14 ms·

Fridge 0.2

584 points by Breadmaker 8y ago

Gravityloss 8y ago
Demand elasticity.
- maliker 8y ago
  With zero quality of service impact to boot (once the 1/2 gallon milk bug is fixed).
Scoundreller 8y ago
Any luck with phase change materials for more dense « cold » banking? You do say « However, this needs a material that freezes at a higher temperature than water, and most such are oils, which are less dense and so store less cold overall. », but I wouldn’t underestimate the enthalpy of melting. Depending on your climate, a long heat pipe would be interesting to move heat outside when it’s cool enough outside (even if only during a few hours overnight). But that’s getting complicated to fabricate oneself. Oops, edit: you have it outside already. How do you prevent freezing everything ? (Again, climate dependent).
- komali2 8y ago
  >How do you prevent freezing everything They don't. If it's too cold outside for too long, everything will freeze.
  - joeyh 8y ago
    Or add a small heating element, but it's not been necessary so far, it would probably need a full week below zero to freeze. I do some minor adhoc regulation by putting leftovers in the fridge when they're still piping hot on colder days, vs letting them cool down more on warmer days.
starbeast 8y ago
One thought, if this is combined with a freezer and there is a pumped heat exchanger between that and the fridge, you can effectively use the freezer as the battery.
- Scoundreller 8y ago
  Small boats used systems like this: freezing blocks of ice to provide convective cooling to a cooler so that things stay cold without the engine running. A lot of people hated them enough (and the gas used while sailing) to replace it with solar based systems.
- edaemon 8y ago
  Regular refrigerators use the same principle, albeit with a mechanism much simpler than a heat pump. They have holes between the freezer and refrigerator compartments and use a fan to push cold air from the freezer to the refrigerator. A heat pump would make that exchange much more efficient.
  - JoeAltmaier 8y ago
    I doubt that heat pumps could be more efficient than direct exchange of cold air?
    - edaemon 8y ago
      There are periods where you don't want the cold air to move into the refrigerator. Direct exchange allows the cold air to move around at all times -- regular refrigerators just turn a fan on and off, but some heat is always exchanged through the holes. A heat pump would just make the exchange more controllable.
      - ndnxhs 8y ago
        I have a fridge that works with just holes. You can either have the fridge or the freezer at the right temp but not both.
sthgrau 8y ago
For putting the thermal mass above the food, could a workaround be to put a heat sink on the bottom of the lid, and connect it to the thermal mass with an equally heat conductive material? Also, before I saw what the heat sink was, I wondered if you could use shotcrete on the walls of the freezer, to act as the thermal mass.
- wpietri 8y ago
  I was wondering if this might work better with a traditional freezer-on-top refrigerator where you just use the freezer as pure thermal mass.
  - nightbrawler 8y ago
    The chest style is optimal because with a traditional freezer-on-top refrigerator, you lose a lot of cold air each time you open the door. Whereas with the chest style, hardly anything is lost because the cold air doesn't rise.
    - Scoundreller 8y ago
      > Whereas with the chest style, hardly anything is lost because the cold air doesn't rise. Depends how quickly you open it and slam it shut afterwards.
    - wpietri 8y ago
      I think we might be talking about different kinds of optimality. I think the chest style is best for total energy consumption. But as we saw, his biggest problem was around thermal stability. If we put the freezer/fridge fan under computer control, you might be able to get more stable fridge temperatures despite the air loss because you can drive the freezer temperature much lower, getting more stability value from the thermal mass. (And it's also worth filling in any big air spaces in the fridge with more thermal mass, so that opening the door is not a big deal.)
_salmon 8y ago
Seems strange to call it a "zero-battery-use fridge" and then follow it with "It ties into the typical offfgrid system of a solar charge controller, battery bank, and photovoltaic panels"
- dang 8y ago
  We changed the title from "Fridge 0.2 offgrid, solar powered, zero-battery-use fridge has made it through".
- Scoundreller 8y ago
  Mostly agreed. The big issue with off-the-shelf AC fridges is the current draw required for them to start. If you want to go completely zero-battery, you’ll need to highly-oversized your PV array just to handle the 1-2 second inrush starting current. Or devise a slow-start function, overriding the AC flow to the compressor. So instead of starting at 60hz, you would start at 1, then 2, then 3hz, etc. I guess OP means they could add a fridge to their off-grid setup without changing their existing battery budget for their other needs.
  - realityczeque 8y ago
    Or you can just buy a DC refrigerator.
    - Scoundreller 8y ago
      They’ll cost you a lot of extra $$$. Consumer stuff is cheap, but once it’s built slightly differently for the specialized off-grid market, the price skyrockets.
  - nerpderp82 8y ago
    One could have a high current lipo connected to the inverter that can supply > 2kw for seconds. A 14.8v 4Ah 50C battery can supply 3kw for 72 seconds, more than enough to even out start/stop and shade cycles.
linase789 8y ago
> Using a supercapacitor to provide power while shutting down on loss of solar power, instead of the current few minutes of use of batteries. I wonder why this is necessary. I've also seen it mentioned in the wiki, but no explanation. Isn't a compressor the only electrical thing in a fridge? I know you must be careful with leaving some time between restarts, but why can't you just shut it down immediately on power loss?
- Scoundreller 8y ago
  I thought so too. Even if they’re all mechanical, it usually makes sense to keep the fan running across the evaporator to prevent moisture buildup (which will then sit in a place susceptible to freezing). It can also be more efficient to push this residual cold into the vessel. My car’s AC gets funky if I don’t remember to turn off the AC a few minutes before shutting down.
  - mulmen 8y ago
    I think there is a drain near the condenser to prevent this, if your car smells nasty after turning off your A/C you may want to make sure that’s not clogged. Also, if equipped on your car replace the cabin air filter.
    - Scoundreller 8y ago
      It drips underneath on a muggy day, so I assume it's draining OK. My main gripe is that they don't auto-run the fan for 3-4 minutes after key-off.
- lambda 8y ago
  https://fridge0.branchable.com/battery_bank/ https://fridge0.branchable.com/battery_bank/ > Fridge0 does not need a big battery bank, since it stores cold in its thermal mass and runs only when solar power is available. > But, at least a mimimal battery is needed to run the computer control. Probably on the order of 5 watts for a computer like a raspberry pi; this could be reduced more with a more embedded computer like an arduino. > Enough battery to run the fridge for a minute or two is also needed. Consider what happens when the fridge is running, and the sun goes behind a rain cloud. Suddenly, there's not enough power to run it, but it's still turned on. The inverter will try to run with whatever small solar power is still coming in, but it's not enough. Some inverters might manage a clean power off, probably accompanied with loud beeping. Other inverters might fail in more interesting ways. > To deal with this situation, the computer needs to check the incoming solar power frequently, and power off the fridge if there's not enough. The battery is needed to keep the inverter and fridge running until that happens. Basically, it sounds like the answer is because with a solar panel, there are states that are between "off" and "on," you rather just get an amount of power proportional to the amount of sunlight, and there's a concern that those states could cause problems if you don't provide a more constant power supply and active switching to fully shut off the power when your solar panel is not producing enough power for the "on" state.
deleted 8y ago
[deleted]
raphinou 8y ago
What milk can be kept 2 or 3 weeks in the fridge? Is there a special methodology? I never reach that conservation time with milk.
- komali2 8y ago
  Huh, what country you in? I usually get a solid 2 weeks in California from just regular Safeway or trader Joe's branded milk.
  - merlincorey 8y ago
    Organic milk seems to last even longer (with longer in the future sell-by dates printed), as well.
    - komali2 8y ago
      Organic meaning what? Not to be pedantic, but the word doesn't mean anything to me anymore.
  - BozeWolf 8y ago
    Fresh bio milk is ok for about 2 weeks here in NL (6deg Celcius fridge). Only a few days after opening it. Unless it is treated with heat. pasteurized or even sterilized milk. But that changes the taste. After a day of four you notice the quality degrades: making cappucino milk foam is more difficult then.
    - phreeza 8y ago
      Can you actually buy unpasteurized milk in NL (except from the farm directly)? I thought there was some sort of EU rule against that.
      - icebraining 8y ago
        The EU only enforces clear labeling of unpasteurised milk. Member states are free to choose if it can be sold.
rmtech 8y ago
Probably the best cold battery is to have a freezer compartment that's full of salt water which freezes at several degrees below 0, and some kind of adjustable heat link between the freezer and the fridge.
- joeyh 8y ago
  That was my original plan, but I went with the simplest possible thing before trying it, and so far the simpler plan has worked.
  - nerpderp82 8y ago
    One could have frozen 1 gallon milk jugs in the freezer and manually put them in the fridge compartment as needed.
    - smolder 8y ago
      I freeze quarts and half gallons. They preserve seemingly indefinitely when frozen and the jugs hold up fine. Give it ample time to thaw before you use the milk, and it'll be normal. In a single person household without much home food prep this prevents a lot of waste without excessive trips to the store. As an aside, the stuff that comes from a partially thawed jug is interesting. It seems concentrated, as if the full water content is the last part to return to the liquid.
gumby 8y ago
Great project, not just doing it but monitoring the data. Makes me wonder about the energy cost of losing (i.e. replacing) a 1/2 gal of milk vs the energy cost of a gas cycle fridge. I know food wastage is a huge resource lost but I’ve always overlooked the fact that energy is a huge one of the resources. Thanks for writing this up!
- throwaway12iii 8y ago
  (pulling random data points from around the internet) It takes approximately 255 liters of water to make 250ml of milk. So 1020 liters per liter of milk. There's 3.78542 liters per gallon. So that makes about 1930 liters per half gallon milk. 510 gallons of water for 0.5 gallons of milk. It takes between 2500 and 5000 joules of energy per liter of tap water depending on the water source (2000 times that for bottled water). So up to 9,650,000 joules of energy per half gallon of milk for the water(about 2680 Wh). 1.25 to 1.44 kg of feed to produce a liter of milk (0.2645 gallons). To produce 1kg of wheat requires between 500 and 4,000 liters of water. But then you need to transport the feed to where the cows are... Then you have to transport the milk. How far is it, and what sort of fuel is used? What sort of bottle is used? If it's come across the country via truck in a plastic bottle, that doesn't get recycled, that could be a lot of fuel. How long was the milk refrigerated before it reaches a home fridge? There's 4 million joules to make a PET 1 liter plastic bottle. So about 7.5 million joules for a half gallon one(2 kilo watt hours). Often the transportation uses more than that for the bottle, but varies greatly. One amount mentioned is 4 million joules per liter. That's 4 kilo watt hours just for the bottle. There's lots more to it, but I guess 1-2 days of solar power production from a 5kW solar system for a half gallon of milk.
  - groby_b 8y ago
    That data (1000 gallons for a gallon of milk) comes from Natural News, which is... not a very precise source. A cow consumes, worst case (2000 lbs, lactating, it's hot) ~80 gallons per day. That same cow produces 3-4 gallons of milk a day. On top of that, most of that water is excreted again - otherwise, your cow would gain 640lbs a day. Or, with the 1000 gallons/gallon of milk scenario, some 12,000 lbs/day Assuming that that water is tap water is also... well, a most pessimistic assumption. If you wish a quick sanity check of your numbers, US milk production is ~25 bln gallons/year. Roughly ~70 mln gallon/day. Assuming it took one day at 10kW for a gallon of milk, that'd be 700GW continuous energy consumption for our annual milk production. This is a substantial part of the total US energy production. Second check: Assuming really cheap energy ($0.09/kWh, 10kW, 24h), that gives us a milk energy price of ~$21.00/gallon. Just the energy. This does not quite match, either. $14/gallon if you go exclusively with wind energy, which is IIRC the cheapest right now.
abraae 8y ago
Kudos to the author! The best thing about this project is that it does not require any tricky mechanical modifications to the fridge itself. Mucking around with wires, inverters, and panels is scalable - I could build this myself using parts I already have in the event of the Apocalypse. Some of the comments about heat pipes, heat transfer between freezer and fridge compartments etc. miss this point. I got trapped in a fascinating rabbit hole like this a while ago trying to create hot water without (significant) batteries. The best solution seemed to be coupling the DC from the panels more or less directly to the heating element of the hot water cylinder. Once you have a few of these lash-ups powering your new age off-grid sanctuary, it sounds like divvying up the power from the panels becomes the next major challenge.
- bufferoverflow 8y ago
  Creating hot water is much easier and much cheaper. You run a copper or stainless steel pipe with water, paint it matte black, and put it in an enclosure with a transparent side. The sun will hear it up. It's quite popular in Greece and Italy. https://c8.alamy.com/comp/D24NWW/solar-hot-water-glass-tube-heating-panel-on-tiled-house-roof-D24NWW.jpg https://c8.alamy.com/comp/D24NWW/solar-hot-water-glass-tube-...
  - icebraining 8y ago
    I've seen it done in Northern Spain with just a long black PVC tube in a spiral pattern on top of a roof. Worked well enough for three showers/day, even during the winter.
    - reaperducer 8y ago
      I've seen this occasionally in the deserts of the United States, though usually in poorer communities and neighborhoods. Perhaps electricity is cheaper there, since that's where it's grown (solar farms).
    - newnewpdro 8y ago
      PVC and ABS aren't recommended for hot water, nor are they particularly well suited to sustained UV exposure. It'll work in a pinch, but if building something permanent with the luxury of options I'd ignore those.
nowarninglabel 8y ago
Would it be possible to run a comparison vs. some of the ultra-efficient mini-fridges out there? I had previously seen a few folks on youtube showing some of their setups with existing mini-fridges. I live out on some land with just solar power and batteries for stretches of time and am weighing refrigeration options.
adrianN 8y ago
Joey Hess is an all around hoopy frood and all articles on his website are highly recommended.
- snazz 8y ago
  He really knows where his towel is. (for those of you who are unaware: https://www.urbandictionary.com/define.php?term=A%20really%20hoopy%20frood https://www.urbandictionary.com/define.php?term=A%20really%2...)
- war1025 8y ago
  I've always felt he was one of the more interesting personalities on the tech scene. Surprised he doesn't have a bigger following than he does, though I think maybe he likes it that way.
aidenn0 8y ago
As far as peanut oil goes, it's actually not that much lighter than water by volume (91%), but it has half the specific heat, so it stores 45% as much heat per unit volume. I couldn't find a reliable source for the phase-change energy for peanut oil, but it would have to be pretty high to make up for the difference.
- jakobegger 8y ago
  Latent heat of fusion is typically 100 times bigger than specific heat. I couldn't find a source for peanut oil, but [1] has values of around 200kJ/kg for various vegetable oils. Heating 1kg of water by 5 deg Celsius would take only 22kJ, so the oil should be a lot better. [1]: https://doi.org/10.1007/BF02549465 https://doi.org/10.1007/BF02549465
brianolson 8y ago
tl,dr: chest freezer hacked with extra thermal mass and smarter control maintains temperature while only running when the sun shines on the solar panels.
vram22 8y ago
From the same site - moreutils, Unix utilities; just posted it here, after seeing this thread, and due to seeing moreutils recently: https://news.ycombinator.com/item?id=18772237 https://news.ycombinator.com/item?id=18772237
newnewpdro 8y ago
The thermal mass trick applies to all refrigerators/ice boxes, not just off-grid scenarios. I tend to keep a number of filled water jugs occupying any otherwise unused space in mine since I don't keep them brimming with food stuffs. It smooths out the temperature swings from opening the doors, and generally results in the compressor running less as a result. Edit: it also buys more time before food spoils in power outages.
sixstringtheory 8y ago
Awesome idea and writeups. Something I didn’t see mentioned as a consideration was an in-ground installation... not that I know it would benefit, and I know it’d be a whole heap of extra logistics. But root cellars and pit refrigeration were things before the appliance was invented. TIL about the Yakhchāl (https://en.m.wikipedia.org/wiki/Yakhchāl https://en.m.wikipedia.org/wiki/Yakhchāl) which I found searching for an example of a pit style. Also that 7-Eleven sprang from an icehouse company in Texas (https://en.m.wikipedia.org/wiki/Ice_house_(building) https://en.m.wikipedia.org/wiki/Ice_house_(building)).
walrus01 8y ago
One of the interesting possible uses for 'thermal mass', with photovoltaics, is as an energy storage method for cooling purposes. I've seen whitepapers and prototypes of systems designed to implement the following for office building air conditioning, with no batteries, and no energy drawn back from the grid: 1) Build a big PV array 2) Use the surplus energy from the PV array during the day to chill water into a big block of ice. 3) Use a standard chilled-water-loop air conditioner system to run the AC chillers off the meltwater from the giant block of ice. 4) Repeat next day. In this example the big block of ice becomes the energy storage method (surplus kWh used to freeze water), and is 'consumed' when it melts. https://www.greentechmedia.com/articles/read/ice-energy-launches-the-combined-rooftop-pv-ac-energy-storage-system https://www.greentechmedia.com/articles/read/ice-energy-laun... https://cleantechnica.com/2016/11/25/time-shift-excess-solar-ice-storage/ https://cleantechnica.com/2016/11/25/time-shift-excess-solar...
- Scoundreller 8y ago
  I've dreamed of programming an HVAC thermostat to run the A/C or heat extra-hard just before peak electricity pricing kicks in.
charliebrownau 8y ago
Sounds interesting Yet no actual photos of the Fridge and setup and no detailed info how to make it All just Im great, look at these graphs
DanBC 8y ago
> Fridge0 aims for 0.5C to 5C, but it may sometimes heat up to 8C on a rainy week, and that's no real cause for alarm. I wonder what testing they've done to be able to say that a warm fridge isn't a source of alarm, other than "the milk doesn't go bad"?
- davidbanham 8y ago
  His methodology stated in the article is that he's been eating the food in it for a year now and hasn't gotten sick.
masukomi 8y ago
if you find this interesting Joey (the creator) is regularly posting updates on this and his other off-grid projects, as well as working through the core ideas with others on Scuttlebutt ( https://www.scuttlebutt.nz/ https://www.scuttlebutt.nz/ )
sn9 8y ago
I'm surprised nobody's talking about how the code is mostly Haskell, and how it's being used to control electronics which seems to be a rare usecase (AFAICT): https://git.joeyh.name/index.cgi/joey/homepower.git/tree/ https://git.joeyh.name/index.cgi/joey/homepower.git/tree/
- kragen 8y ago
  But Haskell has been Joey's favorite programming language for years. Why would it surprise us that he uses it for this? It's not like turning off the fridge needs submillisecond guaranteed response times!
  - sn9 8y ago
    Not everyone knows who Joey is . . . .
    - kragen 8y ago
      They're one of today's lucky ten thousand!
crazy2be 8y ago
Thermal masses are a super cool way (ha!) to store energy, and I'm surprised they don't get more attention, both in the media, and in terms of research / investment. Heating and cooling accounts for somewhere around half(!) of residential energy use [1], which could be easily time-shifted with some very cheap thermal mass and some economic incentive to do so. This is actually used in some commercial buildings in places where energy is cheaper at certain times of the day (for example, at night) [2], by freezing ice when energy is cheap, and thawing it when it isn't. That being said, although this is a super cool project (I have the same inverter, and I made a similar control board ;)), this thermal mass doesn't seem like it would be particularly practical in most cases. Water has a relatively high specific heat capacity of 4.186J/gC, but given the narrow range of temperatures acceptable for a fridge, this doesn't end up being very much - only 79Wh per degree Celsius that the fridge is allowed to swing. If you consider 1C - 6C "acceptable", you only end up storing 395Wh. This is about 30-40% of the capacity of a $100-$200 "deep discharge" lead-acid battery, and is also a much wider range than most consumers would be used to (and may result in frozen veggies, for example). In order to make this more practical, you really want something that can freeze around fridge temperature. For the same amount of water used above, freezing and thawing the water would store 6,308Wh(!), around 16x as much. If you could get something that freezes at 3C/4C with a similar heat of fusion to water, you could have a much smaller thermal battery that lasts _much_ longer, without the substantial temperature swings you see with your current design. [1] https://www.eia.gov/tools/faqs/faq.php?id=96&t=3 https://www.eia.gov/tools/faqs/faq.php?id=96&t=3 [2] https://en.wikipedia.org/wiki/Ice_storage_air_conditioning https://en.wikipedia.org/wiki/Ice_storage_air_conditioning
- joeyh 8y ago
  Interesting we made similar control boards! You need to take into account efficiencies of getting the cold into the fridge too. It takes around 10-15 hours of runtime to cool the thermal mass down from 5 to 0.5 degrees C (at 14C exterior temp), and the fridge needs 120 watts to run. Measured this way, the thermal battery is storing ~1200-1800 watt-hours. But then, if it were powered from batteries, there would be significantly more power needed to fully charge the batteries and maintain good health -- my 860AH battery bank (4 deep cycle batteries) needs at least 1kwh input to charge up from 12v to full). Another way to come at the question is, how many batteries are typically specced out to power an offgrid fridge, and banks costing 10-20k dollars are not at all uncommon, though they're also shared with other household needs.
benj111 8y ago
Re thermal mass. Could you not section of the part of the freezer with the cooling elements, and fill with water. You could then cool that below zero increasing the effectiveness of the thermal mass. You'd also get some freezer space into the bargain. The only issue would be passively moving cold into the fridge proper. I know greenhouses use wax cylinders that expand in heat to open louvre vents, I wonder whether something like that would work.

Fridge 0.2

584 points by Breadmaker 8y ago

Gravityloss 8y ago

Demand elasticity.

maliker 8y ago
With zero quality of service impact to boot (once the 1/2 gallon milk bug is fixed).

Scoundreller 8y ago

Any luck with phase change materials for more dense « cold » banking? You do say « However, this needs a material that freezes at a higher temperature than water, and most such are oils, which are less dense and so store less cold overall. », but I wouldn’t underestimate the enthalpy of melting. Depending on your climate, a long heat pipe would be interesting to move heat outside when it’s cool enough outside (even if only during a few hours overnight). But that’s getting complicated to fabricate oneself. Oops, edit: you have it outside already. How do you prevent freezing everything ? (Again, climate dependent).

komali2 8y ago
>How do you prevent freezing everything They don't. If it's too cold outside for too long, everything will freeze.
- joeyh 8y ago
  Or add a small heating element, but it's not been necessary so far, it would probably need a full week below zero to freeze. I do some minor adhoc regulation by putting leftovers in the fridge when they're still piping hot on colder days, vs letting them cool down more on warmer days.

starbeast 8y ago

One thought, if this is combined with a freezer and there is a pumped heat exchanger between that and the fridge, you can effectively use the freezer as the battery.

Scoundreller 8y ago
Small boats used systems like this: freezing blocks of ice to provide convective cooling to a cooler so that things stay cold without the engine running. A lot of people hated them enough (and the gas used while sailing) to replace it with solar based systems.
edaemon 8y ago
Regular refrigerators use the same principle, albeit with a mechanism much simpler than a heat pump. They have holes between the freezer and refrigerator compartments and use a fan to push cold air from the freezer to the refrigerator. A heat pump would make that exchange much more efficient.
- JoeAltmaier 8y ago
  I doubt that heat pumps could be more efficient than direct exchange of cold air?
  - edaemon 8y ago
    There are periods where you don't want the cold air to move into the refrigerator. Direct exchange allows the cold air to move around at all times -- regular refrigerators just turn a fan on and off, but some heat is always exchanged through the holes. A heat pump would just make the exchange more controllable.
    - ndnxhs 8y ago
      I have a fridge that works with just holes. You can either have the fridge or the freezer at the right temp but not both.

sthgrau 8y ago

For putting the thermal mass above the food, could a workaround be to put a heat sink on the bottom of the lid, and connect it to the thermal mass with an equally heat conductive material? Also, before I saw what the heat sink was, I wondered if you could use shotcrete on the walls of the freezer, to act as the thermal mass.

wpietri 8y ago
I was wondering if this might work better with a traditional freezer-on-top refrigerator where you just use the freezer as pure thermal mass.
- nightbrawler 8y ago
  The chest style is optimal because with a traditional freezer-on-top refrigerator, you lose a lot of cold air each time you open the door. Whereas with the chest style, hardly anything is lost because the cold air doesn't rise.
  - Scoundreller 8y ago
    > Whereas with the chest style, hardly anything is lost because the cold air doesn't rise. Depends how quickly you open it and slam it shut afterwards.
  - wpietri 8y ago
    I think we might be talking about different kinds of optimality. I think the chest style is best for total energy consumption. But as we saw, his biggest problem was around thermal stability. If we put the freezer/fridge fan under computer control, you might be able to get more stable fridge temperatures despite the air loss because you can drive the freezer temperature much lower, getting more stability value from the thermal mass. (And it's also worth filling in any big air spaces in the fridge with more thermal mass, so that opening the door is not a big deal.)

_salmon 8y ago

Seems strange to call it a "zero-battery-use fridge" and then follow it with "It ties into the typical offfgrid system of a solar charge controller, battery bank, and photovoltaic panels"

dang 8y ago
We changed the title from "Fridge 0.2 offgrid, solar powered, zero-battery-use fridge has made it through".
Scoundreller 8y ago
Mostly agreed. The big issue with off-the-shelf AC fridges is the current draw required for them to start. If you want to go completely zero-battery, you’ll need to highly-oversized your PV array just to handle the 1-2 second inrush starting current. Or devise a slow-start function, overriding the AC flow to the compressor. So instead of starting at 60hz, you would start at 1, then 2, then 3hz, etc. I guess OP means they could add a fridge to their off-grid setup without changing their existing battery budget for their other needs.
- realityczeque 8y ago
  Or you can just buy a DC refrigerator.
  - Scoundreller 8y ago
    They’ll cost you a lot of extra $$$. Consumer stuff is cheap, but once it’s built slightly differently for the specialized off-grid market, the price skyrockets.
- nerpderp82 8y ago
  One could have a high current lipo connected to the inverter that can supply > 2kw for seconds. A 14.8v 4Ah 50C battery can supply 3kw for 72 seconds, more than enough to even out start/stop and shade cycles.

linase789 8y ago

> Using a supercapacitor to provide power while shutting down on loss of solar power, instead of the current few minutes of use of batteries. I wonder why this is necessary. I've also seen it mentioned in the wiki, but no explanation. Isn't a compressor the only electrical thing in a fridge? I know you must be careful with leaving some time between restarts, but why can't you just shut it down immediately on power loss?

Scoundreller 8y ago
I thought so too. Even if they’re all mechanical, it usually makes sense to keep the fan running across the evaporator to prevent moisture buildup (which will then sit in a place susceptible to freezing). It can also be more efficient to push this residual cold into the vessel. My car’s AC gets funky if I don’t remember to turn off the AC a few minutes before shutting down.
- mulmen 8y ago
  I think there is a drain near the condenser to prevent this, if your car smells nasty after turning off your A/C you may want to make sure that’s not clogged. Also, if equipped on your car replace the cabin air filter.
  - Scoundreller 8y ago
    It drips underneath on a muggy day, so I assume it's draining OK. My main gripe is that they don't auto-run the fan for 3-4 minutes after key-off.
lambda 8y ago
https://fridge0.branchable.com/battery_bank/ https://fridge0.branchable.com/battery_bank/ > Fridge0 does not need a big battery bank, since it stores cold in its thermal mass and runs only when solar power is available. > But, at least a mimimal battery is needed to run the computer control. Probably on the order of 5 watts for a computer like a raspberry pi; this could be reduced more with a more embedded computer like an arduino. > Enough battery to run the fridge for a minute or two is also needed. Consider what happens when the fridge is running, and the sun goes behind a rain cloud. Suddenly, there's not enough power to run it, but it's still turned on. The inverter will try to run with whatever small solar power is still coming in, but it's not enough. Some inverters might manage a clean power off, probably accompanied with loud beeping. Other inverters might fail in more interesting ways. > To deal with this situation, the computer needs to check the incoming solar power frequently, and power off the fridge if there's not enough. The battery is needed to keep the inverter and fridge running until that happens. Basically, it sounds like the answer is because with a solar panel, there are states that are between "off" and "on," you rather just get an amount of power proportional to the amount of sunlight, and there's a concern that those states could cause problems if you don't provide a more constant power supply and active switching to fully shut off the power when your solar panel is not producing enough power for the "on" state.

deleted 8y ago

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raphinou 8y ago

What milk can be kept 2 or 3 weeks in the fridge? Is there a special methodology? I never reach that conservation time with milk.

komali2 8y ago
Huh, what country you in? I usually get a solid 2 weeks in California from just regular Safeway or trader Joe's branded milk.
- merlincorey 8y ago
  Organic milk seems to last even longer (with longer in the future sell-by dates printed), as well.
  - komali2 8y ago
    Organic meaning what? Not to be pedantic, but the word doesn't mean anything to me anymore.
- BozeWolf 8y ago
  Fresh bio milk is ok for about 2 weeks here in NL (6deg Celcius fridge). Only a few days after opening it. Unless it is treated with heat. pasteurized or even sterilized milk. But that changes the taste. After a day of four you notice the quality degrades: making cappucino milk foam is more difficult then.
  - phreeza 8y ago
    Can you actually buy unpasteurized milk in NL (except from the farm directly)? I thought there was some sort of EU rule against that.
    - icebraining 8y ago
      The EU only enforces clear labeling of unpasteurised milk. Member states are free to choose if it can be sold.

rmtech 8y ago

Probably the best cold battery is to have a freezer compartment that's full of salt water which freezes at several degrees below 0, and some kind of adjustable heat link between the freezer and the fridge.

joeyh 8y ago
That was my original plan, but I went with the simplest possible thing before trying it, and so far the simpler plan has worked.
- nerpderp82 8y ago
  One could have frozen 1 gallon milk jugs in the freezer and manually put them in the fridge compartment as needed.
  - smolder 8y ago
    I freeze quarts and half gallons. They preserve seemingly indefinitely when frozen and the jugs hold up fine. Give it ample time to thaw before you use the milk, and it'll be normal. In a single person household without much home food prep this prevents a lot of waste without excessive trips to the store. As an aside, the stuff that comes from a partially thawed jug is interesting. It seems concentrated, as if the full water content is the last part to return to the liquid.

gumby 8y ago

Great project, not just doing it but monitoring the data. Makes me wonder about the energy cost of losing (i.e. replacing) a 1/2 gal of milk vs the energy cost of a gas cycle fridge. I know food wastage is a huge resource lost but I’ve always overlooked the fact that energy is a huge one of the resources. Thanks for writing this up!

throwaway12iii 8y ago
(pulling random data points from around the internet) It takes approximately 255 liters of water to make 250ml of milk. So 1020 liters per liter of milk. There's 3.78542 liters per gallon. So that makes about 1930 liters per half gallon milk. 510 gallons of water for 0.5 gallons of milk. It takes between 2500 and 5000 joules of energy per liter of tap water depending on the water source (2000 times that for bottled water). So up to 9,650,000 joules of energy per half gallon of milk for the water(about 2680 Wh). 1.25 to 1.44 kg of feed to produce a liter of milk (0.2645 gallons). To produce 1kg of wheat requires between 500 and 4,000 liters of water. But then you need to transport the feed to where the cows are... Then you have to transport the milk. How far is it, and what sort of fuel is used? What sort of bottle is used? If it's come across the country via truck in a plastic bottle, that doesn't get recycled, that could be a lot of fuel. How long was the milk refrigerated before it reaches a home fridge? There's 4 million joules to make a PET 1 liter plastic bottle. So about 7.5 million joules for a half gallon one(2 kilo watt hours). Often the transportation uses more than that for the bottle, but varies greatly. One amount mentioned is 4 million joules per liter. That's 4 kilo watt hours just for the bottle. There's lots more to it, but I guess 1-2 days of solar power production from a 5kW solar system for a half gallon of milk.
- groby_b 8y ago
  That data (1000 gallons for a gallon of milk) comes from Natural News, which is... not a very precise source. A cow consumes, worst case (2000 lbs, lactating, it's hot) ~80 gallons per day. That same cow produces 3-4 gallons of milk a day. On top of that, most of that water is excreted again - otherwise, your cow would gain 640lbs a day. Or, with the 1000 gallons/gallon of milk scenario, some 12,000 lbs/day Assuming that that water is tap water is also... well, a most pessimistic assumption. If you wish a quick sanity check of your numbers, US milk production is ~25 bln gallons/year. Roughly ~70 mln gallon/day. Assuming it took one day at 10kW for a gallon of milk, that'd be 700GW continuous energy consumption for our annual milk production. This is a substantial part of the total US energy production. Second check: Assuming really cheap energy ($0.09/kWh, 10kW, 24h), that gives us a milk energy price of ~$21.00/gallon. Just the energy. This does not quite match, either. $14/gallon if you go exclusively with wind energy, which is IIRC the cheapest right now.

abraae 8y ago

Kudos to the author! The best thing about this project is that it does not require any tricky mechanical modifications to the fridge itself. Mucking around with wires, inverters, and panels is scalable - I could build this myself using parts I already have in the event of the Apocalypse. Some of the comments about heat pipes, heat transfer between freezer and fridge compartments etc. miss this point. I got trapped in a fascinating rabbit hole like this a while ago trying to create hot water without (significant) batteries. The best solution seemed to be coupling the DC from the panels more or less directly to the heating element of the hot water cylinder. Once you have a few of these lash-ups powering your new age off-grid sanctuary, it sounds like divvying up the power from the panels becomes the next major challenge.

bufferoverflow 8y ago
Creating hot water is much easier and much cheaper. You run a copper or stainless steel pipe with water, paint it matte black, and put it in an enclosure with a transparent side. The sun will hear it up. It's quite popular in Greece and Italy. https://c8.alamy.com/comp/D24NWW/solar-hot-water-glass-tube-heating-panel-on-tiled-house-roof-D24NWW.jpg https://c8.alamy.com/comp/D24NWW/solar-hot-water-glass-tube-...
- icebraining 8y ago
  I've seen it done in Northern Spain with just a long black PVC tube in a spiral pattern on top of a roof. Worked well enough for three showers/day, even during the winter.
  - reaperducer 8y ago
    I've seen this occasionally in the deserts of the United States, though usually in poorer communities and neighborhoods. Perhaps electricity is cheaper there, since that's where it's grown (solar farms).
  - newnewpdro 8y ago
    PVC and ABS aren't recommended for hot water, nor are they particularly well suited to sustained UV exposure. It'll work in a pinch, but if building something permanent with the luxury of options I'd ignore those.

nowarninglabel 8y ago

Would it be possible to run a comparison vs. some of the ultra-efficient mini-fridges out there? I had previously seen a few folks on youtube showing some of their setups with existing mini-fridges. I live out on some land with just solar power and batteries for stretches of time and am weighing refrigeration options.

adrianN 8y ago

Joey Hess is an all around hoopy frood and all articles on his website are highly recommended.

snazz 8y ago
He really knows where his towel is. (for those of you who are unaware: https://www.urbandictionary.com/define.php?term=A%20really%20hoopy%20frood https://www.urbandictionary.com/define.php?term=A%20really%2...)
war1025 8y ago
I've always felt he was one of the more interesting personalities on the tech scene. Surprised he doesn't have a bigger following than he does, though I think maybe he likes it that way.

aidenn0 8y ago

As far as peanut oil goes, it's actually not that much lighter than water by volume (91%), but it has half the specific heat, so it stores 45% as much heat per unit volume. I couldn't find a reliable source for the phase-change energy for peanut oil, but it would have to be pretty high to make up for the difference.

jakobegger 8y ago
Latent heat of fusion is typically 100 times bigger than specific heat. I couldn't find a source for peanut oil, but [1] has values of around 200kJ/kg for various vegetable oils. Heating 1kg of water by 5 deg Celsius would take only 22kJ, so the oil should be a lot better. [1]: https://doi.org/10.1007/BF02549465 https://doi.org/10.1007/BF02549465

brianolson 8y ago

tl,dr: chest freezer hacked with extra thermal mass and smarter control maintains temperature while only running when the sun shines on the solar panels.

vram22 8y ago

From the same site - moreutils, Unix utilities; just posted it here, after seeing this thread, and due to seeing moreutils recently: https://news.ycombinator.com/item?id=18772237 https://news.ycombinator.com/item?id=18772237

newnewpdro 8y ago

The thermal mass trick applies to all refrigerators/ice boxes, not just off-grid scenarios. I tend to keep a number of filled water jugs occupying any otherwise unused space in mine since I don't keep them brimming with food stuffs. It smooths out the temperature swings from opening the doors, and generally results in the compressor running less as a result. Edit: it also buys more time before food spoils in power outages.

sixstringtheory 8y ago

Awesome idea and writeups. Something I didn’t see mentioned as a consideration was an in-ground installation... not that I know it would benefit, and I know it’d be a whole heap of extra logistics. But root cellars and pit refrigeration were things before the appliance was invented. TIL about the Yakhchāl (https://en.m.wikipedia.org/wiki/Yakhchāl https://en.m.wikipedia.org/wiki/Yakhchāl) which I found searching for an example of a pit style. Also that 7-Eleven sprang from an icehouse company in Texas (https://en.m.wikipedia.org/wiki/Ice_house_(building) https://en.m.wikipedia.org/wiki/Ice_house_(building)).

walrus01 8y ago

One of the interesting possible uses for 'thermal mass', with photovoltaics, is as an energy storage method for cooling purposes. I've seen whitepapers and prototypes of systems designed to implement the following for office building air conditioning, with no batteries, and no energy drawn back from the grid: 1) Build a big PV array 2) Use the surplus energy from the PV array during the day to chill water into a big block of ice. 3) Use a standard chilled-water-loop air conditioner system to run the AC chillers off the meltwater from the giant block of ice. 4) Repeat next day. In this example the big block of ice becomes the energy storage method (surplus kWh used to freeze water), and is 'consumed' when it melts. https://www.greentechmedia.com/articles/read/ice-energy-launches-the-combined-rooftop-pv-ac-energy-storage-system https://www.greentechmedia.com/articles/read/ice-energy-laun... https://cleantechnica.com/2016/11/25/time-shift-excess-solar-ice-storage/ https://cleantechnica.com/2016/11/25/time-shift-excess-solar...

Scoundreller 8y ago
I've dreamed of programming an HVAC thermostat to run the A/C or heat extra-hard just before peak electricity pricing kicks in.

charliebrownau 8y ago

Sounds interesting Yet no actual photos of the Fridge and setup and no detailed info how to make it All just Im great, look at these graphs

DanBC 8y ago

> Fridge0 aims for 0.5C to 5C, but it may sometimes heat up to 8C on a rainy week, and that's no real cause for alarm. I wonder what testing they've done to be able to say that a warm fridge isn't a source of alarm, other than "the milk doesn't go bad"?

davidbanham 8y ago
His methodology stated in the article is that he's been eating the food in it for a year now and hasn't gotten sick.

masukomi 8y ago

if you find this interesting Joey (the creator) is regularly posting updates on this and his other off-grid projects, as well as working through the core ideas with others on Scuttlebutt ( https://www.scuttlebutt.nz/ https://www.scuttlebutt.nz/ )

sn9 8y ago

I'm surprised nobody's talking about how the code is mostly Haskell, and how it's being used to control electronics which seems to be a rare usecase (AFAICT): https://git.joeyh.name/index.cgi/joey/homepower.git/tree/ https://git.joeyh.name/index.cgi/joey/homepower.git/tree/

kragen 8y ago
But Haskell has been Joey's favorite programming language for years. Why would it surprise us that he uses it for this? It's not like turning off the fridge needs submillisecond guaranteed response times!
- sn9 8y ago
  Not everyone knows who Joey is . . . .
  - kragen 8y ago
    They're one of today's lucky ten thousand!

crazy2be 8y ago

Thermal masses are a super cool way (ha!) to store energy, and I'm surprised they don't get more attention, both in the media, and in terms of research / investment. Heating and cooling accounts for somewhere around half(!) of residential energy use [1], which could be easily time-shifted with some very cheap thermal mass and some economic incentive to do so. This is actually used in some commercial buildings in places where energy is cheaper at certain times of the day (for example, at night) [2], by freezing ice when energy is cheap, and thawing it when it isn't. That being said, although this is a super cool project (I have the same inverter, and I made a similar control board ;)), this thermal mass doesn't seem like it would be particularly practical in most cases. Water has a relatively high specific heat capacity of 4.186J/gC, but given the narrow range of temperatures acceptable for a fridge, this doesn't end up being very much - only 79Wh per degree Celsius that the fridge is allowed to swing. If you consider 1C - 6C "acceptable", you only end up storing 395Wh. This is about 30-40% of the capacity of a $100-$200 "deep discharge" lead-acid battery, and is also a much wider range than most consumers would be used to (and may result in frozen veggies, for example). In order to make this more practical, you really want something that can freeze around fridge temperature. For the same amount of water used above, freezing and thawing the water would store 6,308Wh(!), around 16x as much. If you could get something that freezes at 3C/4C with a similar heat of fusion to water, you could have a much smaller thermal battery that lasts _much_ longer, without the substantial temperature swings you see with your current design. [1] https://www.eia.gov/tools/faqs/faq.php?id=96&t=3 https://www.eia.gov/tools/faqs/faq.php?id=96&t=3 [2] https://en.wikipedia.org/wiki/Ice_storage_air_conditioning https://en.wikipedia.org/wiki/Ice_storage_air_conditioning

joeyh 8y ago
Interesting we made similar control boards! You need to take into account efficiencies of getting the cold into the fridge too. It takes around 10-15 hours of runtime to cool the thermal mass down from 5 to 0.5 degrees C (at 14C exterior temp), and the fridge needs 120 watts to run. Measured this way, the thermal battery is storing ~1200-1800 watt-hours. But then, if it were powered from batteries, there would be significantly more power needed to fully charge the batteries and maintain good health -- my 860AH battery bank (4 deep cycle batteries) needs at least 1kwh input to charge up from 12v to full). Another way to come at the question is, how many batteries are typically specced out to power an offgrid fridge, and banks costing 10-20k dollars are not at all uncommon, though they're also shared with other household needs.

benj111 8y ago

Re thermal mass. Could you not section of the part of the freezer with the cooling elements, and fill with water. You could then cool that below zero increasing the effectiveness of the thermal mass. You'd also get some freezer space into the bargain. The only issue would be passively moving cold into the fridge proper. I know greenhouses use wax cylinders that expand in heat to open louvre vents, I wonder whether something like that would work.