Vacuum tube solar heat collectors can be as much as 80% efficient!
Solar Water Heaters: Solar Hot Water Heaters For Home, Commercial & Industrial Solar Water Heating
They are used all over China, in great numbers. The latest designs AFAICT are a glass tube with a copper heatpipe inside and a (near) vacuum in between them. The top of the heatpipe has contact with the water in the header.
If one of the tubes is broken, it can be unplugged and replaced.