Installing serial solar panels

[ramblinrod]

Originally Posted by noelex 77

1. Virtually all solar panels come with internal bypass diodes as standard. So you do not have to be concerned you may be buying a panel that has no bypass diodes.

Incorrect.

Larger panels, ~ 300W may very well have bypass diodes.

Smaller panels, ~100W rarely have bypass diodes.

Larger panels are great in a residential installation because you get more W/$, but IMHO they are not so great on a cruising boat, where you may need to take them down and stow them away due to a pending storm, hurricane, or when laying up on the hard.

Just try handling a ~300W panel in 25 knots. Fun.

Now try stuffing it down the companionway.

I generally recommend an array made up of 100W panels to my customers, so that they are more manageable, and if one is damaged, it's not such a big deal, until it can be replaced.

In my experience, shading on smaller panels connected in series is devastating to performance, parallel, no biggy, and locating/mounting large panels is too limiting, and one is forced to mount in location that will be prone to shading.

[newhaul]

Originally Posted by ramblinrod

Incorrect.

Larger panels, ~ 300W may very well have bypass diodes.

Smaller panels, ~100W rarely have bypass diodes.

Larger panels are great in a residential installation because you get more W/$, but IMHO they absolutely suck on a cruising boat, where you may need to take them down and stow them away due to a pending storm, hurricane, or when laying up on the hard.

Just try handling a ~300W panel in 25 knots. Fun.

Now try stuffing it down the companionway.

I generally recommend an array made up of 100W panels, so that they are more manageable, and if one is damaged, it's not such a big deal, until it can be replaced.

Rod I agree with using multiple smaller panels.
However I disagree with your assumption that smaller (100watt) panels dont have bypass diodes. The panel's I install do have the diodes. If you are getting panels from your curent supplier that dont have any diodes I would strongly suggest you consider a new supplier that does install the diodes.

[ramblinrod]

Originally Posted by DotDun

Specify the wrong in my post with facts!

Smaller wire = true!
Less voltage drop = true!
Easier to install ( due to smaller wire and easier connections) = true!
Shading has same effect on paralleled panels that have diodes! = true!

The open circuit voltage on my (3) 60 cell panels is 108v, far less than my 240v shorepower, and I ain't scared of either one!

I did in the previous post, where your statement was incorrect.

Specify what is wrong with these facts:

1. Series connection increases voltage.
2. Danger of electric shock and electrocution increases proportionally with voltage.
3. Lower voltage components like switches and breakers are less costly.
4. Shading has a devastating effect on performance for series connected panels that do not have bypass diodes.

[noelex 77]

Bypass diodes are primarily fitted to stop overheating of the cells. The biggest factor is how many cells the panel has in series, not the wattage. Any panel that can charge a 12v battery needs to have at least 32 cells (more commonly 36), even the smallest. More than about 20 cells (depending on how they are constructed) in series is not advisable without bypass diodes.

I have a small 10w Kyocera panel that has two internal bypass diodes. I looked up the specifications for the current Kyocera panels and even the smallest (40w) still has at least two bypass diodes. Kyocera publish detailed specifications so they are easy to look up, but other companies produce similar products.

If you can find any (12v or greater) monocrystalline or polycrystalline
panels of any wattage without bypass diodes, I would be very wary of their durability.

If you want to connect your panels in series an external bypass diode around the whole panel is worth considering even if the panel has multiple internal bypass diodes this still applies.

[john61ct]

I have a use case where I can use the "semi-flexible" panels only, so obviously durability is already out the window.

100W is the biggest I've seen, but down to 20-30W will help maximise space efficiency.

Do these even have bypass diodes? I assumed I'd need to put them in myself.

Also, links or google-search model#s to per-panel small MPPT (hopefully outdoor-rated and reasonably priced) controllers would be appreciated.

[TeddyDiver]

Originally Posted by ramblinrod

I did in the previous post, where your statement was incorrect.

Specify what is wrong with these facts:

1. Series connection increases voltage.
2. Danger of electric shock and electrocution increases proportionally with voltage.
3. Lower voltage components like switches and breakers are less costly.
4. Shading has a devastating effect on performance for series connected panels that do not have bypass diodes.

Nothing wrong but only half of the thruth..
1. And has better effiency considering resistance and wiring
2. I thought that debate was over when Tesla beat Edison
3. Components for higher amperage are more costly
4. Shotky diodes $4 a piece. Having one for each panel will do..

BR Teddy

[DotDun]

Originally Posted by ramblinrod

I did in the previous post, where your statement was incorrect.

Specify what is wrong with these facts:

1. Series connection increases voltage. Yep, ohm's law at it's best!
2. Danger of electric shock and electrocution increases proportionally with voltage. If this bothers you, maybe you should find another profession. Who works on your shorepower?
3. Correction! Lower voltage current components like switches and breakers are less costly. I.E., costs go up in parallel installations!
4. Shading has a devastating effect on performance for series connected panels that do not have bypass diodes. A good reason to not buy them!

I really don't care how you connect your customer's solar panels, but please be honest about the options.

[ErikElmgren]

Originally Posted by ramblinrod

This is the issue with putting panels in series.

What size of panels?

3 x 100W panels in each string, two strings in total. For safety I calculate with 60V and 8A although real numbers will be about 50V and 6A.

Originally Posted by ramblinrod

It is not recommended that MC4s be disconnected with current flowing, but it is no big deal for a couple hundred watts.

Even with a huge array, if one starts at the panel level, disconnecting MC4s as they work toward the controller, no issue.

What is the concern with shading a panel to reduce current?

That the shading can not be observed while I'm inside working on the electrical system and could in theory be removed by e.g. wind. I admit it's unlikely but as the voltage gets in to the danger zone I want to be cautious.

Originally Posted by ramblinrod

In a series string, one just needs to shade one half of one cell of one panel to bring the current down to near zero.

Which is a major drawback to series connection.

Any shading on any cell of any panel in the string, and output drops to near zero.

Going above 50 Vdc increases risk of shock/electrocution hazard.

So why connect in series?

I have a 24V system so at least 2 panels in series is necessary. 3 panels per string is the recommendation of the MPPT controller and sensible as partial shading will not bring the voltage below the needed charge voltage. (I found no MPPT controllers capable of boosting low voltage)

Originally Posted by ramblinrod

Saving money on lighter gauge cable only to spend it on other devices, with the shading issue, and shock hazard doesn't seem wise.

[ErikElmgren]

Originally Posted by newhaul

My big question is are the panels in each string in series or in paralel and the second is what type controler you are using.

3 panels in series in each string, two strings in total.
Victron 75/15, one for each string.

[ErikElmgren]

Originally Posted by noelex 77

I would not connect the panels in series, but if you want to do this you need a breaker rated at 60v +. One of the Din rail MCB is the best choice and they are also good as general purpose circuit breakers with some advantages over traditional "marine' breakers.

As others have said 60v can give you a a serious jolt. Anthing above 50v is potentialy lethal.

Thanks, this is likely where I'll end up, just need to find another space for a Din electric panel.

[travellerw]

I thought I would post to inject some real life experince in the conversation about series panels.

We have been living aboard for a year and a half now (through all the seasons) down here in the Caribbean. We have 3, 300 watt solar banks connected in series (each bank to its own MPPT controller).

Bank 1 = 4 X 75W Shell solar panels (roughly 65V at MPP)
Bank 2 = 2 X 150W Renogy solar panels (36V at MPP)
Bank 3 = 3 X 100W El Cheapo Amazon panels (51V at MPP)

First to the shading issue.. We have NEVER, EVER seen the current drop to zero on any of our banks (each MPPT has its own display). I have literally spent days watching the displays and analyzing the shadows on the panels. The shading has never been the issue that it seems to be made out here. To be fair, we don't have a ton of shading (we are a catamaran). However I have watched the mast shadow covering 1/2 a panel and our current did not drop to zero (it dropped to about 2/3).

Second.. The shock hazard.. ABSOLUTELY, this is an issue with series panels. Ask me how I know? Let me tell you, 65V DC doesn't just sting, but hurts like hell, and dummies like me do it twice to make sure it hurts. Don't underestimate this. Ensure you use proper safety proceedures if you do wire in series.

Finally.. Diodes.. All our panels came equipped with bypass diodes from the factory (even the 15 year old 75W Shell panels). However.. The elcheapo panels have had all those diodes fail in the last year and a half. I have had to replace all the diodes in those panels. I replaced them with quality diodes from Digikey and none have failed since. The Shell and Renogy panels have not had that problem.

Personally, I still think series was the right choice on our boat. I agree its not right for every boat. It sure was nice to not spend a fortune on wire though.


P.S. back to the original question about MC4 connectors.. We USED to have MC4 connectors on our panels. I cut all of them off after we had multiple (4) failures. We no longer use them on our boat and I wouldn't rely on them as a "cutoff" for the panels. Not the best solution, but we throw towels over the panels.

[ramblinrod]

Originally Posted by s/v Jedi

I'm so happy that others who know how it works came forward because it's hard to deal with the ignorant alone

For the person that asked me to clarify my math: yes, I meant 1/6th of total, i.e. 1/3rd of the panel. You only loose the affected string. In parallel you loose the whole panel because it's voltage goes below that of the other.

First of all, calling others "ignorant" is not cool. (I believe I've called you on this before in another thread.)

What is the rule about voltage sources connected in parallel?

Oh yeah, THEY MUST BE EQUAL.

So you are completely wrong, or is that "ignorant" to you?

If you have two voltage sources in parallel, they must be the same voltage. It's the law.

When a boater has two solar panels in parallel, the shaded panel producing zero current, produces zero current, it does not affect the unshaded parallel panel whatsoever.

So before you go calling others names, get your "alternative facts" straight.

[TeddyDiver]

Originally Posted by ramblinrod

First of all, calling others "ignorant" is not cool. (I believe I've called you on this before in another thread.)

What is the rule about voltage sources connected in parallel?

Oh yeah, THEY MUST BE EQUAL.

So you are completely wrong, or is that "ignorant" to you?

If you have two voltage sources in parallel, they must be the same voltage. It's the law.

When a boater has two solar panels in parallel, the shaded panel producing zero current, produces zero current, it does not affect the unshaded parallel panel whatsoever.

So before you go calling others names, get your "alternative facts" straight.

Aaaargh!
Isn't that just what he said... So you're wrong saying he's wrong when you are both right. The point is in parallel you loose the other panel completely but in series you loose only 1/3 of that same panel.

BR Teddy

[ramblinrod]

Originally Posted by s/v Jedi

Also agree that series connection is much cheaper because the current is lower and thus components are cheaper.

OK, lets look at a very common scenario, comparing apples to apples, and using Blue Sea Marine products as the source (which I highly recommend BTW).

Common Scenario:

3 x 100W panels rated 15 Vdc at 5 A ea.

Connect them in series and an SPST switch, rated 45 Vdc or better costs $48.

https://www.bluesea.com/products/900...Battery_Switch

Connect them in parallel, and a Blue Sea Contura III, 8282 costs $12.

https://www.bluesea.com/products/828...Black_-_OFF-ON

How many switches?

One per panel for 3 panels?

Series = 3 x $48 = $144 + Tax

Parallel = 3 x $12 = $36 + Tax

Now lets talk breakers

Series = 3 x 7080 = 3 x $54 = $162

Parallel = 3 x 7402 = 3 x $27 = $81

Or, put 3 switches in a nice little panel with a switch and resettable breaker for each for $111

https://www.bluesea.com/products/827...ite_3_Position

Big, clunky, costly components for series connected panels, or small unobtrusive, affordable components for parallel connected panels.

The choice is yours.

[TeddyDiver]

Originally Posted by ramblinrod

OK, lets look at a very common scenario, comparing apples to apples, and using Blue Sea Marine products as the source (which I highly recommend BTW).

Common Scenario:

3 x 100W panels rated 15 Vdc at 5 A ea.

Connect them in series and an SPST switch, rated 45 Vdc or better costs $48.

https://www.bluesea.com/products/900...Battery_Switch

Connect them in parallel, and a Blue Sea Contura III, 8282 costs $12.

https://www.bluesea.com/products/828...Black_-_OFF-ON

How many switches?

One per panel for 3 panels?

Series = 3 x $48 = $144 + Tax

Parallel = 3 x $12 = $36 + Tax

Now lets talk breakers

Series = 3 x 7080 = 3 x $54 = $162

Parallel = 3 x 7402 = 3 x $27 = $81

Or, put 3 switches in a nice little panel with a switch and resettable breaker for each for $111

https://www.bluesea.com/products/827...ite_3_Position

Big, clunky, costly components for series connected panels, or small unobtrusive, affordable components for parallel connected panels.

The choice is yours.

If that's the way and components you want to use
Series = 1x$48+1x$54=$102 one string, one breaker
Parallel = 3x$12+3x$27=$117 three strings...

BR Teddy