Solar Panels and Shading

[BroncoHauler]

Originally Posted by REF

...I made a storage box for it mounted under the rear shelf

Brilliant way to keep it accessible and keep it safe.


Herb

[TomH]

Brian F. (SMB-W) just told me that they are going to have some new panels that are less susceptible to partial shading killing off as much power. No details yet.

[Scalf77]

Sunpower Solar makes solar cells that have a built in bypass diode. They generally make grid tie only solar panels, and generally cell in the home systems market.

They do dump a lot of their B-grade solar cells on the open market, and can be picked up on Ebay. Many people use these to build DIY panels. I have seen multiple sellers that have flexible panels using there cells.

There was one company that was discussing using their cells for a hard panel.
http://www.sportsmobileforum.com/for...own-18975.html

That said, the bypass diode only does so much and when it does you would still loose the current and voltage of that cell. The issue being that you would still be limiting the all the cells to the same current as the partially shaded cell(s) until the shading was bad enough to make the bypass diode kick in.

Don't get me wrong, they would still be an improvement.

-greg

[1der]

Greg - perhaps you can shed some light on the combining of panels of different wattage. I have read what I consider very informed information about the inefficiencies of combining panels of differing wattage. Say a 100 watt additional panel is added to a my 300 watt panel. I am of the understanding that the 300 watt panel will be restricted by the 100 watt panel and thus the system will be 200 watts not 400. Is this correct? Does it matter if they are hooked up in parallel or series?

The other question is the practice of adding a portable panel to an all ready installed fixed system This is where the panel leads from the portable panel are added to the PV-In terminals on the existing solar controller. What happens here and is it really different from the above? Thanks!

[Scalf77]

Originally Posted by 1der

Greg - perhaps you can shed some light on the combining of panels of different wattage. I have read what I consider very informed information about the inefficiencies of combining panels of differing wattage. Say a 100 watt additional panel is added to a my 300 watt panel. I am of the understanding that the 300 watt panel will be restricted by the 100 watt panel and thus the system will be 200 watts not 400. Is this correct? Does it matter if they are hooked up in parallel or series?

The other question is the practice of adding a portable panel to an all ready installed fixed system This is where the panel leads from the portable panel are added to the PV-In terminals on the existing solar controller. What happens here and is it really different from the above? Thanks!

Ray,
Sure, mixing panels of different specifications can lead to issues, and worse it can be easy to do because we tend to focus on the wattage rating of the panel. The wattage rating is really made up of two major specifications of the panels Vmpp x Impp = Wattage.

I previously had an Kyocera Panel 140 watt panel it had Vmpp of 17.7 volts and Impp of 7.91 amps to get 140 watts (17.7 X 7.91= 140.007). I was looking to upgrade to a second panel and looked at Grape Solae 180 watt panel. This panel had a Vmpp of 19.67V and Impp of 9.71 Amps.

The simple math would sat that I have 180 + 140 = 320 watts. But lets dig deeper, since I have an MPPT controller I could have put the new panel in series or in parallel, either one of these could give me different results. If I chose to put them in series I would added the voltage 17.7 + 19.67 = 37.37 Volts. The current in series would be restricted to the lowest current panel, in this case 7.91 amps from the Kyocera Panel. If I do the math 37.27 X 7.91 = 295.6 watts. That is a Far cry from the 320 watts expected.

If I chose to go in parallel I would now add the currents, 7.91 + 9.71 = 17.62 Amps. For the voltage we would take the lesser of the two panels, in this case 17.7 volts. We do the math, 17.7 X 17.62 and we get 311.87 watts. While again this is not the 320 watts that we expected it is better than 295, we would have produced in series. In short, I decided to sell the Kyocera and purchase two new GS– 180 panels, so that they were matched.

Now if you were to take some panels that were mismatched even worse, the problem gets even worse. Take a LG 300 watt panel Vmpp = 32 volts x 9.4 Amps & a Renogy 100 watt panel Vmpp of 18.9 X Impp of 5.29 amps. The specs are much farther apart, so let’s do the math again.
First in Series: 32 + 18.9 = 50.9 X 5.29 Amps = 269.261 Watts.
In Parallel: 9.4 + 5.29 = 14.69 X 18.9 Volts = 277.641Watts.
In both cases the combined output of the mismatched panels is worse than original 300 watt panel.

Generally, if you are hooking up a portable panel it is done in Parallel to the hard-wired panel and it is done at the controller. Will this be a perfect solution, a lot depends on the specs of your panels, generally if they were close it won’t be so bad.

Hope this helps

[Twoxentrix]

Wow - Thats certainly more involved than the math I was using (1+1=2). Appreciate you guys clarifying this prior to buying my auxiliary panel. Thought I had read enough to perform an effective upgrade. frustrating part is now I know I dont know crap about what I should - starting to appreciate the comfort of ignorance.

[seasmith]

I have a Renogy 100 watt panel with
Renogy Wanderer -- 30A Advanced PWM controller i leave hooked up to the single house battery, while parked at the high camp in CO.

Thinking of getting a small BatteryMinder 5 watt unit to hook to the starter battery, as there is strong sun up there all morning.
Would this be in effect a parallel circuit config ?

Any one see a looming disaster in the works ?

Thanks

[1der]

Greg, awesome explanation, best one I have read because of the calcs and examples you included! Thank you!!

[1der]

Originally Posted by seasmith

I have a Renogy 100 watt panel with
Renogy Wanderer -- 30A Advanced PWM controller i leave hooked up to the single house battery, while parked at the high camp in CO.

Thinking of getting a small BatteryMinder 5 watt unit to hook to the starter battery, as there is strong sun up there all morning.
Would this be in effect a parallel circuit config ?

Any one see a looming disaster in the works ?

Thanks

I think we need a bit more info:
Are the two battery banks completely separate or are they connected together either directly or through a separator/isolator? If a separator/isolator what is the model?

[Scalf77]

Originally Posted by seasmith

I have a Renogy 100 watt panel with
Renogy Wanderer -- 30A Advanced PWM controller i leave hooked up to the single house battery, while parked at the high camp in CO.

Thinking of getting a small BatteryMinder 5 watt unit to hook to the starter battery, as there is strong sun up there all morning.
Would this be in effect a parallel circuit config ?

Any one see a looming disaster in the works ?

Thanks

This configuration does not fall into either Parallel or Series Panel configuration.
The Battery Minder 5 watt panel is it's own controller. So the above panel discussion were all based on the panels going to the same controller. Not that multiple controllers can't be a issue in their own right.

As Ray says we really need to understand you Battery/Isolator/Separator solution. In general if while camped your house and starter batteries were isolated from each other this would be an acceptable solution.

If you have bidirectional voltage monitoring separator, the Battery Minder would be redundant, as Renogy system would raise the voltage and cause the Batteries to be joined in parallel. This allows the renogy system to take care of both your house and starting batteries. That can be considered a plus or minus, depending on what you are intending and preference to taking care of your batteries.

The two solar controllers in parallel would could be a negative. If we take a look at most solar controllers (or any batter chargers) they tend to monitor voltage of the battery to determine what charge state to be in, if you have multiple controllers this could cause them to work against each other.

The common misconceptions is that multiple controllers would added to each other, that in most cases is wrong. There are systems that are destined to be connected, with stacking or master-slave solution.

-greg