Question for the Solar Panel experts????

[scanzel]

There is some Kyocera panels on ebay at a good price the 130 watt TM or GT 12volts. I have a 24 volt agm battery system with a Magnum 4024 inverter. I can mount 6 panels on my roof, this would be 720 watts of power. How do I connect these panels to give me what I need to charge my battery bank? Series or series parallel? Charge controller will be a 3024i. Any information appreciated, still learning.

[HB of CJ]

You can do it.  It's easy.  Wire two (2) 12 vdc panels to product 24 vdc, then wire the three sets of 2 to produce still 24 vdc again, only with more amperage.  As far as the PV panels go, exactly what kind of panel are they?  Makes a big difference.  Reason I ask is that 36 cell panels are probably the way to go, with the rare hi temp 38 cell panels also being an option.  Depends upon the application.

Would stay away from the older 35 and still older 32 cell panels.  I don't know if they are even still available, but older used stuff still comes up for sale all the time.  Understand that the AGM batteries will REQUIRE a special charging profile which I DO NOT understand.  Perhaps others will help out here.  Important that the PV panels, the charger profile and the batteries all talk to each other.   

[Tenor]

You will need a solar controller too.  It ties in between the solar panels and your batteries.  It will keep your solar panels from cooking your batteries.  I have done some research, but I am a newbie to the systems.  There are 2 different types of controllers.  Look up Outback solar equipment and Northern Arizona Wind and Sun Solar equipment on google.  They have some good postings.  Also, do a search on this board for "Solar Controllers".  Good luck!

[Sean]

Lots to answer here.

Steve, I'm not sure what you consider a "good" price.  I briefly checked out Kyocera panels on eBay and all the ones I found are going for what I consider an "average" price.  FWIW, "good" these days is probably $4.50 per watt, average is just over $5 per watt for name-brand stuff (Kyocera, Siemens, etc.).  For six 130-watt panels (780 watts) less any goodies like mounting hardware, installation, etc., I would definitely not pay anoy more than $5 per watt, or just under $4k, plus shipping at no more than, say, $15-20 per panel.

With all deference to my friend Henry from Cave Junction, AGM batteries do not REQUIRE (emphasis his) special charge profiles.  In fact, one of the beauties of AGM is that they work just fine on a flooded battery profile.  Henry might be thinking of gel batteries, which are very sensitive and require a lower charge voltage than flooded batteries.  AGM batteries will deliver better performance in the long run if your charger has an AGM-specific profile, but the difference is minor.

Also with deference to Tenor, a charge controller is not necessarily required, especially if you have a very large bank, and the amount of solar is only a little more than required to overcome self-discharge and phantom loads.  This is the case in our installation, where our 330 watts of panels barely keep up with the fridge.

That being said, there are advantages to having a charge controller even if you don't need one.  One of those advantages is the ability to match panels of one nominal voltage to batteries of a different nominal voltage.  I recommend the Blue Sky MPPT models, which will optimize the power delivered from the panels at all times.  Your 780 watts might be just a hair too much for their smallest 24-volt model, which is rated for 30 amps.  You could probably get away with it, though, as panels almost never deliver their maximum rated wattage -- the best we ever get out of our "330 watts" is about 7 amps at 24 volts.  If you're nervous about it, go to the next size up.

And, yes, if you have nominal 12-volt panels, you want to pair them up in series to deliver "24" volts, whether you use a charge controller or not.  I would suggest a parallel arrangement of three pairs, each pair in series, rather than the other way around.

HTH,

-Sean
http://ourodyssey.blogspot.com

[H3Jim]

With deference to Sean, (who has more electrical knowledge in his pinky than I have in total), I submit that a charge controller, especially one of the MPPT controllers such as the 3024i, provide more power from a given set of panels no matter the battery bank size, or what you have connected. The charge controller is particularly effective at boosting current in marginal (when you need it most) situtations.  Such as when the sun is setting.

Below is a snippet from the Blue Sky website that talks about the extra amps available using their technology.  If this is true, its like getting more panels for free.  At the very least, you need to have a diode or something in between your batteries and the panels to prevent current drain when there is little or no sun.  As relatively inexpensive as this unit is compared to the panels, I think use of this module is a "no brainer".  Also from their website, the max size of panels  the 3024i should be connected to is 800 watts, more than the panels you are contemplating.  They also have several other technical articles about panel / battery / controller matching that you should read prior to purchase.   

If I recall correctly, I paid around $4.60 a watt for my panels new, no sales tax, no shipping, from a guy in Yuma, AZ.  While thin film is available for less per watt, it also takes up more roof real estate, so for me it was not as attractive an option.

http://www.blueskyenergyinc.com/index.htm


A photo voltaic (PV) module is a constant current type device. As shown on a typical PV module voltage vs. current curve, current remains
relatively constant over a wide range of voltage. A typical 75 watt module is specified to deliver 4.45 amps @ 17 volts @ 25°C cell
temperature. Conventional PV controllers essentially connect the PV array directly to the battery when battery is discharged. When
a 75 watt module is connected directly to a battery charging at 12 volts, the module still provides approximately the same current.
But, because output voltage is now at 12 volts rather than 17 volts, module power production is artificially limited and the 75W
module only delivers 53 watts. This wastes 22 watts of available power.
Solar Boost 3024i's patented MPPT technology operates in a very different fashion. Under these conditions Solar Boost 3024i
calculates the maximum power voltage (VMP) at which the PV module delivers maximum power, in this case 17 volts. It then
operates the module 17 volts which extracts maximum available power from the module. Solar Boost 3024i continually recalculates
the maximum power voltage as operating conditions change. Input power from the maximum power tracking controller, in this case
75 watts, feeds a switching type power converter which reduces the 17 volt input to battery voltage at the output. The full 75 watts
which is now being delivered at 12 volts would produce a current of 6.25 amps. A charge current increase of 1.8 amps or 40% is
achieved by converting the 22 watts that would have been wasted into useable charge current. Note that this example assumes
100% efficiency to illustrate the principal of operation. In actual operation, boost will be somewhat less.

[H3Jim]

And a link to an  article on what is a charge controller and why it's needed.


http://www.blueskyenergyinc.com/homepower1.htm

[Sean]

With deference to Sean, (who has more electrical knowledge in his pinky than I have in total), I submit that a charge controller, especially one of the MPPT controllers such as the 3024i, provide more power from a given set of panels no matter the battery bank size, or what you have connected.

Yes -- that's why I recommended one even when not strictly necessary.  I did say they provided "advantages ... even if you don't need one ... [including to] optimize the power delivered from the panels at all times."

I also specifically recommended the Blue Sky and suggested that I thought the 3024i would work even though the panel output could, under ideal circumstances, approach the 30-amp rating of that unit.

Sorry if I was not clear that this is the principle reason to invest in a charge controller when not otherwise required.  Also, let me be clear that a charge controller is mandatory when the normal output of your panels exceeds the resting discharge rate of your battery bank, otherwise, as Glenn mentioned, you can cook your batteries.

-Sean
http://ourodyssey.blogspot.com

[HB of CJ]

Sean, thank you.  Senior mental moment on my part.  I also got mixed up (in my mind's eye) describing a CHARGE controller when I meant to say a PV voltage/controller/regulator.  If your rooftop PV panels produce a significient high enough voltage, they will fry/boil "dry" (?) your expensive AGM batteries.

For some reason, I was thinking of a gen set recharging the batts, NOT PV panels.  Still, what I meant to say is that with PV panels that are NOT regulated to the batts, you can and will create a situation in full sunlight that the panels will produce too high of voltage for the batts.  There, finally got it right? (?)

Therefore, by implication, perhaps what you will ACTUALLY need are PV panels that are more price attractive towards the total wattage and in particularly amperage and not necessarily overly high VOLTAGE that you will not be able to use with your AGM batts.  Wow, more wine please?