Solar panel check up on our 13QBB

Sylvain · April 22, 2019, 12:29:13 PM

Hello everyone,
Has I mentioned in my " new member" post, we received our 2013 13QBB a few weeks ago. There is a lot of that things that needs attention. I decided to start with the solar panel installation. The first thing I noticed is that the panel itself was not secured properly to the roof. It's a rigid 185w panel that was only glued to the roof with construction adhesive! Four hockey pucks were used at each corners of the panel as supports (see photos)! This morning I removed everything from the roof and my goal is to reinstall it properly with aluminium brackets.

Now my question to the solar professional of this forum! I noticed that my panel was only producing between 0.2 and 0.5 A this morning in full sun. The voltage was around 44v. At 0.3A it means about only 13watts. It sounds a bit low don't you think? The sun was not very high though. I'm just wondering if my panel could be defective.

The other thing I was also considering would be to replace this rigid panel with 2 flexible 100W panels. They would be lighter and more aerodynamic. Is this a good idea?

Please feel free to let me know what you think.

Sylvain

Sylvain · April 22, 2019, 12:30:14 PM

One more.

Sylvain · April 22, 2019, 12:31:02 PM

Third one one.

Sylvain · April 22, 2019, 12:31:40 PM

Construction adhesive and hockey puck once removed from the panel!

P.S. I'm not sure why the images are uploading sideways?

MitchB · April 22, 2019, 01:00:23 PM

Theoretically if the battery is full the amperage would be zero because there's no where for the voltage to go. How did you measure the amperage?

Two 100 watt 12 volt panels could be wired to give you significantly more amperage then your current panel and more amperage means faster charging so that would be a plus in my book.

Sylvain · April 22, 2019, 02:11:09 PM

Quote from: MitchB on April 22, 2019, 01:00:23 PM
Theoretically if the battery is full the amperage would be zero because there's no where for the voltage to go. How did you measure the amperage?

Yes the battery was full. That's probably why I was reading only 0.3A. The amperage reading was from the display that is connected to the solar regulator.

DavidM · April 22, 2019, 02:34:32 PM

Yes, if the battery was full, the amps from the solar controller will be low. Most controllers have LEDs which will tell you if the controller has switched to "float" which it does when the battery is full.

If you want to check how your panels are really doing then let the batteries run down to about 50% and try again. The solar controller will first go into "bulk" mode which pushes all the amps it can. Then after a fixed time, usually 30 minutes, it switches to acceptance where it slowly raises the charging voltage where it peaks out at about 14.5 and then switches to float. During acceptance you will measure declining amperage as it gets closer to full.

I don't quite understand what MitchB is saying about wiring two 100 watt panels to get more amps than your current panel. Yes it will be a little more than the 185 amp panel, but not much. Maybe he is thinking about reduced voltage drop in series- see below.

I actually like flexible panels a lot. They are thin and weigh 1/3 as much as rigid ones. That means for a portable installation you can store them behind a couch or bed and easily pull them out and hook them up. They have recently gotten cheaper, about $1.25 per watt, maybe lower. I am helping a Class A RV friend install two flexible panels. He will not mount them to the roof, so he can place them anywhere in a sunny spot. That is the big downside to permanently installed panels. We always look for shady campsites and rarely get any sun on the trailer.

He is installing his two 175 watt flexible panels with 50' of 8 gauge MC4 cables so he can place them in the sun. He might even get another pair of 50' MC4 cables so he can reach farther. With his two watt 175 panels he will wire them in series if the spot he places them in has full sun. If not he will wire them in parallel with Y connectors, so that shading of one doesn't affect the output of the other panel.

A slight downside is when he does put his panels on the roof if he has full sun they will be laying on the roof and won't have an air circulation space underneath. Solar panels lose output the hotter they get so you want to keep them as cool as possible with about a 1" air gap underneath.

He should complete the installation in a week or two and I will report how they work.

David

GrampaKilt · April 22, 2019, 03:02:20 PM

Hi Sylvain, this reply is in regards to the 1 image per post. Please disregard this if the 1 image per post was intentional, but the "images are uploading sideways" comment caught my eye. This shouldn't be happening given the current forum software. Anyhoo, in case you were wondering how to add multiple photos, click on (more attachments) to bring up another Choose File box.

Since I usually want to annotate photos, the easiest way for me is to bring them into PowerPoint, do the annotation thing and save the slides as individual PNGs before uploading. As I found out recently, saving as JPGs can cause uploading issues. For reasons far beyond my IQ to understand, PNG is the preferred format for the Web.

Looking forward to following your fixing and mod journey. GK

Merlin · April 22, 2019, 03:33:33 PM

Good for you to be checking the installation! That was an awful and dangerous method of installing a rigid solar panel.

A panel with those parameters (voltage output) can't effectively use just any old charge controller. It needs to be an MPPT controller (maximum power point tracking). I wonder if your system has that, given the sloppy nature of the mechanical installation.

I do highly recommend flexible panels and not permanently mounting them. I use a Renogy 100 watt flexible panel and with a long wire attaching it to the controller I can get it in the sun for best performance. By being able to put it directly in the sun, I need only one 100 watt panel for all my electrical needs (except of course the appliances that can't be used off the grid like microwave and A/C. I'll dig up the post with my installation and put the link below.

Here ya go; post #29
https://aluminumcamperforum.com/index.php?topic=164.msg7557#msg7557

MitchB · April 22, 2019, 04:09:21 PM

If you get two 100 watt panels and wire them in parallel then the amps will be additive vs. wiring them in series where the voltage is additive.
As an example if you get two 100 watt panels that are rated at 5.2 amps (it will state it right on the panel) when you wire them parallel you'll get 10.4 amps (in the perfect world). That's a pretty good jump over the single panel you have now that is rated at 5.76 amps.

As Merlin said, an MPPT charge controller will convert some of your excess voltage into amperage. In my opinion the 36 volt panel you have now isn't particularly well suited for a small single panel system like you have, your plan for two 100 watt panels is good and if it were me I'd wire parallel and be happy. In fact I did that very thing going from a single 70 watt panel to two 60 watt panels.

Merlin · April 22, 2019, 05:37:24 PM

Quote from: MitchB on April 22, 2019, 04:09:21 PM
If you get two 100 watt panels and wire them in parallel then the amps will be additive vs. wiring them in series where the voltage is additive.
As an example if you get two 100 watt panels that are rated at 5.2 amps (it will state it right on the panel) when you wire them parallel you'll get 10.4 amps (in the perfect world). That's a pretty good jump over the single panel you have now that is rated at 5.76 amps.

As Merlin said, an MPPT charge controller will convert some of your excess voltage into amperage. In my opinion the 36 volt panel you have now isn't particularly well suited for a small single panel system like you have, your plan for two 100 watt panels is good and if it were me I'd wire parallel and be happy. In fact I did that very thing going from a single 70 watt panel to two 60 watt panels.

I'll jump in here for a moment and DavidM can fill in more details. The parameter you're missing in the math is the voltage difference. Start wit the total watts output and figure from there. When you do that, 200 watts is not much more than 185 watts. Divide BOTH by the same voltage to get a comparison of amps. V X A = W. A = W / V.

MitchB · April 22, 2019, 06:02:59 PM

Except that in this case he's got a 36 volt panel so 185/36 vs 200/17 (or whatever the 12 volt panels will be). The difference is significant.

DavidM · April 22, 2019, 06:04:59 PM

Yes, as Merlin said.

In addition the solar controller, assuming it is rated for the additional voltage, will convert the series voltage to greater 12V amps. Wiring two nominal 12V panels in series is functionally identical to a single nominal 24 V panel.

A word about the nominal term used above. When solar panels first came out for charging batteries they were typically made with 36 solar cells. The 36 cells results in a maximum open circuit voltage of about 21 and a maximum power point voltage of about 17 which a MPPT controller converts to 12-14 volts for battery charging. But you can also connect such a panel directly to a battery and it will charge it at whatever voltage its current capability will achieve and it will also over charge with no controller. That is why we have controllers.

A 24V nominal panel has double the cells and all of the voltages noted above are doubled. The MPPT controller converts these voltages to what the battery needs and does so very efficiently. You can also hook a 24V panel directly to a battery and it will charge it again at whatever voltage its current capability will achieve, but it will REALLY over charge your battery once it gets full and the voltage starts spiking way beyond. 12V.

Finally a pulse width modulation controller if it is rated for the higher voltage can be hooked up to a nominal 24V panel and charge a battery just fine. But here you are wasting about half of its current output due to how the PWM controller operates. It just pulses faster with a higher voltage and those pulses waste at least half of the amperage capability of the panel.

Always use a MPPT controller on 24V nominal panels.

Whew. Time for a beer!!!!

David

DavidM · April 22, 2019, 06:12:09 PM

Quote from: MitchB on April 22, 2019, 06:02:59 PM
Except that in this case he's got a 36 volt panel so 185/36 vs 200/17 (or whatever the 12 volt panels will be). The difference is significant.

Like I said above the extra voltage of 36 is directly converted by the MPPT controller to extra current to the battery which will be somewhere between 12 and about 14V. Think of a MPPT controller as a very efficient DC transformer.

David

Sylvain · April 22, 2019, 07:06:52 PM

Thanks everyone for your input! I wasn't expecting that much reply so fast! It's very intersting information. I like the idea of having a panel installed on the roof since it does keep my battery always fully charged when the trailer is in my driveway or when I'm on the road. My controller is indeed a MPPT and it can handle up to 260W so I was thinking about adding a portable panel to my set up so I can move it in a sunny area if needed. I really like the idea of the flexible panel on the roof since they would be lighter and I would not have to drill trough the roof to install them.

Thanks again.....Sylvain