Unfortunately this book has not had an update since the first edition. Nevertheless, as a cientist in the area of solar energy I still use it very often, both for teaching and for reference. To my knowledge, this book is the best general account on the subject of solar collector optics, specially regarding imaging concetrating systems. For non-imaging systems I would rather recommend the book "nonimaging optics" by Winston et al.. But the book is also very good regarding the heat transfer analysis of solar collectors and the economic analysis of solar energy systems. It is simply a must for engineers developing solar thermal systems, along with Duffie and Beckman's "Solar engineering of thermal processes".