The book is over 7 years old now, published just before PV prices crashed. Here are the citations for the 10% figure: <a href="http:&#x2F;&#x2F;www.withouthotair.com&#x2F;c6&#x2F;page_47.shtml" rel="nofollow">http:&#x2F;&#x2F;www.withouthotair.com&#x2F;c6&#x2F;page_47.shtml</a><p>Overall I thought the book was excellent. Some of the numbers are slightly off but a lot of the calulcations are intentionally back-of-the-envelope. What were the other issues you had with it?