Local app - the mystery deepens

[dgd]

I did discuss pv voltage with a solar installer on the basis of what we have and the advice was to leave it as it is.  I also ran a  thread on it on "http://www.solarpaneltalk.com" and was advised that parallel or series was swings and roundabouts, with higher line losses at higher currents, plus higher voltages tend to run warmer which means you're wasting watts heating the air.   Also the VOC of our panels = 22, and as the Classic Lite Quick Start Guide tells me the "SOLAR mode is best suited for .... un-shaded PV arrays that are at least one nominal vote above the battery voltage."  As parallel gives me at least one nominal volt above the battery voltage what possible reason should I have for rewiring the array into series?

Ok, unfortunately the solar installer gave you poor advice. Its NOT best to leave it (the PVs wiring) as it is.
Again whoever on solarpaneltalk.com told you parallel and series was swings and roundabouts also was simply incorrect, in your case of using an MPPT controller where panel nominal voltage is same as battery voltage.

Sice you have 3 PVs my simple advice is to wire them in series for a MPV over 50 volts and use the Classic in solar mode.
I have looked at the online Classic quick start manual and I can't find the part about 1 nominal volt above battery voltage. However this makes sense as NOMINAL voltage means 12volts for your PVs and battery so the only way you can get one nominal volt above battery nominal voltage is to series connect at least TWO nominal 12 volt panels or use a nominal 24volt panel.

And that part about higher voltage PVs running hotter and  heating the air is nonsense -  especially in your setup with a mere 240watts of PVs.

OK, I'm sorta worn out on this issue.
Final advice:
1. Update the Classic's firmware
2. Rewire your 3 panels in series.
3. Set Classic into SOLAR mode.
4. Relax     one of those Marlborough Winery tours always did it for me 

dgd

[Halfcrazy]

Viola
I also tire from the constant barrage of over and over negativity towards MidNite. I get the fact our documents are not up to expectations but also you must realize the Classic just like the Outback controller or the Morning Star controller or any others are electrical devices and the manufacturers assume a level of knowledge on the Solar systems as a whole. With that said I am more than happy to help and explain anything that needs explaining all I ask in return is you maybe tone down the negativity in every post please.

As DGD pointed out the statement about one nominal voltage above the battery is true. What that is saying is you have a 12 volt battery so you need a 24 volt "Nominal" panel. the VOC in your case is 22 so the Nominal voltage of those panels is 12v.

I concur with DGD that all 3 should simply be wired in series and all will work very well.
Ryan

[Westbranch]

I believe somewhere in your statements was the fact that you want to add another AP to the system.  If that is the case, it might behoove you to look for a similar Voltage but of slightly higher out put (90W?) and use the 4 panels in 2 parallel/series configuration.

The higher output panel will be tempered by the smaller one to match the output. Thus you would have 2 strings of equivalent voltage (at 24 volts) and more amperage as needed.

If your expansion is greater than that, get all new panels and buy a few extra...

[viola]

Going back to a professional solar installer to tell him that he was fundamentally wrong should be interesting.  It might also be amusing letting the good folks at solarpaneltalk know that according to Midnite they don't know what they're talking about.

Was rather surprised to see this - attached pic - just before lunch, but it only lasted a few moments and the Classic has been limping along at a nice safe 30 or so watts since.

I've wasted too much time on this - the local app panel is just eye-candy anyway.  Even with out-of-date firmware the Classic should still be capable of doing a basic job but patently it isn't.  Best thing I can do is to pull it out and put the Xantrex back with its POTS tweaked to accommodate the AGM. 

We might one day have use for the Lite on one of our less critical feeder sites, and until then it's pretty enough to make a conversation piece as a door-stop.

[viola]

I believe somewhere in your statements was the fact that you want to add another AP to the system.  If that is the case, it might behoove you to look for a similar Voltage but of slightly higher out put (90W?) and use the 4 panels in 2 parallel/series configuration.

The higher output panel will be tempered by the smaller one to match the output. Thus you would have 2 strings of equivalent voltage (at 24 volts) and more amperage as needed.

If your expansion is greater than that, get all new panels and buy a few extra...

Hi Westbranch.  It's only for a couple of weeks either side of mid-winter that power has been potentially an issue for us - and then only in a prolonged spell of overcast weather.    Our radios will run down to 8 Volts and we've a backup system that cuts in when the main battery voltage drops to 11v.  That happened occasionally in previous winters with the Xantrex in the system and I was hoping that the claimed greater efficiency of MTTP would give us a little more elbow-room, but with a new bigger battery anyway I doubt that adding another 1 amp maximum to the draw will give us a problem for 98% of the year if ever.

At our other main stand-alone site -  built to incorporate the lessons learned with our first - we've a 200 Watt pv panel plus a 700 Watt wind generator with the same 235 AH 12v AGM running through an IVT 18318 Controller and have never had anything less than 95% availability, so if we do find we need more power at the other site just adding a wind generator is as far simpler option than rebuilding the frame for the pv panels.  And as I recall we simply set up the IVT according to instructions and it's performed beautifully every since.  It probably hasn't seen the light of day for more than two years.  But then again, it's German of course. 

[dgd]

Viola,

The comments I made about the professional installer was that you received poor advice.
I do not represent Midnite and I am quite capable of defending my views to anyone whose advice is that parallel and serial PV connections are swings and roundabouts. Pure nonsense.
Perhaps the advice you received from these people may have been different if you had explained you were installing a Midnite MPPT controller and you had three parallel wired 12v panels.

I think that if you do indeed use the Classic as a door stop then that really is a poor decision - when all you really need to do is invest a little effort updating the firmware and rewiring your PV junction box.

dgd

[MGP]

Viola, You are quick to shoot down the C150, but you have purchased Chinese floor scrapings for batteries and then use them in a critical situation, have you checked that the batteries are not sulphated??
Why did your supplier not update the classic before it was sold? 1070 is old firmware needs upgrading,

Dgd is on the nail get the basics right, and all will be well in the world ..


MGP

[viola]

Viola, You are quick to shoot down the C150, but you have purchased Chinese floor scrapings for batteries and then use them in a critical situation, have you checked that the batteries are not sulphated??
Why did your supplier not update the classic before it was sold? 1070 is old firmware needs upgrading,

Dgd is on the nail get the basics right, and all will be well in the world ..


MGP

G'day.

No reason to think the battery is defective but there's always the chance the Vendor flicked a duff one onto us.   After all, it seems the Classic must have been sitting on a shelf gathering dust for a terrible long time.  Of course with the Lite there's no way one can ascertain the firmware version until you have local app access.

dgd, I dedicated an hour this afternoon to Googling 'pv: series or parallel' but it seems to me nowhere near as clear-cut as you suggest.   Indeed, it all comes across as somewhat big-enders v. little-enders.  Sure MPPT doesn't work well within a volt or so of the battery charge, but on the other hand it seems too wide a separation doesn't work as well, either.  Most often the argy-bargy came down to suck it and see.

The quote was from the Midnite Solar Classic Lite Quick Start Guide 07/05/12, p.17.  On the same page Midnite tells us:  "If the array has a VOC (Open Circuit Voltage) of less than 125% of the battery voltage Solar mode will not work as well so Legacy will be a better choice."   It seemed from that reasonable for me to assume that a VOC of 180% the battery voltage should be OK in Solar.  Indeed it seems to suggest to me that Midnite have spent a lot of time refining algorithms to work in exactly the kind of low-voltage scenario we have, and I haven't seen anywhere in Midnite's documentation a recommendation that high-voltage/low current is preferable to the reverse.

Our bottom line is that we built our solar-panel frame to cope with the winds sometimes experienced on the hill-tops around here with the result that getting to the junction boxes and re-wiring the panels is NOT an insignificant operation.  Had I recieved any warning from anywhere when researching this upgrade that a change to series would be required I would not have bothered.

Next time I can get back up there I intend swapping the Xantrex back in and if it does as good or better a job of servicing the battery as the Classic - which wouldn't be difficult given its present performance.  If it does ....  anyone want to buy a barely used, possibly dodgy Classic Lite 150? 

[boB]

Viola,  did you try Legacy mode rather than "solar" mode ?

Please give it a try before changing the Classic out for the XW again.

Thanks

[RossW]

Still have to arrange a totally unnecessary trip up the mountain to the device in order to ascertain its registration code so that I can unlock the app and not have to go up the mountain

May or may not assist, but if you can get my newmodbus code onto a supported machine (mac, FreeBSD or Linux basically), it can tell you the serial number of the device and save you a trip up the mountain.

# ./newmodbus -d `cat classic.addr`
Read 2 (data) bytes from addr 28673
Read 2 (data) bytes from addr 28674
Read serial number 5007 from device

[jimbo]

What was the outcome of this?

BTW i use 24v panels with my 24v lead acids in Legacy mode and it works great. I will eventually run them in series but so far it's doing a great job. Some how i feel there are quite a few things wrong with the setup in question.

[zoneblue]

You are using 60 cell panels on a 24V bank? Are you certain? and how do you know it works great?

Most people find that an unworkable arrangement unless the panels are 1foot from the controller, and the controller has top of the line headroom requirements, synchronous rectification etc.

Havin said that though some 60 cell modules actually have vmps up into the 32, 34 range. That will help!

[jimbo]

Well technically they are not 24v panels but that's how they are advertised. The Vmpp is 35.5v. They might struggle in summer when it's hot but the days are so long and sunny it doesn't matter. 

I originally had the controller in solar mode which cut my production a fair bit but so far its great in Legacy.  If i read the Midnite's efficiency graph they seem to be the most efficient when the input voltage is closer to the output voltage. The gain might be negated by the higher voltage drop i will be seeing through my cables.  By the way my panels are a good 30m from the controller and before the classic i was using a simple PWM (Plasmatronics) controller.

[zoneblue]

Well technically they are not 24v panels but that's how they are advertised. The Vmpp is 35.5v. They might struggle in summer when it's hot but the days are so long and sunny it doesn't matter. 

Yes, the 12/24v labal has long outlived it usefulness, if it ever had any.
Also true about summer. If you study the IV curves the power falls off much quicker above vmp than it does below. The real challenge may be holding absorb if you set point is higher eg 29+.

I originally had the controller in solar mode which cut my production a fair bit but so far its great in Legacy.  If i read the Midnite's efficiency graph they seem to be the most efficient when the input voltage is closer to the output voltage. The gain might be negated by the higher voltage drop i will be seeing through my cables.  By the way my panels are a good 30m from the controller and before the classic i was using a simple PWM (Plasmatronics) controller.

30m is quite a bit for 30V. When you double the voltage you quarter the power loss. What size cable are you using? Im fairly sure you will be losing more in the cable than in the controller.

[jimbo]

My absorb voltage is 29.4v but temperature compensated drops that to 29.2 (off the top of my head).  It doesn't like to equalize in summer with much load on the system.

I haven't actually measured the cable size (i did not install the system) but i'm sure there will be a small loss. I have been meaning to change all the wiring but never get around to it.