Challenges with Solar on boats

[mitiempo]

Originally Posted by newhaul

Ok im going out on a bit of a limb here and assuming your windless was installed with 2/0 or simmilar cables so no there would not be any appreciable or noticeable difference between that and the original install (except likely better performance out of your windlass.)

That's true but as a rule I dislike banks split by more than a couple of feet.

[john61ct]

There will be I'm balances within the bank, but if minimized, just slight inefficiencies and reduced lifespan.

The bank as a whole lives as long as the weakest members.

[mitiempo]

Originally Posted by john61ct

There will be I'm balances within the bank, but if minimized, just slight inefficiencies and reduced lifespan.

The bank as a whole lives as long as the weakest members.

The windlass at the end of a long cable run (of the correct gauge) is not an issue because the engine is running when the windlass is, raising the voltage to the windlass.

By moving 4 batteries to the bow you are creating the weakest members that will shorten their lives as they will rarely be fully charged. Shouldn't have much if any effect on the batteries aft in my opinion.

[newhaul]

Originally Posted by mitiempo

That's true but as a rule I dislike banks split by more than a couple of feet.

Personally I would rather have a bank split by distance rather than a high draw motor on an extension cord.

[mitiempo]

Originally Posted by newhaul

Personally I would rather have a bank split by distance rather than a high draw motor on an extension cord.

2/0 or larger wire is hardly an extension cord. As well with the engine running the originating voltage is much higher (14.4) than a resting bank of 12.7 or less. With even a 15% drop in voltage the windlass receives 12.2 volts.

Putting a battery or more forward for windlass use means maintaining it and replacing it on a regular basis. You only buy the wire once.

[CapnCrunch]

Yes, the windlass is wired with 2/0 cable and I'm sure it will be happier with 4 batteries closer to it. HOWEVER, the reason for moving the batteries was to get some of the weight out of my stern NOT to improve windlass performance. Would it help the life of the forward group if I connected one of the solar panels/SCs directly to those batteries?

Which brings up two more questions:
1. Will moving only about 200 lbs to the bow area be worth the effort since I'd have to fabricate a suitable enclosure?
2. Maybe I've missed it but I've never seen any mention of where the output leads from the charge controllers is connected to the system (I was assuming directly to the batteries).

[CapnCrunch]

Nuther question:

Despite all of the discussion about available solar charging hours, I haven't seen any mention of adding a wind generator to the mix. Wouldn't one of those make sense to take advantage of any available wind overnight while the panels are not producing?

[newhaul]

Originally Posted by CapnCrunch

Nuther question:

Despite all of the discussion about available solar charging hours, I haven't seen any mention of adding a wind generator to the mix. Wouldn't one of those make sense to take advantage of any available wind overnight while the panels are not producing?

Wind generators are an entirely diferent discussion full of personal opinions. I would say for me yes but for you it depends on your sailing area and available winds.
As far as your previous query yes the solar charge controller is hooked directly to a battery bank .

[john61ct]

For a single bank, all the input and output wires should be connected to the same pair of posts.

Just like the advice that all interconnect wires should be the same gauge and length.

If you're violating that, may as well the other.

Personally, I would probably create two "separate" banks, but have them automatically combined in normal operations, only isolated when SoC drops below X%, set low enough that they are only very rarely separated.

Then putting separate charge sources on each if you like would not be controversial.

[rabbi]

Originally Posted by john61ct

No, those are the precise specs for your panels.

The argument was with me about the possibility of using 75/15 instead at less than half the price.

Since Justin apparently reversed what he wrote me, I concede there would be more wastage of peak power output than most would want.

However the other 240w panels would I think be OK, in my situation well under 5% loss overall.

If anyone has the gear to test the argument I'd be willing to front for the 75/15, as long as there is a corresponding friendly wager on the other side if I'm right, just to make it interesting 8-)

If not, then I'll test myself one day and post the details.

My real world observations on a cat with very little shading:

I have 2 panels 280w (32,2v / 9.2A) each connected to its own Victron MPPT 75/15, both feeding the same house battery bank.

Observations:
The peak charge output of this controller is 15A each, but this happens rarely even with slightly oversized panels like mine.

To produce anywhere near 280W takes quite a few details: Perfectly clean panels. No shade. Full sun at the right angle. No clouds or mist. That doesn't happen often in the real world.

Alignment is never perfect, and good only around noon time on my boat (I could tilt the panels but I never do). There is dust on them (sahara dust in the Med) and I clean maybe once a weak.
Peak production during a normal day is closer to 230-240W and even that is just for a few moments.
Which the 75/15 handles well.


Also keep in mind: The battery needs to accept the charge. Solar charge typically starts around 7am in the Med, and my batteries are full by 11am latest. Two hours later when the perfect conditions for my solar panels arrive the available energy is just waisted (OK, in my case it's redirected to the cockpit beer fridge).
EDIT: We have two new Trojan batteries of 150Ah each, and our deepest discharge was 55Ah (fridge, LED lights, a handful of USB charged phones/tablet/gadgets, small sine inverter running 24/7 to charge other electronics).

Given the price difference between the 15A and the 30A controller I would certainly suggest to go for the 15, at least with a 290W panel. A 30A controller will add very little unless you go for much more panel area.



The only thing that I dislike about the Victron MPPTs is that they use an internal sensor for temperature compensation. Under load they get warm (not hot!) and think that the battery is the same temperature which its not.

[john61ct]

- real world observations

Thank you!

Originally Posted by rabbi

I have 2 panels 280w (32,2v / 9.2A) each connected to its own Victron MPPT 75/15
...
peak charge output happens rarely even with ***slightly** oversized panels like mine.

To produce anywhere near 280W takes quite a few details: Perfectly clean panels. No shade. Full sun at the right angle. No clouds or mist. That doesn't happen often in the real world.

Peak production during a normal day is closer to 230-240W and even that is just for a few moments. Which the 75/15 handles well.
...
Given the price difference between the 15A and the 30A controller I would certainly suggest to go for the 15, at least with a 290W panel.

Exactly the points I've been trying my best to make and feels like just getting ridicule back.

[newhaul]

Originally Posted by rabbi

My real world observations on a cat with very little shading:

I have 2 panels 280w (32,2v / 9.2A) each connected to its own Victron MPPT 75/15, both feeding the same house battery bank.

Observations:
The peak charge output of this controller is 15A each, but this happens rarely even with slightly oversized panels like mine.

To produce anywhere near 280W takes quite a few details: Perfectly clean panels. No shade. Full sun at the right angle. No clouds or mist. That doesn't happen often in the real world.

Alignment is never perfect, and good only around noon time on my boat (I could tilt the panels but I never do). There is dust on them (sahara dust in the Med) and I clean maybe once a weak.
Peak production during a normal day is closer to 230-240W and even that is just for a few moments.
Which the 75/15 handles well.


Also keep in mind: The battery needs to accept the charge. Solar charge typically starts around 7am in the Med, and my batteries are full by 11am latest. Two hours later when the perfect conditions for my solar panels arrive the available energy is just waisted (OK, in my case it's redirected to the cockpit beer fridge).

Given the price difference between the 15A and the 30A controller I would certainly suggest to go for the 15, at least with a 290W panel. A 30A controller will add very little unless you go for much more panel area.



The only thing that I dislike about the Victron MPPTs is that they use an internal sensor for temperature compensation. Under load they get warm (not hot!) and think that the battery is the same temperature which its not.

Ok so 24 volt panels. Your specs dont seem correct to me 280 watts/ 24 volts = 11.8 amps which is just fine for the 75/15 controller if you have a 24 volt battery bank . With a 12 volt bank that is 23+ amps which would mean you are maxing the controller for most of the day. No wonder your bank is full early and your controller is in overheat mode.
Editeven with your estimated 230 watt output that is still over 19 amps with a 12 volt battery bank.

[john61ct]

Originally Posted by rabbi

Peak production during a normal day is closer to 230-240W and even that is just for a few moments. Which the 75/15 handles well.

So you're saying the 75/15 is actually outputting peak amps at or above 16A? Since the critical specs aren't even close to being exceeded, that tilts things even more in favor of over paneling. IMO

Originally Posted by rabbi

Solar charge typically starts around 7am in the Med, and my batteries are full by 11am latest. Two hours later when the perfect conditions for my solar panels arrive the available energy is just wasted (OK, in my case it's redirected to the cockpit beer fridge).

Is that a holding plate unit? How do you hold off charging that until the bank is full? Also, how is Absorb hold time set on your Victron?

Do you use a battery Monitor as well?

Originally Posted by rabbi

The only thing that I dislike about the Victron MPPTs is that they use an internal sensor for temperature compensation. Under load they get warm (not hot!) and think that the battery is the same temperature which its not.

Yes, it would be nice to compare for Voltage variation between the 75/15 and a larger unit with external sensor wire.

I suspect the advantage of one panel per controller overcomes the temp comp issue.

Thanks so much again for chiming in!

[rabbi]

Originally Posted by newhaul

Ok so 24 volt panels. Your specs dont seem correct to me 280 watts/ 24 volts = 11.8 amps which is just fine for the 75/15 controller if you have a 24 volt battery bank . With a 12 volt bank that is 23+ amps which would mean you are maxing the controller for most of the day. No wonder your bank is full early and your controller is in overheat mode.
Editeven with your estimated 230 watt output that is still over 19 amps with a 12 volt battery bank.

your 12v / 24v assumption is a bit oversimplified

I have a 12v Trojan battery bank, which is charged @14.8v bulk as per spec, and 16.2v for equalizing.

15Amps x 14.8v is 220W.

The question is: how often will the panel produce more than 220w? The real world answer is: On rare days for maybe an hour around noontime but only if I cleaned the panels with fresh water the same day and if there is absolutely no shade.


The 280W panel rating is valid only under controlled conditions that nobody can ever reproduce in a real world installation on a boat.

After a few year the panel's production will be lower anyway. Aging of solar panels does happen, even if its just tons of micro scratches from cleaning all the dust and salt crystals.

[rabbi]

Originally Posted by john61ct

So you're saying the 75/15 is actually outputting peak amps at or above 16A? Since the critical specs aren't even close to being exceeded, that tilts things even more in favor of over paneling. IMO

I have never seen charge output in excess of 15A, but it seems to produce a bit more if you also use the load output (like 13A going to the battery and 3 A going to the fridge).

Originally Posted by john61ct

Is that a holding plate unit? How do you hold off charging that until the bank is full? Also, how is Absorb hold time set on your Victron?

No, just a BDF 35 with a normal plate. But if you add enough beer it acts like a holding plate :-) .

I run the fridge only if battery voltage exceeds 13.2v which is slightly below float voltage to take care of the temperature compensation (as said its over-compensating because its warmer than the battery). Unfortunately Victron does not want to add a function to burn only surplus energy (i.e. switch on the load when entering float mode). So there is a little on/off cycling on cloudy days but thats a rare thing (they do have a few minutes delay between on and off so there is no heavy instant cycling of the load).
To reduce / remove the cycling I could couple the voltage switch in the solar controller with the State-Of-Charge relay of the BMV battery monitor but this seems like overkill ( I have the wiring in place, but feel no need to do this as it just plain works).

The beer fridge is large (it could easily cope with two 21y old nephews visiting us), the beer is ice cold (3-4 celsius) in the evening and still OK (9-10 celsius) in the morning.

Absorption time on the Victron is set to 6h max, but the controller calculates the actual absorption time by itself, depending on minimum voltage and charge time.

Originally Posted by john61ct

Do you use a battery Monitor as well?

Yes, BMV with the bluetooth Dongle to extract data

Originally Posted by john61ct

Yes, it would be nice to compare for Voltage variation between the 75/15 and a larger unit with external sensor wire.

I suspect the advantage of one panel per controller overcomes the temp comp issue.

I don't consider this a huge issue. As the temperature compensation kicks in and the charge rate is reduced, the temperature of the controller falls and gets closer to the battery temp so the difference get smaller.


Overall I think that 280W panels are a good fit for the MPPT 75/15. I'd rather spend money on 350w panels than on a MPPT 100/30. As said, the panels will age over time and will eventually no longer be able to make full use of the controller.