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             The Tiltable Fresnel, the best solar powered steam generator you ever made yourself
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Frenel Array
        The Fresnel array is a bank of spars arranged in a rectangle six feet high by some length.  The array tilts to track the sun with a single low torque mechanism.  The array's job is to take all the sunlight that lands on spars and direct it to the evacuated tube at all times.
        The array consists of two bars and tilt mechanism.  The bars are 1.5 inch aluminum angle stock 1/8 inch thick and as long as the array.  The tilt mechanism consists of one long bar generally 1/2 inch by 1/8 inch as long as the array and a number of short bars with one for each spar.  It is suggested to drill all three bars at the same time so as to make the holes line up exactly.  The hole spacing is generally spar width (1.5 inch) plus 1/10-2/10 inch.  The extra spacing allows for mechanical tolorances and geometry so the mirrors dont conflict with each other when tilting.  The smallest hole spacing on the array is going to create the biggest problem so measure and drill accurately or else allow extra spacing.  The bottom bar and the long bar from the tilt mechanism need clearance holes for a 6-32 screw.  The top bar must have holes to match the unthreaded standoff used as a bearing on the spars.
        The spars are supported by the two array bars (1.5 inch).  The array bars will bolt to the structure.  The array bars have to hold the spars high enough so they dont conflict with the structure, generally putting the holes 1/4 inch from the top of the bar is good for 1.5 inch spars.  The top bar actually holds the weight of the array as the spars pull down on it.  The bottom bar is more of a stabilizer and gets a small fraction of the weight.
        The short bars for the tilt mechanism must all be the same length.  Usually short segments of 1/2 inch by 1/8 inch aluminum strip are good, but if you can find pre drilled stock this is better.  The bars can be any length 2 inches or greater.  Each bar has a 6-32 unthreaded hole near each end.  The holes must be exactly the same distance apart for all spars.
        One end of each short bar gets pinched by the screw at the top of each spar.  A star lockwasher here guarantees a tight fit.  The other end goes to a loose screw at the top bar.  When the bar rotates 10 degrees, the spar must also rotate 10 degrees.  
        To tune the array, one needs a sunny day.  Lock the top bar by tightening one of the screws into the top bar.  One at a time, loosen the screw at the top of the spar.  Tilt that spar so sunlight reflects on the middle of the evacuated tube.  Tighten that screw, move on to the next spar.  Work quickly, the sun is always moving.  Loosen the tight screw in the top bar when done.  To track the sun, move the bar until sunlight is focused on the evacuated tube.