Wiring different volt panels together

SirCaptain

Hi All,

I've been reviewing several different threads trying to find the answer to my questions below, but I'm still confused on what I can do and how to do it. I hope someone will have some simple clear directions on how I can proceed:

I have 2 Dupont Appollo 95watt, 100v open circuit panels and 1 UL Solar 90watt, 22.2 volt open circuit panel. I'm using a Sunny Boy 700 Grid Tie Inverter which can process up to 250volts, no problem.

I do understand the differences in wiring in series (higher volts) vs parallel (higher amps). I've watched a youtube video that explains that wiring a lower volt panel in series to a higher volt panel will damage the lower volt one. Is this true?

I will be using MC4 connectors and can use MC4 MFF/FMM combiners depending on what the advice indicates on how these 3 panels should/could be wired together.

Thanks in advance for your help.

By the way, as of this morning, I've just been given approval by my local AEP office that I can now officially connect my entire PV Grid Tied System!!

BB.

Re: Wiring different volt panels together

SirCaptain wrote: »

I've watched a youtube video that explains that wiring a lower volt panel in series to a higher volt panel will damage the lower volt one. Is this true?

I will be using MC4 connectors and can use MC4 MFF/FMM combiners depending on what the advice indicates on how these 3 panels should/could be wired together.

When connecting panels in series--Ideally the Imp of the panels should match to within 10%... If the mismatch is larger, your efficiency will go way down. If the current mismatch is large enough, the smaller current panel will not do anything useful (the bypass diodes will simply bypass the current--And if current is, roughly, over 2x the smaller panel's rated current--you will overheat it and it will fail).

When connecting panels in parallel, the Vmp voltages should also match within 10% or better... A greater mismatch can confuse MPPT type charge controllers (they look for the Peak Power production and adjust the current draw to achieve that... With Vmp mismatches, you have multiple power peaks and no MPPT controller is designed to find the best peak). Also, the farther the mismatch the less efficient the lower voltage panel will be... Much more than 10% difference, the lower voltage panel will not help at all.

To combine your 2 high voltage panels with 1 low voltage panel... The only way is to put the 2 high voltage panels on one MPPT charge controller and the 1 low voltage panel on a second charge controller. Then connect both charge controllers to the same battery bank.

This is assuming you have a 12 volt battery bank.

If you have a 24 or 48 volt battery bank, the connected "low voltage array" will have to use several panels to achieve the higher voltage to charge the battery bank.

-Bill

SirCaptain

Re: Wiring different volt panels together

Hi Bill,

Thanks for the quick reply. I'm not using any batteries or charge controller, as this is a grid tie connection system. The only components I'm using in my system (which has already been approved by AEP) are:

Panels ---> DC Disconnect ---> Inverter ---> AC Disconnect ---> Main Breaker Box

Should I simply wire the 2 100v panels together in series, and then wire that with the 22.2 volt panel in parallel directly to the inverter?

Thanks again,

SirCaptain

mike95490

Re: Wiring different volt panels together

Wire the 2, 100V panels in series, to the GT inverter.

Your 22V panel is not at all compatible with the other 2

95W 100V = .95A
90W 22V = 4A

You could use it to charge a 12V battery though. Or sell it.

More importantly, the Appollo 95watt, 100v open circuit panels, what is their V max power ? That is what the GT inverter is also going to need, Their open ckt cannot exceed the max DC, and the V max power needs to be above the min DC in.

BB.

Re: Wiring different volt panels together

Sorry, there is an "Apollo" battery charge controller company too...

No, there is no way to use the third low voltage panel with the GT inverter unless you got ~10 of them and put them in series, then in parallel with the other panels (Vmp-12 volt panels = Vmp-apollo-array within 10%).

By the way, a 200 watt GT setup is pretty small. What are you using for your GT inverter?

-Bill

SirCaptain

Re: Wiring different volt panels together

Mike,

The max v for the 2 Dupone Apollos is 73V., max 1.28 Amps.

The DC Disconnect box I have can fit 2 breakers in it. Can the Appollos be wired to one breaker and the UL Solar panel be wired to the other breaker? The DC Disconnect box would then simply have one wire going from it to the Inverter. Does this solve my problem, or still the same?

Thanks.
SirCaptain

SirCaptain

Re: Wiring different volt panels together

Bill,

I have a SunnyBoy 700. Volt range of min 75 to max 250.

Yes, I am starting very small. But, I've got to start somewhere. I do plan to continue to add more panels, after I get over the initial start up costs/shock. And...to prove that it works and will cut our electric bill at home.

Also, I've already built my own 54 watt panel at home...just got the 400 watt off grid inverter today!

So I'm starting slowly and steadily with both a Grid Tie and Off Grid System.

SirCaptain

mike95490

Re: Wiring different volt panels together

SirCaptain wrote: »

Mike,

The max v for the 2 Dupone Apollos is 73V., max 1.28 Amps.

The DC Disconnect box I have can fit 2 breakers in it. Can the Appollos be wired to one breaker and the UL Solar panel be wired to the other breaker? The DC Disconnect box would then simply have one wire going from it to the Inverter. Does this solve my problem, or still the same?

Thanks.
SirCaptain

Still a problem. Your panels do not all match.

BB.

Re: Wiring different volt panels together

You are almost trying to figure out how to match 12 volt car batteries with one 2 volt single cell battery... It just does not work.

-Bill

ggunn

Re: Wiring different volt panels together

SirCaptain wrote: »

Mike,

The max v for the 2 Dupone Apollos is 73V., max 1.28 Amps.

The DC Disconnect box I have can fit 2 breakers in it. Can the Appollos be wired to one breaker and the UL Solar panel be wired to the other breaker? The DC Disconnect box would then simply have one wire going from it to the Inverter. Does this solve my problem, or still the same?

Thanks.
SirCaptain

Still the same. All the breakers do is current protect the lines; the connections are still the same. Your smaller module will cripple the output of the larger ones no matter how you connect it.

tsak_waw

All,

Need your help. I am from the Philippines and new on solar energy. I have 3x200W 12v panels(china) and planning to upgrade, but the problem now is I can not find similar panels in the local market. All that is coming out from manufacturer is 24v 200w. Question is can I have another string 3x24v 200w panels and wire it on the same combiner box? My SCC is tristar60 PWM 3000w 48v inverter.

Thank you in advance.

tsak_waw

BB.

Need to know the Vmp and Imp of the panels, how many of each you want to install.
The likely answer is that you probably cannot mix the panels together. "12 volt panels" tend to have Vmp around 18 volts, and large 200 watt panels tend to have Vmp around 30 volts.

For your PWM charge controller, you want Vmp-array to be around 72 to 80 volts STC (standard test conditions). You need 4x ~18 volt Vmp panel in series, or (with some losses) 3x ~30 Vmp panels in series. There are some Vmp~36 volt panels around--2 of those in series would work.

If you can make any of the strings above, then you can put the above strings in parallel together (fuse/breaker per string). Will not be optimum, but probably not bad cost/benefit for your needs.

the other option is to start over... Look at Vmp~72 volt array + PWM controller, or Vmp~90 volt array + MPPT controller. See what costs best for you.

Also, if you are thinking about adding to the array later (as money permits), you might be better off starting with parts that will match what you can get in the future (always a guess)... Vmp~30 panels are most common right now in larger format--Give away/sell your 12 volt panels + PWM controller--Many times, you can get pretty good prices on the  resale market.

-Bill

solarnewby

BB. said:

Re: Wiring different volt panels together

SirCaptain wrote: »

I've watched a youtube video that explains that wiring a lower volt panel in series to a higher volt panel will damage the lower volt one. Is this true?

I will be using MC4 connectors and can use MC4 MFF/FMM combiners depending on what the advice indicates on how these 3 panels should/could be wired together.

When connecting panels in series--Ideally the Imp of the panels should match to within 10%... If the mismatch is larger, your efficiency will go way down. If the current mismatch is large enough, the smaller current panel will not do anything useful (the bypass diodes will simply bypass the current--And if current is, roughly, over 2x the smaller panel's rated current--you will overheat it and it will fail).

When connecting panels in parallel, the Vmp voltages should also match within 10% or better... A greater mismatch can confuse MPPT type charge controllers (they look for the Peak Power production and adjust the current draw to achieve that... With Vmp mismatches, you have multiple power peaks and no MPPT controller is designed to find the best peak). Also, the farther the mismatch the less efficient the lower voltage panel will be... Much more than 10% difference, the lower voltage panel will not help at all.

To combine your 2 high voltage panels with 1 low voltage panel... The only way is to put the 2 high voltage panels on one MPPT charge controller and the 1 low voltage panel on a second charge controller. Then connect both charge controllers to the same battery bank.

This is assuming you have a 12 volt battery bank.

If you have a 24 or 48 volt battery bank, the connected "low voltage array" will have to use several panels to achieve the higher voltage to charge the battery bank.

-Bill

Hi Bill, I'm reading up on this connecting multiple panels with varying voltage and thought I had it figured out with blocking and bypass diodes but ran across this thread.  My question is what is the difference when some of the panels are shaded while others receive full sun compared to running with varying voltage panels?

BB.

If the panels are in series--The shaded cells go "high resistance" and you need the bypass diode(s) for current to go "around" the shaded cell/cells. Typically, the bypass diodes will be wired around ~12 volts of cells (maximum) at a time (varies a lot--more accurately typically ~1/3 of panel Vmp at a time).

I.e., a Vmp~36 volt panel with one cell blocked will have now have Vmp~24 volts (and another ~0.5 to 2.0 volt diode drop).

I would not worry about adding/using blocking diodes. Typically these were to prevent leakage current from flowing backwards through the array at night when directly connected to the battery bank. Solar panels are really just very large diodes--But not very good as they have high leakage current.

Today, almost everyone uses a series solar charge controller (the standard type) that turns off voltage to the array at night--So no leakage current.

And I would not worry about shaded cells in parallel connected panels--There is still back scattered light from the sky and such--The panels will not back flow any significant current.

Lastly, I believe people used blocking diodes instead of fuses/circuit breakers in older installations. Diodes prevent current from flowing backwards if a panel/string in the array was shorted. Works OK, but you have the losses of the diodes (0.2 to 2.0 volts of forward drop), and diodes are not really that reliable (vs fuses and breakers)--Diodes can fail shorted (or open) and if failed shorted, then they would not protect against a sorted panel/string.

Does this answer your question?

-Bill