Strange strange solar panels.

[deepakpandey2403]

The main thing which I can think of that could cause an unexpected voltage drop even though the inverter automatically reduces its current demands would be partial shading on the panels in the series string. If the panels are not built with bypass diodes, the current output of the entire string will be reduced to that of the most shaded panel. This can have the side effect of severely dropping the output voltage at Imp, under your algorithm.
If the panels are equipped with bypass diodes, then you will see little reduction in the string current, but the string voltage will sharply drop by the total Vmp contribution of the shaded sections, plus an additional loss of up to 1 volt for each bypass diode that is activated.

in this respect you will see a great difference between the behavior of a mono or polycrystalline silicon panel versus a thin film amorphous panel.

Hey inetdog

Thanks for the answer. Helps ! I did not get your bypass diode concept though. The drop(of 1V, or 0.7V ) is understood, but could you throw some more light on bypass diodes in PV panel.

Thanks

[inetdog]

Hey inetdog

Thanks for the reply. Two things here
Number one : I am aware of PV cells I-V-P characteristics, Temp-P characteristics.
Number Two: I myself has worked on off-grid inverters w/o any battery system and has almost achieve the ideal MPPT characteristics with some of the cells. So, there exists an inverter in the market throughout the world, on which I have worked on, which runs w/o any battery system.
I have seen other inverters as well w/o battery system.
P.S : My discussion is on off-grid inverter which normally do not extend above 22kW rating. Sorry if i had not mentioned earlier.

Please counter me , it will be appreciated. No offence meant in any way.

Regards
Deepak

The main thing which I can think of that could cause an unexpected voltage drop even though the inverter automatically reduces its current demands would be partial shading on the panels in the series string. If the panels are not built with bypass diodes, the current output of the entire string will be reduced to that of the most shaded panel. This can have the side effect of severely dropping the output voltage at Imp, under your algorithm.
If the panels are equipped with bypass diodes, then you will see little reduction in the string current, but the string voltage will sharply drop by the total Vmp contribution of the shaded sections, plus an additional loss of up to 1 volt for each bypass diode that is activated.

in this respect you will see a great difference between the behavior of a mono or polycrystalline silicon panel versus a thin film amorphous panel.

[deepakpandey2403]

All PV cells to a greater or lesser degree will deliver a constant open circuit voltage over a wide range of incident light. But the current available from them and the position of the Voltage versus Current graph will change as the light changes. This may result in the voltage dropping if the panels cannot supply all of the power the load needs, and this in turn reduces the amount of power available from the panels even more than just the drop in current would.

Well, this is one reason that all (except one line from SMA) GT inverters will not run off grid and off grid inverters will not run without batteries.

If you used an MPPT charge controller to feed batteries which fed the inverter, the fluctuation in solar PV output would have little immediate effect on the off-grid inverter.

Basically you cannot easily use a grid tie inverter off grid because there will not be a load capable of absorbing the full but varying output of the panels. The main exception is when you use the panels to directly drive a pump motor which has been designed for this kind of use.

And you cannot use an off grid inverter which tries to supply whatever the loads try to draw without a battery or equivalent energy storage of some kind.

More info please....

Hey inetdog

Thanks for the reply. Two things here
Number one : I am aware of PV cells I-V-P characteristics, Temp-P characteristics.
Number Two: I myself has worked on off-grid inverters w/o any battery system and has almost achieve the ideal MPPT characteristics with some of the cells. So, there exists an inverter in the market throughout the world, on which I have worked on, which runs w/o any battery system.
I have seen other inverters as well w/o battery system.
P.S : My discussion is on off-grid inverter which normally do not extend above 22kW rating. Sorry if i had not mentioned earlier.

Please counter me , it will be appreciated. No offence meant in any way.

Regards
Deepak

[inetdog]

Solar panels of different make behave in weird ways. I hope you'll all agree with me by the end of this thread.

Here's my observation (and I would appreciate if somebody could correct my errors)
1) I have an inverter (off grid, running MPPT) which has been tested around with different make of cells.
Anyone who can put a light on this property of different makes and also a possible solution to make my algo independent of the same.

I would appreciate if somebody could share some good out-of-box solar PV character document/link/ref etc.

All PV cells to a greater or lesser degree will deliver a constant open circuit voltage over a wide range of incident light. But the current available from them and the position of the Voltage versus Current graph will change as the light changes. This may result in the voltage dropping if the panels cannot supply all of the power the load needs, and this in turn reduces the amount of power available from the panels even more than just the drop in current would.

Well, this is one reason that all (except one line from SMA) GT inverters will not run off grid and off grid inverters will not run without batteries.

If you used an MPPT charge controller to feed batteries which fed the inverter, the fluctuation in solar PV output would have little immediate effect on the off-grid inverter.

Basically you cannot easily use a grid tie inverter off grid because there will not be a load capable of absorbing the full but varying output of the panels. The main exception is when you use the panels to directly drive a pump motor which has been designed for this kind of use.

And you cannot use an off grid inverter which tries to supply whatever the loads try to draw without a battery or equivalent energy storage of some kind.

More info please....

[deepakpandey2403]

Solar panels of different make behave in weird ways. I hope you'll all agree with me by the end of this thread.

Here's my observation (and I would appreciate if somebody could correct my errors)
1) I have an inverter (off grid, running MPPT) which has been tested around with different make of cells. Its a 2.2kW inverter and i have hooked up a 3kW configuration to it. Now when there is a sudden change in weather (cloud passing by , rains etc) , different responses have been observed with different makes.
a) sudden change in intensity means sudden drop in cell voltage, this will cause the inverter to trip in some case, while in others it gives sufficient time for the algo to work and gradually reduce the voltage(and current) intake (2-3 seconds etc) from the inverter.

Anyone who can put a light on this property of different makes and also a possible solution to make my algo independent of the same.

I would appreciate if somebody could share some good out-of-box solar PV character document/link/ref etc.

Thanks