Solar Powered Fridge

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Re: Solar Powered Fridge

Postby John61CT » Sat Mar 16, 2019 1:27 pm

The efficiency losses of front-opening vs chest style is grossly overestimated by most.

The air you lose has little thermal mass.

If your contents are filling most of the internal space

as is strongly recommended in any case, fill up with water bottles as you go through the food

then the difference is minimal, far less than adding say another 1/4" of insulation, or

just opening a bit less frequently, or

ensuring good ventilation around your hot bits.
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Re: Solar Powered Fridge

Postby flboy » Sat Mar 16, 2019 1:56 pm

At the end of the day, I think efficiency can be overestimated and overrated on any single appliance given the law of diminishing returns and in view of a total system. It is so easy to spend 2X - 3x or much more for an individual appliance to get that last 10% out of something that is a small number to start with in the scheme of system energy consumption/management. I know why Marketing Managers like it because I know a few.. But I guess it can come with bragging rights. Many times the charge controllers are throttling back the free sun as the battery is already at a high SOC or the gen is running with only a few lights because charger is finished up. So you use a few more aH overnight on a 225aH bank.. no comprender except that I understand theoretical arguments are fun.

I have found that an extra 100W solar panel (about a dollar a watt these days) more than makes up for any minor consumption/efficiency issues and if you are running a generator occasionally to charge. .... there is no measure especially if it is not an inverter generator that throttles down based on load... but even then... a couple thimble fulls of gasoline aren't deal breakers.

If the compressor comes on because you opened the door and dumped some cold air and your battery is already charged and the sun is out.... what difference does that make in the overall system when the charge controller throws a few more free amps that way?? Think of your CTC as a system... not just a refrigerator. Does a few watts of compressor heat dissipating in the cabin make any difference if the windows are open and a breeze blowing or the Maxxair fan on, or the AC is already on and you just happened to open the front door, or... if the windows are already closed because it is cool outside and now you can use the heat?? Just something to think about. Look at the big picture. There is more than only one way to go. ;)

If all you have is a battery and a small refrigerator and no way to charge the battery, then I get it for sure.. but then I'd say your money would be better spent on a means to charge that battery :shock:
Last edited by flboy on Sun Mar 17, 2019 5:49 am, edited 1 time in total.
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Re: Solar Powered Fridge

Postby jwh92020 » Sat Mar 16, 2019 3:07 pm

Thank you all for the info. I'm going to try and find a good deal on a 12v unit and go with that. I've used a couple of calculators and using a less efficient frig, I'll need right at 300 watts of panels & 200 amp hrs of batteries. I'll be frig shopping this week. Wish me luck.
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Re: Solar Powered Fridge

Postby John61CT » Sat Mar 16, 2019 3:07 pm

Of course there is a cost / benefit calculus involved, but energy efficiency can be a very important factor to take into account.

In a mobile context, often the space to mount panels is the limiting factor.

And usage demand rarely is reduced over time, usually grows.
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Re: Solar Powered Fridge

Postby flboy » Sat Mar 16, 2019 3:15 pm

jwh92020 wrote:Thank you all for the info. I'm going to try and find a good deal on a 12v unit and go with that. I've used a couple of calculators and using a less efficient frig, I'll need right at 300 watts of panels & 200 amp hrs of batteries. I'll be frig shopping this week. Wish me luck.



Good luck on your fridge and certainly you should get what you are comfortable with. No doubt those are good and efficient refrigerators and will give you many years of service. You absolutely cannot go wrong with one.

That being said, not sure what you were using for calculations, but that has to be off for just a fridge. I ran a whole CTC with an Inverter and 3.2 CU 115VAC fridge, Television, Lights, Fans, etc.. with 200W of panels and 225aH of batteries and never had any issues for many years. Need to check the math. Will be higher than a 12VDC fridge head to head due to inverter related losses , but no way that much power for just a fridge all else being equal.

Also, I'd never plan on solar to be the end all in any case unless maybe I lived in the desert... it works less than half the time due to night and clouds, trees , shade, etc.. Have a good battery bank (size it with some margin to spare), some solar, and the means to supplement solar with the Tow Vehicle, Generator, or etc.. I put a lot of time and money into mine and it does work and works well when I have full sun. What I am finding out is that, often enough I do not get full sun in the Southeast. Most camping places are shady for good reason, there is no sun at night, and a lot of days we have partly cloudy skies. My routine if I do not have full sun for most of the day is to run the gen for a few hours after sundown if the batteries need a boost for the overnight consumption. I take the opportunity to heat my water in electric mode and do a few other more power hungry things to utilize the gen while I am at it. So far I find I have to do that about 50% of the time and I have 500W solar and now have 430ah of Batteries.
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Re: Solar Powered Fridge

Postby PrecisionLook612 » Sat Mar 16, 2019 4:35 pm

jwh92020 wrote:Thank you all for the info. I'm going to try and find a good deal on a 12v unit and go with that. I've used a couple of calculators and using a less efficient frig, I'll need right at 300 watts of panels & 200 amp hrs of batteries. I'll be frig shopping this week. Wish me luck.


Let us know what you get! I am in the process of trying to find the right fridge for my CTC as far as cost vs efficiency and I keep coming back to the dometic 40ish Liter coolers. CC vs CF vs CFX and they are coming in at $500 vs $820 vs $930.
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Re: Solar Powered Fridge

Postby jwh92020 » Sat Mar 16, 2019 6:16 pm

flboy wrote:
jwh92020 wrote:Thank you all for the info. I'm going to try and find a good deal on a 12v unit and go with that. I've used a couple of calculators and using a less efficient frig, I'll need right at 300 watts of panels & 200 amp hrs of batteries. I'll be frig shopping this week. Wish me luck.



Good luck on your fridge and certainly you should get what you are comfortable with. No doubt those are good and efficient refrigerators and will give you many years of service. You absolutely cannot go wrong with one.

That being said, not sure what you were using for calculations, but that has to be off for just a fridge. I ran a whole CTC with an Inverter and 3.2 CU 115VAC fridge, Television, Lights, Fans, etc.. with 200W of panels and 225aH of batteries and never had any issues for many years. Need to check the math. Will be higher than a 12VDC fridge head to head due to inverter related losses , but no way that much power for just a fridge all else being equal.

Also, I'd never plan on solar to be the end all in any case unless maybe I lived in the desert... it works less than half the time due to night and clouds, trees , shade, etc.. Have a good battery bank (size it with some margin to spare), some solar, and the means to supplement solar with the Tow Vehicle, Generator, or etc.. I put a lot of time and money into mine and it does work and works well when I have full sun. What I am finding out is that, often enough I do not get full sun in the Southeast. Most camping places are shady for good reason, there is no sun at night, and a lot of days we have partly cloudy skies. My routine if I do not have full sun for most of the day is to run the gen for a few hours after sundown if the batteries need a boost for the overnight consumption. I take the opportunity to heat my water in electric mode and do a few other more power hungry things to utilize the gen while I am at it. So far I find I have to do that about 50% of the time and I have 500W solar and now have 430ah of Batteries.


Don - I'll have 30 amp shore power wired in and I carry a Ryobi 2300 watt inverter generator. The calculations were for fridge, lights, water pump, tv, sat dish, microwave, blow dryer ( vanity is a terrible thing). Right now, I'm looking at a 435 watt panel, 2 - 100 ah batteries, 30 amp mppt controller & 2000 watt inverter. I can always add another panel & more batteries down the road if need be. BTW. - found a place in Phoenix that sells a 435 watt mono panels for $200. I saw a youtube video of a guy using one mounted on his vehicle to supplement his rv roof top set up & he runs 2 5000 btu generators off his system.
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Re: Solar Powered Fridge

Postby jwh92020 » Sat Mar 16, 2019 6:18 pm

PrecisionLook - I'll post what I get and the specs on it.
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Re: Solar Powered Fridge

Postby bdosborn » Sat Mar 16, 2019 6:40 pm

John61CT wrote:The efficiency losses of front-opening vs chest style is grossly overestimated by most.

The air you lose has little thermal mass.
<snip>


YES! Finally, someone gets it! :thumbsup:
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Re: Solar Powered Fridge

Postby flboy » Sat Mar 16, 2019 7:05 pm

Jwh. that makes more sense on power usage.. If you can get a 435W monocrystalline panel for $200... do not hesitate. Buy that thing. I'd buy one in a minute and I do not even need it.

Best of luck.

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Re: Solar Powered Fridge

Postby McDave » Sat Mar 16, 2019 11:57 pm

bdosborn wrote:
John61CT wrote:The efficiency losses of front-opening vs chest style is grossly overestimated by most.

The air you lose has little thermal mass.
<snip>


YES! Finally, someone gets it! :thumbsup:
Bruce


Ah, yes finally... although let's talk about this "replacement mass". It does have more thermal mass than the air you lost while retrieving your cold mass, but..
it is warm mass. Which will require compressor run time to cool. Presumably you don't just open the door to see if anything exciting is going on in there. You either add or subtract mass or both. And how is this mass cooled if it is not in contact with the evaporator? What is the vehicle for the transfer of heat? What is the thermostat sensing? Probably some sort of colorless, odourless liquid or gas,... which may fall out if it was heavier or more dense than the surrounding air. But if it was kept in a bucket instead of a closet well then... and surely this heavier more dense gas or liquid wouldn't only fall out when the door opened, any leak would be constant. Could the door even be functional if the seal was perfect? Surely there would be a pressure differential between the cooled area and the surrounding atmosphere so the door wont stay closed or would be vacuumed shut, unless they can equalize via some sort of .. well, leak. An additional .25" of insulation can't really solve that, and anything that leaks out is replaced by something, probably warmer. Like rust, leaks never sleep. How is it possible that supermarkets have frozen goods in the center aisle with no cover or door on the cooler? It ain't PFM. It's a bucket that holds the cold and keeps it from falling out and spilling all over the floor. Why doesn't the cold just come out the top? That's not what cold does, cold falls, heat rises.
Just my thoughts, but like most people I may be grossly over estimating. I'd have to see the data to know for sure.

Erin Go Bragh, Y'all

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Re: Solar Powered Fridge

Postby John61CT » Sun Mar 17, 2019 9:49 am

McDave wrote:Why doesn't the cold just come out the top? That's not what cold does, cold falls, heat rises.

a bucket that holds the cold and keeps it from falling out and spilling all over the floor.
"Cold" is not a thing, just an attribute, an absence of energy.

Two points. Opening from the top, the turbulence does pull lots of cold air out, warm air mixes in.

Second, air has **so little thermal mass** it takes very little energy and time for temps to recover even if all the air is swapped out.

As long as the space is Full, of things **with** thermal mass.

Which is important to efficiency regardless.

If you take out a gallon of heavy, and replace with a gallon of heavy, say water, yes the fridge will work for hours to recover.

But over time that process is more efficient than leaving that gallon to be replaced by air alone.

Of course for a weekend off grid, probably a wash,

but can get by without a fridge easy in that use case,

my assumptions are long term living off grid.

And the main point is that the overall energy consumption **difference** between chest and front opening is insignificant, especially compared to lots of other factors under our control.

Adding a 1/4" extra insulation was just one of many examples, none of which are that significant, but all more so than that choice.


______
As to the rest, no idea what you mean. In normal operations of course insulation, door seals etc need to be optimal.

And with grid / shore power, energy efficiency is of lower concern, by factors of magnitude.
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Re: Solar Powered Fridge

Postby flboy » Sun Mar 17, 2019 2:11 pm

John61CT wrote:And with grid / shore power, energy efficiency is of lower concern, by factors of magnitude.


Very true and true to lesser degree with a generator and a properly sized solar/ battery combination, of course, within reason.

The size and kind of appliance we speak of in this case are all relatively low usage in the first place. Really not a major factor.



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Re: Solar Powered Fridge

Postby bdosborn » Thu Mar 21, 2019 6:37 am

Saw a review on Youtube about this fridge, the price sure is lower than most. The Amazon reviews don't look too bad either:

costway fridge


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Re: Solar Powered Fridge

Postby jwh92020 » Thu Mar 21, 2019 6:11 pm

bdosborn wrote:Saw a review on Youtube about this fridge, the price sure is lower than most. The Amazon reviews don't look too bad either:

costway fridge


Bruce



Bruce - I saw that review the other night. I'm calling Costway tomorrow to talk to them about it and their portable hot water system..
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