Now I know many of these are not applicable to OP, but it's what worked for me before I moved onto writing GPL software instead of ebooks.
Intel's top Atom chips have a 10W TDP. Of course the chipset/RAM also play a large factor, but still -- this is an amazingly frugal CPU
At IDF, Intel also talked about upcoming 5W Atom chips that will be out at the same as Haswell
The means-and-ends moralists, or non-doers, always end up on their ends without any means. -- Saul Alinsky