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

[Almot]

tpi wrote:
1. Several mentioned the controller clipping when fed above rated wattage. I'm familiar with audio amplifier clipping-and I assume controller is some kind of switching power supply. What is going on when the controller is clipping? The pulses can only be to a certain level?

2. When the batteries are fully charged what is the mechanism for the controller to back off the charging? I would assume it not shunt the excess power into heat.

1) No. With MPPT controller you can input as much amps as you want, and it will block the excess. You only need to watch out for input volts - max input voltage of the controller should not be exceeded.

2) No, MPPT controller won't shunt the excess into heat when battery is full.

When battery state is nearing Full, its resistance rises and current drops. Controller simply can't push into battery more current than it would accept. The only thing that controller "controls" at this stage, is the volts. At ~80% charge the controller enters Absorption stage where it's keeping the voltage constant and slightly elevated, 14-15V. Cheaper/simpler controllers have non-adjustable timed Absorption, usually 60 minutes. Better/more expensive controllers have adjustable timed Absorption (you can adjust the time), and also current-based absorption - the Abs stage ends when current drops to certain level (this level you can also adjust). Some other controllers change the duration of Abs stage depending on the voltage at the beginning of charging. Bluesky is not the most advanced line of MPPT, they are a "OK" line.

When Abs stage ends, controller enters the Float stage - at this stage it's keeping the battery at constant low voltage ~13.6V until the charging current drops to zero or sun goes down. Then controller shuts down.

As noted by others, we are talking here about MPPT controllers because with 24V panel you can only use MPPT. PWM controllers have the same Abs and Float stages, but they work differently when it comes to "clipping".

[BFL13]

smkettner wrote:
22a is max with 12v panels, 11.8 is max with 24v panels.
That is the max rating. I realize the wattage is not equal but neither is the output.

why 30a at 12v vs. 22a at 24v? I just take these things at face value. Otherwise the magic smoke comes out. The current limit appears to be controlled by the heat sink temperature. (see thermal protection p6) I assume if the controller is over driven too much it may burn out before thermal protection limits the current.

Morningstar has a max amp limit regardless of voltage.

It is just goofy. They allow for 1.25 like NEC says, but also say with 24v panels (60 cell) that Voc limit is 40v and 290w. (My 230 w panel is 37Voc so that is ok) My Eco-worthy "20 amper" has a 42 or 45v Voc limit depending on which spec you read so the 40Voc limit with a "22 amp" controller sort of fits in I guess. Except it does not allow for putting two 12v panels in series. The Tracer MPPTs at least will do that at their 100Voc limits for extra $ above the Eco-W, but the BlueSky 3000 is more for less 😞

The 11.8a Isc limit makes no sense wrt the 22v clipping limit that I can see. IMO the clipping should be at say 1.25 the Isc at STC limit if the controller must have an Isc limit. Most only have Voc limits.

It is all so weird!

[CA_Traveler]

Last fall I paid $200 for 250W from SB for a different Chinese brand so that is a good $/W price.

Check Morningstar controllers as they handle over paneling. For mine the only restriction is to not exceed the 150V input spec. Otherwise they derate to the maximum output amps. ie The occasional derate at say noon time vs more overall day power may be a reasonable option with the current decreasing panel prices.

[time2roll]

22a is max with 12v panels, 11.8 is max with 24v panels.
That is the max rating. I realize the wattage is not equal but neither is the output.

why 30a at 12v vs. 22a at 24v? I just take these things at face value. Otherwise the magic smoke comes out. The current limit appears to be controlled by the heat sink temperature. (see thermal protection p6) I assume if the controller is over driven too much it may burn out before thermal protection limits the current.

Morningstar has a max amp limit regardless of voltage.

[BFL13]

smkettner wrote:

BFL13 wrote:
Repeating--

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

Should not be confusing. The panel will either meet the specs or don't use it.
Looks like this controller is not real good at clipping power to protect itself.

I don't understand the 11.8a vs the 22a

[time2roll]

BFL13 wrote:
Repeating--

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

Should not be confusing. The panel will either meet the specs or don't use it.
Looks like this controller is not real good at clipping power to protect itself.

[BFL13]

To clarify, you must use an MPPT controller since only they have the buck converter to go to 12v at the battery. You can use a PWM controller with the 24v panel if the batteries are 24v too.

[Ed_Gee]

tpi wrote:
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

IF you are going to use a MPPT type charge controller, this will be a good panel for you as the MPPT charge controller can make good use of the excess voltage this panel can put out.

IF you don't use an MPPT charge controller, then you are wasting money and should get the 12V type panels with the nominal 17 - 22 Volt DC output.

[BFL13]

Repeating--

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

[westend]

1) The controller limits the output would be a better description than "clips". It is nothing like audio amplifier clipping where the excessive power flattens the AC waveform.
2)The controller measures voltage and amperage acceptance through the output. When the batteries reach a certain level of charge (say 80%) the controller outputs a lower voltage than the bulk or absorption stage. Some cheaper controllers have time-based charge settings where the different stages of charge are controlled by duration. My understanding is the Blue Sky operates in the former situation.
Some controllers are able to be programmed as to output voltage and duration of charge cycles.

[tpi]

Thanks for all the information-and various points of view. This has been very helpful. I have a couple general questions about controllers raised by this thread. Hopefully someone has a link or quick answer..

1. Several mentioned the controller clipping when fed above rated wattage. I'm familiar with audio amplifier clipping-and I assume controller is some kind of switching power supply. What is going on when the controller is clipping? The pulses can only be to a certain level?

2. When the batteries are fully charged what is the mechanism for the controller to back off the charging? I would assume it not shunt the excess power into heat.

Thanks again..

[2oldman]

smkettner wrote:
What spec are you looking at?

The description of the framing, and the fact that they made an effort to discuss that.

[time2roll]

2oldman wrote:

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.

What spec are you looking at?

[BFL13]

Nit-pick, the wiring for a 24v panel set-up to 12v battery is only different for the panel to controller section (can be thinner with 24v). The section from controller to battery is 12v, so it is the same gauge. If the batts were also 24v, then the wiring on that section could be thinner too.

[Almot]

tpi wrote:
At least from my limited knowledge, the 24 volt panels work for my friend on his bus.

1. The physical size works for him. Works with what is already on the roof.

2. Running at a higher voltage it appears from the controller documentation that the wiring sizes can be smaller. Wiring from panels to controller-which translates voltage to what is appropriate to batteries.

3. Cheaper per watt.

Thanks for the input. Ordered the panels.

Too late to discuss since you've ordered already, but:
1) Sizes of 250W panels differ very little from brand to brand or model to model. So, any 250W panel will work "with what is already on the roof".
2) Wiring sizes are always smaller for 24V panel than for 12V, obviously. This is not brand-specific.
3) Also not brand-specific. Most any 24V panel is cheaper per watt than 12V.

However, what is important - and what was not addressed, is the frame quality - profile and thickness.

Also, what Don Pianotuna mentioned - the number of diodes. Not every manufacturer provides these data.

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 don't see anything. Solarworld perhaps. New or little known Chinese brands are a gamble - no information and quality varies. For better assurances you have to pay more, and it would be not "a few bucks" difference. I personally don't view $100 difference as a major setback when talking about a long-term project like 15-20 years. If your friend's goals are not of this scale, then I wouldn't worry at all.