Questions on over paneling with Grid Interactive Inverter.

verdigo · September 2014

I currently have 2320 watts of rated PV power and as far as the math is concerned I need around 3500 to make my 46 amps for 464 ah of battery at 48 volts. The other day it was a coolish day in the 60s and partly cloudy with the sun popping out from time to time. The panels were cooler than I have experienced since this is my first year operating my system. I was looking at the Classic's display and seen 2500 watts at 45 amps. By the time I got my phone out to snap a picture I was looking at this.

My plans have been to buy four more 300 watt panels to get to 3520 watts rated power. My question is if left unattended can I hurt my batteries with too much charge current in cold weather or will the inverter dump the extra into the grid? During this summer in full sun I usually see 1700-1800 watts at 30-34 amps

Thanks
Dennis

BB. · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

464 AH / 8 hour charge rate = 58 amps "max" charging current (no remote battery temperature sensor)

I would not be worried--And I would worry less if you have the remote battery temperature sensor connected (reduces charging voltage for "hot" battery bank).

I do have a bit of concern about the 60.6 volt input--On hot summer days, the array's Vmp may depress enough that it will prevent the controller from pulling full Imp from the array on a 48 volt battery bank (i.e., Vmp-array below 58 volts, and battery charging voltage >58 volts).

That 30-34 amp typical charging current may be the result of low Vmp-array working voltage in hot/summer weather.

If these are Vmp~30 volt panels, they should really be setup as 3x series strings for Vmp-array ~90 VDC.

-Bill

verdigo · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

I was calculating 10% of the 464 ah for a 10% charge rate. Am I doing this wrong. The panels are in strings of two 37 volt vmp. The Classic's display input voltage has always dropped when the current has some place to go and without selling with charged batteries will typically show around 80 volts

BB. · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

verdigo wrote: »

I was calculating 10% of the 464 ah for a 10% charge rate. Am I doing this wrong. The panels are in strings of two 37 volt vmp. The Classic's display input voltage has always dropped when the current has some place to go and without selling with charged batteries will typically show around 80 volts

Your batteries should take ~13% rate of charge without issues. And with remote battery temperature sensor, you can go as high as 20%-25% just fine:

464 AH * 0.13 = 60 amps
464 AH * 0.20 = 93 amps

2*37v=74v for Vmp-array should be fine... I would have expected the Midnite to have a slightly higher input voltage -- What is the gauge/length of wire run from the array to the Midnite charge controller--Voltage drop on the high side (could use larger AWG cable)???

Regarding the readings on a typical charge controller--I would trust them within +/- 5% for power/current unless you have double check calibration (charge controller does not need to be more accurate to work well).

-Bill

verdigo · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

The string cables are typical stuff from NAWS 10 AWG no more than 8 ft from the combiner. Combiner to CC 4 AWG. Combiner to battery positive bus in the e-panel, and negative shunt 4 AWG. I just looked at the Classic display and it shows 57v input, 55 battery voltage, 1800 pv watts at 34 amps. The Outback Mate showed 1400 watts AC selling. The Classics input has always shown input a couple of volts above the battery voltage while loaded. I checked the combiner out voltage with a DMM within .3 volts of the Classic's display.

BB. · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

I don't know anything about the internals of the Midnite--But it sounds like there could be a programming/setup issue. The Vmp-array should not really track the battery voltage directly like that.

-Bill

verdigo · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

Now you got me worried. Any Classic users like to chime in? I updated the firmware when I installed the wizzbang jr.

niel · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

BB. wrote: »

I don't know anything about the internals of the Midnite--But it sounds like there could be a programming/setup issue. The Vmp-array should not really track the battery voltage directly like that.

-Bill

that's wrong bill as you must use the battery voltage as a reference. the vmp means nothing if it should fall below the necessary voltage of the battery bank for the idea is to charge the batteries and you aren't sending the power to a resistive load that doesn't care what voltage it is at. go from say a 48v battery bank to a 24v battery bank with the same pv array and cc and the mppt will change again to close to the battery voltage, roughly by that .3v as that is most likely the passthrough voltage loss of the fets and such. it sounds to me like it is doing exactly what it's supposed to do and that is to optimize the current at a usable voltage.

SolarMusher · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

verdigo wrote: »

Now you got me worried. Any Classic users like to chime in? I updated the firmware when I installed the wizzbang jr.

Did you check each PV string vmp at the combiner?
Did you VMM your classic after update?
Why didn't you wire this array with x3 panels per string?

Vic · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

Hi Dennis,

The latest Production Firmware for the Classic, is 1849 4/21/14

Some earlier FW had some Tracking situations, where the Vin could be dragged down to just a few volts above Vbat.
Latest FW, generally does not do this.

Assume that you are running Solar mode on the Classic -- this is generally where the mis-tracks that I've seen occur. Legacy P&O, generally alleviated the tracking issue.

You implied that this could have easily been an edge-of-cloud effect, as this pic shows big power from your array, with this low Vin -- usually, the mistracking represents a significant reduction in power produced, as by definition, the mistrack is NOT at correct MPP.

Have never seen a Classic produce good power vs array size with Vin just a few volts above Vbat, but Edge effects could fairly easily be a cause, in my opinion.

IMO, the Classic might like a bit higher string Vmp than 74 V, but the next step up for strings of 37 V PV, is probably too high.

FWIW, just opinions. Good Luck, Vic

verdigo · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

The CC input is around 2 volts higher than battery volatge. The .3 volt is the difference in the voltage as measured at the combiner output than the Classic's display. It is almost always a couple of volts higher than the battery voltage when the inverter is under a load in full sun.

Vic · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

Hi Dennis,

Well, the fact that your 74 Vmp String voltage gets pulled as low as it appears to, AND, at the same time produce that much power.

I have not ever watched a Hybrid or Grid-Interactive power system do its thing, however.

I know nothing, and that is ALL that I know. Vic

verdigo · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

It really shouldn't matter much whether its hybrid or off grid as all of this is going on in the Classic CC. This is the only solar power system I have ever seen operating so I am not qualified to say one way or the other. There should be lots of Classic users here though. I guess I should ask some questions over at Midnite's forum.

Thanks

Vic · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

Dennis,

There are some aspects of CC Charger settings on Hybrid/GI systems, that have always appeared BIZARROOOOOooooo to me.

We do have some Classic charged systems here, but each and every one of these are off-grid.

PV modules are nominally Current Sources, but this low Vin with the high power output is still surprising to me.

All Solar power systems are basically similar, but they can each be considerably different from others in the small details of operation ... this is all that I was trying to say.

FWIW, Good Luck, Vic

gww1 · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

I looked at my outback cc and the pv voltage was 74 volts on one and about 78volts on the other cc. I was equalizing the battery at 63.4 volts. My aray is three panels in series for 90 volts. I went to the midnight string caculator and my set up was marginal to the 150 volt maximum. Most times I look at the cc's I see a differance and closer to 80 volts. one cc always shows a bit higher incoming voltage. One is a mx60 and one is an fm80. They have identical arays but the mx60 usually runs about 200 watts more then the fm80 and also is the one that has the highest imput voltage.

I would say that midnight and outback are about identical with regards to the operation of mppt. If your production is what you would expect I would say it is working. If you production goes down in the summer due to heat causing the imput voltage to be lower then the battery you may need to rethink the 2 panels in series. I believe there are also efficancy charts on voltage fed to cc's. (to high is not quite as efficiant)

I can't believe that 15% charge rate could hurt batteries that are basically being kept in flote so that you can sell to the electric company. It would seem that the cc would get you to absorb voltage and start cutting amps to the battery very quickly in this situation. Even 25% charge rate for a very short time shouldn't hurt (should it?). I guess if you had an outage and drew the batteries down there might be some worry.

I can't wait to be corrected as I am more then willing to learn.
gww

verdigo · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

Well I am happy I am doing so well at the lower input voltage, but I will go ahead and buy the four more panels I had planned. I will try them out in strings of three to see what works best under the same conditions as best as I can duplicate for a test and report back.

All in all I'm pretty happy to be beating the rated output of the panels thought I suspect they under-rate them to have them perform at 80% after 25 years.

Thanks for the replies
Dennis

boB · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

Came here from the Midnite version of this thread...

Try Legacy P&O mode but this is pretty good output power from that array.
If 80V is with noplace for power to go and/or full battery, then VMPP would be
around 64 volts (80% of Voc) or even lower. It's really hard to say. Might be
hot array or partial shading or maybe SOLAR mode is not the best for
this low Voc array. Remember that label ratings are usually STC (25 degrees C)
and as soon as they get put in the sun, that temperature goes higher and
power and VMP goes down.

Will be interested to see what Legacy does.

boB

mtdoc · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

Just to confirm what others have said. I see about 80% of string VOC (VOCs about 105V) at my classics. Same inverter as you - nothing to do with it being grid interactive. I only see above STC production briefly with cloud edge effects or the rare very cold, sunny days.

verdigo · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

boB wrote: »

Came here from the Midnite version of this thread...

Try Legacy P&O mode but this is pretty good output power from that array.
If 80V is with noplace for power to go and/or full battery, then VMPP would be
around 64 volts (80% of Voc) or even lower. It's really hard to say. Might be
hot array or partial shading or maybe SOLAR mode is not the best for
this low Voc array. Remember that label ratings are usually STC (25 degrees C)
and as soon as they get put in the sun, that temperature goes higher and
power and VMP goes down.

Will be interested to see what Legacy does.

boB

I'll give that a try and see what happens this weekend.

verdigo · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

boB wrote: »

Will be interested to see what Legacy does.

boB

Not sure what "Legacy" Is this found in Setup? I did find in TWEAKS and this statement in the "Just the Facts" manual.
"
LMX LoMax, This enables the Classic to track the input voltage all the way down to Battery voltage. When
disabled the Classic will stop tracking the input around 5 volts above the battery voltage. When the input voltage is
within a couple volts of the battery voltage the inductors can “Sing” this is usually not very loud and will do no harm"

This is set to ON on my CC.

Do I need to re-run Setup to select Legacy mode?

CDN_VT · September 2014

Re: Questions on over paneling with Grid Interactive Inverter.

verdigo wrote: »

Not sure what "Legacy" Is this found in Setup?

This is set to ON on my CC.

Do I need to re-run Setup to select Legacy mode?

Yes I believe you can see it under basic setup , Solar / wind / Hydro area. Going off memory from an old & in the way fluff .

VT

Vic · October 2014

Re: Questions on over paneling with Grid Interactive Inverter.

verdigo wrote: »

Not sure what "Legacy" Is this found in Setup? I did find in TWEAKS and this statement in the "Just the Facts" manual.
"
LMX LoMax, This enables the Classic to track the input voltage all the way down to Battery voltage. When
disabled the Classic will stop tracking the input around 5 volts above the battery voltage. When the input voltage is
within a couple volts of the battery voltage the inductors can “Sing” this is usually not very loud and will do no harm"

This is set to ON on my CC.

Do I need to re-run Setup to select Legacy mode?

Dennis,

You will find Legacy P & O in the Mode menu ... just right arrow from the Charge menu, to find Mode. You will find the different Modes on the right of the screen. Just scroll through them and select.

FWIW, Vic

verdigo · October 2014

Re: Questions on over paneling with Grid Interactive Inverter.

Thanks Vic. I found it. Hope its sunny this weekend.

Questions on over paneling with Grid Interactive Inverter.

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