24 volt solar panel recommendations?

[tpi]

Is this panel decent? Or is there reason to buy one of the slightly more expensive panels from Solar Blvd? Friend has Blue Sky controller capable of using the 24 volt panels.

https://www.solarblvd.com/product_info.php?cPath=1_270&products_id=3005

[pianotuna]

Hi Jfet,

It might boil down to the poly panels having more diodes than the mono. I don't know the answer to that question.

My unisolar panels have diodes between every cell. They work extremely well but are, relatively speaking, huge. They also outperform in high heat situations and because I went with a parallel/series wiring for a controller input voltage of 33, do well by me. I followed the 125% capacity suggestion and so have lots of head room for cloud effects.

[Jfet]

pianotuna wrote:
Hi,

It is the experience of folks on the forums that poly panels do some what better in shade or partial shade.

No scientific research that I have found backs that up. The better shade performance is likely to do quality panels vs inferior panels, the poly being higher quality than the mono they are compared against.

[BFL13]

I see it is rated for 30a at 12v and 22a with 24v, but am confused by this warning-

"....Do not connect a PV array capable of delivering greater than 24 amps of short circuit current ISC at STC with 36 cell modules, or 11.8 amps with 60 cell modules....."

http://www.blueskyenergyinc.com/uploads/pdf/Manual_BSE_SB3000i.pdf

[pianotuna]

Hi,

I see 17 amps of output (mppt controller) from 256 watts of panels with a flat fixed install. Input voltage is 33.

JiminDenver wrote:
My pair of 245w panels peaked out at 34a and that was at 10,000 ft and tracking the sun on a cold morning. I don't think he will see much clipping in a flat mount.

[pianotuna]

Hi,

It is the experience of folks on the forums that poly panels do some what better in shade or partial shade.

The extra efficiency of mono only allows a slightly smaller panel. If a poly panel fits--then the end result is the same number of watts.

Jfet wrote:

pianotuna wrote:
Hi tpi,

I believe solar panels work, or they don't. So long as there is an ability to exchange a non working panel I'd go on best price.

I would want as many diodes per panel as possible, and I'd probably favor Poly over Mono.

Why?

"Monocrystalline cells have a higher efficiency than polycrystalline cells due to the structure being made from one large crystal as opposed to many small ones. In addition to having an overall better efficiency, monocrystalline panels can perform up to 10% better than polycrystalline panels in high ambient temperatures."

[tpi]

Thats his plan-if the controller is maxxed out too frequently he'll upgrade. Westend thanks didn't realize that was input. Thought it was output..

[westend]

tpi wrote:
Westend, what you're saying is it is essentially OK to let the controller limit the output to the 22 amps? There was nothing in the documentation that sounded too dire if you were to exceed the recommended input.

Edited my above post. The 22 amp current limit is INPUT. As 2oldman said, a bigger controller won't be tossing away charge current but I'd doubt there will be much to toss with two modules.

[2oldman]

tpi wrote:
There was nothing in the documentation that sounded too dire if you were to exceed the recommended input.

It'll probably just get hot.

I would hope an upgraded controller is in the future should that be the situation. That's lost power.

[tpi]

Westend, what you're saying is it is essentially OK to let the controller limit the output to the 22 amps? There was nothing in the documentation that sounded too dire if you were to exceed the recommended input.

[westend]

tpi wrote:
https://www.solarblvd.com/index.php?cPath=1_270

Is there any on this list notable for high quality?

I don't think he cares about spending a few more bucks if it reliably translates to quality.

I've heard good things about the Canadian Solar modules. They are built for the North so have good durability.

In a previous post you said that the user is going to switch one module so that the controller won't be affected by a large current. I'd suggest that he wire both in parallel and switch the single power lead before the controller. I'm not familiar with Blue Sky controllers but most MPPT controllers clip the input at whatever the rating is and continue to push the rated current to the batteries. There would be little reason to halve the available harvest to get under the controller's rating.

Edit: Did a little reading about the Blue Sky controller. It is limited by 22 amps of INPUT from 24V modules. It's going to be difficult to get two modules with a short circuit current rating of 8 amps to deliver 22 amps.

[tpi]

I'll study more.. I'm sure I can upgrade when I go to pick them up.

[2oldman]

tpi wrote:
Is there any on this list notable for high quality?

Take a look at the most expensive panel on that page. Read the specs. Now go back to the cheapest one. A lot of difference there.

Imagine trying to get a warranty fulfilled by a Chinese company. Unless they have a presence in the US, almost impossible. I don't think solar panel failure is all that common, but I did have a BP panel short out a few years ago. Big burned spot on the back. After 4 years of use (with a 5-year physical warranty), they replaced it in a few days, no questions asked, no charge, no return. This just happened to be around the time of the big gulf oil spill, and I think BP was doing everything possible to be a good citizen.

[tpi]

https://www.solarblvd.com/index.php?cPath=1_270

Is there any on this list notable for high quality?

I don't think he cares about spending a few more bucks if it reliably translates to quality.

[2oldman]

RoyB wrote:
It could be the 24VDC Solar Panel DC OUTPUTS work better with SOLAR CONTROLLER but to me the final DC output going to the RV Battery setup should remain at 12VDC so that you can utilize all of the working elements the RV TRAILERS has to use.

They work better with the WIRE from the roof to the controller. Thinner wire can carry lots of volts but not lots of amps.

The OP has indicated the trailer system remains at 12v. If you want a '24v system' however, then you need a DC/DC converter with enough amps to handle the jacks and slides. I have one, and the nice thing about that is I can set the trailer to 12.5v, and it never fluctuates due to battery charging or equalizing.

As for buying stuff on the cheap, I rarely do that because it just doesn't work for me. They have to cut costs somewhere - diodes, weather-proofing, frame.. something.

[BFL13]

This summer I intend to run a test of my 24v panel with MPPT to the 12v battery bank, vs the same panel with PWM on the same batteries wired as 24v.

I am suspecting the summer heat on the panel reduces the power enough to put the PWM on 24v ahead in amps to the battery.

Even if the 24v PWM comes out ahead, the problem remains to get 12v to the trailer. Anyway first to see if it is better, then see if it is "worth" solving the 24 to 12 problem.