As kids, we all tried the magnifying glass trick outside, using the sun's rays through the glass to burn paper. My question is, is this simple magnification used to increase solar heating of water in (rooftop) solar heating systems? If not, why not? Potential downsides realized......perhaps it generates too much heat for plastic materials used typically? Metal perhaps could be used then, but metal is expensive and may not be cost effective? How about this magnification in low sunlight areas, such as Canada and northern Europe? Just thinking.