What is that thing??

This is a fairly common sight where we live:

But this one has generated a lot of questions.

Most people are familiar with drying clothes using the sun and warm air moving.  But you can also dry lumber using the same principles.  This small building is our solar kiln, for drying lumber.  All the glass is south facing to collect heat from the sun.  It is painted black for the same reason.  It was designed by the Wood Technologies department at Virginia Tech, and we attended a short class there on the subject (which was great and we recommend it to anyone interested not just in kilns but wood/woodworking in general).   The solar panel on the left runs two 12 volt attic exhaust fans that circulate the warm air.  We can dry 1200 board feet of lumber in about 5 weeks, give or take.  This wood will be ready for cabinet-grade work, about 8% moisture content.

So why is this important?  Commercially dried lumber uses huge amounts of energy in the drying process.  In fact, 80% of the embodied energy in the average piece of lumber bought at a lumber yard is in the drying.  Also, most commercially available wood travels a long way to get to your local home improvement store.  Oftentimes, this is literally half-way around the world.  We live in an area with wonderful wood available, but it can't be used for interior work without being dried first (or finished products will shrink and warp when brought into climate-controlled space). 

Having the ability to dry lumber has allowed us to custom cut trees for people with the portable sawmill, dry it and build cabinets, trim, mantles, furniture, etc, often with trees from their own property.  These trees frequently become waste at a job site so this is an added benefit.  In addition, we are able to use tree species that are normally quite expensive to buy but are common in our forests such as black walnut, figured maple, cherry, quarter-sawn oak, etc. 

If you are interested, there are more pictures on the Flickr page.