Using only rudimentary aluminium casting techniques, is it possible for me to make a mechanical system that causes a large (2m across maybe) parabolic dish to track the sun, without using electrical power?
Also, how easy is it to make solar-powered thermoelectric generators?
a small solar panel, a battery and a linear actuator and levers.
using a solar panel would be cheaper and easier than any other option. although, if you wanted, you could build some kind of complex orrery powered by hamsters or the suffering of mortys.
Even when dealing with extremely concentrated sunlight, is a solar panel superior to a thermoelectric generator?
Pi square metres of sunlight is a lot of energy for a small solar panel to take...
no your problem is that you need power to be input to the system. equal and opposite force. laws of physics here. so one way or another, you need power. a small solar panel say a 40w and battery will give you enough power to shift a parabolic dish across 60 degrees once a day for sun tracking purposes and return to starting position for tomorrow. now what is your dish for? why do you think a small scale thermoelectric generator is better than a solar panel for your application?
I'm thinking that a thermoelectric generator could possibly be more efficient in this instace,I'd have no idea.
Also, this thread is partly to ask if it's possibly to have a purely mechanically powered system, like an old clock through preferrably without a big pendulum.
clocks need to be wound.
I'm sure its possible to do. but you would need a ridiculously large spring to move a 100kg mass back and forth. the pendulum just keeps time. the spring stores the energy.
How can I get an extremely slow and constant-strength release of energy then?
Actually, now that I think about it, if there was some way to charge a mechanical system with the rain, that'd be pretty neat.
a water wheel. geared up ridiculously such that it would need to spin thousands of times in order rotate the dish by even a degree.
catch rain in a tank. have it drop water at a constant rate onto wheel.
>solar-powered thermoelectric generators
You can attach thermoelectric generators (pic related) directly to the back side of solar panels. Just sandwich the thermoelectric generators between the solar panels and heatsinks. This will use the hot solar panels as the heat source for the generators. You'll be converting light into electric and waste heat into electric at the same time.
>TEGs fucking suck.
As a proud owner of some TEGs, I agree. They are just not good for low temp-difference applications. They are pretty good for high temp-differences though. They are fun to play around with at least.
>they are pretty good for high temp-differences
So, might they be superior to solar panels in my case?
Because pi square metres of sunlight is a huge amount of heat, to the point that I might be at risk of melting even a TEG made out of iron (cast iron would possibly be best for a TEG heated by sunlight)
do you actually use them to generate power? because they suck at this. great for if you need a small lab for super low temperatures where a compressor would come at a ridiculous cost though.
>> They are pretty good for high temp-differences though.
No. The efficiency of TEGs is around 5-8%. Stirling engine driven electric generators have attained 32% sunlight conversion efficiency:
>>might they be superior to solar panels
no. The thermal conversion efficiency of TEGs is around 5-8%, solar panels regularly attain sunlight conversion efficiencies of 22%:
>>Because pi square metres of sunlight is a huge amount of heat
it's a shit-ton of heat. Yes you could melt iron, hell you could probably even vaporize it. Whatever you use to convert your sunlight into electricity, you are gonna need to cool it. Like really do some engineering to make sure whatever is in the beam ain't gonna melt.
>>TEG made out of iron (cast iron would possibly be best for a TEG heated by sunlight)
you have got to be fucking kidding me. You gotta use weirdo fucking semiconductors like Bismuth telluride and calcium manganese oxide if you want anywhere close to 5 - 8% efficiency.
You could do it entirely mechanically.
Option 1 is some mechanism that uses prestored information to point at the sun. IE you know today is day 34 of the year and it's time t, therefore dish should be point y.You could probably do this with a barrel cam(cams are insane to design and machine), a really complicated linkage, or hell just have a mechanism that rotates at a constant rate with the sun.
Option 2 is to use feedback to track the sun. Sensing the sun mechanically is interesting, but it can be done. One way to sense the sun mechanically is have a lense that points at the mechanism inside one of those gauge thermometers. If it's pointing at the sun, the sunlight will make it heat up and the gauge will move.
The gauge moving doesn't really have much torque, but lucky for us there's this cool device called a torque amplifier(pic related). It amplifies torque, so we could use the motion of the gauge to trigger other parts of our mechanism. With two of these gauge thermometer things we can make a mechanism that looks at the difference between the two and decides where to point the dish.
This is really fucking complicated, not to mention it'd probably need quite a bit of power.
Now if you aren't averse to using pneumatics, NASA actually investigated making a steampunk satellite in the 60s to study the sun. Essentially they did the mechanical thing above, except they used something called fluidics. Fluidics is using fluids to do pretty much the same stuff electronics does, in place of electrons you have fluid, in place of transistors you have fluidic amplifiers. Cool thing about fluidics is it can work in extreme conditions. Fluidics doesn't care if it's inside a nuclear reactor or so hot it's glowing.
So what they did to sense the sun is they had a lens shine on two bolometers. These perform the same function as our gages in the above, they get hot in sunlight and we get a signal out. Bolometers are coils of tubing you pass fluid through, when light shines on the bolometer, the fluid inside the tubes heats up and decreases in viscosity, so the 'resistance' of the bolometer decreases. By comparing the output from the two bolometers and amplifying it into thruster/reaction wheel output the people at NASA were able to make a simple system that would make a satellite point at the sun purely mechanically(pic and link related)
Of course you still need a prime mover, that could be done with stored energy IE you wind the thing up, external energy sources like wind or water, using some of your sunlight to drive a heat engine(stirling engine, steam engine, etc)
I was wondering if there was a way to mechanically sense the sun, so it's interesting that you've actually described one.
It's all a bit confusing though, and it certainly doesn't sound easy to get one that is able to figure out where the sun is and then point to it.
No, it isn't very good for stuff like that. You'd need too many to get the amount of energy you wanted. I still think a Stirling Engine would be the best thing. Those things go up to 10kwh for solar power without a problem.
They are okay for refrigeration in tiny tight spaces. But, it is contact cold, the object you chill needs to touch it as much as it can.
You need to check out the datasheet of any TEG to find out their temperature tolerances.
For the size of a TEG they are good for stuff that needs to be very light and/or small. Like camp rechargers for phones. For electric, they are best used as energy savaging devices than for high-output electrical generators.
>have it drop water at a constant rate onto wheel
not gonna happen, its pretty much impossible to have something drip at an constant rate because the volume thus the presuer will decrease
I am a bit autistic, and I really like fluidics and torque amplifier so there might be a simpler way to do it. This crazy thing might be one of them:
>> its pretty much impossible to have something drip at an constant rate
the ancient greeks would like to have a word with you:
I was thinking of the same thing only using low temp-melt wax. Similar to those auto-opening, wax-filled hydraulic arms used to open/close greenhouse windows.
>I am a bit autistic, and I really like fluidics and torque amplifier so there might be a simpler way to do it. This crazy thing might be one of them:
there is two problems with this:
,,,the hydraulic cylinder is going to leak. also would have a lot of stiction
,,,in the US at least, you can't get freon cheap anymore, or anything else that would work like it at the same (low) pressures. All those plans are from the 1970's, did you notice?
there used to be a way that used four tanks and no cylinder.
each side had a tank that was mostly liquid and that was connected to another tank that was mostly vapor.
I can't recall how it was all hooked up tho. I never had one or saw one IRL.... :|
the solar panels were fixed at the angle necessary for your lattitude, and then the freon parts of it tilted them left-and-right properly.
I would use an arduino, myself
balance the moving part well so it doesn't take much force to tilt it
forget the sun-sensing part of it, just use a clock module and have a table of angles for the time of day
make it so that it would only move every 5 minutes or so
Arduino is the boring option though.
By the way, since this is going to be focusing a concentrated beam of sunlight, I could possibly use the pressure of expanding metal to tilt the dish instead since the beam being slightly off will cause the wrong thing to be massively heated.
Unfortunately, while the expanding metal should give me enormous pressure, I can't figure out a good way to make it tilt the dish since it'll only expand slightly.
Actually, on that note, I can't figure out a good way to get the concentrated sunlight to go in a beam that is in one place and pointing straight down. If I use a mirror that is vertical when the dish is vertical and at 45' when the dish is at 90', that works perfectly when the dish is heavily tilted, but when the dish is pointing nearly straight up some angled light will miss the mirror entirely.
And I have the opposite problem if I use a convex lens, where if the dish is at a heavy angle
Maybe I can somehow use a prism for this...
>Arduino is the boring option though.
Yea but it would work. And the most complicated part of it (the arduino) costs $3 from China. The actuator would cost a bit but if you keep it dry it shouldn't wear out any time soon.
I've never seen any of these things that were non-electric, totally-self-powered and that used anything other than Freon.
>Actually, on that note, I can't figure out a good way to get the concentrated sunlight to go in a beam that is in one place and pointing straight down.
Well no shit........ If you could do that, you wouldn't need to automatically tilt anything, Nigerian.
Look OP, I think you are trying to do too much at once. I think you are gonna have a hard enough time making a 2 m parabolic dish and generator system. Why don't you get a small version without automatic sun tracking working first?
You are probably gonna have a hard enough time getting your electrical generation stuff to work. It can be difficult to make stuff like this not melt.
Some friends of mine tried doing something similar with a fresnel lense and a kit stirling engine. It worked great until the stirling engine melted. You really gotta do the math on the heat flow to make sure it's not going to melt.
I would still need to automatically tilt stuff, but what I mean is that if I have the dish face the sun, reflecting light into a smaller dish that reflects light back through a hole in the larger dish, I've got a beam that I've made through automatically tilting stuff and yet I've still got the problem of getting the final beam to stay in one place.
>I would still need to automatically tilt stuff, but what I mean is that if I have the dish face the sun, reflecting light into a smaller dish that reflects light back through a hole in the larger dish, I've got a beam that I've made through automatically tilting stuff and yet I've still got the problem of getting the final beam to stay in one place.
Go look for information on "fixed eyepiece telescopes". There is a bunch of ways to do this.
Most involve fixing the east-west rotation axis at the proper angle for the latitude you are located at, and then the optical image (or rather--the beam you want) is produced on that axis.