If you boondock a lot . . .

[solarman]

That degree means nothing to me

neither does your post, it's completely non sequiturs.

Your big miss mr engineer is that the compressor fridge does not run all the time. That is my pet peeve for people answering forum post who do not have experience with the subject. No offense, but people who own compressor fridges know they do not run 100% duty cycles. You know what you know, but not what you need to know. Now you know more.

i'm quite aware that the duty cycle of a fridge will be less than 100% most of the time, if you step back and look at the calculation, it should be apparent that it's a worst case figure, it's a starting point for further refinement, not an absolute.

I can't tell the OP what % his fridge runs. I just guessed 20% as a round number. This means 12 minutes of every hour. So every 5 hours you get a full 60 minutes of run time. Probably that big front door fridge runs more.
As you know in reality, the solar panels work in morning and evening light. My panels will have the system charged back sometimes before I get up, before your 4 hour imaginary window. Panels do not need to be at 100% efficiency to do work. They are always at 18 volts but the amps vary with light.

sun insolation is not "imaginary", feel free to PM me, I can educate you on industry practices, they are quite different from DIY

My fridge starts up with 4 amps and runs on 3 amps, the battery will be back to full voltage, even with the fridge still on, in the morning off of only 200 watts, before the magic hour, in the forest woods. I also run lights and fans and charge devices etc.
The panels will have extra capacity available during a normal sunny day, so the battery will not be drained in the daytime. Batts will charge and run the electric items at the same time. I always try to charge my devices early in the day when the sun can charge it so I start the evening with full battery and no drain from chargers.
Doing math is good but you have to consider all variables. Leaving some out ruins it all. Thinking an 8 amp fridge will pull 192 amp hours (2304 watt hrs I guess) in one day is a big doodo.
For the 20% duty cycle possibility then 460 watt hours if I did that right.

I use amp hrs not watts.

as would most DIY, you are blinkered into a 12V box. there are very good reasons to use wattage units.

You used 4 amps in your math, so thats just half, so 230 watt hours not the 1152 you came up with. The fridges must run more than 20% of the time because these are small numbers, but they do not run all the time.
So, there ya go. Hope this helps.

correct, I used your figure as a starting point. In real use the actual duty cycle will be a function of many different environmental conditions, some constant, some variable. calculating a starting point as an estimate is obviously incorrect by your standard..

So for a big 8 amp electric fridge it is a harder decision to make than for a 3 amp fridge because you will need a bigger battery bank than most RVers have to cover for cloudy/rainy days.
My experience is that it is worth getting more battery to have the electric fridge. They do not need to be level and can run 30 Degrees off level and be fine, vs the 3 degrees the propane ones tolerate.
I would get an electric induction cooktop if I were to do it over, and just keep a camping stove for backup.
Batteries can last 6-10 years. If say 7 years then a $600 set of batteries cost $85 per year. Propane is $17-22 or so per tank. You have to have batteries anyway, so lets say normal would be a $300 set of batteries, but you did a $600 set for the electric needs, so thats an extra $43 per year or two tanks of propane. You still need propane, but a full time boondocker will need 1 tank just to run a fridge per month times 12 = 500/year. yikes. Even if my math is off a little bit these are big numbers.

?

 

[Alontheway]

lol, that was pointless. you feel better?
You lost me at using 100% duty cycle for a calculation. That is not a starting point, thats a pointless point. That's like saying my car gets 1 mpg when drag racing so let's start with that to estimate fuel consumption on my next trip, but you're the engineer I guess.
Good luck with it all.

 

[JayArr]

Slagging engineers is not going to make you any friends on the forum.

 

[Alontheway]

I doubt he is an engineer. Not everyone is who they claim. Guy claims to be, says he has years experience then proceeds to fumble everything. Us Rv'ers who are learning and trying to figure it out might fumble here n there, but years of experience building solar systems and he gets the entirety of it wrong? No. I called him out, all he could do was attack my character, not admit his blunder, not apologize, just attack me, and never correct his blunder or admit he was wrong. I'm not rude, I'm just blunt and he does not like that he is not treated as a king here. He demonstrated his lacking himself.
He gave bad advice and wanted the OP to spend hundreds more installing way way more solar and battery than was needed. This might float in a sleazy RV sales store to make more profit, but on a forum we are here to help each other out.
If you are going to claim to be an engineer and claim to be a professional solar guy then we will expect more than junk math and wrong assumptions and we will hold you to higher standards. If you just say you are an RVer and this or that worked for you then we will take it with the grain of salt. Big difference.

 

[Sierranevada]

The wife and I have 50 years of boondocking. At first it was with truck camper's with a block of ice in the ice box. Now it is a nice 26 ft aljo trailer with a popout and gas - elect fridge (120 volt for shore power). In that 50 years we have camped in a RV park with shore power a total of maybe 20 days. We also live off grid in a 2700 SQ ft home with all the convenience's. Boondocking and living off grid teaches you to conserve on your elect usage. If you are going to boondock, elect fridge 12v DC or 120v ac is not the way to go. Solar panels are cheap right now if you have enough Space for them. Charge controller, inverter and batteries are not cheap. Alot of trailers do not have enough room for the amount of batteries it will take to keep system running 24 hrs a day ( I am too old and set in my ways to go the lifpo battery route). Maintenance of an off grid system is not easy in a travel trailer or home. Have a nice day. George

 

[Alontheway]

nice. SIerranevada, what was your cost to have refrigeration? I assume no DC fridge, only propane? Interesting to hear the cost compared between DC fridge on CG batts and solar to tanks of propane.

 

[Sierranevada]

Alontheway. Our off grid home has a full size 120 volt fridge with ice maker. This is the list of elect appliances we run 120 volts on. Chest freezer, 65" tv, washer and gas dryer, microwave, desktop computer, dishwasher, 7 ceiling fans, water softener, water booster pump. We have 5000 watts solar, wind generator, inverters, 3 charge controllers, 1379 amp hour forklift battery (20 hour rate), backup 12 kw diesel generator that auto starts if 24 volt battery bank need help. Solar well pump that keeps our 5000 gal water tank filled and keeps our plants and trees watered. Our propane usage is about $900.00 a year. We have 2 gas heaters but mostly heat the home with 2 wood stoves. We also run a propane refrigerator for soda and beer and it keeps our water heater room warm enough to not freeze in winter. No air conditioning needed we are at 6500 elevation. I don't know if this answers your question? Enjoy life. George

 

[Alontheway]

thats quite an RV

 

[JayArr]

My little RM2510 fridge uses about 1 pound of propane per day.

My current propane cost is about 88 cents (USD) per pound.

We camp about 30 nights per year.

30 * .88 = $26.40 per year

I just replaced the refrigeration unit on this trailer for the first time since it was built in 1992. I'd like to think they all last that long but just to be conservative let's say it will last 25 years.

Propane to run this fridge for 25 years will be 26.4 * 25 = $660

The fridge is currently selling for $1954.61

Add in $55 for each propane bottle every ten years to re-certify them 2 * 55 * 3 = $330

Total cost of ownership will be $2944.61 over a 25 year period.

That will be $117.76 per year.

What is the cost if I buy a 12V fridge, two or three 100W solar panels, a charge controller and a bank of Lithium batteries?

Then there is another important question - what is the lifespan of the solar panels, the charge controller and the lithium batteries? Will they last 8-10 years? Will I need to buy them three times to get to 25 years?

 

[DonTom]

what was your cost to have refrigeration? I assume no DC fridge, only propane? Interesting to hear the cost compared between DC fridge on CG batts and solar to tanks of propane.

When boondocking, cost is measured in amphours used, not dollars.

-Don- USA Parkway (near Tesla battery plant charging motorcycle at the Recharge Restaurant)

 

[solarman]

Slagging engineers is not going to make you any friends on the forum.

quite true, this chap also seems to be belligerent with his replies, yet also doesn't seem to understand English. he claims I gave bad advice when in fact I gave none, clearly refuses to accept and dismisses the notion of established engineering practices and rants apparently about how I "wanted the OP to spend hundreds more installing way way more solar and battery than was needed".. all rather odd..

 

[Alontheway]

out

 

[JayArr]

You're kind of going apples to oranges on me. I'm not interested in full time numbers, I'm just interested in reviewing my situation to see if solar would be right for me.

To make the comparison equal I'll expand your estimates out by 2.5 to get 25 years.

Charge controller to 25 years at a cost of $125

Panels at $280 extrapolated to 25 years would be $700

The solar panels will likely come down in price in the coming years but I'm going to ignore that because I left out the cost of labour to replace the panels twice.

Batteries - I can work with GCs - lets say $650 for 25 years.

Looks like total for 25 years with solar will be in the ballpark of $3429 or $137 per year. That's regardless of whether they camp 30 days or 365.

For a full timer the Solar fridge is looking cheaper. For a part timer the propane makes more sense.

Propane fridges struggle in the heat.

That's just not true they transfer the same amount of heat from inside the fridge to outside in the atmosphere as compressor fridges. If it's hot they both struggle. Nice try.

JayArr

 

[JayArr]

quite true, this chap also seems to be belligerent with his replies, yet also doesn't seem to understand English.

Yes, his grammer is bad and the sentences are malformed which makes it harder to understand what he's trying to put accross. Perhaps in his country beligerance is a good trait and people like argumentative know it alls.

Still, I'm glad he prodded me to do some math to compare costs of solar to propane as it applies to a fridge only. Maybe the discussion will help others.

If you hover your mouse arrow over his name you will get a pop up box that has as an option "ignore". I think that will make it so that none of his posts show up when you browse the forum. It's like making him disappear.

 

[solarman]

Yes, his grammer is bad and the sentences are malformed which makes it harder to understand what he's trying to put accross. Perhaps in his country beligerance is a good trait and people like argumentative know it alls.

Still, I'm glad he prodded me to do some math to compare costs of solar to propane as it applies to a fridge only. Maybe the discussion will help others.

I would agree that propane is more economical for part timers, the numbers do suggest solar and dc fridge would be better for long term. as you say, solar has a cost even when unused..

If you hover your mouse arrow over his name you will get a pop up box that has as an option "ignore". I think that will make it so that none of his posts show up when you browse the forum. It's like making him disappear.

that's certainly an option.. LOL

 

[Alontheway]

.some people just are sad. we have fake engineers and fake psychiatrist on here now discussing feelings and inadequacies. bye I did ignore the fakes. thanks

 

[JayArr]

More and more I'm coming to realize that the solar solution is perfect for a younger generation. In order to get the most out of it you have to buy in early in life and not have any stranded assets. A young person who's first car is a tesla and first house is off grid run on solar will find it all very economical. Asking me to throw away my furnace and spend $30k-$50k on solar to ditch the four gas powered cars I own to replace them with electric is always going to be an uphill struggle. The number of years required to break even on a solar system are long, too long for the Baby Boomer generation to gamble on.

It reminds me of walking through the mall at Christmas and this gung ho kid salesman comes out of a knife store and tells me that this knife in his hand is guaranteed to last 50 years. I laughed and then told him to take a good look at me and try to figure out how many years I've got before I die. I don't need a 50 year knife, I'm sure it's a really nice knife but I'm 58 and I doubt I'll live to 108. I need a 10 year knife - go sell your 50 year knife to a 25 year old.

 

[JayArr]

One other factor to consider is the carbon footprint of the two systems.

Compare the carbon emissions of 25 years of propane use to the carbon emissions of the manufacture and disposal of three sets of solar panels, charge controllers and lead acid batteries.

A pound of propane is 22000 BTUs, at a pound a day for 25 years that's 9125 pounds and 200.75 million BTUs

Propane releases 139 pounds of CO2 per million BTUs so a 25 year carbon footprint of about 14 tons.

The manufacture and disposal of the panels, charge controllers and batteries isn't anywhere near 14 tons BUT

Do the calculations again for the part time camper...

25 years x 30 days x 1 pound x 22000BTUs = 16.5 million BTUs

16.5 x 139 = 1.14 tons

The manufacture of solar panels is a very high energy activity, it takes a lot of emissions to make glass and to turn the silicon into crystals the amount of heat required means that coal is the usual choice to burn to create the components. I read one article that estimated that a single 220 watt solar panel requires 600 lbs of CO2 to manufacture. This forum usually talks about 100W panels so lets say they take 300 lbs of CO2 emissions to manufacture. that makes the 3 solar panel option above a 300lbs x 3panels x 3replacements = 2700lbs = 1.35 tons.

For a part time camper it may actually be friendlier to the environment to use propane instead of solar.

 

[solarman]

The DC only refrigerator in the 2022 Thor Axis draws 8 amps. It also has a "night mode" (whatever that means) and then draws 5 amps.

from the Norcold site, night mode is a reduction in compressor speed, it lowers the noise level by 3dB and power consumption accordingly. the Polar N8DC spec claims 5A ( 60 Watts ) normal and 3A ( 36 Watts ) in night mode. night mode runs for 8 hrs when enabled.

I've been looking at them now out of curiosity and most appear to consume around 80 to 90 Watts active cooling down and 25 to 40 W to maintain temps.
pump down claims are 3 hours for ambient to 15F

 

[JayArr]

So you hit the nighttime button as you go to bed and the unit goes into a power saver type mode? That's pretty clever.

3 hours from ambient to 15F would be great, no more starting the fridge the night before we leave.