A knol author advocates that writing online textbooks on Knol can be rewarding. Authors can write a textbook in the form of 300 knols as one knol for each section in a chapter. If thousand persons read the book fully in a year around $300 to $400 income will come to an author. This can be a comparable income with print books on an expected result basis. If the book is read by 10,000 persons fully in year the income will be $3000 to $4000 per year.
While the per copy income will be low in online books, the probability of getting more visitors and readers is high on Knol as readers are accessing it free of cost and also readers from any country can access it at any time they want.
The knol comparing online publishing and print publishing