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

[Salvo]

So your data is not from a typical charge profile.

I have 130W and usually go into absorption by 1 pm. Unless you're really using a lot of power, with 500W, the battery should be in absorption by noon. That means max charging current is cut back.

I would add an amp meter (or Turnigy Watt Meter) to the charge controller to monitor max current. Otherwise, you're in the dark whether to switch one panel off or not.

CA Traveler wrote:

Salvo wrote:
What was Vbat when charging at 43 A? Was it held down?

CA Traveler wrote:
As another reference point my 3x250W flat panels on 3/3/15 in Phoenix with a clear sky produced 43A or 600W at the controller output. This was for 1.5 hours before the clouds moved in. There were several peaks of 48A. For 2X panels this would product 28A or 400W.

I wanted to determine the panel and controller output capability and used the inverter, etc to draw the maximum amps from the controller. The controller kept the battery voltage at about 13.8V.

[CA_Traveler]

Salvo wrote:
What was Vbat when charging at 43 A? Was it held down?

CA Traveler wrote:
As another reference point my 3x250W flat panels on 3/3/15 in Phoenix with a clear sky produced 43A or 600W at the controller output. This was for 1.5 hours before the clouds moved in. There were several peaks of 48A. For 2X panels this would product 28A or 400W.

I wanted to determine the panel and controller output capability and used the inverter, etc to draw the maximum amps from the controller. The controller kept the battery voltage at about 13.8V.

[tpi]

Re: Needed power- He doesn't want to store the RV with partially discharged batteries. He must store in a storage lot without power, can't park in front of house to get a full charge after returning home. He also wants to have full batteries to use inverter system to work on RV in storage.

Open circuit battery voltage at the end of trip is another factor here. Last three day trip he dipped to 11.95 volts on the batteries (without solar installed). There's approx 400 AH of house batteries. He's working on consumption w/ LEDs etc. but w/ kids it is a struggle..

[tpi]

Switching one panel on and off is not practical. It requires climbing the roof to connect-disconnect MC4 plugs, or running an extra wire loop all the way to the inside of trailer with a switch on it. Either scenario is complicated, and you might not even be there at that exact moment when switching is necessary.

Run two drops to the controller, one for each panel and switch at least one. Only one extra wire down would be necessary (one negative and two positives). Controller is probably going to be centrally located in the RV.

The primary function of this system is to charge/maintain the batteries during storage, and to attempt to end weekend outings with a greater state of charge in the batteries. This rig is not used for extended boondocking. He has wife and two small kids and the camping is a mix of hookup RV parks and dry camping w/o hookups. Generally no extended times in any one place.

Look at it this way, it is an inexpensive system using one extra inexpensive panel that can be switched in in poor conditions. If the need crops up for more power out of the system, he can replace the controller and possibly add more panels.

FWIW, I wouldn't bother switching off one panel. It's too much of a hassle, and your buddy would be a slave to the limits of the controller. The controller will probably work fine. Nothing is really lost if it quits working.

He'll install the switch so it is left unsupervised on one panel, but I hope you're right on this... If he could get the 22 amps that would be great.

[CA_Traveler]

Almot

I agree. At this point the 20A controller has some value but later maybe not so much.

[Almot]

tpi wrote:
He already has the controller-and he will upgrade it if he's switching off a panel too often and giving up needed power.

Switching one panel on and off is not practical. It requires climbing the roof to connect-disconnect MC4 plugs, or running an extra wire loop all the way to the inside of trailer with a switch on it. Either scenario is complicated, and you might not even be there at that exact moment when switching is necessary.

He will not know how much of "needed power" he will be giving up. It doesn't sound like he has proper means of monitoring this. One thing is certain - with 20A unit he WILL be giving up some power in Ca in winter, and yet more power in summer.

But, like Salvo implied, if it goes up in smoke, this won't be a big loss. Because then he will do what should've been done from the beginning - get a 40-45A controller.

[Salvo]

What was Vbat when charging at 43 A? Was it held down?

FWIW, I wouldn't bother switching off one panel. It's too much of a hassle, and your buddy would be a slave to the limits of the controller. The controller will probably work fine. Nothing is really lost if it quits working.

CA Traveler wrote:
As another reference point my 3x250W flat panels on 3/3/15 in Phoenix with a clear sky produced 43A or 600W at the controller output. This was for 1.5 hours before the clouds moved in. There were several peaks of 48A. For 2X panels this would product 28A or 400W.

A 20A controller sounds marginal.

[tpi]

Thanks for the data points. He already has the controller-and he will upgrade it if he's switching off a panel too often and giving up needed power.

[CA_Traveler]

As another reference point my 3x250W flat panels on 3/3/15 in Phoenix with a clear sky produced 43A or 600W at the controller output. This was for 1.5 hours before the clouds moved in. There were several peaks of 48A. For 2X panels this would product 28A or 400W.

A 20A controller sounds marginal.

[Almot]

One of features - that cheap 20A controllers are usually lacking - is a remote display. This means, you not only have to route additional wires to and from that additional controller, but also mount it in easily accessible place where you can see the on-board display and push the buttons. In all but very big RVs it's difficult enough to find a good permanent location (in terms of both technical requirements and esthetics) for one remote-less controller, not to mention two of them.

Portable setup is a different logistics, you can use several small controllers, a milk crate placed upside down under the trailer - away from rain - will carry 3 or 4 of them, and a few car jumper cables will take care of wiring. That's what I did with my single controller before mounting everything permanently.

2*250W array requires 35-45A MPPT controller. 20A unit may or may not go up in smoke when hitting 20A limit, but some energy will be lost. If the OP is concerned about getting as much energy in winter as possible, it's better to get a controller bigger than 20A, to me this is a no-brainer.

[JiminDenver]

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.

[Almot]

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.

[tpi]

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..

[time2roll]

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.