Help Suggest and fix my friend's new DIY Solar system....

hmong2017 · April 2019

Okay, I know It sounds stupid... But a friend offgrid had someone order a solar kit for him. I know a little about DIY 12V and 24V Solar stuff.... But I am not familiar of bigger setups.

I know what I am about to explain is REALLY off and wrong. So please help me help him get the right stuff to finish his setup. He's spent a lot already, and the guy that bought the stuff is a self taught solar guy off of criagslist... (I KNOW!!!! RIGHT!!!!)

my friend currently have these stuff:

SOLAR PANEL:

- GCL SOLAR Brand

- 335WATT

- 38V

- 8.82A

- Model is GCL-p6/72335

- TOTAL OF 12 PANELS in Parallel

Combine Box:

- Liket Brand, Prewired

- with 6 Breaker rated 20A each

- Each breaker handles 2 panel

Now HE HAVE A 80A Charge Controller (We don't know how the Volt, because it doesn't say it anywhere. Weird....)

Then to 8 Batteries... AND, here's the Specs;

- Trojan Brand, Model SSIG 06 475

- 6VOLT

- 475 AH

- They have tried to Series it and Parallel....

The Power Inverter, is a 5000W, 24V unit.

What I don't understand is, he said they managed to get power from the batteries and had the power inverter worked for a day and, then after that it just never worked anymore, like the panels aren't charging the batteries.

That's when they thought something is wrong with the batteries and started playing series and paralleling the batteries... So I was not sure if they used parallel or series at first for the batteries.

Besides, can a 24V power inverter really work with 6V batteries? How?

Any Idea how they got 6V batteries to work with 24V Power Inverter?

tell us what he needs to change, do what to get the panels to charge his battery bank.. (I personally think the batteries isn't suitable for the setup, but...) is his 38V panels is considered a 36V so that he should stick with 36V parts?

Please no harsh comments... try to help him out... Thanks. He's offgrid.

Photowhit · April 2019

All lead acid batteries are really just strings on 2 volt cells, so a 6 volt has 3 cells in series and a 12 volt has 6 cells in series. so to create a 24 volt battery bank you will have 2 strings of 4 - 6 volt batteries. Ignore the ah rating, the wiring should look like this;

You did not say what brand of charge controller, It might well be a MPPT type charge controller, which can handle higher voltages and adjust them to low battery bank voltages. Nothing weird about the Charge controller not saying what voltage, most can handle more than 1 voltage.

Since the system came with a pre-wired combiner box with 6 breakers, and a 24 volt inverter, then I would assume it's a MPPT type charge controller. These select the proper voltage when you connect the battery bank 1st, if the solar panels are connected first then it is likely to confuse or choose a higher system voltage. This is where you likely messed up. Always connect the charge controller to the battery bank first.

You should have some other breakers and/or fuses in between the charge controller and the battery bank, between the inverter and the battery bank. As well as proper grounding.

Estragon · April 2019

For 24v, the 6v batteries should be wired 4 in series (+ive on one to -ive on the next). With 8 batteries, you make 2 series strings, the parallel the 2 strings by taking a wire off each of the end +ives and end -ives to a single +ive and -ive. This wire should be quite heavy (2/0 or 4/0), and the wire used to make the parallel connections should be equal lengths. Single +ive and -ive wires (as short as practical, and also heavy) then go to buss bars.

The charge controller and inverter are wired to the buss bars using wires and breakers sized as specified in their manuals.

For panel wiring, you need to know more about the controller and panels. If a pwm type, putting the panels in parallel may work. Check the maximum string fuse size on the panel though (should be on the spec label), to be sure putting 2 in parallel to each breaker isn't too high. Also check voltage drop on pv wires if there's much distance from pv array.

If mppt type controller, you neeed to know the maximum voltage it can handle. The operating voltage (Vmp) on panels in parallel is likely to be a problem, so strings of 2 or 3 will likely be needed. The string Voc adjusted for record low temperature at your location needs to be comfortably lower than the controller limit.

If you can get the missing info, and controller make/model, we can go from there.

Solfyr · April 2019

Overall , it appears , that everything is within specifications :

Vmp minus temperature coefficient for high temperatures might get below 24 Volts , though .

Downloaded a datasheet for GCL p6 72 335 bifacial from enfsolar :

0.3% TempCoEff @ 37.77 Vmp gives me ± 0.11 Volts per Kelvin ( Celsius ) ,

and 65 Kelvin ± 7.365 Volts from 25 °C at 90°C , should still give enough Volts at ~30V to

feed the batteries .

Those panels have also specs printed for rear-side exposure inside the data sheet ,

since bi-facial , and there would be even slightly higher Voltages available .

Summa Sumarum : This pre-configured setup should work as-is ,

and should input 30Volts and ~8Amps x12 = 30V*96A ≈ 3000 W at high temperatures.

96+ Amps might be too much for a 80A controller , though :

Looking into a Victron datasheet for a 150/85 CC , though output is rated at 85 Amps ,

the input is set to 70 Amps Isc max .

One could reduce the panels to 5 to 10 , to see if that would work , then :

5 panels *9 Amps = 45 Amps ; 6 *9 A = 54 A ; ... ; using 9 Amps here , instead 8 to take into account high tempratures ,

since Amps rise , while Volts fall with high temperatures .

And then , a second Charge Controller could be deployed , and a second combiner box ,

with just one panel each breaker .

Estragon · April 2019

MPPT controllers generally want 20-30% "headroom" voltage to buck down from string to charging voltage. With cool/cold FLA bank, absorb might be 29-30ish volts, so CC might want ~ mid-30s, which hot panels might have trouble supplying in parallel.

CC capacity is DC out. 335w x 12 = ~4kw ÷24v bulk charging = ~167A, so a second 80a controller should be added.

In series strings of 2, 4kw ÷ Vmp ~60v = ~67a input to controller, but output current too high for a single controller IMHO.

All assuming an MPPT controller.

Photowhit · April 2019

@hmong2017

We really need more information about the charge Controller and also the wiring.

You say of the panels "- TOTAL OF 12 PANELS in Parallel", Are they wired in parallel into the breaker or are they in series?

If the pairs of panels are wired in parallel, then they are not correctly setup for the breakers, but would work with a PWM (cheaper) charge controller. I only know of a couple 80 amp pwm charge controllers, y-Solar makes one that is repackaged/branded for some others, and a din rail modular system from the EU (I think)

It sounds to me, and I think most of us, that it's a MPPT type charge controller, lots of those in 80 amp versions. You would want to check the specs, so see if you can come up with a brand or a picture of the label. Very likely you can use the panels wired in series into the combiner box for a 80 amp MPPT type charge controller. With 12 panels of 335watts you would have an array of 12 x 335=4020 watts, this would be well over paneled for single 80 amp charge controller, it would normally be able to produce about 3015 ÷ 28 volt =(charging voltage for a 24 volt battery bank) = 107 amps. Usually these charge controllers can handle this type of over paneling, but some can NOT.

To clean up the system you might consider adding a charge controller and sticking with a 24 volt system, If you do check the quality of the inverter, inexpensive 5000 watt inverters are usually energy hogs.

If you find the inverter of poor quality, and you have a reasonable quality working MPPT charge controller, you might consider switching to a 48 volt system. since charge controllers usually handle the same amperage regardless of voltage, you wouldn't need to replace it. Just find a 48 volt inverter.

hmong2017 · April 2019

https://forum.solar-electric.com/discussion/comment/397421#Comment_397421

Will a Renogy Rover Li 100A Amp MPPT Solar Charge Controller work for replacement of the 80A charge controller? That controller got returned to the guy. It was a MPPT charge controller.

Photowhit · April 2019

I don't know if that will work or not.... Not a fan of Renogy, They state Max array for a 24 volt system is 3900 watts. Likely that's the most to use cost effectively.

https://www.renogy.com/rover-li-100-amp-mppt-solar-charge-controller/

hmong2017 · April 2019

But it can handle all those panels, right? like the 8.82A x 12 = 105.84A

The controller is 100A... would it be too much for the Controller?

Photowhit · April 2019

@hmong2017 "But it can handle all those panels, right? like the 8.82A x 12 = 105.84A "

Charge controllers are rated on output, so In theory you should have a potential of 12 x 335 = 4020 watts. 4020 watts divided by output voltage of 28 volts = 143 amps. But once the panels are warm they produce about 75% of their panel rating so about 3015 watts so the largest cost effective size would be roughly 100 amps x 28-29 volts = 2900 watts, 2900 watts divided by .75 = 3867 watts (or roughly the 3900 watts of the spec sheet.

PWM can only 'pass through' the amperage so you are correct for a pwm type charge controller.

Photowhit · April 2019

If you are using a MPPT type charge controller you should have the panels wire in series to each 20 amps breaker.

Solfyr · April 2019

https://forum.solar-electric.com/discussion/comment/397439#Comment_397439

Probably not : Got me the manual for the 20 and 40 A version , and on top of it , it should not exceed the output Amps at page 1

Do not exceed 20A (ROV-20) or 40A (ROV-40). The Short Circuit (Isc) of the solar

array should be less than 20A (ROV-20) or 40A (ROV-40).

though claiming , that it could limit the input amps if too high on page 19 :

PV Overcurrent

The controller will limit the battery charging current to the

maximum battery current rating. Therefore, an over-sized solar

array will not operate at peak power.

But since Isc and Imp usually differ by just 0.5 A , the path is tight .

Hmmm ... 2x475Ah = 950Ah * 24 = 22.8 kWh Battery capacity .

21 kWh ÷ 3 kWh continuous consumption = 7 hours of usage , with a battery finally at less than 10% State of Charge .

To charge that battery again , it would also need that many kWh , without any losses .

If the panels just produce 100 W * 12 panels for 8 hours , then that would charge ~ 10 kWh into the batteries , recharging them to just 50% SoC , which might be already too low for 3 kW loads .

80 Amps CC output ÷ 2 battery strings = 40 Amp each battery string , and 12 hours of charging would be needed , to fill the batteries up again from SoC of 0% to SoC 100% ( without losses ) .

100 A / 2 = 50 -> 10 hours of recharging needed .

When one has to guess , it appears , that the batteries were discharged completely the first day , and if not just for testing purposes , the kW supplied by the panels might not be enough for everyday purposes .

Guess , at Normal Operating Conditions , the power supplied by the panels is just 2/3 in hot climate and 4/5 in cold climate , those ~ 4 kW panels deliver 2.6 to 3.2 kW , that could be not enough for 20 kWh needs each day , to refresh completely .

The lesser , the batteries are discharged , the easier to recharge each day . Since probably deep discharged , they would need to be recharged several days by solar .

Probably your friend should consider to calculate his needs correctly , before ordering a kit .

For the CC , if not noted in the datasheet , my guess would be Idc in max = Idc out max .

Since 6 breakers * 20 Amps are deployed , that would make 120 Amps total allowed as Idc input . 2 x 60A CCs would work best , then , if the combiner box is capable to be split into 2 different outputs .

Estragon · April 2019

https://forum.solar-electric.com/discussion/comment/397439#Comment_397439

Even though the 100a controller may be able to handle the panels, it may not be wise for a couple of reasons:

- although the output from panels warmed by the sun will likely be 75-80% of (STC) rating, there can be situations where output is higher than rated. At altitude, for example, or on a cool/cold day when the sun emerges from behind a cloud. At best, you don't get the benefit of the extra power.

- even in normal operation, running a controller at capacity will produce more heat and shorten life expectancy. In the long run, it may not be much, if any, more expensive to use 2 slightly smaller controllers at lower utilization than a single controller flat out. Having 2 also keeps the lights on when 1 dies.

MrM1 · April 2019

I do not think you can wire the panels in any series / parallel combo so that one 24v Charge Controller can handle 4020 Watts. I have a MidNite Solar Classic 150 24v CC and have it very near maxed out at 2565 Watts. 9 285Watt panels wired 3Series 3parallel. I wanted to add 1-3 more panels, but using the Midnite solar string tool, could find no series / parallel combination to safely do it. I think you will need 2 controller if you are going to use that many 335 watt panels.

Estragon · April 2019

Changing the panel series/parallel config (within the controller acceptable voltage range) has very little to do with size. Bucking from ~60v to 24v is a bit more efficient than 90v or 120v, but not really by enough to affect array size materially IMHO.

For materially more than your 2565w, it's pretty much either a second controller or going to 48v. Another possibility is a cheap pwm controller for a few extra panels, maybe in a different orientation if that would help for more hours of production, better winter tilt, etc.

Help Suggest and fix my friend's new DIY Solar system....

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