In winter time the south side, of an east - west street, remains in shadow all day. The ground on the north side of the street gets some sun, while the upper stories of the south facing buildings, on the north side of the street, remain bathed in a golden radiance for most of the day. (assuming clear skies of course)

If ice has formed overnight then it will linger on the south side of the street all day where as it often melts away on the north side. If we could reflect the energy falling on the walls of the south facing buildings down to ground level then the whole street, at ground level could have more sun light for longer, possibly helping to raise the temperature of the ground so that any ice there will melt and possibly inhibiting ice from forming the following night.

Using plain mirrors to reflect the light would have drawbacks, it would create many 'suns' potentially causing a hazard for motorists and inconvenience for every one else. So some element of diffusion would be needed. Would a frosted mirror work?

In order to get the best out of the sun the mirrors would have to direct light into the street over the longest possible time span. Reflecting it onto the upper stories of the buildings opposite is no good. Sun tracking, I think, is out of the question as it would make the system far to expensive.

So here is the question: To make this work a material that is capable of directing and diffusing a beam of light from a moving source into roughly a constant place. Of course in winter (northern hemisphere) the sun describes quite a flat path across the sky so this might not be a problem.

any thoughts, fellow demi boulangers?
-- rambling_sid, Dec 21 2004

This could work, and I have heard it proposed many times. The main opposition to it is the glare factor involved that you had mentioned. Now regarding diffusion, I think if you diffuse the light, it probably would not work. The sky dome has a lot of diffused light already (north light is diffused). What might work is using the solar energy captured from the south facade to heat the south side of the street (with hot water loops?) Alternately, I think what might work better is to have reflectors on the north side of buildings reflect downward so that the light comes from above, and doesnt hit people in the face.

You would probably need this on the north side of the street for streets with reasonably high buildings. The winter sun profile angle gets really low as you go further north (generally where it snows). This means that the building on the south side of the street would shade the entire street.
-- energy guy, Dec 21 2004


For people wondering what I am rambling about, I have a sketch, but no way of linking it. No personal website sorry.
-- energy guy, Dec 21 2004


It's at geocities I've heard. Set up a free site there for your stuff or blogspot it.
-- mensmaximus, Dec 21 2004


// To make this work a material that is capable of directing and diffusing a beam of light from a moving source into roughly a constant place. //

In the general case, what you're asking for there is known as a universal collimator, and it's impossible by the laws of optics (which are backed directly by the laws of thermodynamics). Otherwise, [+]—I think just a slanted semi-diffuse reflector would be enough.
-- notexactly, Apr 08 2019



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