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Nickel-Iron technology Off Grid Solar Power

Q19: Adding a third Solar String

Let's add the third solar panel string to the power house.

A view of the steel posts and steel joists bolted to make room for a third set of solar panels.

A view of the space from above.

What the new solar panels will look like.

How the new panels looked, when placed up.

View under the panels, not hooked up yet. Will do two in series and two in parallel.

The third MPPT box, is on float already because of wrong settings. The wires are done OK and screwed in, but program settings need to be done.

A view of all three MPPT boxes, 1, 2, and 3.

The Victron may require updates.

Like so

Set the user defined voltages for all three MPPT boxes as showm

  • absorb 33 V
  • float 29 V

    The equal voltage is 34V but not used.

    Trina, is showing bulk while others show absorb. This is NOT OK.

    Slightly different voltage settings will overcharge things, so I set Trina (the copper wire is slightly longer, hence lower V settings you get from it) to a lower setting for Absorb

  • This is: Absorb 32.7 V

    The other two are set as:-

  • Absorb 33.0 V

    Now both Trina and Zeus are in Absorb while my new string (called Sola) is in Float.

    Since the new string (Sola) is in float and is the shortest copper wire, this allows it to switch off most charging earlier. And the other two to remain active most.

    Will test the new system tomorrow for better results for the Ni-Fe batteries.

  • Trina is 9 amps bulk
  • Zeus is 8 amps bulk
  • Sola is 9 amps bulk
  • All great for a cloudy day after rain at 9 am in the morning.

  • Trina is 25 amps bulk
  • Zeus is 20 amps bulk
  • Sola is 25 amps bulk
  • Fantastic for a cloudy day after sunshine peeks through at 9:15 am in the morning. Notice this is a total charging of 70amps in bulk !!

  • Trina is 30 amps bulk
  • Zeus is 24 amps bulk
  • Sola is 30 amps bulk
  • On full sunshine at 9:25 today on the first day, the total charging is 84 amps. Voltage: 30.2 V

    Absorb does not start until reach 33.0 V.

    Will see how long bulk takes at this rate.

  • Trina is 18 amps Absorb 32.7 V
  • Zeus is 26 amps Bulk 32.7 V
  • Sola is 29 amps Bulk 32.7 V

    It's 12 noon, 3 hours later.

  • Notice Trina has reached Absorb now. Trina is capable of 29 amps as Sola is, but Trina is folding back the charging rate, saving the loss of water, and slowly getting the amps down to a trickle. This will happen when all three MPPT boxes reach Absorb.

    All this is normal, and at a higher Battery Storage, hopefully the full 500 Amp/hours.

    It's now 1:15 pm, with both Trina and Zeus on Absorb, but not Sola.

    This is bad, lead to overchar ging and losing water.

    So I user define Sola to 31.7 V. And now Sola is in Absorb.

  • Trina Absorb setting is 32.7 V
  • Zeus Absorb setting is 33.0 V
  • Sola Absorb setting is 31.7 V
  • I note the amps coming in is funny for Sola.

  • Trina is 15 amps Absorb 32.7 V
  • Zeus is 26 amps Absorb 32.7 V
  • Sola is 4 amps Absorb 32.7 V

    It's 1:15 pm, 4 hours later.

  • Because I can't check the settings everyday, I will leave it as this for now and see what happens over the week.

    It's now 1:30, just 4.5 hours of charging and Sola is on float.

  • Trina is 25 amps Absorb 31.5 V
  • Zeus is 15 amps Absorb 31.5 V
  • Sola is 0 amps FLOAT 31.5 V

    It's 1:30 pm, 4.5 hours later.

  • This is desireable and great !! It means my batteries are getting to fully charged and NOT overcharged. My water loss will be minimal. My battery storage will be maxiumum. And all this in 4.5 hours on a dull day in winter.

    Did some watering for an hour, Bore pump also came on. About 40 amps required.

  • Trina is 15 amps Absorb 28.7 V
  • Zeus is 10 amps Absorb 28.7 V
  • Sola is 0 amps Float 28.7 V

    It's 2:00 pm, 5 hours later.

  • Not fully convinced the amps coming in is matching amps going out.

    So I user defined Sola again to Absorb 32.5 V.

    But could not move Sola to Absorb, it remained in Float.

    So leave this for a week and see.

  • Trina Absorb setting is 32.7 V
  • Zeus Absorb setting is 33.0 V
  • Sola Absorb setting is 32.5 V
  • The recordings of data will confirm somewhat how things will go for this week.

    These different settings are not allowing each MPPT to reach float, some didn't reach float all week.

    So this week to make settings are:-

  • Trina Absorb setting is 33.0 V
  • Trina Float setting is 29.5 V

  • Zeus Absorb setting is 33.0 V
  • Zeus Float setting is 29.5 V

  • Sola Absorb setting is 33.0 V
  • Sola Float setting is 29.5 V
  • Now let's see how this works...

  • Trina is 30 amps Bulk 32.9 V
  • Zeus is 22 amps Bulk 32.9 V
  • Sola is 30 amps Bulk 32.9 V

    It's 10.20 am.. Sunshine begins in winter.

  • Overnight the battery voltage got to 18 volts, refusing to run water pump, so batteries went dead flat. The voltage goes from 24 to 18 volts rapidly as the motor runs using 27 amps when batteries are flat but only 19 amps when sunshine hits the batteries , ie: the MPPT are getting amps to the batteries.

    So I suspect at 80 amps now, it should take 6 hours to charge, longer as the batteries do Absorb stage. We will see.

  • Trina is 30 amps Bulk 33.1 V
  • Zeus is 22 amps Bulk 33.1 V
  • Sola is 30 amps Bulk 33.1 V

    It's 10.30 am. Half hour later.

  • So if one MPPT reaches Absorb before the others, do the other MPPT's get a chance to reach Absorb also?

  • Trina is 29 amps Absorb 33.2 V
  • Zeus is 22 amps Bulk 33.2 V
  • Sola is 30 amps Bulk 33.2 V

    It's 11.00 am. One hour later.

  • Notice Trina has reached Absorb already, but the current coming in is still 29 amps.

  • Trina is 29 amps Absorb 33.3 V
  • Zeus is 22 amps Bulk 33.2 V
  • Sola is 30 amps Bulk 33.3 V

    It's 11.30 am. Two hours later.

  • When the water pump runs with 32.0V the current drawn drops to 16 amps.

  • Trina is 29 amps Absorb 32.2 V
  • Zeus is 21 amps Bulk 32.2 V
  • Sola is 28 amps Absorb 32.2 V

    It's 1.00 pm. Three hours later.

  • Washing machine, water pump and bore pump is running as well.

    Might reduce the Absorb setting for Zeus, so it's on Absorb.

  • Trina Absorb setting is 33.0 V
  • Trina Float setting is 29.5 V

  • Zeus Absorb setting is 32.3 V
  • Zeus Float setting is 29.5 V

  • Sola Absorb setting is 33.0 V
  • Sola Float setting is 29.5 V
  • And now we have

  • Trina is 29 amps Absorb 32.5 V
  • Zeus is 13 amps Absorb 32.5 V
  • Sola is 28 amps Absorb 32.5 V

    It's 1.30 pm. Three & half hours later.

  • Notice Zeus has folded back from 25 amps to 13 amps, while the others are still pouring in at their maximum of 30 amps (about).

    The washing machine is off, water pump off, but bore still going. So will see how long the Absorb lasts. Only 2 hours of sunshine left.

    A new day, overnight the voltage went from 28 down to 27. Great!

  • Trina is 21 amps Bulk 31.5 V
  • Zeus is 13 amps Bulk 31.5 V
  • Sola is 22 amps Bulk 31.5 V

    It's 9:00 am. Full sunshine begins.

  • All MPTT boxes begin on Bulk.

  • Trina is 29 amps Bulk 32.6 V
  • Zeus is 18 amps Absorb 32.6 V
  • Sola is 29 amps Bulk 32.6 V

    It's 10:00 am. One hour later.

  • I have set Zeus to trigger Absorb at 32.3V, and so it has already.

    Soon the other two will trigger Absorb.

  • Trina is 29 amps Absorb 33.3 V
  • Zeus is 0 amps Float 33.1 V
  • Sola is 29 amps Bulk 33.2 V

    It's 11:00 am. Two hours later.

  • It didn't go as I expected. Zeus is on Float and switched off. Sola is still on BULK !! Trina is on Absorb but has full amps pouring in.

    It's been 2 weeks now and the MPPT boxes need synchronizing, as one goes to absorb before the others, sometimes remains on bulk too much, not enough charging is done.

    I note that Victron Cerbo GX is a box that seems to join 3 VE ports together as one MPPT control. Which seems what I want.

    Except it costs $500. And has only three ports, to join three MPPT together.

    No point looking at cheaper alternatives, 3 boxes at $300 + GX $500 = $1,400

    Not much different to Larger 250/100 MPPT (100 amp controller) for $1,300 (no need for GX box).

    I also compared one large inverter at 5,000 watts verses 5 inverters at 930 watts, I am roughly over $1,000 in front. Plus redundancy, if a large inverter goes you have no power and a large bill, if one smaller inverter goes you have a small inconvenience and a small bill.

    So looks like the $500 Cerbo GX box is the last piece of a perfect, cheap system.

    Last two weeks, fog and misty rainy days meant no power, 18 volts.

    Lost all power to house with dead flat batteries, Happened twice already.

    So grateful for Nickel-Iron, peace of mind. They keep on forgiving. You cannot do them harm within reason. With Lead/ Acid or Lithium, we would be out of pocket by now for another $8,000 for new batteries.

    With sunshine again together, the Ni-Fe batteries charge again, and our system keeps on keeping. What a nice feeling.

    With Cerbo GX box, synchronizing the three MPPT's, should finish a perfect system.

    My friend has a similar issue with MPPT synchronization, the last piece of the puzzle is a Victron Smart Battery Sense.

    This device measures the battery voltage, and wirelessly sends the signal pulse to the Cerbo GX box, which wired to each MPPT, they function as one, either all on bulk, all on absorb or all on float. Problem solved. Another $70 for this device.

    Update on Victron products:

    I have become deceived by old Victron products that do not scale up, and I cannot discuss this directly with Victron, only the salesman dealer, in other words Victron does not care.

    So the "BLUE SOLAR Victron MPPT" is rubbish.

    No wonder the price has gone for the 100 amp Blue Solar from $700 to now $250 injust 9 months.

    You cannot use a Cerbo GX for anything useful either, such as make three Mppt boxes work as one.

    You cannot get three Blue Solar Mppt boxes to work as one.

    Using one Blue Solar MPPT is OK, but no good for larger old grid systems.

    So much for advice. Where is advice on the Internet?

  • Update Feb 2022 - one year later
  • Blue Solar MPPT do work OK. It does not matter if one box is on bulk and the other two are on float, they all do eventually get to float. I have since learned the older blue boxes are fine, so it's hype to have them synchronized. Not necessary.
  • Not sure if having them all Smart Solar and sycrhonized will help reduce overcharging and losing water from my cells?

    Experience always comes with a cost...Hmm?

    For new comers, I suggest you purchase Phonex 1200 VA for $630 each, most applicances run under 930 W. Keep your battery loads small, less than 20 amps from each inverter. My Son in law has a big off grid system, with one 5,000 watt inverter and four Smart Solar MPPT, and a huge 1000 Amp Hr battery storage, the grand cost of the system is running past $30,000 +. I am looking into the future when things break down, replacing a $600 inverter is cheaper than a $2500 one.

  • OK for readers out there, make sure you purchase the more expensive

  • SMART SOLAR MPPT from Victron, especially if you purchase 3 of them, and they need to work as one.

    Do you purchase One 100 AMP MPPT, with all panels new and the same? (Expensive to replace when it fails)

    Or purchase 3 Smart 30 AMP MPPT, with all panels different and cheap? (Cheaper to replace when they fail)

    Right now, Our system works OK.

    Overcharges a little. Uses 250ml of water per cell, per week.

    Need to wire in a daylight switch for water bore pump

    Also daylight switch for water pump. AND

    Hook up 24V fresh water pump for house, used 24 hrs, at night.

    This should reduce loads at night.

    And purchase 20 second hand panels at say 2 to 3 amps each, for cloudy days, to switch on a fourth string.

    You can get 200W old panels for $50 each, say $1000 (is this worth this?)

    So on a cloudy day, I might get 3 strings at 6amps + 1 larger string at 20amps, per hour.

    Things to try and experience.

    Next we consider a shunt and the Victron BMV 712 monitor of the batteries.

    Ni-Fe battery technology

    . ...

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