hich solar collector is most efficient?
U tube collectors are about a half a percent more efficient than copper heat pipes; almost the same, in other words (see www.freefuelforever.com downloads, test reports and certification for numbers). Copper heat pipes are more slightly more efficient than glass heat pipes, with faster starting in low light, but yearly average performance is very similar. Any heat pipe is more efficient than water in tube. Any vacuum tube collector is more efficient than a flat plate collector if the air outside is more than a few degrees cooler than the hot water inside.
U tube collectors are almost exactly the same efficiency as copper heat pipes under standard conditions. In persistant low light, the U tubes should be better than any heat pipes, since they have no minimum start up light required. Copper heat pipes are slightly more efficient than glass heat pipes, with faster starting in low light, but yearly average performance is very similar. Any heat pipe is more efficient than water in tube. Any vacuum tube collector is more efficient than a flat plate collector if the air outside is more than a few degrees cooler than the hot water inside. Lowest cost is a different story-the all glass heat pipes win on that.
