Another confused solar poster

[trailguy]

Hi all. I have just spent hours perusing the posts on solar and charger compatibility on this forum and am possibly more confused than when I started.

I have a pocket cruiser that I'm getting ready to put solar on. Since I trailer the boat frequently I've opted to go with a 100 w. Sunpower flexible panel. I can temporarily attach it to the bimini then store it under the cushions on the V-berth when the boat's on the trailer.

I really wanted to use a Victron Solar Smart mppt controller for it, but if I'm reading the specs right, the single 100 watt panel won't meet the minimum power requirement for even the 75/10. My preference would be to run the 75/15 as I plan to add a chart plotter and tiller pilot and want the benefit of the increased amp output. Am I reading the specs right? Nominal PV power for the 75/10 is 145w, 220w for the 75/15.

I'm not worried about the battery bank for day trips, as I can recharge on SP. but am planning some week long excursions where SP won't exist, hence the solar panel.

I would appreciate any and all advice/education on
A: the correct MPPT charge controller for this panel
B: a better understanding if I'm not reading the specs correctly

Thanks in advance for any help.

[sailorF54]

I've never read anything about a minimum power requirement for a solar charge controller.
Reference ?
A Victron 75/10 can accomodate UP TO about 150 W of 12V solar panel(s), a MAXIMUM limit...

[noelex 77]

If you can provide a link to the panel you are planning to purchase it would be help, but a larger controller is fine with a smaller panel/array.

[trailguy]

Welcome to my confusion.
Here's a link to the spec sheet for the Victron series.
https://www.solar-electric.com/lib/w...-15_100-20.pdf

Line 3 states "Nominal pv power 12v 145w under the 75/10 heading and 220w under the 75/15 heading.

[trailguy]

Here's a link to the panel....

https://us.sunpower.com/sites/defaul...spec-sheet.pdf

[Dsanduril]

The key metric is the Max PV current of 13A, as long as your panels put out less than 13A you will be fine, the nominal is just a suggested value to get the most out of the controller without overloading it. The Sunpower panel has a 6.3A Isc, so in theory you could even connect 2 of them in parallel to the 75/10 and not exceed 13A, but you would end up limited on the output side (see the note at the bottom of the data sheet about excess PV). With the 75/15 you would have room for a second panel if you decided to go there.

Either the 75/10 or the 75/15 will be fine, they don't need to be maxed out to work. The Sunpower panels are fine, but for others reading this, do pay attention to the note at the bottom that the Victron controller requires 5V above battery voltage to start charging. That basically means you need a panel that can output ~18V to reliably start the controller. The key value is the Voc, if the controller is not charging the panel will rise to Voc with very little sun and start the controller. The Sunpower panels are 21V so no problem, but some other small (100W range) panels may be very close to that 18V limit.

[noelex 77]

Either the Victron 75/10 or 75/15, or even one of the larger Victron controllers will be fine.

The smaller 75/10 will deliver as much power as larger controllers with a single 100w panel. The limitation is the 100w solar panel output, not the the controllers maximum current. The larger controllers will only deliver more power if you plan to add more solar panels in the future.

The only caveat is the Victron controllers require (in theory) a high start up voltage. This does not seem to be a practical problem so I think it is probably best ignored, but if you are in a hot climate and installing a flexible panel with little ventilation there is a theoretical risk the Victron controllers (of any size) may be slightly late in starting in the morning. They would still work even in this scenario, but may deliver slightly less than optimum power.

[trailguy]

Originally Posted by Dsanduril

The key metric is the Max PV current of 13A, as long as your panels put out less than 13A you will be fine, the nominal is just a suggested value to get the most out of the controller without overloading it. The Sunpower panel has a 6.3A Isc, so in theory you could even connect 2 of them in parallel to the 75/10 and not exceed 13A, but you would end up limited on the output side (see the note at the bottom of the data sheet about excess PV). With the 75/15 you would have room for a second panel if you decided to go there.

Either the 75/10 or the 75/15 will be fine, they don't need to be maxed out to work. The Sunpower panels are fine, but for others reading this, do pay attention to the note at the bottom that the Victron controller requires 5V above battery voltage to start charging. That basically means you need a panel that can output ~18V to reliably start the controller. The key value is the Voc, if the controller is not charging the panel will rise to Voc with very little sun and start the controller. The Sunpower panels are 21V so no problem, but some other small (100W range) panels may be very close to that 18V limit.

That's what I needed to hear. Thank you! I think I was looking at the word "nominal" as meaning "minimum".

[trailguy]

Originally Posted by noelex 77

Either the Victron 75/10 or 75/15, or even one of the larger Victron controllers will be fine.

The smaller 75/10 will deliver as much power as larger controllers with a single 100w panel. The limitation is the 100w solar panel output, not the the controllers maximum current. The larger controllers will only deliver more power if you plan to add more solar panels in the future.

The only caveat is the Victron controllers require (in theory) a high start up voltage. This does not seem to be a practical problem so I think it is probably best ignored, but if you are in a hot climate and installing a flexible panel with little ventilation there is a theoretical risk the Victron controllers (of any size) may be slightly late in starting in the morning. They would still work even in this scenario, but may deliver slightly less than optimum power.

Thank you for explaining that for me.

I know heat is also going to be a problem (going to FL and sailing to Dry Tortugas). I've read several posts on fires starting on bimini's with flexible panels. So I'll be monitoring it closely.

[john61ct]

Originally Posted by trailguy

Line 3 states "Nominal pv power 12v 145w under the 75/10 heading and 220w under the 75/15 heading.

Translation:

Lower power than this is fine.

You can also go quite a bit **higher** rated watts/amps than this

called overpanelling, but let's not get into that here.

Most critical is Voltage.

Going with a nominal "24V" panel, rated ~40Voc would give you a bit more output efficiency from the MPPT.

But you **must** not go over the 75V spec, 65-70 to be safe.

And the **minimum** actual voltage for startup is I think 5V above your charge output to the bank.

TL;DR you're fine

[GILow]

Originally Posted by trailguy

...My preference would be to run the 75/15 as I plan to add a chart plotter and tiller pilot and want the benefit of the increased amp output....


I'm not worried about the battery bank for day trips, as I can recharge on SP. but am planning some week long excursions where SP won't exist, hence the solar panel..

That first bit I’ve quoted does not make sense. Your power output is going to be limited by the panel, not the regulator. Also, be aware that, depending on the nature of the boat being steered, tillerpilots can chew up a lot of power. One battery may not have enough capacity for a full day of sailing, particularly if solar input is down due to cloud cover.

As for the second bit I quoted... what are you saying there? Makes no sense as written. “The SP won’t exist, hence the Solar Panel”. A week long excursion without the solar to recharge the battery will be a problem unless you have some other means of charging. Or a seriously huge battery bank.

[rgleason]

For smaller and lower power PV panels that don't have as many cells and thus have lower voltages there is the option of using Gensun mppt or Gensun Booster mppt which may be more effective for individual panels, but they don't have the Bluetooth App of Victron's.

[Jim Cate]

Originally Posted by GILow

That first bit I’ve quoted does not make sense. Your power output is going to be limited by the panel, not the regulator. Also, be aware that, depending on the nature of the boat being steered, tillerpilots can chew up a lot of power. One battery may not have enough capacity for a full day of sailing, particularly if solar input is down due to cloud cover.

As for the second bit I quoted... what are you saying there? Makes no sense as written. “The SP won’t exist, hence the Solar Panel”. A week long excursion without the solar to recharge the battery will be a problem unless you have some other means of charging. Or a seriously huge battery bank.

Matt, I think that in this case "SP" means shore power, not solar power. (Just guessing due to context).

Jim

[john61ct]

Yes as accurate as possible an Ah per day energy usage budget is the foundation, everything in the overall system design is derived from that.

Unless you just get lots of ICE sources and a big LFP bank to create electricity off grid.

Being dependent on just a bit of solar requires precision and being very conservative.

[GILow]

Originally Posted by Jim Cate

Matt, I think that in this case "SP" means shore power, not solar power. (Just guessing due to context).

Jim

Thanks Jim, I think you have it. Shore Power is an alien concept to me.