24 volt solar panel recommendations?

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.

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.

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..

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.

Almot

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

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.

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.

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.

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.

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.