Custom Solar Panels

OK...I could really use a clarification.

I have found a manufacturer that will make me solar panels in the size I need. They all have blocking diodes and are weatherproof (resistant!) I have to choose between 18V and 36V. Assuming I am using an MPPT controller which voltage would you choose and how would you wire them to be most efficient?

Thanks,

Rick

Wanderman said:

I have to choose between 18V and 36V.

Click to expand...

The charge controller will knock down the 18V to the 13.6-14.4 VDC the battery requires.  I would think the 18V is the appropriate choice as other than possibly some military vehicles as (almost) all vehicles are 12 VDC.

Tony,
Many high quality MPPT controllers will use almost any voltage you can get to them. My question related to the advantages and disadvantages of sending the MPPT controller 36 volts rather than 18 volts. Is there a benefit?

Rick

The only benefit would be half as much current so half as much voltage loss along the wiring between the panels and the controller.

Check with the manufacturer of the controller you intend to use and see if it will work properly with 18 volts, I am pretty sure it will.

OK...I am just about ready to order my custom, semi-flexible panels.

I have 3 panels totaling 410 watts. (170w/140w/100w)

Now I have to decide on a voltage. I can choose 18v/24v/36v

Bearing in mind I will be using an MPPT controller what is the best way to go voltage wise and wiring wise. Series or parallel? 2 on one and 1 on the other? (i.e. 2 18v panels in series for 36v and the other panel at 36v?) or all three at 18v? 24v? 36v?  Some mix of the above?

I am looking for low light and overall efficiency. Obviously shading is an issue, but they are set up with diodes.

What controller???? So far I am liking the Bluesky 3024iL with the IPNPro remote. Which will give me 40 amps at MAX 500watts of panels.

I am using #6 wire at the panels to an AM SOLAR CB style combiner box at the fridge vent. #4 from the combiner to the Charge controller and then #2 to the battery bank. Which run should be shortest to be most efficient??? What types and quantities of connectors do I need from the panels all the way to the battery bank?

Lastly, I currently (pun intended!) have 2 Trojan 27MTX batteries totaling ~220 amp/hrs giving me ~110 amp/hrs to play with. I will be replacing these next season with Trojan SCS225s which will fix in the existing slide out tray and give me a bit more power to use (~130 amp/hrs). I am toying with the idea of adding 1 or 2 additional batteries. Either up front or under the couch in a dual vented box. (5-6 ft to the existing bank)

One odd question, I have an inverter under the couch that is fed by the existing dual battery bank through 2/0 battery cables. I know if I shut off the inverter I could use these wires to charge the battery from the solar controller. What would happen if both were on at the same time, i.e. charging current TO the battery in one direction and power feed FROM the battery TO the inverter in the other, at the same time?

I use around 80 Amp/Hrs per day (night) as an average. Not being super conservationalist.

Any suggestions, comments???

Thanks!

Rick

Wanderman said:

Now I have to decide on a voltage. I can choose 18v/24v/36v

Click to expand...

I would go for 24 volt panels. That's because that's the open circuit voltage on all the ones I have used and they all work fine with any solar controller I've tried. I think 24 volts is the most common voltage used for RV solar controller inputs. At least all of mine have been 24 volt.  The ones I have now are rated at "Peak voltage: 23.57 volts open current" as shown here:

http://www.harborfreight.com/45-watt-solar-panel-kit-90599.html

"Series or parallel? "

Parallel if all the solar panels are the same, such as all 24 volt. Series only if you have to mix them because of different voltage panels.