Solyndra panels

Re: Solyndra panels

I think you are referring to positive or negative grounded battery systems (telecom vs "standard" system grounding).

As far as I have read, I do not remember reading anywhere that battery/array grounding matters for the Solyndra products. They are just thin film panels in round tubes (as far as I know).

when positive ground is used in pv

The only manufacturer that "requires" positive grounding is SunPower (as far as I know) due to their high efficiency panel design.

Grounding in general (bonding Array + or - , or battery + or - to earth/safety/green wire ground) is an electric code issue. Panels and systems will usually "work" if they are floating.

In system design, we normally tie one power line to earth/safety ground reduce the chances of electric shock/shorts (and the other power leg goes through a circuit breaker or fuse).

A true "floating power" system requires dual pole breakers (in US Electric Code) to reduce the chances of shock/fire (our utility power system has a "grounded" Neutral or Return (white wire) in our 120/240 VAC power systems (the Neutral is the "center tap" of the distribution transformer and never has a switch/breaker/fuse in that cable. The "hot" leads, red and black are where fuses/breakers are installed).

There is another Code Requirement for Solar for a DC Ground Fault Detection System... If there is short from power leads to ground, it causes a >1 amp current flow in the safety ground wire, which usually pops a fuse or ganged breaker to turn off the Solar Array Current:

http://www.solar-electric.com/mndc-gfp.html

There are reasons why I do not like the NEC DC GFI system... But that is for another post (if that is your question).

For newer Grid Tied AC Inverters and MPPT type solar charge controllers, many now have an internal ~1 amp fuse between array + or - cable (choose one) and safety ground wire. If there is a short on the array to earth ground somewhere, it pops the fuse and the GT inverter or Charge Controller will shut down. This is intended to be used a method to reduce the chances of fire in the solar array wiring.

This was a solution cobbled together from existing hardware (fuses and circuit breakers) because it is very difficult to "protect" against wiring short circuits in solar arrays (solar panels are roughly constant current devices and when you short a solar panel, the output current does not surge like a battery bank would, and therefore fuses/breakers are not really usable to protect against short circuits).

Grounding and "Arc Faults" (DC arcs sustain very nicely--I.e., DC Arc Welders are very nice--And are very difficult to "protect against"--One mfg. is offering "arc fault" detection/shutdown as a solution--basically there are electronics that look for the electrical noise spectrum associated with arcs (sparking) and will shut down if detected--We have Arc Fault Breaker requirements in the United States for AC home/building wiring).

Sorry for the long response--Grounding/Safety is a long and complex discussion and there are many different issues regarding grounding--And issues specifically with DC power systems.

From your question (more of a general grounding question) and being out of India (I guess)--Makes your question a bit more complex (different countries have different requirements). And we did not even talk about lightning and grounding issues yet.

-Bill

Re: Solyndra panels

Functionally, there is no need to ground the solar panel + or - leads.

You would normally ground the metal frame and mounting racks to earth/safety ground (you do not want to short to the frame to "energize" the framework where somebody could touch the metal and get electrocuted).

A Transformer type GT inverter will (generally) "ground" one lead (most negative ground, a few for Sunpower will positive ground) through a fuse for "ground fault" detection (if there is a short to ground in the array, the GT inverter will shut down).

I do not know enough about transformerless GT inverters to understand how they ground/ground fault detect (which is a US/European requirement--trying to reduce the chance of fires). But the GT inverter should take care of the grounding "as part of their design". You would just ground the GT inverter per their instructions (green wire to bonding screw inside unit, etc.).

Note that transformerless GT inverter solar arrays are "not isolated" from the AC mains--So I would guess if you did attempt to directly ground either + or - from the array, it will cause a short to ground and the GT inverter to shut down.

If you are designing/manufacturing a transformerless GT inverter--I have some guesses about what they do, but I do not know.

-Bill