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Post by mikesd on Sept 17, 2016 8:23:13 GMT -8
First things first. I'm an electrical engineer, albeit not a power person. I have a good understanding how all this works, and how to calculate currents, wire sizes, power needed, etc. My problem at this point is trying to understand some of the specs in the manuals on this site.
Second, this is an academic project for me. I'm looking to build a quality system. Not particularly looking for places to find low cost batteries or cut corners. My questions are academic in nature.
I'm beginning a solar power project that is roughly going to be a 2000-3000 Watt system, with inverter and batteries. I will ultimately use a 24 or 48V battery setup, depending... Goal is four panels (maybe five) and batteries (24V or 48V) to run 2000-3000W inverter.
* two 12V in series for a 24 system (may parallel another bank, or two, like this) * four 12V in series for a 48V system (may parallel another bank, or two, like this)
But I will be starting slowly and adding as I go, to learn the system.
I may start with two 12V batteries in parallel and just a single PV panel, but as I build it, will move to more batteries to a 24V or 48V system. I want a system that has plenty of storage, to account for no sun days, so it may be an overkill on batteries. And I know, since I haven't specified loading throughout the day, or peak loading and such, a lot of flags are going up. For this exercise, that really isn't important at this point, since my questions are related to charging the batteries, not the load. I will work the loading to fit my system. That is, I'm not going to build a larger system, if my loading is more. And I'm not shrinking the system, if my loading is less. But I want to get the controller and inverter chosen at the beginning, to make expansion easier. I will probably just make one jump from one panel to four or five and two batteries to whatever I calculate will be needed.
I'm looking at 100W panels, so I guess I will be 400W with four and 500W if I use a fifth, for charging. So my system will be 400W-500W input and 2000-3000W output.
My first question is regarding the controller/charger. I see that Renogy has couple that I'm looking at.
* Commander (Renogy 60A) * Tracer (Renogy 40A)
Aside from the 40/60 difference
* what are the differences in these two series? Looks like the Commander might be software controllable? * Why would one choose one over the other? * It looks like the Tracer is for 12/24 systems. Does that mean a 48V battery setup isn't possible with this controller? * What are limits on number of PV panels? * The manual list parameters "Maximum Solar Input Power". I'm a little confused by this spec, since this looks like the power output of panels, that is input to the controller charger. But PV panels don't come in neatly packed 12, 24, 36 or 48V outputs. So that's confusing. Most are 18V range. So, I'm confused about what this spec really is.
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Post by rabird on Sept 19, 2016 4:45:28 GMT -8
first the manufacture's manual for the 60A www.epsolarpv.com/en/uploads/news/201512/1449042525937914.pdfpage 10-11 may be helpful. Note the 150v input limit for series panels is really 138v @ rated 25C temps panels are rated. At very cold temps the panel's Voc increases. 12v panels have a Voc of ~23 for a max of 6 panels (138/23) in each series string. can parallel multiple strings. Their chart suggest max of 4 for 12v system, I assume this is due to the 'bucking' efficiency from 138v down to 12v! charging 12v battery 800 watts is all the controller will 'produce' so going much above 800 watts of panels is not needed, the controller will limit input if you go over 800 watts, spec is up to 2400 watts input. Have more than 800 watts panel can allow for more power in poor light conditions. Consider 60 cell '24v' panels (Voc ~38). 138/38 yields 3 in series, 1600 watt charging max @ '24v'. same number of 60 cell panels in series for 48v with 3200 watt charging @'48v' (misprint of page 11!) 24v system, so for 60 cell say 240 watt panels, 3 in series, 2 or more strings of 3 in series in parallel. 720 watts per series string, 2 strings in parallel would be 1440 watts total. if you intend on a 24v system, there is no need to use '12v' panels, 60 cell '24v' panels are available at a better price/watt. |
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Post by mikesd on Sept 19, 2016 10:23:45 GMT -8
I guess one thing that was confusing me was calling the panels 12V when they are actually ~23 (oc) output and typically in the 16V-17V output under load. Guess the 12V is really a designation for what type of systems they are meant to charge.
So let's get back to my 1st question. Just to make it equivalent, say I was talking about a 24V battery system. What would be the pros/cons of a Commander over the Tracer series, and visa versa?
And, if I did decide to go with a 24V system, I guess it makes sense to use 24V panels. Any pros/cons to a 24V panel over 12V, and visa versa. Looks like I would have a higher charging power, so with the 24V panels, I could charge the batteries quicker? Whenever I gain something, I look for even-steven to balance out. What would I lose, if I had a 24V battery system, and went with 24V panels? |
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Post by rabird on Sept 19, 2016 18:06:52 GMT -8
look at the IV/power curve in the manual Figure 1-2 Maximum Power Point Curve A 12v panel has a couple of volts overhead. the peak power changes with light and temp so to charge at 14.6v for a 12v battery the panel must have over head for voltage drop from the panel to controller and the changes in Vmp with panel heating.  12v cells are 36 cells and '24v' are generall 60 cells, note not double so you'd likely use 24v panels in series with MPPT to exceed 2 * 14.6v charging. I'm not comparing controllers. There are many brands, Morningstar has a nice string calculator string-calculator.morningstarcorp.com/ which incorporates temperature. nice read www.victronenergy.com/blog/2014/07/21/which-solar-charge-controller-pwm-or-mppt/then be sure and read the white paper linked at the end of the article. |
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