R-pod Owners Forum Homepage

This site is free to use.
Donations benefit a non-profit Girls Softball organization

Forum Home Forum Home > R-pod Discussion Forums > I need HELP!!!
  New Posts New Posts RSS Feed: Computer board refrigerator
  FAQ FAQ  Forum Search   Calendar   Register Register  Login Login

Computer board refrigerator

 Post Reply Post Reply Page  <12
Author
Message
podwerkz View Drop Down
Senior Member
Senior Member
Avatar

Joined: 11 Mar 2019
Location: Texas
Online Status: Offline
Posts: 267
Post Options Post Options   Quote podwerkz Quote  Post ReplyReply Direct Link To This Post Topic: Computer board refrigerator
    Posted: 13 Jun 2019 at 4:23pm
Yep but I use and power refrigeration with solar all year long and not just in the summer, so I am generalizing about panel performance over an entire year rather than trying to type out an entire solar 101 course, season by season, latitude by latitude, panel by panel. Neither have I suggested that a 100 watt panel will power a fridge directly, or 'power chill' warm food all day long.

Flat roof-mounted panels WILL under-perform in the winter, by more than 50%. Portable (or tilting) panels can be moved to grab every available photon from sunrise to sunset in December, January, and February when sun angles are very low. 

I'm not including every situation or detail, and assumptions are made that appropriate batteries, solar controllers, and panels are used for each situation. Assumptions are also made that most of the food or drinks going in are already cold, the same as with an absorption fridge.

I have successfully operated 2 different dorm fridges over several years in all seasons with solar, batteries, and inverters. It does work. Inverter losses can also be minimized, using the appropriate pure sine inverter, not some cheapo from Harbor Freight or Amazon. These inverter should have a power saving mode, but, with these, the fridge must have a mechanical thermostat and NO electronics. Most small dorm fridges do not have an interior light, and they have a tiny 'freezer' coil, although some larger dorm fridges do have 2 doors, LED interior lights, and a separate freezer compartment.

There are ways to control an inverter with the mechanical thermostat in the fridge, but this will add complexity and additional points of failure.

Most small dorm fridges use a 'skin' condenser so this means ventilation around the unit (all sides) must be provided. They also do not have a latching door, so that must be improvised. And they have a very high start-up surge which must be considered when sizing the inverter, or a 'soft-start' kit can be added. Physical mounting must also be improvised. Yes there are solutions. But generally speaking, a 12v portable or built-in fridge avoids all these issues, for the most part.

So, it's easier (much easier) for most people to simply buy a 12v compressor fridge. Yeah it costs more but it's almost plug-and-play simple.

Again, in my case, if and when the existing Dometic 3-way fridge stops working after the warranty is out, I will be installing a Truck-Fridge, 12v compressor fridge, which I am familiar with from using them in commercial trucks.


r・pod 171
Back to Top
offgrid View Drop Down
Senior Member
Senior Member


Joined: 23 Jul 2018
Online Status: Online
Posts: 1423
Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 13 Jun 2019 at 7:36pm
Actually in winter a single axis tracker will outperform horizontal flat plate by about 2x. But it doesn't matter to most of us, because few of us are camping in the middle of winter anyhow. That's why horizontal solar roof mounting works just fine for most Rv'ers.

In any case, as I said, feel free to move your portable modules around as often as you want to capture as much of that solar flux (aka those sneaky little photons) as possible. Its got entertainment value for a lot of folks I guess. For me, having designed and built more trackers and done more outdoor solar module testing than I care to remember, it's like the proverbial busman's holiday. Now, designing an RV roof mounted solar tracking system might be a fun project. You could use it for emergency air braking too. LOL

That 2x from tracking in December is still only about 2/3 of the horizontal fixed orientation output in June, so even if you more your modules around all day in the winter you're still going to need as much or more solar in winter than with horizontal fixed for summer use. The point is that one thing I learned long ago in the solar biz is that generalizing does not work when doing system design. You need to define some basics: when, where, how are you mounting, what are you trying to run and for how long, how reliable do you need your system to be. None of this is an upper division university level course, just basic stuff, same as knowin' what you're towin' when you select a tow vehicle. 

Everybody necessarily puts some warm stuff in their fridge sometimes, I do quite often.  If you do that with an absorption fridge it will get warmer inside for while. If you do that with a vapor compression fridge it will consume more energy.  That energy has to come from somewhere. The specs from the manufacturers generally assume that this isn't happening, and also assume no door openings. That's why they usually appear to be more efficient than they really are in practice. Marketing BS.

I agree with your inverter requirements and the requirement for eliminating fridge electronics. I would go with a higher end Chinese inverter now though, they've gotten a lot better and more sophisticated. And proper ventilation is required for the location of the condenser in whatever fridge you pick.  A lot of our forum members are really good cabinetmakers so I think the installation of a dorm fridge would be pretty easy for them, and much cheaper than a DC fridge. 

But I think if you're comfortable with the Truck fridge product then that's a fine solution, and no more expensive (if that) then a comparable Dometic. For most folks though, unless they're using a portable generator, adding the 300 watts or so that or the dorm fridge  is going to require (and the battery that goes with that) is more than they're going to want to deal with.

For me too, I'll stick with the absorption fridge and its negligible propane usage simply to free up solar array and battery capacity for running air conditioning, for which there is no satisfactory alternative available for boondocking. If I was going to do it, I'd place a 300-350 watt grid tie module behind the roof ac. Batteries are another issue, I'd probably just stick with my two GC2's and plan on running the generator daily for an hour or two unless is was really sunny. 

2015 Rpod 179
2012 Toyota Highlander
Back to Top
podwerkz View Drop Down
Senior Member
Senior Member
Avatar

Joined: 11 Mar 2019
Location: Texas
Online Status: Offline
Posts: 267
Post Options Post Options   Quote podwerkz Quote  Post ReplyReply Direct Link To This Post Posted: 13 Jun 2019 at 9:12pm
I agree except to say this: I was not designing anything for anyone here...I was very briefly saying what I do and what can be done with a few panels, a few batteries and a small DC fridge.

And hey, if you have not tried winter camping/boondocking in southern Arizona, you don't know what you're missing. A million snowbirds can't be all wrong!

Quartzsite especially, has a lot to offer in January/February/March. Even the Big Bend area in West Texas can be comfortable in winter. 

You sure dont want to be in either place in mid-summer tho!




r・pod 171
Back to Top
offgrid View Drop Down
Senior Member
Senior Member


Joined: 23 Jul 2018
Online Status: Online
Posts: 1423
Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 13 Jun 2019 at 11:16pm
I get that, but it sounded like your suggestion was to replace a dead dometic with something equivalent in capacity and utility powered by solar at 12vdc. 

That would require a decent size solar array and battery bank, and either a properly installed dorm fridge and good quality inverter or a good quality properly installed danfoss/secop dc fridge. I agree that that is certainly very doable but its not a trivial investment in either design, cost, or labor.   Is it the best choice? Probably not for most folks quite yet, more because of the batteries than the solar.

One thing I wanted to circle back to you on was your comment about 2-4 year working life on the dc fridges. That's pretty disappointing, so maybe product quality has degraded from the earlier Danfoss units, which lasted much longer than that. If that's the case then maybe the several acquisitions of Danfoss. latest being Nidec (Japanese) which acquired Secop (German) which acquired Danfoss (Danish) have resulted in a drop in quality in what was a great product. That might be one reason to go with a dorm fridge, should last longer and is much cheaper to replace when it does break. 

i used to live in Tempe and camped quite a bit in the desert in southern AZ, but usually not earlier than March, by which point there is good sun (6 kwh/day on the horizontal). Lots of flowers in the spring  too. Of course, we're talking about the 1980's,  back then solar was $10 a watt so most folks didn't consider it. i worked for a manufacturer and had all the reject modules I could fit on my old Westy bus though Tongue

If you want to get the irradiance for anywhere and any month in the US for any tilt/orientation array the PVWatts calculator is super easy to use (solar 101 course not required). Besides, our tax dollars paid to develop it, we might as well get the benefits. You can rough in a design for a household system on there too, right on your actual house if you want. 





2015 Rpod 179
2012 Toyota Highlander
Back to Top
podwerkz View Drop Down
Senior Member
Senior Member
Avatar

Joined: 11 Mar 2019
Location: Texas
Online Status: Offline
Posts: 267
Post Options Post Options   Quote podwerkz Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jun 2019 at 4:13am
Originally posted by offgrid

I get that, but it sounded like your suggestion was to replace a dead dometic with something equivalent in capacity and utility powered by solar at 12vdc. 


Way back in this thread I said:

"Not that I want my fridge to stop working, but a failure after 4 years or a $500 repair would be all the excuse I would need to replace it with a 12v compressor fridge."

That is not a suggestion, it is a statement about what *I* will do. Certainly it opens the door for discussion, but there was no attempt in this (or subsequent) posts on my part to suggest what others SHOULD do, only what I HAVE done and what CAN be done.

My explanations had to get more detailed as the thread progressed because the replies by you were indicating it wont work, or that I had made errors, which I didn't......and 12v fridges do work, but as I also said early on, they are certainly not for everyone, but they do work. As do dorm fridges on inverters.

I was originally trying to keep it brief and simple, respecting the original topic. 

The statement about the average life of these 12v compressor fridges, or any dorm fridge in 24/7 use (especially in a vehicle) is a huge generalization, and again, 24/7 usage. That part is important to emphasize. These days, it seems that few $500 complex electronic devices from china last more than a couple of years except maybe cameras and some flat panel TVs used a few hours a week. No news here.

Planned obsolescence, as is seemingly the case with the Dometic absorption fridge in the original post. 

The old Norcold absorption fridge (USA-built in late 1986) that was installed in my old 1987 Winnebago Itasca lasted about 25 years, running 24/7 (mostly on shore power) for about 12 of those years, believe it or not. BTW, in year 2000 I bought my first 'large' panel, 64 watts. It was $500!

When the Norcold finally died (due to neglect) I replaced it with a cheap dorm fridge (about $125) which lasted less than 5 years. 

Again, nothing new here. We generally dont expect a long service life out of most of our electronic devices these days.




r・pod 171
Back to Top
offgrid View Drop Down
Senior Member
Senior Member


Joined: 23 Jul 2018
Online Status: Online
Posts: 1423
Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jun 2019 at 12:23pm
Peace, its all in how one interprets the emphasis isn't it? Easy to take different meanings from what was perhaps intended.  In any case I think we've covered this topic very well at this point, and made more info available for everyone who might consider switching to electric refrigeration so its all good. 

I do still expect more than 2-4 years service life from my fridges, RV or household. Even a dorm fridge, but if not it would at least be cheap to replace. They aren't as good as they used to be for sure.  I had an old Norcold unit and it was very reliable. But I've had a couple of Dometics that went well into their second decade and one into its 3rd as well. 

When I started in solar in 79 the modules were about 30-35 watts and manufacturer dock pricing was about $15 or $20 a watt. Most were used for navigational aids. The customers used to call them 2 amp sticks because that was their 1 sun max power current and they were long and skinny. 

Was your 64 watt module by chance a Solarex MSX64?  I was engineering manager at Solarex then.  $7-$8/watt retail was about right for that point in time. Manufacturer dock pricing was about half that.  The distribution channels still could get a good markup back then, with direct internet purchasing now that's long gone. 


2015 Rpod 179
2012 Toyota Highlander
Back to Top
podwerkz View Drop Down
Senior Member
Senior Member
Avatar

Joined: 11 Mar 2019
Location: Texas
Online Status: Offline
Posts: 267
Post Options Post Options   Quote podwerkz Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jun 2019 at 3:03pm
It was made by UniSolar. Back then they made rigid frame amorphous panels with clear Tedlar 'glass', supposedly hail proof, and I mounted it on the top of my motorhome for mainly battery maintenance when boondocking. I fabricated a tilting mount to use when parked.

It worked well for about 17 years, although as it aged over the years, the output amps dropped off a bit.

It never received any damage from hail, but the motorhome A/C cover and corrugated sides of the coach got beat up pretty good a couple of times, so I guess the Tedlar did it's job, the panel never suffered any hail damage.

In that time frame I went thru 3 solar charge controllers (probably surge or lightning damage) and 2 or 3 sets of house batteries....so I would say the panel was a good product. It was still working when I sold the motorhome a couple of years ago.
r・pod 171
Back to Top
offgrid View Drop Down
Senior Member
Senior Member


Joined: 23 Jul 2018
Online Status: Online
Posts: 1423
Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jun 2019 at 8:12pm
Unisolar made an interesting and unique product. They made their amorphous SI depositions directly onto a stainless steel sheet substrate which was then cut up and encapsulated with as you say a clear tedlar superstrate. By doing that they were able to create a truly flexible system (unlike the so-called flexible modules you can buy today that use crystalline Si cells) and several unigue products including long skinny peel and stick modules for standing seam roofing,  and shingle modules. Their reliability was quite good, a 0.5-1% or so annual performance reduction is to be expected for any modules, and  they didn't have any major catastrophic failures that I ever heard of.  

Their big problem was poor efficiency (about 6% like all the a-Si products) and as crystalline Si modules got cheaper and more efficient it got to where Unisolar couldn't even give their modules away, the cost of mounting alone for 6% modules was more than the cost of mounting and modules for 15-18% modules. So, they declared bankruptcy in 2012. Another interesting and inventive US manufacturing company bites the dust... 
2015 Rpod 179
2012 Toyota Highlander
Back to Top
podwerkz View Drop Down
Senior Member
Senior Member
Avatar

Joined: 11 Mar 2019
Location: Texas
Online Status: Offline
Posts: 267
Post Options Post Options   Quote podwerkz Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jun 2019 at 11:30pm
I still own a small UniSolar 5 watt panel I bought around the same time, and it still works...about 20 years old now, exposed to drenching West Texas sun and up to tennis ball size hail for 14 years on my pickup headache rack.

Recently I have seen some N.O.S. UniSolar flexible panels that were 10 or 12 feet long and about a foot wide for sale on ebay...tempting, but not THAT tempting.


r・pod 171
Back to Top
offgrid View Drop Down
Senior Member
Senior Member


Joined: 23 Jul 2018
Online Status: Online
Posts: 1423
Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: Yesterday at 11:55am
No, at 6% efficiency the product just doesn't cut it anymore, unless you have plenty of space and really want true flexibility (the so-called "flexible" crystalline cell modules are NOT). 

The 144 watt ones are actually about 18 feet long. But if for example you wanted to  curve one of those long skinny modules front to back over your rPod  performance would be significantly lower because of differences in irradiance from one end to the other. Interesting idea though, and the modules do have bypass diodes in them so a good MPPT controller should still be able to extract whatever power is available.

The standard IEC hail impact test for PV modules that everyone needs to meet is to fire 1 inch ice balls at multiple spots at the terminal velocity. I know west TX gets bigger hail than that but if you do and your rPod is outside you'll probably be replacing more than just a roof mounted PV module. LOL
2015 Rpod 179
2012 Toyota Highlander
Back to Top
 Post Reply Post Reply Page  <12

Forum Jump Forum Permissions View Drop Down

Bulletin Board Software by Web Wiz Forums® version 9.64
Copyright ©2001-2009 Web Wiz