Micro Inverter vs Optimizer/Inverter vs String

**Naptown** · 09-17-2015, 07:55 PM

Partial shading such as a chimney is a good case for micro's or optomizers.
A tree that shades late afternoon may not be as strong a case. In many instances creative stringing can obercome a lot of that.
There are many inverters out there that have 2 mppt inputs so panels facing in 2 directions or unequal strings are feasable with no losses.
Every situation is different. A sun study by a pathfinder or solmetric eye is the most axcurate way to determine shading issues

**sensij** · 09-17-2015, 07:58 PM

Originally posted by mdb

I also understand the issue with a string inverter is that if one panel is shaded, the output of all the panels drops to match the shaded panel.(?)

This isn't really true. If hard shade hits one panel but not others, the bypass diodes will allow the full current of the other panels to be maintained, basically taking the shaded panel (or portion of the panel) out of the circuit.

**inetdog** · 09-18-2015, 05:51 AM

Originally posted by sensij

This isn't really true. If hard shade hits one panel but not others, the bypass diodes will allow the full current of the other panels to be maintained, basically taking the shaded panel (or portion of the panel) out of the circuit.

So the string voltage will drop by as much as the Vmp of the bypassed section within a panel plus ~1volt for the diode drop in the bypass.
When partial shading affects a panel it becomes very important how the shade pattern overlays the bypass groups of cells.
Worst case spotty shade on only three panels could take out the power output of the entire panel if there are three bypass groups.
If the partial shade hits three cells which are all in the same bypass group, you will lose only the output of that group.

Note also that it does not take much of a decrease in Isc (down to or below Imp of the unshaded cells) to cause all of the power from that group to be lost.
If you had the panels in parallel to a PWM CC or connected to micros or optimizers you could still get Vmp times the reduced current of the panel as useful power.

**solar_newbie** · 09-20-2015, 06:23 AM

I heard that if an optimizer fails, the whole string is gone until replacement. Is that corrected? How often does an optimizer fail?

**ButchDeal** · 09-20-2015, 08:00 AM

Originally posted by solar_newbie

I heard that if an optimizer fails, the whole string is gone until replacement. Is that corrected? How often does an optimizer fail?

This is not true of solarEdge, the other timizers compensate as long as there is a minimum of 6 remaining good optimizers on the string to get the voltage in range.

**solar_newbie** · 09-20-2015, 12:55 PM

Originally posted by ButchDeal

This is not true of solarEdge, the other timizers compensate as long as there is a minimum of 6 remaining good optimizers on the string to get the voltage in range.

Are all optimizers connected serialized? If yes, do they have fail to wire feature? Otherwise how you could send electrons thru open circuits of the failed optimizer... Please explain in the technical term and made sense rather than statement.

If that is true. SolarEdge carries the worst of both worlds : String Inverter and Micro Inverter.
String inverter : one fail --> lost entire string
Micro inverter : put equipment directly to the heat --> easy to fail.

**ButchDeal** · 09-20-2015, 02:44 PM

Originally posted by solar_newbie

Are all optimizers connected serialized? If yes, do they have fail to wire feature? Otherwise how you could send electrons thru open circuits of the failed optimizer... Please explain in the technical term and made sense rather than statement.

If that is true. SolarEdge carries the worst of both worlds : String Inverter and Micro Inverter.
String inverter : one fail --> lost entire string
Micro inverter : put equipment directly to the heat --> easy to fail.

The go into any pass mode which is the default using bypass diod type architecture.

http://www.solaredge.com/files/pdfs/application_note_module_embedded_power_optimizer_service_procedure.pdf

They also use simpler and more reliable electronics

**solar_newbie** · 09-20-2015, 03:02 PM

Originally posted by ButchDeal

The go into any pass mode which is the default using bypass diod type architecture.

http://www.solaredge.com/files/pdfs/application_note_module_embedded_power_optimizer_service_procedure.pdf

They also use simpler and more reliable electronics

Is it automatically? I see you need to do the jumper? If I need to go to the roof to do it, what is the point ?
Plus, you might need to remove panels in order to access the optimizer. How homeowner can do it?
Can I switch from my garage or can I fix the middle panel without touch the rest?

The solution is for professional

**sdold** · 09-20-2015, 03:13 PM

Another minor consideration: If something fails, are you locked into a replacement part from one manufacturer? One of the reasons I used microinverters (besides shade) is that I'm not stuck with that brand if replacement becomes necessary. If Enphase is gone in ten years and I have a failed microinverter, I might be able to use another brand with a little re-wiring, or just do without that one panel.

**ButchDeal** · 09-20-2015, 04:07 PM

Originally posted by solar_newbie

Is it automatically? I see you need to do the jumper? If I need to go to the roof to do it, what is the point ?
Plus, you might need to remove panels in order to access the optimizer. How homeowner can do it?
Can I switch from my garage or can I fix the middle panel without touch the rest?

The solution is for professional

It is automatic. These are older documents only ones I could find easily. They default to bypass one volt injection for installation. They recommend 8 module minimum string length but 6 is absolute minimum to operate based on their capabilities and inverter min voltage requirements. I am sure that there is a rare failure mode with the string broken but would be pretty rare .

**SolarFamilyGuy** · 09-21-2015, 08:14 AM

Originally posted by mdb

My understanding is that a string inverter effectively takes all the dc power produced by all panels and converts it to ac power. I also understand the issue with a string inverter is that if one panel is shaded, the output of all the panels drops to match the shaded panel.(?) I assume we are referring to shade from neighboring houses, trees, etc. What about the shade cast from a vent pipe or chimney? Is that enough shade to worry about?

From reading this forum, I also understand that Enphase micro inverters effectively distribute the inverter to each panel. Therefore, if one panel is shaded, the it does not affect the other panel outputs. The issue here is multiple points of failure...and I guess their track record is somewhat spotty? In addition, somewhat costly to fix since the devices are on the roof.

I also read that the SolarEdge Inverter system is somewhat of a hybrid of the above two technologies. Optimizers are places on each panel and the interverter is on the wall near the electrical box. I imagine the inverter in this system is easier to replace? I also assume the optimizers would be more work to replace (same as the microinverter tech). Can any vouch for the durability of the SolarEdge optimizers?

What is the relative cost of each inverter system listed above?

My system will most likely have 2 seperate arrays. Should/could I consider using 2 string inverters? Would this save any money? (assuming no shade issues)

Micro inverters will fail. If you have an array installed into your roof, you will have to climb up onto your roof, remove a bunch of panels just to access the bad inverter, replace the inverter, re-install the panels, and climb down from your roof.

Every time you climb onto your roof and start messing with your panels, you risk damaging something other than the bad inverter. You also risk damage to your roof every time you climb up there. On a ground mounted array, micro inverters are easy to replace. But up on a roof of a home, a string inverter is preferred, IMO.

**solar_newbie** · 09-21-2015, 10:52 AM

Originally posted by SolarFamilyGuy

Micro inverters will fail. If you have an array installed into your roof, you will have to climb up onto your roof, remove a bunch of panels just to access the bad inverter, replace the inverter, re-install the panels, and climb down from your roof.

Every time you climb onto your roof and start messing with your panels, you risk damaging something other than the bad inverter. You also risk damage to your roof every time you climb up there. On a ground mounted array, micro inverters are easy to replace. But up on a roof of a home, a string inverter is preferred, IMO.

That is why the key for the installer is to make sure you can access any single Micro inverter by just open 1 panel. This is what I will enforce it on today installation.

**mdb** · 09-23-2015, 12:52 AM

Originally posted by solar_newbie

That is why the key for the installer is to make sure you can access any single Micro inverter by just open 1 panel. This is what I will enforce it on today installation.

Exactly what I was thinking. I plan to do the same.

**igerstein** · 09-24-2015, 07:04 PM

Originally posted by mdb

Exactly what I was thinking. I plan to do the same.

If you have a large installation i'm not sure how you could really do this without A, leaving gaps for walking room (which is a waste of space and looks ugly) or B spacing all panels (also ugly, still have to walk over panels)

Micro Inverter vs Optimizer/Inverter vs String

Micro Inverter vs Optimizer/Inverter vs String

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