Series v Parallel Panel Specifics Question

[dspackle]

I have solar panels flat mounted on the roof of my vehicle. I travel the country full time, which means I am in a wide variety of environments, from full sun to partial shade to mostly shade with just a little sun filtering through trees. I don’t want to change the panel configuration continually, since my vehicle is very tall and I move fairly quickly from one place to another - I’m not really nesting in one area for any predictable length of time. I want to set the panels up in whatever way is going to give me, on average, the best performance in whatever circumstance I happen to be temporarily experiencing.

I’ve been doing this for four years and I have always had my panels connected in parallel in the past, because my understanding was that, when I am in partial shade, it will have a significant effect on the performance of a series array. But recently, I was convinced by someone who is more experienced than me that I will get better performance overall from a series connection. Only problem is, he can’t seem to explain WHY, just says “trust me.” Well, I am someone who really likes to know why. So… why? I understand that higher voltage is “better” but I’m not sure WHY it’s better. I understand that if the voltage is too low I can’t charge the battery. But series or parallel, the voltage is not going to be too low. So why, in plain English, is less watts and more volts better?

Let’s say I am charging a 2000 WH all-in-one device that has an MPPT controller built in, rated for up to 150v of solar, and I have (2) 200w panels (18v vmp) available to charge it. If I connect them in parallel, I’ve got 400w going in to the device at 18v, and If I connect them in series I have 200w going in at 36v… right? So why is the higher voltage better? Both voltages are adequate for charging, so why is series going to give me better performance overall? I know this is probably a stupid beginner basic question but I cannot seem to get an answer that actually satisfies me.

And also… what really does happen to that series array when it’s partially shaded? Is it less drastic than I always believed? Has something changed in solar panel technology in the 5 years I’ve been using a parallel connection?

 

[Cuemaker]

Wiring is series will let you use a smaller gauge wire + I believe you will have less overall wattage drop.

 

[efficientPV]

You will trust who you want to trust. You didn't say what kind of panels or battery voltage. That can make a big difference. There is no one kind of shade.

 

[PunchySunshine]

I have solar panels flat mounted on the roof of my vehicle. I travel the country full time, which means I am in a wide variety of environments, from full sun to partial shade to mostly shade with just a little sun filtering through trees. I don’t want to change the panel configuration continually, since my vehicle is very tall and I move fairly quickly from one place to another - I’m not really nesting in one area for any predictable length of time. I want to set the panels up in whatever way is going to give me, on average, the best performance in whatever circumstance I happen to be temporarily experiencing.

I’ve been doing this for four years and I have always had my panels connected in parallel in the past, because my understanding was that, when I am in partial shade, it will have a significant effect on the performance of a series array. But recently, I was convinced by someone who is more experienced than me that I will get better performance overall from a series connection. Only problem is, he can’t seem to explain WHY, just says “trust me.” Well, I am someone who really likes to know why. So… why? I understand that higher voltage is “better” but I’m not sure WHY it’s better. I understand that if the voltage is too low I can’t charge the battery. But series or parallel, the voltage is not going to be too low. So why, in plain English, is less watts and more volts better?

Let’s say I am charging a 2000 WH all-in-one device that has an MPPT controller built in, rated for up to 150v of solar, and I have (2) 200w panels (18v vmp) available to charge it. If I connect them in parallel, I’ve got 400w going in to the device at 18v, and If I connect them in series I have 200w going in at 36v… right? So why is the higher voltage better? Both voltages are adequate for charging, so why is series going to give me better performance overall? I know this is probably a stupid beginner basic question but I cannot seem to get an answer that actually satisfies me.

And also… what really does happen to that series array when it’s partially shaded? Is it less drastic than I always believed? Has something changed in solar panel technology in the 5 years I’ve been using a parallel connection?

 

[dspackle]

You will trust who you want to trust. You didn't say what kind of panels or battery voltage. That can make a big difference. There is no one kind of shade.

Not sure what the "trust who you want to trust" comment means. I'm just trying to understand the principle behind it, looking to learn rather than just do what someone says. Here are the panel specs. And the batteries are 12V.

 

[dspackle]

MEDIA=youtube]5rYy0gHZepI[/MEDIA

thank you!

 

[MisterSandals]

I am charging a 2000 WH all-in-one device

So at 12.8V nominal voltage that is 2000Wh / 12.8V = 156Ah battery? If lead acid, 50% usable so 78Ah.

and I have (2) 200w panels (18v vmp) available to charge it. If I connect them in parallel

The problem with 18Vmp is that in low light conditions, it may have trouble reaching your SCCs minimum voltage (usually battery voltage +5V).
So while an all parallel array may perform better in partial shade, if it cannot make minimum voltage you get squat.
It will start charging later in the morning, stop sooner in the evening and may not work with partially overcast skies.

2S2P is a great compromise.

While i always respected the Solar Queen, (may she RIP), blocking diodes, in my experience have never worked as advertised.

You can verify this all for yourself and only have to trust yourself. Determine you SCCs min startup voltage. On consecutive days see if 2S2P starts earlier or on overcast days compare 2S2P with 4P. Thats the only way to really tell. And maybe one setup works better in different parts of the country than the other (really sunny south vs low sun in the north).

 

[dspackle]

So at 12.8V nominal voltage that is 2000Wh / 12.8V = 156Ah battery? If lead acid, 50% usable so 78Ah.


The problem with 18Vmp is that in low light conditions, it may have trouble reaching your SCCs minimum voltage (usually battery voltage +5V).
So while an all parallel array may perform better in partial shade, if it cannot make minimum voltage you get squat.
It will start charging later in the morning, stop sooner in the evening and may not work with partially overcast skies.

2S2P is a great compromise.

While i always respected the Solar Queen, (may she RIP), blocking diodes, in my experience have never worked as advertised.

You can verify this all for yourself and only have to trust yourself. Determine you SCCs min startup voltage. On consecutive days see if 2S2P starts earlier or on overcast days compare 2S2P with 4P. Thats the only way to really tell. And maybe one setup works better in different parts of the country than the other (really sunny south vs low sun in the north).

Thanks very much.

 

[RV8R]

Here is my Cabin small 600W Array 3S2P




5:55am the Sun barely up & behind the south(ish) facing panel & behind tall trees. Yet almost 33 volts & charging my 12volt AGMs ,,, only 1 amp but at least it is on the side of positive “filling up the tank”.

Like @MisterSandals wrote my Victron requires battery voltage plus 5 volts to start (or close to 18 volts). If I had my panels 1S6P not a chance would I be charging this early in the morning.

In rough terms 3S for my panels is 3 * 20 volts or 60 volts & the 2P is 2 * 5 amps or 10 amps. My charger easily handles that setup.

There is way more to it than Series or Parallel of course, but as the others have suggested, it is easy enough for you to alter the S & P with connectors & you can sort it out yourself for what is better for you & your application.

Then there is “Theory” & “Reality”. On a van with an ever changing environment just one thing like panel tilt can change your harvest ability ( are you always parking dead flat ?? Etc ).

You can “Theorize”, but in a world of ever changing tech & a large selection of panels, it is my belief the best thing is to research, take in the info, ponder it, & experiment yourself.

Good luck with whatever you decide.

 

[efficientPV]

60-70% of my panels are in shade at any one time, I run 2S6P. A shaded panel will always produce some power and my system is designed to run on almost ambient light. My system is designed to run at natural power point. Due to the number of panels each seeing different shading multiple minor peaks can occur and a controller can lock into these. Disconnecting the array can reset this. I can do anything in electronics so this isn't a problem. With a 60V array it could be possible to go into bypass mode as each bypass diode covers about 9V of a panel. In parallel you could never go into bypass. It is also highly unlikely that a single section of panel sees isolated shade. That would only happen with a leaf covering one or two cells. Shade from a tree is devastating to power. I can still get sufficient power with clouds. Two panels on a van is a no win situation. In parallel, both panels will supply power even if one is shaded. Given the same condition, in series only one will provide power when the other goes into bypass mode. Everyone has their preference based on their type of shade and array. I don't like panels going into bypass. Some panel manufactures have warnings in their data sheets. I've seen FLIR heat images of sells as the string starts to go into bypass and the weakest cells overheat. Long term that isn't good. All this solar stuff is so temporary it likely doesn't matter and degrees of terrible performance doesn't either.

I have a transfer switch in my garage where I change my 60V array to 120V when I do laundry. You could do that and run some experiments for us. Below is a southern view of my property. See any panels? I know about shade and I even have excess power.

 

[efficientPV]

For those wanting to try parallel vs series, this is what I have done. This is a TOMZN transfer switch (under $10 shipped) that only allows one to be on at a time.

 

[RV8R]

For those wanting to try parallel vs series, this is what I have done. This is a TOMZN transfer switch (under $10 shipped) that only allows one to be on at a time.View attachment 159436View attachment 159437

What happens if you accidentally switch both on ?

 

[MisterSandals]

What happens if you accidentally switch both on ?

 

[efficientPV]

It is a transfer switch designed to only allow one up up at the same time. Flipping one on will force the other one down. Unless you have a big hammer. Both can be down and nothing will go to charge controller.

 

[MisterSandals]

is a transfer switch designed to only allow one up up at the same time

Happen to have a link to it?

 

[dspackle]

Here is my Cabin small 600W Array 3S2P

View attachment 159318


5:55am the Sun barely up & behind the south(ish) facing panel & behind tall trees. Yet almost 33 volts & charging my 12volt AGMs ,,, only 1 amp but at least it is on the side of positive “filling up the tank”.

Like @MisterSandals wrote my Victron requires battery voltage plus 5 volts to start (or close to 18 volts). If I had my panels 1S6P not a chance would I be charging this early in the morning.

In rough terms 3S for my panels is 3 * 20 volts or 60 volts & the 2P is 2 * 5 amps or 10 amps. My charger easily handles that setup.

There is way more to it than Series or Parallel of course, but as the others have suggested, it is easy enough for you to alter the S & P with connectors & you can sort it out yourself for what is better for you & your application.

Then there is “Theory” & “Reality”. On a van with an ever changing environment just one thing like panel tilt can change your harvest ability ( are you always parking dead flat ?? Etc ).

You can “Theorize”, but in a world of ever changing tech & a large selection of panels, it is my belief the best thing is to research, take in the info, ponder it, & experiment yourself.

Good luck with whatever you decide.

Thanks so much, that info and the questions you posed give me a lot to think about!

 

[dspackle]

For those wanting to try parallel vs series, this is what I have done. This is a TOMZN transfer switch (under $10 shipped) that only allows one to be on at a time.View attachment 159436View attachment 159437

I think I'm going to have to chew on this one for a while. It's a bit above my understanding what exactly you've done but it sure looks efficient. Thanks for the detailed reply!