solar watts LOW - RV-Dreams Community Forum

whitelight · RV-Dreams Community Member

solar watts LOW

Bill and Linda · RV-Dreams Family Member

#4 would be the smallest I would consider and then only if I had a problem getting #2 down from the roof. I have always used #2 from the roof. It is easy to have a lot of loss with 12 volts and the relatively higher amperage vs. the voltage. Tenths of volts count.

Can’t say that’s the exact reason in your case, but #6 is too small IMO for 20 feet.

That said, recall at this time of year if the sun is at a low angle you will have less output even though the 400 watts you were expecting is nominal with direct sun.

whitelight · RV-Dreams Community Member

I now see that these are 24volt panels Renology monocrystaline panels. Am I going to have to switch to 12volt panels?

-- Edited by whitelight on Sunday 5th of October 2014 11:13:41 AM

bjoyce · RV-Dreams Family Member

You could replace the TS-60 with a TS-MPPT-60 and stay with 24-volt panels.

whitelight · RV-Dreams Community Member

How would that work? How come my TS-60 wouldn't work?

bjoyce · RV-Dreams Family Member

The TS-60 is PWM, which will take the 24volts to whatever volts is needed and keep the amps the same. The TS-MPPT-60 is MPPT, which transforms the 24volts to the proper volts and thus you get more amps. Volts times amps equals watts, with MPPT the watts are preserved with a little efficiency loss. 24 volt panels generating 400 watts will be 400 / 24 = 16.67 amps. With PWM you will get 16.67 amps at 12 volts or 200 watts. With MPPT you will get close to the 400 watts and a little loss since the transformation is not 100% efficient.

whitelight · RV-Dreams Community Member

Good info thank you!! With 500 watts of panels is a mppt-45 big enough it do I need a ts-mppt-60?

Jack Mayer · RV-Dreams Family Member

I would get the 60 since it leaves room for expansion.

A-S Travelers · RV-Dreams Family Member

Here is a link to a voltage drop calculator to help determine the wire size you should use. Shoot for a 1% drop if possible, but many folks find that 2% is OK.

By the way, how far N are you? Also we are in the start of winter, almost 4 months past the peak sun season.

If you haven't read Jack Mayer's website here is a link for great solar & elect info.

whitelight · RV-Dreams Community Member

I'm going to rerun the wire from the roof to the charge controller. Also I think I can be more efficient and take off about 5ft of the wire length by rerouting it. I'm in CA central valley. Thx for the info

-- Edited by whitelight on Monday 6th of October 2014 07:27:47 PM

whitelight · RV-Dreams Community Member

Would it be adventagous to wire these two 24 volt panels in series since I will be using an mppt-60 controller? Would 6 gauge wire then be OK or not?

Lonney Wade · RV-Dreams Family Member

6 gauge black jacket wire is only good for 75 amps, the wire I will be using is 4 gauge with the thicker orange jacket, good for 140 amps.

Compare the orange 4 AWG wire (140 amps) to the black 4 AWG wire (100 amps) and the price.

http://www.wireandcabletogo.com/4-AWG-Welding-Cable-Class-M-UL-CSA.html

http://www.wireandcabletogo.com/Welding-Cable/

I usually buy 100 foot of this wire on a spool.

I will be using this for my solar panels (576 watts) from top of roof to mppt-60 controller to (630 amp) of batteries.

Lonney

-- Edited by Lonney Wade on Thursday 9th of October 2014 06:15:00 PM

Bill and Linda · RV-Dreams Family Member

whitelight wrote:
Would it be adventagous to wire these two 24 volt panels in series since I will be using an mppt-60 controller? Would 6 gauge wire then be OK or not?

Independent of other considerations, remember if you wire panels in series then any shade on any panel reduces the output of the other panel. IMO, only if you believe that you will never be in an environment where there will be zero shade on a panel should you wire in series.

A-S Travelers · RV-Dreams Family Member

Lonney Wade wrote:
6 gauge black jacket wire is only good for 75 amps, the wire I will be using is 4 gauge with the thicker orange jacket, good for 140 amps.
Compare the orange 4 AWG wire (140 amps) to the black 4 AWG wire (100 amps) and the price.
http://www.wireandcabletogo.com/4-AWG-Welding-Cable-Class-M-UL-CSA.html

http://www.wireandcabletogo.com/Welding-Cable/

I usually buy 100 foot of this wire on a spool.

I will be using this for my solar panels (576 watts) from top of roof to mppt-60 controller to (630 amp) of batteries.

Lonney

-- Edited by Lonney Wade on Thursday 9th of October 2014 06:15:00 PM

The thicker wire insulation (jacket) may allow more current to be carried by the wire, I'm assuming, because the heat the extra amperage generates can be more safely handled by the thicker insulation.

With solar installations, the issue is not how much total amps the wire can carry but making sure that the wire size is large enough to carry the amperage you have for the distance you need to go, without more than 1 to 5 percent voltage drop. I don't believe how thick the insulation is on the wire will have an affect on the voltage loss over distance.

Lonney Wade · RV-Dreams Family Member

The black wire has 374 strands and the orange wire has 1045 strands of wire, the finer the wire the more amps it can carrier.

Because DC amps are carried on the outside of the wire, not the middle or the diameter of the wire.

Lonney

whitelight · RV-Dreams Community Member

Good point with the shaded panel that is a good enough reason not to wire then in series. Also good info on the wire strands I didn't know how important the number of strands in a wire were for DC current. Thx!

jimindenver · RV-Dreams Family Member

Once you get a MPPT controller your two panels should be good for 35a at peak. My pair of 245w mono panels peak out at 34a. Then again that is a clear cold day at 10,000 ft so YMMV.

My panel will be installed over the off season and I'll probably go with the TS-MPPT-60 not because I have more room on the roof but because it can track multiple arrays. That will let me use a 230w poly panel with different characteristics and voltage along with the 245s. Put them simply all on one controller and the different voltages can confuse the MPPT program. The three panels together at peak should be good for 50a of charging/ load offset at peak.

-- Edited by jimindenver on Friday 10th of October 2014 09:38:37 AM

whitelight · RV-Dreams Community Member

If I have 500 watts in panels @ 24 volts 500/24 = 20.83 amps is best case senerio correct?

jimindenver · RV-Dreams Family Member

Only if you use them on a 24v bank. 500/12 =41.6a but I doubt you will ever see that realistically or actual 500w. Like I said I can see 34a off of 490w.

The way it works is the MPPT controller takes in the higher voltage and converts it down to a useable voltage for our battery banks. The excess voltage is coveted into extra amps, that's why you get more amps than the panel is rated for.

-- Edited by jimindenver on Friday 10th of October 2014 05:01:33 PM

whitelight · RV-Dreams Community Member

Ahh that makes sense, I will be happy with 35amps.

-- Edited by whitelight on Friday 10th of October 2014 04:56:29 PM

-- Edited by whitelight on Friday 10th of October 2014 04:57:15 PM