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New Idea: Parabolic Trough + Fresnel Lens!

Posted by sterlanator on June 15, 2011

I’ve been having a debate with myself over the last week (as well as being super busy with my sister’s wedding) and I have finally reached a conclusion!  My main problem has been deciding between using my free fresnel lens or paying more to build a parabolic trough.  They each have pros and cons, which I will outline below.  Then, after hours of researching which would be better I struck gold!  Why not do what one person did and use both?  Well, that’s just too smart for me haha!

Comparison of Devices

Parabolic troughs and fresnel lenses are very similar in purpose but they have differences when it comes to our desired uses.  A parabolic trough setup requires more work to build as you need to create a parabola whereas a fresnel lens only requires constructing a simple tilting frame.

Parabolic Trough

  • Requires precision labor to create and setup
  • Has evenly distributed heat to a line of pipe
  • Heats pipe up to (and maybe over) 500*F efficiently
  • Doesn’t require much movement for solar tracking (pivoting around pipe is all)
  • Heats under the pipe based on reflections
  • Effective unit may take up to 10ft x 3ft space or more

Fresnel Lens

  • Requires basic woodworking skills to create pivoting stand
  • Focuses heat to a center line (or small linear area for liner lenses)
  • Superheats pipe to over 1000*F effectively (depends on lens, apparently)
  • Requires more creativity or more movement to incorporate solar tracking
  • Heats over the pipe based on magnification
  • Effective unit may take up to 2ft x 3ft (62in. screen)

The big battle I was having was the difference between heating on top of the pipe vs. under the pipe as well as the focal length vs. spot focusing.  Again, thanks to another researcher with creative intellect, he merged the two ideas into one system that seems obviously simple!  What he does first is heat the water to about 130*F with a solar collector setup (not exactly a parabolic trough, but similar) and then the hot liquid gets sent to a 62″ fresnel lens that superheats the hot liquid into steam almost instantly.  This steam goes to a turbine (not a tesla, sorry peeps) that spins a generator and then back to the collector to heat up again.

So here’s my idea: have a parabolic trough, say 5 ft in length, heat the water to boiling state or almost boiling, whatever it will put out.  When I created my 2x3ft parabolic trough that bad boy made the water scalding hot, but it didn’t have enough umph to boil it for a while.  A 5ft trough should do it to create really hot water, if not low pressure steam.  Then when it goes through the system and gets zapped by the fresnel lens’ instantaneous 1000+*F, the steam superheats and has much more pressure right before entering the turbine.  More pressure, better functionality, more power output, and thus more power generated.

Since I still have the materials (just not the cardboard box) from my mini parabolic trough and I have a gigantic fresnel lens, I’m going to see if I can get this water to boil!  Stay tuned, I’ll have to recreate my parabolic trough as well as frame my lens so I don’t have to hold it still for a long period of time.

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Great Status Update!! Fresnel Lens, CD Turbine, and More!

Posted by sterlanator on June 4, 2011

Good morning everyone!!  I have been busy at work this week working on so much stuff and had to put my project on pause.  However, these last couple days I was able to kick start my project and bring it back to life.  So what did I do?  Well, first off I went to my local Home Depot and bought a few supplies to finish the bare bones of my tesla turbine CD generator.  Second, I was graciously donated a 62″ DLP TV from a nice man on craigslist so I could use it for the project.

The CD Turbine Status

My CD tesla turbine is coming along quite nicely!  It still doesn’t have an enclosure, but as I am typing I just got another idea for what I could temporarily use or try.  But first, let me tell you my status on it.  Like I mentioned above, I was traveling around Home Depot with my CD turbine in hand (just the CDs drilled and bolted together) in search of a worthy and cheap shaft (remember my $400 budget!) for the cause, as well as some nozzles and bearings (or something close) and an enclosure.  The staff was all over me like a pack of wolves on fresh meat, especially after I found some threaded 5/8″ rod that screwed on perfectly to my turbine for a shaft without any modification.  As I wold walk around the store and brainstorm, workers and other customers were asking me “Woah, what’s that!” and other fun phrases that helped me to introduce a tesla turbine over and over again.  It felt good to be a local celebrity for once haha!  Anyway, back on topic.

While I was there I upgraded my 5/8″ threaded rod idea to just a 8″ 5/8″ partially threaded bolt, which was much cheaper and I wouldn’t have to cut it up.  Bonus!  Also, I got myself some 1/2″ copper bushings because unfortunately, they don’t sell bearings at the store.  Total cost was $3 for the parts, woot woot!  I pieced it together real fast, and for testing purposes, cut up a piece of cardboard and made a basic holder for my glorious turbine.  I have yet to test it since I need an air hose spray nozzle, frankly because breathing to make it go isn’t enough to make it budge.😦

What’s the DLP TV For?

The TV was a sight for sore eyes!  After trial and error of trying to get my small parabolic trough to effectively turn my water into steam and only getting hot water, I sadly had to chuck the cardboard box that made the trough because my wife said it was cluttering the house.  Good thing she let me keep the reflective material, just in case I need it again!  With a fresh start, I started looking into building a larger trough, which would mean more money to spend.  I didn’t like that idea, so then I remembered about a fresnel lens doing the trick!  These are basically sheet plastic cut specially to focus into a fine point like a really, really big magnifying glass.

I hit the internet searching far and wide for where I could obtain such lens for cheap, if not free.  Things weren’t looking too promising at upwards of $100 for a square meter, but then I heard that they are stored in old rear-projection and DLP TVs!!  Hallelujah!!  Then came the freebie search on my local craigslist and I couldn’t have been on any better timing; someone was giving away their electrically dead 62″ TV!  What’s better is they lived nearby, double score!  So I grabbed the TV last night and headed home, taking it apart this morning.  It’s pretty easy to do, making mostly for just tons of screws to remove.  Here is a video I found on YouTube of a man taking his out of his similar TV.

I didn’t play around with it too much as I thought it was time to update my blog!  But when I finished, I tested the power on some nearby ants.  Sure enough, this gargantuan magnifying glass zapped each ant I touched almost instantly!  This should be perfect for solar water boiling if I can just figure out a solar tracking system to make for it.

Total Cost Summary

Okay, so here’s a breakdown of where I’m at so far.  I have the DC motors, a 62″ wide fresnel lens, an almost complete CD tesla turbine, loads of research, and some copper pipe.  The total cost after today has been a whopping $21, keeping me well within my $400 budget for the rest of the system.  Pretty much all I need at this point is a solar tracking setup (cheap to build), a container for the water to boil in, some more pipe and tubing, a radiator for cooling, and a legit stainless steel or aluminum tesla turbine (the CD one is only for temporary R&D and would melt instantly with steam contact).  I’m probably going to have to splurge on getting the final turbine laser or water jet cut by professionals to maintain precision, but that should only be about $150 of the total cost and it would last a very, very long time.

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Awesome Tesla Turbine Research to Read!!

Posted by sterlanator on May 25, 2011

Hey everyone!  So my paper turbine got smashed the other day (note: do not leave paper turbines on the ground, oops!) so I’ve been trying to build a CD turbine now that I’ve learned what I could from my easy paper project.  The main thing I learned was that the disks, if not spaced apart with spacers or affixed to a shaft, will naturally force themselves together so the thickness is *assumed* the desired thickness for the boundary layer effect to efficiently take place!  This means that spacers *may* not be a requirement, but for that to be true we can’t have the disks connected to a shaft, which means there’s no usable power output.  So I guess toss that idea in the trash…

So my CD turbine is pretty much on hold until I can recharge my power drill and finish the holes I’ve been drilling, otherwise it’s only got two outlet holes on 8 disks.  Better than nothing!  It can’t spin on breathing through a straw or pen like my paper turbine did, but that’s just because it’s heavier and harder to turn, meaning it needs more force to get started.  However, when I spin the turbine and then start blowing, it will maintain it’s momentum pretty well even without bearings yet.

Now to more research that I found today!  Thanks to a very generous group writing a very detailed report on various options a tesla turbine may include, I am now looking into adding three more gas inlets, totalling 4 to gain the highest torque and efficiency from my turbine.  Again, I want to emphasize that I believe torque is the most important factor in our tesla turbine Organic Rankine Cycle (ORC) application.  That’s just another fancy word I found on the internet for the solar thermal parabolic trough setup I am planning on making, by the way.

Another note of the document that Versita Publications printed is that their R&D shows that the tesla turbine generates power almost linearly with the increase in pressure (aka. mass flow rate).  What does this mean for us?  As we increase the temperature of the water vapor (steam) in the parabolic trough, we increase the steam pressure exponentially.  A slight increase in temperature will cause an exponential growth in steam pressure, meaning more and more inlet pressure is going to the turbine, which means more and more electric generation.  Long story short, the sun is working a little bit harder to provide more umph to our generator; go sun, go!

If you’re pretty savvy with math or even would like to look at fun, colorful pictures I would highly recommend you have a look at the document that I’m referencing to in this post.  If you haven’t clicked any of the links above quite yet, be sure to click the one found here: http://versita.metapress.com/content/l9vx5nn573458241/fulltext.pdf

Keep on working on those ORC turbine setups!

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Tesla Turbines From Paper? No way!!

Posted by sterlanator on May 17, 2011

Good morning!  After my brain-pounding post about how a tesla turbine is properly constructed, I decided to start experimenting with different turbine ideas.  Luckily for me, the local Wal-Mart has a ton of free NetZero CDs, so I was in post-AOL heaven!  Of course I had myself to a free trial CD or two which gave me enough to test a simple CD turbine.  Unfortunately, my power drill died last night drilling all the holes so I’m waiting for it to charge back up before I finish my CD turbine.  In the mean time, I’ve got plenty of NetZero card stock that I just don’t want to throw away, so it’s paper turbine time!

Last night I hacked away at some makeshift disks 2.5″ in diameter (thanks to a hard drive platter stencil) and started building!  Thanks to Tesla and the boundary layer effect, a tesla turbine can be made of virtually any material, including paper or card stock.  Basically the turbine I made has 8 disks and is glued to a thin piece of coat hanger wire as the shaft and is powered by a bicycle pump going to some water bottle storage tanks and then the inlet hose.  It helps to see how the turbine works and allows me to experiment with different varieties of disk combinations, input pressures, and other fun little things to experiment with.  It helps to have a tesla turbine period than non at all!

I also plan to change the shaft out to an empty pen ink tube and connect it directly to an RC car motor (I knew my xmod was good for something) so I can get some juice out of it.  This will help me see how a tesla turbine reacts to a load and other variables that will be helpful in the final construction.

Unfortunately, I went to ACE Hardware and purchased some screws, washers, and tubing for the setup as well as for the CD turbine setup, so I’m $6 more into my $400 budget; now I have spent $21, oh my!

Stay tuned and I’ll make some videos of tests that I believe will help everyone with load variations and other things like that.  Also, I spoke to the renouned AOL CD turbine creator and he told me to research labrynth seals for the final turbine to help seal the air better with a load on the turbine.  Now to reaserch and more development of small turbines!🙂

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Tackling the Tesla Turbine! What Are We Doing?

Posted by sterlanator on May 12, 2011

Good morning everyone!  I’ve been spending the last few days doing very in-depth research on the design of an efficient tesla turbine, and I’ve come to share my results thus far!  To be honest, I never knew a tesla turbine could be so complicated and advanced even though there are few moving parts and construction seems so simple.  However, do not be fooled!  For this turbine to have descent torque, high horsepower, and obtain efficiency up to Tesla’s claimed 95%, this turbine requires an engineer’s intellect to be properly calibrated to the most fine detail and precision.  Anyway, I hope I don’t blow your mind and I provide enough sources to appease the wiki readers!🙂

Three Main Factors

The most important thing to keep in mind on building a tesla turbine is the fact that we know something is important on it, but what?  Well, I went out seeking an answer to this trivial question and it seems that there are three main factors in obtaining the best torque and horsepower ratio: inlet nozzle size and configuration, disk spacing and geometry, and outlet nozzle sizing. With these three factors in mind, we can build a tesla turbine that is not only extremely efficient, but we can also fine-tune for the need of more torque or higher horsepower, similar to an automobile engine.  Some experts say to work backwards from the outlet nozzle size to the disk configuration and then the inlet nozzle, but others say the reverse while some don’t care which comes first, the chicken or the egg!  With that in mind, I will list what I have learned in respective order to how the system flows and let you decide from there.

Inlet Nozzle Configuration

The most important part about the inlet nozzle or hose is that it can deliver a high-powered jet stream directly to the gaps in the turbine.  This part is tricky because to get proper distribution to the plates’ spacing inside the casing, there much be quite a few little holes to jet the pressurized whatever in between the plates.  The key here is the more precise, the higher the efficiency.  One thing to focus on with this then is to make sure the plates do not move side to side once positioned in the casing.  If they move even 1mm from the lining on the preset holes, the overall efficiency will decrease since gas has to bounce off the top of the plate (even though it’s thin) and then flow back through the gaps, causing that loss in efficiency.  Just how much of a loss is this?  Well, that part is still unsure but I aim to test the theory and punch numbers for everyone to know once this project is finished!  It may be astronomical, it may be miniscule to bother precision tuning.

Another key factor to consider with the inlet nozzle is the form of the nozzle to provide both a high-pressure boost.  For example, if you try to smash 40psi coming from a one inch diameter hose into a 0.1 inch diameter hole, the 40psi will be amplified up to, if not faster than, the speed of sound!  This is the theory of compression at work, costing you virtually nothing.  But to get such high compression from such a small inlet, you have to consider durability over time.  What will handle the 400psi at the tip of the nozzle?  The first thing that comes to my mind is a copper fitting, mainly because copper can withstand hundreds of psi just on the tubing itself!

And now for the actual design of the nozzle.  Fortunately, for us there are a variety of input nozzle configurations that we can choose, but one stands out from the rest.  It is similar to an old calligraphy pen shape, which is also called a traditional convergent-divergent nozzle.  The convergent (compressing) part in the figure below is “A” where the pressurized gas gets squeezed through point “d” (diameter) and then goes to the divergent (expanding) part to get un-scrambled.  After that, it forces itself back into the parallel section of the nozzle to straighten the flow of the gas for direct injection into the turbine.

This nozzle seems difficult to manufacture for some, so a simpler model was designed which achieves the same effect.  Below is an example of what it looks like.  NOTE: The same calculations from above must be followed!


Disk Geometry and Spacing

The next thing we need to consider is the size of our disks or platters and their construction, mainly focusing on spacing.  Before we choose a material for our excited platters, we have to ask ourselves a few questions.  First, how fast do we want the turbine spinning and which materials will handle that consistently?  Second, what disk spacing would be optimal for our specific use and psi rating (believe it or not, there’s an equation for that)?  Then finally (from my research so far), what design should I cut onto the disks for the exhaust holes?  The last part I have yet to research in depth as there is much speculation on various groove designs.

Nicola Tesla was a genius when he invented the tesla turbine.  Whether he intended for it or not, he allows for as much customization on his turbine as iPhone has apps for, maybe even more!  If you want more torque, you just have to squeeze the disks closer together.  If it’s horsepower you want, make the disks a smidgin’ larger.  Every little thing you do to the platters used in your turbine will affect efficiency, torque, and horsepower.  As far as disc materials go, you could use almost anything as long as it holds up to some air pressure (you would have to use appropriate liquid-resistant materials for liquid pressure, of course).  Common household items such as CDs, hard drive platters (now my original post makes sense, huh?), and even cardboard could be used to fabricate the sophisticated device!  These options only require that your material hold up to the elements of durability and longevity that you desire it run with.  For example, cardboard is not a smart option for a steam-powered turbine because cardboard swells in water.  However, aluminum or CDs would work well for testing purposes, but stainless steel would probably be best for the final product once all calculations and revisions are made.

Torque is the rate or force at which something can increase its speed at an instant.  To put it simply, if a young child tries to twist your arm (aka. Indian rug burn) there isn’t much heat generated because they can’t apply as much “twist” in one instant.  However, if a grown weight lifter were to twist your same arm, he has so much instantaneous force that it might snap your limb in two!  This is a very simple demonstration of torque and how it applies to the real world.  So how does that affect a tesla turbine?  If we don’t have enough torque to turn the turbine when it’s connected to a generating motor, the system won’t spin and we generate a whopping 0 watts!  However, if we have enough torque to start the system from a stop then our generator will be able to accelerate as the day goes.  So how do we adjust torque?  There are a variety of ways for the tesla turbine, but the key focus is gapping between the plates.  There is a dispute over how much space you really need in a tesla turbine, but one user came up with a calculation to provide the most efficient spacing for a turbine.  Remember, the shorter the gap, the more torque we generate!

Formula for disk spacing: 1376 x (Kinematic viscosity / RPM), Kinematic viscosity being in square feet per second (sq. ft./sec.)

From what I know, you just kind of wing it for the RPM you are aiming for.  For example, my DC motors spin at about 2700RPM and 3250RPM if I remember right, meaning if I did a direct connect to the turbine for one I would be shooting for about that much.  The tesla turbine is meant to spin at crazy high RPMs (over 20,000RPM) so I will probably need to gear and belt the setup to run both motors at once.  As you can tell, the higher the RPM the closer you can put the disks.  For the author of the article I found, he had his disks around .017″ apart, meaning 1/5 the thickness of a CD (super thin!).  Anything more than your ideal range is just lost efficiency because air just exits without being used.  The viscosity for the liquid you want to use can be found through researching it.  Here is an example of the formula in action:

Water in steam form has a kinematic viscosity of 0.317sq. ft./sec. and I will be using steam to power my turbine.  I want it to spin at around 25,000RPM so I would plug it in like this: 1376 x (0.317 / 25,000) = 0.01745″, so I need a really thin washer between each plate for maximum efficiency.

Exhaust Valve Construction

Finally, the third element we need to consider with our tesla turbine!  After all that crazy math and science above, now we are somewhere short and sweet.  From what I know now, the exhaust port size will vary three variables: torque, horsepower, and efficiency.  Sounds familiar, right?  Well it’s much like the inlet nozzle except for the fact that it’s not so complicated…yet.  The rule of thumb is that the larger the turbine exhaust port, the more torque and horsepower is achieved, but the lower the efficiency.  The goal here is to keep the exhaust port in proportion to work effectively and help boost efficiency to the system.  That’s it!🙂

Congratulations, you passed the boring math of the technical aspects involved in making a tesla turbine!  I didn’t think there would be so much math involved until I dove into research, but I’m glad I did because now my solar thermal tesla turbine will be much more efficient than it originally would have been!  Now we get to the fun part, looking at pictures!  Here are a few different designs and materials that people use to create their ferocious turbines.

AOL CD Tesla Turbine – wouldn’t you like your internet to be that fast?

Hard Drive Platter Tesla Turbine – overclock your hard drives!

Hard Core Tesla Turbine – so beefy it will blow your socks off!

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Solar Trackers: Buy, Build, or Use At All?

Posted by sterlanator on May 9, 2011

Here’s an idea that I have been researching today: whether or not a solar tracker is worthwhile for my system.  If you know anything about how a solar tracking system works, you’re probably jumping off your seat screaming “Do it, do it, do it!”  For everyone else, you may or may not know but a solar tracker is one of those things that you’ll want to add to your system, whether solar panels or solar thermal (solar anything, really).

Now that we have that part out of the way, what is a solar tracker and what does it do anyway?  Well, it’s put simply in the title; it tracks the sun!  This ensures that the optimum amount of energy is being gathered by whatever your solar array is (in my case, solar thermal) to make your system even more efficient.  Let me give you an example of how this works.  A sensor (think of a small solar panel) says to itself “Hey, it’s the sun rising from the East, I like that!” and tells a motor to move all the solar panels (in my case, it will be a parabolic trough) to face directly against the sun.  Ooohhh yeah, those panels enjoy the warmth.  However, as the day goes, the sun decides to run away from the panels, but the little sensor is wise.  When the sun moves, the sensor keeps telling the motor to nudge all the panels on the line a little more so they all receive maximum exposure to the sun’s heating rays.  Once the day is over and the sun disappears over the west horizon, the sensor either says to go back to East or to sit tight in West until tomorrow morning, depending on the system you have.

There you have it, a solar tracker’s daily routine!  All it does it stay right under the sun each and every day so the solar panels or parabolic trough get their maximum efficiency.  So how much does this thing cost?  Well, it could either be a few dollars if you have insane soldering skills and a PCB board to play with, to a few hundred dollars if you really think the marketing of the shiny device in a box is better than the cheaper “generic” model.  Fortunately, my goal is to be cheap but I don’t have easy access to a PCB board, so I’ll help you choose easily but effectively.

The model I have my eyes set on so far comes from one of two ideas.  The first uses two small solar panels to counteract each other, turning a small motor as the day goes by, one tiny nudge at a time.  This way there is no power required to turn the motor because it comes from the solar panels, but the problem lies there as well; to power a larger motor, larger solar panels must be used.  Also, once it hits night and the sun comes back in the East the next day, the solar panels are stuck facing West because they cannot “see” the sun.  This is fixed with a mirror facing against them though, which also takes up space.

The second idea that I have for a solar tracking device is much more compact and user-friendly, but costs a little more to buy (you can build it if you have a PCB board and soldering skills for a few bucks).  This method is similar to the first but instead of solar panels, it uses 2-4 LED lights on a circuit board to determine where the sun is shining.  This setup can cost up to $70 depending how fancy you get, but even the basic $30 model purchased will push a fairly large motor up to 10A if I remember correctly.  This will serve plenty of purpose for me, so I’ll take it!  The nice part is that when the sun sets and rises the next day, the 4 LEDs will still be in the same spot and the far East sensing LED will turn the motor so the solar panels or parabolic trough faces the proper direction and angle.  Reports are saying that these little 4-sensor setups can be effective as 0.7 degrees off from the sun, incredible!  This will yield up to 50% efficiency increase for solar panels and who knows how much more heat and steam production for parabolic trough users.

For me, the LED tracker is the route I will choose.  This will let me buy a cheap DC motor to hookup to the sensor, plant the sensors under a jar or some waterproof container, and let the system fly!  I may attempt doing this without a circuit board (pretty much hanging wires all over, but protected of course!) first so that I can create a cheaper setup, since parts for the whole thing are only a few bucks.  Stay tuned, this will be later down the road once the whole system is complete!

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Garage Sale… SUCCESS!!! DC Motors Achieved!

Posted by sterlanator on May 7, 2011

Guess what! Today, my wife and I went garage sale shopping for some DC motors from treadmills, fans, and other random junk people were selling. Unfortunately, we didn’t have success at the initial garage sales themselves, too many people were selling clothes and furniture this time around… lame. However, I posted an ad looking to buy a DC motor from a treadmill (sources say they are high HP and low cost) and someone called immediately after and said he had not one, but TWO motors from treadmills in almost new condition he would sell! Well heck, for $10 each you can’t pass that up, especially since they were already ripped out of the treadmills.

When I went to meet him, he showed me the two 2HP motors. Man, were they just what I was looking for!! The nice part about these ones is they both have a flywheel to help the inertial of the motor once it’s going, but they are removable with set screws so I’ll have to test efficiency with and without them. With two motors, I’m going to have to build a larger turbine, but hey, at least I can connect the two generators and the tesla turbine together on a belt to have both generate electricity!

Remember, 1HP = 734w of electricity, so 4HP total would be 2936w, or 2.93kw of energy. That’s assuming full speed production, of course. Below are some pictures of the motors so you can see them in real life🙂

Sorry this picture is so blurry, the camera couldn’t focus on the shiny metal label

The guy who sold these to me was super nice, offering to sell both to me for just $10!  The nice part is that earlier today I sold the scrap laundry dryer (minus the motor, of course) for the $10 I bought it for.  Let’s take a look at total project cost now:

  • Clothes Dryer AC Motor – FREE (sold dryer for $10 and kept motor)
  • 2x Treadmill DC Motors – $10
  • Reflective Poster Board – $4.50
  • Other materials for parabolic trough – FREE
  • Total Cost so far = $14.50!!
Would you look at that!  I’m still about $15 into my budget and I have 3 motors now, two DC and 1 AC.  What will I do with the AC motor?  Probably sell it to go negative into my project cost, I’m not quite sure.  I spoke with my local electric provider and they said they prefer a DC to AC grid tie inverter setup and not to use the AC motor.  This means time to sell!

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Part One Complete! The Parabolic Trough is Alive!!

Posted by sterlanator on May 6, 2011

Good morning everyone, I have great news! My small-scale parabolic trough is now up and running efficiently! It was a pretty easy setup once I got the idea to use coat hangers to “stiffen up” the drooping sides of the poster board, and I’ll have pictures on later today or tomorrow (my battery was dead). Here’s a nutshell of how the setup looks though, drawn in MS Paint quickly🙂

Note that the reflective poster board’s length is a little longer than the cardboard box, so when it’s lying down it takes the form of the parabolic shape.  The coat hangers that are attached to the box are there to hold the copper pipe in place at the focal point.

This setup is quick to build, easy to set up, and even allows for quick disassembly giving it some portability.  Based on the assumption that 1 sq. meter of reflective material is 1kw of solar energy, this setup outputs exactly 2kw of solar energy.  When I was finding the focal point of the parabolic dish (to verify it was the same on my stencil paper) my hand heated up to burning in just a few seconds!  I would say that’s sufficient enough for my testing purposes.

I slid the copper pipe into the coat hangers and let it sit angled at the afternoon sun for about 10 minutes.  When I came back to see how the pipe heated, I could barely hold it, ouch!!  So be careful and wear cooking mitts if you want, that got pretty hot really fast.  Just imagine the complete setup with a DIY solar tracker to follow the sun all day, man it’s going to get hot!  If 212*F boils water, this parabolic trough will do just the trick.🙂

UPDATE: Here are a couple pictures of the trough!

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Random Thought: Using A Bicycle to Turbo Boost Your Home!

Posted by sterlanator on May 5, 2011

Think of this: you jump on your bike for a nice workout and while biking, your electric bill is going down. Okay, okay, so the idea isn’t very new and it isn’t exactly practical, but for testing purposes I think I might do it!

Why would I attempt such a random project? To put it simply, I want to test my DC motor (which I will find at a garage sale Saturday) and make sure it generates and generates well. Also, I want to make sure that the only few connections I need for DC to AC grid power are the DC motor, wiring, and the AC grid tie inverter (GTI). If this is the case, then I’ve got the electrical connection part down! Instead of the bicycle wheel turning the motor, it would be the tesla turbine. Instead of me spinning the bike wheel, it would be the steam heat from the sun.

See how it all comes together so simply? Stay tuned and I’m going to dust off my bike, hookup a DC motor to the rear wheel, and get myself a GTI to connect to the wall outlet. In theory, if it works (which it should) then the meter should spin slower, or even go in reverse *gasp*! From some small research, a human can produce up to 300w on a bike, but not for longer than about half an hour. For the sake of testing, I’m going to hit the bike as hard as I can to see that meter slow down for just a few minutes to prove my point!

Stay tuned for a video providing my demonstration and bike concoction! I still need to buy a GTI, so it’s not going to be right away sadly…

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Why Choose A Parabolic Trough for Solar Thermal Power?

Posted by sterlanator on May 4, 2011

When it comes down to choosing a shape and design for a solar reflector, there are two main contestants.  One could choose the circular or dish-shaped reflector, which is precise and focuses a lot of energy on one point.  This type of dish is efficient for things like solar cooking or the need to burn the heck out of one particular spot.  However, for solar thermal energy, this style is tough because at the focal point (aka. the focus) there needs to be a container for the fluid.  One idea I had for this was to get a small steel block (or other high-heat absorbant metal) and wrap copper around its outside, so the copper is heated from the block.  This would lose some efficiency just from thermal transfer, plus making all that sounds expensive and you would have to have a nice pump to return the liquid back to be re-steamed.  I threw this idea out pretty fast.

The more cost-friendly option and one that made more sense to me was the parabolic trough.  Essentially it’s one piece of reflective sheet that’s bent like a long parabola and has the tube run throughout the length of the trough, giving full coverage of heat and minimal thermal loss.  With this, the liquid heats up at the beginning of the trough’s tubing and continues to turn into steam and get hotter throughout the trough’s tubing.  The more the liquid heats, the more compression you will get, which means the faster the turbine will run, ultimately leading to a better producing generator and more electricity output.  Long story short, the trough is more efficient and way easier to make.

The key of making any parabolic anything is precision: the more accurate and finite the focus of heat, the higher quality heat transfer you will get out.  Think of a magnifying glass to a small ant, for example.  When the magnifying dot from the sun is really really small, like a pin point, the ant will wither away in seconds.  However, if the light isn’t focused and is the size of, say, a dime, the ant will wonder why it feels hot and move on with life.  Cooking the ant in the first situation is easy breezy, but the second requires the ant to sit there for a long period of time, and even then it may not disintegrate.

The nice thing about a parabolic trough setup is that if you have some sort of flexible material or sheet, gravity will do all the hard work for you.  Once you have calculated the desired parabolic shape, cut out a stencil on cardboard and start cutting supports to hold your reflective material!  Once you’re done, place the material on top and voila!  Instant parabolic trough.  The most important part is making a hole on the convex part of the stencil where the focus will be.  Doing so will make finding the best focus much easier, as you just have to slide your copper tube through a few holes and you’re done!

What kind of parabola works best?  Thanks to the folks at another solar blog for cooking, a focal point of 2/3 the height of the parabola works best for ultimate wind resistance, reflection, etc.  Too high and wind will cool the pipe down, too low and you will only get a few hours of sunlight thanks to the trough shadowing itself and the pipe.  Another great rule of thumb is that for every square meter (3 square feet here in America) you will get 1kw of solar energy.  Now, from what I know a home uses an average of 16-20kwh of energy a day, so after energy losses we’re looking at about 4-5 meters of reflective material to get 2kwh for 10 hours of the day out.

A parabolic trough doesn’t have to be huge.  After calculating, I’m actually planning to have my whole system to power the house take up a 10ft x 10ft area, or 100 square feet.  The trough will take up most of that space, being 10ft x 3ft, or 10 square meters, which is an ideal output of 10kw of solar energy.  After energy loss, I’m hoping for 4kw of energy being pumped into the grid and assuming peak efficiency with a 10-hour day of sun, that would be a whopping 40kwh!  That’s enough energy to power two homes, let alone one!  Of course, that’s strictly math and some guessing, so don’t quote me on that with my finished product.

Here is a video showing the construction of a parabolic trough in 20 minutes using basic materials:

 The reflective part of parabolic troughs can be made out of many varieties of material.  Since I was cost-concious on a small-scale model, I stuck with reflective mirror-like poster board found at my local Michael’s.  However, That was almost $5 for 6 square feet (2 sq. m) and would not last rain, let alone many other elements.  Other materials that I have researched to be used include anything that it reflective or mirror-like, including:

  • Mirror or reflective mylar sheet (the thicker, the better)
  • Aluminum foil (don’t recommend, I first tried this and it crumbles too easily, thus killing the focus point)
  • Chrome vinyl or “adhesive decal” sheet (works great attached to plastic, according to one source)
  • High-polished aluminum sheet (I believe the finish is called #8 or mirror)
  • Mirror finish stainless steel sheet (this one’s expensive, but should last for a loooong time)
  • Again, anything reflective at least 90% should work, it’s all about durability!

Feel free to be creative!  Reply with what materials you have used and pictures of the setup, if possible.  Let’s expand our options to save money and produce cheap energy!

Posted in How To | Tagged: , , | 1 Comment »


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