Non-matching PVModules

1 Posts
Apr 29, 2004 03:34 pm
Non-matching PVModules

Can you connect different size modules to a charge controller. I have one 80W and one 40W and each is protected by a diode, and then run right to the batt. i just bought a controller that has "non-diode" reverse blocking, so i don't want to use the diodes on each module as i am now. will that hurt anything if i remove the diodes and run the modules directly into the controller, thanks, dave
 
29 Posts
Apr 30, 2004 06:18 am
Re: Non-matching PVModules

Hi Dave,
normally you join modules of same technical specs to one controller.
Possible combinations:
1) seriell connection to 24V system then the Ampere strength is different e.g. 4.5A and 2.4A or whatever these PV modules yield. So the 80W module would heat up the 40W module and output if any at all is 24V system @ 2.4A.
2) parallel connection to 12V system : I guess the 40W module has only approx 16V peak but the 80W has 18V peak ?! So also parallel combination will run at lower Voltage and you loose power even with MPPT controller. Keep the diode in any case as otherwise the higher Voltage module will 'feed' into the lower Voltage module.
3) Even when using 2 identical modules paralell: when there is partial shading of one module (even a leaf lying on the module is enough) the Diode will prevent that the working module will 'feed' the shaded module instead the controller. So Diode ensures at least half Ampere from the  working module is used.
---------------
The only constallation to combine a 40W with a 80W module into same controller could be working without module Diode if the controller provides 2 separate input strings with Diode inside controller.




 
May 2, 2004 07:09 am
PV module ratings

There is really no easy answer to your question without knowing all of the specs. of each PV module along with the specs. on the battery bank and how you use power from them. For example; if you have a 1200 amp hr. bank @ 12v nominal, and in a 24 hr. period you use only 20%, and this happens on a regular basis, then with 120 watts of PV module a charge controller may not be nescessary, especially if the PV modules rated voltage (what I call working volatge) is below 17 volts and you live in a climate that is hot most of the year. I started with 6-MSX 77's; 4.5 amps @ 16.9 volts charging a 1320 amp hr. battery bank. I live in the southeast of USA. At the time we were using approx. 150 amp hrs. in a 24 hr. period. During the summer months I could bypass the charge controller because the battery voltage would never get above 14 volts. 13.8 to be exact. But during winter months I would need the charge controller because without it battery volts could soar to 15. Of course its always a good idea to have a charge controller for safety sake, even though the NEC states an exception when the PV source is only 3% of the battery storge after all NEC factors have been caculated, including ambient tempretures. The NEC book can be purchased at most electrical supply house's for around $35. Its a good thing to have. Article 690 relates to Photovoltaics and the supporting systems.
 

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