Suggestions for hooking them up?

softdown · October 2016

     Roof is a 1/12 slope making it an almost flat ~6% grade. According to PVWatts, both the east side and west side should yield over 900 KwH/year....per side. The two, newer and more efficient, southern facing panels at 45 degrees should yield over 700 KwH/year. Total KwH/year from all three banks = Over 2500 KwH/year.

     Thought about running them all into the Renogy 40 amp 24 volt MPPT charge controller. Now thinking that each bank should likely have its own charge controller. I have five 24 volt charge controllers...no shortage. Three are Zantrex PMW, one is a Morningstar PMW (currently hooked up), and one is a Renogy MPPT (currently hooked up).

     The Voc on these panels runs from 40 volts to 44 volts depending on conditions. This is a 24 volt system using a Cotek PSW 1500 watt inverter. I have other inverters but I would prefer to sell one and have the other for back-up.

     Battery banks: 1650 lb forklift battery in good condition......12 two volt cells
                               850 lb diesel locomotive battery in fair/good condition......12 two volt cells
                               850 lb diesel locomotive battery in fair/poor condition.......12 two volt cells (four cells are not prime...voltage~2.0 instead of 2.2-2.4)

     I have a lot of used BP 150 watt panels. Lots of charge controllers.

     Usage: Freezers and refrigerators...frozen food is worth plenty.

     All of these panels are ~32" x 62" in size. Five inch cells with VoC ~42. East and west panels are 150 watts/each. Souhern panels are 180 watts/each.

     NOTE: The west bank is not hooked up yet. Waiting for more MC3 connectors to finish the wiring.

mcgivor · October 2016

Not claiming to be an expert, here is some information I gathered whilst researching.

PV arrays for MPPT should consist of panels of identical size and manufacture oriented in the same plane and direction and are more tricky to set up sizing than PWM.

PWM allows for mixed panels of different wattage in parallel as long as the outputs are similar within reason and therefore more forgiving.

PWM requires larger cables as the voltages are lower, can get expensive over longer array to controller distances, less than 50' still reasonable.

Depending on geographic location the benifits of MPPT could be insignificant, for example in tropical it is less, assuming the aforementioned distance is kept short, in cold climates MPPT take advantage of the higher efficiency of the PV array being cooler.

Personally I have no practical experience with MPPT as based on my findings, my choice was PWM. No doubt there is other information missed but a choice had to be made at some point.

If you have PWM controllers, more than one inverter a mixed batch of panels and frozen food is worth plenty, perhaps redundancy would not be a bad idea.

Simplicity has a quality of its own.

BB. · October 2016

If these are all Vmp-array~36 volt wired array--Just stay with a PWM controller is option one. As Mcgivor says, keep it simple.

If you want to try an MPPT charge controller (more output in sub freezing weather--Or wire for higher voltage/less voltage drop/smaller awg wiring from array to charge controller)--Why not try it with all 3 strings in parallel.

Get a DC Current Clamp Meter (like this one from Sears) and measure the current from each string. Also measure the Vmp-array with a volt meter (while battery bank is charging, controller in Bulk mode). See if you get the amount of power/energy expected. If cell temperatures are reasonably close together (10-20C or less differential), then the Vmp-temperature dependent is not too far apart.

One old time poster here who had a lab and designed MPPT charge controllers--His answer was to ALWAYS have a separate MPPT controller for each separate/different plan solar array for optimum harvest.

-Bill

Raj174 · October 2016

I remember a post where someone put 2 equal east/west arrays on one MPPT controller. I believe this method is called virtual tracking. Might be worth a try.

softdown · October 2016

Raj174 said:

I remember a post where someone put 2 equal east/west arrays on one MPPT controller. I believe this method is called virtual tracking. Might be worth a try.

This "virtual tracking" has a pretty big fan who is also a mod at an Australian solar board. My memory is a bit fogged by now but he thought that an MPPT controller could handle these three strings (all the panels are the same size and similar output).

Then we have this advice from BB: "One old time poster here who had a lab and designed MPPT charge controllers--His answer was to ALWAYS have a separate MPPT controller for each separate/different plan solar array for optimum harvest."
A designer of MPPT controllers ought to know what he is talking about.

I am using the MPPT controller on the east facing bank. It was initially wired with 10awg for the last run...which is ~10'. I would kind of prefer to keep using the 10awg because it is now almost inaccessible and runs through a very crowded hole in a 12" wall. The east bank is most able to take advantage of very cold morning temperatures...it can reach -30F here. So, two reasons to utilize the MPPT on the east bank.

I have three clamp meters and have never been able to get reliable readings from using the clamp. I...kept trying and have now given up on clamp meters for the time being.

I don't have a problem with using a different charge controller for each string. It seems logical to do so. I continue to be moderately perplexed with how to best use the three separate 24 volt battery banks. The purists will scream bloody murder but I am tempted to simply run ~2/0 jumper cables with monster clamps to take advantage of all three....if the plan backfires, it is easy to remove monster clamps. Lowering the load on any battery. Yes....this would be mcgivored for sure. They sit outdoors....too heavy to bring indoors.

Otherwise...the thought of running all three charge controllers to one battery sounds like the electronics in each charge controller would be "fighting" the other charge controllers.

It is somewhat mcgivored to be sure. These are all pretty much "leftover materials" from unrealized ambitions.

westbranch · October 2016

on the contrary... ...the thought of running all three charge controllers to one battery sounds like the electronics in each charge controller would be "fighting" the other charge controllers.

You have to synchronize the offsets for voltage on each controller, if they have that, and sett all the charge parameters the same , then if you see one out in the bushes, adjust its settings... ... essentially they should all go into Absorb an Float at nearly the same time... Each CC 'sees' the battery independently and acts accordingly...

Suggestions for hooking them up?

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