Differences between Evacuated Tube Solar Collector and Flat Panel Solar Collector

Blog | July 27th, 2018

Today’s post is aimed at pointing out the differences between two popular sustainable energy solutions. They’re both rooftop-mounted modules, and they’re both designed to capture the sun’s heat, but that’s where their similarities end. Kicking off the match-up, evacuated tube solar collectors sport an array of equispaced cylinders. Clearly, then, flat panel solar collectors have opted for an entirely dissimilar architecture. Here, take a closer look at the design differences.

Geometrical Opposites

Everyone’s seen flat panel solar collectors mounted on neighbourhood rooftops. They have a low-profile build, come packed with heat exchanging inner assemblies, and the rectangular blocks are topped with flat black glassy coatings. They look a little like huge attic windows, but their smoky, reflective glass outlines expose their true purpose. Built to absorb the sun’s energies through that flatly glazed frame, they heat a home’s water and introduce significant energy savings. Now, from a distance at least, evacuated tube solar collectors look like their flat panel counterparts, but that’s all this is, a passing similarity. Viewed up close, the flat surface is gone, replaced by a group of cylindrical tubes, which are all closely aligned.

Chasing the Sun

Well, why should a series of glassy tubes, all arranged in parallel with one another, squeeze more energy out of the sun? For the answer to that question, look at the sun’s path. It rises in the east, it flies across the sky, and it sets in the west at day’s end. Now, flat panels glazing, covered in that blackened glass, can efficiently absorb solar energy when that great ball of fire is high in the sky, but their efficiency ratings drop off as the day progresses. Evacuated tube solar collectors have an advantage. Made from curved glass, the tube surfaces are always positioned perpendicular to the sun, which means they’re always receiving the maximum amount of solar energy, no matter the sun’s position. As for their inner workings, there are actually two tubes in each row. A smaller cylinder is installed within each large glass tube. A vacuum forms between those two layers of glass, and the generated heat is siphoned off towards a manifold or header assembly, where the energy then heats the header water pipe.

Flat panel solar collectors operate as ingeniously built direct conduction devices. There’s no vacuum, no header section, and no double-lined and coated tubes. Instead, the plated black glass conceals a network of pipes and insulation. Granted, flat-panel tech has improved greatly over the years, but it’s hard to beat evacuated tube systems; they’re always using their curved surfaces to capture energy, even when the sun is low on the horizon.

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