My Solar Project

[DonC]

Well said Steve - those are my thoughts about why I'm going parallel. This is from the AM Solar web site:

"Case in point ... We have two customers who both have the same solar panels and controllers. They ended end up parking side by side in the desert by chance. One of them had four 100 watt solar panels in series and the other had four 100 watt panels in parallel. They decided to see how the two systems compared since they were both in the same climatic conditions. They looked at the charging amperage when both systems were in full sunlight with no shade on the panels and found the guy with the paralleled panels had a slightly higher charging amperage. Then they had their wives monitor the charging amperage while they went up on the roof of their RVs. They stood so that their shadows fell on one out of the four panels on each of the arrays. The guy with the four panels in series had a drop in charging amperage that was very dramatic, almost to the point of having none! The guy with the four panels in parallel found that his charging amperage only fell by one quarter. The three unshaded panels kept on cranking out their power. The message here is that in the world of RVs (where shade can happen depending on where you park and where you place the panels), it is better to have your solar panels wired in parallel.'

 

[kmacafee]

This has been a very useful discussion. Not to muddy the water, but I have one question I cannot seem to find an answer to that seems relevant if you are considering solar.

Do solar panels need to be installed with a gap beneath them for cooling? I have seen installs that glue the flexible panels directly to the roof and others that have suspended them a few inches above the deck to allow air to pass underneath. I always assumed that an air gap was preferred but it does cause issues with aerodynamics and makes the panel more visible from the ground.

Thanks

 

[DonC]

I sent an email to Renogy about which option is ok or preferred for the bendable panels (4lbs for 100W).
- gluing directly to the surface of the camper
- mounting to an aluminum platform that has cut-outs and then mounting this to the Yakima track. This would raise the panel about 1/2" off the camper and allow air flow to the panels through the cutouts.
- which glue to use.

This is their response:

"We do not have a glue that we recommend to glue your panel to your roof.
Any time we recommend adhesive we generally just recommend any silicon
adhesive. As long as the panels are securely mounted, I see no issue in
either method"

So air flow under the panel does not actually seem to be an issue from Renogy. I still think I will go with the aluminum platform rather than glueing directly to the camper. It gives me a place to put wires, and if/when I need to change panels, I don't have a mess on the camper.

 

[NorCalSteve]

That is a great question and I will take a shot at it.

I have read that solar panels also have an optimal operating temperature. I am not sure what this temperature is but I am thinking it is in the 70 or 80 degree range (may vary between panel types as well). So a very dark solar panel in the sun on a truck not moving will probably be above this temperature. I also have to admit that I don't know what the amount of loss is. So, if you want to squeeze everything you can out of your panels, you might want some airspace between the panels and the roof. Unless I heard that the loss of efficiency from heat is a large number, "I" would not worry. The light weight of the installation will probably outweigh the loss of efficiency due to heat. I think the Renogy panels look like a real nice way to go but I have not studied them at all other than looking at prices on the web.

Steve

 

[MarkBC]

...Do solar panels need to be installed with a gap beneath them for cooling? ...

Everything I've read says that voltage drops (and so, power drops) as the temperature of the silicon incrreases -- it's a fundamental fact of the silicon PV chemistry. (I'm basing this on what I've read, not my own knowledge of the physical chemistry...)
And since they tend to be black that means they tend to heat up in the sun. So seems like it would make sense that enhancing the ability to cool -- by providing an air gap under the panel -- would improve the performance.

That said, I made the strange decision to mount my (rigid) panels without any air gap under the frame.

Sure seems like the flexible ones are intended to be attached directly to the roof material without a gap.

 

[PaulT]

The FWC roof is white painted aluminum which may be a lower temp than the dark PV panel in full sunlight. The roof may actually act as a heat sink for the panel as aluminum is the most common material for heat sinks to dissipate heat in electronic systems.

Harbor Freight sells a remote infrared thermometer for less than $40 that works quite well. Measure the surface temp of the roof and the surface temp of the panel with the panel laying on the styrofoam shipping cushion on the roof and then with the panel laying directly on the roof. Choose the cooler temp if other considerations are even,

You may need to allow some time between measurements to let the temps in each position stabilize. Ten minutes to half an hour should be enough. Watching the current displayed on your monitor to see which position works better may provide the best answer.

Paul

 

[ntsqd]

The issue that I see in trying to use the roof as a heat sink is that it's not smooth, which will greatly reduce the contact surface area. Anecdotal evidence of how important contact surface area can be: General Motors High Energy Ignition ("HEI") modules require a thermal conducting grease between them and the machined smooth mounting pad on the aluminum distributor body or they cook themselves to death. I tried using copper anti-seize which worked great, for about 2 months. Then it failed three blocks from work and made me late by a couple hours. The new module has thermal grease under it and has been in place for nearly 6 months now.

So unless you're prepared to use something thermally conducting that will ~100% conform to both surfaces I'm not sure that it would be all that successful.

On my single rigid panel install I made the brackets to have a slight slope towards the front, and I drilled several large holes in the rear face of the panel's frame. The former was done to promote air movement due to hot air rising and to also encourage drainage of water off the top. The latter was done to give that hot air a way to get out as the frame itself would have trapped about an inch and quarter worth of hot air under the panel.
I'm not expecting these mods to make a huge difference in performance, with my limited understanding of how panel's function best I just couldn't not do them.

 

[DonC]

My plan is to go with the Renogy bendable panels, because even mounted on aluminum platforms, the combination will be less than half the weight of regular panels. These will then be mounted on the Yakima tracks giving about 1/2" space under the platform.

If aluminum itself is a heat sink, is there any advantage to the added costs of creating cutouts in the aluminum platform, or would it be better to have a solid aluminum platform underneath?

Regarding mounting, the panels have 3 grommets on each side, so I was going to bolt them to the aluminum through these, and add some glue around the edges.

 

[longhorn1]

DonC
I have been reading these posts very closely. I have an e-mail into Brenda at FWC. When I purchased my Grandby with the 100-watt panel on the roof and the solar plug on the back my plan was to get a 80-watt panel the following year. My panel and controller are Zamp and the controller is set to add the 80-watt panel. In a previous e-mail Brenda told me to get the Zamp 80-watt portable without the controller. The plug wire goes to the controller.

My camper is in storage and covered. Every 4-6 weeks I have to pull the tarp back to allow the solar to re-charge my batteries. I would rather plug in the portable while i'm at work and un-plug on my way home, not having to mess with the tarp.

My question to Brenda is whether the panels are parallel or in series. She was checking on the answer.

I also plan on taking the extra panel when I know I will be camping without shore power access.

Any thoughts would be appreciated. Thank you for posting. It is interesting watching a post just explode with members giving input.

Happy New Year.

jd

 

[DonC]

jd - that's a great question and I look forward to the answer. I never thought to ask how the rear plug relates to the roof plug - series or parallel.

 

[DesertDave]

Longhorn1, the rear wall plug on mine is run into the controller such that the portable is in Parallel with the panel on the roof, ie the voltages stay the same and the amperages are additive, as in 'positives connected and negatives connected'.

The Zamp Controller literature (for the factory-installed 15A controller) states it can handle up to 255 watts. I will test this out soon enough by adding a 50W panel to the roof, in addition to the 100W Factory panel and the 100W Renogy portable.

 

[Wandering Sagebrush]

jd - that's a great question and I look forward to the answer. I never thought to ask how the rear plug relates to the roof plug - series or parallel.

It appears to wire directly to additional terminals on the controller. My assumption is that it's electrically parallel.

 

[billharr]

It appears to wire directly to additional terminals on the controller. My assumption is that it's electrically parallel.

I agree, I looked at wiring my portable panel and 100w on the roof in series and realized I would need to install switches to do that. Combined with the shade problems and need for a MPPT controller, not worth the effort for me.

 

[RC Pilot Jim]

Kmacafe.

you asked a question about panel cooling. Renology answered that question a few days ago. Click on the highlighted link for their answer.

 

[SLEDAWG]

I enjoy reading everyone's posts on SOLAR. Here is a summary of my setup that more than exceeds my power requirements for a FLEET and a wife who enjoys the 65L compressor fridge, lots of light, heat and a daily shower. Hope it helps with those planning their installs.

Two RENOLOGY 100W FLEX Panels glued to roof wired in series.

Based on my research and background as a Elec. Engineer wiring in series is the best option with a MPPT controller. Regarding shading issues on solar panels, I have found if one panel is shaded I still get sufficient voltage keep the system charged. Interesting discussion on cooling. Based on the specs provided by RENOLOGY the panels work at max efficiency up to 116F. Max operating is 176F. Using the pre-wiring of FWC the MPPT controller "sees" 42V unloaded and 37V loaded(using power).


RENOGY® Tracer 20Amp Negative grounded MPPT Charge Controller 100VDC Input 2210RN

This controller got good reviews and is reasonably priced. The monitor is integrated into the controller. System works great. I mounted the controller above the battery compartment to allow sufficient air cooling. I also added a voltage meter that I can see through the back window of the camper.

I also found the wiring provided by FWC insufficient to charge the two AGM batteries in camper off of the 130A alternator from the TACOMA. I ended up shorting out the FWC installed isolator, adding 6 gauge wire (hot and ground) along with fusing and a manually controlled isolator installed in the engine compartment and controlled manually from the cabin. Running the solar power and engine power at the same time is no problem. I'll flip the switch in the morning for an hour to top off when running the truck and let the solar maintain the system the rest of the day

This works for me! Hope this helps for those working on their systems.

 

[DonC]

Sledawg - looks great, nice and neat. I can't quite tell if you have brackets holding the wire bundle to the roof. If so, can you tell me a little about your parts and how you mounted to the roof.

 

[SLEDAWG]

DonC:

Thanks. I read in other posts that folks had problems with the solar cables and connector rubbing the paint off the roof. I bouught UT WIRE D-Rings from Home Depot in the cable organization section. I coated them with silicon to protect from water and UV, removed the adhesive sticky tape and glued them on the roof with the same 3M semi-perm glue that I used for the panels. I placed them so no wires or connectors touch the roof. Took some time....hope they last. If not, easy to remove.

 

[DonC]

That sounds like a variation of what I need to do. I searched for "3M semi-perm glue" and did not find a specific product. If you like it and think its going to work, can you provide the full product name?

 

[SLEDAWG]

3M Marine Fast Cure 4000 UV SEMI PERM. Expensive....but better than seeing your $200 panels in the rear view mirror!
Credit to RC Pilot's post in this forum back in SEPT. Check the thread out on "Adhesive for Flex Solar."
I tried using another adhesive from Home Depot for my panels which worked great until the sun heated up the panels...the glue got soft!

 

[DonC]

ah yes, Jim told me about that for gluing his panels down. Makes sense that the same stuff can be used for gluing the odds and ends also.