bypass diodes

[paara]

i am new to diy solar panel, but are planing to build some as a spare time project. I have a small wind turbine and a grid tie inverter that can accept pv dc from 100-450v. Mppt?

I am planing to make 4 panels: each 27,5v in series for total 110v 8a.

I understand bypass diodes protect cell strings when part of the panel is shaded.

What I dont understand is how to calculate the voltage rating for the diodes.

I have read 2 different answers.
1:voltage for whole array. In my case 110v
2: voltage for bypassed celles which could be like 5v depending of how many diods per panel.

I find very few bypass diodes that will handel 110 + v.

Can someone clarify this for me? I have read and searched for 3 days prior to posting this.

Thanks for any help

[bcroe]

i am new to diy solar panel, but are planing to build some as a spare time project. I have a small wind turbine and a grid tie inverter that can accept pv dc from 100-450v. Mppt?

I am planing to make 4 panels: each 27,5v in series for total 110v 8a.

I understand bypass diodes protect cell strings when part of the panel is shaded.

What I dont understand is how to calculate the voltage rating for the diodes.

I have read 2 different answers.
1:voltage for whole array. In my case 110v
2: voltage for bypassed cells which could be like 5v depending of how many diods per panel.

I find very few bypass diodes that will handel 110 + v. Can someone clarify this
for me? I have read and searched for 3 days prior to posting this.

The BYPASS diodes let current flow around a group of cells that aren't producing
(because of shade or a fault). They allow the operable cells to continue to operate,
at a reduced overall voltage. The bypass diodes can see the maximum forward
current the array can produce. But generally a diode only is wired to bypass 10
or 20 cells. So the maximum output voltage (blocked by the bypass diode) will
be 5 or 10 volts. Allowing for extreme conditions, the diode would only need to
be rated double these figures.

An array SERIES would see all the voltage; this type often isn't used if possible
due to the power loss. Bruce Roe

[paara]

The BYPASS diodes let current flow around a group of cells that aren't producing
(because of shade or a fault). They allow the operable cells to continue to operate,
at a reduced overall voltage. The bypass diodes can see the maximum forward
current the array can produce. But generally a diode only is wired to bypass 10
or 20 cells. So the maximum output voltage (blocked by the bypass diode) will
be 5 or 10 volts. Allowing for extreme conditions, the diode would only need to
be rated double these figures.

An array SERIES would see all the voltage; this type often isn't used if possible
due to the power loss. Bruce Roe

So the bypass diods in my 4 panels in series would only need to be rated for 5,5v and 8a if I am using 5 diodes per panel (11cells per diode)? Regardless of total array voltage (110v).

Could you recommend 1 bypass diode over another?

[bcroe]

So the bypass diods in my 4 panels in series would only need to be rated for 5,5v and 8a if I am using 5 diodes per panel (11cells per diode)? Regardless of total array voltage (110v).

Could you recommend 1 bypass diode over another?

Diodes are typically selected with a PIV double the expected circuit voltage. To keep
the forward drop minimal, you might use Schottky diodes. Just make sure they will
handle the current; current at maximum rating will mean maximum voltage drop.
Some need a heat sink; an insulated tab can be bolted to the aluminum frame.

Bruce Roe

[paara]

Diodes are typically selected with a PIV double the expected circuit voltage. To keep
the forward drop minimal, you might use Schottky diodes. Just make sure they will
handle the current; current at maximum rating will mean maximum voltage drop.
Some need a heat sink; an insulated tab can be bolted to the aluminum frame.

Bruce Roe

Thank you for your answers. You been very helpful now I only have to descide how to encapsulate the panels and I am set to start.