Mini solar tower (ver. 4) powered by fresnel lens

[Prontest]

why not boil water with the fresnel and use that to capture the power? steam engines are simple and used for solar, nuclear and fossil fuel to convert heat to power. using air is difficult and likely not to efficient. still its fun to do things in a round about way lol i do similar things and its a good way to keep busy.

[RimstarOrg]

@Prontest I figured with an estimated 600 watts of sunlight input that I'd get at least 5 or 10 watts out. Didn't expect it to be as inefficient as it was. And since steam had already been done many times... Oh well, I learned a lot from it anyway.

[RimstarOrg]

The video for version 5 of the mini solar tower is now available! See the end of the above video or the description below it.

[andodesign]

your right rifling is counter productive. In australia keeping cool is paramount. A house i saw recently used a trombe wall to our S.W (our worst aspect) with 4 passive exhaust fans atop. The idea i feel was limited in its application however. Using your ideas combined with a deeper trombe wall ie greater air volume, using linear fresnel paneling (cost??) and channeling the hot air into a restricted exhaust cavity could be used to turn energy producing fan blades. looking forward to next chat

[andodesign]

omg those formulas look very scary! But i understand that rifling would be counter productive. I live in Australia where keeping cool is important and using passive means even more so. I have seen a house that dedicates a trombe wall to the S.W (our worst aspect) atop of this they placed 4 passive exhaust fans. The idea is there but limited in its application i feel. Using your techniques, increasing the cavity of the trombe wall ie greater air volume and an array of linear fresnel lens panels

[RimstarOrg]

@andodesign Have a closer look; the formulas contain just multiplication, division and a square root. They say that cross sectional area is very important. However, increasing cross sectional area increases heat loss and volume of air to heat, and temperature is also a factor. Height is also important, but less so than area. Anyway, I'm almost able to turn a very light paper turbine. Hopefully last tests today and then another video. Nice idea with the wall, lot's of cross sectional area.

[andodesign]

watched video absolutly brilliant work! Thankyou. Iv been wanting to create my own thermal / solar chimney for some time but have lacked the resources know how. Slowly iv been compiling infomation and was thinking have you considered using soap stone to absorb and retain the heat? I was thinking about using it like slate and linning the interior of the chimney as i think its relatively inexpensive. Please keep up the good work and look forward to your next installment.

[RimstarOrg]

@andodesign Thanks! I'd forgotten that some people use solar chimneys with their houses. Prior to this version I did some reading up on chimneys and that tought of adding thermal mass did cross my mind. My next version is at least made of a long aluminium tube with about a 1/8" thick wall.

[field16]

I'm enjoying watching you try to get air to move using the sun. I've wanted to do this, too. I've been at the mouth of a cave before and felt a constant air stream coming in.  I bet cave openings could create electrical energy. Anyway, your idea is similar. I wonder if the tube should be longer. I hope you get some success.

[andodesign]

@field16 mentioned about the mouth of a cave. This is quite pertanent as the air that is coming in is quite cool and the way i understand the boyancy effect (ie the pressure difference) is that to create a greater updraft you need to cool the air before it enters the tube (chimeny). I would suggest that for speed of the air to increase you would need to do 3 things. FIRST chilling the incomming air using pools of water and plants, SECOND "riffeling" the chimney THIRD Increase the heat

[RimstarOrg]

@andodesign A greater temperature difference definately helps. Why the rifling though? I think that would cause more heat transfer from the air to the tube and decrease the buoyancy. I was doing some calcs yesterday. Go to wikipedia and look up "Stack effect". Then scroll down to "The flow induced by the stack effect" and see the formula for the draught flow rate. The cross sectional area of the tube seems to be the biggest factor - surprisingly.

[RimstarOrg]

@field16 My next tube is 34" long, so it is much longer. As long as the sun stays out I should be testing it this morning. Thanks for the encouragement.