Solar Refrigeration Options & Mullings

Hi, everyone! We've struggled with refrigeration on our off-grid homestead for the last two years or so. Previous to that -- and off and on during that time period, really -- we'd just gone without (mostly my partner had; my arrival was the impetus for working on it, because I insisted on a more diverse diet). We do have a small DC Sundanzer freezer that works great as long as the batteries don't give out. Our constraints are cost (I guess you could say we've taken a vow of poverty; in other words, we've chosen careers that don't pay and therefore chosen to live cheap rather than do things we don't believe in) and the knowledge that not only are things like batteries expensive to replace, but we haven't figured out how to manufacture them at home yet (it's an ongoing project) and may not be able to replace them in the future. I'm starting this string to tell you what we've tried and how it's worked, hear what others have struggled with when it comes to refrigeration, and find out what solutions you've tried and how they've worked.

So here are some things we've tried. Most of the following options work better in the winter, spring, and fall, but so far none of them work very well in May-August or so when it's over 100 during many days:

We've tried zeer pots of various types and various cooler arrangements. The former works when it's hot and dry (so, from April or so until June or July when our monsoon starts), for keeping a small amount of leftovers cool enough long enough to finish it off. The latter works for a few days if there's enough room in the freezer to freeze and cycle out several water bottles a day.

We got a small used Magic Chef AC chest freezer and an external Inkbird thermostat to convert it to a chest fridge. We plugged this in to our main array and inverter (the freezer is on its own array and charge controller). That worked from January to April or so of last year, and then as the desert heat increased and we were running fans and two computers so we could work from home, the compressor kicking on kept knocking the inverter off and crashing our computers. Our inverter is a good one, so we think it's a combination of it being an older freezer, not a newer Energy Star model, and perhaps not having enough batteries in our system. An off-grid neighbor does this successfully with a smaller system but a newer freezer (still non-Energy Star, I believe, just a cheap new Medea chest freezer). We and he both turn(ed) it off at night using an automatic timer.

After we lost too much work on our computers and had to disconnect the converted chest freezer, we started using a small Igloo Kool Mate 36 DC car cooler connected directly to a single 40 watt solar panel, no batteries, no charge controller, etc. So obviously it also turned off at night. We put one or two new ice bottles from the freezer in it every day or so (less in winter, more when warmer). In September-April or so, this reliably kept things in the 50's or so, which was enough to keep produce or leftovers (which we usually freeze first and then put in the cooler to defrost) for a couple days. We definitely lost some food that we didn't get to in time, and it was also a very small space. I think these are about 1.7 cubic feet interior? We actually have two of them, and would sometimes use the second one without power, just frozen stuff to keep it cool, since it didn't work as well. We did this for about a year and a half.

Somewhere during this time, we (throughout, please understand that "we" primarily means my partner) tried converting an old RV fridge (ammonia cooling, running either on electric or propane) to run directly on solar by trying to construct a parabolic solar heat collector to try to heat up the element and trigger the ammonia cooling. But the two or three old RV fridges we'd accumulated in our "resource pile" seemed to be too broken to work. Either that or we just weren't collecting enough heat. We'd like to keep tinkering on this idea in the long-run, so if you have any thoughts or suggestions or things you've tried along these lines, please respond and let me know!

Those Igloo Kool Mate-type DC coolers work using peltier chips and fans rather than a compressor, and we liked that idea. Peltier chips are cheap. So we bought two new 60 watt peltier chip units with fans built in (one on the cooling side, one on the heating side) and an additional 100 watt solar panel. My partner took apart one of the broken old RV fridges, removing its "guts," reinsulating it, and re-covering it. He cut holes in the lid to insert the cooling ends of the two peltier chip units, built a bracket to hold them on securely, and attached an old piece of rain gutter on hinges with latches to cover the units and let them ventilate heat out the sides. The lid got new insulation and sealing all around. We built (/are building -- not quite done) a new outdoor kitchen space to shade it and mounted 140 watts of solar panels on its roof. Pictures are (hopefully) attached.

So... This new fridge works... OK. Like the car coolers, it seems to cool to at best in the 40's. It's been over 100 most of the days since we turned it on, so with occasional opening of the lid, fixing a fan that already wants to go bad, adding new produce, etc., it sometimes spikes to the 80s. It is at least twice the capacity of the old car cooler, which is nice, but we've definitely lost some food to the non-fridge temps and the condensation that builds up in there (especially in the mornings, I assume responding to the chips turning on and starting to cool things down again). We're going to expand the roof shade and see if we can improve the lid seal anymore. We're drafting plans to expand to more peltier chip units in future -- perhaps liquid-cooled rather than air-cooled -- but this would also require more solar panels, so that won't happen immediately.

I have a confession to make: I like to ferment stuff. I have been called a Kitchen Science Witch. In addition to the normal sort of thing like cultured escabeche, pickled yucca blossoms, beet kvass, etc., I made a couple small batches of mesquite and agave small beer/mesquitatol/o'oki navait during the trial period with this new peltier chip cooler. The first batch taught me that this stuff ferments fast and then goes sour. So for the second batch, after primary fermentation, I wanted to bottle it in time to build a little carbonation before they started to go sour. This worked a little too well, given that -- unlike a traditional fridge -- this cooler didn't slow down the fermentation of the bottled mesquitatol much at all. There may have been a couple explosions. OK, maybe three. Inside the new cooler. That we had to clean up not long after turning the thing on. This may not have been the most helpful thing for keeping the box cool (i.e. closed). Alright, confession over.

Do you get lots more sun in summer, compared to winter? You might be able to run a mains power bar fridge in summer if you have an inverter that will handle the initial surge of it, and enough batteries to run it overnight.

I used to have a standard chest freezer that I would have switched on for only 3-5 hours a day. This didn't work well on the hottest days, but was fine for most of the year. I think relying on panels without batteries would have a similar effect where the freezer just isn't insulated enough to keep food cold overnight in hot weather without being switched on.

Australian camping fridges such as Engel, Waeco, Bushman, Evacool have reviews up for how they handle hot weather. These are very expensive, and still may need batteries overnight in very hot weather, but they use less electricity than normal fridges.

We went through last summer without a fridge or freezer at all. We would go to the shops once a week, use the most perishable stuff first, and then rely on the other stuff (or on reheated leftovers) for the rest of the week. It helped a lot that we have our own goats for milk.

There is a thread here where there are some fridge-free tips shared: https://permies.com/t/56871/kitchen/Recipes-tips-fridge-cook

Thanks, Kate! We get a few hours more sun in summer than winter -- we're between latitudes 31 and 32 north. What is a "mains power bar fridge"? Sorry, I did try Googling it, but I got no search results!

We definitely have tricks for going without refrigeration, too. We can't go shopping anywhere near once a week because of how far any decent food stores are from our place. We make a big food run once a month or so as well as using an old-fashioned cooperative-type shared truck delivery for organic dry goods in bulk, get produce that we can use within its fresh period or otherwise ferment, dehydrate, freeze, etc. We have a few standards that we make large batches of (chili, stews, etc.) and then we freeze them. (That takes up most of the room in the Sundanzer.) We're also always working towards growing more of our own because often the best way to keep produce fresh is by not picking it yet, right? ;) We gave up on fresh milk despite there being a great source close by (closer than any store) because it's just me drinking it and I can't go through a half-gallon before it spoils. I've gone back to the childhood habit of using powdered milk, to be honest. There's higher quality stuff available now that's whole and organic, luckily, and I just use a little in my coffee anyway.

In the long run we plan to dig a root cellar so that things like storage vegetables, my more stable ferments, etc. can have more space to hang out in the 50's F (sorry, I should have specified in my OP that my temp. ranges were in F). I think I also forgot to say in my OP that the current project cooler (converted old RV fridge) is about 3 cubic feet inside.

We'll keep working on DIY lower cost options that work within our constraints. We're currently exploring liquid-cooling rather than air-cooling in combination with the peltier chips in the new cooler (watching videos right now). My partner gets very excited about these kind of projects, and I always hope we'll come up with something that will help others as well.

I appreciate the ideas, thank you!

In the old days, sawdust was used as insulation to keep big slabs of ice all summer long without power in ice-houses.
Maybe you could invent a way to combine the two, like using solar to cool a liquid that only circulated through the refrigerator that is covered by a huge amount of sawdust.

By mains power I mean standard on-grid appliance, so 110v in the US I think.

Another idea, since you have a freezer, would be to freeze ice bricks and add these to the fridge when the sun goes down.

Good that you're building a root cellar, that is on my to-do list here as well.

could you share how many watts are in your main array, your charge controller model, your inverter model and your battery bank? Older fridges had a huge kick on startup as you discovered. Some inverters handle it better then others. A secondary inverter to handle the computers might work as well. It could be the surge turning off the inverter or voltage drop on the batteries. A new energy start rated chest freezer running on the new R600 refrigerant should have a much smaller start up draw and daily usage. The peltier solution is interesting but their efficiency is not good, using several times the electricity of a compressor to achieve the same amount of cooling. Hope it works out for you whatever route you choose.
Cheers,  David

Thanks for the information and suggestions, David!

First let me say that I don't think we're interested in going back to a compressor-type fridge, especially on AC, maybe even on DC. The main reason for this is the batteries. We'd prefer to expand our capabilities in ways that don't rely on that regular outlay of cash to replace dead or dying batteries that have to be disposed of carefully. Batteries are the weak link. That's time and money we'd prefer to spend in other ways. Here's how my partner just put it: "We have a vote of no confidence in lead acid battery technology." Now, once we've figured out the junk metal batteries we've been planning, let's talk some more about batteries! Call it Appropriate Technology, or soft-tech.

Kate suggested trying a compressor fridge without batteries: When we had a battery on our devoted array for the Sundanzer freezer die, we briefly tried running that just directly connected to the solar panels, without a battery. Now that's a super-efficient Danfoss compressor (75 watts DC on a 220 watt solar array), and even that compressor can't run consistently (i.e. keep stuff frozen) without at least one battery. So although we did consider replacing the compressor in our older Magic Chef AC chest freezer with a Danfoss compressor, we still run up against that battery problem. Also, although the Magic Chef is not brand new, we think we remember it using 200 watts or less -- that's why we bought it -- not like the even older compressors (sorry, the label is buried under amps and guitars right now so we can't look).

That brings us to the peltier chips. While it seems clear that you're right in general, David, that they're less efficient than compressors, it seems to us that that statement should have at least one asterisk attached. That is that the peltier chips will run no matter how much power they're receiving (overcast day? they cool less, but then on overcast days they don't need to fight the outside temp. as much anyway!), and they don't need a battery to cover a surge to get them started up. Another potential asterisk for peltier chips -- that we have plans to test out as funds become available for parts -- is that setting them up for liquid-cooling might be more efficient than their standard air-cooling set-up with fans. Once we get this going, I'll report back!

But! To answer your questions, David, our main array is:

500 watts of panels,

3 deep-cycle 12 volt marine batteries (122 amp hours, 845 cranking amps each),

a Xantrex C40 charge controller, and

a Xantrex PROwatt SW 2000 inverter (True Sine-Wave AC output with 1800 continuous watts and a high surge capability which we think is up to 4-5,000 watts).

It's not that we haven't looked into using golf cart batteries instead, FWIW. But then when a battery went dead, we'd have to replace it immediately for anything to work, because it takes two to make 12V, and unlike the marine batteries (sometimes -- when they're in stock), those aren't available locally. Plus they're three times as expensive. We'd rather put that money into figuring out new solutions.

What does your array look like, David and others? And what solutions have you found for batteries and refrigeration? Is anybody out there making their own batteries, by any chance?

I want to make sure to shout out to this great thread on storage-less PV: https://permies.com/t/54282/Storage-Solar-PV. And I also want to stress that a lot of the reason we choose not to devote too much money to this refrigeration game is that we can do quite well without, and I'd certainly encourage others to move that direction as well. If we forage or grow or buy some kind of vegetable or fruit and it starts to wilt before we've managed to eat it all, we dehydrate it or freeze it or ferment it.

We live in the desert, so basic dehydration is simple. We want to build one of the cool tower-like solar dehydrators, but in the meantime old-fashioned horizontal drying racks -- either uncovered, or covered in either an old trampoline (to allow airflow and heat without too much UV) or pieces of roofing metal (during rain) -- work quite well. The drying racks are on a low shed framework that doubles as shelter for motorcycles during monsoon when the racks are covered in roofing metal. We forage and dehydrate cholla buds and fruit, yucca blossoms, mesquite beans, devil's claw, prickly pear fruit, amaranth leaves and seeds, etc. Things that take a long time to dry completely, like cholla buds, eventually move to a drying rack hanging from the ceiling inside. Same for things we grow in the garden: beans and corn dry on the plants, peppers on racks, more devil's claw in clusters on strings from the ceiling inside. Meat and bones we smoke over a mesquite wood fire using a stone fire enclosure and things like halved barrels and pieces of metal to prop things up, keep them out of the direct heat, etc. When the mesquite beans are fully dry, we roast them using a similar set-up. We make mesquite cakes out of the flour we grind using Magic Bullet blenders (these work great on our solar array) and whatever we don't eat that week we dehydrate and store just like those who lived here before us, only we use 5-gallon plastic buckets until we get better at making large ceramic storage vessels out of our local clay. :)

We cure our squash and sweet potatoes (although the latter crop is on hold pending a garden modification) and then they store in the uninsulated house just fine until we eat them all.

I haven't done any canning yet here just because I prefer fermentation and don't want to kill the good microbes with excessive heat. If I end up with too much fruit of some kind someday, I might make jam or something and can that. I ferment a lot, for preservation, flavor, and health.

We do make full use of our DC freezer, both for food preservation (including leftovers and things we batch cook, as mentioned above) and for ice bottles to put in the chip cooler.

The only food we manage to truly lose is when our eyes are bigger than our stomachs and we defrost too much chili or stew or whatever and then we get distracted by all the other exciting food options and forget to eat the leftovers before they spoil. It happens a few times a year. So I definitely second what Joseph Lofthouse and many others on this forum have said about there not being as much need for refrigeration as we were taught to assume.

Hi Beth, Thanks for clarifying the system. Theoretically of course I think I would change your charge controller out for a MPPT unit and add some panels for earlier charging, later charging, and less stress on the batteries you do have. That alone would add a lot of longevity to the lead acids you already have. The name brand units have relays built in that you can use to turn on diversion loads. Here we use it for water heaters in summer but for you an efficient deep freezer set so cold it would always cycle on when power was applied. The larger array would very quickly saturate your small battery bank then the relay would divert to the freezer but only power it when the batteries were topped up thus avoiding wearing out the battery for running the freezer. So technically you would be running on solar directly with a small back up for lights. You have such awesome sun there so I get why you would want to pursue the peltier route. Solar is so cheap right now as well. You could stack the peltier plates to achieve a much higher temperature differential as well. If you add liquid cooling plates you could be on to something. I played around with them for power generation only but the theory is the same if in reverse.
You asked so: I have 960 watts of solar running through a 60 amp Outback charge controller to a bank of 8 l16 batteries. I use a magnum 4024 inverter... I only run half the house on solar these days as I grew tired of the propane backup generator for our long dark winter. I use grid power to top up the system in winter and run non essential stuff like a dishwasher, sat tv/DVR and the internet router.
Cheers,  David

Sounds like the Sun Danzer has proven its value. When refrigeration was not possible it was producing ice to aid in heat removal! A matching fridge would likely end your issues with a slightly improved pv system.

If you ran 4 golf car batteries you would have the benefit of the paralleled sets (and the detriments) and would always have a 12v set to use if a battery failed.

Marine batteries cost as much or more to run. I say more because they will wear out quicker and do not have the capacity ah for ah (name plate) especially at deeper dod at higher rates and over as many cycles.

Dissapointment is a type of cost associated with alternatives also.

With the numbers and costs given for thermostat modified deep freezers used for refrigeration, they must be considered. You have.

We have a challenging pv site. About 80 percent solar window, 3.75 hours peak average yearly, 1.2 hours peak winter average. No generator allowed (pv purist, self limitation).

With 1640W pv and 440Ah/24V comprising the main system we discontinue refrigeration amd freezer operation about late october or early november and use an outdoor storage for frozen foods and a large cooler brought in and out to moderate temps for produce. Leftovers go in a cabinet on the porch to freeze overnight. This lasts til almost april some years with loss of reliable freeze in late march.

We have 3400 more Watts pv in the garage waiting for upgrades, but even doubling battery capacity would likely not allow absolute reliable deep freezer and conventional refrigerator/freezer operation year round without a dedicated and or auxilliary battery system or backup generator.

I have recorded up to 14 days consecutive days of almost no charging at least once a winter. Our system will do 10 with conservation and 6 without, at 0%-5% array input over 8 or so hours. 14 days requires turning off the inverter when we are done using it and a transition to another system.

There is an auxilliary system used for communications radio, personal battery charging and backup lighting (male to male extension cord gets it done as we are wired 120v only) and coffe grinding. It also runs the dhw boiler circulator and has its own 200w inverter, 90Ah battery, 15a MPPT CC, 224W module, etc.

This is used for maintenance and backup.

435Ah/48V and 3600W PV is the cure at my location and usage profile as i have most of the stuff laying about at any given time, but our fridge is not high performance and off grid pv requires high performance/high efficiency and so refrigeration could likely be a non issue with a $2600-$4500 investment in proper appliances.

With a year worth of wild game meat on the line and a set of batteries, is not the most extreme thing to spend system budget on.

We keep it on grid and off site for now, its an evil secret to our off grid living, shhhh!

Dont give up on lead acid. It is simple, robust and state of the art technology as opposed to "state of the finnicky coin flip" and your system will function without dissapointment and with longevity if you dont place unrealistic demands on it.

That’s some great multi faceted experimentation your doing. Thanks for the interesting descriptions. I’m curious to learn more about the direct DC cooling project. Sounds like you’re very involved with your food and energy which sounds great.  
Digging a root cellar, dehydrator, etc makes total sense. Use all the passive possible. My understanding is there are wide temperature changes there in the semi arid region. That makes design a bit more challenging and opens up possibilities. As was mentioned earlier that placing food outside at night or seasonally can be effective.
I wonder if you could run water through “chillers” at night and store cold water. Basically solar hot water panels running in reverse. A tank in the ground (root cellar) and a tank up in the air above the collectors. You would have some cold water and some hot water most of the time. And a pump may not be necessary if it can thermosyphon due to convection.
There are large “chiller” panels from big refrigeration walk in coolers. I had one and wish I still had it. It was aluminum and I think it originally had ammonia or a refrigerant in it. These would be interesting to play around with.

Yes, my chest freezer is on grid and off site as well.  Has been for over twenty five years now.  Cost's me $100 a year...  sounds cheap until you multiply by 25...

This summer I am finally purchasing sundanzer 14.7 cf dc chest freezer, and moving it home.
Cost to get it home is about $1750... I have 4 150 watt solar panel's, they cost me $320. A pair of 105 6 volts for another $350 and a small solar charge control around $100
Hmm, I'm not the best mathematician but I think I should have done this 25 years ago.

I will need to rent a manlift to get the panels mounted on the barn roof...

Hi, everyone! Here is a progress update. We've had to replace one of the fans already because it failed (cheap Chinese part). It's been insanely hot here with our delayed monsoon start, and the unit just has a lot of trouble keeping up. We realized that we need to open up the hinged cover on top of the outside fans when it's hot or too much heat sticks around by the chips. We're going to scrimp and save and spring for another panel and additional peltier chips with a liquid cooling set-up and add that on to what we already have.

The good news so far is that it maintains root cellar-like temperatures pretty well without having dug a root cellar yet. This means that, since it's dark and cool, the chayote I bought at the Mexican grocery store and hadn't eaten yet sprouted, as I described in this thread: https://permies.com/p/956187. The bad news is that my fermented beverages are still exploding, or at least, one more exploded yesterday (tepache like I mentioned in this thread: https://permies.com/p/956468). We didn't have ice bottles to add for a few days because we'd filled up the Sundanzer freezer with a huge batch of chili, and although we use those frozen containers of chili (used plastic ~2 lb. coffee containers) in a similar way to the ice bottles, cycling them into the cooler when we need to start defrosting them, it doesn't work out quite as well in terms of timing and cooling.

One thing we figured out is to keep produce in shoebox-type plastic storage containers -- with a towel or cloth in each one to absorb moisture -- inside the cooler so that the condensation doesn't make things mold. Mostly, though, we try to just use produce right away, freezing or fermenting or dehydrating it if we're not going to cook and/or eat it soon. For example, I bought ingredients for a batch of giardiniera/escabeche (carrots, onions, mixed hot peppers, cauliflower, jicama, garlic, oregano) and got a gallon crock of that fermenting, but had hot peppers left over, so chopped them up and froze a quart bag full of them in preparation for this latest batch of chili.

Jeremy Baker wrote:My understanding is there are wide temperature changes there in the semi arid region. That makes design a bit more challenging and opens up possibilities. As was mentioned earlier that placing food outside at night or seasonally can be effective.
I wonder if you could run water through “chillers” at night and store cold water. Basically solar hot water panels running in reverse. A tank in the ground (root cellar) and a tank up in the air above the collectors. You would have some cold water and some hot water most of the time. And a pump may not be necessary if it can thermosyphon due to convection.
There are large “chiller” panels from big refrigeration walk in coolers. I had one and wish I still had it. It was aluminum and I think it originally had ammonia or a refrigerant in it. These would be interesting to play around with.

Thanks, Jeremy! There are wide temperature changes here in many seasons, but unfortunately when it's hottest -- after monsoon clouds have started swirling but before we've had any significant cooling rains -- the humidity rises and keeps the overnight temperatures from dipping very much. This is always the most challenging period of time for us with refrigeration.

I need to find out more about the chiller panels you mention! Got to do some digging. Thanks!

frank li wrote:Sounds like the Sun Danzer has proven its value. When refrigeration was not possible it was producing ice to aid in heat removal! A matching fridge would likely end your issues with a slightly improved pv system....

Dissapointment is a type of cost associated with alternatives also....

Dont give up on lead acid. It is simple, robust and state of the art technology as opposed to "state of the finnicky coin flip" and your system will function without dissapointment and with longevity if you dont place unrealistic demands on it.

Thanks, Frank! It's true, the Sundanzer is great and we make heavy and satisfied use of it, but (unfortunately or fortunately, depending on perspective) we can't afford another -- either the unit itself or the system expansion it would require -- especially given that, as I've mentioned, we can do without and it's not really that much of a sacrifice (by our standards -- we are crazy desert rats, I'll admit). We do feel a substantially smaller investment to continue the current experiment and try to improve its performance is both doable and worthwhile.

I have definitely spent most of my life agreeing with you about disappointment being a cost associated with alternatives. I would describe myself as deeply risk-averse. It kept me safe, i.e. I kept jobs I hated rather than start my own business or go freelance, and although I'd been obsessed with off-grid sustainable living and things like permaculture (although I didn't learn of such a design system until later) since leaving my parents' home, I didn't really do much about it. That is, until I started to throw caution to the wind, at least every once in a while. Since then, I'd say a relatively small percentage of my attempts or experiments have been successful, especially in a way most of the world would recognize, but I'm a good deal happier, and I'm learning a huge amount every day. Not only that, but even though individual attempts may fail, somehow we seem to have still accomplished a lot. My partner either learned these lessons far earlier than I did or started out less risk-averse. Either way, he was already off-grid and quite self-sufficient by the time I joined him here, and much of our experimentation originates with him. I believe that if we let disappointments -- failed plant experiments, earthworks not flowing the way it seems like they should, etc. -- get in our way then we're not learning as much and we're not innovating in a way that I believe we all need to in order to make it through our current planetary challenges. I know you weren't saying that disappointment should stop us necessarily -- just that it is a cost -- but I wanted to throw that out there, as a manifesto or modus operandi.

Is there a good discussion about batteries here that I haven't found yet? Can we at least seek better alternatives to lead acid, even if we don't give up on it entirely? What I've heard/read is that there are arguably already multiple better alternatives to lead acid that have been around a long time -- like the Edison nickel iron battery, which even though it's early 1900's technology is still called the "most rugged and longest lasting battery option available today" -- but got pushed aside by moneyed interests and agendas, but this is far from my area of expertise and I'd love to learn more.

here is a link to some interesting work that that you may like. design and principles behind desiccant based air conditioning. This extremely efficient, DIY air conditioner is inexpensive to build and costs less than one half as much to run as a conventional, compressor based air conditioner.
https://www.youtube.com/watch?v=R_g4nT4a28U

That sounds really interesting, thanks, johnny! Looking forward to watching it.

One cool thing about compressor driven refrigeration, the proper appliance can be put inline to take the heat from the fridge/freezer and put it in your domestic water.

https://www.hotspotenergy.com/heat-recovery-air-conditioners/

Interesting, thanks, frank!