When I traveled in Mali in 2006, some villages had a single fridge running on a generator to keep water for tourists cool. Tourists can't drink well water, and selling them bottled water is a source of income for the villages. But having a generator running for that is wasteful. A cheap solar fridge would be a perfect solution.
Yes, but it's probably one of those things where the village can justify spending $100 per month on diesel for the generator, but wouldn't be able to justify $1000 for a solar panel large enough to run the fridge.
How could they not justify paying for 10 months of diesel to never have to then pay for diesel in the 11th month and on? There are micro-finance options available in many developing areas, should be a no-brainer with your hypothetical math.
Because your current system is portable and well known in a place where land use and other rights are less solid?
Because no one around you has the technical capacity to update / maintain / repair the system?
Because if you invest in something in a less developed area - someone may come and take it (yes, this includes the govt and various officials who may start talking about permitting etc etc).
Interestingly, this same question is asked and answered at the country scale for major industries. Why ship unrefined / unprocessed product that takes up 10x the volume when you could process locally for the whole country? Because the market doesn't trust the systems in that country well enough to invest $5B that has a 20 year payback even if its "easy math".
If you want to experience some culture shock, read about some Westerners who have spent significant time living with Africans. Not just "living in Africa" in some expat enclave, but living with the people.
I don't feel I have enough of a grasp to summarize it. And I'm not saying it's bad or good in particular. I'm just saying, expect serious culture shock in this area of culture. You'll come away with a greater understanding of why attempted Western interventions have been less successful than expected, if nothing else.
Poverty is a big factor in long term planning. For example in America poor people pay more for toilet paper because they can’t buy a large pack of toilet paper rolls, instead they often can only afford to buy one roll at a time. This is a well documented effect of poverty or financially constrained living.
It's not the only factor though. I've talked with my father-in-law who does a lot of work in Haiti. His observation is that it is a much more systematic problem. Kids don't learn to plan ahead because the schools only teach memorization and they don't play with toys like building blocks. It's very frustrating for him because he finds himself having to hand hold a lot when doing construction projects like building schools, even when the people doing the work are supposed to be professionals.
For example, if he orders a truckload of gravel he has to watch the entrance like a hawk and be ready to rush out the instant the truck arrives, because if he doesn't the truck will just dump the gravel right in the middle of their entrance and block everybody in until he can round up people to shovel it into wheelbarrows by hand. The idea that you might want to ask where to dump the load is not something that will ever cross the truck driver's mind. The project manager won't think about it either unless my father-in-law asks him explicitly where he is planning to store the gravel he just ordered. It's these kinds of problems day in and day out that makes reconstruction so difficult.
Learning how to think ahead is something we take for granted in the west, but it's not an innate human skill. It has to be taught. Worse, if you never learned it yourself then you won't notice that your kids lack the skill. It's a difficult cycle to break.
Have you met any poor people? Once you're poor you only buy something that you can afford right now, it doesn't matter that spending more would save you more money in the long run.
“The reason that the rich were so rich, Vimes reasoned, was because they managed to spend less money.
Take boots, for example. He earned thirty-eight dollars a month plus allowances. A really good pair of leather boots cost fifty dollars. But an affordable pair of boots, which were sort of OK for a season or two and then leaked like hell when the cardboard gave out, cost about ten dollars. Those were the kind of boots Vimes always bought, and wore until the soles were so thin that he could tell where he was in Ankh-Morpork on a foggy night by the feel of the cobbles.
But the thing was that good boots lasted for years and years. A man who could afford fifty dollars had a pair of boots that'd still be keeping his feet dry in ten years' time, while the poor man who could only afford cheap boots would have spent a hundred dollars on boots in the same time and would still have wet feet.
This was the Captain Samuel Vimes 'Boots' theory of socioeconomic unfairness.”
I believe HackerNews ran an article that covered a similar situation but the product involved was baby diapers. That if you're buying in bulk, from say, Costco, you can save a lot of money on baby diapers. That's good for those that can afford it. But those on welfare (in the US) will never have enough cash on hand to make that initial bulk purchase and achieve those savings. As a result they have to buy the smaller packages which are significantly more expensive and eat up much more of their welfare check.
Disposable diapers are a luxury item. Buy cloth and reuse them a hundred times. I could afford disposable and still bought cloth to save a literal crap ton of money.
Cloth diapers are a luxury item. They are for people with access to washing machines and sufficient time to handle them. They might financially seem cheaper, but poor people often need to work multiple jobs to keep their heads above the water. They can’t afford spending extra time. (Same goes for junk food vs. cooking stuff that you cheaply sourced from a market, ...)
I believe people in developing countries without access to washing machines use cloth diapers, so it’s not lack of access to washing machines. Cultural issues probably pay a role, however.
We bought ours on eBay (third hand, and they did for 3 kids and still were good enough to sell on), they were more work than disposable but certainly cheaper. But, we had a washing machine -- again, second hand (fixed and plumbed in by me).
There's also the aspect that nice things require other nice, expensive things to keep them up. Having a nice set of boots isn't going to help much if it's sitting in the rain overnight regularly.
This all points to the lesson that wealth and riches aren't the same thing. Rich people are rich because they have wealth, even poor people can amass riches, say by winning the lottery, but can't be called wealthy until they actually have wealth.
A person can become wealthy off the efforts of other people, but if we want wealth for all, then it's society itself that must hold the wealth. This was Karl Marx's conclusion, but all attempts to build a society capable of holding wealth for all failed.
So we're stuck with trickle-down, the idea that the surplus wealth of the wealthy is good enough for all.
Half my childhood we were the kind of broke where you chose between meat besides hotdogs or the electric bill. We clipped coupons, shopped for sales, and made every penny count. Never in a million years would we have bought a single roll of toilet paper at any kind of markup; we'd have done without until we had enough to get it on sale. Course if we were that broke, I'd have been sent to knock on doors asking for odd jobs until I had enough to cover whatever crisis was at hand.
At any given month they may only have $100 to spare, so at that point it doesn't matter if spending more upfront saves money in the long term because they may not have the amount needed for the upfront cost.
I love how people are going to argue socioeconomics for days for some fridge running on a generator 13 years ago which has likely gone out by now or replaced or not even a thing anymore.
I wonder if they could put up a sign saying "please help us reduce pollution by accepting our bottled water at room temperature, power isn't as available here" or something better worded and skip refrigerating it.
Perhaps get ahold of some d2o. It freezes at 38.8°F so (I think) a 50-50 mixture of d2o & h2o would have it's phase change right in the middle @ 35°F. That's an ideal point for refrigeration, and a phase change thermal mass battery has a lot more capacity.
Thanks to you and the other commenter on these options, would love to replace my current A/C unit with something that seems more intelligently designed.
I wonder how efficient water is for storing and transferring energy as opposed to something like a lead acid battery.
Ice takes a lot of energy to freeze. That means your freezer is going to be really inefficient for a long period of time once the power kicks back on. Also, any other food you put in the freezer is a thermal mass as well. It might be the last to thaw but it could also be the last to freeze if you deplete the "battery" and have to start the process over.
I'm surprised he didn't invest in further insulating the freezer. Deep freezes are not well insulated and waste more cold than your typical cheap foam beer cooler.
I feel like preserving ice over long periods of time has become a bit of a lost art, but before mechanical refrigeration, ice was sent extreme distances by ship and rail and stored for months at a time, see: https://en.wikipedia.org/wiki/Ice_trade
You need to throw out your fossil-economy preconceptions. Efficiency is irrelevant when you're running off direct solar energy. Sure, you could drop the price of a complete unit if it can run on a smaller panel, but the significant variable is not energy efficiency, its resilience to intermittent insolation.
It takes up space in the boat, it requires labor to extract the ice. If you're buying 10 times the boat and 10 times the labor the price is going to have to support it.
This is why Tudor ended up in debtors prison before he got the business model right.
Well, yes, but that means it also takes a the same amount of energy to thaw. That's the whole idea: large heat capacity to create a temperature buffer.
Sure, there is overhead. But it is not immediately obvious whether or not GP was referring to those particular energy inefficiencies, or the relatively large heat capacity of water.
It is also not immediately obvious whether the losses when freezing ice would be less efficient than energy losses due to the heat produced by charging up a battery, and the leaking of charge. If you take all energy loss into account, the questions of efficiency can have counter-intuitive results[0].
I'm not clear if you're describing this project or a conventional freezer, but freezers/fridges are counter-productive to air conditioning because they vent the evacuated heat into the surrounding environment (your home). This is still operating on the same principle, and no matter how poorly-insulated as long as the R-value of the freezer is greater than 0 it's not going to be helping you cool your space.
I've often wondered if there's not meaningful efficiency to be gained in piping the coolant to remote coils outdoors like we do for A/Cs (with a control system to vent the heat indoors when heating is desired, or even use atmospheric cooling instead of the compressor when the outside temp is low enough).
Like a "swamp cooler". The problem is the melting happens in transit. By the time it gets to you there's very little ice and it is thus very expensive. Too expensive to leave by your bed side at night next to a fan to cool you... unless you were wealthy.
Something that I see rarely discussed when it comes to solar power and inverters is how a large part of the expense of an inverter stems from its internal temporary energy storage eelements (could be capacitors, could be inductors).
Assuming illumination is constant in timescales of minutes (so thousands of electrical AC cycles), one can observe the following conundrum: a solar panel produces DC electrical power, while most consumer devices assume AC power input. So when designing (or choosing) an inverter one can make 2 choices in theory.
If one draws on average half the current a solar panel can supply, the other half of the energy will simply recombine in the solar cell, heating it up.
I will assume a resistive load (as a well designed product should not reflect energy back in the grid).
An AC grid voltage is sinusoidal, and for a resistive load the current is also sinusoidal (the relation of course being U=RI)
The power is P=UI=RI^2. so the power is also oscillating sinusoidally, centered about the average power.
This seems to forces us to choose between the following 2 options:
1) have the inverter use all the incoming power (requiring electrical energy storage within the inverter: energy storage capacitors or inductors, which is expensive) or
2) have the inverter draw half the solar panel power (the other half is wasted as heat in the ), or have 2 solar panels (half the energy again wasted) to reach the same output AC power as 1); the inverter can theoretically convert the DC power to AC this way
But in reality there is a third way, if you don't mind having 2 outlets where the AC voltages come out in quadrature. If two AC outlets deliver the same average power with the voltages in quadrature, then the powers will be in counterphase, so no energy storage capacitors or inductors are needed (cheaper inverter per watt), and no energy is wasted (full utilization of the solar panels). The only downside is that you can't deliver the total power to one and the same device. But consider some high-way stop convenience store in the desert with multiple refrigerators, say an even number of off-grid refrigerators, then who cares if half of the refrigerators use AC power in counterphase with the other refridgerators?
A similar reasoning could be used for houses in a street, where the even houses and the odd houses are powered in counterphase (voltages in quadrature), which would substantially decrease the costs for inverters.
The hilarious thing is that so many modern appliances are moving towards variable frequency drives and pile on even more waveform synthesis. Would be nice if they could just accept direct DC input.
> Would be nice if they could just accept direct DC input.
The thing is, lots of appliances do accept DC input (most electronics and probably all inverter-based stuff like washing machines and aircos). If only there was a standard for DC they could adhere to. Then they could add yet another adhesive to proudly proclaim the feat.
>> If only there was a standard for DC they could adhere to.
There are. 12v automotive (13.9v) is one. Then comes 24v, a standard in aviation. There was once a push for 48v in cars so that air conditioners and braking systems could be made all-electric, but it never became widespread.
In any case, neither system appears to have defined a plug standard, which IMO is the real issue as far as supporting end user applications, and where USB and the 12V cigarette lighter plug have been such winners. It's only ever going to be useful for installed applications (RV fridges and the like) if it's something you have to wire in.
You still wouldn’t want to, especially if your house is fairly large. DC transmission line losses are actually pretty big over distances you might think are short.
I'm not sure that's correct. My understanding is that for a given voltage the transmission losses are basically the same (actually possibly slightly better for DC since they don't suffer from the skin effect). The problem comes when you try to get the same power down a low voltage DC circuit which naturally requires high currents.
My understanding is AC is safer at higher voltages than DC - and if you have a choice between 12v DC and 120v AC, the latter needs radically smaller cables.
I haven't seen any truly high quality data on voltage safety, due to the obvious ethical issues with performing properly controlled experiments. It's possible the reason you see 120v in every home but 120v DC almost nowhere is inertia rather than safety.
So, there is a lot of bad, anecdotal information out there about which is worse, AC or DC. The reality is that it _depends on the situation_.
In the case of shock and electrocution DC is _less dangerous_ than low frequency AC (sub ~1kHz). The "let go" currents for DC are several times higher than that of low freq AC, meaning it requires a higher DC voltage to prevent someone from being able to let go. The same is true for the currents where danger of injury and death can occur. DC is still safer than low freq AC.
This has been scientifically tested numerous times in both ethical and non-ethical ways. Here is a paper that shows actual numbers for "let go" currents and dangerous currents vs frequency (from DC up to 10kHz): http://www.wright.edu/~guy.vandegrift/wikifiles/Electric%20s...
In particular look at Fig 3 on page 3 of the above PDF. (One really interesting thing to note in this paper is that women have lower "let go" and dangerous current levels!)
However! There is another factor here where AC can be safer than DC. Fire safety! It is much more difficult to prevent DC from arcing and potentially caused fires than AC. This is because the zero crossover of AC which you mentioned generally causes any arcs to quickly extinguish at lower voltages. DC doesn't cross zero volts and will produce far more arcing at the same voltage.
This is why if you look at the ratings for switches, relays, plugs, etc the DC rating is always much lower than the AC rating.
Why woud AC be safer than DC? AC has a higher peak to peak voltage (factor sqrt(2)), so if it's breakdown voltage related DC would be safer. but in cases dielectric breakdown happens for both AC and DC, I can imagine AC being safer since it regularly crosses zero current, potentially allowing the breakdown plasma to extinguish...
the 12V DC vs 120V AC is an apples oranges comparison, with 12V AC and 120V DC it's the other way around. both would be false comparisons.
why would voltage safety tests be unethical? why would one actually test flesh, instead of the theoretical safety models?
The reason we have AC everywhere is simple, historically it was easier to step up and down with transformers (which don't work with DC), but nowadays DC-DC converters are a solved problem.
I don't know if it's only anecdotal or if there is some actual study to verify it, but the typical reasoning on why AC is "safer" than DC is that AC has a "zero-crossing" point, whereas DC (obviously) does not. Why is this considered "safer" (again, possibly anecdotal)?
Because if you accidentally contact DC at a high enough voltage to shock you, your muscles contract - and stay contracted. AC, on the other hand - at least at the relatively low frequencies typically used (50/60 Hz) - crosses a "zero point" where the voltage is "zero" - and lets your muscles relax - briefly - long enough to be able to move away from the current (or in worst case - ungrip your hands).
Again, I don't know if any study has been done on this potential "mythological" reasoning (I would be surprised if there hasn't) - but that's usually the reasoning given.
> why would voltage safety tests be unethical? why would one actually test flesh, instead of the theoretical safety models?
Well, Edison did it that way because it made for better PR for people to watch criminals or elephants being killed by deadly ac, than to have them read papers on theoretical safety models.
Stepping AC up/down is relatively easy, all you need is a transformer. I'd say the invention of the transistor / IC made it possible for DC. But it took a while to perfect those designs - wall warts changed from transformers in the 1990s?
hmm, mostly mass manufacture, but also very low ON resistance mosfets, very emcheapened "microcontrollers" (yesteryear's microprocessors) with more performance, dedicated SMPS chips, and of course ... china
As others have already noted, cheaper and high-power low-resistance MOSFETs are likely the reason - and that did mostly happen in the 1990s.
Something to look at from that period are hobby-grade RC (radio control) cars. Most used NiCad battery packs, and had some extreme amounts of power behind the motors (which were all brushed DC - BLDC was in the future). These motors pulled a lot of amperage (550 and 750 can styles), which the battery packs could deliver, however, there weren't motor controllers small enough to control that much power.
So instead - pretty much up until the 1990s at some point - hobby RC cars used a "resistor speed controller" - something like this one (also known as a "mechanical speed controller":
Basically it was a multi-tapped high-power resistor (or multiple smaller value high-power resistors) that was tapped in a "variable rheostat" manner with a switch operated by a servo. You would usually have three speeds - high (direct to battery), medium, and low; the resistor would "bleed off" excess current as heat (boy, did they get hot!). Yes, it was inefficient, but it was small, robust, and simple to repair or replace.
Of course, there usually wasn't a "reverse gear" (though I am sure someone hacked something together back then). Most of the time, this wasn't a real issue in the hobby - you spent most of your time going forward.
Such controllers actually have a long history - the earliest electric cars used a similar system (just much larger resistors - usually open coil):
In both cases, switching was done either mechanically, or using large relays or contactors. While it is very inefficient, it is also fairly robust if designed right. Which is why it is still used in a lot of automobiles (though this is rapidly changing with newer models using electronic PWM control) - where?
The AC/heater blower motor! On many cars, there's a "resistor pack" that plugs into the control switch/knob for setting the speed of the blower, and it looks virtually the same as ever - here's one for an older vehicle:
About the only difference is the addition of a heat sink. Newer models from even more recent vehicles don't look much different, and they all work on the same principle. They are usually installed in the blower duct work, so that the air rushing by keeps them cool. Unfortunately, if they are designed improperly, or they don't get enough air cooling (or the fan motor dies) - they can heat up extremely hot and melt or catch the car (ductwork - which is usually plastic) on fire! This is especially true if the fan is on "medium" or "low" speeds and the motor seizes (maximum current draw); high speed wouldn't be a problem because the load would short things out and hopefully a fuse would blow (though - not always - sometimes the "fuse" is the wire itself!). This would cause the resistors to get extremely hot - glowing red even - and can cause a fire. I'm certain more than one automotive fire has started this way.
Today, though, thanks to low cost and highly efficient mosfets - and BLDC motors - more and more cars are implementing true variable speed blowers, and using more efficient motors as well. This comes at a cost of more complexity and (depending on how it's implemented) more difficult to repair/replace control and motor systems, but they tend to be safer, and more efficient (this isn't really an issue with ICE vehicles, but very important on electrics for obvious reasons).
strange that you would call a pair of wires carrying DC a "transmission line".
what makes you think identical lengths of identical cable with the same resistance R powering identical loads R_L will dissipate more heat when carrying DC than AC?
the total resistance of the pair of wires R and the load R_L form voltage divider
in the DC case: P_cable=RI^2
in the AC case: P_cable=R*(I_RMS)^2
they should dissipate the same heat, you may want to brush up:
>For alternating electric current, RMS is equal to the value of the direct current that would produce the same average power dissipation in a resistive load.
and
>Because of their usefulness in carrying out power calculations, listed voltages for power outlets (e.g., 120 V in the USA, or 230 V in Europe) are almost always quoted in RMS values, and not peak values.
The only association with higher resistance losses would be when using low voltages but high currents... and even then the resistance losses would be equally high with low voltage high current AC since the fraction of energy dissipated in the cable versus the load is the same in both cases I^2 R / R_L
correct, but I don't know how large these are typically, an anecdote: I visited a friend who had a lamp socket (with shade) above his desk, and he was complaining about the fluorescent bulb he put in, in comparison with the resistive filament bulbs he usually put in: it was ticking even though the switch in the wall was turned off. At first I suspected a bad contact, but that didn't really make sense. Then I realized what was probably happening: capacitive leakage, so I ask if the socket has 2 switches? sure enough. the distance between the switches was long enough so that the parallel wires embedded in the wall effectively formed a long capacitor, so in both of the off states AC current was flowing through this unintentional capacitor. AC will also have inductive losses yes.
It's ac that has transmission line losses, not dc. DC just has resistive losses, which are the same for ac (rms) and dc, but bigger for low-voltage systems. DC is safer, in most ways, at the same voltage as ac (rms).
So the issue isn't that running your house on dc is less efficient; it's that running your house on 12 volts is less efficient.
Vacuums and hair dryers invariably use universal motors that run the same on ac or dc. AC motors aren't that common in household appliances because their speed is set by the powerline frequency, which is slow. Typically you find them in microwave oven fans.
They're more common in industrial equipment, but a lot of them there are being converted to run off VFDs, which of course internally run on dc.
But currently every appliance has it's own inverter, so running a fixed voltage add through the house would do little good since every DC appliance wants a different voltage.
All those modern lightweight wall warts are switching DCDC converters anyway—they just have a rectifier and capacitor on the front end to get an approximate DC waveform to start from. That's also why modern power supplies are almost always universal for 240@50Hz or 120@60Hz. The frequency is irrelevant and the DCDC can adapt to a huge range of input voltages because the ratio isn't locked in by the wiring in a transformer.
Modern power electronics are not just more flexible, smaller, and lighter, they're more efficient as well.
this is certainly true, but in the mean time there are still a lot of appliances in current operation, just rolled off the assembly line, and still coming off assembly lines that do not accept DC input.
a lot of the material effort that was put in to them would be wasted if we replace them before they break down
and if we keep using them, and keep opting for the single AC outlet inverter, we are wasting energy storage elements at volume of 0.01 Joule per Watt (think of the total PV energy production at least in residential solar [I would be uncomfortably surprised if commercial solar parks don't use this already, but then again that would require the grids to be split in an in-phase grid and out-of-phase grid, which would also be new knowledge for me...])
this also affects adoption, as less expensive storage-less inverters would decrease the time until the solar set-up pays itself back!
Large-scale power generation, including solar parks, is invariably three-phase, which has a more constant total absolute voltage than the two-phase system you're suggesting.
... except I am suggesting a 4 phase system: 2 outlets with each the usual 2 phase AC!
consider 4 phases in 90 degree turns (I wish HN had a button to render LaTeX or so when a reader wants it on demand):
V_0 = V/2 sin(w t + 0 pi / 2)
I_0 = I sin(w t + 0 pi / 2)
V_1 = V/2 sin(w t + 1 pi / 2)
I_1 = I sin(w t + 1 pi / 2)
V_2 = V/2 sin(w t + 2 pi / 2)
I_2 = I sin(w t + 2 pi / 2)
V_3 = V/2 sin(w t + 3 pi / 2)
I_3 = I sin(w t + 3 pi / 2)
Now outlet "in" (in-phase to avoid clashing with "I") is across terminal 0 and 2, and outlet "qu" (quadrature) is across terminals 1 and 3, so the current and and voltages are:
Vin = V/2 sin(w t + 0 pi / 2) - V/2 sin(w t + 2 pi / 2)
= V/2 (sin(w t) - ( - sin(w t) ) )
= V/2 (2 sin( w t) ) = V sin(w t)
Iin = I sin(w t)
Vqu = V/2 sin(w t + 1 pi / 2) - V/2 sin(w t + 3 pi / 2)
= V/2 (sin(w t + 1 pi / 2) - ( - sin(w t + 1 pi / 2) ) )
= V/2 (2 sin( w t + 1 pi / 2) ) = V sin(w t + 1 pi / 2)
= V cos(w t)
Iqu = I sin(w t + 1 pi / 2) = I cos(w t)
and the powers flowing through the outlets are:
Pin = Vin Iin = V I sin(w t) sin(w t) = V I sin^2(w t)
Pqu = Vqu Iqu = V I cos(w t) cos(w t) = V I cos^2(w t)
so the total power is
Ptot = V I (sin^2(w t) + cos^2(w t)) = V I
constant total power out, just like constant DC power into the inverter so no need for storage capacitors / inductors.
QED
It makes sense for solar parks to use 3 - phase because the back-bone power distribution of the grid is 3 phase.
Do you know if the inverters from solar park panels to 3-phase use storage capacitors to convert to 3 phase?
Do you know if any residential inverters are commercially available that split into 4 phase (2 AC outlets) like I describe, without unnecessary storage capacitors / inductors?
>China now leads in total solar energy capacity followed by Europe with 114 GW.
>Remarkably, 64 percent of solar systems in the EU are installed on rooftops, 26 percent of them residential, 18 percent commercial and 20 percent industrial.
so residential solar in Europe is 26% of 114GW = 29.64 GW
so a line frequency of 50Hz in europe implies single AC outlet inverters need an energy store of 0.01 Joule per Watt (in the US only 0.008333... J per W, because they have 60Hz)
This amounts to 296.4 MJ (mega joule) of capacitor / inductor energy storage, elements whose raw materials must be sourced, must be built, must be bought by the consumer aand which are potential points of failure (what is not present can not break down). That could have been avoided. Which we still can avoid for future inverters, without replacing all our consumer electronics with DC consumer electronics.
constant total power out, just like constant DC power into the inverter so no need for storage capacitors / inductors.
Whoa, you're right! Assuming a perfect power factor and perfect balancing on the loads, of course. Your four-phase scheme is very ingenious! I'm sorry I didn't appreciate this at first.
But here's a thing I'm not understanding: yes, the powers sum to a constant. But the way an inverter produces real sinewave power (as opposed to modified square wave) is to PWM an H-bridge to ramp the voltage up and down, filtering it with an inductor (and usually a capacitor, and maybe more than one of each, but those are inessential). An inductor's time integral of voltage, and thus its average voltage drop (disregarding losses to winding resistance, hysteresis, eddy currents, etc.), must be zero to keep its current finite. So the output side of the inductor has the same average voltage as its input side. So, for example, a 25% PWM duty cycle produces 25% of the full-scale output voltage.
However, in your four-phase scheme, when one of the phases (let's say in) is at ±25% output voltage and thus 6.25% peak output power, the other (qu) is at 93.75% output power and thus ±96.8% peak output voltage. This implies that, during that part of the wave, the active in MOSFET needs to be on 25% of the time, while the active qu MOSFET needs to be on 96.8% of the time. That means that between 18.7% and 25% of the time, both MOSFETs are on, so the two phases are actually shorted to each other (though not on the load side of the inductors). Is that okay? I guess it means that the current generated by the solar cells is being shared between the two phases during that time.
Still, it makes me worry that an imbalance of loads or power factors between the four phases could produce some kind of hazardous condition.
You say that the four-phase system doesn't need any energy-storage elements. To a first approximation you're right, again assuming well-balanced, power-factor-corrected loads on the phases: there's no need to store energy harvested close to the zero-crossing for, assuming 50 Hz, the average 5 milliseconds until it can be released close to the peak. 5 milliseconds is a long time, so these storage or filtering elements need to be quite large, 5 millijoules per watt (I think you dropped a factor of ½ in your calculation there, presumably calculating for a full half-cycle instead of a quarter cycle). By contrast, if you're PWMing a sine wave with a PWM frequency of 100 kHz --- a reasonable thing to do with modern IGBTs or power MOSFETs --- the filtering elements only need to store the energy for a maximum of 10 microseconds, and less if the PWM duty cycle is above the minimum. 10 microseconds is 10 microjoules per watt, 500 times smaller. So you only need 0.2% of the energy storage elements you need for what you're describing as typical current systems.
(All that happens if your power factors or loads are imbalanced is that the inverter isn't drawing a consistent amount of current, so potentially the panels become less efficient.)
A thing I'm not sure about is the junction capacitance of photovoltaic cells. A photovoltaic cell is a diode, reverse-biased in normal use, and reverse-biased diodes have a junction capacitance; we'd expect their enormous junctions to have significantly larger junction capacitance than the pF-scale capacitances we see in small-signal diodes. How large is the ½CV² = 50 nJ/microfarad (at V=0.316 V) energy-storage capacity of the PV panel itself? In particular, is it much larger or much smaller than the 5 mJ/W = 5 ms number you'd need for a single-phase inverter to not be wasteful?
As for your questions about the current designs of power-generation inverters and residential inverters, no, I don't know about them. Typically, in both the US and here in Argentina, one side of a normal power outlet is "neutral" (see http://amasci.com/amateur/whygnd.html for the reasons around this) and violating that expectation might cause some problems --- notably, electric shocks from the outside of Edison-screw-type lightbulb sockets.
However, I don't think you need to violate that expectation; you've described a four-phase system, but I think you get the same advantages with a two-phase system, with the phases in quadrature just as you proposed, but with the two phases sharing a neutral wire. The voltage from neutral ("ground") to the in terminal would be V sin(ωt), much as before, while the qu terminal would be at V sin(ωt + ½π), which is to say, V cos(ωt) --- both relative to the neutral wire. In effect you need only a single H-bridge with four MOSFETs (or IGBTs) and two inductors to produce the two voltages, controlled with a scheme slightly different from the usual H-bridge scheme, because it makes sense to have one side of the H-bridge turned on (in, say) while the other side is turned off.
Option 4: output square wave power instead of sinusoidal and hope you don’t destroy the downstream equipment.
In practice, isn’t most of that storage used as part of a boost converter to get a higher output voltage than you input? You either need to switch capacitors between series and parallel or feed a step-up transformer with low-voltage, high-current A/C, which ends up being enough copper wire to get heavy and expensive.
transforming to a higher or lower voltage can be done with small capacitors / inductors (just switch at higher frequency, for each doubling of frequency you can halve the capacitance and thus cost of capacitors / inductors)
but given a desired AC output wattage implies a specific output power, cycled at twice the line frequency, so with only 1 outlet you need to either throw away half the solar power energy, or have storage capacitors or inductors to store energy for the timescale of the line frequency (which is much much longer than the timescale for using capacitors or inductors for merely stepping up / down the voltage.
for example an ideal inverter drawing 10 kW DC and delivering 10 kW AC at 50Hz line frequency will by definition require an energy store of 10 kW / 2 50Hz = 100 J,
square waves would also work, but would still require 2 outlets, and would require the downstream equipment to tolerate it.
You’re assuming there’s a common ground between the two sides of the inverter. If it’s allowed to float, whichever terminal is supposed to be lower at the moment can be connected to the DC ground while the other is connected to the stepped-up voltage.
This is dual to using a full-wave bridge rectifier to get DC from AC, where a half-wave rectifier is simpler but needs energy storage to ride through the negative half of the cycle.
yes, now you display you understand what it would address (a good design that delivers clean sinusoidal wave forms for all combinations of output power -which sum to smaller than or equal to the total supported power, a square region of power combinations- would be non-trivial but is theoretically absolutely feasible without energy storage elements [other than small ones for stepping up or down, control etc])
it would be nice if a flexible (supporting all operating points in the power square) 1 DC-in 2 AC-out quadrature voltage storage-less inverter had an open-source design.
[One can not make a single outlet sinusoidal without equivalent storage capacitors / inductors, its simple mathematics, constant DC average power in - clean AC power out = power stored and released or simply wasted in sinusoidal oscillating fashion (regardless of implementation).
to avoid storing energy, while requiring clean sinusoidal output, 2 AC outlets is the lowest number of output outlets that admit an exact solution since the sum of 2 power sinusoids in counterphase result in a constant output power.]
the power operating point square is delimmited by 0 and 1/2 total power for each AC outlet.
Why? The use case of plugging a solar panel directly into a device is pretty niche, IMO. It's much more common and practical to put solar panels on your house so they can power everything, but you can still draw from the grid at night.
I agree that it would be niche today, but for devices that don't switch location in a house, one time wiring for DC "straight from the panels" so to speak makes sense for those devices that can draw a lot of power: it decreases the energy storage requirement on the inverter
Redesigning them so that in addition to AC, the devices have terminals for DC would probably not add that much to the cost. And off-grid may be niche, but partially because it's inconvenient to connect some of the larger loads that may require AC to your solar panels: if your going to buy energy buffering AC inverters for the house anyway, and don't understand or want to think about the price gradient for the energy buffer, people will obviously choose the setup you describe.
Totally off the wall fourth way (which probably has a ton of reasons it would not work): have shutters in front of each panel, and as power the load draws fluctuates, block and unblock panels so that a given panel only generates power when that power can be fully used.
If the panels are small enough, you could get a pretty good approximation to a sinusoidal output from the array of panels.
The shuttering system doesn't actually have to be shutters. Anything that can block panels with the right timing would do. You could probably do something with rotating discs with holes or slots in them, where the phase between adjacent discs can be adjusted to control have often the holes or slots align to let light through.
How is what you’re proposing different than split-phase, which is already how houses are wired, and how inverters connect? This is why inverters generate 240VAC and why your electrical load panel had alternating circuits across the split phase.
Just provide 3-phase power. The load is nearly constant, and lots of equipment already handles it fine, e.g. motors much prefer 3 phases even at low power, due to this constant power/symmetry.
sure 3-phase would work towards the future, and saves a conductor too, I'm trying to save all consumer equipment (since they universally use 2-phase AC) AND the energy buffer capacitors / inductors in the inverter.
Maybe the real thing here is to get more inductive load equipment shipped with 3-phase as the default. Dryers and stoves are, but they're mostly resistive, and it's for load reasons— 1500W just isn't enough for those applications.
But thinking of air conditioners, fridges, washing machines, central vacs, etc; those are all typically shipped today with a two-phase plug but could use 3-phase. OTOH, if they're not actually driving the motor with the 3-phase and are all just rectifying the power and generating their own waveform with a VFD then there's no point; they should have an option to accept DC.
a single AC outlet still pulses power sinusoidally, could you provide a diagram? the 240V split phase is just with a center tap to ground, so each phase is 120V with respect to ground... I don't see the relevance here (unless I misunderstand you)...
The GP is saying (IIUC) that you should have 2 outlets and opposite phases. But that’s exactly what split-phase looks like in house wiring, right? (Whether that’s how the inverter functions or not).
with 2 outlets he means 4 conductor terminals, and with "opposite phases" he means voltages in quadrature (so that power is in opposite phase, since out of phase voltages means in phase power)?
I wonder if, for the stated design goal of a zero-battery solution, something like a solar thermal concentrator + Einstein–Szilard refrigerator would work. Something as simple as an icyball or two kept charged via the solar thermal system might work as well.
When I see articles like this I immediately go to Ali Express and search for the appropriate term - in this case "solar power refrigerator".
The exact solution isn't there but there are DC fridges for sale and examples of the set-up you require for solar charging. So this is a solved problem.
Shenzhen is well ahead in the hardware innovation game. If you have a hardware idea look there first.
A DC fridge does not "solve the problem". The problem the author solved was not having to use a battery to keep the fridge cold at night or when it rains. He did this with a thermal mass (a large tank of water in the fridge) that takes a while to heat up. Kind of like using an ice pack in a cooler box.
I'm assuming that he used an AC fridge / freezer with an inverter because he already had one. Besides, I've never seen a large inexpensive DC fridge before. They just don't enjoy the same economies of scale.
I've used the thermal mass of water to keep the darn thing quiet at night in a studio flat - put bottles of water in the ice box and turn it off over night.
A modern "inverter" fridge has a three-phase AC motors with, well, an inverter in front of it. It would be easy for the manufacturer to makes such fridges accept DC without a major redesign.
There's a good chance that such a machine may accept DC just fine without even knowing it. Assuming the inverter/VFD has a simple full-bridge as its first stage, the DC would just flow through the same half of the bridge all the time.
A lot of PSUs can do this too; I just bought a Mean Well RSP-1500-48 which specifies its input voltage as AC 90-264V, or DC 127-370V. This means I can run it straight from the traction battery in my car (200V DC) if I care to...
Many likely already do exactly that. It's similar to computer power supplies, which can often (at least if they don't claim active PFC) just take DC at 320 V if set to 230 V AC, because the current handling on the bridge rectifier is specified for 115/120V, which results in a their current rating only being half-used at 230 V.
Which reminds me to check a modern server power supply for whether it could just be switched over to a battery bank at a suitable voltage on power loss. Most load should be easy to shed in a couple seconds by triggering suspend-to-RAM, and UPS are wastefully expensive if they only exist to tank full load for a moment and standby/idle for long enough to handle manual filling and starting of a generator.
Of course this is the long term solution, but replacing all refrigerators in operation, even the ones just manufactured is a total environmental waste compared with getting efficient inverters for solar panels!
To go slightly higher tech than a water tank, you could line the inside of the fridge with bags of phase-change material keyed to around 2.8°C. Then you program the thermostat to shut off at 1.0°C and turn on if 2.8°C or greater (and powered).
That ensures that the phase-change material is always completely frozen after a long period of being powered, and keeps the fridge at a good refrigeration temperature.
Tetradecane paraffin seems like a good starting point. It's not always easy to find phase-change data on heavier organic molecules, even plain old alkanes, but here are a few in about the right range:
The closer the branch is to the center of the chain, the lower the freezing point. It's likely one could get a decent refrigerator-liner phase-change material just by chilling liquid mixed alkanes to 4.0°C, filtering out any solids, then chilling to 1.0°C, filtering again, and keeping those solids. Those are exactly the types of molecules refiners hate. Similar isomers are already removed and reprocessed to improve the cold-temperature characteristics of diesel fuel, because otherwise they gel, and gum up cold-flow filters. Rather than cracking them all into more desirable fuel molecules, some could be diverted as fridge wax.
For actual historical temperature data, see here. [1] It looks like a general range of 5-9 C is the norm, with 12, 15, and 30 C (53, 59, 86 F) spikes over the last 2 months of data. For that kind of failure rate, I wouldn't depend on it without some failsafe warnings for when the temp had dropped below safe levels.
Neat project though, and I might build one if the reliability improves.
Any sharp spike on that graph is a bad sensor read; the 1wire protocol has a pretty weak checksum and you can get bad data that crcs ok when you're reading lots of data. That covers the 30C, 15C.
The spikes to 12C or so that then slowly drop back down are generally the fridge being filled with groceries and taking time to cool back down. If you measured your conventional fridge you might see similar events.
I did have the arm board hang twice this summer. Once I was on vacation, luckily it froze with the fridge turned off (so it didn't freeze down to -5C which is where the dumb thermostat is set), and the fridge was fine for the 24 hours or so until I got home, creeping up to maybe 10C. I need to find a more reliable embedded computer.
I love the simplicity of removing the requirement for a battery. In applications where one is necessary, and portability is not an issue, we have been looking at saltwater batteries. Non toxic, 15 year lifespan, 100% DOD, heavy so hard to steal…
https://www.bluesky-energy.eu/en/greenrock-saltwater-energy-...
It's a very cool, back to basics approach. To me it sounds like building a solar freezer makes its own ice (not literally), so it's an ice box when there's no power. When it comes to "when all you have is a hammer" type thinking, HN tends to use high-tech, trendy approaches as its hammer. Sometimes taking a step backwards and looking to simpler solutions gives us the better approach. I read the phrase "once battery technology improves" so much on articles about solar power I've become numb to it, so I found this a refreshing read.
Looks very interesting. Is this you? What are the physical dimensions (LxWxH) of say 5 kWh and 10 kWh batteries?
Edit: Okay, found it [1]. For 2.7KWh it is Height 929mm, Width 313mm, Depht[sic] 329mm. That's large but definitely within acceptable usage.
Follow up question: What are stacking limitations? How much clearance do you need between different two modules or wall and module? Can you stack vertically?
Great ideas if you are dead against batteries, but there are massive downsides. Batteries are not evil or expensive, at least if you go with traditional lead-acid ones. They are a thousand times more reliable and efficient than compressed air storage. Compressed air storage has many dangers, from explosions (metal fatigue) to fire (compressing gas creates heat).
The best and most reliable method of non-battery storage of energy is the traditional water tower. It used to be standard practice for buildings to maintain water storage tanks on their roofs. Mate a water tank with some solar panels and you can create an energy storage system without heat, high pressures, chemicals, high voltage or even moving parts (the pump has only one moving part).
Pumped hydro storage is great. The difference between it and batteries is that batteries can be constructed off site by a third party and then transported to your location.
Water towers have to be built on site, which can be difficult. Not to mention, to get appreciable storage, you have to build a really tall tower or a really big one. This is difficult too. Especially if you are in a location where the soil shifts or you get high winds. Because now your tower has to survive the elements.
There is definitely a strong case against water towers for distributed energy storage.
Conversion to or from electrical power is one option, but an elevated water storage (tower or simply up hill) reduces the need for larger water pumps. It means you don't have to run your well during dark hours. So it saves on electric use rather than provide actual electricity.
I'm not dead against batteries, we've got an off grid cabin that runs on 4 6v Trojan lead acid batteries and they are great.
However there's something about living off grid that makes one want to simplify, and batteries are one of the big, expensive, and limited life time components of a solar system. If you can reduce the load on, and the required capacity of your battery bank, then you have improved reliability significantly.
As you say, pumped hydro is certainly a great storage system if the situation permits. It just takes a very large storage system to store as much as batteries. If you have a pond or lake and an easy supply of water it would certainly be my choice.
A lot of the household energy load is either heating (water, cooking, surviving winter) or cooling (fridge, feeezer, surviving summer). You don't have to be dead against batteries to see a lot of potential in using thermal energy storage to decouple renewables energy sources from energy use.
No they don't. Case in point, I live off grid with a 24v system composed of 2v lead acid marine batteries. They were 2 years old when I got them and have put them through over 1000 days of use since.
Mind you, I don't discharge the system past 23.5v ever, and I check my electrolyte levels weekly adding distilled water as needed, but lead acid are cheap, effective, long lasting, and recyclable with minimal effort. The only thing against them is maintenance, and they are big and heavy. My house doesn't seem to care.
If you don't discharge below ~60% of system capacity, use flooded cells, and keep up with balancing charges, etc, you should be able to squeeze ~1,000 cycles out of a deep cycle/marine lead acid battery. A partial discharge only counts as a partial cycle, so you're within the expected range by your description.
At well above the cost of lead acid batteries. And the Tesla battery pack is very difficult to recycle. Recycle companies will pay for old lead acid batteries. They are of value even when dead.
I disagree with the 1000 cycles concept. Modern battery controllers are very good at preserving oldschool batteries. I don't see every off-grid house replacing their batteries every few years, just as I don't see automotive or marine batteries die so quickly.
Lead acid batteries also recycle in to reloaded bullets. You can use subsonic loads with just cast lead or swag the bullets into casings and get into higher performance hunting loads.
Assuming off grid prepper mentality is being used.
I fully expect to get another 5 years out of this set. As long as we get back to float the next day, capacity diminishing doesn't really matter for a house. That's more a function of sizing the input and output to the system than battery capacity.
>the Tesla battery pack is very difficult to recycle.
Are you sure about this? Lead-acid batteries are highly recyclable, but lithium cells are straightforward to recycle, too. I know that Tesla has a recycling center set up at their gigafactory.
The cycles you get is dependent on the depth of discharge (and more).
See the chart in [0], where 100% discharge nets 200 cycles, 50% gives you ~500, 30% is ~1200. One would expect that if you discharge 50%, thats half a cycle, and therefore get 400 cycles, but in reality you get 500.
Lead batteries can be rejuvenated, with a device mostly called "A pulser/desulfator/refresher" Short story: I had a completely dead 12V car battery. It was at 0V and would not accept a charge at all. Connected it to a bench power supply and slowly cranked the voltage up until it charged with a couple mA @ 30V. Slowly it accepted more amps so I constantly dialed the voltage down until it was charging at 14volts. Then hooked up the desulfator and left it for couple of weeks. Every other day checked voltage and hooked it up to a charger for couple hours. After that it was perfectly able to start my car(oldtimer) again.
This kind of work requires a supply of power though, which is something of a catch 22 if the battery you are rejuvenating is your power source.
That said, this thread has descended from a comment about apocalyptic scenario planning and this general principle of maintaining batteries makes sense. Learning how to build and repair lead acid batteries doesn't seem to be beyond the realms of possibility.
I believe desulfating is based on trickle charging, so doing it via just solar might work. And if we're talking apocalypse, it'd be good to have a secondary source of power like something that can run off of organic material such as wood gas.
The desulfator i speak about is powered by the 12V battery itself. It's a small box with just get hooked up to positive and negative. Technology differs but basically it charges a capacitor and produces very short high voltage charging pulses that break the formed sulfur crystals.
Yes, this will deplete the battery if it's not charged otherwise.
I do something similar to that. Living off-grid and my solar setup is quite small (1.6kwh of solar panels and a bunch of batteries). However I depend on electricity for most things, including cooking(induction) and hot water (electric water heater/tank).
So in sunny days I let the water tank heat as much as possible(usually around 70-80C), and can go 3-4 days without even needing to turn it on. We are 4 in the household and it holds nearly 100liters of water. It is a kind of battery :)
I find it ironic that this sort of thing is so overlooked with solar/wind power on the electric grid. Consumer electricity prices should be allowed to rise and fall with the availability of solar and wind. Then, you can heat one hot water tank only when electricity is cheap, and also use that tank to heat your house in winter. In summer, a separate tank can be chilled when power is cheap, and used to cool the house.
Or even simpler, a pile of rocks will work.
With such a scheme, the need for grid batteries would be reduced enormously. Instead grids have the problem of what to do with the extra power when there's too much of it.
well.. I guess water and rocks, at a scale that make them useful for other purposes will definitely have a size problem for most people. While a battery (especially the new lithium ones) can fit in a drawer :)
Your dwelling, just as it is, has a lot of thermal mass that can be used as a "battery". For example, cooling it to the low end of the comfort zone when electricity is cheap, and letting it drift to the high end when it is expensive.
For example, the power goes out around here often. I've noticed it can take up to two days for the house to cool down. The water in the hot water tank is hot enough for a comfortable shower for 3 days.
Water/rock batteries are cheap as dirt, no maintenance, no fire risk, etc.
I don't have a source handy but hot water storage is really cheap, maybe an order of magnitude cheaper than a lead acid battery. Plus you have infinite cycle count.
I don’t think a good solar electric hot water system would ever work if it was running only when the sun was shining. It takes _so much energy_ to get water up around the requisite 110+ degrees, that even a very efficient storage system wouldn’t benefit it all that much. Honestly, the best solar powered hot water system is a black plastic bag full of water in the sun. Anything else will require a battery bank at minimum.
Depends on the size, but if you have even a modest size solar system you should be good. On a sunny day, a 2kw solar system can drive a 1kw hot water cylinder to full temperature easily. And to avoid legionnaires disease - a risk of inadequately heated water - you only need to drive the temperature up high from time to time, not continuously. Once a day is plenty.
Don't use solar PVCs to heat water! Solar water heaters are much more efficient than PVCs. Even the lowest-efficiency system listed is 46%, compared to 19% for standard solar cells.
> NO TECH MAGAZINE – We believe in progress and technology
> No Tech Magazine hosts all links and updates from Low-tech Magazine. We refuse to assume that every problem has a high-tech solution.
Is it a parody site? Is it a "Low Tech Magazine" mirror site? Or is it sister site operated by low-tech magazine fans, just with a slightly different altitude towards technology, hence the joke?
It looks as if this is using liquid water as a thermal capacity. While water has a high thermal capacity (4.2 J/g), the energy required to melt ice is much larger (334 J/g) and a melting ice block will maintain the 0°C until molten. So it would be more efficient and better guarantee the temperaturs in the fridge, if it worked with melting ice as the thermal buffer.
The data linked shows the fridge sitting above 40 degrees F for days at a time. From what I understand about food safety, those conditions will allow bacteria to propagate. It looks like a good start on a project, but I'd be super nervous about using it in a 'production environment' for any period of time.
Vaccines are transported in a cold chain from the manufacturer all the way out to the last village on the end of tracks so poor only motorcycles can ride on them. The last part of that cold chain is off grid, using solar, diesel generators, ice packs, and kerosene fridges.
The first rule of operating an off grid cold chain is to always, always, always keep the freezer full to the top with ice packs.
The ice packs will of course be needed to pack coolers to distribute the vaccines, but they are also your backup system. A freezer filled to the brim with ice packs will be able to bridge a 3 or 4 day interruption in fuel (or failed generator, or burned up wiring, or security evacuation, or, etc, etc, etc), and save hundreds of thousands of dollars of vaccines from loss, not to mention possibly human lives.
For AC applications, though, water is not the perfect heat storage medium. The efficiency would be better if the freezing point was higher. But then again, I do not know of any material with melting point at +10 celsius, heat capacity close to water and yet, would be having a reasonable cost compared to water.
The best hack I've seen for refrigerators is piping the outside air into it in winter. In Alaska and other cold places like that people can use refrigerators passively cooled by outside air for half a year and more, using almost zero electricity.
Except then you’re actively pumping cold air into your home, increasing the load on your heating system.
While a fridge works by extracting the heat from the stuff you put in your fridge and heating your home with it, decreasing the load on the rest of your heating system before even accounting for the compressor inefficiencies.
Kinda like when hotels put their ice machines in some tiny room on each floor: that room gets really hot because it’s tap water in and ice out.
You're pumping cold into the fridge, which is insulated as well as the piping, so I imagine it doesn't significantly affect the room temperature. You're right that fridge does heat up the room, but it's not that significant when it's -20^C (-4F) outside, you'll need to heat that house a lot more anyways.
The fridge is much more poorly insulated than the walls, with more surface area to boot. And any wind outside will suck out warm air or push in cold air with every opening.
Point being, that low-tech fridge (ice box connected to outside) is thermodynamically inefficient if you’re heating inside, while an electric fridge is an efficient heat pump.
In a cabin with poor insulation and “limitless” wood, go for it. But for a modern structure, it’s not fully thought out.
What would really make sense is a fridge that moves heat outside in hot climates.
You misunderstood how it's constructed (my explanation sucks I know), it's a heat exchanger pipe with one side out, and the other inside the freezer. The copper pipe is closed, so it's not literally pumping the air inside, as that would dry your food because air is extremely dry when temperatures are that low. The flow of the air inside the pipe is passive as it's almost vertical, so as the air cools down it will go down into the freezer, while heated air goes up the pipe outside the house. The same principal as geothermal heating/cooling, except that they use their extremely cold weather instead of the ground as the "infinite" heat sink. I'm sure that could be also improved with some electromagnetic valve to control the air movement and thus the temperature in the freezer...
That sounds better, but it still throws a lot of thermodynamic theory out the window.
When it's cold outside, and you want to heat inside, you want to use indoors as the heatsink. Even if it's -20 outside and +20C inside, you can still heat the inside by removing heat from something +10C and making it -20C.
If you put liquid water into your electric freezer, a fridge pumps heat OUT of the water to freeze it and exhausts it indoors. A net benefit.
While the heat tube system moves the heat from the water outside when you really want to move that enthalpy into the home. But it instead moves that heat outside. That's bad when you're trying to heat inside. It's just throwing away energy.
I'm curious how the real world numbers work out here. Assuming that you're using electric heat to heat the house, I get that a traditional fridge is better than venting heat outside.
But, if you have a ground source heat pump as your home's heat (sourcing from 45° ground temps) - wouldn't it be more efficient to use the outside air as a source for a fridge?
The ground source heat pump works exactly the same as the fridge does. And the fridge is extracting heat from an approx. 40F heat source. So not much of a difference. The ground source heat pump will be pretty efficient if it's hitting deep and wet soil to get a good heat exchange.
But if we're comparing to resistive heating, an air-source heat pump near/below freezing points, propane or even natural gas, the economics move in favour of the electric fridge.
A related idea I’d love to explore is an off-grid fridge cooled via the Stirling cycle [0]. It’s essentially a Stirling engine run in reverse, using power to move heat vs. the other way around. No refrigerant is required, just an external source of power e.g. a DC electric motor. Such technology is used today for ultra-low-temperature cryonics. At least one Stirling cycle mini-fridge has been developed and brought to market; it got rave reviews from the boating community to whom it was marketed, but went out of production and was never followed up [1]. I’d love to find out why this technology hasn’t been more widely deployed.
The solar panels are shared between the fridge and some batteries. His house computer is connected to the charge controller of the panels, to the fridge AC inverter and to thermometers inside and outside the fridge to decide whether to turn on the AC inverter. It also generates graphs of the temperatures, running times, etc. And it warns him if the fridge temperature gets too low.
Ah, that's reassuring, I'm rather afraid of anybody who brags about how many LoC their thing is - ideally it is somewhere near the lowest reasonable LoC to get a thing done cleanly and expressively.
Seems like it's a chest freezer used as a fridge, so there needs to be some set point adjustments. And depending on what's being stored, aggressive thermal banking (if you blow -5C air at your carton of milk, it's not going to freeze for a while, so do it anyway).
Yes, it's a technique to argue in bad faith and to shift the burden of proof. And let's see how it applies here...
> 3000 lines of control software? Seems a bit excessive. Why does it need a computer at all?
It really means,
> 3000 lines of control software is unbelievable. It's excessive, it doesn't even need a computer at all!
Sure, it's criticism. But I don't see any bad faith argument here. So I guess "Just asking questions" doesn't apply here.
And from the Guideline,
> Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something.
So it's probably the reason for downvoting.
But consider the fact that other readers have already responded to the question/criticism with more information on the author's intention, I think downvoting this is unnecessary.
At risk of causing further dancing on the head of a pin style argument I'd like to point out that contrary to what some people seem to believe it was a sincere question based on my own experience of writing similar control software in an industrial context.
I meant exactly what I said, there was no subtext. I wanted to know the answer and it was provided by icebraining.
If I had intended to say that the number of lines were in actual fact excessive I would have omitted the word seems.
Some months ago there was an interesting article here about some startup using "AI" to determine the precise design of compressors for a given refrigeration design specification.
In that article it was suggested that getting the exact size and shape of the compressor elements was more fiddly and troublesome than "it was worth". So this start-up's value proposition was making it way easier to develop very well balanced refrigeration / heat pump designs... which in turn are significantly more efficient than current state of the art in mass production.
I worked at a startup and designed the thermal battery and pumping systems for a solar powered milk chiller/storage system for the Indian market. About 500L of milk chilling & cold storage capacity, also storing solar energy as cold (not ice)
Depending on where you are, you need a whole bunch of insulation to not condense vapor on the outside of your storage, because condensation is a killer for efficiency. My system needed about 50mm of foam rubber for the worst case, around a 1000L thermal storage medium tank, which makes these systems very large.
It would be interesting to know how much of refrigerator power consumption is due to door opening/insertion of warm food and how much is imperfect insulation.
Given that the writer of the article doesn't appear to have space issues, it would be cool to see a homebuilt unit with much higher insulation using an existing freezer to mine for parts. I really like the redneck Yeti coolers that people build.
A more trivial modification might be to put strips of plastic across the opening so that less air interchange occurs when you put stuff in or out.
I'd also be curious to know how much of it is the fridge being too close to the wall. I assume you need to be able to get decent air flow over the radiator for it to work efficiently, and that you won't get decent air flow if it's only a couple cm away from the wall, or recessed into some cabinetry that's built tightly around it.
You see refrigerators that are propane/electric or both but use the ammonia/water cycle to produce a chill. You make heat to boil off the ammonia(I think it's 60C) and then hold that in a vessel and let it recombine as needed. Ammonia is hydrophilic and the reaction of them is endothermic.
There are a lot of ways of getting heating to 60C and doing this. I have always thought that a system could use evacuated solar tubing to generate the heat.
Its a little frustrating that the author didn't include a cost for the project. I understand that some if not all the parts are generic and can be swapped out, but a ballpark sum would be helpful to compare against products like this: https://sundanzer.com/product/dcr165-dcf165/
Could you improve this further by somehow automatically controlling heat exchange between the thermal mass and a separate grocery compartment? That way the thermal mass would really act like a battery, you could save all the energy during a sunny week and use it over time?
IIRC some PFCs have a higher heat capacity than water (one reason why they are used in fire extinguishers). I don't know if its sufficiently higher to merit the extra cost though.
It just happened a few years ago while travelling a lot (by train), but then I found that idea interesting and never bought one, just to see if I "can do it" without.
After a few years I do not even know what I would store in a refrigerator.
Yes, of course, I am living in a city, with everything I need in markets around me, but it really just takes a little bit of planning and thinking to not need that thing even in remote places, I did that, it worked.
Each year I purchase a half-share in a CSA[1], which means that each Thursday from May to October I go to a local farm and pick up a wealth of fresh vegetables. By the next Wednesday, some of the vegetables are visibly starting to deteriorate, and that's with refrigeration. Most of the time I finish all my vegetables during the week, but if I didn't refrigerate, I'd be throwing away a lot of food.
Perhaps I'm conforming to a cult of prosperity. Or perhaps I'm supporting local business, helping the environment by reducing food transportation, eating healthily, eating good food, and meeting local people with similar interests.
I think there's a tendency people have, especially prevalent on Hacker News, to do something unusual and cool, and then assume everyone else isn't doing it because they're stupid/conformist/etc. It's great to do something off the beaten path, but don't go that extra step and start making assumptions about people.
I'll also add that in the past, I've lived in some poor neighborhoods, and even very poor people who certainly aren't in any "cult of prosperity" in the US usually have refrigerators. I think this has more to do with the cost savings associated with buying bulk food than to do with any "cult of prosperity".
I've been living without a fridge for a few months too. It sucks. My eggs keep far longer in the fridge. I can keep leftovers, but only in a closed, sterile pot on the stove. Even sliced prosciutto starts to smell funny after a week. I got some Roquefort the other week that started growing black mold within two days after I bought it; I had to throw a corner of it out. I have a lot of canned food now, but it's more expensive and tastes worse.
These sorts of strange delusional comments, followed up by a claim that they can’t understand normal perspectives on things like “what would you do with a fridge”, are surprisingly common on HN. I have no idea what sort of thinking goes into a comment like this, but I suspect it’s sort of role play where they imagine the world would be such a great place if only everybody else also prescribed to their fringe view on fridges.
On the other hand it’s always worth questioning these things as what everybody else finds normal might just have been effective marketing by someone with something gain.
Well, the normality of fridge usage (in developed countries) can’t really be called into question, regardless of how it got that way. But this idea that somebody who’s chosen to live without a fridge can’t understand why somebody could possible want to have one is just completely disingenuous, and honestly it’s a form of rhetoric that’s unsettlingly common here.
I'm not agreeing with software limits comment, neither do I agree with your reaction to it. Clearly modern fridge usage can be called into question, that's what this whole discussion is about. Binary responses aren't interesting, there is a continuum that can be explored.
I mean, if words aren’t going to have defined meanings anymore, then I guess you can question anything. But the Oxford definition of normal is:
> conforming to a standard; usual, typical, or expected.
Having a fridge is entirely normal, and to claim otherwise would require quite an extraordinary justification.
If you wanted to question whether people really need them, that would be a much more reasonable line of inquiry. But for anybody posting here to claim that they cannot understand why people would want to have one is frankly not believable.
there's plenty of ways to store things without refrigerating them. you can keep meats and other things for a long time without refrigeration.. using for example salt.
This would combine well with another low-tech battery solution, stacked weight, which would store without loss or reliability worries for those few days in the year you need them.
Edit: Actually, while this idea sounds good, a fridge requiring 1 million joules for a rainy day would need 10,000kg @ 10 meters, even before considering efficiency losses.
