24 volt solar panel recommendations?

The $100 controllers are fine as long as you don't need the features. Other than that they are functional and durable. I use multiples units in my portables because they can be split up between banks. I'll go with one large one for mounting.

I have heard of one person going over a pass at 12000 ft on a cold day here and blew their Blue sky controller. Blue sky replaced it with a larger one saying it was sized right but there was just the perfect set of events to push the panels pass what was expected of them. So don't max out your controller and start cruising over passes on a cold day I guess.

tpi wrote:
This is the plan I'm thinking-

1. Have panels switched between panel and controller, so on June 21 midday (or similar seasonal) in clear weather one of the panels can be switched off if there is chance of exceeding controller capability. When in storage-just operate on one panel for maintenance.
2. On an as needed basis, when present in the RV maybe he can push the envelope a bit with the controller and let it limit to the 22 amps..in the event he needs the power. If something starts to smell hot, feel hot etc. he can shut off a panel. Depends on his comfort level with that.

3. Living in CA he does a lot of camping fall winter or spring where all capacity could be used. Mornings and afternoons in the summer too. Overall he should get good bang for buck on the panel installation. And he's open to another controller in the event of it being too restrictive.

1) and 2)
In theory - yes. You can test the install on the best day and estimate whether you will exceed the limit. In practice - despite that estimate, you might still exceed the limit on a cold clear day, and when you smell something burning, it can be too late. My 2*245 flat install does exceed 20A at times in the "neighboring state" of Baja California in winter at sea level. I have 30A MPPT, and the manual suggests max array 430W (I have 490W), but they are not too stern about dangers of exceeding the limit.

With your 20A controller it all boils down to how well this particular model takes the heat - the more amps, the more heat in the circuit. Plus, high amps are often accompanied by high ambient temps in summer. Panel output decreases when ambient rises, but there is A LOT more sun radiation on the flat panel in summer, so in the end, in summer you'll get more amps AND more heat.

Yes, in storage I switch one panel off. This involves climbing the roof, which is not something too enjoyable, so I'll probably stop doing it because chances of exceeding my 30A limit in storage are zero due to batteries in storage being Full all the time. When it's Full, there is no current. But you plan on climbing the roof suddenly when you smell something burning, and when you're are in a hurry, bad things happen. Better get a 40-45A controller for that 500W array.

3) Yes, there are 20A MPPT Chinese clones that can be had for $100, I won't comment on their features, but adding another 20A controller is too much pain. You would need to run another set of wires, and install another breaker, and to find a room for that another controller. There is usually very limited room in trailer. It's better to get a 40-45A controller instead.

Almot wrote:

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".

Thanks for this and all the other comments. The documentation is not particularly stern with warnings about going over the limits temporarily. Neither was the Blue Sky tech- but he did indicate it was protection not a feature. This is the plan I'm thinking-

1. Have panels switched between panel and controller, so on June 21 midday (or similar seasonal) in clear weather one of the panels can be switched off if there is chance of exceeding controller capability. When in storage-just operate on one panel for maintenance.
2. On an as needed basis, when present in the RV maybe he can push the envelope a bit with the controller and let it limit to the 22 amps..in the event he needs the power. If something starts to smell hot, feel hot etc. he can shut off a panel. Depends on his comfort level with that.

3. Living in CA he does a lot of camping fall winter or spring where all capacity could be used. Mornings and afternoons in the summer too. Overall he should get good bang for buck on the panel installation. And he's open to another controller in the event of it being too restrictive.

I'll follow up with how it all works out..

Almot wrote:
With MPPT controller you can input as much amps as you want, and it will block the excess.

Blue Sky gives specific warning against over driving the controller.
I would stick to the manual.

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".

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!

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.

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.

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

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.