Harbor Freight 100 watt panels

[rmkrum]

Look at the HF panels carefully. If they are like mine, they are a very thin single sheet of glass in the frame with silicon stripes vapor deposited on the back of the glass. One minor impact could easily crack the glass and kill the panel immediately. A higher quality panel will have multiple layers and thicker glass. Look for construction like gator.bigfoot describes for framed panels. Much sturdier.

To put it politely, Harbor Freight designs and builds their products as cheaply as possible. That’s why their prices are low. It works for their business model, but I expect stuff to last a lot longer when it’s solar panels on my Airstream roof.

Some of their tools and supplies are just fine for their intended use. I do shop there for some things—just not solar panels. I have AMSolar and Renology panels and MPPT controller on my trailer.

[Keyair]

All good points!
The frames look like plastic... difficult to tell.
I've been fishing for a solar setup for a while, and just really dislike the look of the ridged framed panels, and wanted to go with flexibles. The cupping and failures of those has put me off.
I see you are in Corona, RmKrum, so you know how brutal the sun is out there, and my Motorhome is stored in Riverside County too. Sun degradation is a big deal!

[TouringDan]

Originally Posted by Keyair

For reference, I just bought 2 Renergy 100w/5.7a compact panels off Renergy themselves on eBay. $100 each, inc shipping but plus CA tax. $218 shipped to my door. 25 year warranty.
42” x 19.5” x 1.38”. These are almost 4” narrower than the normal size which allows the to sit flatter the the roof when stowed.

These are the same panels I bought- high quality narrow monocrystaline panels for $108 each. I can fit 6 of them on my Tradewind and 16 on my 34’ after I remove the top mounted AC and center the skylight.

Dan

[rmkrum]

Our rig is parked in outside storage in Victorville at the moment. Much more intense up there. The 150 watts of solar and MPPT controller from an AMSolar kit years ago does keep the batteries hot and runs a fantastic fan under a cover to keep some of the heat down. I just top of battery water once a month as a precaution. More evaporation from the heat than battery charging losses.

I know whereof you speak. I keep replacing tire covers. The fabric falls apart in 3-5 years in the sun no matter how good the fabric is. Glad the trailer is aluminum...

Keyair, Someday we should get together to swap war stories and get a tour of your motor home.

Our panel is mounted proud of the roof and tilted down on the leading edge to help the aerodynamics. It’s visible, but the frame shines aluminum like the rest of the trailer, and DW isn’t tall enough to see it and decide it looks ugly. It’s safe for now, and two more panels are going up there sometime this year to provide even more power.

As you can probably tell, the whole thing is an engineering project that gets fiddled with a lot when we’re not out traveling.

[Keyair]

Yes indeed!
I feeling like we are drifting off topic, so excuse me, but I feel it’s relevant in the HF Panels W per $ discussion.
Look what I got in the mail today!


I’m gonna see where they fit best next time I’m there.
Yes, let’s connect via PM RmKrum!

On the subject of heat, intense sunlight and Airstreams, can I share one thing as a Heads up warning.
I put Reflectex sheets in my windows to try to keep the heat intrusion down. They were secured with Velcro strips. It got so hot, the adhesive failed. Some of the panels slipped and curved slightly, causing what I can only assume to be a parabolic mirror effect.
Look at the vinyl interior covering now....


Don’t know where to post this as a warning!

[TouringDan]

Keyair

Your panels are the same as mine, except the specs are slightly different. I bought mine in October, 2018.

Regarding the window insulation, that is unfortunate. Thanks for the warning. We have a 34’ without awnings on the street side. I have been thinking about designing a window covering to install outside that would hang from the awning rail. Time for another thread.

Dan

[Fair_Enough]

Dan, that’s the lowest Vmp ive seen. My Renogy 100w (Eclipse bought because of size) are 17.7 Vmp and 5.7 Imp.

I recently added a Zamp panel (80w) in parallel to my 300 watt set. It’s Vmp was 18.2. Thus reducing that panel Imp by about 5% or so. People adding mismatched panels need to consider that. The panel was free so I didn’t care.
Clint

[Fair_Enough]

Reflectix damage. I wonder if there was reflection from something that caused that heating. A window close by or? I’ve use reflectix for years on various campers and have never seen anything like this. But good to know it can.
Clint

[Keyair]

Nope, pure sun power. That’s the worst spot but there is damage on other windows too. Not a big deal, as I planned to strip the vinyl anyway.
Anyone suggest the appropriate place to post a warning?

[TouringDan]

Originally Posted by Wolfwhistle

Dan, that’s the lowest Vmp ive seen. My Renogy 100w (Eclipse bought because of size) are 17.7 Vmp and 5.7 Imp.

Clint

Clint

Is lower better? See how much I know about solar.

Dan

[Paprika]

Whether or not 16 V panels will do a good job depends upon how you connect them--in parallel or in series.

Most solar charging controllers require that the voltage coming in from the panel exceed the battery voltage by a certain margin--"battery voltage plus 5 V" is common. That makes sense, as the controller needs some margin to work with. (Bear in mind that to charge a 12V-rated battery takes several volts more.)

A Vmp rating of 16 V doesn't give you much of a margin, so you're not likely to have a very efficient system no matter how many of these panels you put in parallel. On the other hand, if you wire pairs of them in series, yielding 32 V per pair, you can do quite well--assuming you have an MPPT controller that can handle the voltage, of course. But you'd want that anyway for efficiency.

[TouringDan]

Originally Posted by Paprika

Whether or not 16 V panels will do a good job depends upon how you connect them--in parallel or in series.

Most solar charging controllers require that the voltage coming in from the panel exceed the battery voltage by a certain margin--"battery voltage plus 5 V" is common. That makes sense, as the controller needs some margin to work with. (Bear in mind that to charge a 12V-rated battery takes several volts more.)

A Vmp rating of 16 V doesn't give you much of a margin, so you're not likely to have a very efficient system no matter how many of these panels you put in parallel. On the other hand, if you wire pairs of them in series, yielding 32 V per pair, you can do quite well--assuming you have an MPPT controller that can handle the voltage, of course. But you'd want that anyway for efficiency.

Thank you for the explanation Paprika. I have lithium batteries with six 100 amp panels, so I will wire either 2 or 3 in series than in parallel. I have a Victron MPPT 100/20 solar controller.

Dan

[Paprika]

"I have lithium batteries with six 100 amp panels, so I will wire either 2 or 3 in series than in parallel."

With that many panels, I'd suggest three series pairs of panels, rather than two sets of three in series. That way you get the benefits of higher voltage, while minimizing the chance that a shadow will shut down multiple panels in a series string.

I went this route on my Airstream, using six Renogy Eclipse panels (like Wolfwhistle, bought because they were the smallest 100-watters I could find) wired as three series pairs, feeding a couple of Victron 160 Ah lithium batteries (wired in parallel) via a Victron MPPT 100/50 controller. The system has worked very well year-round.

"I have a Victron MPPT 100/20 solar controller."

If you have 600 watts of panels and are running a 12 V system, you'll need to replace that solar controller. Victron's specs for the 100/20 say that it can only handle 290 watts in a 12 V system. "If more PV [solar panel] power is connected, the controller will limit input power," they say. In other words, your 100/20 will throw away any power from the panels that exceeds 290 watts. Obviously you don't want that!

The MPPT 100/50 is a much better fit for your proposed system, as it will efficiently handle all the power your six panels can throw at it.

[Fair_Enough]

Dan, Paprika nailed it. Your 20A SCC isn't enough. Solar array to SCC you are under but SCC to battery bank you could have around 35 amperes.

Paired in series and the three pairs in series is a good way to go. I would't be too concerned with that 16 Vmpp... 32 volts in series is good. When you plan which panels you will wire in series, look at how a shadow or shade might fall and if a certain two would be shaded in that Airstream / sun orientation event, pair those two if you can.

You begin charging discharged batteries as soon as your charging voltage is higher than the battery bank. And depending on how discharged they are, you might only need 13.1 or slightly higher for Float or 14.4 or higher for Absorb at that moment in time. The idea is that is panels are in series will exceed what the batteries need sooner and in less light. Which is also an advantage of MPPT.

You should also consider voltage drop and get your wire gauge sized correctly. Voltage drop too high will also hurt you meaning what the panels are producing voltage wise, is reduced by loss in the wire. The lower the loss the better, but sizing the cables too big just wastes money buying more copper than you need. IMO any charging source should be less than 3%. Your panel arrangement, roughly, at 18.75 amps at 32 volts will probably need 10 awg from panels to combiner and 6 AWG from combiner to the SCC.

For my next solar project, I am looking at trying SolarEpic MPPT 150/40A SCC that used MT50 Remote. Not as well known or as trusted as Victron, but at under $200 with cables and temp sensor I am going to give it a try.
Clint

[TouringDan]

Originally Posted by TouringDan

Thank you for the explanation Paprika. I have lithium batteries with six 100 amp panels, so I will wire either 2 or 3 in series than in parallel. I have a Victron MPPT 100/20 solar controller.

Dan

Paprika and Wolfwhistle

Sorry, but my error. The 100/20 solar controller is for my 200 watts of portable panels. I have not yet installed the 600 watts of permanent panels or the Victron 100/50 controller.

I am planning on #10 wire to the SCC and #6 to the batteries.

Thanks for all your help.

Dan

[AirMiles]

Originally Posted by TouringDan

Paprika and Wolfwhistle

Sorry, but my error. The 100/20 solar controller is for my 200 watts of portable panels. I have not yet installed the 600 watts of permanent panels or the Victron 100/50 controller.

I am planning on #10 wire to the SCC and #6 to the batteries.

Thanks for all your help.

Dan

Its awesome to hear that you are going to put 600W on the roof in series-parallel with #10 wire. I believe you will be the first with this configuration and I can't wait to see your results. I'd put them in three series pairs. The Victron controller prefers the double voltage of a series pairs.

Can the factory #10 prewire be used with 600 watts of panels wired series/parallel, making the equivalent of three 200 watt panels?

Short answer:
YES because the key is to do series/parallel groups of panels. 600 watts in three sets of two 100W panels would work great! By my calculation below in the "long answer" is that this configuration would be capable of producing 588 watts to the controller for a total loss of only 2.0%.

Long answer:
Doing six 100 watt panels on a 30' Airstream would require 54' of 10-2 on the roof. There would be three runs averaging 18' each at 34 volts with 6 amps. Using this calculator: https://www.calculator.net/voltage-drop-calculator.html the voltage at the rooftop box would be 33.78. Then we need to use the 30' of factory 10 AWG prewire to send 33.78V at 18 amps to the controller. At the controller we get 32.7V at 18 amps, or 588 watts using the same calculator.

Now let's redo the calculation using a full parallel design and 4AWG from the rooftop box to the controller:
We would need 96' of 10-2 on the roof. These runs would average 12’ in length running 17V at 6A using the same calculator the voltage at the rooftop box would be 16.86V. Then we need to use the 30' of 4 AWG to send 16.86V at 36 amps to the controller. At the controller we get 16.32V at 36 amps, or 588 watts using the same calculator.

Based on these calculations, a 600W system run over the factory prewire using three 200W series/parallel runs is equally as efficient as running the system in full parallel with 4AWG to the controller. The higher voltage and lower amps of the series/parallel design is very efficient on 10 AWG.

[Mollysdad]

Originally Posted by gator.bigfoot

I'm just wondering what credentials you have in the solar industry?

If everyone here had to show credentials, there'd be very few posts and those that were allowed would be boring.
This is a place for opinions, and lots of anecdotal evidence, take it for what it is.
Sorry, I have no dog in this fight, but I like to hear diverse opinions, including mine. The next time someone says they like their Champion generator, am I to ask if they're mechanical engineers?
It's called "ad hominem", or simply, "If you can't attack the message, attack the messenger."
Carry on.

[TouringDan]

AirMiles

I don’t believe there is any factory prewire on a 66 Airstream[emoji16]. My plan has been to connect 3 panels on each side in series, then parallel each set of 3 panels back to the 100/50 SC. I was going to do it this way because I have a 2 way splitter. I don’t know if a 3 way splitter is available. I want to wire it which ever way is best. I don’t believe the distance from the furthest panel to the SC will be more than 15 ft (of #10 wire).

Thanks for all your help.

Dan

[AirMiles]

Originally Posted by TouringDan

AirMiles

I don’t believe there is any factory prewire on a 66 Airstream[emoji16]. My plan has been to connect 3 panels on each side in series, then parallel each set of 3 panels back to the 100/50 SC. I was going to do it this way because I have a 2 way splitter. I don’t know if a 3 way splitter is available. I want to wire it which ever way is best. I don’t believe the distance from the furthest panel to the SC will be more than 15 ft (of #10 wire).

Thanks for all your help.

Dan

I'm certain there is no factory prewire on a 66. My point was that the #10 wire you plan to use is the same gauge as the factory prewire. Therefore, your installation will be equivalent to using the factory prewire on a newer Airstream. If you make two series of three panels, your voltage will be higher and your amps will be lower, both of which will make your system even more efficient, but with greater shading affects. There's always positives and negatives with each configuration decision.

[pdavitt]

I'm going to stay out of the argument about what is best and who is qualified to say it. All I will say is, stay away from panel manufacturers and sellers who do not provide data sheets like those attached. Without those datasheets their is no way to know what you are buying.


Pat