Melting snow for water is a time and fuel consuming part of winter camping and many overnight snow climbs.  If you have a base camp and the sun is out, try passive solar power to get some extra water. You do need a large black garbage bag for this to work, which is something you probably want to have in your pack anyway, because it serves lots of other purposes, like a pack cover, glissade device, and emergency shelter.

Here's two methods to melt snow via solar power.

First, the simplest method, if you have some exposed rocks nearby. Put some snow in a black garbage bag, secure the top, and put the bag on the (somewhat) warm rock. This should melt the snow in an hour or two.

Second, slightly more complicated, works on snow when you don't have any exposed rock.

1. Find a slight downward slope on snow.

2. Make a slight concave surface in the snow, slightly larger than your garbage bag.

3. Lay a sleeping pad on the snow, and put the garbage bag on top of it.

4. Pack some snow around the edges of the pad and bag so it doesn't blow away.

5. Put a small amount snow on the surface of the bag in a shallow layer, and add a picket to make a “V” for the meltwater.

6. Put a cook pot at the bottom underneath to catch the drips. Monitor, and add more snow as needed.

From the always awesome book, “Glacier Mountaineering: An Illustrated Guide to Glacier Travel and Crevasse Rescue, by Andy Tyson and Mike Clelland.