Is it possible to add switch for an additional solar panel?

[atperci]

I installed 2 - 111 watt MiaSole thin film panels on our MH last year. These are 12v nominal panels that output 19.4v and 5.7a at STC . I bought them a couple of years ago for $0.45/watt. They work great in full sun, the batteries are fully charged part way through the day. But are mounted toward the front of the rig. While on our last trip, this area stayed in the shadows while the back of the MH had at least some sun throughout the day. I would like to add an additional panel or two to the rear of the roof, for when we are parked in the shade at a SP or NP campsite.

The power characteristics of the current panels are difficult to match, but I have finally found ones that are very close. They are Topoint 190w panels with STC rating of 37.2v and 5.24a. At $150 each, locally available, they are a pretty good deal. It will require placing the current panels in series and adding the new panel(s) in parallel with the old.

I have a 30 amp controller and can easily add 1 more of these panels, but I was wondering if I could add 2 more, then place one panel on a switch that I could connect when we are under shaded conditions and need extra power. But disconnect to keep from overloading the CC when in full sun. I know, I know, just buy or you should have bought a 40 amp controller, unfortunately that's not in the budget at this time. At some point in the future a 40 amp CC and 2 extra 6v GC batteries will be. But thats wishful thinking for now though.

So what do you think? I have the room in the combiner box for more wire and maybe a (remote) switch of some sort, but the flexible conduit from the combiner to the CC is filled with 6awg wire, so can't add a separate run. I don't particularly want a carry out panel that size and we are often away from the rig most of the day so I don't want to leave it out. Could a relay of some sort work?

Thanks in advance! I appreciate any and all ideas that you can think of.

Tom

[jrnymn7]

yoosmart has good prices. And the tracer BN (user programmable) series is only $25 more, including the remote display.

3215 RN

3215 RN with remote display

3215 BN with remote display

[atperci]

jrnymn7 wrote:
I've seen 300w out of two 140w panels, on a mild, mostly cloudy day, so I wouldn't count on clouds to "protect" the controller. One break in cloud cover, and some edge of cloud effect, could possibly overload the controller. You may be best to just run a separate circuit, and parallel the two systems. (Or bite the bullet for a larger controller.) You wouldn't have the hassle of matching panel specs to the old panels, either, if you went with two set-ups.

Thanks for the info. I didn't think about the edge of cloud effect. I might even have to separate both additional panels or as suggested run them through a different controller. Thanks again!

[jrnymn7]

As for voltage drop, I'm seeing less than 1/6th of one percent (0.05v / 33v), thru 50' (one way) of 6awg, at 8a from panels to controller. You may be over-estimating your losses? Have you checked them with a dmm?

[jrnymn7]

I've seen 300w out of two 140w panels, (pointed), on a mild, mostly cloudy day, so I wouldn't count on clouds to "protect" the controller. One break in cloud cover, and some edge of cloud effect, could possibly overload the controller. You may be best to just run a separate circuit, and parallel the two systems. (Or bite the bullet for a larger controller.) You wouldn't have the hassle of matching panel specs to the old panels, either, if you went with two set-ups.

[atperci]

The two 111w panels and one 190w panel total 412w total and 11.58a. With fixed panels, flat mounted, and voltage losses that should keep the three panels under the 390w limit of the CC. 6awg wire from the roof. No problem there.

I would still would like that extra switched panel, for times when its cloudy or shaded. Pulling the MC4 connector would work, but that would leave the connector exposed to the elements when not in use. And they aren't the easiest to pull apart. A switch would work, but would still have to go on the roof.

Could I use a relay and small wire guage run to a switch inside?

[jrnymn7]

switchable cb's

I see no voltage drop (to two decimal places) thru a 30a, at 7a from panels in mppt.

I see 0.08v voltage drop thru a 50a, at 45a from converter. Will likely go with a higher rated one for the converter, to see if that reduces v.d.?

[westend]

Any single pole switch will work as long as it's rated for the voltage and amperage of the continuous current. I used one of these Midrange manual breakers. It has posts that accept larger lugs and is panel mounted.

[full_mosey]

MiaSole, scroll down.

HTH;
John

[time2roll]

I think you are good to go. No switch needed.

[atperci]

Sorry, I should have posted what my controller is. Initially I did have PWM CC, but within a week I realized how much energy potential was being wasted. Max amps I saw was about 7. After I purchased a 30a Tracer 3215RN MPPT I've seen up to 10. I know its not a popular (read, more expensive) brand, but its been working well so far, so I am not complaining. It has a max 390w input from the panels, that's what has me thinking I need to switch one panel.

So, now that that's straightened out, what do you think? Will the set up exceed 390 watts? If so, how can I set up the switch for one of the panels?

Thanks, again!

[Bend]

Seems to me that you will need a new controller anyway. I'd be a nickel your current system is 12v PWM. I doubt it will handle the 12v MPPT voltage you envision.

However, you can chose some 19-22v panels that would work and do the switch(s).

[Chandalen]

Unless you have an MPPT controller, your excess voltage (over 19v) is useless. You could run thinner wires as the voltage loss is not a factor. Make sure your controller can handle the voltage supplied. Some PWM can not.

You can easily use a switch to turn panels on and off if you desire.

I'm not seeing over 22 amps if they are all connected and at full power.. 5.7x2 and 5.24x2. Did I miss some math?

Renogy has 19.5v 100w 5.27 amp panels for $135 ea if that helps.

[Helimech]

If you have a good controller, you won't need to switch the panels off.

[time2roll]

You really need an MPPT controller if you plan to run at those voltages.

What controller do you have?