Diodes and bypass diodes

**solarrules** · 01-13-2011, 09:35 PM

Hi Mike,

Well I hate to admit it, but the final use has not been thought out well enough.... I've read a lot of posts here, and I'm building it for the best reasons -- hobby and to learn -- as opposed to some financial savings. At one time, I was going to buy the whole house system and then maybe sneak this one build onto the array. That's no longer the case.

So now I might be charging a battery array.

My nominal voltage will be more like 72x0.55v = 39.6v

I've had fun, although by the time I'm finished it will have been expensive fun.

The reason I'm currently foregoing doing a whole house purchase installation is because Ohio's incentives officially came to an end on 12/31/2010. The state got behind on their paperwork so they unofficially ended the program at the beginning of November 2010. The November election gave us a change of party in state government, and, although hopeful, I'm not optimistic that the new state government will support solar

As for the whole house thing, I'm in a holding pattern until probably June or so to see what the state may or may not do to solar incentives.

When it comes to solar incentives, Ohio just went from second best in the nation to a tie for 50th.

**Mike90250** · 01-14-2011, 10:27 PM

Generally, and always in the USA with the National Electric Code, only UL components can be connected to a house wiring. A panel to charge a camping battery, or a electric bike is fine for homebrew. Learning by doing is the best way, as you are finding out.

Enjoy.

**solarrules** · 01-15-2011, 11:20 AM

So technically, only my inverter is hooked to the grid, yes? (I like the enphase micro-inverters for going to the grid). My panel is hooked to the inverter. The inverter, which is UL-approved, is connected to the grid.

**russ** · 01-15-2011, 12:50 PM

Wrong - the system is connected to the grid.

Russ

**solarrules** · 01-15-2011, 01:45 PM

Well I'm playing devil's advocate and "fighting city hall" at the same time, but if I pay a solar installation company to install an entire system for me, that system is not UL certified. Nobody from the Underwriter's Laboratories comes to my house to certify it.

So I still may contend that the inverter is U.L. certified and therefore I can connect that to the grid.

**russ** · 01-15-2011, 01:53 PM

You are pissing into the breeze - hope it does not get too damp! Please don't call it 'playing the devil's advocate' - you are simply breaking the rules which you have been made aware of and know the basics at least.

Fighting city hall? Again I would not call tilting windmills fighting city hall - hope you have you own Pancho Sanchez (think that was his name) to pick you up and put you back on your mule when you collide with the system.

Individual components of the system must be approved by UL or an equivalent agency.

The UL didn't come inspect individual computers either - representative samples are tested and approved.

No problem, you can certainly do it but don't whine when everything goes down the toilet sometime in the future.

Russ

**bcroe** · 04-03-2012, 01:13 AM

Bypass Diode Function

As I understand it, these diodes are only used to preserve some power output,
when part of a panel is shaded. This would be esp important with several
series connected panels. So protecting the panel from destruction is not part
of the function?

In my case, I expect to lose a whole panel at a time (tree shadow blocks a
panel at certain times of day). And I won't have panels connected in series,
I prefer to operate around 30 VDC. So I really don't need bypass diodes?

As for parallel connections, even a shaded panel generates pretty much
full open circuit voltage. So if connected in parallel with another panel
not shaded, I would not expect any reverse current in the shaded panel,
as long as its open circuit voltage at least equals a loaded panel voltage.
So no series diodes for each parallel panel are needed either? Bruce Roe

**Mike90250** · 04-03-2012, 10:00 AM

You really should have bypass diodes, and you should re-site panels to avoid shade

With no diode, any shade, anywhere on the array , will cut output way down, and the shaded panel will tend to overheat

**bcroe** · 04-03-2012, 03:22 PM

Bypass Diode Function

Originally posted by Mike90250

You really should have bypass diodes, and you should
re-site panels to avoid shade
With no diode, any shade, anywhere on the array , will cut output way down, and
the shaded panel will tend to overheat

The issue of overheating seems to occur, when good cells develop enough
voltage to force their current through a shaded or defective cell. The overheating
would be at the non functional cell?

Putting a bypass diode on each cell, would apply about 1V (diode drop) reverse
voltage on a non producing cell. That seems to be accepted as OK for shade,
don't know for a cracked cell.

I don't see anyone putting a bypass diode on every cell. Short of that, the voltage
applied to a non functioning cell will that of the other cells being bypassed by the
diode, plus about a volt drop in the diode from overall array (bypass) current. So
my question would be, how many cells (or how much voltage) can one diode
safely bypass?

There will be no panels on roofs here, in the country. But for now there are some
convenient spots to put them. In one spot I see 200 to 800 W (clouds or sunny) till
early afternoon, when the sun moves behind a grove of trees. At that point I am
willing to have another similar array come out of the shade for the rest of the day.
I am willing to duplicate those resources for the locations.

To put up panels never shaded by all the trees, I would have to go 1/8 mile away
from the house. That would happen if expanded to the 10 KW level. But first I
would need a power handling system able to cover that distance with good
efficiency, have a few ideas on that. Bruce Roe

**Mike90250** · 04-03-2012, 09:40 PM

Bypass diodes are usually Schottky diodes, with sufficient power rating (and heat sink) to only have about .5V drop across them. At the MOST, I would go no more than 18 cells without a diode.

**S0L0R** · 07-30-2014, 01:04 PM

Diodes

Designing an array of 18volt, 4 Amp, 172 Watt solar panels and need to decide what bypass diodes and blocking diode to use...

**inetdog** · 07-30-2014, 02:15 PM

Originally posted by S0L0R

Designing an array of 18volt, 4 Amp, 172 Watt solar panels and need to decide what bypass diodes and blocking diode to use...

When using a modern charge controller a blocking diode is not necessary or even useful. It just costs you power.

**inetdog** · 07-30-2014, 02:17 PM

Originally posted by russ

...hope you have you own Pancho Sanchez (think that was his name) to pick you up and put you back on your mule when you collide with the system.

Sancho Panza, but who's counting.

**cosuroca** · 10-05-2014, 09:09 AM

Hello, sorry if I change a bit the topic of the post or ask somewhat out of place. But my question or ask is for Mike90250 and longwolf, I saw your posts and I really like your figures that they uses for show diode bypass.

Mike90250 :

Diodes and bypass diodes - Solar Panels - Solar Panels Forum

http://www.solarpaneltalk.com/showthread.php?2188-Diodes-and-bypass-diodes&p=10700&viewfull=1#post10700