300W 36V panel with MPPT controller for a 12V bank: does it make sense?

[Lagoon4us]

750 watt x 36volt, GSL MPPT Controller 400 amps LITHIUM, it sings.....

[noelex 77]

Originally Posted by Wellington

Could I possibly "make do" with that VICTRON 70V/15A, that costs less than 1/4 of a 150V/45 or 60A?
Victron Energy Blue Solar MPPT 70/15 Solar Regulator
Would the only drawback be an electricity production limited to 15A rather than a maximum theoretical 25A? Or would it fry?

I think goboatingnow is wrong and this is a completely unsuitable controller for 300w (with a 12v battery)

However, most controllers will not be damaged by exceeding their current specifications. They just self limit to protect themselves (in this case to maximium of 15A output)

I have not checked this is the case with the Victron but I would be surprised if this was not what happens.
So, no it would not fry, but a maximium of 15A from 300w is very limiting and will cost you a lot of AHrs.


For this size panel the Rogue would be my choice:
Rogue Power Technologies

Rogue are about to release a new model so if you can wait I suspect the new model will be even better.

[sailorboy1]

Originally Posted by Wellington

Could you please tell me how many Amperes you typically produce around noon?
Also, may I ask what the dimensions of your panel are, and how much you paid for it? Thanks

the other day with the batteries at 90% the system was putting out 22amp at about 14V at noon otherwise it normally is doing less as the batteries are charged by noon on sunny days

77"x44"

$286 US

[Wellington]

Originally Posted by noelex 77

However, most controllers will not be damaged by exceeding their current specifications. They just self limit to protect themselves (in this case to maximium of 15A output)

I have not checked this is the case with the Victron but I would be surprised if this was not what happens.
So, no it would not fry, but a maximium of 15A from 300w is very limiting and will cost you a lot of AHrs.

With a potential 24A from the panel, do you think the VICTRON 70V / 15A would keep delivering 15A (instead of, say, 19A around noon on a partly clouday day), or would it switch off? If it doesn't switch off, and if I accept the loss of Ah, I understand that I could get a flat 15A from, let's say 10am to 4pm, correct?

[noelex 77]

Originally Posted by Wellington

With a potential 24A from the panel, do you think the VICTRON 70V / 15A would keep delivering 15A (instead of, say, 19A around noon on a partly clouday day), or would it switch off? If it doesn't switch off, and if I accept the loss of Ah, I understand that I could get a flat 15A from, let's say 10am to 4pm, correct?

Yes I would expect it deliver 15A rather than switch off, but sometimes, particularly at higher ambient temperatures, the thermal management is insufficient for continuous maximum output, especially when the input exceeds the design parameters.

I really don't feel this is a good idea. You will waste a good deal of power and are operating the controller outside its specifications, relying on its self protection mechanism, with unpredictable results.

The manufacturer lists the maximium solar panel size for this controller as 200w (with a 12v battery). 300w is not wise.

[Wellington]

Originally Posted by noelex 77

Yes I would expect it deliver 15A rather than switch off, but sometimes, particularly at higher ambient temperatures, the thermal management is insufficient for continuous maximum output.

I really don't feel this is a good idea. You will waste a good deal of power and are operating the controller well outside its specifications, relying on its self protection mechanism, with unpredictable results.

You're right. And I can live with 15A, produced by a smaller panel. If I build my system around this VICTRON 70V / 15A (the only MPPT model I have found in Panama City) what would be the highest power you would recommend for a 36V panel?
I'm a bit confused because the Victron website indicates that the maximum PV power for this controller is 400W in 24V. So 300W in 36V shouldn't be a problem... What am I missing?


Maximum battery current 15 A
Maximum PV power, 12V 1a,b) 200 W (MPPT range 15 V to 70 V)
Maximum PV power, 24V 1a,b) 400 W (MPPT range 30 V to 70 V)
Automatic load disconnect Yes, maximum load 15 A
Continuous/peak load current 15A / 50A

[noelex 77]

Originally Posted by Wellington

You're right. And I can live with 15A, produced by a smaller panel. If I build my system around this VICTRON 70V / 15A (the only MPPT model I have found in Panama City) what would be the highest power you would recommend for a 36V panel?
I'm a bit confused because the Victron website indicates that the maximum PV power for this controller is 400W in 24V. So 300W in 36V shouldn't be a problem... What am I missing?


Maximum battery current 15 A
Maximum PV power, 12V 1a,b) 200 W (MPPT range 15 V to 70 V)
Maximum PV power, 24V 1a,b) 400 W (MPPT range 30 V to 70 V)
Automatic load disconnect Yes, maximum load 15 A
Continuous/peak load current 15A / 50A

The confusion is understandable.

Like all controllers this model has a limited capacity for current. With a 24v battery the output current is half that of a 12v battery for the same wattage solar panels.

So the controller is rated for a maximium of 200w solar panels if you have a 12v battery and 400w solar panels if you have a 24v battery.

Using a 300w solar panel with a 12v battery is well outside the maximum specifications.

[Wellington]

Originally Posted by noelex 77

The confusion is understandable.
The controller has a limited capacity for current. With a 24v battery the output current is half that of a 12v battery for the same wattage solar panels.

So the controller is rated for a maximium of 200w solar panels if you have a 12v battery and 400w solar panels if you have a 24v battery.

Using 300w solar panels with a 12v battery is well outside the specifications.

Thanks for the clarification. I believed 24V was the PV tension, not the battery bank, hence the confusion. Now it makes sense of course. So 200W is what this controller could handle for a 12V battery

[s/v Jedi]

Originally Posted by Wellington

Thanks for the clarification. I believed 24V was the PV tension, not the battery bank, hence the confusion. Now it makes sense of course. So 200W is what this controller could handle for a 12V battery

If it can handle a 12V battery at all; I believe most Victron gear is not selectable for battery voltage but another model instead.

[Opie91]

Originally Posted by Don L

the other day with the batteries at 90% the system was putting out 22amp at about 14V at noon otherwise it normally is doing less as the batteries are charged by noon on sunny days

77"x44"

$286 US

The real question:
Is it keeping your beer cold like you wanted???

[roetter]

The Victron MPPT 70/15 spec sheet says this:

- Battery voltage 12V or 24V auto selecting
- Maximum battery current 15A
- Absorption voltage for 12V batts 14.4V
- Float voltage for 12V batts 13.8V
- Charge algorithm multi stage adaptive
- Maximum power solar panel 200W (12V battery) 400W (24V battery)
there is a foot note for this last statement saying:
"If more PV power is connected, the controller will limit input power to 200W resp. 400W"

PV=Photo Voltaic

I wish more people would read the online manuals and not speculate.

So here you are:
If there is more than 200W available for charging from the solar panels, then the charger will limit itself to 200W. Since your panel will rarely deliver more than 200W with the heat correction factor in tropical locations, I don't think you are giving up much. Most of the day the sun will not be vertically over the panel, so you get less output.

I had a 950W solar installation and never saw more than 650W being delivered by the Outback charger. The Outback charger records a lot of data for each day for the last 128 days, so one can go back and look at the maximum output for every day.

On temperature: My installation (5 panels in series) had an open circuit voltage (VOC) that slightly exceeded the 145V maximum. Only on one very cold day (less than 10 Celsius) did the Outback complain about over voltage. Throwing a towel over one panel dropped the VOC and the load kept it low enough once we removed the towel. This is just to say that it requires cold temperature to reach the maximum rated power of the panel. On top of that the panel has to be facing the sun directly.

Your panel will be rated for 300W at 25C panel temperature. In Panama you can expect at least 50C panel temperature. At about 0.5% decrease in panel efficiency for every degree C over 25C, you loose about 12% or 36W. Now consider losses for the panel not being perpendicular to the sun and you quickly reach the 200W.

My suggestion. Go for it. You will be happy.

[sailorboy1]

Originally Posted by Opie91

The real question:
Is it keeping your beer cold like you wanted???

yes

plus even some sandwich makings to go along with the beer, and some steaks and burgers in the freezer, and coffee cream, bacon, eggs, and soda, +++++

In the end no one really cares about solar panels and controllers; all that matters is whether the beer is cold! All this other techno BS just distracts one from the real goal.

[noelex 77]

Originally Posted by roetter

I had a 950W solar installation and never saw more than 650W being delivered by the Outback charger. The Outback charger records a lot of data for each day for the last 128 days, so one can go back and look at the maximum output for every day.

You should be doing much better than this at least as a peak output. I think it is worth examining your system connections etc for a fault.

To give you an example my system is 330w. This was the result from today, nothing spectacular, just an average summers day, but you can see peak of 300w or 23.2 amps. (This would corresponds to about 860w for your system a long way above 650w and this is just a typical day, not the best)

I would also suggest being very careful about exceeding the maximium voltage input for the controller. They can be damaged by be damaged by an even very brief voltage that higher. The Outback will be damaged immediately if you exceed 150v. In some conditions the panels will exceed their STC outputs. Most manufacturers recommend a significant safety margin and suggest a Voc well below the the maximium input voltage.

[hlev00]

Originally Posted by Wellington

Also, do you have a recommendation for a small output, 36V-compatible MPPT controller? The VICTRON 70V/15A is rather cheap and would be ideal if it could deliver more than 15A. The VICTRON 150V/60A (or MORNINGSTAR 150V/45A) are much heavier and expensive.
I guess I would need a 25A model as the 36V 300W panel I'm considering delivers 8,31A (i.e. potentially 24,93A into my battery bank, if I got it right).

Check out Genasun. I think they can handle that voltage. If the online specs don't show it, call and they might be able to customize a stock version.

[goboatingnow]

Noelex is right in that the controller is rated for battery voltage, I should have spotted that

dave