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!
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.
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.
Now that's an understatement. Every time I get sent some info from that site I know I'm going to spend the next 15-20 minutes debunking it with real sources and explaining that while it looks like they source their info, all their links go to blogs that either aren't sourced, source each other, or misinterpret the data.
Actually, now that I think about it, it's amazingly similar to what the fake news and Russian sites did in 2016, but Natural News has been doing it for at least 6-7 years, as that's when I started noticing them. Could be longer.
Does that only include the periods when the cow is lactating or is it an average that takes the cow's entire lifespan into account?
> On top of that, most of that water is excreted again - otherwise, your cow would gain 640lbs a day.
Wait. Is the 80 gallons per day figure referring to the water that is consumed by the cow directly, or does it include the water used to produce the cow's food?
And 3-4 gallons/day is a rough average. Lactating cows produce 6-7 gallons of milk, for about 10 months after calving. And after 12 months, they calve again. (But really, all these numbers are very rough estimates. It doesn't matter because they're used as a ballpark sanity check for OPs post, not as accurate numbers)
This seems pretty important in discussions of resource use : how the waste is handled / recycled etc.
I assume most of the water needed to sustain cows is spent on the plants they eat.
If approximately 73% of the milk price is subsidized, that is about $12.96. Also, oil is heavily subsidized, which is the main cost of plastic bottled milk dispatched by oil using trucks.
And if you read the actual data, you'll realize that 73% of the returns come through subsidies. Or $0.35(cdn)/liter, so ~$1.40/gallon.
Really, that energy/water consumption number in the OP is bogus. There's no way around that. It doesn't mean that milk is particularly environmentally friendly, but neither is it anywhere near as devastating as OP made it out to be.
That said we recently had to fund raise for farmers due to too dry weather and supermarkets increased the price a little bit explicitly to help them out.
I assume Australia has some?
How is this different from normal supply and demand?
I've done a business studies degree so surprised I hadn't come across the term.
The subsidies they received are baked into the current market prices you see for a barrel of oil.
Milk prices vary wildly from market to market in the U.S.
Where I live, where cows are rare, it's $2.39/gallon. In greener regions nearby it's closer to $1.89/gallon.
When I lived in Ohio, the hypermarkets always had it for 99¢/gallon as a loss-leader.
I can only assume that $3.50/gallon is normal for... San Francisco, maybe? Or if you're buying organic, free-range, ultra-filtered, sustainable milk.
In Quebec, it's illegal to sell milk for less than US$4.89/gallon.
I don't think it's legal to sell regular milk there - it has to be either nut milk or raw milk.
That figure includes fodder production, processing, Tetra-Pak type cardboard packaging and transport to retail. It's based on the Norwegian dairy industry, but the US dairy industry should be in the same ballpark - the transport inputs are probably greater, but the inputs in production are probably lower due to lower welfare and biosafety standards.
> 1.25 to 1.44 kg of feed to produce a liter of milk ... 1kg of wheat requires between 500 and 4,000 liters of water
Not sure which specific sources of random data-points you've picked from around the internet, but generally to arrive at the figure of x litres of water per y litres of milk, a full life-cycle analysis is done which would typically account for feed production and feed transport. So there's going to be a lot of overlap in your figures.
Secondly, the energy requirements for getting fully treated drinkable water to residential taps is going to be significantly different than that required to supply agricultural water for irrigation, etc.—at least a portion of that should be untreated/reclaimed waste water.
Which I guess is a way of saying that these numbers factor in a lot of externalities that don't get factored in to other parts of the discussion. So the value judgment ends up skewed much more than it should be.
We must be close to running out of water on Earth, if it's vanishing away so quickly.
No cream in the coffee, people. Coffee is made without water, right?
Terrestrial marketed energy consumption will increase by one to two orders of magnitude due to an explosion in photovoltaic production. The cost of photovoltaic panels has been dropping exponentially for 40 years, which was hard to notice when photovoltaic energy was still more expensive than energy from other sources — it was still restricted to marginal uses where grid power wasn't an option, like Joey's house.
Unsubsidized photovoltaic energy is now cheaper than energy from coal or oil in all of the tropics and a substantial part of the temperate zone; this started around 2016, but it's gradually spreading to more and more of the planet as photovoltaic costs continue their exponential descent. In fact, in many places, it's now cheaper to build new photovoltaic plants than to buy coal to keep existing coal power plants running.
Photovoltaic energy production is on track to exceed current world marketed energy consumption in the late 2020s. This doesn't mean it will be the only source of energy — there are still places and applications that will use fossil fuels — but it does mean that the cost of energy for more flexible applications will begin to drop.
How long will that continue? Probably as long as there are places to install photovoltaic panels (which total hundreds of times current world marketed energy consumption), materials to construct them (which are abundant), and demand for the energy — the only real possible bottleneck during the next several decades.
So I predict one to two orders of magnitude increase in world marketed energy consumption by 2118. Three orders of magnitude is not out of the question.
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.
That pipe is HDPE, and corrugated to boot, so it can go through quite a few freeze/thaw cycles before it starts leaking. It's true that it won't provide you hot water when it's freezing outside unless you put it under glass or at least plastic, though, and that drives the cost up.
I was expecting to find that you were ridiculously wrong, but actually it seems like the costs for a passive solar collector that can produce hot water in freezing weather actually might be about equal, or in any case no less than half the cost of photovoltaic. Bravo! And thank you for the insight!
But I guess they must be rotated to follow the sun, which is more complicated than just pipes on the roof.
The very first solar power plant, in Egypt in I think about 1910, was actually a steam plant that worked on precisely this principle. Photovoltaic is cheaper in most of the world than a steam engine now, though.
Some people also run them in sequence with an electric one. i.e. Solar one first & that feed the elec one. Meaning that you'll always have guaranteed hot water, near double the capacity but the solar one picks up most of the work.
In my case I'm trying to put all my investment into a heap of solar panels, as that's a more general purpose infrastructure.
I assume you have gas heating & cooking then? If they're elec its usually cheaper to buy new ones than up-spec the solar PVs.
I like the way that your project is a kind of glue that hooks up some of these things. I could really see people shipping and using a product like this.
TIL about the 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)).
(for those of you who are unaware: https://www.urbandictionary.com/define.php?term=A%20really%2...)
It has a shelf life of months, it's highly popular in southern Europe.
Once the seal has been broken, it should age and spoil at around the same rate as normal pasteurised milk.
1) small packages, portion size
2) a way of extracting milk that keeps the contents sealed. Something like a bag-in-box wine container?
Then you could do without the fridge completely.... for milk
But I'm finding I can keep non-UHT for 2 weeks or more in summer in fridge0 when it's the same 0.01-0.5C as the thermal mass.
In the Alps it has been a century old trick to put a silver spoon into the milk to make it last longer.
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.
Looking at other comments, and FWIW this is non-organic whole milk.
This is actually used in some commercial buildings in places where energy is cheaper at certain times of the day (for example, at night) , 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.
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.
It has the added benefit of stabilizing the temperature a lot. I recall reading somewhere (who knows, maybe one of the earlier blog entries here) that turning on a cooling element costs a lot of energy too on top of it just running, to the point where that effect on energy savings should not be underestimated.
All in all I saved quite a bit on my energy bill with quite a simple hack.
Water is the easy choice.
A material that can be frozen would be better, because it takes a lot of extra heat to melt a frozen material and so more cold could be stored.
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.
This is an open research area.
But yeah, back in the day they would get blocks of ice from nearby lakes and put them underground, it'd last all year.
Some of the things I found crazy when reading about it is that they can get the ground temperature up to 80 degrees celsius by the end of the summer, and then the ground stores enough heat (without just dissipating off to the environment) that it can provide a majority of the heating for 52 houses over the course of a cold Alberta winter.
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?
> 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.
My car’s AC gets funky if I don’t remember to turn off the AC a few minutes before shutting down.
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.
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.
I couldn't find a source for peanut oil, but  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.
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).
They don't. If it's too cold outside for too long, everything will 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.
A lot of people hated them enough (and the gas used while sailing) to replace it with solar based systems.
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.
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.
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.
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.)
Depends how quickly you open it and slam it shut afterwards.
I live out on some land with just solar power and batteries for stretches of time and am weighing refrigeration options.
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"?
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.