Question about MPPT and a single solar panel

System

I am new to the RE world and like so many others have become addicted. I am trying to figure out if I will see any benefit from using a MPPT charge controller if I only have a single 130 watt solar panel?
My Current configuration is:

1 x Kyocera KC130TM 130 watt panel 17.6V Vmpp, 7.39A Impp
MorningStar SunKeeper 12PWM controller
224Ah 12V Battery Bank

I have been looking at the Blue Sky 2512iX charge controller and wonder if I would see any benefit over my current SunKeeper 12PWM controller?

icarus

Re: Question about MPPT and a single solar panel

Probably not worth the effort on it's own. If, on the other hand you are thinking of adding on in the future, an mppt controller would be helpful. I use the same BS 2512ix controller and I am very happy with the harvest. I get somewhere between 10-20% better harvest during bulk charging. As my battery approaches full, the advantage begins to be lost. It also is better in cold weather.

Having said all that, if I had to do it over again, I would consider a different controller. The 2512 series will only take 12vdc (nominal) input, so even if you have a number of panels, you can't run them at a higher series voltage to reduce line loss. Also, there is not a lot of 'headroom' to grow my system. 25 amps of 12vdc doesn't allow a lot of room to grow,,,in my case none. 200 watts and I am up against the ceiling on a cold clear day.

Icarus

PS. To some extent, the answer lies more in what is it you expect from your system. If your current configuration works well, then the answer would certainly no. If, on the other hand, you ALMOST get fully charged every day but not quite, then you might be able to make the case, but for the ~$200 you spend on the controller, perhaps you can get another panel which would put you way further ahead.
T

n3qik

Re: Question about MPPT and a single solar panel

If you do not plan to add more panels, then no, stay with what you got right now. If adding more panels later, then it is worth a look at.

System2

Re: Question about MPPT and a single solar panel

icarus and n3qik, thank you for the quick reply! I literally just got the expanded battery bank today so I will need to use it for a while to see how it pans out. I had a 28Ah battery before that was just not enough power since I am trying to stay above 20% discharge. I had a feeling MPPT would not give me a lot until I get more panels. And of course we all know I will cause just like potato chips, you can’t have just one! But for now I will be happy with what I have.

icarus

Re: Question about MPPT and a single solar panel

Just to contradict my previous note,

One ADVANTAGE of the BS controller is the availability of a remote temperature sensor. This can add considerably to the longevity of the battery. Especially if you have a very small battery bank, it MIGHT make sense to use a temp control. ( I don't believe that a temp control is available for your controller)

It is also possible that the efficiency curve of the mppt controller drops off significantly with small battery/small panel configuration, you might want to look at that.

Tony

PS. My wife gets really upset with me when I argue both sides an argument!

niel

Re: Question about MPPT and a single solar panel

tinysolar,
with your expanded battery bank you have a need for expanded pv as the charge rate from that pv will be 7.39a/224ah=3.3%. it is best to get to at least 5% for charging if you can and that's about 11.2a and closing in on your 12a limit. that sunkeeper does have the ability to have an rts that i'd advise for you to get.

Moe

Re: Question about MPPT and a single solar panel

icarus wrote: »

...there is not a lot of 'headroom' to grow my system. 25 amps of 12vdc doesn't allow a lot of room to grow,,,in my case none. 200 watts and I am up against the ceiling on a cold clear day.

Tony, the Blue Sky 2512i is rated for up to 340W of panels, such as four KC-85s in parallel, each putting out 5.0A Imp with a 25% boost to 25A.

Why are you maxing out the 25W output with 200W of panels?

Thanks,
--
Moe

icarus

Re: Question about MPPT and a single solar panel

Moe,

I'm not sure you have the math correct. (I don't have the spec. sheet in front of me, and I am away from home fora bit so I don't have the hardware in front of me either, so this is from memory.)


If you take your 340 watts of panel @ 12vdc you end up with ~28 amps.
340 watts @ 14.6vdc ~23.23 amps

So if you take the former example, you are already over the max rated for the 2512 series.

In the latter, the 23.23 amps, add in 10% (2.32 amps) of mppt boost and you are right at the limit. Now add some cold weather, snow reflection etc, and you are way too close for comfort.

In my case, real world situation, 210 watts of panel, put out, on a good summer day, routinely put out ~ 15 amps. (I have two ammeters, one on the panel side of the controller, one (Trimetric) on the battery side, so I can see the MPPT advantage just for kicks. Low battery and low temps run ~15% but can be higher. I don't let my batteries get low enough to really get the advantage) Edge of cloud bumps that a bit. Now in the winter with very cold temps, low battery soc, and much reflection off the snow, and I can see 20 amps every now and again. Too little headroom, and not enough room to grow into. I could add perhaps one more ~50 watt panel and still get in under the wire.

In your case, how have you come to believe that the 2512 will handle 340 watts. I confess I may be badly mistaken here. (wouldn't be the first time)
By my rough calcs, the KC85 could out out greater than 7 amps each.

It occurs to me that maybe you are using or considering using 24vdc panels. In that case, your numbers make sense. The only problem is, the 2512 won't accept any other than 12vdc (nom) panel input. (I made the same mistake when I bought the 2512, thinking I could run my panels at higher voltage,,turns out you can only run 12vdc) Looking at the kc 85s they are 12vdc, so I am stuck!

Tony

Moe

Re: Question about MPPT and a single solar panel

Tony, the 2512i(X) owner's manual (first attached picture) puts max watts at 340W STC, max Imp at 20A STC, and max Voc at 28V STC. Elsewhere it puts absolute max Voc at 35V.

The KC-85 specs (second attached picture) gives Imp of 5.02A, four being a hair over the 20A Imp rating, and a 21.7Voc x 1.25 = 27.125 which is under even the 28V STC max, much less well under the 35V absolute Voc max. The 340 watts is 20.8 amps at 17.4 volts. [edit: oops... just noticed the KC-85 is listed at 87W STC... so four are also a hair over 340W].

This seems to be a decent, reasonably priced controller with a much more reasonable capacity than the tiny Morningstar MPPT for someone with a small 12 volt system. The next step up in MPPT is much more than double the price for a FlexMate 60, which is only $40-something less than the 80. On the other hand, the Outbacks are less expensive than two 2512 with IPN. It would be nice if there were a 40A MPPT controller in the $300-something range.

I really appreciate you sharing your cold weather off-grid real-world experience here. I found the post where you detailed your system very enlightening. Must be great to have a pure source of water in that lake!

Thanks again,
--
Moe

icarus

Re: Question about MPPT and a single solar panel

Moe wrote: »

Tony, the 2512i(X) owner's manual (first attached picture) puts max watts at 340W STC, max Imp at 20A STC, and max Voc at 28V STC. Elsewhere it puts absolute max Voc at 35V.

The KC-85 specs (second attached picture) gives Imp of 5.02A, four being a hair over the 20A Imp rating, and a 21.7Voc x 1.25 = 27.125 which is under even the 28V STC max, much less well under the 35V absolute Voc max. The 340 watts is 20.8 amps at 17.4 volts. [edit: oops... just noticed the KC-85 is listed at 87W STC... so four are also a hair over 340W].

This seems to be a decent, reasonably priced controller with a much more reasonable capacity than the tiny Morningstar MPPT for someone with a small 12 volt system. The next step up in MPPT is much more than double the price for a FlexMate 60, which is only $40-something less than the 80. On the other hand, the Outbacks are less expensive than two 2512 with IPN. It would be nice if there were a 40A MPPT controller in the $300-something range.

I really appreciate you sharing your cold weather off-grid real-world experience here. I found the post where you detailed your system very enlightening. Must be great to have a pure source of water in that lake!

Thanks again,
--
Moe

Well said, well documented. As I said, I was responding from memory. I love my 25121x. for what it costs vs what it does it is a pretty good deal. I do wish it were bigger, and that would accept 24 or 48 vdc input. I now run two parallel systems ~200' apart. If I could run the 2512@48 vdc I would only have to run one system. Also, where the house is (and the loads are!) has rather poor solar exposure. If I could move the panels the 200' they would get ~2 hours more sun in the summer, and perhaps a hour more in the winter. Winter is easier since I move the panels out on the ice for ideal exposure. It would be nice if someone would make a ~40 amp, 48 (good) mppt controller.

Tony

RWB

Re: Question about MPPT and a single solar panel

Yea it would be nice if Morningstar made a MPPT CC that handles 30amps instead of the puny 15amps.