Passive Solar Heaters not only save you money, but are very eco-friendly. Learn how to make your own for less than $10! <embed src="http://www.metacafe.com/fplayer/920774/easy_free_home_heat.swf" wmode="transparent" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash" height="345" width="400"> Easy FREE Home Heat!
interesting - but do you think there is a better "cheaper" alternative to using pennies? (and what are the pennies for anyway? it's not like you are passing electricity - are they just for holding the heat????) what other metals are also conductive - like the slugs you can find at a construction site???? those are also bigger who's gonna build one and test the alternative metal theory?? i don't have room to do so in my house right now, but that would work pretty good during the winter - then hide them in the attic during the warmer months!
To collect enough solar heat to be able to realisticly use it as the primary home heating source requires a good deal of surface area. This usually can only be acheived by restructuring the house as just about the whole side facing the sun needs to be a collector. Unless your home was purpose built for this it usually is pretty expensive to retrofit. Even then you still need a backup for cloudy days and extra cold days. Plenty of info on the net on this subject.
The pennies are used as a heat exchanger to increase the surface area air is exposed to to transfer the heat. I imagine you can use anything including aluminum foil folded accordion like to do the same thing (painted black of course).
The link below takes you to an article on Mother Earth News for a wall mounted solar collector which operates on the same principal, but a bit more sophisticated: http://www.motherearthnews.com/Renewable-Energy/1985-01-01/Tap-The-Sun.aspx I believe there are other designs available on their site, as well. - Tristan