Sunday, April 29, 2012

How to make a thermal solar powered Stirling engine - Part 2

Part 2: Building the Solar Thermal Panel


What You'll Need for this Project

Materials:

  • Corrugated Cardboard
  • Aluminum Foil
  • CPVC Pipe
  • CPVC Tees
  • CPVC 90 Degree Elbows
  • 14Gauge Wire
  • PVC couplings if you went the 2' pipe route
  • Foam Sheeting or other covering

Tools:

  • Drill
  • Standard Drill Bits
  • Metal Snips (Or Scissors/Box Cutter if you have them)
  • Pen or Permanent Marker


  1. First, you'll need to determine the trough size you'd like to build. I built mine as a 36" x 36" square, which meant the radius for my trough was 18 inches. 
    • Be aware, that the smaller the trough, the less energy you will obtain. Likewise, if you are sticking with a square structure, you'll also be reducing the length of your Electrical Metallic Tubing (EMT) - less pipe exposed to the increase in temperature translates to less air pressure. If the air pressure is too low, it won't be able to overcome the weight of the crankshaft.
    • You can overcome the smaller trough problem by increasing the number of EMTs in the trough.
  2. Alright, now that you've determined your trough size, you'll need to build your quarter circle. So get a sheet of cardboard and cut into a square that is the same size as the radius you have chosen for your trough.
    • Next, get out your measuring tape and draw a grid on one side of your cardboard. The grid should be in increments of whatever unit you are using. So, if you are using inches, draw lines spaced one inch apart, then turn your board 90 degrees and draw more lines 1 inch apart. If done right, you should have 1 inch squares along your entire sheet.
    • I've developed a simple chart that you can use to find out where you need to draw your points along your grid to make a quarter circle. Here.
    • Draw your points just like you did back in 5th grade math. Starting at (0,0) - the bottom left corner of your cardboard. Count the lines until you reach x and then count up to reach your y - then mark each point.
    • Once all points are made, it should look like they follow a quarter circular pattern.
    • Stab a nail, or the pen through each point, so that you now have a hole for each point.
  3.  Make an L with your PVC pipes, and attach them with a 90 degree elbow.
    • Put your cardboard form over the pipes. You want the curve to be on the inside of your L. Visualize it as if you had a full circle and a full square, the entire circle would be inside of your square. Make sure that the edges of of your cardboard are in the center of your pipes.
    • Get a marker and mark a dot on the pipe at each corner where the cardboard touches the pipe.
    • Mark a dot at each hole where you can see the pipe though the hole.
    • Drill holes through the PVC at each mark.
  4. Now, you'll need to make a cross piece of pipe to get those other holes. (Needs Edit)
  5. Forming the trough
    • Get 2 new piece of pipe and form another L. Repeat steps 2 through 4 until you have 4 L's and 4 cross pieces with holes drilled.
    • Connect two L's with a Tee to make a semicircle trough. Repeat with the other two L's
    • Use elbows and additional pipe pieces to connect your two troughs into one long trough.
  6. Making the reflective cardboard pieces (Needs Edit)
    • Make the trough panels
    • Make the side panels
  7. Putting it all together 
    • Tape all of the panels together. Apply tape only to the non shiny side.
    • Put the panels into the frame and loosely conform it to the shape of the holes in the pipe.
    • Stick a nail (or coat hanger strips) through each hole in the pipes.
    • Press the nails through the center (the corrugated part) of the corrugated cardboard so that the nails are in between the front and back of the cardboard.
    • Cover the sides and bottom of the frame with tarp or other covering
      • Staples work. Glue works well too.
  8. Glue/seal on the top
    • Glass is best because it thermally insulates the heat.
    • Acrylic works fine, but will become translucent with age. 
    • Plastic wrap works too and is cheap, but it will not hold up in high wind or rain.

2 comments:

  1. So how did you build the Stirling engine part of this apparatus?

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    Replies
    1. I used PVC pipe and elbows shaped in the form of a bracket ([). One side had a crude piston connected to the crankshaft. The other side had a valve that released into a chamber (a longer PVC pipe section). When the piston reached close to it's maximum height, the pressure release valve would open, allowing the piston to drop back down from the loss of pressure. As the piston dropped, the pressure valve closed and pressure was able to build back up in the system, repeating the cycle.

      I'm currently in the process of building a better prototype. This version simply did not have enough pipes within the thermal panel for the heat to provide enough air pressure.

      I'm also been planning a circular system that spins a fan or corkscrew within the loop, but I haven't yet planned out how to maintain a pressure difference within the system, but I imagine it will be similar to how a refrigerator works.

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