Solar Charging

[wildblue]

 I'm new to solar energy and trying to find out how much power I should be getting from my pv panels. I have 2, 255 watt, 5 amp, 48 volt panels wired in parallel to a bank of 8 12v batteries also wired 48 volt. My charge controller is a Xantrex C-40 and my inverter is a Xantrex XW6048. My first question is how much power can I expect from my panels on a sunny day. (Amps, watts.) My second is more complicated. My C-40 doesn't seem to be passing the full current of the panels through to the batteries when charging, but when I put a load on the inverter the C-40 passes the full amps to the load. For example my amp meter will read 2 amps on a sunny day when charging batteries but when I put a 400 watt load on the batteries the amp meter will rise to 6 amps. My batteries are not fully charged when I do this so shouldn't the C-40 pass the full current to the batteries until they exit the bulk stage of charging? I've read all the books that came with the equipment and can't find an explanation. Any help would be appreciated.

[Watt]

I'm new to solar energy and trying to find out how much power I should be getting from my pv panels. I have 2, 255 watt, 5 amp, 48 volt panels wired in parallel to a bank of 8 12v batteries also wired 48 volt. My charge controller is a Xantrex C-40 and my inverter is a Xantrex XW6048. My first question is how much power can I expect from my panels on a sunny day. (Amps, watts.) My second is more complicated. My C-40 doesn't seem to be passing the full current of the panels through to the batteries when charging, but when I put a load on the inverter the C-40 passes the full amps to the load. For example my amp meter will read 2 amps on a sunny day when charging batteries but when I put a 400 watt load on the batteries the amp meter will rise to 6 amps. My batteries are not fully charged when I do this so shouldn't the C-40 pass the full current to the batteries until they exit the bulk stage of charging? I've read all the books that came with the equipment and can't find an explanation. Any help would be appreciated.

Welcome aboard.

It sounds to me like your load brings the battery voltage down and allows the panels to produce rated power at lower than battery charge voltage.  What I mean is, as battery SOC voltage raises, your panels produce less power.  Have you put a voltage meter on the batteries and tested at all stages mentioned above?

I hope you are not confusing the c40 as a MPPT controller.  Can you give a bit more panel information such as brand, Voc, Vmp and so on?

[XeonPony]

First you do realize it is rar to get more them 90% of the rated power out of the pannel? And depending on where you are tilt angle and azmith will effect out put as will time of day and air qualities right?

That said as batery volts go up amps to the battery goes down with a non Mppt charger, 48v pannel to 48v battery = 0A
You all ways need the charge source to be higher then the battery being charged! Hence the reason you need a controler to clamp the voltage at the ideal point so you don't cook the batteries

Do some more (Ok Allot) reading up on the forum here to get a base understanding of solar, then chances are you'll answer your own question, and if not you'll be able to frame your question more percisely with the benifit of better comprehension of the answer!

[Frank S]

Do some more (Ok Allot) reading up on the forum here to get a base understanding of solar, then chances are you'll answer your own question, and if not you'll be able to frame your question more percisely with the benifit of better comprehension of the answer!

10-4 on a lot of reading

[wildblue]

A lot of reading indeed. I've been at it for 2 weeks and am just scratching the surface. My panels are Canadian Solar CS5P-255Ms. They have a VMP of 49v an IMP of 5.21a and a VOC of 59.8v. When I disconnect the panels from the batteries and test the panel volts I get 55v on a sunny day. The SOC voltage of the batteries without a load hangs around 55v and with a load, 52v. I am aware that the C-40 is not an MPPT and am looking into getting one. I have my system set up so the current from the panels can go directly to the inverter/loads when needed so that's why my amps rise under load. (C-40 acting as load control basically.) As I understand XeonPony my panels will never get the batteries to the bulk voltage of 57.6v without an MMPT charger right? Would wiring my panels in series solve this? (Be patient with the new guy .) Many thanks for the help. More reading (a lot) for me.

[Watt]

A lot of reading indeed. I've been at it for 2 weeks and am just scratching the surface. My panels are Canadian Solar CS5P-255Ms. They have a VMP of 49v an IMP of 5.21a and a VOC of 59.8v. When I disconnect the panels from the batteries and test the panel volts I get 55v on a sunny day. The SOC voltage of the batteries without a load hangs around 55v and with a load, 52v. I am aware that the C-40 is not an MPPT and am looking into getting one. I have my system set up so the current from the panels can go directly to the inverter/loads when needed so that's why my amps rise under load. (C-40 acting as load control basically.) As I understand XeonPony my panels will never get the batteries to the bulk voltage of 57.6v without an MMPT charger right? Would wiring my panels in series solve this? (Be patient with the new guy .) Many thanks for the help. More reading (a lot) for me.

No worries on being patient, some got it, some don't.  You need answers now and I understand as while you are reading, your batteries are taking some abuse. 

I'm afraid you will be needing to series the two panels and go MPPT via the best controller you can afford.  If you do series without MPPT, you may find you only get ~275 watt/hr but you will be able to charge the batteries indeed although at a substantial panel loss and I don't know what kind of voltages the c-40 is capable of controlling.  I can preach Midnite Solar but unless you are going to continue to add the same panels of the same type to your array, there are other controllers out there that may better suit your need with just these two panels at nominal 510w.  I say this because at 48 nominal volts float will need just over 52 volts as you mentioned.  Bulk and absorb are even higher than that, not to mention equalizing stage.  So far, you don't have near the voltage needed to do anything more than what you have discovered.   At this stage, you may have enough voltage to keep your batteries from ruining so long as you have another source to completely charge your batteries.  I'd suggest that you do just that and put the system on hold until you can better configure your panels for actual battery charging or do the above scheme for a substantial loss.  At best, you have a grid tie set of panels if you have an inverter which can track that voltage and current into the grid.

As far as what you will get from your panels, right now you may actually only get ~300 watt/hr from your set, while with mppt you could get over panel ratings of course depending on your complete system layout.   What is the amp/hr rating of your battery set?  If your group is too large, your available power ( as configured at the moment ) may only be enough to maintain your battery group.  So, at the moment, this advice is nothing more than a guess.

Glad you asked now instead of waiting and wondering why your batteries will no longer produce voltage as label rated.  Good luck.

[XeonPony]

He'll only get less power as the voltage rises on the batteries due to their internal resistances rejecting the additional power driving the voltages up, then the C40 will start to pwm it down.

MppT will be very good for your system, I run my pannels at 44Voc or 33 Vmp to charge my 12v bank for a 48V bank you need 50 Vmp or better my tristar recomends 52Vmp if I recall correctly higher makes for better ability for equalization.

you need to pull up data for your batteries as well to configure the set points for the absorption rate and such

Now you need to make sure the C40 can handle the input voltage with the pannels seriesed. but don't put to much on the current flow just means the batteries are fairly charged.

[wildblue]

That's exactly what I wanted to know and is very much appreciated. The C-40 can handle up to 125vdc so I'll wire my panels in series and then get an MPPT charger. I'm completely off grid but have been charging my batteries every 2-3 days with a generator so I can maintain them until I get my system set up and working right. My batteries are wired with 4 sets of 2 106 amp-hour batteries wired in parallel (essentially making 4 12v, 212 amp-hour batteries) and then those wired in series for 212 amp-hours total. (Not sure if I explained that right.) I have the bulk charge set to 57.6v and the float set to 54v.  I intend to get 2 more of those same panels and then wire them series/parallel. Is that enough to keep my battery bank charged? Seems like it would be, at least in the summer.

[Watt]

He'll only get less power as the voltage rises on the batteries due to their internal resistances rejecting the additional power driving the voltages up, then the C40 will start to pwm it down.

MppT will be very good for your system, I run my pannels at 44Voc or 33 Vmp to charge my 12v bank for a 48V bank you need 50 Vmp or better my tristar recomends 52Vmp if I recall correctly higher makes for better ability for equalization.

you need to pull up data for your batteries as well to configure the set points for the absorption rate and such

Now you need to make sure the C40 can handle the input voltage with the pannels seriesed. but don't put to much on the current flow just means the batteries are fairly charged.

How is he going to get the batteries to rise?  For bulk stage he needs more voltage than his panels will produce with any usable current!

The range he needs is 52.+ to 60.+ not even temperature compensated could be even 62.+ volts and so on. 

I gotta be confused with what you are saying in this post.  Are you referring to his current configuration working?  Then, going on to MPPT later in your post?

[birdhouse]

i didn't read all the responces past 49Vmp...  your panels produce their best at 49v.  you have a 48v system, so once you hit absorb  58v??, you've fallen off the panels curve. 

IE:  you have heavy hitter panels for bulk charging, but less than ideal panels for equalize ect...

adam

[Watt]

I don't think these are even great bulk panels, he reads 55Voc.

That's ~2.29v per cell 0 amps. 

[birdhouse]

i missed that part. 

i think you're best bet is to put those two panels in series with a new charge controller.  mppt. 

problem is a cheap mppt that can handle atleast 110Voc. 

tristar mppt-45 comes to mind, especially if he's gonna add two more additional panels. 

good thing he's using a genny to keep his batteries from getting low!

adam

[Watt]

That's exactly what I wanted to know and is very much appreciated. The C-40 can handle up to 125vdc so I'll wire my panels in series and then get an MPPT charger. I'm completely off grid but have been charging my batteries every 2-3 days with a generator so I can maintain them until I get my system set up and working right. My batteries are wired with 4 sets of 2 106 amp-hour batteries wired in parallel (essentially making 4 12v, 212 amp-hour batteries) and then those wired in series for 212 amp-hours total. (Not sure if I explained that right.) I have the bulk charge set to 57.6v and the float set to 54v.  I intend to get 2 more of those same panels and then wire them series/parallel. Is that enough to keep my battery bank charged? Seems like it would be, at least in the summer.

As far as your battery facts, losses and so on....  Just one of many possible links for reference.  http://www.windsun.com/Batteries/Battery_FAQ.htm  At this stage, you just don't have much wattage to use as for loads and battery maintenance.  You definitely need a usage scheme and careful considerations. 

[wildblue]

Thanks for the link Watt and I agree about the usage scheme. I'll wire my panels in series tomorrow and see what I get from that set up with the C-40. MPPT on the way soon!

[Watt]

Thanks for the link Watt and I agree about the usage scheme. I'll wire my panels in series tomorrow and see what I get from that set up with the C-40. MPPT on the way soon!

Have fun for sure.  However, I don't want to mislead you with this system. 

As temperatures drop, your Voc will go up and could potenially damage the c-40 if your voltage goes beyond that 125v you have stated for being safe.  If you get a good MPPT, you will not need that c-40 and I would definitely look into something beyond 125v as your Vin could reach 130v in cold mornings.  I'm not sure where you live, but even in West Texas where I live, my Vin gets dangerously close to putting my Classic in HyperVoc.

Also, as your gap between charge voltage and Vin increases, your system efficiency decreases.   

[DamonHD]

Also, as your gap between charge voltage and Vin increases, your system efficiency decreases.

Sorry to butt in, and I've probably misunderstood, but is that true for MPPT at all?  Indeed the reverse may be true at the bottom end once there is reduced proportional diode and wiring losses on the high side...  Tell me why I'm wrong!

Rgds

Damon

[Watt]

Also, as your gap between charge voltage and Vin increases, your system efficiency decreases.

Sorry to butt in, and I've probably misunderstood, but is that true for MPPT at all?  Indeed the reverse may be true at the bottom end once there is reduced proportional diode and wiring losses on the high side...  Tell me why I'm wrong!

Rgds

Damon

Damon

Without this comment looking like an argument, how can we efficiently charge a 48v battery from 125v?  While the voltage as at or slightly higher than battery voltage, 100% clamping or near can take place but as the gap grows, the time spent clamping that voltage decreases to keep panel voltage at Mpp and to keep battery voltage at what ever voltage is required per charge stage.  Modulating that voltage comes at a price and larger the gap, the less efficient that transition will be. 

[bob g]

sorry i have to also ask, probably because i misunderstand the assertion
or read something into it?

as the differential widens the efficiency goes down?

if by differential widening you mean the difference between the battery voltage and the panel voltage widening, wouldn't a mppt take advantage of this spread and covert this spread to additional amperage?
generally accomplished by a buck converter and controlled by the microcontroller?

or are you referring to this drop in efficiency with this spread if you are using a standard charge non mppt controller such as the C40?

if the latter is the case, i understand, if however it is the former
i really don't understand?

thanks
bob g

ps. not trying to be argumentative, just trying to understand the "group" understanding of just what "mppt" really is and what it does.

[birdhouse]

according to morningstar with their tristar mppt series, watt is correct.  the greater the difference between solar array and battery volts, the less efficient the transition is. 

http://www.morningstarcorp.com/en/support/library/TSMPPT.IOM.EN.04.pdf

adam

[wildblue]

Thanks for the link Watt and I agree about the usage scheme. I'll wire my panels in series tomorrow and see what I get from that set up with the C-40. MPPT on the way soon!

Have fun for sure.  However, I don't want to mislead you with this system. 

As temperatures drop, your Voc will go up and could potenially damage the c-40 if your voltage goes beyond that 125v you have stated for being safe.  If you get a good MPPT, you will not need that c-40 and I would definitely look into something beyond 125v as your Vin could reach 130v in cold mornings.  I'm not sure where you live, but even in West Texas where I live, my Vin gets dangerously close to putting my Classic in HyperVoc.

Also, as your gap between charge voltage and Vin increases, your system efficiency decreases.   

I wired my panels in series this afternoon and got 104.6 volts. When I connected to the batteries I got 4 amps. Much better than previous setup. I live in west-central Idaho so I will have to watch my Vin on cold mornings. I'll get an MPPT with some voltage headroom as well.

according to morningstar with their tristar mppt series, watt is correct.  the greater the difference between solar array and battery volts, the less efficient the transition is. 

http://www.morningstarcorp.com/en/support/library/TSMPPT.IOM.EN.04.pdf

adam

True but according to the chart at the very bottom of the tristar manual (unless I'm reading it wrong) there is only a 2% efficiency difference between 98vmp and 52vmp.

[XeonPony]

No matter what ya can't go wrong with a morning star! and at 104v the thing will be a very happy unit! I recomend spend the extra and get the 60A version, you will not regret  it in the long run!

[thirteen]

Hey wild blue I have a place near Grangeville, Id. I'm headed there to night I got three days off where are you located.

[thirteen]

I used to live in Emmett, ID but know I am in Butte, Mt but plan on retiring next May and going up to live back in the woods. I turn off at the bottom of Whitrbird hill and go back in to Joesph plains area, You must be down near or below New Meadows or maybe lower Council. Just guessing.Later MntMnROY

[boB]

as the differential widens the efficiency goes down?

This is generally true for the charge controller hardware.

BUT, the system or "net" efficiency can be higher than the extra loss of the charge controller itself just
because of wiring losses and/or array operation and/or controller tracking efficiency  etc.

boB

[Watt]

as the differential widens the efficiency goes down?

This is generally true for the charge controller hardware.

BUT, the system or "net" efficiency can be higher than the extra loss of the charge controller itself just
because of wiring losses and/or array operation and/or controller tracking efficiency  etc.

boB

Thanks boB, you have done well by teaching me this stuff.   

I wasn't trying to make a mountain out of a bucket of dirt, I was just trying to say that there are losses with the most being not able to harvest power ( as was configured ) vs. series and clamped to battery voltage.  Mppt, does have losses associated ( even if 2% is nothing ) and he may see some when he goes that route.  I didn't elaborate on the Classic due to his having 510 watts of panels.  However, since he has now mentioned installing more panels, he very well should consider the Midnite Classic and at least check the specs.

[wildblue]

I'm looking at the TriStar MPPT-45 charger because of the 150vdc capacity (haven't looked at Midnite yet). Advice?

[boB]

I'm looking at the TriStar MPPT-45 charger because of the 150vdc capacity (haven't looked at Midnite yet). Advice?

They are both good controllers.   The Classic will put out more power most likely but 45 amps may be enough
for you.  Since the Classic Lite is coming out, the price of it may be even better but I'm not sure of the street price
of either the Lite or the MPPT-45.

boB

PS, I am biased towards the MidNite but I have to admit that I believe the TriStar MPPT is also a very good controller.
And they are also very nice people.

[Watt]

I'm looking at the TriStar MPPT-45 charger because of the 150vdc capacity (haven't looked at Midnite yet). Advice?

MidniteSolar.com

Check out the Classic simulator, Classic sizing chart and also their forum.