Challenges with Solar on boats

[mitiempo]

Originally Posted by barnakiel

The regulator (at max 15A) is not very likely to limit us. It is a small unit for smaller installations.

I think the more likely challenge is absorption rate at battery closing on to full.

BTW How do you interpret this statement from Victron: "PV voltage must exceed Vbat +5V for the controller to start"?

Do they mean every morning or just the first start (out of the box).

Because it takes quite some time in the morning for my panels to get to say 17 Volt (wrong assumption?). And I am not willing to wire 24/12 for the sake of getting the Volts higher and the regulator happy.

Thanks in advance of your opinion.

Cheers,
barnakiel

The Victron 75/15 is designed to limit incoming wattage to 200, any surplus is wasted.

A solar panel usually has a fairly high voltage in sun, even with low amp output.

If you wish to charge both earlier in the day as well as later in the evening find a shade free area on the boat and series 2 panels. 2 panels that are at 9 volts in the morning or evening will be at 18 volts if in series.

Victron's controllers needing higher voltage to start or continue charging haven't been an issue in any install I have seen nor has any customer had a problem with it.

[mitiempo]

Originally Posted by newhaul

Yea I noticed that after I did the thunking with the statement of it being a 36 volt panel. So even with a 24 volt panel and that controller they would be wasting as much as 20 ah per day . Still worth getting a bigger controller imho.

Definitely worth getting a larger controller - 100/30 is probably the best choice.

As far as panels go, a 12 volt nominal panel has 36 cells @ 1/2 volt each.

A 24 volt nominal panel has 72 cells @ 1/2 volt each.

There are no panels I know of with more than 72 cells.

ps. Don't blame us for all the smoke, there are some fires in Washington as well.

[StuM]

Originally Posted by mitiempo

There are 2 limits in play with any controller. Maximum panel wattage and maximum solar array voltage.

The Victron 75/15 is limited to 200 watts of panels. You can use 1000 watts if you wish - there will not be any damage to the controller. It will however limit the incoming panel wattage to 200. It is not logical to use the 75/15 with more than 200 watts of panels.

No it's not. It has a "nominal PV power" of 440W if using a 24V battery bank.

These controllers "load limit" on output Amperage, not input Wattage.

[newhaul]

Originally Posted by mitiempo

Definitely worth getting a larger controller - 100/30 is probably the best choice.

As far as panels go, a 12 volt nominal panel has 36 cells @ 1/2 volt each.

A 24 volt nominal panel has 72 cells @ 1/2 volt each.

There are no panels I know of with more than 72 cells.

ps. Don't blame us for all the smoke, there are some fires in Washington as well.

Except the winds are out of Frazier valley way and our fires are due east of me. Its all your doin Paul
On my defender I have 200 watts and a 30 amp controller. It was definately worth the extra 10 bucks ( p30l pwm controller)

[mitiempo]

Originally Posted by StuM

No it's not. It has a "nominal PV power" of 440W if using a 24V battery bank.

These controllers "load limit" on output Amperage, not input Wattage.

Correct, the panel wattage doubles if the battery bank is 24 volts. Earlier in this thread it was posted that if panel voltage doubled allowable wattage doubled, which is incorrect. That is the point I was making.

As I posted earlier it is 200 watts for a 12 volt bank and 400 watts for a 24 volt bank. The 220 and 440 are errors. For confirmation call Justin Larrabee @ Victron in Maine.

[noelex 77]

The easiest rule to remember is if a regulator is rated at 15A then 15A is the maximum anywhere, in any wire, that is connected to the controller.

Likewise if the regulator is rated at 75v then 75v is the maximium anywhere, in any wire that is connected to the controller. This is even more critical because exceeding this value, even briefly, will probably destroy the controller. Therefore you must make sure that all voltages listed on the solar panel (added together if the panels are in series) are comfortably below this value. Occasionally solar panels can put out more voltage than their STC rating suggest, so some leeway is needed.

[Sailsgood]

Originally Posted by Utahsailor

In my 12V system of 840W Kyocera panels, dual Morningstar controllers and 10 Trojan T105s, I have to add water every week. Today I added nearly 1/3rd gallon after 1-1/2 weeks. This seems excessive and I notice that the Morningstar are putting more amps into the batteries at nearly full charge than the Balmar controller on the engine or the Xantrex when hooked to shore power. Does this seem excessive?

I do not know the Morningstar charge regulators, but in so many others you can select the maximum battery voltage point that the controller stops charging. Have you tried with a tester to see how many V have the batteries?

[barnakiel]

Originally Posted by john61ct

(...)

First start every morning. That is why nominal 12V panels are often 18-22V to start with.

Low cost PWM are often the same, there just isn't any effective power available until volts climb well above the charging point.

Very efficient cells like SunPower help, but only a bit.

By "regulator" are you talking about the solar controller or something else?

Yes. 'Regulator' I use interchangeably with PV 'charge controller'. I mean the same thing.

Right now we have a PWM one that works fine but I am considering one of the small MPPT Victrons which seem good value. We have enough charge with what we have BUT I am yet to find a boat that gets too much energy from its solar bank.

I was imagining, possibly wrongly, that some of my benefit would be for the new regulator to kick in earlier (morning) and ramp up faster. But I am not going to wire our 12V panels into a 24V array as then I would lose the ability to quickly bypass the regulator and connect the panels right onto the battery. This meant as an emergency procedure offshore where I cannot buy a new regulator or quickly bypass a broken panel.

Alas, reading more carefully the plate on the panels I found indeed it says 22V sc voltage, so I will measure the voltage tonight as the sun comes down and see at which point we get at the required "+5V" level. Tropical dusks and dawns are brief, so possibly I am worrying over practically marginal gains.

Thanks for your input!

Cheers,
barnakiel
150W monocrystals & sunsei PWM / batt 110Ah car / 12V

[foggysail]

Originally Posted by barnakiel

Yes. 'Regulator' I use interchangeably with PV 'charge controller'. I mean the same thing.

Right now we have a PWM one that works fine but I am considering one of the small MPPT Victrons which seem good value. We have enough charge with what we have BUT I am yet to find a boat that gets too much energy from its solar bank.

I was imagining, possibly wrongly, that some of my benefit would be for the new regulator to kick in earlier (morning) and ramp up faster. But I am not going to wire our 12V panels into a 24V array as then I would lose the ability to quickly bypass the regulator and connect the panels right onto the battery. This meant as an emergency procedure offshore where I cannot buy a new regulator or quickly bypass a broken panel.

Alas, reading more carefully the plate on the panels I found indeed it says 22V sc voltage, so I will measure the voltage tonight as the sun comes down and see at which point we get at the required "+5V" level. Tropical dusks and dawns are brief, so possibly I am worrying over practically marginal gains.

Thanks for your input!

Cheers,
barnakiel
150W monocrystals & sunsei PWM / batt 110Ah car / 12V

It's not about a regulator/controller "kicking in" early, it is about the panels providing energy. But back to you PWM. The voltage difference between your battery and the panel's Vmp multiplied by the panel's current is power lost. That loss includes wiring along with controller switching losses although the switching losses are small. Wiring losses are a controlled variable determined by what you wired your panel connection with.

So if Vmp is about 18v @ 5 amperes for example, the power that can be provided, not that it will be provided by the panel is 90 watts. Your batteries with a PWM and a battery voltage of 13V will never see more than 65watts, 25watts is wasted! Battery input current will be the same as the panel's current but if you had an MPPT the battery current would approach 6.9 amperes while the panel is providing only 5 amperes.

You're only going to get about 70% of the panel's available power capacity. You really should consider an MPPT controller.

Final comment--- You posted: " But I am not going to wire our 12V panels into a 24V array as then I would lose the ability to quickly bypass the regulator and connect the panels right onto the battery."

I don't know what you mean. Maybe I missed clarification in one of your earlier posts. If you meant your panel that has a Voc of about 20-22v, that is exactly what you do when you connect your so panel to a PWM controller.

[newhaul]

Originally Posted by foggysail

So if Vmp is about 18v @ 5 amperes for example, the power that can be provided, not that it will be provided by the panel is 90 watts. Your batteries with a PWM and a battery voltage of 13V will never see more than 65watts, 25watts is wasted! Battery input current will be the same as the panel's current but if you had an MPPT the battery current would approach 6.9 amperes while the panel is providing only 5 amperes.

ZYou're only going to get about 70% of the panel's available power capacity. You really should consider an MPPT controller.

Would you please clarify these statements in laymens terms so those among us can get a wrap on this concept. Provide links to the technical aspects as well please
(Im really trying to learn more on this to explain it to customers better)

[john61ct]

Originally Posted by barnakiel

But I am not going to wire our 12V panels into a 24V array as then I would lose the ability to quickly bypass the regulator and connect the panels right onto the battery. This meant as an emergency procedure offshore where I cannot buy a new regulator or quickly bypass a broken panel.

Not that I'm endorsing that idea, but.

Just bring all panels' wiring to near the bank and SC, and you can re-configure to your heart's content.

Just adds cost to the wiring.

[Quadrille in JB]

Originally Posted by john61ct

No, those numbers are **pure** fantasy, not even in the ballpark.
John61ct
Even in clear skies at the equator on top of a frozen mountain with a natural bowl of snow focusing a noon sun's rays on that panel.

Your challenge was "If you're willing to test it install that panel on a real boat with a fixed mount on a real boat. I'll bet you the price of a controller that you can't get it to produce 60 ah to the bank in less than 4 hours, more than 5 days a year. "
Put your money where your big mouth is. Attached is a pic of the Victron monitor screen from last month. The panel is mounted on my "real boat."
The performance was even better when we were in the Bahamas last week but I'm not at the boat and I don't have a screen shot.
My Isotherm fridge/freezer draws 7+ amps and the water maker draws 4+ amps. That's 11+ ah right there plus the draw on the 2000w inverter and other things. It's pretty easy to get 15 ah out of that and it happens all day long, every day to bring the bank up to full charge each night.

[newhaul]

Originally Posted by Btimmerman49

Your challenge was "If you're willing to test it install that panel on a real boat with a fixed mount on a real boat. I'll bet you the price of a controller that you can't get it to produce 60 ah to the bank in less than 4 hours, more than 5 days a year. "
Put your money where your big mouth is. Attached is a pic of the Victron monitor screen from last month. The panel is mounted on my "real boat."
The performance was even better when we were in the Bahamas last week but I'm not at the boat and I don't have a screen shot.
My Isotherm fridge/freezer draws 7+ amps and the water maker draws 4+ amps. That's 11+ ah right there plus the draw on the 2000w inverter and other things. It's pretty easy to get 15 ah out of that and it happens all day long, every day to bring the bank up to full charge each night.

Makes me unhappy that they deleted my response post to his challenge he does owe me a nice mppt controller. And I do it with a mere 200watts of 12v panels and a cheap pwm (p30l) controller

[john61ct]

OK couple of different issues here.

About the "challenge wager" I edited to withdraw that within a minute of posting, not only felt I might lose but was too "big mouthy" even for me. Apologies to you guys who would have liked to take the bet, I didn't see any photos attached, feel free to post for our education if you like.

[john61ct]

Next thanks for the contact info for Justin at Victron he cleared up some issues. My query:

My understanding is, from a "possible damage" POV only the 75V is critical, and use panel Voc.


The 15A is the limit for **output** charge current, and even the stated input rating of 20A isn't necessarily a hard one, just wasteful of potential peak PV power output to use anything higher. And the same must also hold for the max watts rating?


I've also been told although the PDFs all say "220w" for 12V banks, that in reality should be 200w.


Please confirm or correct the above.


For an example scenario, I'm looking to have a single controller per panel, and therefore want to use the 75/15 rather than the more than double in price 100/30.

Panel 1: 250w, Voc: 43.0V, lsc: 8.65A

Panel 2: 290w, Voc: 38.8V, Isc: 9.58 A

My feeling is that in real-world flat-mounted usage, using either panel 1:1 with the 75/15 will only be "wasteful" by say 5-10% in relatively rare "peak conditions".

The controller will cost much more than the panels if I have to go to 100/30.

---------

Justin confirmed the critical spec to not exceed is the Voc rating, 75V for the 75/15.

And that the max wattage rating - 220/440 is actually correct - is looser and proportional to the incrementally varying voltage of the **panels** not the nominal bank type.

So work off the total charging current spec, in this case 15A. At 14.4V that's where they get max output of 220W.

This is not a hard limit on panel spec, which is 20A in any case, and 24V nominal **panels**, the wattage rating is around 440W.

Yes, if "over panelling", the SC limits the output wattage to the 15A rating.

Given that for my situation, real world performance of panels will rarely match the data sheet, I would use the 75/15 one per panel, even for the so-called 290W version. Getting closer to max output in sub-optimal conditions will be especially helpful in the earlier part if the day, when the bank has higher current acceptance.

Bottom line: for the sake of the controller, the 75V is NOT to be exceeded (Voc, watch out for bright snowy mornings!), and the 20A has some wiggle room, OK to base on real world output.

But the watts rating can just be considered an output limit, not a "might damage the controller" absolute, it varies with the actual panel volts output.

Hope that helps clear up some of the confusion.