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"A little time, a little trouble, your better day"
Badfinger
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Disclaimer: I know next to no theory and math behind heat pumps, solar panels and such. I have heard of 'carnot engines', but never learned enough math to understand the theory. So these thoughts come from an ignorant amateur  .
In 20 years, solar panels have improved their efficiency by a few percent points, from slightly below 20% to slightly above. I am talking about commercial, affordable panels - not what is demonstrated as lab prototypes.
Solar heat collectors can pick up well above 80% of the radiation energy. Furthermore, they are far less dependent on the direction to the sun, and collect a fair amount of energy even in diffused light, when the sun is hidden behind a cloud. Problem is that we get it as heat. Electricity is much more generally useful. So is there a way to get more electricity than the 20% from solar panels?
I came across this 'Betz law', setting a theoretical limit on a wind turbine: It can at most take 59.3% of the kinetic energy of the wind. Again, I do not understand all the math, but it makes intuitive sense: If all the kinetic energy were tapped out, the air would stop completely immediately behind the wind turbine, having to pile up to quite some heap of air. It must retain a minimum of kinetic energy in order to get out of the way. I trust the calculations of Albert Betz, that this requires a very minimum 40.3% of its original energy.
A hydropower water turbine in open air doesn't have this limitation: The water jet hits the turbine blades to set it spinning, and ideally transfers all its kinetic energy to them, falling vertically of the blades, driven by gravitation only. The water gets out of the way, without blocking the water following behind it. Hydropower turbines have an efficiency of 95% or more.
So I get this - probably crazy - idea:
Take a glass tube, strong enough to take both some heat and some gas pressure. Make a fresnel cylinder lens the langth of the tube: It need not be of high optical quality, but e.g. a thin plastic board, to collect all the sun hitting it, as a burning stripe in the glass tube. You could insert a coal black ceramic rod in the center of the tube, to absorb as much heat as possible.
Lay the tube horizontally, and fill it partially with a fluid that will evaporate and create a gas pressure when heated by the sun. Mount the fresnel cylinder so that its burning stripe hits (the black absorber in) the tube. When the fluid starts boiling, let the pressure out of the glass tube through a vent to a nozzle aimed at a gas turbine with an electric dynamo. The gas will not be much above the boiling point for the liquid (it has just evaporated and escaped through the vent without significant further heating). So when it hits the turbine blades, giving off some of its energy to them, it cools down and condenses to a fluid, that can be pumped back into the glass tube for a new round of evaporation. As it has just condensed, it will be not much below its boiling point. It shouldn't take that much solar energy to evaporate it - the evaporation energy, of course, but little energy for heating it up to its boiling point. The glass tube, turbine chamber and pumping the fluid back to the glass tube makes a closed circuit.
Assuming that the gas condenses when loosing energy to the turbine, maybe Betz law doesn't apply, or not fully, since the condensation will reduce the gas pressure on the back side of the turbine. Even if Betz applies, a theoretical 59.3% is still three times the 20% from solar panels. If you need some heat as well, you migth lead away some of the heat energy, the one that couldn't be transformed to electricity, to where you need the heat. That would probably have a good effect on the condensation of the gas, to reduce the gas pressure, and facilitate pumping the fluid back to the glass tube. The combined energy extracted, the electricity from the turbine dynamo plus the heat tapped from the condensation chamber, could possibly exceed the Belz limit for turbine alone.
There may be fluids far better suited than water for such an evaporate - turbine - condense closed circuit. That doesn't affect its principal operation.
For all I know, solar electricity generators working according to this principle may be commonplace. Or my crazy idea may be original. Or there may be some theoretical obstacle that makes the idea completely worthless.
Does this idea have any merit at all?
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First, all ideas have merit and an idea that seems crazy today can suddenly become possible with technological break throughs tomorrow.
Second, I do not have degrees in any of the supporting fields for what I am going to share, so take what I say with a grain of salt.
What I know about solar cells and their low efficiency. A solar cell converts light (which exists as both a photon and wave) into an electrical current. The solar cell is composed of two materials that are bonded together. There is an electrical barrier where the two materials meet. When light shines on the material we must consider the dual nature of the light. As a wave it has a wavelength (hold this thought, I will get back to it in a moment). As a photon light packs a wallop when it collides with either the atoms of the material or the electron cloud that surrounds the atom. What we want to do is to have the photon collide with the electron cloud and pass the momentum that the photon is carrying on to the electron, breaking the electron away from the atom and sending it over the barrier to the other material on the other side of the barrier. The barrier can be thought of as a hill that separates the two materials. Once the electron passes over the top of the hill it rolls down into the other material and can't go back. As more and more electrons roll over the hill the material on that side of the barrier becomes negative and the material that was stripped of electrons becomes positive. Connect a wire between the two sides and electricity will flow.
But there is a complication to happy state of electron flow. The wave length of the light. If the wave length is too long the atoms of the material and not the electron cloud absorb the momentum of the light photons. This shows up as heat, the atoms of the material begin to giggle around more and more. This becomes a problem because as the atoms bounce around more the barrier weakens (the hill gets lower) and electrons begin to cross back over from the other side to their original side. So heat is a killer problem for solar cells. If the wave length is too short the photons pass through the material like it was transparent (like a glass window) and strike whatever mounting material is holding the cells. So only a narrow band of light wave lengths will do the magic of getting electrons to flow in the material.
A solution to the wave length problem is to find two more materials that work with the shorter wave lengths and create a solar sandwich of materials. Each set of materials picking off a different narrow band of light wave lengths. This is exactly what you are reading about in the announcements from labs that are experimenting with thin films that have the materials vapor deposited on the film material. These thin films are sandwiched together to convert more wave lengths of light. These are pushing efficiency claims to near 40% and in some cases beyond.
There are problems with these lab methods. One; can the thin films be reliably coated with the chemicals (the yield of usable cells per meter of material). The second is management of heat. The films that hold the chemical materials accumulate heat (sandwich more films together and trap more heat) and as we know heat is a killer for the solar electric effect. (even more so when you are vapor coating a thin film, there is not much material to mess with). Another is longevity of the materials. Oxygen in our atmosphere is very corrosive and will degrade many of the thin film composites. The industry generally wants a 25-30 year 80% rule. Where a solar cell that is deployed in the field will continue to generate at 80 percent of it's max rating after 25 - 30 years. Many of the labs are trying to do rapid aging tests to satisfy this metric since they really don't want to wait 25-30 years before going into production, but electric companies don't want to buy cells that are not rated for the minimal longevity.
So new solar cell materials show much promise, but it will be a while for new materials to make it into the accepted commercial deployment.
Hydro power generation is taking advantage of mega evaporation cycles in the earth's weather patterns to take water deposited in a high area and generate power by controlling it's flow to a lower altitude (usually a drop of several hundred feet. A column of water several hundred feet high weighs a lot and can overcome the massive torque requirements for the turbine generators.)
Converting heat to electric power is tricky. To get the pressure you need to overcome the magnetic field resistance in the coils of the generator, you generally need a large difference in the hot side versus the cold side of the heat conversion machinery. This translates into large pressure changes. So glass tubes might need to be replaced with copper or aluminum or titanium tubes depending on the heat and pressure. The amount of work that can be extracted from a mechanical heat conversion is roughly proportional to the difference in the temperature of the gas or liquid from the hot side to the cold (or cooler) side. Big difference in temperature = lots of energy for work. Small difference in temperature = little energy available for work. If you are going to drive a turbine generator, then you need to estimate the amount of torque needed to turn the blades through one revolution. As an example, if you have a hybrid vehicle with regenerative breaking, you can feel the car slow rapidly when applying the regenerative brakes (it is converting the momentum stored in the car to electricity to charge the battery.) So there is a lot of resistance in turning the generator against the magnetic fields in the coils to generate the electricity. This is not to say that you can not scale a generator to be extremely tiny and reduce the torque requirements. I don't know how small you can go. I am not a mechanical engineer.
However, there are some advancements in nano engineering that are interesting. Just read an article where a university has created a nano material that creates a tiny electric flow from the humidity in the air. (sorry it's late and I don't have a link to post for the article). The theory is that as the humid air works it's way through the narrow nanometer scale channels it rubs against the walls and creates a static like charge, a small collection of free electrons, that can be extracted. Currently, too small for practical use, but if it scales it could mean that you never have to charge your smart watch, or other small wearable devices. They would power themselves from the humidity in the air.
Keep thinking and working on your idea. There might be something amazing that can come out of it.
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As far as I can see, the problem with this is that you are running a heat engine in which the temperature differential is miniscule. The efficiency of such engines is given by (Tin - Tout)/Tin, where T stands for temperature Kelvin.
It is likely that this is much less efficient than your standard photovoltaic cell.
The above applies when there is no phase transition (e.g. gas to liquid). If there is a way to harness the heat of condensation as well, this may change the efficiency calculation. Perhaps you should look into the efficiency figures for air conditioning systems, which do something similar.
Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.
-- 6079 Smith W.
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Except that what I described quite explicitly included a phase transition.
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reminds me of a question I missed in Thermodynamics…
better to store as pure energy (potential energy) or heat.
The wrong answer is “heat” because the equation above incurs a conversion tax to take it back to energy.
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Great idea!
I'd like to share an alternative approach to generating electricity, distinct from solar, wind, or heat. This concept revolves around harnessing gravitational force, a ubiquitous and constant force available everywhere. By utilizing a hoist or lever, we could potentially sustain the motion of a heavy object in a circular manner with the assistance of gravity.
While I'm unsure of the technical details, I believe someone with expertise in this field could explore this idea further.
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From what I know, this would violate the Second Law of Thermodynamics. There have been attempts for making Perpetual Motion Machines, over the past more than 200 years, and none of them seem to have been perpetual enough.
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We do utilize it, in all hydropower stations. The potential energy of a high mountain reservoir, given by mgh, comes from the gravitational force, given by g.
In a weightless environment, there would be no way to exploit the position of a body of water for energy production this way.
If we build a huge toroid shaped space station, or consider Earth's equator similarly, we could in theory exploit centrifugal forces in a similar way (some like to say the opposite way!): At Equator, throw a mass, attached to a rope, into space beyond geostationary orbit. That is, more than 36,000 km up. It won't follow Earth's rotation but drag behind. You can use that drag in your rope to pull a generator for generating electricity.
One 'minor' problem: We don't have a strong enough rope. A 36,000 km long rope would be so heavy that even if you had a place to fasten it, up there, it would be torn off by its own weight somewhere down the rope. I have seen claims that today we do have nanotechnology that could in principle be used to create a strong enough rope. Maybe that is true. So maybe, a few years from now, equatorial countries are major electricity produces for the rest of the world. And airplanes crossing the equator must zigzag though a maze of ropes running up to energy producing weights forming a Saturn-like disk around the Earth.
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Your idea does exist. Solar power tower - Wikipedia[^]
As for "must be directional"I beg to disagree. IMHE my solar panels charge - a bit - even on overcast days.
"If we don't change direction, we'll end up where we're going"
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Sure, I know of those, but they are a few (or several) magnitudes away from being a replacement for those 250-300 W solar panels people mount on their rooftops!
These installations use large areas covered with mirrors to concentrate the energy into a single, super-hot point. (The very first solar oven, the Odeillo furnace in France, did not produce electric power, but pollution free heat up 3500 °C, valuable to a lot of industrial processes.) Using moderately sized (maybe like 50 by 20 cm) fresnel cylinder lenses (pressed from cheap plastic), concentrating the radiation to a burning line on absorber immersed in an evaporating liquid would keep the temperature below, or possibly slightly above, the boiling temperature of the liquid. This is quite different from having to handle 3500 °C or molten salts.
For the question of directionality: At a microscopic level, the active element of a PV cell lies at the bottom of a 'valley' with steep mountain sides. The sun goes down behind the mountains long before it goes down at a flat plain. One of the improvements in PV cells for the last decade or two has been to reduce the depth of the valley (or if you like: The height of mountains), to maintain the efficiency over a larger range of angle of incidence. At increasing angle, there is a breakpoint after which power output falls quite rapidly. This has been such an embarassment for the PV manufacturers that even though it has improved significantly, they still do not want to publish diagrams showing the falloff as function of incidence angle, only the output for perpendicular radiation, which really hasn't changed a lot.
I am not surprised that your solar panels charge even on overcast days (I would be surprised if not). But all tests I have read shows that for solar heat collectors, the reduction in energy output is less than for solar panels. Heat collectors will to a larger degree accept radiation from all directions.
The other, 'large scale' directional aspect is pure geometry: If the angle between the surface normal and the direction to the radiation source (the sun) is v, the panel covers only cos(v) of the energy flow, compared to a panel perpendicular to the flow. The only way to compensate for this is to re-orient your panel, preferably with an automatic mechanism following the sun during the day and during the seasons. The cost of the mechanics (and the maintenance of it) may rise the cost of your 'free' solar power noticeably! 
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I hear the argument that solar panels lose efficiency as they heat up, the panels on my house gather the most energy in the summer when there is lots of sun. Obviously there is more sunlight hours in the summer, but I'm saying that even with the heat, they still put out lots of useful power.
I'm glad to jut be a consumer of these wonderful math problems as most of the computations just go right over (around/under/through) my head 
Hogan
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Agreed, but I do tend to get (slightly) more power in May/June than the hotter July and August.
TTFN - Kent
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The temperature dependency of solar panels is promoted strongly here up in the north: Central Norway, where I live at 63° north is like Fairbanks, Alaska. In winter time, the sun doesn't rise much above the mountain tops, and only for a handful of hours a day. Its sloping path through the atmosphere is serval time that at summer time, so a lot of energy is absorbed. Often, there is lots of ice crystals in the air, spreading the rays in all directions. Not to forget: If the panels are mounted with in a fixed orientation, and the angle between the surface normal of the panel and the direction to the sun is v, then the panel area covers only cos(v) of area of the radiation flow, compared to the gross area of the panel. You really should tip your panel up by 63° (at our latitude) and rotated to follow the sun during the day, but the machinery to do it is expensive and may be iced down in the next snowstorm. (On the other hand: Raising the panels to 63° is a good help to keep them from being covered by a meter of snow!)
With all these negative aspects, solar panel proponents bring up this undisputable argument: But the efficiency of solar panels increase when the temperature goes down. So there! That makes them a great solution for Norway at winter time! Disregard all of the critical remarks - they are compensated for by the higher efficiency.
Oh well. The efficiency typically improves by 0.3% per °C. That is the increase in power output, not in efficiency percentage points (such as from 20% to 20.3%, but rather 20.06%). 20 °C colder (that is 36 °F colder) gives you 6% more electricity. Not exactly revolutionary. You gain far more in summer from the sun hitting your panels perpendicularly, the rays' shorter path through the atmosphere, the longer days, and the lack of icy frost or snow on your panels. Nice if you need electricity to run your air condition. That is not a primary need up north. We need the power in winter time.
Even here, solar panels provide some electricity during the winter months, but those promoting it are usually very reluctant to show their actual energy meter readings over the year. They are much more eager when they can talk about the higher efficiency in winter, without quoting any figures.
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Over 40 years ago I did a degree in Energy Studies, shortly after the Middle East "oil crisis". Everyone was looking at alternative energy sources to oil. (At the time Global Warming / Climate Change was barely being talked about). The peak of my mathematical achievements was understanding and reproducing the Betz law and verifying that theoretical limit. I was never able to repeat that feat, wouldn't even know where to begin these days!
As for your idea, what are you using to pump the condensate back into the tube of boiling liquid/high pressure gas? [Note; I am not saying that the energy needed to do that outweighs the energy output from the generator. I think it probably will, and will certainly reduce the overall efficiency of the system.] But you might want to look up "steam injector"; a device fitted to steam locomotives that uses the high pressure steam from the boiler to inject feed water into the boiler. Doesn't sound like it should be possible but it works. That said, injectors are usually the trickiest bit of a steam loco to design, maintain and operate.
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DerekT-P wrote: what are you using to pump the condensate back into the tube
Hehe ... you make it sound as if this is something I've got ready to put into production! That is far away, and I honestly don't expect it to ever become reality. When I present the idea, one of my goals is to understand why the idea sounding so great to me hasn't been realized by others a long time ago. So I hope for other people to tell me what's wrong with it, the reasons why it hasn't been realized.
Your response is great example of that. So thanks a lot . I haven't been considering that as a problem. To try to make up a response:
If the evaporated liquid, the gas, had not condensed to significant degree, the gas pressure would be roughly the same from the boiling surface, through the nozzle and turbine, all the way to the surface of the liquid on its way back. The nozzle would reduce the pressure in the turbine chamber part of the circuit to a lower value in than in the boiling chamber; I don't know by how much. And one fundamental idea is that the vapor does condense, reducing the pressure at the back side of the turbine. So the pressure at the surface of the condensate will be significantly lower than that in the boiling chamber. I don't know how much lower. The more reluctant the vapor is to condensate, the smaller the difference. This difference must be overcome by a pump. Maybe the pump will take a significant part of the energy produced by the dynamo. I guess that it depends on the properties of the liquid/vapor.
One possible solution:
To serve as an alternate to solar panels, I guess that I would mount a stack of such evaporation tube, maybe 6 to 8 of them, in a frame a meter tall, 50 cm wide (if the tubes are 50 cm long). The front lenses would concentrate an energy inflow of 50 by 16 cm per tube. Raw energy inflow, perpendicular to the sun, is 1100-1300 W/sqm. There are several minor losses, but at best we could get 80 W to each tube, close to 500 W for a half square meter, 6-tube frame. (This is not to say that I expect to achieve 500 W electric power from a half square meter panel; it is the theoretical very maximum with no losses and efficiency of 100%. For that area, solar panels provide about 100 W under ideal conditions - that is what we try to beat!)
Assume we let only 5 of 6 tubes be boiling at the same time; they cyclically get a rest period. If the tubes are 3/4 filled with liquid at the start of each cycle, most of it could evaporate without any refill (if that black heat absorber is located near the bottom). When the tube gets closed to empty, it is given a rest: The condenser lens is turned away to stop the boiling, the tube's surplus pressure is let out, and new (i.e. recycled) liquid is poured in, without having to fight against any high pressure. The condensation chamber would most likely be over-pressurized, so it can press the condensate into the now low-pressure evaporation tube, or can at least help a pump doing it with moderate energy consumption. Filling the tube with new liquid would probably be quick, compared to the cycle time, so the tube could come back into operation within a short time; it wouldn't be unproductive for the full 1/6 of the cycle time.
If the six tubes in a stack each have nozzles to the same turbine wheel, electricity production would be fairly stable. The five active tubes would ensure that the pressure in the turbine/condensation chamber is more or less maintained, to drive the condensate back to the tube currently under filling without the need for a supplementary pump.
Again: Someone who knows this field may rise up and declare: That wouldn't work, because ... That is exactly what I want to hear: Qualified objections / explanations of why my ideas are not workable in practice
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trønderen wrote: you make it sound as if this is something I've got ready to put into production
Disappointed if you've not got a prototype running by now...
Bear in mind there's a lot more to boiling a liquid than just raising its temperature to boiling point - look up "latent heat" if not sure. Plus of course the boiling point rises with pressure; (why tea tastes awful up a mountain - the water's not hot enough). So the more pressure you want (to drive your turbine) the more heat you have to supply.
In terms of feed water (or whatever liquid you're returning to the boilers)... you could use a valve arrangement such that each tube in turn has a part at the top of the tube that can be isolated (you'd only need 1% - 2% of the total volume). Open that valve, and the condensate can literally just trickle in under gravity. Close the inlet valve, open the valve to the main boiler, and already the sudden increase in pressure on the newly-admitted liquid will significantly raise its temperature. Of course now instead of one moving part - the turbine fan - you have many. Valves and camshafts and control systems, and apart from anything else, these all introduce losses into the system.
Another feature to consider is super-heat - a technique where you pass the high-pressure steam back through the boiler which further dries it and adds additional energy. Once again, technology from steam railway locomotive design, that can make a huge difference to performance, especially if you have "spare" heat to provide - which you do, since you can add extra tubes at relatively low cost and with free solar energy to power them.
Regarding the turbine - there HAS to be significant pressure drop across it, otherwise you're not taking out any energy. The whole objective, really, is to maximise that pressure drop (and condensing your steam/vapour in the process is the best way to reduce the volume, and thus pressure).
Overall, though, my doubts are around getting a high enough rate of heating + evaporation to do anything more than light a single LED.
That said, your idea (or a version of it) has already been generating hundreds of megawatts out in the Mojave desert, for many years. But the site takes up hundreds of acres, with a vast array of parabolic reflectors concentrating sunlight onto a boiling vessel that generates steam to power a conventional turbine. In fact I answered a question on Quora about this only a couple of days ago: Quora[^]
You could certainly scale it down, but this installation suggests that you will need to collect a lot more sunlight than your lenses could do.
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You might like to research the Gas Powered Refrigerator. Not "gasoline", but many decades ago (5 or 6 or so), domestic refrigerators that ran on town gas (produced from coal) were available; and much to my amazement, at least here in the UK, they are still available for campers and caravanners.
And of course if nothing else, a refrigerator is a heat pump!
So in principle, an air-to-whatever heat pump should be possible. But as ever, the devil will be in the detail, and most likely the killer will be efficiency. Can you get sufficient quality heat from your thermal collectors as the energy source to replace the gas flame? I have no idea, I'm an electrical engineer.
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BarrRobot wrote: but many decades ago (5 or 6 or so)
Not even new then
The History of the Propane Refrigerator[^]
Choosing a Recreational Vehicle is all about deciding whether to power it with electric or propane. Electric means you need to have an external outlet which usually means a campground with a hook up.
Propane can power everything that electric does. Plus provide a hook up for an external propane grill.
I would be surprised however if you can't get both in one vehicle.
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So it seems to be impossible to create an automation task on the iPhone for certain events unless you manually allow the task to run.
I can automatically send a text message to Phil every day at 4am saying "Wake up, you filthy monkey!", but can't automatically turn on airplane mode when I arrive home. The second one asks me whether to run it and there's no option to disable this. Defeats the purpose of having a stupid automation in the first place. (I don't want to do any of these, just examples)
If you look at all the events that don't allow automatic execution, all are something that are a "security risk" in the sense that you can use them to blow things up remotely. Or something similar.
Am I imagining things or is someone at Apple super paranoid?
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Nope, you're not alone. I work with a guy that has a race tracking app on Android and Apple. In Android, he has a timer and every time the timer goes off, Android gets the GPS, does some math and goes back to sleep. This is great for battery life. On Apple, this isn't possible. The OS will trigger a GPS event when the device has moved an undisclosed amount and the app can receive the update. This means that the OS is sampling GPS fairly often to decide when to kick off the event. Its the best that Apple offers...
Hogan
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Indivara wrote: Am I imagining things or is someone at Apple super paranoid?
You'd think it's your phone, you can do whatever you want with it, right?
People complain when Windows doesn't let them do something they want (or does something they don't want it to), as if it's now Microsoft's computer, not theirs.
iPhones were never theirs to begin with.
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#Worldle #634 2/6 (100%)
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https://worldle.teuteuf.fr
no map needed
"A little time, a little trouble, your better day"
Badfinger
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