Hi Robert, I would suggest you review this website www.solartubs.com for all techinical information on our SunRain TZ58/1800 30R collectors.Our collectors are not effected by the leaves getting on the surface the heat transfer occurs at the top of collector head not thru the tube.
SunRain's International patented interference film coating 3 Hi” vacuum tubes use 3 systems to ensure the most effective heat absorption. This included a AL-N/AI layer but also a separate aluminum and copper layer. The added layer conduct heat better and also stabilize the coating allowing for a much longer lifespan of 20 year or greater.
Thank-you
Alan Anderson
Northern Lights Solar Solutions
#20 305 McKay Avenue
Winnipeg, MB R2G 0N5
Canada
1-800-317-9054 ext. 226
e-mail [email protected]
www.nlsolarheating.com