24vdc Solar to 12vdc Battery Bank

[witzgall]

Yep, this is why we have two 24v panels, wired in parallel. 24v to the controller for lower line loss, Paralell wiring between panels to reduce the effect of any shading.

Chris

Originally Posted by idpnd

By putting the panels in series, you end up with a higher voltage and lower current. Lower current means less loss in the wires between your panels and the inverter. Downside for in series is if any of the cells in either panel is shaded you lose the output of both panels. In parallel only the panel with a shaded cell stops working.

http://www.cruisersforum.com/forums/...tml#post344058

[senormechanico]

Originally Posted by hellosailor

" the MPPT Bluesky controller goes into the MPPT phase during the day."
MPPT controllers in general, and the BS for sure, don't "go into" a special phase at all.

I just got a BlueSky MPPT controller and it does indeed "go into the MPPT phase" when there's enough solar power to make it advantageous to do so.
You hear a relay click and the "load" light comes on when that happens.
If there's not enough power to do that, it reverts to a PWM series regulator.

It states this in the manual.

[ChuckSK]

A typical panel has 36 cells, divided into 2 sub-panels, each with 18 cells. Each 18 cell sub-panel has a shunt diode across its output. If a cell in a sub-panel is shaded, the voltage drop across the shaded cell will cause the shunt diode to turn on, thus bypassing the sub-panel.

The result is that in a series string of panels, any shaded sub-panels are bypassed. The voltage of the string is reduced, but only by the voltage in the bypassed sub-panels.

For example: four 130 watt panels in series (8 sub-panels) with no shading produce 520 watts. If 1 cell is completely shaded, then that sub-panel is bypassed, leaving 7 sub-panels producing power. The output would be 455 watts (7/8 *520 = 455). There is a small loss across the bypass diode (7 watts) leaving a total output of 448 watts.

If the four panels were in parallel, 1 shaded cell would reduce the voltage of 1 panel by half. That panel could never contribute to the output. The resulting total output would be 390 watts.

This example assumes a 100% shaded cell. Partially shaded cells produce somewhat different results, but in very few cases do the results favor parallel connections.


On a slightly different subject, MPPT controllers are most efficient when the difference between the panel voltage and the battery voltage is least. That would indicate parallel panel connections would be favored. With no shading, parallel would be best.

Except! Because of higher voltages, the series connections seem to turn on earlier in the morning and stay on later in the evening. I have not tested the total amp-hours produced by series vs. parallel, but my panels are connected in series.


Another issue is the frequency the MPPT controller calculates the maximum power point.
With a boat swinging at anchor and the shade moving across the panels, it is important that the MPPT calculations are frequent. I use a Xantrex XW MPPT 60.

Chuck

[hellosailor]

Steve-
Sounds like they've "new and improved" things in the past year or so. What model controller is that? It sounds like that "click" is actually a relay engaging/vs/bypassing the entire controller, so that there's zero power loss to operate the controller (when it is out of circuit) when the panels are putting out barely enough voltage to charge the battery. Not a mode change, per se, but simply bypassing the whole thing, I'd guess. (Which might be a clever idea.)

[senormechanico]

It's a Blue Sky Solar Boost 2512iX.

[hellosailor]

Very interesting, Steve. That is a "new" model, and totally unlike their previous ones. On reading the manual, they are very clear about it being 3-stage--but they don't go into programming it for battery capacity, etc. the way their older higher-capacity units have to be set up. It makes me wonder if this is really MPPT technology, or "just" a smarter version of a 3-stage. Have you done any charging cycles with a voltmeter hooked up, to see if the output shifts in three discrete levels, rather than continuously changing amperage and voltage over time?

i.e. page 8 of http://www.blueskyenergyinc.com/uplo..._BSE_SB2KE.pdf

With the IPNPro-Remote Blue Sky Energy Inc. | IPN-ProRemote or the ability to otherwise monitor amperage as well as voltage, "MPPT" and "three-stage" become very visibly different, even if they are referring to bulk-vs-float "stages" elsewhere.

[Windsun]

The Blue Sky controllers are analog MPPT, nearly all others such as Outback Power, Xantrex, and Morningstar are digital. In general, the digital controllers track and convert the power coming from the solar panels better and more efficiently under less than perfect conditions. On the other hand, analog is cheaper and easier to manufacture.

[Masquerade]

Hummingway,
this is a good question and one that I am interested in because it appears to me that many of the 24 volt panels are somewhat cheaper than the 12 volt panels for the same output. I may be wrong in this perception but as I am currently looking around for bits and pieces to power the boat your question is very relevant.

Now because my ignorance is greater than my knowledge or experience here could someone explain the MPPT in a little more detail. If have 2,3,4 batteries (12 volt) can it pander to the needs of each? Secondly, how does it integrate with a wind turbine should I get one?

I prefer the parallel arrangement of solar panels in principle because of the redundancy if nothing else, but, here again, would welcome comments, advice, wisdom

The maximum distance between panels and batteries will only be about 6 metres so, if using the correct wire, there should not be any significant reduction at the batteries/inverter (I think but I did say this is based on ignorance.)
Colin

[goboatingnow]

On a slightly different subject, MPPT controllers are most efficient when the difference between the panel voltage and the battery voltage is least. That would indicate parallel panel connections would be favored. With no shading, parallel would be best.

I dont see your reasoning here. solar panels are most efficient outputing at a certain voltage depending on sunlight values, see panel I/V curves. with modern DC DC convertors efficiencies are approaching 98%, a lot of MPPT controllers actually drop out when the panel voltage comes close to the battery voltage.

There seems to be a fundemental mis-understanding of MPPT. Firstly MPPT has nothing to do with battery charging, it doesnt define that the controller is a 1,2,3 or anystage charger. MPPT means that the controller tracks the maximum power output point of the panel. This is because solar panels do not have a constant I/V realtionship, there is a knee in the curve, for various sunlight levels, there is an optimum panel voltage whereby at that voltage maximum current is extracted from the panel.

Becuase the MPPT point voltage is often well away from the charging voltage the controller then needs to convert the panel voltage to a suitable battery charging voltage, this is done by using a DC-DC programmable convertor, essecially a switch mode power supply. After that is the battery charging control phase, MPPT controllers have vary degrees of charging sophisication.

[senormechanico]

Originally Posted by hellosailor

Very interesting, Steve. That is a "new" model, and totally unlike their previous ones. On reading the manual, they are very clear about it being 3-stage--but they don't go into programming it for battery capacity, etc. the way their older higher-capacity units have to be set up. It makes me wonder if this is really MPPT technology, or "just" a smarter version of a 3-stage. Have you done any charging cycles with a voltmeter hooked up, to see if the output shifts in three discrete levels, rather than continuously changing amperage and voltage over time?

i.e. page 8 of http://www.blueskyenergyinc.com/uplo..._BSE_SB2KE.pdf

With the IPNPro-Remote Blue Sky Energy Inc. | IPN-ProRemote or the ability to otherwise monitor amperage as well as voltage, "MPPT" and "three-stage" become very visibly different, even if they are referring to bulk-vs-float "stages" elsewhere.

Mine's the SB2512iX which is quite different. For example, it has no adjustment pot of any kind. It needs to be programmed externally if you want different parameters. It sure sounds like a digital unit to me.

So far, we've not had any sun to speak of, although for January, the Seattle area has had an average temp of over 47 degrees!

I did manage to stick a voltmeter on the PV input leads today during a brief bit of filtered sun with the 'load' light on. I think this indicates MPPT operation vs. PWM series regulation. Anyway, it lights at about 1 A to the batteries, and goes off at about 0.8 A. While the battery voltage was 14.2V, the panel voltage was 19.5V.

I like to think of an MPPT controller as an electronic version of a continuously variable speed transmission.

Here's the manual for mine.
Let me know what you think.

http://www.blueskyenergyinc.com/uplo...E_SB2512iX.pdf

[ChuckSK]

goboatingnow

Simply look at the efficiency curves published by MPPT controller manufacturers.

Chuck

[goboatingnow]

BTW , as I undertsand the "Load" indicator and relay on the BlueSky unit is to do with the second charge outlet. WHen the controller has space capacity from the solar panel, that isnt needed to charge the main batteries it swicthes on the load led and closes teh relay. It doesnt indiacate the it is or isnt charging the main battery

[Masquerade]

Is it possible for someone to produce a diagram of what is needed. It seems to me that the physics should be relatively straightforward but the jargon, knowledge or whatever seems a little beyond me and yet I know I will have to address this in the future.
Could someone produce or refer me to an annotated diagram starting with the panels and ending at the batteries.
MPPT controller, DC-DC programmable convertor, a switch mode power supply...
Ignorance is not bliss
Colin

[cal40john]

Originally Posted by Masquerade

Is it possible for someone to produce a diagram of what is needed. It seems to me that the physics should be relatively straightforward but the jargon, knowledge or whatever seems a little beyond me and yet I know I will have to address this in the future.
Could someone produce or refer me to an annotated diagram starting with the panels and ending at the batteries.
MPPT controller, DC-DC programmable convertor, a switch mode power supply...
Ignorance is not bliss
Colin

Hook solar panel to terminals labeled panel on the charge controller, hook terminals labeled battery on charge controller to battery. Done.

If your charge controller is MPPT, then it has inside of it a DC-DC converter which in other words is a switch mode power supply. You don't have to know what that means unless you are interested. What it does get you is that you get more of the power from the panels into your battery than you would if you used a different controller. Also you only get this added benefit if your batteries are discharged enough that the charge controller is trying to put as much as the panel outputs into the batteries as the panels can generate. If it is in a current limiting mode i.e. acceptance or float, then it is deleberately throwing away power to not overcharge the batteries, so won't be in MPPT mode.



I thought this wasn't too bad of an explanation of MPPT
Increase efficiency of street-light solar panels using a maximum peak-power tracker | Power Management DesignLine Europe

The details get more complicated if you have more than one panel to connect and multiple battery banks that you want to charge. In that case, it depends on what your priorities are, there isn't one answer.


John

[Windsun]

Originally Posted by Masquerade

Hummingway,
this is a good question and one that I am interested in because it appears to me that many of the 24 volt panels are somewhat cheaper than the 12 volt panels for the same output. I may be wrong in this perception but as I am currently looking around for bits and pieces to power the boat your question is very relevant.

Not all 24 volt panels are really 24 volt panels

Look at the spec sheet, a true 24 volt panel will have a Vmp of around 34 volts. A lot of the "24 volt" panels are made for grid tie systems, and are actually more like a 23 volt panel.

And a lot of the higher voltage panels are much larger physically, which can be an issue on a boat.