I am trying to decide between the classic 150 or the 200. My panels are 59.8 vmmp 78.8 voc. If I go with the 150 I will have to use one panel in series if I go with the 200 I will go with two in series. 4000 watts of panels. Is 59.8v enough for a 48v battery? The online calc seems fine with it, but why does the calculator add 2V to it? Is it better to have close to charging voltage coming in or as high of voltage as the controller can handle?
Thanks
Dave
these are the rough guidelines for charging,
12 V needs ~17 volts to cover all losses etc. from PV to battery
24 V needs 38 V
48 V needs 64 V...
simple, at anything less you do not get a proper charge!
those grid tie panels don't make it in single panels, you need 2 in series...
Quote from: BigCountry on September 22, 2015, 08:39:35 PM
I am trying to decide between the classic 150 or the 200. My panels are 59.8 vmmp 78.8 voc. If I go with the 150 I will have to use one panel in series if I go with the 200 I will go with two in series. 4000 watts of panels. Is 59.8v enough for a 48v battery? The online calc seems fine with it, but why does the calculator add 2V to it? Is it better to have close to charging voltage coming in or as high of voltage as the controller can handle? Thanks
Dave
Hi Dave,
You really have no choice. You would need strings of two of these PVs, and that is not a good fit with a Classic 150.
You have run the String Sizer, so you must know that for your coldest temperatures, that the Classic 200 will probably not ever be in Hyper Voc, or, at least not very often, or for a long period of time ... guessing, we know very little about your situation.
4,000 watts of PV might be a little bit much for a Classic 200, but the String Sizer, with good data to work with will indicate the recommended Classic model and judge if the amount of PV is excessive.
FWIW, Vic
Thanks for the input, any idea why the sizer tool shows it is fine with 1 panel in series? I am also trying to grasp exactly how all this works together, why is there a limit to how many watts of panels? Won't the classic only draw the amperage that it is set for? With the current cost of panels vs the other equipment wouldn't it be wise to oversize the watts of panels even if the max potential is never used?
Dave
Hi Dave,
First, the Sizer seems to be primarily checking for max Voc, and output current verses the model of Classic entered.
The concern that the Sizer does not seem to check for minimum Vin has come up before. BUT, the Sizer knows about the characteristics of the Classics, but there are many vagaries of individual systems that this program cannot know, and this data, if entered into the sizer by the user, might create many more questions than could be easily answered ... at the edges of system design there is a lot of grey, and few absolutes, and so on.
The Classic manual may go into the minimum requirements for the PV input ... forget.
By far, the string configuration errors, seem to have been mostly on trying to run too high Vin, especially on other brand CCs, with an absolute maximum input voltage of 150 V.
Regarding over PVing CCs by a huge amount, and letting the CC Limit the output current; This can overwhelm the CC's ability to protect itself in a Fault condition, and will tend to increase the operating input voltage by a large amount, due to the PVs, often being lightly-loaded. This light loading causes the PVs to approach the Voc, for the temperature of the PVs at that time. This, generally causes CC to be considerably less efficient, making them run warm or HOT for long periods, even at fairly light loads.
So, using the Sizers recommendations, perhaps as a maximum recommendation.
Also, there are environmental temperature conditions that should affect just how much over PVing should be used.
I am just a member here, and the MidNite Engineering and Tech/Sales folks do not seem to be too concerned about reasonable over PVing MidNite CCs, and the temperatures in which their CCs operate, but, this simply cannot be too good for any Power electronic devices, IMO.
This kind of become my mantra, as have designed systems that have fairly high string Vmp, and at times with a bit too much PV power, but in these cases, try to choose a cool place for the power electronics and batteries, or using A/C in the power room.
EDIT, I should add that, Opportunity Loads can help load the CC, and then, in turn the CC will add loads on the PVs, when the battery charging is done or mostly done. This will reduce the input voltage to the CC when there is unused PV power.
Opportunity loads are; pumping water, heating water, running A/C or heat pump, and so on.<
Just my opinions, Vic
Thank you for the detailed replys. I apprieciate the time to help me understand. I will be using opportunity loads hopefully direct to the panels bypassing the controller. I was only planning on 3500 watts but ended up with 3920, and possibly another 2600. I can't help the whole go big or go home mentality untill i start pricing the other parts to go with the panels, mostly the batteries. Lol. I may not keep the additional panels or find a way to use them direct to load.
Dave