Connect parallel two different voltage solar panels using voltage step up converter

Thread Starter

ac909

Joined Oct 29, 2017
4
Is it possible to connect two different voltage solar panels using step up converter? I understand that if the voltage is different, you will get voltage to lower voltage when you connect parallel. End up losing voltage and wattage. For example, connecting 18v and 24v panels. You end up getting 18v after connecting parallel. How about using step up converter to boost 18v to 24v and then connect 24v panel? Will it be 24v since two panels has same voltages? Thank you for your comments.
 

N11778

Joined Dec 4, 2015
174
You will get 24v and the 18v panel will do nothing it will be on vacation.
no watts from the 18v panel.
What are you trying to do with the panels charge 12v batteries or what?
 

bug13

Joined Feb 13, 2012
1,705
Guessing you want more power? Put the two panel in series, then use a DC-DC step down converter to convert to the voltage you want.
 

Thread Starter

ac909

Joined Oct 29, 2017
4
Thank you all for your comments. I am learning from you guys. If you see my attached picture it shows that it puts out lowest voltage and added amps. That is why I thought that it is possible to use step up converter to boost lower voltage to match higher voltage. What I was trying to do is. I have one 150w panel, Ipmax 6.2a, Vpmax 24v and two 100w panels Ipmax 5.81a, Vpmax 17.2v. I was thinking connect two 100w panels parallel first and get 17.2v 11.62a. Then use step up converter to boost 17.2v to 24v and connect parallel with 150w panel. Then theoretically you get 24v and 17.82a(maybe less because voltage was boosted). I know there is MPPT charge controller to handle if you connect all series. But I am trying to use existing charge controller and avoid to purchase new MPPT charge controller. Does it work in real setup or just my stupid ideas? or MPPT is the only options? Thanks.
Solar Parallel Connection.gif
 

Bernard

Joined Aug 7, 2008
5,254
What is the intended load. If charging a 12 V Pb- H2SO4 battery, I would parallel all 3 with diode isolation on each. Current would be around 15 A or 210 W.
 

bug13

Joined Feb 13, 2012
1,705
Hi ac909,

I think I will point out that your 24V panel will not always putting out 24V, on a sunny day, it maybe more than 24V, on a cloudy day, it maybe less than 24V.

Keep this in mind :)
 

Thread Starter

ac909

Joined Oct 29, 2017
4
Hi Bernard
My intended load is 24v. Two 12v batteries connected in series.
 

Thread Starter

ac909

Joined Oct 29, 2017
4
Hi Bug13
I am just trying to match higher voltage closest possible using step up converter. It never be same voltage since they are different panel, but at least it will be close to higher voltage. I think... but what do you think?
 

bug13

Joined Feb 13, 2012
1,705
Hi Bug13
I am just trying to match higher voltage closest possible using step up converter. It never be same voltage since they are different panel, but at least it will be close to higher voltage. I think... but what do you think?
For charging 24V batteries, I would just use the 24V panel connect to your MMPT then your batteries.

If you want the extra speed, I still think put the 24V panel and 12V panel in series, connect to your MMPT if your MMPT can take 36V inputs.

Or buy one of these: (notes these rated up to 10A, but I don't think your panel can reach the max Amp rating, unless you are in a very tropical location, I think it will work) (note2: beware of fire safety if you are using these, or get a proper Mean Well buck converter)
https://www.ebay.com/itm/DC-DC-Converter-10-12-15-20A-150-250-300-400-1200W-Step-up-Step-down-Buck-Boost/382219150784?hash=item58fe0965c0:m:mCHY1nLxgu47cYpdyd1LmDA

Step it down to the max input voltage of your MMPT, then charge your batteries.

What's the AH rating of your batteries? If they are seasonal small, your 24V panel + MMPT is good enough
 
The charge regime of your batteries is important. If you are charging 24v flooded lead-acid you will need to supply up to or greater than 30v for a complete charge. The 24Vp panel will probably not reach sufficient voltage. You will need to put your panels in series. Eg the two 17Vp panels in series would be ideal for 24v charging.

If you just hook your 2x17vp panels directly to the batteries in series they will charge the batteries approximately to completion in a simple bulk charge, but you will have to disconnect them when the voltage reaches 29 volts.

As suggested, an MPPT controller would be ideal for charge management. If it's Vin max was high enough, you could put all your panels in series and maximise your charge power. Or if you obtain a buck-boost mppt charger (there are a few) you could hook your panels all in parallel if you preferred.
 
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