gen2 parabolic solar collector progress 2

click any pic to enlarge

This is the back of the DIY gen2.0 reflector with the parts labeled. If you are familiar with the original design, you will see that the "furring strip" (also called "hat channel") previously used for the side channels (shown in the pic below) has been replaced with standard aluminum angle sections. These should be easier to source worldwide. I have added a brace (a plain aluminum strip) along the back which greatly improves the strength of the assembly. The rib shape has been simplified and made narrower to reduce weight. The original parabola profile (with a focal length of 10 cm) is the same as the original. The hanger shown is for the uninsulated 1-1/2" (3.8cm) collector pipe.

This is an end view of the old and new. Gen2.0 is the top one. Although Gen2.0 may seem delicate, it is in fact lighter, stronger and stiffer than the original and I hope you would find it be easier to construct. You can also see that the fastening method I am using between the side channels and the ribs has changed. The new method makes for a more precise and rigid reflector.

On the paper sheet is printed in gray at full scale the computer model of the rib part which will provided with the book as a .dxf. The hand made pattern that I have been using up to now for Gen2.0 is on top of the paper. The grid pattern is to check points on the curve against the original calculation. The match between the hand made pattern and the computer model is very good, within about 1mm. I hope to have CNC water jet cut ribs made next week. I will do the performance testing using the CNC ribs.

What looks like a car windshield wiper above is just that, but inverted so that the blade curves in a near parabola shape. I had to figure out how to take it apart without breaking it. I will show how I did that. I need a 4mm pin to attach it to a long pole but I am hoping that this will be a practical way to periodically clean the dirt off the surface of the parabola sheet. A single swipe when the reflector is covered with morning dew should clean it quite nicely. I am not worried about abrasion with the acrylic mirror since it is rear surface - the aluminum metalization is on the back so the shiny surface can't be scratched.

An early morning shot today of the insulated Gen2.0 on the test rack from the motor drive end. The reflector is connected to the motor drive (orange arrow).

You can see (red arrow) that the 180cm evacuated tube extends well beyond the four foot (122cm) reflector. I am not sure whether to cover this extra length or to ignore it's effect. Since the concentration ratio of the reflector is about 15:1 with this evacuated collector at the focus, the extra length should only contribute a small amount of un-concentrated heat to the chamber, less than 10%. Not sure yet.

The gap distortions at the edge of the reflective sheet (yellow arrows) will be corrected by adding small plastic angle channel sections to the back of the reflector sheet at the side channels. The photo makes the gaps seem larger than they are because of the shadow and the mirror. They are only about 1-2mm wide. The edge distortion is worse with the acrylic reflector than with the polished aluminum which might not need this addition but the strips should be the cure whenever that is required.

Thank you for your interest.

George Plhak

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