I second Johnlee’s post. If you are just starting out, use an extension ladder with stand-off stabilizers and clean it with your normal window cleaning tools, what is termed “Face to Glass” cleaning. It is going to be more efficient with quality results that way. Though a 20’ ladder is going to run about $150 new, the 16’ pole was only $250 and is more rigid than any of the aluminum cheaper poles. Flex at length is what makes poles harder to use and do detailed work.