solar panels with diodes between each cell

FWC wrote:

rlw999 wrote:
There are specialty low loss "diodes" made for applications like this. They aren't traditional diodes but use a controller that switches a MOSFET. Essentially it acts as a switch that turns on when it senses forward voltage and off when it senses reverse voltage.

Here's an example that has a 26mV forward voltage.

Bypass diodes can use standard P-N or Schottky diodes, they are only forward biased (on) if a cell/string is shaded to allow the current to pass around the shaded cell. Definitely no need for a MOSFET 'ideal diode'.

They can, but as I said, there are specialty diodes made for applications like this that limit the power loss due to high forward voltage. The manufacturer even says that's why this product was developed:

Texas Instruments SM74611 Smart Bypass Diode is used in photovoltaic applications and provides an alternate path for string current when parts of the panel are shaded during normal operation. TI SM74611 Smart Bypass Diode has a lower forward voltage drop than PN junction and Schottky diodes. It has a typical average forward voltage drop of 26mV at 8A of current. This translates into typical power dissipation of 208mW, which is significantly lower than the 3.2W of conventional Schottky diodes. The SM74611 is also footprint and pin-compatible with conventional D2PAK Schottky diodes, making it a drop-in replacement in many applications.

pianotuna wrote:
FWC,

I'm still waiting to hear about your power system.

I am not sure why this is relevant.

rlw999 wrote:
There are specialty low loss "diodes" made for applications like this. They aren't traditional diodes but use a controller that switches a MOSFET. Essentially it acts as a switch that turns on when it senses forward voltage and off when it senses reverse voltage.

Here's an example that has a 26mV forward voltage.

Bypass diodes can use standard P-N or Schottky diodes, they are only forward biased (on) if a cell/string is shaded to allow the current to pass around the shaded cell. Definitely no need for a MOSFET 'ideal diode'.

Edit: Should have read the data sheet first - you are right they are selling these for use as bypass diodes. Seems to me that this would be more important for blocking diodes that are always in the circuit.

There are specialty low loss "diodes" made for applications like this. They aren't traditional diodes but use a controller that switches a MOSFET. Essentially it acts as a switch that turns on when it senses forward voltage and off when it senses reverse voltage.

Here's an example that has a 26mV forward voltage.

FWC,

I'm still waiting to hear about your power system.

Nice Diagram Time2roll Thanks!

Gde,

As I said. I don't know the technology--but it is clear they are producing something of great interest.

Here is 85 pages of information / sales https://ae-solar.com/wp-content/uploads/2018/10/NEW-CATALOGUE-23.pdf

pianotuna wrote:
Gdetrailer,

I don't know how they are doing it or what diodes they are using. However, they are producing them.

Yep, they may be making them but the "devil is in the details".

As I mentioned, standard silicon diodes in parallel with each solar cell because of their inherent high forward voltage drop would not be of any advantage for a small series string.

each single solar cell only develop .5V but placing a silicon diode in parallel to create a bypass is going to drop .7V..

Now if they are Shottky diodes at .3V drop that might make better sense..

From my POV I suspect perhaps a large series string of panels may have a bigger potential benefit, perhaps at least 3 panels in series and more panels in series would be even better since you spread out the losses over a greater area.. But then you run into max input voltages of the MPPT controller issues..

Depends on which poison you want to take..

Not sure I would be very concerned about if the panel had them or not for series strings of two or three..

Seems to me, putting the money into a few good high wattage panels and finding a good spot with minimal panel shading through the day most likely will work just as good.

Diodes of any kind represent a loss, just can't get around that fact.

They are marketing a circuit "diode" now. It consists of a MOSFET that blocks reverse current. They have something like .008 vf.

Typical 60 cell panel wiring diagram. Yes a diode for each cell would put the diode on the panel vs in the J-Box.
Diodes are in parallel with the cells.