (nearby vent pipes, chimneys, overhead power lines, trees, etc.)?

That all 8 (or 16?) panels failed the same way (7 volt Voc on each panel?)... Sort of makes it sound like two strings connected in parallel incorrectly (one string "reversed polarity" as an example). Reverse polarity connection of an array directly to a battery bank can also "instantly" fry the string with over current from the battery bank (fuses/breakers probably would not save the panels/string/array).

There are other failure modes for solar panels (water leaks through edges of panels or punctured rear plastic membranes), poorly designed/manufactured panels, overheating of internal panel wiring--again design issue, etc.)....

In any case, I am still a bit confused... What inverter-charger inverter do you have? I gave a link to one I found and it had a max Vinput-array voltage of 145 volts... Not 290+ volts? (I have a bad/wrong link in above post for the inverter-charger model--I will fix in a minute):

https://www.photonicuniverse.com/en/catalog/full/371-Iconica-5000W-48V-hybrid-pure-sine-wave-inverter-with-80A-MPPT-solar-controller-and-60A-mains-battery-charger-with-parallel-capability.html

-Bill