A lot of work has gone into making better absorbers for solar energy, and one of the areas receiving a lot of attention has been on micro-treatments of the absorbing surfaces, to minimize the fraction of the incoming that just gets reflected back out.

Obviously the b-can heat excangers could be significantly improved if the cans were wrapped with those Christmas tree "rope style" tinselly thingies to make them more fuzzy - or once the tubes are assembled one might just spill some beer on them (even Budweiser surely would work for that) and wait for them to grow their own green fur.

John