Solar panel wiring

[Last Call]

Good afternoon all !

I've been working on my schematics planning on installing panels
What I have done so far is :

2) 12 volt 30 watt panels on both port and starboard each set wired in series to 24 volts at 3.3 amps

1) 100 watt panel at 12 volts 5.6 amps between the mast and companionway door.

I have these three groups in parallel with all the appropriate diodes and bypass diodes.
To my question. Is this order of 24 12 24 volt panels in parallel to the controller a no no? It was the charger situation driving my choice . Is this doable? It sounds wrong to me.

Thanks,

Bobby

[StuM]

Very bad idea. Here's a good video which show exactly what will happen (the 12V will pull the 24V panels voltage down without increasing the amps)

https://www.youtube.com/watch?v=JfzT8u205co

[cptcptcpt]

is there a reason for the different size panels? you will do better if they are the same and angled the same way

will make the biggest difference when sun is less than ideal, which can be often

[marty9876]

My understanding is mixing different voltage strings into one controller will end up with the whole array dragged down to the lowest voltage. In your case, your 24v string will be dragged down to 12v (nominal voltage for the panel) negating your series benefits,

You seem to have in essence a series-parallel setup which has its own pros and cons as everything does in solar. Options I see- keep the 30w panels in parallel (most conservative play) or get separate controllers for the panel sets. Gensun makes some relatively cheap controls worth a look.

BTW I think in general you should only series panels on the same side of a boat as if shading hits any part it will kill the output of the whole array.

[john61ct]

Originally Posted by Last Call

It was the charger situation driving my choice.

Please explain.

Have a look at Victron MPPT 75/15. At under $100 you can buy a few, and parallel them to the bank.

Have all panels per one SC be matched, ideally same model, and from the same angle and direction. For good efficiency voltage should be 24V nominal, up to 60Voc max, so if you have 18-30Voc, within the previous rules, wire in series to get volts up.

But even 1:1 between SC and panel is OK if needs must, infinitely better than mixing different voltages or from opposite sides going all to one SC.

[smac999]

Get 3 controllers.

Make sure the series panels are facing same way and don't get blocked. If one is partly blocked neither will work. Series isn't the best for boats.

[Last Call]

The size difference was just dictated by where I had to put them.

[Last Call]

Originally Posted by cptcptcpt

is there a reason for the different size panels? you will do better if they are the same and angled the same way

will make the biggest difference when sun is less than ideal, which can be often

The difference was due to physical size needed to mount on my hand rails and fold straight down when not needed. All panels are on adjustable mounts, well along the long axis anyway.

Thanks for the reply.

[Last Call]

Originally Posted by cptcptcpt

is there a reason for the different size panels? you will do better if they are the same and angled the same way

will make the biggest difference when sun is less than ideal, which can be often

Originally Posted by Last Call

Good afternoon all !

I've been working on my schematics planning on installing panels
What I have done so far is :

2) 12 volt 30 watt panels on both port and starboard each set wired in series to 24 volts at 3.3 amps

1) 100 watt panel at 12 volts 5.6 amps between the mast and companionway door.

I have these three groups in parallel with all the appropriate diodes and bypass diodes.
To my question. Is this order of 24 12 24 volt panels in parallel to the controller a no no? It was the charger situation driving my choice . Is this doable? It sounds wrong to me.

Thanks,

Bobby

Didn't know how to continue this post so I'm listing variables I'm dealing with here. The reason for my mixture of different size panels was strictly due to available space. When this started project I planned to have a 12 volt bank for house batteries and a LP kicker motor. I decided to install a 48v 50 amp max continuous electric drive which is nearly completed. Many folk run 2 banks one for the starter or propulsion side and one for house. After weighing the pros and cons for multiple battery banks listed on the electrical forum section I decided one bank was the way to go for me. I have one bank of 48 v now and will be adding four more batteries to a total of eight on one bank at 48 volts or possibly two banks of 48v. As for the 12 volt house side I am running a single 48v dc to 12v dc converter at 30 amp output to my distribution fuse blocks for all 12 volt needs. This is low amperage for everything when you add them together so I will most likely ad a second converter in parallel, Not totally efficient but my electrical needs are small when not using anchor winch or any of the pumps, bilge, wash down or potable water. I would have 60 amps at 12 volts like this so I'm good on the house end.
If I were to wire the panels strictly in parallel the solar charger I would be looking at is a Gensun brand that claims to charge up hill from 12v to 48v which seems good. ( felt uneasy about this uphill deal) I would wire all the panels with bypass diodes around each panel and blocking diode
for the array in total. This panel configuration put my peak voltage around 18v and the amps around 12. I'm not sure but I think in the stepping up of the voltage from 12 to more than 48 by this charger will be reducing my amps to do so. I couldn't find documentation to back that up (yet). I could be wrong in this thought process. Changing the motor to 48 volt electric as a after thought introduced more issues to deal with. Now I have a 12 volt charge controller I'm getting rid of.

So in summary I have the following hardware:
one- 48v AGM battery bank
two- 30 watt 12 volt panels @ 1.65 amps ( My plan was to make it four)
one - 100 watt 12 volt panel @5.23 amps
Total 12 volts 220 watt @ 8.53 amps Parallel



Panel wiring to configuration and charger type to be determined.

I have made some dubious choices so far due to my change in propulsion from LP to electric. The mistakes are getting expensive and time consuming. I could use help going forward with what I have on hand.

I need suggestions on the best wiring configuration for the panels and a appropriate MPPT charger.

Thoughts?

Thanks

[Bleemus]

I may be missing something but a total of 160 watts of panels trying to keep up with an electric drive is a losing situation. If your committed to electric drive you need to seriously increase the solar array.

[Last Call]

Its not trying to keep up with that. Its just to offset losses from all lights, ventilation fans, chargers for computers and phones etc. My sailing will involve the Chesapeake bay and sounds. The motor is just for getting out of the marina maybe loss of rudder etc. I will have a generator if push come to shove for the shore charger. The motor has regenerative braking which is only going to help on rare occasions due to drag offsetting benefit. I will spend some time recharging at marinas around the coast.

[Last Call]

I posted one reply via quick reply but I dont see it. Perhaps those go directly to the person your replying to if so sorry about that.

My traveling will be limited to the Chesapeake Bay and its tributaries , Pamlico and Albemarle sounds. I will use the motor to get off the dock. The panels are just to keep the battery losses down from all lights and small chargers for phones and ventilation fans. I know I say I will not use the motor that much and I'm going to have to restrain myself. That may prove to be easier said than done. I will be doing day or weekending for the most part. As for my commitment I already bought everything for this install so there is no turning back and I will do what I have to to make this work. The Motor is a marinized 3 phase axial air gap brushless motor with regenerative braking. Due to drag and internal gear ratios in the foot I dont see that being helpful unless I have maximum safe winds. I machined a intermediate adapter and then mounted the motor to a 15 hp Johnson outboard with the power head removed with a 4 blade 10 inch high torque 5 pitch prop. It runs at 50 amps continuous max.
Hopefully my array will keep up if not I'll have to add more.

[john61ct]

The solar will be a negligible contributor to a propulsion bank in regular use, the genset will allow for time-shifting, maybe run only 20-30% of your motoring time, depends on your 48V charger's amp output running off shore, power or the generator.

Needing to charge 48V really limits your SC choices, to the point I'd recommend a smaller 12V bank sized to store all solar output when sunny for three days in AH (*1.1 if LFP, *2 if lead).

Only use the 12V bank for low-amp loads.

Use the 48V circuit besides propulsion for big-draw House loads.

Two shore-power chargers off shore power or the genset, no need to B2B charge.

[Last Call]

Originally Posted by john61ct

The solar will be a negligible contributor to a propulsion bank in regular use, the genset will allow for time-shifting, maybe run only 20-30% of your motoring time, depends on your 48V charger's amp output running off shore, power or the generator.

Needing to charge 48V really limits your SC choices, to the point I'd recommend a smaller 12V bank sized to store all solar output when sunny for three days in AH (*1.1 if LFP, *2 if lead).

Only use the 12V bank for low-amp loads.

Use the 48V circuit besides propulsion for big-draw House loads.

Two shore-power chargers off shore power or the genset, no need to B2B charge.

I do not understand " three days in AH" Please explain. How many amps would you call low loads? If I am understanding correctly you recommend two banks a 12 volt bank , and 48. Hook small loads I would say, six amps or less which is the VHF Radio on the 12 volt bank. Then just use two different shore chargers for the bulk charging of both banks and just use the solar to maintain the 12 volt bank.
Is this correct.

[john61ct]

Originally Posted by Last Call

Is this correct?

Yes

Originally Posted by Last Call

How many amps would you call low loads?
...
Hook small loads I would say, six amps or less which is the VHF Radio on the 12 volt bank.

Sure, LED lighting, screens & entertainment systems, navigation electronics.

Bigger "House loads" like refrigeration or a loud stereo used many hours a day probably best fed off the 48V bank via 12V converter

Originally Posted by Last Call

I do not understand " three days in AH" Please explain.

Originally Posted by john61ct

a smaller 12V bank sized to store all solar output when sunny for three days in AH (*1.1 if LFP, *2 if lead).

Measure AH per day produced by all your solar panels on a clear sunny day, using efficient (and efficiently deployed) SCs charging well-depleted batteries. Let's say that's 100AH per day, three days is 300AH.

If going LFP, I'm saying size the bank around 330AH, and if lead go to 600AH.