28x2 MPPT Success, 50v 35amp ,2.1Kw Panels

PiCaxeDB

New Member
Hi,
I have got my MPPT Unit up and running (2 months now). So I thought i would share any and all my info, to any one that it may be of interest to.
The idea was to run my hot water system from solar . I was given 6 panels 360watt JA Solar (chinese brand) so I mounted them on 2 frames that i intend to make into trackers.
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The panels are arranged 2 series x 3 parallel gives me OS voltage of 96v and max amps at MPP of 30amps and 78v.
The hotwater element is 1500w at 48v, software limits the voltage so everything seems to be running just fine so far.
MPPT is running from 96% to 85% on sunny days.(my very limited knowledge of how to measure this acceratily).
The whole project is still in development so some of it will change. I am very pleased with the results so far.
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lbenson

Senior Member
Excellent. Congratulations. You may be a "New Member", but this is obviously not your first electronics project.

What PICAXE 28X2 module did you use?

Why did you go for a 96 volt system rather than a 12V system?
 

premelec

Senior Member
@PiCaxeDB - very good project! Lots of hot water for sure... can you dump excess power into local grid? BTW one thing to check is rating of thermostatic switches for DC - AC ratings must be derated about 8x for DC to prevent arcing failures - I haven't heard of 48v heater elements so perhaps the whole system tank & Tstats is made for DC.

@Ibenson 2.1 KW at 12 volts = 175 amps - that would be pretty hefty wiring... ;-0
 

PiCaxeDB

New Member
Excellent. Congratulations. You may be a "New Member", but this is obviously not your first electronics project.

What PICAXE 28X2 module did you use?

Why did you go for a 96 volt system rather than a 12V system?
Hi lbenson thanks for that.
First time that I've designed the PCB and put a system together, This is version 2. I have used the AXE201 28x2 Module
The 96v is 2 panels in series and 3 lots of 2 connected in parallel to get the amps. I originally had the hot water element connected direct to the panels, software then limited the voltage but the system never went above 50v . It worked well enough to supply all my hot water 95% of the time. But I wanted to challenge my self to build the controller.
 
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PiCaxeDB

New Member
@PiCaxeDB - very good project! Lots of hot water for sure... can you dump excess power into local grid? BTW one thing to check is rating of thermostatic switches for DC - AC ratings must be derated about 8x for DC to prevent arcing failures - I haven't heard of 48v heater elements so perhaps the whole system tank & Tstats is made for DC.

@Ibenson 2.1 KW at 12 volts = 175 amps - that would be pretty hefty wiring... ;-0
Hi premelec
I already have a grid connect system and if I alter it in any way I will loose the feed back tariff of .44c/kw that I get now and go back to 6c/kw so no grid connect for this system. Hope to one day soon development this 2.1kw system to run my pool pump (700w) as well.
The thermostat is not connected, I have installed 2 temp sensors in the Hwater tank and software looks after the control of temperature and any part of the system fails it fails to off.
 

J G

Active member
That would make a bit more sense as I was trying to work out how it was calculating the MPP :).
I see in your original code you are uploading / have made allowances for uploading data to pvoutput. Is this done through a usb-serial converter and a small computer or something fancier?
Looks like a good project, even if a little scary for me from the high currents :)
 

PiCaxeDB

New Member
That would make a bit more sense as I was trying to work out how it was calculating the MPP :).
I see in your original code you are uploading / have made allowances for uploading data to pvoutput. Is this done through a usb-serial converter and a small computer or something fancier?
Looks like a good project, even if a little scary for me from the high currents :)
Hi JG
Right now I ues my Pc. I'm trying to get my Raspberry Pi4 to handle the job. The Pi4 is uploading my data from the grid tie system. At the moment the Pi is very new to me so a big learning curve for me.
My systems on PVoutput.org are : DKB Hot water & DKB PV4. 4
 

J G

Active member
Hi JG
Right now I ues my Pc. I'm trying to get my Raspberry Pi4 to handle the job. The Pi4 is uploading my data from the grid tie system. At the moment the Pi is very new to me so a big learning curve for me.
My systems on PVoutput.org are : DKB Hot water & DKB PV4. 4
Looks like they are quite productive systems in terms or outputs. I have been uploading our smaller 2.2kW system (NottingHillTestSystem) by getting data from the inverter's RS232 port. The first version of that had an arduino acting as a controller and baud rate converter to an old router running openwrt and wget to make the requests (there wasn't enough flash to install curl or anything better to allow it all to be done on the router). Needless to say, that certainly taught me a lot about working with linux without a gui :).
Good luck and have fun with the project.
 

fernando_g

Senior Member
The best approach to test a MPPT algorithm:
While monitoring and recording volts and amps in real time, cause a disturbance yourself. I.E, briefly put a towel over the array.
If the power point recovers up to its maximum again when the towel is removed, with a very small undershoot as it exceeds the maximum, then the algorithm is working correctly.
 
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PiCaxeDB

New Member
The best approach to test a MPPT algorithm:
While monitoring and recording volts and amps in real time, cause a disturbance yourself. I.E, briefly put a towel over the array.
If the power point recovers up to its maximum again when the towel is removed, with a very small undershoot as it exceeds the maximum, then the algorithm is working correctly.
Hi ferando
Thanks for that info. I have been using a manual input to adjust the pwm, record the highest and then let it run and compare. I've been very happy with the results. PWM@100khz and voltage/amps sampling at 20 Hz the response is nice and quick under 1 second.
 
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PiCaxeDB

New Member
Managed to tick off another todo box today
The Raspberry Pi4 is now uploading data to PVoutput.com (DKB Hot water )
I am using Node-red to do the heavy lifting
Next job is to build the auto tracking system (I move the system manually right now
 
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lbenson

Senior Member
Great project. I'll be interested to see what motors and drive arrangements you come up with.

What kind of wind can your mounting structure withstand?
 

PiCaxeDB

New Member
Hi lbenson
I've tryed to make the pole mounts good enough for 150kmh winds with panels parked horizontal. The system will be exposed to tropical cyclones so fingers crossed I did a good job.
 
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