This update to the Clear Walk project is to demonstrate its performance in the snow, but first I should show the android app I made to run this test. Note it is in the style of Star Trek LCARS because the Clear Walk system is also the "Main Deflector" in my Star Trek Alcove project.
I have been itching to try out the Clear Walk system, but it never seems to be sunny when I have time to work on it. We have lots of snow, but today was the first day that had sunshine while I was at home. So I went down to the basement to bring out the apparatus only to discover it was so large it couldn't quite fit up the stairs. After removing the solar panel and rotating the mirrors in both axes several times during the trip, I was able to negotiate the wrap-around staircase and get it outside.
You can see from the shadows the sun is at a low angle - lower than I had expected when designing the system in the summer. This caused some issues getting the mirrors to tilt down enough, but I was able to tilt the apparatus enough to try the following experiment, melting snow and ice from the steps. The air temperature is -4C and this is also the temperature of the snow in the yard.
This sequence of pictures was taken over the course of about 25 minutes...
Canadians don't generally get the "Mind The Gap" welcome mat, but Londoners will certainly know where the phrase comes from.
The brick in shade is at -3C
The brick in direct sunlight is at +1C
The brick in sunlight plus mirror light is at +16C
The snow in direct sunlight is at -3C
The snow in direct sunlight plus mirror light is at +1C on the surface
The 2 bright stripes are from the 2 mirrors.
Note - I went back for a second pass to melt the snow at the end of the black mat.
The brick temperature in combined sun and mirror light had risen to +26C by the end of this 25 minute sequence. The snow in shade was still at -4C and the snow in the yard (direct sunlight was at -3C.
It takes a while to melt snow even when the temperature is well above zero, but the Clear Walk mirrors definitely made a difference in heating the bricks up. I discovered an amazing phenomenon - when the brick was warm but just still slightly wet and the air was still, remaining moisture would suddenly evaporate in a little cloud of water vapour. I tried to get a picture of this happening, but it is not visible in a still image. I guess the moving vapour (as it rises) is much easier to see.
Observations and Notes
- Increasing the amount of sunlight reaching a location using mirrors does help raise the temperature enough to melt snow, even when the outside temperature is below zero.
- The mirrors need to be pretty large to make a big difference - it is obvious from the images above that the fairly large mirrors only resulted in fairly narrow strips of extra light.
- The mirrors must be able to tilt to significantly negative angles (pointing down) to focus light on the ground.
- The quantization of movement needs to be small - the system was set up to have much coarser vertical rotation than horizontal. Horizontal quantization was fine, but vertical was a little too coarse.
- My walkway is not ideally positioned to make optimal use of reflected light - a second set of mirrors might improve efficiency.
- If you build one in a basement, make sure it will fit up the stairwell.
Conclusions
The Clear Walk system works, but it is more of a proof-of-concept system than an optimized solution. I think a simple manually positioned mirror resting on the ground would work just as well without as much danger of blowing over.
I did try beaming sunlight into a window, and that works well.
Will I end up using it? Probably not much - it currently needs some supervision and the number of days where conditions are ideal is quite limited. There are a few improvements I could make, such as better granularity of vertical motion and a more acute downward tilt angle, but I don't think the effort is worth it - I would rather design a better system at ground level.
Standing around waiting for snow to melt is like watching grass grow - not terribly exciting. But while standing there, I came up with a new use for the system that may prove very useful. Our house has a tendency to grow icicles off the roof directly over our front stoop. They are difficult to reach to remove, but the mirrors may do a great job of melting the attachment point to the roof.
Relevant Links
Make Life Accessible: Winners Announcement
The full set of Clear Walk project blogs can be found here:
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