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General => General Technical Chat => Topic started by: snipersquad100 on May 06, 2015, 11:13:03 am

Title: Solar Panels Question.
Post by: snipersquad100 on May 06, 2015, 11:13:03 am
Im running a 12v battery bank and using 2 identical 175W 37v solar panels in parallel to give me 350watts at 37volts to charge the bank. I've got hold of another 175w panel but only 30v open circuit. Can I put this in parallel with the other two panels? if so what would happen to the voltage.
Thanks
Title: Re: Solar Panels Question.
Post by: firehopper on May 06, 2015, 12:23:10 pm
get a 3 input solar charge controller!
Title: Re: Solar Panels Question.
Post by: suicidaleggroll on May 06, 2015, 03:12:00 pm
Quote from: snipersquad100 on May 06, 2015, 11:13:03 am
Im running a 12v battery bank and using 2 identical 175W 37v solar panels in parallel to give me 350watts at 37volts to charge the bank. I've got hold of another 175w panel but only 30v open circuit. Can I put this in parallel with the other two panels? if so what would happen to the voltage.
Thanks

You'd be wasting the power of the 30v panel by not running it anywhere NEAR its MPP (maximum power point).

Hopefully you're using a charge controller anyway, in which case just give the 30v panel its own.
Title: Re: Solar Panels Question.
Post by: snipersquad100 on May 06, 2015, 04:39:47 pm
Im using a 400w pwm charge controller and was planning on upgrading to a mppt controller which can handle around 550-600 watts.
So you think I should use a separate charge controller per different voltage panel, and that's ok to connect to the same batteries?
I did make a mistake, the new panel is 185 watts not 175.
Title: Re: Solar Panels Question.
Post by: suicidaleggroll on May 06, 2015, 05:00:19 pm
Quote from: snipersquad100 on May 06, 2015, 04:39:47 pm
Im using a 400w pwm charge controller and was planning on upgrading to a mppt controller which can handle around 550-600 watts.
So you think I should use a separate charge controller per different voltage panel, and that's ok to connect to the same batteries?
I did make a mistake, the new panel is 185 watts not 175.

You should ask the manufacturer of the MPPT controller, but chances are yes it will work fine.  If there's a chance one of the two panels you currently have in parallel will be shaded while the other is not, or if they're pointing in different directions, you might consider using separate MPPT controllers (or separate panel inputs on a multi-input MPPT controller) for them as well.
Title: Re: Solar Panels Question.
Post by: electr_peter on May 06, 2015, 05:08:23 pm
Add low Vf diodes in series with panels if you have parallel configuration. 37V panels likely have max power at less than 30V anyway.
Title: Re: Solar Panels Question.
Post by: snipersquad100 on May 06, 2015, 05:14:53 pm
Thanks for the help guys.
Title: Re: Solar Panels Question.
Post by: mtdoc on May 06, 2015, 05:15:34 pm
To ensure reasonable efficiency, panels (or strings of panels) in parallel should have close to the same voltages (Voc and Vmp) - within 10% or so.  For panels in series Imp should be close to the same (also withing 10% or so). 

As noted, with those panel voltages. for a 12 V system you'll have very poor efficiency without an MPPT controller.