Solar In The Desert

[Ducky's Dad]

I am adding a solar panel (100W Renogy mono) in an attempt to keep my AGM batteries happier than they have been. Just got off the phone with Ctek tech support re using a D250SA (new model) as my controller for a three-battery system (one starter and two house). The question of the moment is whether the D250 (or any controller) will actually allow current into the batteries under extreme heat conditions. Most controller specs say they have an operating range up to about 134F (the Ctek is 122F), and Ctek tells me that their unit will reduce output voltage as temps rise. Waiting for more info about whether extreme temps will shut the unit down completely or just slow it to a trickle. Ctek guy thinks it may shut down completely, but he is researching that issue. My truck often sees ambients between 110 and 120F, sometimes higher, and when the truck is parked on hot asphalt or hot sand, things really cook (cab temps above 180F while parked). But that is exactly when I need the solar panel to supply current to the house batteries running the fridge. So for those of you with solar in extremely hot climes, what have you seen in terms of actual charging when things get that hot? Thanks.

 

[luthj]

If it is rated to function, albeit somewhat limited at 122F, it will still work. Most solar controllers I have seen will produce full output with ambient temps (where they are mounted) up to 104-110F.

The ctek will be monitoring the internal component temps, which can hit 180f+ during operation. If they get above a certain threshold the Ctek will start to reduce output. I would make sure the unit gets good ventilation (install a extra fan if needed), and is not in direct sun.

 

[Scoutn79]

Put the controller in the fridge.....I don't have any answer other than the smarta$$ one.
But seriously if you could find a way to run the cables in and out of the fridge and keep the lid sealed well enough I would think it may work every once in a while.

Darrell

 

[luthj]

Is the Ctek unit passive (no fan) or active cooled? If it is passive, adding a small fan to blow air over its heatsinks can make a big difference.

The reality is that it will rarely be 120F for long, especially in the desert. You might loose some solar harvest, but I doubt it would be major.

 

[Ducky's Dad]

No direct sun on controller or batteries, but house batteries under the cab will certainly be above 200F when parked mid-afternoon. Starting battery in engine compartment may hit 250 or more, don't really know. I carry a small digital thermometer for the cab, and will start carrying an infrared thermometer to check battery temps, just so that I know. Where we go, it's usually 110F before noon.

 

[Ducky's Dad]

The reality is that it will rarely be 120F for long, especially in the desert.
The air temps will push 120 for long periods of time between Yuma and Gila Bend in August and September. There are nights when it does not drop below 95, so everything is preheated when the sun comes up. The bigger problem is the thermal mass of whatever the truck is parked on, whether it's asphalt, concrete, sand, or just dirt, compounded by the heat sink that is the truck itself. Once the truck heats up, it stays hot and there is seldom any shade for parking. Don't know if the D250SA has a fan, but Ctek sent me four PDFs this morning that I'll try to go through tonight. Thinking about mounting it under the back seat (which is directly under the fridge), so there may be room for a computer fan under there. Was also looking at Bogart and Morningstar controllers, but they seem to have similar operating temp range without the features of the Ctek. FWIW, Ctek told me that the SmartPass is not necessary for battery banks that are under 300a/h or even a little larger and my best case is about 250a/h, based on physical space limitations.

 

[john61ct]

Mount on an aluminum sheet / plate with air circulation both sides

A low-current PC fan blowing at the SC will help.

The panels will have heat specs published, higher the better

 

[john61ct]

Mount on an aluminum sheet / plate with air circulation both sides

A low-current PC fan blowing at the SC will help.

The panels will have heat specs published, higher the better

 

[dwh]

The voltage reduction is normal. It's the same as "tempurature compensation".

In other words, as battery temperature rises, the charge controller (or shore charger if it has temp compensation) will reduce the voltage to the battery. All decent solar charge controllers have an internal temp sensor to do temp compensation. Some have a RBTS (remote battery temp sensor) to read the battery temp directly. The 250s has RBTS.

That is all about adjusting the output voltage to the battery to prevent overcharging a hot battery. It has nothing to do with the operating temp range of the unit itself.

And when the battery is cold, it will raise the voltage.

The 250s is a waterproof unit intended to be mounted in an engine compartment. No external heatsink. It's also bigger than it looks in the pics.

Keep in mind that the solar panel will put out less when hot. And it will get hot; it's black and it's glass. It's rated 100w - at 70 degrees Fahrenheit STC (standard test conditions). Baking in the desert sun...I wouldn't be surprised to see it producing 50% or less of its STC rating.

 

[Ducky's Dad]

The voltage reduction is normal. It's the same as "tempurature compensation".
I know that. Just trying to figure out if my solar will shut down completely when it gets really hot, which is when I mostly need the solar to augment house batteries for the fridge. When it's 70F outside, the batteries should be able to hold their own, but with a fresh pair of Grp 34 AGMs and no solar, I can't get 24 hours in the desert.

 

[dwh]

I wasn't talking about batteries at 70F. I was talking about a solar panel rated to put out 100w at 70F.

Most lose like half a percent per degree F over STC. So if it gets to 180F, it'll be producing around half its rated output.


Worrying about the charge controller, when the solar is only putting out 50w, might be barking up the wrong tree.

 

[Ducky's Dad]

Worrying about the charge controller, when the solar is only putting out 50w, might be barking up the wrong tree.
Well, 50W equivalent might give me a couple of amps while parked, which is more than I have now. Tech support at Ctek seemed to think that high temps would affect both the controller and the batteries, panel issues aside. They are looking into that and are supposed to get back to me. Guy did say that I should put temp sensors on both house batteries, and let the factory temp sensor take care of the starting battery.

 

[john61ct]

The SC built into the CTEK dcdc charger is not nearly as robust efficient nor full-featured as a standalone unit.

I highly recommend Victron's SmartSolar MPPT series, cheap enough at the low end to buy 1:1 with panels for ideal partial shade handling, or the larger ones can handle a roof full load of them.

 

[luthj]

Not to discount your experience, but weather averages for Gila Bend are as follows.

Month High/Low
June 106° / 71°
July 109° / 80°
August 107° / 79°
September 103° / 72°

I am almost certain your batteries are not getting to 200F. Maybe in the engine compartment, but I am skeptical.

Regardless, operating a battery in high temps requires temperature compensation. This means a remote temp sensor at the battery. Without temp compensation, the batteries life will be dramatically reduced.

As mentioned, adding a bit of extra cooling/airflow can allow electronics to operate in elevated temps without de-rating.

 

[Ducky's Dad]

Not to discount your experience, but weather averages for Gila Bend are as follows.

Month High/Low
June 106° / 71°
July 109° / 80°
August 107° / 79°
September 103° / 72°

Not to discount your averages, but this was Aztec on 8/31/15, mid-afternoon, dirt roads at 30mph, headed from Dateland toward Gila Bend: