Advise on Solar panel for sale

[TMfor4ofus]

A friend has this solar panel for sale. He doesn't know much about it and neither do I. So I'm trying to see if I can use this. The pics tell the story I hope. I want to know if its a decent panel and what controller would work with it. Also what would be a good price? I'm thinking I could take it off his hands for 60-75 bucks. How about those connectors? Are they standard? Help, Advise please. Thanks

[rickst29]

Although you'd want to use an adapter to convert into MC-4 connectors. (Or, you could cut off the existing connectors, and re-wire stripped ends into new MC4 modules).
However, if you decide that you need more power later, you're not real likely to find a similar 120W panel on the market (same amps, same volts). You could end up with a need to choose choose between parallel wiring and series wiring when incorporating a second panel, matching EITHER the voltage (for parallel) OR the current (for series). Series connections require an MPPT controller, which is somewhat expensive.

[TMfor4ofus]

Originally Posted by rickst29

Although you'd want to use an adapter to convert into MC-4 connectors. (Or, you could cut off the existing connectors, and re-wire stripped ends into new MC4 modules).
However, if you decide that you need more power later, you're not real likely to find a similar 120W panel on the market (same amps, same volts). You could end up with a need to choose choose between parallel wiring and series wiring when incorporating a second panel, matching EITHER the voltage (for parallel) OR the current (for series). Series connections require an MPPT controller, which is somewhat expensive.

Okay so lets say I just want to use this one panel. What adapter cables and low cost controller would complete the package? Thanks

[BrucePerens]

One 16.8V panel might be a bit too low voltage to charge your battery reliably. The required charge voltage for a 12V battery is very close to what this panel puts out in optimal conditions only, especially considering voltage drops in the wires and controller. Two in series will work much better. Brand new panels of similar power rating cost as little as $100 but you shouldn't wire this one to any new panel, only to one that matches its current rating approximately.

You can just cut off the connector and permanently wire to a cheap PWM controller like this one on Amazon.

[Padgett]

According to www.nrel.gov/docs/fy12osti/51664.pdf, you can expect about .5% to 1% deterioration per year depending on contitions so part depends on how old it is.

Personally new monocrystalline panels are cheap enough that that is all I'd consider unless a real deal.

[TMfor4ofus]

Okay Thanks guys. I'll see if he's willing to let me try it out. Maybe I dont even need a controller since it will be charging 2 GC2 batteries? We dont have high electrical consumption. LED's and the water pump occasionally with the usual drain from the system. When we need more we have the gen.

[rickst29]

Originally Posted by BrucePerens

One 16.8V panel might be a bit too low voltage to charge your battery reliably. The required charge voltage for a 12V battery is very close to what this panel puts out in optimal conditions only, especially considering voltage drops in the wires and controller. Two in series will work much better. Brand new panels of similar power rating cost as little as $100 but you shouldn't wire this one to any new panel, only to one that matches its current rating approximately.

Bruce know a lot about electrical stuff, but I have other opinions WRT this particular project.

The voltage requirement at the TM Battery Bank is only about 14.4V. If we assume that age has "worn down" panel performance by a bit, we're probably still good, somewhere above 16V. The wiring distances and wire gauge are the most important remaining factor. I don't know the mounting point and resulting wire distance you have in mind, but most TM installations are built using #10 cable (and some people have used bigger stuff than that). Use an online calculator to determine your losses.

For cable from the panel to the Solar Controller, you can buy a double-length "solar extension cable" with male and female MC-4 connectors on the two ends, then cut in the middle. The MC4 "ends" go the to new connectors on the panel leads, while the "cut" ends connect into the charge controller terminals. (The reason you buy a solar extension cable, rather than visit a big-box hardware store, is the high UV resistance and quality of insulation within the "Solar Cable".)

Originally Posted by BrucePerens

You can just cut off the connector and permanently wire to a cheap PWM controller like this one on Amazon.

I don't like this idea (skipping the weatherproof MC4 connectors), and I don't like the controller, either (for different reasons). MC-4 Connectors are designed for outdoor use and connect with very solid clamps, while cutting and splicing loose wire ends might be less reliable (with the non-MC-4 assembly maybe wrapped by electrical tape, which could start to flap in the wind after a few hundred miles of highway travel). I may be wrong, but non-standard connections seem more likely to fail in some way, loosening up (more resistance) or leaking power into the TM roof. The connectors cost next to nothing, and they're easy to assemble. A single set of these, for barely a dollar, would do the job: http://www.ebay.com/itm/Sodial-R-MC4...S/172204296563

Second, I don't see that particular controller advertising negative ground/common. The cheapest PWM controllers tend to be positive-ground, and charging the negative-ground Trailmanor battery bank with a positive ground controller can act wonky, and fail to deliver much power. (My first PWM controller had such "wonkiness", and I had to throw it away.)

Negative-Ground PWM controllers tend to cost much more. The lowest price I see is a Renogy "open box" return item called the "Wanderer", https://www.renogy.com/renogy-wander...-box-like-new/.

You will also need panel mounts (so-called "Z bracket", with flat bottoms). Maybe buy from Renogy at the same time as the controller (and save some shipping charges). You DON'T screw the panel mounts down, you use double-sided VHB tape to avoid piercing the TM roof. VH-B is readily found on Ebay.

Total costs, above and beyond the panel:
$50 for the controller (includes shipping).
$10 for the set of Z-brackets (you don't need any screws).
$5 (or less) for MC-4 connectors.
$25 for weatherproof solar cable (the "extension cable" to be cut in half).
$5-10 for double-sided 3M VHB tape.

And also recommended:
About $20 for a few plastic "cable channels" from a big box store (both straights and corners). As with the "extension cable", your cost depends on your mounting location and length of exposed cable run. You can stick them down using more VHB tape. Don't buy "adhesive-backed" channels, (the adhesive isn't very good, it's only intended for indoor use).

Have fun!

[rickst29]

Originally Posted by TMfor4ofus

Okay Thanks guys. I'll see if he's willing to let me try it out. Maybe I dont even need a controller since it will be charging 2 GC2 batteries? We dont have high electrical consumption. LED's and the water pump occasionally with the usual drain from the system. When we need more we have the gen.

The relatively high voltage of the Panel (above 15V, will cook the batteries to death, in very short order, if a Controller isn't used to lower the Voltage - in multiple steps - to levels which the batteries can handle.

If the batteries are discharged, the controller will allow 14.2 -14.4V. But after a while, as the batteries become more fully charged OR the battery temperature gets "too high", the controller will reduce the effective voltage in one or two steps, ending at a "Float" Voltage when it detects the batteries to be nearly full.

[TMfor4ofus]

Thank You Rick. I plan on using it as a portable panel. I'll have to look at it first hand. I'll try to test it as you suggested then look into a decent controller and connectors if I decide to take it.

[Padgett]

I have been using one of these controllers for a few years and does very well with my two 100W panels in parallel and feeding two GC2 batteries.

I particularly like the digital readout of a number of parameters.

It is mounted in my vented rear compartment along with the batteries and a cut off switch.