Ever heard of the Black barrel filled with oil in the sun all day? attracts and maintains heat,, If only I could get enough oil and barrels..
Try barrels, buckets, cat litter containers or what have you. Water should work well if you can't get the oil. All you really need is a medium to store thermal energy.
If you're lucky, you might find a book entitled "The Mother Earth News Handbook of Homemade Power" published by Mother Earth News magazine about 1973 or so. Contains several interesting examples of passive solar heating.
__________________ "We are forces of chaos and anarchy. Everything they say we are we are, and we are very proud of ourselves!" -- Jefferson Airplane
Dick Naugle says: 1. Prepare food fresh. 2. Serve customers fast. 3. Keep place clean.