choosing the right micro inverter

[mike84]

i have 6x6 cells and im trying to figure out what micro inverter to go with. when the inverters require a certain number of cells for each panel i dont think they mean the 6x6 size . im having a little bit of trouble shopping for one because it might not be compatible, but im new. anyone have experience with these cells?
any advice is appreciated.thanks

[Mike90250]

most micro inverters need about 24v - 90v to start up. A PV cell, no matter what the size, puts out about 0.5V. Larger sizes produce more amps. To increase volts, many cells must be wired in series.

Many 200W + panels produce 20 - 95 volts, depending on how the cells are wired internally. You can see the rows of cells in the attached image of a damaged panel.

BrokenModuleCloseup.jpg

[mike84]

yes i know, an example of what I mean is the enphase m215 , it says it only works with 60 cell modules. why does it matter how many cells there are? shouldnt it just matter the amount of watts ? I can make 215 watts with 50 of my cells, can i connect that to the m215?

[Naptown]

You could but you may be out of the range of the inverter.
A 60 cell module will produce about 36V open circuit and about 30V @ max power.
Remember that .6V per cell OC and .5V per cell VMP Rough estimation but fairly accurate.
Now match the voltages on the microinverter to the cell count.
I will tell you that an M215 will work on a max 60 cell module (60 in series)
An m190 would be for a 72 cell module

[inetdog]

You could but you may be out of the range of the inverter.
A 60 cell module will produce about 36V open circuit and about 30V @ max power.
Remember that .6V per cell OC and .5V per cell VMP Rough estimation but fairly accurate.
Now match the voltages on the microinverter to the cell count.
I will tell you that an M215 will work on a max 60 cell module (60 in series)
An m190 would be for a 72 cell module

A very good point. While it has to employ some means of accommodating slight differences in Vmp with panel type and temperature, as well as wide variations in available current, a micro-inverter does not need to be designed for the wide range of input conditions that a string MPPT inverter has to handle.
Another point is that if the panel uses other than silicon PV cells, the number of cells to get the same output voltage will be different. (That may not be an issue right now with the economic dominance of mono and poly silicon, but that may change in the future as other chemistries are developed.)

[mike84]

Appreciate the feedback but im not quite understanding those replies. Can I match those volts required with less cells? one of my cells produces at least 4 Watts .

[inetdog]

Appreciate the feedback but im not quite understanding those replies. Can I match those volts required with less cells? one of my cells produces at least 4 Watts .

The wattage of the cells is important, but is not the real point. Since a micro-inverter will work just fine with shaded panels and with early morning, late afternoon sun, it will be perfectly happy with less power from the panel that it is rated for.
But the voltage range from the panel, from Voc down to Vmp must be within the design range of the inverter. What you need to do is check the voltage specifications of the micro-inverter you are interested in and then use a number of cells which produces an output in that voltage range (from coldest to hottest temperatures) and does not produce more watts than the inverter is rated for.

How did you determine that one of your 6x6 cells produces at least 4 watts? If it does, then 60 cells in series will be too much for either of the inverters mentioned. And 50 cells in series might not give a high enough voltage.

[Sunking]

I am surprised no one has mentioned anything about DIY panels in a Grid Tied System. A micro-inverter implies you are wanting a GTI system. There is no code compliant manner which you can use DIY panels in a grid tied system or any system that is part of the house premisses wiring system.

No electric utility will you allow to connect without a certified and inspected system. No Authority Having Jurisdiction is going to issue a permit or pass a inspection, and no insurance company is going to give you coverage, and no mortgage company is going to let you carry a loan on a house that is not insured.

You cannot use DIY panels, they are not listed and tested with a recognized testing agency like UL.

[mike84]

why didn't anyone just tell me each cell is half volt? I think the the m215 will work with 60 of my cells, thats 240 watts and producing 215W with the m215, right?

[mike84]

I am surprised no one has mentioned anything about DIY panels in a Grid Tied System. A micro-inverter implies you are wanting a GTI system. There is no code compliant manner which you can use DIY panels in a grid tied system or any system that is part of the house premisses wiring system.

No electric utility will you allow to connect without a certified and inspected system. No Authority Having Jurisdiction is going to issue a permit or pass a inspection, and no insurance company is going to give you coverage, and no mortgage company is going to let you carry a loan on a house that is not insured.

You cannot use DIY panels, they are not listed and tested with a recognized testing agency like UL.

are you saying I can not have it inspected then give the ok? Has anyone ever heard of diy on the grid? I dont want an off grid system and im not going to empty my savings for something that will take years to pay off.
I realize an electrician will be required to connect to grid but I can do everything else.

[inetdog]

are you saying I can not have it inspected then give the ok? .

No we are not saying that.
The inspection has to be done by UL or another recognized national testing lab.
That involves giving then 10 or 20 panels to be tested to destruction in various ways and paying tens of thousands of dollars. Then if you decide to change anything about the way you build them you have to go through most of the process all over again.
OK, I guess for practical purposes, we are saying that.

[Sunking]

are you saying I can not have it inspected then give the ok?

You will not even be allowed to get a permit. No permit, no inspection, no connection to the grid. Electrical codes require all material to be listed and approved by an acceptable testing agency like UL. On the permit application you will have to list materials. DIY panels is automatic rejection no questions asked. You loose your application fee.

[russ]

UL approval is an expensive and time consuming process. No one will have such a thing done for DIY panels.

Without UL approval your apartment house insurance is most likely to be useless in the event of an incident - as in cancelled with no pay out.

Your tenants could sue you direct - this entire thing is a very bad idea gotten worse.

You are trying to cut corners to skin the cat - forget it and no more discussion of it here.

We try to stick to things that are legal, follow code and are safe for those involved - your prospective project does not meet that criteria.

Russ

[Sunking]

Without UL approval your apartment house

This is a commercial application? ROFL!

Not a Snow Ball chance in Hell this will ever happen.

[russ]

This is a commercial application? ROFL!

Not a Snow Ball chance in Hell this will ever happen.

My mistake - this is an individual dwelling. Another Mike (I think) was talking about an apartment house.