Solar panel elements and method of manufacture thereof

A heat exchanger element comprising metal tubing substantially continuously secured along its length to a metal strip which is wide relative to the cross-sectional dimension of said tubing and which is thin relative to its width, said tubing being secured to said strip by metal of at least one of said tubing and said strip which has been melted and cooled to form a cast weld between said tubing and said strip, said cast weld being formed by at least two similarly shaped, continuous and discrete volumes of weld metal per inch of the tubing length, each of which volumes has a first end and an opposite second end, the first end of one volume commencing at the second end of the next adjacent volume and the longitudinal cross-sectional dimension of the weld metal at the first end of a volume being substantially greater than the cross-sectional dimension of the weld metal at the second end of said last-mentioned volume, whereby the strength of the weld at the first end of each volume is substantially greater than the strength of the weld at the second end thereof and at the second end of the next adjacent volume, so that the strength of said weld varies in the longitudinal direction of said tubing at a rate of at least two times per inch of the tubing length and said tubing is secured to said strip by welds of greater strength separated by welds of lesser strength.