Solar output

[cloud william]

clev, what kind of connectors did you use to link your 10 gage to your 4 gage wires on your roof? There's a lot of choices out there and I'm curious how you chose to do yours. I'm in the process of installing 2 165 watt panels on my coach, each has built in 10 gage wiring which I plan to connect in parallel and then to 6 gage to connect to a 30 amp mppt controller. I'm also curious, where did you locate your controller in your coach?

Also, is it OK have your panels on and charging while you're travelling? I always assumed that was one of the attractions of RV solar panels since you could arrive at your destination with a near full battery charge. But something occurred to me: with all the variable sunlight, especially when travelling through areas where there is shade from trees as they go by and then full sun and then back to shade many, many times, doesn't that cause large spikes in the amps going into the controller? Is that hard on the controller and/or the batteries? I thought the batteries like a nice steady current, especially when in bulk and absorb charging modes. Maybe this is no different than the panels being stationary with mixed sun and clouds? I have the 4 flooded 6 volt batteries that DRV installed at the factory.

[wingnut60]

Driving down the road in full sun is some of the best solar power you will get--no problem from clouds or passing tree shade.
Set it up right, you'll love the near-auto charging.

[scrubjaysnest]

Originally Posted by clev

Scrub, thank you for the reply, and no offense, but I didn't understand a thing you posted. "in the lab at 77"????? "Dust, shade, hazing, temperature impact output"?? You did read, "New system, mid day, no clouds, no shade...etc"??? Right?? How does that answer my question?

You don't indicate where in TX you are but west TX has plenty of dust storms at times. Any dust on the panels or in the air reduces panel output. Any time the air temperature, there for panel temperature goes above the laboratory rated temperature panel output goes down. Typical mid day temperatures are around mid 80's this time of year.
As soon as the panels were installed some dust was bound to be on the surface of the panels.
Battery charge condition will also determine how many watts they will except. The lower the charge the more current they will accept.


Panels are rated at specific laboratory conditions which are not real world.


What you noted is perfectly normal and I just added several of the items that impact panel output in the real world.


I find current into or out of the batteries more use full because it represents a percentage of the actual 20 HR aH rating of the battery.


Since 2012 the only time I have seen my system reach close to panel wattage rating was with the batteries at 50% charge and air temperature in the 40's.

[Thehobe1]

Consider yourself fortunate to get that much out of the solar panels! They are probably specified for maximum output at the equator at a time of the year when the angle of the sun is totally perpendicular to the solar cells. I have never measured the peak output of solar cells to match the claimed amount even when tilting the panels, maximizing the output at peak sun exposure.

[anijet]

Solar panels also produce more at lower temperature. Cold, cloud free days with bright sunshine produce the most energy. The hotter the panels the lower the output.

[clev]

Originally Posted by cloud william

clev, what kind of connectors did you use to link your 10 gage to your 4 gage wires on your roof? There's a lot of choices out there and I'm curious how you chose to do yours. I'm in the process of installing 2 165 watt panels on my coach, each has built in 10 gage wiring which I plan to connect in parallel and then to 6 gage to connect to a 30 amp mppt controller. I'm also curious, where did you locate your controller in your coach?

Also, is it OK have your panels on and charging while you're travelling? I always assumed that was one of the attractions of RV solar panels since you could arrive at your destination with a near full battery charge. But something occurred to me: with all the variable sunlight, especially when travelling through areas where there is shade from trees as they go by and then full sun and then back to shade many, many times, doesn't that cause large spikes in the amps going into the controller? Is that hard on the controller and/or the batteries? I thought the batteries like a nice steady current, especially when in bulk and absorb charging modes. Maybe this is no different than the panels being stationary with mixed sun and clouds? I have the 4 flooded 6 volt batteries that DRV installed at the factory.

Cloud, I sincerely apologize for the late reply but I've been preparing for a trip and not paid attention to this site lately.

1. My Renogy panels came with 10 gauge wire and I used MC-4 connectors to wire them in parallel, but only 2 because of amperage restrictions of the connector.

2. I had my coach prewired at the factory with 4 gauge wire. The connection was done on the roof with a properly rated copper, tube type connectors, with the 4 gauge going into one end and the 10 gauge going into the other; both ends secured with a screw type clamp system. And, I used heat shrink wrap to seal the connection. Based on everything that i read, 4 is the smallest gauge that I would use.

3. I used the 60 amp mppt commander controller from Renogy. Again, everything that I read (I'm just learning), suggested installing the larger capacity controller. If two 165 watt panels are all you plan on using, perhaps the 30 amp will suffice.

4. As far as solar charging, the controller 'controls' that. It prevents spiking and inconsistencies. I've never read anywhere to disable while traveling or any other time.

5. I don't know the dimensions of your panels, but if you have not purchased, I recommend that you get on your roof and measure the available space. I failed to do that and ended up 'wedging' a couple in tight spaces.

6. I hung the controller on the wall beside the inverter. When I open the belly, the inverter is on the right, and the controller is directly in front of me.

[Fulltimer50]

Considering solar output: How important is the controller in the amount of solar output. Does the type or brand matter as long as it has the proper Amp rating?

[clev]

Full, the controller is the main component, in my limited knowledge and experience. I searched, asked, you tubed, posted in forums, etc... and did not cut corners. Mine is 60 amp mppt and was almost $600.

[Bob Denman]

Since I'm still paddling around in the "kiddie-pool" end of the knowledge spectrum: do they have a formula for figuring out how many amps your controller should be able to handle?
(Based upon the theoretical wattage output of your panels?)

[clev]

I don’t have a clue.

[jpmihalk]

Basically the controller should be able to handle the aggregated amp total of all panels at peak. There are two major types of controllers - PWM (Pulse Width Modulation) and MPPT (Maximum Power Point Tracking) with PWM being a basic method for managing both output and charge cycle management. MPPT allows for partial charging in low light or with dirty panels and can handle much larger installations.

[clev]

I apologize, Bob; mine was not a good answer. You are supposed to calculate your usage by totaling up everything that you use. Four hours of tv times it’s amperage, 15 minutes of coffee pot times it’s amperage, etc, etc. There were just too many variables in our daily camping life to figure that, so I just installed a good sized system and a quality controller.

[Chance]

Originally Posted by Bob Denman

Since I'm still paddling around in the "kiddie-pool" end of the knowledge spectrum: do they have a formula for figuring out how many amps your controller should be able to handle?
(Based upon the theoretical wattage output of your panels?)

You can find many papers like this one comparing the two types of controllers if you do an Internet search.


https://www.morningstarcorp.com/whit...pt-technology/


The main advantage to MPPT is that it can convert excess panel voltage to additional current rather than wasting the energy. That makes MPPT more efficient most of the time. However, according to technical paper there are times when PWM may be a better choice.

[Bob Denman]

Originally Posted by clev

I apologize, Bob; mine was not a good answer. You are supposed to calculate your usage by totaling up everything that you use. Four hours of tv times it’s amperage, 15 minutes of coffee pot times it’s amperage, etc, etc. There were just too many variables in our daily camping life to figure that, so I just installed a good sized system and a quality controller.

Please: no apology is necessary...
I guess that I was wondering if there was some sort of equation that sort of figured out that "If you have X amount of wattage coming in: you'll need to be able to handle X amount of amps with your controller."

But thanks for your explanation!

[Chance]

Bob, rather than stress your brain, it’s easier to look it up on specs.

On the paper linked above, for example, a 30 Amp controller is good for:

400 Watt nominal panels for 12-Volt batteries

800 Watt nominal panels for 24-Volt batteries

1,600 Watt nominal panels for 48-Volt batteries


It follows pattern of:

Required Amps = Constant X Panel Power / Battery Voltage


The constant isn’t “1” because of controller inefficiency and also that batteries don’t always charge at their nominal voltage.

[Bob Denman]

"It follows pattern of:

Required Amps = Constant X Panel Power / Battery Voltage"

My "De-Stressed Brain" is forever in your debt...
Thanks!

[Fulltimer50]

Does it matter if the controller is used to control say 2 120 watt 12v panels used to keep the battery up on long trips to run a res. fridge?

[jpmihalk]

Originally Posted by Fulltimer50

Does it matter if the controller is used to control say 2 120 watt 12v panels used to keep the battery up on long trips to run a res. fridge?

That would depend on the controller but most basic PWM controllers can handle 30A for your 12V system. We have 4x100W panels and a 30A PWM controller set up for AGM batteries. It is normally good except for really cloudy/rainy days.

[Bob Denman]

No doubt: Sunshine matters!

[Porthole]

Another simple way to look at it - if your SOLAR panel array as wired is capable of outputting 60 amps - you don’t want to use a controller rated for 30 amps.

And if you size the system for 30 amps, do you plan on ever increasing your array size?

Quality MPPT controllers are pricey, but a small one now and a second one later is even more expensive.