Tuesday, July 8, 2008

New Results

Latest solar trough configuration:

A few details:

  1. Those are just simple, band-sawn parabolic arches. The mirror is attached with velcro. Works awesome. Ly.
  2. I suspended the mirror from the pipe thinking that would keep the focal length constant while allowing simples changes of elevation. Why do I always go straight for the complicatedest solution in the universe?
And data from same:

The highest temp on there is almost 140°C. That's over 280°F. According to my rough calculations, the four steepest upward slopes indicate powers in the range of 20-25 watts. (Some of those dropouts are me messing around with the setup, some are cloud cover. Also, I later discovered that true solar south is like 15 or 20° east of where I've been pointing.)

Two big changes from the last run, other than the already-mentioned one of shortening the excess pipe.

  1. Painted the pipe flat black.
  2. Used a laser pointer to adjust the focus. I mounted a frosted glass square (I happen to have a bunch I bought for just such a use as this) at what I thought would be the focal length. Then I stood back and aimed the laser pointer in a roughly perpendicular way and looked where the point fell. This really needs a System to keep it perpendicular, but anyway I was able to determine that my focus was off by over an inch.
I'm thinking the Mark III will be the last iteration. Pointing in the right direction, and simplifying the pointing a little, may let me add another 10-20 degrees to the peak but that will be about as far as I can go with these simple materials and using an open-air design.

1 comment:

  1. Two addendae:

    1) Last night I discovered that the velcro isn't quite as awesome as I thought. Probably the focus was an inch off because some of the velcro had pulled off the ribs. But for a permanent installation, this could be liquid nails or something.

    2) I just remembered why I wanted to suspend the mirror from the pipe: So the pipe doesn't move as sun elevation changes. If the pipe moves, the fittings have to be flexible and/or use hoses or something.