New PV setup

[Dad-07]

Hello to all from OZ,

As with any new forum member I have a gazillion questions of which some will be pertinent and some downright stupid (slap me about the head now).

I have a reasonable understanding of things PV related and electrical  but still working on the meaning of life.

At present I have a temporary off grid PV system setup and I am in the process of upgrading to a permanent installation.

To start with it will be a 24V system and looking to go up to 48V in the future.

INPUTS

I have 8- 24v 200W Jinko panels,
panel specifications

      STC          NOCT

Pmax   200Wp   149wP
Vmp      36.9V   34.3V
Imp      5.42A   4.33A
Voc      45.6V   42.4V
Isc      5.80A   4.67A

Efficency STC(%)     15.67%
Operating Temp(C)   -40 ~ +85
Max system V          1000VDC (IEC)
Max series fusing    10A
Power tolerance      0 to +3%
Temp Coeff Pmax     -0.40%/C
Temp Coeff Voc        -0.29%/C
Temp Coeff Isc        -0.05%/C
NOCT                       45+-2C

24v 750 ~ 1000W wind turbine with dump load and dump load controller
Chinese 7500W petrol generator ( very reliable so far )

CONTROLLERS

Midnite Classic 250
Powertech 20A PWM

STORAGE

4 - EVL 16-400, 6v 400Ah Vision batteries
10 - N70ZZ 12v 100Ah truck batteries

POWER CONVERSION

A cheap chinese 2000W inverter to run front load washing machine, microwave oven etc.
Dc 24v ~ 12v converters for Led lighting,stereo, UHF's etc.

WIRE RUNS

Panels laid out in 1 row x 8
end of row to power distribution panel( small garden shed with batteries inside) 2~3m max.

QUESTIONS

Best way to arrange array, 2X4 panels or 4x2 panels?
Fusing requirements?

Having looked online so much for these answers I think I can't see the forest for the trees.


Thanks
Peter

[Dad-07]

The system is up and running and I am using 2 different battery banks (bank1-4x 6v 400ah and bank2-10x12v 90ah) to power the house.

I had 2 strings of 4 panels (96V 1600W) and it seemed ordinary in the way of power production, so I decided to try 2 strings of 2 (48v 400W) and it just took off.
No worries getting to float on a good sunny day.

Have set Classic Aux1 to float high with 80A ssr to charge bank2 via an MP3724 pwm CC.

Both banks feed to an Automatic power selector ( basically 2 Schottky diodes to form what i believe is called an 'Oring circuit') and it works. Whichever bank has more charge is used.

About .5 - .75v loss through the Auto selector, but this is minimal considering I have another 4 panels to come online when the fuses arrive and let alone the wind turbine.

Peter

[Robin]

Please make a wiring diagram and attach it. Your system seems weird and it will be more clear with a diagram.
Did I understand you correctly that the system worked better when you disconnected panels? There is something terribly wrong if that is the case. Think about it. Puts out more power by reducing panels? Heck, take all the panels off and it should really rock and roll with that logic!
We can help, but we need to know just what is happening. The diode orred batteries is strange also. Why do you want two separate battery banks?

[Dad-07]

Hi Robin,

Hope the diagram shows up.( as rough as it is )

Had the 8 panels in 2 strings of 4 and was getting up to 120v but bugger all wattage. Now with 2 strings of 2 I get 70+ v and up to 700W. You tell me!!!!!!!!

'Heck, take all the panels off and it should really rock and roll with that logic!' you wanna buy some panels

Having had a trucking business I was always on the lookout for bargains, I scored a pallet of batteries cheap and what was left over from the business was the start of my PV system. I later aquired 4 'proper' deep cycle batteries. I am trying to make use of all the available storage on hand.

The automatic power selector was from a bargain bin at an electronics store, thought it might come in handy one day. It draws only from the highest power source.

So because I have 2 battery banks of different AH configurations charging them from the one source was the problem.

By using Aux1 to activate a SSR when bank1 goes into float excess power is then sent to bank2 via the pwm controller.

I hope this makes sense.

[zoneblue]

Kinda creative, but maybe just too complicated. Couple issues i see:

1. PWM controller uses battery A as source to charge battery B. PWM likely to overheat and blow up without some way to limit the current.
2. with 70-85% charge efficiency times 2 (worse case 50%) youre losing much of the energy by recharging the second bank.

Cant you donate/sell the second bank and call it good. Youll need to keep an eye on your charge rate.  with 8 panels into 400Ah, thats already 0.17C charge rate.

[Dad-07]

Hi zoneblue,

1. The pwm controller was preferred over just directly dumping power from bank1 into bank2 unregulated. From what I can tell from the specs on the controller it should handle it ok.

2. Not really up to speed with charge rates etc, looks like I could do with some help there.

My reasoning was what to do with the excess power, dump it or use it. Have been considering heating various things, water, air in the battery shed etc.

All advice welcome.

Peter

[Dad-07]

'update'

Classic went into float at about 10am here at 27.5v on bank1.
Charging bank2, a slow but steady rise in volts from 24.5v to 25.4v bulk stage. The pwm is showing 26.7v in from PV(bank1) but only .2A.

Classic
V in = 75
W in = 515
Batt V = 27.6
Batt A = 18.6

WBJR
System = 5.6A
Net Ah = 7Ah
Remaining = 391Ah
Soc % = 100

Temps
FET = 47.5C
PCB = 49.2C
Batt = 22.7C

Power is being drawn from bank1.( cheap chinese V/A meter on bank2 showing 0A)
SSR input V = 27.5V
SSR output V = 26.7V

APS temp = 32C
SSR temp = 28C

Peter

[Dad-07]

Well this low amperage from battery bank1 to battery bank2 has me buggered.

I thought Zoneblue might have been right and I cooked the pwm controller.

This morning I connected a single PV panel to it's input and there were 26.5v @ 2.6A  showing, so the controller is working.

Only other thing I can think of is the SSR, with a voltage drop of 1v from bank1 input to bank2 output.

Any ideas

[zoneblue]

Your typical pwm controller has no mechanism to limit current. Its expecting a current limited source like PV. Hence you connect it to a extremely low internal impedence source like a big lead acid battery and the potential for grief if high. However you might be lucky and have a better than average PWM controller than has some kind of thermal cutout, and/or or your cable length and size might be limiting current.

With solar theres always waste, thats a fact of life. Heating hot water is about the best and easiest use for surplus power, but once the tank is hot, you cut that off, and then you stil waste it.

Nice , eh.

BTW hope you have plentry of circuit protection, breakers in all the hot wires in that setup of yours.

[Dad-07]

All circuits are protected as per the standards and then some.

PWM

Specifications

Model                                                                                     MP-3724
Battery voltage                                                                      24V
Maximum PV panel open circuit voltage                                 52V
Continuous load/charge current                                            20A
Maximum charge current (5 mins)                                          25A
Maximum load current (5 mins)                                              25A
Operation current(no Load and no PV)                                  30mA
Voltage across terminals (PV to Battery)                                0.8V
Voltage across terminals (Battery to Load)                            0.4V
Electronic Blocking                                                                  Yes
Battery reverse polarity protection                                        Yes
Overcharge & Over-discharge protection                               Yes
Battery status LED indication                                                 5-State LED Indications
Charging status indication                                                     3-State LCD Display
Recommended wire size                                                        #10AWG
Weight                                                                                   0.47kg
Dimension (WxDxH)                                                               150 x 85 x 45 mm
Fuse                                                                                       30A ( internal blade type)
Operating ambient temperature                                            -10 to 50 °C
Over temperature protection                                                 Yes
Battery charging float voltage setting                                    Adjustable from 24.0-33.0V
Battery charging bulk voltage setting                                    Adjustable from 24.0-33.0V

DC load control mode (For DC load terminal):

Low Voltage Disconnect(LVD)                                                 Adjustable from 16.0-32.0V
Low Voltage Reconnect(LVR)                                                  Adjustable from 16.0-32.0V

Cable lengths and circuit protection,

PV combiner to Disconnect                                                   3m 4mm2
Disconnect to PV breaker                                                     1.5m 4mm2
PV breaker to Classic                                                           .1m 4mm2
Classic to battery Disconnect fuse                                       .3m 10awg
Disconnect fuse to bank1                                                     1.5m 2 b&s
Battery bank1 to bank2                                                       1m 10awg ( including 80A breaker to SSR)
Bank1 to APS                                                                        .5m 2 b&s( including 80A breaker)
Bank2 to APS                                                                        .75m 2 b&s( including 80A breaker)
APS to Pos bus                                                                     1.2m 2 b&s ( including 120A fuse)

Negative Leads

Bank1 to Wbjr shunt                                                            1.5m 2 b&s
Wbjr to Neg bus                                                                   .2m   2 b&s
Bank2 to shunt2                                                                   .75m 2 b&s
Shunt2 to Neg bus                                                                .2m 2 b&s

Hope this paints a bit better picture of the setup.

I still don't understand the low amperage from bank1 to bank2.

case1 - PV to pwm

26.5v @ 2.6A

Case2 - bank2 to pwm( classic in float )

27.5v @ .2A , allow for voltage drop across SSR 26.5V @ .2A

Should I be using a different AUX1 function?

[dgd]

That 0.8v drop between input and output of the PWM controller could be an issue
Since you only start charging when the main bank is in float (26.somethingV ?) then the voltage the from the controller will be that minus 0.8v and the voltage drop across the SSR (0.5v?)
(eg 26.4 float minus 1.3 = 25.1v)
This may be ok when the smaller bank is low voltage but there is a problem when it reaches 25.1 as charging will cease. You will never succeed in fully charging that smaller bank and will shorten their expected life quite significantly.
Thats probably why you see more charge current with a PV as input to the PWM controller as the PV is designed to provide a high enough voltage output to fully charge the battery bank.

As ZB eluded to your system configuration is just not best use of your energy resources.
Solution is (as you discovered) is to connect PVs to input of PWM controller and let it work the way it was designed to -  to charge your battery bank.
Better configuration is to increase size or main battery bank and sell those smaller batteries and PWM controller.

dgd

[Dad-07]

Thanks for that Dgd,

I can understand that better now.

I am intending to buy a better inverter ( outback) when funds are available so I'll keep the pwm and bank2 for the shed.

As I understand it for the 400Ah, bank1, the 4 - 200W panels in 2X2 configuration should be adequate. Again when funds are available more batteries would make sense.

I'll connect up the 1-200W panel to bank2 for the time being and see how things go. At least then I have the 450Ah or so available in the event of inclement weather.

Peter

[dgd]

Since you have 8 by 200watt PVs you should use all of them
Three strings of 2 in series to charge the main bank via mppt controller
and two PVs in parallel to charge the secondary bank via pwm controller

dgd

[Dad-07]

That sounds like a plan.

I still have another 8 batteries in storage which should work for the wind turbine for powering the shed, I am yet to source a controller for it.

Peter