This item is an excellent, very comprehensive textbook on solar photovoltaic systems. It is applicable to those who are just starting out learning as well as to those who are knowledgeable in PV solar. the book is in used, good condition. There are some pencil marks which have been erased but are still visible on some of the worksheets (see pics). There is also a sticker on the inside cover (see pics). This book was how I got my introduction to solar and now I have my own business designing and installing systems (grid-tied and off-grid) for others.