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
"Consistency requires you to be as ignorant today as you were a year ago." -- Bernard Berenson