While I am not writing any books right now, I do believe that there are lots of reasons one might want to explore free energy. Some people will easily benefit from unconventional efficiency gains in existing systems or be inspired to develop alternative energy sources. Other folks will want to see if they can harnass zero point energy.
What I want to offer here are some pointers which will help get you started. These are things I have discovered while doing my own research into various alternative energy ideas.
No matter what your interest, I highly recommend starting at http://free-energy-info.com/ where you can download a 2400 page book plus a lot of other stuff. While the book is available for reading on-line, you can download the complete document as a PDF. I highly recommend this as you will probably want to bookmark various items as you read through the book and most PDF readers will allow you to do this.
The link for the download does not jump out at you but it right after the information on getting Adobe Acrobat (which is easy to find because of the big logo). The book is regularly updated. At this writing, the current version is 20.9 which was released on 2 April 2012.
Besides a lot of information written by of culled out of other source by the author, there are copies of many patents. Thus, the book is an amazing resource. In addition to the free energy information, you will find a whole chapter (12) on Electronics and another (14) on renewable energy devices.
Use that book as a starting point. For example, if you are just interested in solar ovens, find the information he offers and you will surely find links to additional information.
I want to call your attention to a new section called Nikola Tesla: Free Energy Secrets for Everybody by Vladamir Utkin. In my copy it starts on page 5-27. While I have been told that the secret is being non-linear, this section talks about a lot of interesting things (such as asymmetrical transformers) that are clearly non-linear.
I was going to offer some additional resources (and may do so at a later time) but the links from this one web site to videos, other sites, papers and such is pretty amazing. So, I suggest you just start there.