Can i use inverter With Max VOC 145 with array VOC 139.5v

Tariq_Zia

I am using an inverter with 60A, Max Voc 145 VDC and input voltage range 60-115v,  My system is 6 KW and i have 16 Pannels each 340w,voc 46.5v,isc 9.3A,   if i make string of 3 pannels then VOC will be 139.5 v still under max Voc but higher than input voltage range.

If i make 2 pannel string than tot strings will 8 and tot current will be 72 A which is higher than inverter current,

Can i use 3 pannel in series and tot of 5 strings of 15 pannels

mike95490

Is this a Grid tie inverter, or a stand alone battery inverter ?
What is the weather like in your area, PV panels produce higher voltage in cold weather, 139.5 Voc is very close to your 145v max input

Tariq_Zia

This is off grid system, Minimum temperature go to 12 degree in winter and at that temp Voc will be 144v

RCinFLA

The 145vdc maximum Voc is breakdown limit that can damage inverter.  Watch out for cold mornings.

Input of 115 to 60vdc is the inverter's MPPT operating range,  although 60v is getting close to a fully charged 48v system max battery voltage.  MPPT inverter needs some overhead above battery voltage to do MPPT search tests.

As to the 115v end.  It is hard to say if you go above this for panels Vmp voltage.  My guess is the inverter will just load the panels to bring the panel's voltage down to 115v so it can do its voltage downconversion safety with normal switching overshoot margin.  This may result in not extracting maximum MPPT power from panels.  In the worse case it may not allow the inverter to run so you get no output.

PV MPPT charge controllers often check Voc voltage before activating switching converter as the MOSFET's can tolerate higher voltage before destructive breakdown when they are not switching.  The SCC will throw a PV overvoltage alarm and not activate power conversion from panels.

mike95490

Tariq_Zia said:

This is off grid system, Minimum temperature go to 12 degree in winter and at that temp Voc will be 144v

This is really too close to the damage voltage for me to be comfortable with.   While the weather service may report the air temp at 12 degrees. your PV panes are out in the clear, with a view of the night sky.  They can easily get colder than the air via something known as  "night-sky cooling" where heat is radiated out to the sky and objects get colder than the air.
read more here, how to make ice in a warm desert
https://www.realclearscience.com/blog/2018/07/09/how_people_created_ice_in_the_desert_2000_years_ago.html

Your panels can get much colder than you think, and 1 degree is not much margin of safety.
 excerpt:  The secret here is a process known as "night-sky cooling." On dry, cloudless desert nights with the cold vastness of space laid bare above the surface of the Earth, heat can readily radiate from substances like water, escaping from the atmosphere to space itself, where temperatures are roughly 450 degrees below zero Fahrenheit. So much heat can radiate from water that ice can form at ambient temperatures as high as 41 degrees Fahrenheit.

wildlaurel

Perhaps add a small power resistor across inverter input? Voc peak should have high impedance and resistor would drop voltage to acceptable limit.. a more knowledgeable member should advise if the workaround would work..

mike95490

wildlaurel said:

Perhaps add a small power resistor across inverter input? Voc peak should have high impedance and resistor would drop voltage to acceptable limit.. a more knowledgeable member should advise if the workaround would work..

Perhaps a well heat sunk 100 - 200W zener diode could do it.   But your 77F Vmp is 139.5V and a chilly morning could bump that up past what a 200w zener can manage.  And zener's have a pretty wide "knee" at those voltages and even with 1% tolerance, could still damage the inverter.  
 But a resistor is not an answer.

140V 50W $9  1N3345   20%    Not going to work.  150V is next one up, still 20%  tolerance
https://www.digikey.com/en/products/detail/solid-state-inc/1N3345/14548428

Solar Guppy

Solar panels are highly variable and in many instances will have higher voltages than the 77F / 25C specifications. It isn't just low temperatures, but it can also be edge of cloud, which can for short bursts add 10-30% more energy into the panel to convert which can raise the operational voltage.

I would not install a configuration that could exceed the maximum operating voltage and for my own systems I add hardware ( charge controllers, or all in one hybrid inverters ) to share the source and loads. 

For my current hybrid system which is a pair of Solis RHI-1P6K-HVES-5G-SPRT inverters, its good for 500V input, but the arrays run in the 250-300V range.