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# passive solar driveway snow-melt accelerator

don't waste any solar energy heating air
 (+6) [vote for, against]

I've been watching the way sunlight clears snow and ice from driveways and sidewalks, and I think I've learned something useful.

First, some things that are obvious:

After a small area of the driveway snow melts down to pavement, the heat from the sun on the cleared pavement will, of course, help to melt the rest. The sunlight that falls on snow-covered pavement, on the other hand, will mostly be reflected, and will be much less effective at melting snow. So, ideally, one would not want the driveway to melt uniformly; it would be better for some fraction to melt all the way down to pavement, so it can begin right away to absorb solar energy. This would increase the total heat input, and thus melt the whole driveway as rapidly as possible.

That is what happens, in fact, but it doesn't work nearly as well as it should. Instead, cleared areas increase much more slowly than the available energy should accomplish; ice at the edges melts to water, and that water evaporates into dry winter air, taking a *huge* amount of heat energy with it. Meanwhile, the nearby dry pavement gets much warmer than is needed to melt snow, but this energy is mostly wasted. Most of the dry pavement just heats the air; its warmth doesn't melt anything, because asphalt has lousy thermal conductivity.

But increasing the thermal conductivity would not help if most of the driveway were snow covered. In that case, increasing the thermal conductivity would actually be a bad idea, because the large snow covered area would then keep the whole driveway cold enough that ice wouldn't even melt, let alone vaporize.

The crux of the problem, I think, is in getting that melt water out of the picture, so it doesn't suck up energy that could have melted more snow. Draining would help, but my driveway is too flat for this to happen, so snow just sits there and waits for melt water to evaporate.

So (finally) here's my idea:

What I'd like to have is a surface that wicks moisture from melted ice over the entire area of cleared pavement, so the whole area can contribute energy to warm and vaporize it.

I could cover the driveway with canvas, or something, and I think that would help. But my wife would have a cow, and the neighbors would make jokes about curb-to-curb carpeting. Maybe very thin grooves would work, but I'm reluctant to damage my driveway surface, because I'd probably get pot holes. So I'm thinking about using that seal-coating stuff, and putting grooves in that (next summer, of course. Ya can't seal coat in Chicago in February.)

 — colorclocks, Feb 03 2009

Backpack blower moves new snow light snow easily https://www.youtube...watch?v=vdqPERm33Bs
The pavement is left mostly bare for the sun to finish up, if it stops snowing.. [popbottle, Dec 08 2015]

You could get your wife's cow to help; maybe by hiding tasty cow treats under the snow so she digs up the snow to get at them. Wait, have I missed something?
 — spidermother, Feb 03 2009

Not at all, 'spidermother'. I completely neglected to view the cow as possibly a useful item. (I am not -- I am NOT --going to compliment you for thinking out of the box. That would be an udderly tasteless pun, and I'm better than that. Usually I'm better than that.)
 — colorclocks, Feb 03 2009

Hmm - I'm not sure the wicking action would work if the wicking material itself was frozen. However, it would be interesting to see the difference in melting time between two areas of snow where one had been sprinkled with a dark-coloured food dye. The other approach which occurs to me is to have a glass driveway - the upper surface would be some sort of bumpy glass and fibre optic 'light pipes' would funnel sunlight from, say, your roof, down to the driveway. If the light entered at the end of the driveway, it would exit through the bumps on the glass, causing the snow pack to melt from the underneath.
 — hippo, Feb 03 2009

//I'm thinking about using that seal-coating //
Blubber?
Seal skin?
 — coprocephalous, Feb 03 2009

I'm tentatively this summer going to whitewash the drive to reduce the barefoot burn-factor... hopefully it will be washed away and next winter be nice and black again to soak up the sun and melt snow at the beginning and end of winter.
 — FlyingToaster, Feb 03 2009

//paint the snow black//
Yet another use for Carbon dust harvested from CH4>H2 transmogrifiers.
 — FlyingToaster, Feb 04 2009

//paint the snow black// This was tried to hasten the melting of icebergs, but the black stuff ran off too quickly as the surface melted.
 — spidermother, Feb 08 2009

 You could use a modified lawn roller (you know, the huge ones used on bowls greens) with spikes on...

 The spikes would penetrate the snow to give a large number of black hot spots, and the rolling effect would reduce the insulating air pockets in the snow.

 If you were feeling really keen, you could run the roller along every hour or so to 'press' the latent water out.

Another aproach could be to use a thin film of semi-permeable membrane with salt sprinkled underneath it. This would 'suck' the meltwater underneath it as it pooled through osmosis due to the salt concentration gradient. The warm spots would then be able to partly use the meltwater as a heat transfer fluid as it flows eventually to the edge of the drive.
 — Skrewloose, Feb 08 2009

What about a big solar reflector to focus light on a patch, which would move across your driveway during the day?
 — Bad Jim, Feb 11 2009

 An alternative way to deal with meltwater: if you construct your driveway out of what's known as "permeable paving," the water will drain straight downward, through the driveway into the soil underneath.

 Next, if you're digging up your driveway to install permeable paving, you might take the time to also install heat exchange tubing, through which you can circulate a water/antifreeze mix.

To simultaneously heat and circulate that liquid (without using electricity), you can use a "solar bubble pump."
 — goldbb, Jan 08 2014

or, put vertical loops of antifreeze/water in. Convection will carry the cold stuff down, where it will warm up and rise through the other half of the loop. Round and round, passive, 0 energy input.
 — bs0u0155, Jan 09 2014

 // if you construct your driveway out of what's known as "permeable paving," the water will drain straight downward //

If you live in a climate cold enough to make icing a problem, eventually the permeable material will chill to the point that it freezes water on contact rather than letting it drain through, and in short order the ice buildup will have clogged the stuff and caused an ever-expanding puddle of ice to spread across your driveway...
 — Alterother, Jan 09 2014

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