Thursday, September 16, 2010

Magic with Mirrors!

With brackets prefixed, these are ready to lift
16 Sept: This is a special day as I have been wanting to do the eyebrow mirrors for some time now, and only just today had a couple of hours available. Can't sleep thinking about it (anticipating the problems) so wanted to do one now, get it out of my system, discover the difficulties, and then do the second one more quickly. 
One up, and one more to go!
  The mirrors were both ready with their brackets attached and predrilled the night before. Even lying on the ground, there is terrific reflection from them, bright and hot! (the blue colour is the protective plastic skin on them). They are 1.6mm bright alloy, with no additional stiffening required, and can be fixed at 90º to the rooflets of the sunboxes for a perfect Equinox and Winter angle. Under the plastic covering, they really are very shiny!
   Getting them up there is a bit dodgy as I have to use a ladder and tried to drill and fix them from the side, but this will not work, and is too unsafe. I am riveting them on, but you still need to get a firm grip on the riveter with both hands at the moment of truth - dangerous!
  I tried the ladder at the centre of each of the sunboxes, the safest location for working, and boy am I glad I built them strongly, of 6mm skin and stout 25x25x3mm aluminium angle across the top front face. I customised a little wooden worktable to fit in the top of the boxes so the panels don't have to take my weight, or be bouncy once I am up there. It is quite firm once the table is in position. Because the face of the sunboxes is glassy, there is nothing to stop the ladder falling sideways, so the first thing to do up there is to fasten a line to the wall brackets, and fasten myself to the same brackets. 
  Once up there, it was a case of locally drilling a hole in the roofs for the eight brackets, and then using the longest available rivets to fasten the mirrors down. Peel off the blue plastic sheet, and then get down to safety!


Now for the important bit! Before doing this, and earlier in the day, the temperature in the boxes was about 24-25ºC.  The temperature sensor is in the east panel, the one I have done first. the sensor is shrouded in reflective foil to ensure it measures air temperature, not just solar irradiation.
   Within 5 mins of re-sealing the panels and washing the top glass, the air temperature inside zoomed up to 33.5º. The temperature of liquid coming down from the panels went up. A five to eight degree jump is what I had been hoping for. 
It really is high up there!
Later, it rained, so I gave up, but suddenly was clear at about 7pm, so I got up there quickly (having established a working method) and got the west panel fitted during twilight. Tomorrow is a clear day, so I hope to see how the direct sunshine will perform, and I will take a photograph.
The benefit of these should only be when the sun is shining, strong or weakly. On completely overcast days, there will be no downward reflection. But I keep a weather record, as does my roof, so there is an indication of correlation between sunniness and improved harvest.

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