Preserving books against mold?

I have a collection of several thousand books in a part of my
house that gets too humid in the summer time.  The books
can get moldy.

I've dealt with that in the past with dehumidification, but in
the last year electricity costs have gone through the roof
in my state and it's getting really expensive.  Has anyone
successfully controlled mold by cheaper means - air
circulation, lysol spray, ultraviolet light (which can also
damage books), etc.?

Thanks.